最新刊期
卷 49 ， 期 2 ， 2017
- 摘要：Abstract:Based on the current situation of the deep resources exploitation at home and abroad,deep mining has become the norm owing to the exhaustion of the shallow mineral resources.Nevertheless,because of the initial property of the ‘three high’ occurrence environment of the deep rock mass and also the additional property of ‘strong disturbance’ and ‘strong timeliness’ of resource exploitation,the large-scale disasters with high energy level frequently occur in deep engineering.Meanwhile,it is difficult to predict and get an effective control because of its unclear mechanism.The essential cause of this reality is that the existing rock mechanics theories are based on the material mechanics in a static researching perspective,which has lagged behind the practice of nowadays geotechnical engineering.The existing theories are not related to the depth,the engineering activity and the deep underground in-situ environment.It has become urgent to develop new theories and methods of deep rock mechanics with consideration of deep in situ state and mining disturbance to solve the theoretical and technical problems of deep resource exploitation.In the view of China's actual situation that the exploitation of deep mineral resources will enter into a stage of 1 000~2 000 m,the project,oriented with improving the capability of deep resources acquisition,has condensed four key scientific issues:1) in-situ mechanical behavior and stress environment of deep rock mass;2) the analysis, simulation and visualization of deep rock stress field and energy field;3) coupling theory of ‘multi-fields’ and ‘multi-phases’ coexisting in deep resource exploitation under the effect of ‘strong disturbance’, ‘strong timeliness’;4) the theory and technology of high efficiency mining of deep resources with low ecological damage.Meanwhile,combining the connotation of the key scientific issues,five key researching contents have been proposed:1) in-situ mechanical behavior and stress environment of deep rock mass;2) deep mining mechanics and flow theory in ‘multi-fields’ and ‘multi-phases’;3) evolution law of stress field and energy field in deep mining;4) deformation monitoring,safety early warning and stability control of deep rock mass;5) the theory and technology of eco efficiency mining of deep mineral resources.Finally,nine researching frontiers have been specified from the five key researching contents:1) research on the in-situ mechanical behavior of deep rock mass;2) long-term stability analysis and control of deep surrounding rocks;3) deep crustal stress environment and disaster dynamics;4) flow theory of multi-fields and multi-phases under deep strong disturbance and strong timeliness of deep rock mass;5) analysis,simulation and visualization of stress field and energy field under the effect of deep mining;6) the theory of high stress induction and energy regulation in deep;7) monitoring,warning and control of rock deformation in deep mining;8) theory and technology of safe and green mining in deep mining;9) theory and technology of collaborative mining in deep metal mines.Thus,the researching system of deep rock mechanics and mining theory is initially constructed,in order to provide a theoretical basis and technical support for the exploitation of the China's deep mineral resources in the future.关键词：deep environment;mineral exploitation;engineering disaster;rock mechanics;theory and techniques
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发布时间：2023-11-14 - 摘要：Abstract:At present,the ‘Golden Waterway’ of the Yangtze River confronts with new changes of flow and sediment conditions induced by integrated operation of the Three Gorges dam and its upstream reservoir groups.Meanwhile,there are new demands from flood risk management,navigation,electricity generation,water supply and ecology,etc.It is urgent to reveal mechanism of bed morphology evolution and predict its tendency,to develop methods for evaluating waterway capacity and potential,to develop novel waterway technologies satisfying demands of the integrated high efficiency utilization of water resources,and to merge waterway regulation and ecology protection.In the view of actual waterway situation,the project,aiming to enhance the transportation capacity of the Yangtze River and improve the water resources utilization efficiency,has condensed four key scientific issues:1) mechanism of waterway evolution and its tendencyunder variation condition of water and sediment;2) biology and habitat response to waterway regulation;3) theory and technology for shoals groups regulation of the Yangtze River under multi-factors;4) merge and rehabitated technology of waterway regulation based on river completeness.Moreover,combining the connotation of the key scientific issues,five key research contents have been proposed:1) investigate complex dynamic process and interaction between channel and bar for different types reaches,and predict waterway evolution trend;2) build framework and evaluation system for ecologic waterway of the Yangtze River;3) evaluate waterway transportation capacity and its potential for the multi-function river;4) study on technologies for gravel bar groups interlocking in the mountain river under operation of multi-reservoirs,strong erosion in the middle Yangtze River with demands of both flood defense and navigation,channel and bar regulation featuring with multi-channel branches in the lower Yangtze River,coordination regulation and deposition mitigation in the reaches under influence of river and tidal;5) develop merging and rehabitation technology of waterway in the Yangtze River,build framework for ecology-friendly waterway regulation.Finally,eight frontiers have been specified from the five key research contents:1) river evolution mechanism and trend prediction under new water and sediment condition;2) framework and evaluation system for ecological waterway in the Yangtze River;3) transportation capacity and potential of the golden Yangtze River with multi-targets;4) regulation technology of gravel bar groups interlocking under operation of multi-reservoirs;5) regulation technology for strong erosion reaches with demands of both flood defense and navigation;6) regulation technology for channel and bar regulation featuring with multi-channel branches;7) regulation technology for coordination regulation and deposition mitigation under influence of river and tidal;8) regulation technology for typical ecological protection reach in the Yangtze River.Thus,the research system of waterway regulation of the Yangtze River is initially constructed,aiming to provide a theoretical and technical foundation for enhancing the navigation capacity of the ‘Golden Waterway’ of the Yangtze River.关键词：‘Golden Waterway’ of the Yangtze River;regulation technologies;ecological waterway;waterway capacity;research plan and prospects
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发布时间：2023-11-14 - 摘要：Abstract:Electric power system is critical infrastructure of the nation.As one of the most important methods for the whole power grid's stability,power grid control system has become the key target of international network attacks.Against these attacks,China has built network deep defense system in power grid,which is mainly based on network isolation and border protection strategy.However,as the APT attacks whose main technological mean is developing malicious code rapidly,some new problems appear, such as outdated protection technology,business functions limitation caused by security functions,negative effects on the real-time control brought about by security controls,and etc.Trusted computing is a computing model for computing and protecting parallel structure,which provides the platform with the ability of autonomous immunity to malicious code and illegal operation,by keeping the integrity of the computing environment and the computing logic.Based on the trusted computing,our goal is to establish cyber security immune system which provides an active defense mechanism effectively for power supervise and control system.The cyber security immune system consists of the trusted computing platform for power control main station system,trusted network communications and trusted field terminal.The trusted computing platform includes the trusted hardware module as the trusted root,and the trusted software module embedded in the operating system kernel to realize the trusted guidance of the computer,the integrity protection for the operating system and the application,mandatory access control and enforcement control.Based on the standard trusted chain construction method,the power trusted computing platform embeds the measurement code in the operating system guide,and retrospectively evaluates the code integrity of the system boot code through the trusted password hardware driven by the CPU real mode.Compared to the current use of trusted computing technology,the starting point of the measurement is brought from the head of the operating system to the operating system boot,which leads to great improvement in the system security.Combined with the security label mechanism in the power grid dispatching control system,the power trusted computing platform realizes the double mandatory access control of the integrated operating system layer and the application layer.Combined with the scheduling of digital certificate system, the platform achieves the security management of expected value of the application,ensuring that the authenticity and authority of the expected value.The trusted computing platform utilizes the original security features in the compute component,eliminating the need of changes in business processes,logic and system resources, thus avoiding the need for large-scale retrofitting of operational systems.Comprehensive tests and extensive engineering practices show that the trusted computing platform for electric power saves the system resources,its operating efficiency fully meets the real-time requirements of control business and realizes the professional work without any interference.Based on the trusted computing technology,the immune system of cyber security provides the system of the power supervise and control system with a set of high efficiency and high-intensity protection mechanism.It achieves active defense capabilities against malicious code and illegal operation,simultaneously fits other industrial control system with fixed-logic work,in frequent system update and high-level security requirements.关键词：trusted computing;security immunization;active defense;optimization of trusted chain;mandatory access control;mandatory execution control
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发布时间：2023-11-14 - 摘要：Abstract:Dynamic response of concrete lining structure in hydraulic tunnel under seismic load is of great importance for engineering design and safety assessment,and it is the key link to establish a scientific and reasonable dynamic constitutive model and a coupling analysis method of inner water and lining for the seismic research of lining structure.In light of the basic idea of static damage constitutive in strain space, the static tension and compression damage variables for concrete under three-dimensional stress state were defined and solved.According to the similarity principle of constitutive relation curves of concrete under static and dynamic loading,a dynamic damage constitutive model of concrete suitable for programming was developed.Based on the explicit finite element method for analyzing the dynamic response of single-phase solid and fluid medium,combining with the boundary condition at coupling interface,a dynamic explicit finite element analysis model considering the coupling interaction of lining and inner water was presented.This method could directly integrate,solve without simultaneous equations,and greatly simplify the calculation process.Moreover,it could be easily used to analyze wave propagation problems with a variety of mediums.Taking some diversion tunnel as an engineering example,the calculation results show:1) various parts of concrete lining are in a synchronous vibration state,but the displacement of haunch is obviously less than the vault and inverted arch;2) the maximum principal stress quickly increases, and exceeds the tensile strength,in which the haunch is remarkably influenced,leading to great stress increment and serious damage;3) the cracking zones gradually extend from the haunch to each side,and the inner lining directly interacting with fluid is the weak link of seismic design.This model could reasonably reflect the seismic response characteristics of concrete lining in hydraulic tunnel,and an effective analysis method was provided for the aseismic design of hydraulic tunnel.关键词：hydraulic tunnel;concrete lining;tension and compression damage variables;dynamic damage constitutive;fluid-structure coupling;explicit finite element method
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发布时间：2023-11-14 - 摘要：Abstract:The accurate calculation of boundary shear stress is very important to the deep understanding of sediment transportation and river evolution.The current research is limited to straight and mildly curved channels,while for a sharply-curved channel,the flow is complex accompanied by transverse circulation and large transverse slope which was affected by the dual effect of gravity and centrifugal force.As the boundary shear stress was affected by many factors,the applicability of differentcalculation methods requires further study.The distribution of three-dimensional flow velocity and dynamic-staticpressure difference were monitored by ADV as well as Preston tube in a 180°;sharply-curved flume under the subcritical flow condition.The typical features of transverse flow circulation,redistribution of longitudinal flow velocity and turbulence kinetic energy were analyzed.Based on the analyses,four empirical formulae and k-ε model were selected to calculate the boundary shear stress on the control section of the flume.The computational results of turbulence kinetic energy method and Preston tube method agree well with the k-ε numerical simulation not only in distribution pattern but also in magnitude.Therefore,the above three methods are feasible for the calculation of boundary shear stress in a sharply-curved channel.The boundary shear stress in bed and bank slope of the whole flume was calculated by numerical simulation.The results show that the value of boundary shear stress is small and evenly distributed in thestraight section following the flow entrance,then gradually increases and exhibits non-uniformity in the bending section. Finally it reaches the maximum near the bank slope in the straight section in front of the outlet.On the transverse section,the boundary shear stress is well distributed along the bed while strongly fluctuated near the toe of slope in which the flow is complex with large circulation.Under the effect of the bend,the maximum boundary shear stress in the transverse section gradually shifted from convex bank to concave bank,in order to keep up with the mainstream.The maximal boundary shear stress of the flume is located in the convex bank of 110°; cross-section of the bend and the concave bank of the cross-section 0.5 m downstream off the bend outlet.By changing the rate of flow but keeping the downstream water depth constent,the overall distribution of the boundary shear stress is similar and shows the characteristic of strong water flow along straight line while weak water flow along curve line.These researches provided support for flow shear transport mechanism,forecast of river evolution and safety management in the sharply-curved channel.关键词：sharply-curved;boundary shear stress;Preston tube;turbulence kinetic energy;k-ε;model
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发布时间：2023-11-14 - 摘要：Abstract:Investigation on the stress displacement field for the plane stress disk,which is also called the Brazilian disk,has an important theoretical and practical value for elastic mechanics,rock mechanics and fracture mechanics.In order to obtain the closed-form solution to stresses and displacements in the Brazilian disk under different loading conditions,based on the theory of elasticity and a series solution of stress for the Brazilian disk subjected to a pair of compressive forces,the explicit expressions of displacements were obtained for the Brazilian disk under diametral-compression loading.The series solutions to stresses were then derived by using mathematical analysis method and the explicit expressions of displacements were obtained subjected to uniformly distributed pressure.The calculated results showed that the stresses σθ,σr and radial displacement u were symmetric to the loading line θ=0,and the stress τrθ and tangential displacement v were anti-symmetricto θ=0.At the loading point of a concentrated force and the starting point or the end point of the distributed pressure,the stress field and displacement field had a abrupt change.For the same condition,the effect of the loading types on the displacements was less than that on the stresses.On the other hand,the loading type only had an important effect on the stress or displacement distributions near the loading point (i.e.,when ρ was larger),and the effect on the stress or displacement distributions was very small at points away from the loading point or loading range (i.e.,when ρ is smaller).This conclusion agreed well with the Saint-Venant principle.In addition,the radial displacement increased with the increase of ρ,and it had a maximum value near ρ=0.7.The further analysis showed that the series formula obtained by other researcher can be simplified and combined,and the formula derived from the present paper is the simplest form for the Brazilian disk loaded by pressure.关键词：plane stress;Brazilian disk;stress;displacement;series solution
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发布时间：2023-11-14 - 摘要：Abstract:The discriminant formula is a mathematics formula which can decide whether turbidity current plunges.There are an implicit relation between in the discriminant of plunging point,due to the past researchers ignoring or hard to give the mathematics formula on the vertical velocity distribution at the point which could not directly discrete sediment content from Froude number.With mathematic analysis on surveyed data and experiments,physical figure of vertical velocity distribution was decided by parabola.Based on plunging point data during water and sediment regulation period in Xiaolangdi reservoir in 2001 to 2015,and data from tests on physical model of Xiaolangdi reservoir, empirical coefficient of the vertical velocity distribution formula at the point was acquired with calibration,which revealed the theoretical hypothesis was right.Then the momentum correction factor of turbidity current in reservoir is obtained respectively by 1.2 in theory and 1.13,which were closely.Based on the above research,an improved discriminant formula is validated by the data of flumes by Fan Jiahua[13],Cao Ruxuan[14] and Jiao Enze[15],surveyed data of Xiaolangdi reservoir in 2001 to 2005,and data from tests on physical model of Xiaolangdi reservoir.The prediction results of the formula by data from Xiaolangdi reservoir and Sanmenxia reservoir were pretty well with the surveyed.This could be applied in water and sediment regulation program compilation and numerically simulating in sediment-laden reservoirs.关键词：plunging discriminant formula;vertical velocity distribution;parabolic distribution;momentum correction factor;turbidity current in reservoir
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发布时间：2023-11-14 - 摘要：Abstract:For conventional multivariate frequency analysis methods,there are an infinite number of combinations of flood peaks and volumes satisfying the flood prevention standard under the given joint return period(JRP);however,different joint design values would lead to differences of flood hydrograph and maximal water level which occurs in reservoir routing.Hence,how to select reasonable design values under given JRP is very important. In this paper,the Copula functions were used to construct the multivariate joint distributions of flood peaks and volumes,and the OR JRP was adopted as flood prevention standard.The normalized joint probability density function value was adopted to measure the relative occurrence likelihood of flood events,and the general model of Most Likely Composition (MLC) of flood peaks and volumes were established subject to the flood prevention standard.The Lagrange multiplier method was adopted to solve the model.The trivariate and four-dimension MLC design floods of Danjiangkou reservoir in Hanjiang basin were estimated using the proposed method,and the quantiles estimated by univariate identical frequency (UIF) and multivariate identical frequency (MIF) methods were compared with those calculated by MLC.The results indicated that the UIF estimations could not satisfy the flood prevention standard;the UIF method assumed that the flood peak is fully dependent upon the flood volume and all the variables are characterized based on univariate distributions.The UIF method cannot take the correlations of hydrologic variables into consideration,and it does not satisfy the inherent rule of flood events. It is also indicated that the MLC method had a smaller flood peak and larger long-duration volume than those by the MIF method.The Danjiangkou reservoir has the capacity of multi-year regulation and the flood volumes are mainly responsible for flood prevention safety,and thus the MLC estimation values are safer.The joint design values of MLC method are more rational according to the application requirements in Danjiangkou reservoir, and consequently the proposed method had a strong statistical basis and could reflect the inherent rules of hydrological events,and it could be used to estimate the design floods of reservoir.关键词：design flood;joint return period;most likely composition method;general formula;Copula function
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发布时间：2023-11-14 - 摘要：Abstract:Naturally,different bank slope and bank soil compositions can have a combined effect on bank stability and failure.A series of experiments were carried out in a bend flume to study the influence of different bank conditions on bank stability and the interaction between the landslide materials and bed evolution.Experiment results show that bank erosion,the disintegration and transportation of a collapsed bank block and the mixing between the soil and bed evolution have a close relations with turbulence energy near the bank.Bank erosion is a process of repeated interaction between bank toe scouring and bank collapse along with the deposition and transportation of landslide material.Whether the bank soil is cohesive or not,there exists no mixing between riverbed near bank toe and collapsed bank block.With the same bank configuration,riverbed compositions and hydraulic conditions,riverbed scouring volume near the cohesive bank toe is larger than the one near the non-cohesive bank.The erosion volume of cohesive bank is smaller than that of the non-cohesive bank.With similar bank material and the same riverbed compositions and hydraulic conditions,steeper bank is prone to greater instability under water action.The erosion volume and the silting volume of bank-failure materials on the riverbed for the bank with steeper slope are larger than those for the bank with milder slope.The results can be used to guide the protection of bank erosion and river regulation planning.关键词：bank boundary conditions;bank slope collapse;riverbed evolution;hydraulic scouring;flume experiment
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发布时间：2023-11-14 - 摘要：Abstract:In order to study the influence of vegetation patch and bed roughness on flow characteristics in river,this paper used wooden cylinders to simulate emergent circular patch composed by different plant density,with movable bed and fixed bed conditions.By using flow velocity and turbulence kinetic energy,this paper analyzed the formation and development of the upstream adjustment length and the wake flow.Firstly,the results showed that when the diameter of the patch was constant,the upstream adjustment length of patch is independent of vegetation patch density,and in this experiment,the effect of bed roughness could be ignored.Secondly,this paper used the volume fraction φ as a comprehensive characterization of density and diameter of patch.Comparing the contribution of bed roughness and the volume fraction to the complete wake length,it was found that the complete wake length L was related to the volume fraction φ,amely,when φ value was larger the length of the complete wake was smaller.Thirdly,the velocity distribution was mainly controlled by the bed roughness and the volume fraction value backward of the vegetation patchand the steady wake length L1 value was related to the φ value,with L1/D reaching the maximal value in the vicinity of φ=6%.Finally,two turbulence kinetic energy peaks generally appear on the wake region,with its location being mainly affected by the density of patch and the roughness of bed.Due to the different densities of vegetation patch,the development of energy exchange and transverse shear layer was not the same in the wake structure,which was the main factor that affects the position of velocity returning to normal velocity and the formation of stable wake.This paper can provide a reference for the further analysis of the interaction between water flow and vegetation under different bed roughness.关键词：vegetation patch;water flow;volume fraction;movable bed;fixed bed
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发布时间：2023-11-14 - 摘要：Abstract:With the increase of hydropower units and installed capacity in China,the fault problem during the transient process occurs frequently.The signal analysis method is widely used to deal with the problem.The variational mode decomposition (VMD) method,a relatively new self-adaptive method for processing non-linear and non-stationary signals,was adopted to investigate the vibration signals during the transient process of a hydropower unit in the Gezhouba power plant.The first step was to use VMD to analyze the simulated vibration signals of the transient process,and to verify the effectiveness of the VMD method in dealing with non-linear and unstable signals.The Hilbert-Huang transform (HHT) was then used to calculate the instantaneous frequency of each intrinsic mode functions (IMF) decomposed by VMD to obtain the corresponding Hilbert spectrum.These results were compared with those from empirical mode decomposition (EMD) method.From the final vibration signal analysis,the IMF decomposed by VMD could be divided into three parts.The first part was the trend of signal development.The second part was the basic decomposition of the signal with a strong regularity of "spindle" signal reflecting the change law of the transient process.The third part was high-frequency characteristic signals mainly caused by interference noise or unit failure.The corresponding Hilbert spectrum had the characteristics of small fluctuation and stable amplitude.The results showed good consistency between the frequency change of each component and the time-dependent rule of the rotational speed.This suggested that VMD was capable of extracting characteristic frequencies to facilitate the analysis of vibration characteristics.Compared with EMD,the VMD outperformed in self-adaptivity.It provided more accurate and effective analysis results and a better representation of the vibration rule during the transient process of the hydropower unit.关键词：hydropower unit;transient process;nonstationary signal;time frequency analysis;Variational Mode Decomposition
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发布时间：2023-11-14 - 摘要：Abstract:With the rapid development of the Internet under the background of globalization,mining network data for cross-language texts has become one of the most popular research fields in public opinion analysis.Detecting hot topics effectively and timely for texts both in Chinese and English plays a crucial role in grasping the development of public opinion.Internet news,as an important part of the Internet public opinion,has become a significant source of information acquisition for netizens.Firstly,Internet news in Chinese and English network were collected.Secondly,the ICE-LDA model based on LDA model was proposed to detect co-occurrence topics of the mixed dataset.Then,the JS distance and cosine similarity of the topic-text distribution were used to calculate the distance between two topics in ICE-LDA model.Thirdly,a contrastive parallel corpus and a non-colligative corpus were constructed respectively for Chinese and English mixed news data.During model building,the TF-IDF algorithm was used to remove noise words of the text. Finally,two kinds of topic vectors were used to detect the co-occurrence topics.The experimental results showed that the improved topic model proposed by us can not only detect topics in the comparison corpus dataset but also in the non-comparison corpus dataset.关键词：topic model;cross language;ICE-LDA model;TF-IDF feature word extraction;co-occurrence topic
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发布时间：2023-11-14 - 摘要：Abstract:Activity hijacking attack,one type of attack on Android interface,steal user's information by hijacking the original activity interface that users use.In this paper,the effectiveness of activity hijacking attack was experimentally tested on several versions of Android systems and four necessary characteristics with the malicious behavior of activity hijacking were described.A novel static detection method called AHDetecor (activity hijacking detector) was proposed to detect the activity hijacking behavior based on its code features and multiple data flows.AHDetecor determines whether the test app is undergoing an activity hijacking attack based on the following four conditions:1) whether the test app has the permission to send out the data by analyzing the manifest configuration file;2) whether the test app simultaneously has three components:scanning,hijacking and privacy leakage according to its code features;3) whether the test app has the invoking relationship between the components of scanning and user's input;4) whether the test app has the data flows between the hijacking component and the privacy leaking component.If none of these conditions is satisfied,the detection is terminated and the test app is judged as no activity hijacking behavior.In order to evaluate the effectiveness of AHDetector,eighteen malicious Android apps were designed and implemented to cover all the activity hijacking attack logical paths while other four Android app lockers were adopted to check the false positive judgements.The test results showed that AHDetector can effectively detect malicious apps with activity hijacking attack behavior without any false positive judgement.On the other hand,six popular online detection systems (Andrubis,VirusTotal,visualThreat,Security Housekeeper,Tencent Security and Netqin Security) cannot detect 18 malicious Android apps with activity hijacking attacks.关键词：activity hijacking;privacy leakage;data flow tracking
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发布时间：2023-11-14 - 摘要：Abstract:Modern network is subjected to the risk of combined attack.Therefore,a security situation analysis model based on attack and defense behavior is necessary to be build for analyzing the threat of each independent and combined attack behaviors.Aiming at the problems that the defense factors is not taken into account by the traditional attack tree,the defense tree model lacks good scalability and external attacks were hard to be analyzed by fault tree model,in this paper,the game theory was introduced into attack tree model to describe the specific network attack incident scene.Firstly,logical relationship between different levels of aggressive behavior was analyzed.Offensive and defensive attack trees corresponding to different attack levels are then integrated,and the complete network attack behavior tree was lately obtained.Based on the above steps,an algorithm on the network threat offensive behavior tree was proposed.By finding aggression combinations,analyzing its attack probability,and assessing the threat of attack,the network security situation was analyzed.In order to verify the feasibility and effectiveness of the attack behavior tree model,it was built on the basis of BGP(border gateway protocol)attack tree.By calculating the probability,the probability of PATH1 was largest.Meanwhile,the attack success rates of five attack paths were increased in the case of no defense measures.The probabilities of PATH2 to PATH5 were increased significantly higher than PATH1 which is consistent with facts.The experimental analysis showed that the model can calculate the effect of various defensive measures very well,which provides a theoretical basis of carrying out targeted network security defense.关键词：network security;situation analysis;behavior tree;attack behavior tree;defense behavior tree
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发布时间：2023-11-14 - 摘要：Abstract:In order to solve the problem of identifying the meek-based Tor anonymous traffic from the TLS-based cloud computing service traffic,an identification method for Tor's anonymous communication based on traffic feature matching and a classification method of Tor's anonymous traffic based on SVM were proposed.Firstly,based on the analysis of connection,static packet and dynamic traffic of the captured Tor-Meek and non Tor-meek traffic in the lab environment,seven specific static and dynamic features of Tor-Meek traffic were identified.Lately,a traffic feature matching identification method for Tor's anonymous communication technique was proposed,which could be used to quickly detect Tor-Meek traffic and the accuracy rate is over 90% for longer traffic with packets number exceeding 200. In order to be robust to the upgrading and transformation of Tor versions, statistic features of the slicing of Tor-Meek traffic were analyzed including the length and count,length variation,length entropy,sequence of sending and receiving of the sliced traffic. Then 16 statistic features were identified,based on which an identification and classification method for Tor's anonymous traffic by using SVM machine learning algorithm was proposed.Different feature combinations and algorithm parameters were studied experimentally to decide which ones can yield the best accuracy and recall rate of the classification algorithm.It was shown that when the number of packets in one session wa above 40,and the length of each slice of one session was 40 packets,the identification accuracy was above 97 and the recall rate was over 99% for the SVM based method.The experiments results show that while the feature matching methods is effective for quick identification,the machine learning method is more accurate and robust to the changing and upgrading of different versions of Tor browser in identifying anonymous traffic of specific versions of Tor-Meek.关键词：anonymous communication;Tor;traffic obfuscation;traffic identification
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发布时间：2023-11-14 - 摘要：Abstract:In order to solve the problem that there is no enough security assurance of virtual trusted platform module (vTPM) in virtualized trusted platform architecture,a vTPM security enhancement (vTSE) method based on Intel SGX (software guard extension) was proposed.The characteristic of physical memory isolation of SGX was utilized firstly.Then the code and data of vTPM instances was isolated and protected in safety isolation region created by SGX.At the same time,the sealing features based on trusted area identity of enclave was used to confidentially store the nonvolatile data in safety isolation region.The experimental results showed that this method could not only dynamically protect the confidentiality and integrity of code and date during the operation of vTPM instances,but also realized the secure storage of vTPM instances data.Finally,the security and performance evaluation of the system was done.The results showed that while the proper functioning and secure storage of vTPM instances were ensured,the performance overhead added was less than 1 ms.关键词：trusted computing;virtual trusted platform module;Intel SGX
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发布时间：2023-11-14 - 摘要：Abstract:Trusted computing technology can provide trustworthy state and corresponding verification method for cloud infrastructure.The first step of building trusted computing architecture is to build root of trust.The problem of building root of trust for report was not well solved in virtual trusted computing platform because of the differences between virtual machine and ordinary host.No universal and proven solution was developed,which affects the application of trusted computing technology,such as attestation in cloud environment.In this paper,by analyzing related works,it was concluded that the independent identity based on asymmetric key for each VM as well as protected and migratable storage of sensitive data such as platform configuration register (PCR) value and keys used in a VM were all required for constructing trusted computing architecture in cloud infrastructure.Furthermore,the integrity state of a VM reported with PCR should consist of both the physical PCR value emerged from physical booting procedure and virtual PCR value recording VM software boot procedure.With assumption of centralized and virtualization/non-virtualization unified trusted computing platform management,a model of building root of trust for report with virtual attestation identity key (AIK) as a virtual machine's identity was proposed.It can maintain a set of individual virtual and physical combined PCR values for each VM.Then the verification procedure of virtual trusted computing platform to identify itself with VAIK and report its unique integrity state with VPCR to verifiers including attestation challenger were proposed to support this model.At last,it was compared with TCG specification's method from several different management dimensions.Our model can build unambiguous identity for each VM.Meanwhile it can reduce complexity of verification procedure of VM and keep the compatibility of ordinary AIK verification mechanism.关键词：trusted computing;virtualization;credential;attestation
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发布时间：2023-11-14 - 摘要：Abstract:With the increasing complexity and gradual shift to the large scale data of the wireless sensor networks (WSNs),it is very difficult to solve the problem of massive data redundancy and huge energy consumption in sensor networks effectively.Therefore,a mean value filtering algorithm based on graphical node data was proposed to reduce the data redundancy and energy consumption in large-scale WSNs.Firstly,the nodes were clustered and the clustered head nodes were labelled exploiting the relationship of node locations on the basis of the whole deployment topology of the sensor networks.Secondly,the graphical model process was conducted based on the data information from the nodes in each cluster.Then,the mean value filtering was applied to each graphical cluster node by taking the data acquired by its corresponding cluster head node as the reference.Lately,all the cluster nodes were divided into active nodes and sleep nodes.While the data from the active nodes was valid,the data from the sleep nodes was redundant,which will be kept inactive.Simulation results showed that the large-scale and complex WSNs can be divided into several clusters and the graphical modelling of the data from each cluster node can be effectively achieved by the joint verification of the real and simulated data sets.On the premise of the whole data was valid and had no distortion,it were achieved that some nodes in each cluster were regarded as sleep nodes and their states were changed to inactive.Then there was no data produced by or transmitted from sleep nodes,which reduced not only the amount of the whole data in sensor networks but also the energy consumption in the data transmitting.In conclusion,the algorithm proposed in this paper can effectively solve the problem of massive data redundancy and huge energy consumption in large-scale and complex sensor networks.With the proposed algorithm the redundant data and energy consumption were deceased and the network lifetime was prolonged for WSNs.关键词：wireless sensor networks;node data image;mean filter;massive redundant data
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- 1937
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发布时间：2023-11-14 - 摘要：Abstract:In wireless sensor networks,the link quality prediction is a basic issue in guarantying reliable data transmission and upper network protocol performance.In this paper,a link quality prediction mechanism based on dynamic Bayesian networks (DBN) was proposed.The link quality was evaluated by link signal quality,link stability and link asymmetry,instead of a single evaluation index which could lead to a bias evaluation of link quality.The K-means clustering algorithm was then used to discrete the parameters so as to get intervals of parameters respectively.The weight of each parameter was determined by the entropy value method which could eliminate the interference of subjective factors in the process of weighting.Besides,in order to overcome the defects of maximum membership,asymmetry closeness analysis method was employed to construct the comprehensive link quality level indicators.The DBN based link quality prediction model was constructed,after both an initial network and a transfer network of DBN were determined.Finally,DBN parameters were determined by EM(expectation maximization) algorithm.Experimental results showed that it was reasonable to level link quality by using asymmetry closeness analysis method and to predict link quality with DBN model.Compared with the 4C and FLI prediction model,the proposed model based on DBN achieved better accuracy.In a word,the proposed mechanism with DBN model has better accuracy and robustness,which has been evaluated in terms of link signal quality,link reliability,and link asymmetry.关键词：wireless sensor networks;link quality prediction;dynamic Bayesian networks;closeness analysis method
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发布时间：2023-11-14 - 摘要：Abstract:To quickly realize the localization of all sensor nodes in the monitoring area,a movement path planning algorithm of auxiliary locating beacon node in wireless sensor networks (MPPA) was proposed by using movement of auxiliary locating beacon node.In MPPA algorithm,the monitoring area consisting of multiple hexagonal grids was considered.Analyzing mobile characteristic of sink node,four constraint conditions were assumed:1) Sojourn locations of sink node only were centers and vertexes of hexagonal grids;2) The sojourn location was not stayed twice by sink node;3) Three adjacent sojourn locations were non-collinear;4) Each grid was covered by at least three different sojourn locations.Movement path constraints of beacon node and localization constraint of sensor nodes were then proposed.Movement path planning model was flowingly established.Next sojourn location was judged according to the pheromone concentration of neighbor sojourn locations and the pheromone was released and volatilized according to the selected path of ant.After several iterations of ant colony algorithm,the optimal path of beacon node covering all grids was obtained.When beacon node moved along the path,in each sensor node different sojourn location information of beacon node was obtained and RSSI value of communication was collected.Kalman filter algorithm was used to reduce communication noise and maximum likelihood estimation algorithm was used to calculate its own location coordinates.Simulation results showed that according to the location information of centers and vertexes of grids,MPPA algorithm converged to optimal movement path with shortest movement distance and realized the localization of sensor nodes at any location in the monitoring area.MPPA algorithm reduced the movement path length of beacon node and the number of sojourn locations.Meanwhile,it reduced the time that sensor nodes need to know their own locations, and maintained localization error at a low level.Under certain conditions,MPPA algorithm outperforms SCAN,DOUBLE_SCAN,HILBERT,CIRCLES and ZSCAN algorithms.关键词：wireless sensor networks;sensor nodes;localization;path planning
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- 2822
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发布时间：2023-11-14 - 摘要：Abstract:The widely-used EPC Gen2 protocol for backscatter communication is inefficient in dealing with transferring a large amount of buffered data to RFID reader.Furthermore,it is not adaptable to dynamic energy harvesting and channel condition.In order to solve these problems,firstly,the original logic of EPC Gen2 protocol was optimized by adopting burst transmission to reduce the idle slots and introducing erasure code to avoid waiting for the ACK.Secondly,the expression of the throughput under specific energy harvesting and channel conditions was derived.Then the throughput maximization problem was formulated,which was solved by the method of exhaustion.The optimal combination of the frame length,the number of redundant frames and the charging time were obtained.Thirdly,a dynamic frame and charging time adaptation (DFCTA) scheme was proposed,which increased or decreased the frame length and the number of redundant frames at runtime based on the throughput measurement at the reader.Finally,simulations were conducted under different energy harvesting and channel conditions to evaluate the frame length,the number of redundant frames,the achieved throughput and the energy cost of the proposed DFCTA scheme.Simulation results showed that by DFCTA scheme,the throughput performance was remarkably improved compared with current fixed-frame-length scheme in EPC Gen2 protocol and it was quite close to the theoretical optimum.Consequently,the optimization of the protocol logic and the proposed DFCTA scheme were proved to be effective in improving the throughput performance.关键词：backscatter communication;throughput;frame length;charging time;coding redundancy
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- 2194
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发布时间：2023-11-14 - 摘要：Abstract:In multi-monitoring-task mobile sensor networks,different monitored objects have different requirements for real-time transmission.To satisfy those requirements,a multi-layered real-time data routing protocol (MRDR) was proposed to satisfy the requirements of both soft real-time and hard real-time monitoring.In MRDR,a layer mechanism was introduced into mobile sensor networks and the network was divided into layers with equal width.For ordinary event messages with higher delay tolerance,MRDR could enable messages to be forwarded to the sink at as low energy consumption as possible.For emergent event messages with lower delay tolerance,MRDR could send messages to the sink by multi-hop real-time transmission.At the same time,for the problem of energy holes in hard real-time routing,a backward mechanism was proposed to enable emergent event messages avoiding node holes and finally be transmitted to the sink.At last,to reduce message redundancy,message queue management was designed and the principle for discarding messages was presented when the queue was full.To evaluate the performance,simulation was carried out to compare MRDR and other three algorithms in terms of network lifetime, average delivery ratio and average delay.The result proved the efficiency of MRDR.In different network environments,MRDR could effectively be applied to multi-monitoring-task mobile sensor networks and satisfy different requirements of different real-time transmissions.关键词：mobile sensor networks;multi-monitoring-task;real-time;routing protocol;layered mechanism
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发布时间：2023-11-14 - 摘要：Abstract:Compared with the integral imaging (Ⅱ) display based on the micro-lens array,the Ⅱ display based on the pinhole array has lower cost,lower weight,and thinner thickness.Moreover,the Ⅱ display based on the pinhole array is easy to realize a 3D/2D convertible display.The parameter design of pinhole array is one of the most important keys to design the Ⅱ display based on the pinhole array.The 3D viewing angle is also one of the most important parameters in the Ⅱ display based on the pinhole array.The effect of thickness of pinhole array on 3D viewing angle in the Ⅱ display was analyzed.According to the relationships between the aperture width and the thickness of the pinhole array,three imaging models of the Ⅱ display were established firstly.Then,three calculation formulas of the 3D viewing angle of the Ⅱ display were obtained through geometrical optics.Lately,a testing equipment of the Ⅱ display based on the pinhole array was developed.The experiment results proved the optimal thickness of the pinhole array was related to the pitch of the elemental image,the width of the pinhole and the distance between the pinhole array and the display panel.When the thickness of the pinhole array was equal to the optimal value,lights emitted from all pixels of each elemental image on the display panel were only modulated by the assigned pinhole.Thus,the maximum 3D viewing angle was obtained without crosstalk.When the thickness of the pinhole array was smaller than the optimal value,lights emitted from all pixels of each elemental image on the display panel were modulated by the assigned pinhole,and lights emitted from parts of pixels of each elemental image on the display panel were also modulated by the other pinholes.Thus,the maximum 3D viewing angle was obtained with crosstalk.When the thickness was larger than the optimal value,lights emitted from parts of pixels of each elemental image on the display panel were modulated by the assigned pinhole.Accordingly,the 3D viewing angle was decreased and inversely proportional to the thickness of the pinhole array.关键词：integral imaging;pinhole array;thickness;viewing angle
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发布时间：2023-11-14 - 摘要：Abstract:In heterogeneous MPSoC,the parallel tasks were dispatched to each cores by task scheduling algorithm.Therefore,the performance of heterogeneous MPSoC directly was affected by task scheduling algorithm.A novel task scheduling algorithm with load-adaptive capability was proposed.In order to reduce the communication overheads,the algorithm divided task-set into task-subsets based on core types and tasks dependencies.Taking into the account of the cores load,then weighted bipartite graph was then created by task-subsets,cores and the execution efficiency of the task-subsets on each core.Finally,task-subsets were dispatched to appropriate load cores by finding a maximum weight matching in the weighted bipartite graph.In this way,the average scheduling length of task-set was reduced and the utilization of cores was improved,which jointly improved the performance of the heterogeneous MPSoC.Under the simulation scenarios with different number of tasks,maximum number of predecessors,number of core types,and number of cores,the proposed algorithm was quantitatively analyzed in terms of the average scheduling length of task-set and the utilization of the cores.The results showed that the proposed algorithm could effectively reduce the average scheduling length of task-set,and improved the utilization of heterogeneous MPSoC cores while achieving-adaptive loading.关键词：heterogeneous MPSoC;load-adaptive;tasks division;tasks dispatch
- 2285
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- 2005
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发布时间：2023-11-14 - 摘要：Abstract:With the popularization of hydraulic technology,the application of synchronous hydraulic circuit for engineering industry has been widely recognized.Now there has appeared several kinds of circuit, but all the circuit performed badly.So how to realize a synchronization effect,to get more moving modes,and to get higher precision has become a very important task for design of synchronous hydraulic circuit.As a new type of hydraulic components,Double stator output pump is composed of inner pump and outer pump,which can realize the function of multi output,and can realize proportional output according to the requirements.It's inner and outer pump are mutually independent,so it can work alone and also can realize the joint output.By using this new type of hydraulic components for circuit design, making the original hydraulic synchronous circuit be replaced,the characteristics of synchronous circuit driven by double-stator multi-output pump (referred to as double-stator pump) was explored,and the laws of multi-cylinder hydraulic synchronous system driven by it was studied.Based on the analysis of the hydraulic system,the synchronous circuit of single double stator pump and double pump stator were designed.The comparison with the traditional synchronous circuit showed that the new synchronous circuits can achieve the hydraulic cylinder synchronization of different sizes, and have multiple synchronous speeds,in addition,it has the advantages of less power loss and using fewer numbers of pumps.The experimental data of a prototype of double-stator pump with the synchronous system showed that the main factor influencing the synchronous precision of the new synchronous circuit is the volumetric efficiency of the double-stator pump.The application of double stator multi output pump can effectively eliminate some of the current problems in the hydraulic circuit,which provides a new research direction for the synchronous circuit and provides the theoretical foundation for the research of application of double stator hydraulic components.关键词：hydraulic synchronous circuit;double-stator pump;energy saving;synchronous speed;synchronous precision
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- 2033
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发布时间：2023-11-14 - 摘要：Abstract:The dynamic images of gas-liquid-solid three-phase flow in the riser were obtained by the high-speed camera system,the variation of the lifting performance of three-phase flow with operating parameters were studied,and the flow field structure and the movement characteristics of solid particles in the riser were analyzed based on the image processing method.The result showed that the periodic variation of flow pattern is formed in the riser,in turn,spare bubble flow-intensive bubble flow-bubble churn flow-mixed churn flow-spare bubble flow,in which the bubble churn flow is more conductive to lift solid particles.Under the same amount of air inlet,the discharged amount of solid,liquid and lifting-efficiency increases first and then decreases with the increase of submergence ratio.The effect of air inlet on the performance of system is higher than that of submergence under the same operating conditions.During the low flow rate of air,the particle concentration is low and most of it concentrate in the pipe wall.With the increase of air flow rate,the particles move to the core,and the particle concentration and the lifting velocity are more higher than other parts.In addition,the gas-liquid two-phase flow and gas-liquid-solid three-phase flow is appeared in turns in the riser with the change of air let,and the particle distribution and motion state also be affected by it.The system was proved a better performance,compared with the single particle,under the action of group particles.Particularly the velocity of particles in different radial positions are not equally distributed about the center line of the pipe.关键词：airlift;solid phase;high-speed camera;image processing
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发布时间：2023-11-14 - 摘要：Abstract:In order to get the vibration rule of a cylindrical gear with variational hyperbola and circular-arc-tooth-trace (CHATT) at work and design a stable and efficient gear,it's necessary to analyze its nonlinear vibration characteristics.The time-varying stiffness of meshing curve and axial error excitation were calculated by load tooth contact analysis (LTCA),and meshing impact excitation was received according to meshing impact model.The twelve-degree of bending-torsion-shaft multi-factor coupling dynamical model of CHATT was established based on the theory of concentrated parameter,and vibration differential equations were built on the basis of Newton's second law.Then,equations were solved by adopting fourth-order Runge-Kutta algorithm with variable step lengths.Vibration displacement,vibration velocity,vibration acceleration,dynamic load of bearing,vibration displacement & velocity phase and Poincaré section of driving gear and driven gear were calculated,and response amplitude spectrums of above signals were obtained with FFT method.The comparison of numerical solutions of driving gear and driven gear in verticality,torsion,and axial direction showed that the vibration law of driving gear always keeps consistent with driven gear,quasi-periodic motion occurs in verticality and torsion direction,and vibration in axial direction shows a nearly chaotic state of steady state response.Moreover,the influence rule on system vibration characteristics was researched by changing tooth-trace radius,loading torque and inputing speed,and results of vibration displacement & velocity phase indicated that vibration regularity of driving gear and driven gear in axial direction gradually becomes poor,which evolutes from quasi-periodic motion to nearly chaotic motion.The regularity of axial direction vibration is more susceptible by changing these three parameters.The establishment and solution of CHATT vibration model and parameter influencing analysis provide theoretical foundation for the later dynamic design,prediction of vibration response under different parameters,and noise reduction.关键词：variational hyperbola and circular-arc-tooth-trace;load tooth contact analysis(LTCA);nonlinear vibration;dynamic design
- 2291
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- 1945
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发布时间：2023-11-14 - 摘要：Abstract:A novel surface defect detection method based on non-subsampled shearlet transform (NSST) was proposed for detecting defects with random noise,low contrast,uneven background and regularly distributed grinding texture in magnetic tile surface images.The method first employed NSST to decompose the original magnetic tile defect image into one low frequency subband and a series of high frequency subbands with multiple frequency domains and shearing directions.Then,the defect signals were processed pertinently and separately according to the varied characteristics of defects in the low and high frequency domains.In the low frequency subband,the mean images of row and column were computed,and an adaptive threshold surface constructed by extending the column mean image along the row mean image was adopted to remove the uneven background.Meanwhile,as weak defect signals and significant defect signals exhibited large variance,respectively,and energy at the same decomposition scale in high frequency domains and both of them were small in noise and background interference pixels,a discriminator based on the variance and energy of high frequency Shearlet coefficients was proposed for the removal of noise and background interference in the high frequency subbands.Finally,a denoising image with high contrast and even background could be reconstructed by applying inverse NSST to the modified Shearlet coefficients,and the defects could be accurately extracted using an adaptive threshold segmentation method.Experimental results showed that the false positive rate,the false negative rate and the accuracy rate of the proposed method are 8.8%,5.0% and 93.1%,respectively,and the average elapsed time is 0.629 s with the software of MATLAB.Moreover,as the proposed method is effective in eliminating the interferences of uneven background,grinding texture and random noise,it has obvious superiorities over the existing ones in terms of both accuracy and robustness.关键词：magnetic tile;non-subsampled Shearlet transform;adaptive threshold surface;image denoising;defect detection
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发布时间：2023-11-14 - 摘要：Abstract:Rigid body guidance synthesis is a typical problem in mechanism design.In order to avoid the defects by traditional synthesis methods based on Burmester kinematic geometry theory,such as the limitation of mechanism structure type and the uncertainty of mechanism function,a generalized function oriented geometric synthesis method based on similarity transformation of the mechanism function modules was discussed.Since the standard mechanism modules were considered as basic design units for this method,the structure type of guidance mechanism modules need to be extended for a larger solution space,thereforethe geared linkage structure that can generate complex motion patterns was taken into account,aiming at the establishment of corresponding function module through kinematic analysis.At first,the transformation and mapping method between transmission function and guidance function were obtained through the configuration analysis of geared linkage,thus converting the transmission mechanism to the guidance mechanism through changing the rotation center of output gear.Secondly,the complex vector method was introduced for the kinematic analysis to obtain the guidance function,after that the geared linkage function module with full topology information was established,which included the transmission characteristics as well as the guidance characteristics,i.e. the relative dimensional parameters,the guidance angle performance, the guidance point trajectory and the motion geometric identifier.Then,in order to obtain the method for adjusting dimensional parameters of the preselected function module,a bidirectional mapping rule between relative dimensions and achievable guidance functions was revealed.At last,a practical guidance mechanism design task for powder production with partial parallel guidance function requirement was given, the similarity transformation of geometric identifier between geared linkage function module and the guidance task was presented, then the actual solution mechanism size and position parameters which meet the technical requirements were obtained. Finally the validity and practicability of the proposed generalized synthesis method were verified by the analysis of design results.关键词：function module;similarity transformation;rigid-body guidance;geared linkage;generalized synthesis methodology
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发布时间：2023-11-14 - 摘要：Abstract:Polymer materials are used to seal and protect the pipeline layer in the multi layer composite structure flexible pipe in the offshore oil field.The design life of those pipes are more than 25 years,and the long-term working temperature is high (75 ℃),the pressure is 16.5 MPa.After a long period of the compressive stress,the creep of materials can be produced,and at the same time,the specific parts of the compressive strain will be subjected to a constant compressive strain.Therefore,it is very important to study the creep and stress relaxation behavior of these polymers under long-term stress and strain to evaluate the long-term service behavior of the inner pressure sealing layer.The stress relaxation experiments of polyethylene(PE-XRT70),which was used as the specific operating pressure sealing layer of an oifield composite flexible pipe under sea water were detected carried out at the temperatures of 75 ℃,85 ℃ and 95 ℃ by 10% or 20% constant strain and creep experiments which were determined at 75 ℃ and 16.5 MPa constant stress.The shift factor αT was calculated by the time-temperature equivalence and relaxation time distribution of polymer materials.Firstly,the shift factor αT of PE-XRT70 pipe was calculated by the time temperature equivalence and the relaxation time distribution of the polymer materials.Then,by multielement parallel Maxwell model,1 stopt used five parameters was applied to fit the stress relaxation and creep experimental data and forecast mathematical model of the material stress relaxation and creep behavior.The results showed that the Maxwell model and simulation curve fitted well,the balance stress model closed to the experimental values and the value of coefficient of correlation coefficient R2 was above 0.975.The equilibrium strain of the two constant strain at 75 ℃ and the equilibrium strain at constant stress of 16.5 MPa at 75 ℃ were obtained.The simulation and experiment of stress relaxation experiments showed that at 75 ℃,the stress relaxation process of balance stress σ∞ were 3.983 and 7.505 MPa under constant strain 10% and 20%,respectively.The creep test data and mathematical simulation showed that the equilibrium strain of the creep process of the PE-XRT70 was 31.479%,and the creep basically reached the equilibrium in 24 h under the pressure of 16.5 MPa.关键词：polyethylene;stress relaxation;creep;Maxwell model;1 stopt simulation software
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- 2085
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发布时间：2023-11-14 - 摘要：Abstract:A two-sludge system of A2/O+moving bed biofilm reactor (A2/O+MBBR),used to treat wastewater with low carbon/nitrogen (C/N) ratio,was applied to investigate the sludge characteristics and denitrifying phosphorus removal characteristics during the start-up process,and rapid start-up strategy of the system was established based on the metabolic mechanism of nitrogen and phosphorus removals.The results showed that the start-up process was completed by 21 d,the sludge structure was stable with promising sludge settleability and biological activity.The average sludge concentration increased from 1 189 mg/L to 1 760 mg/L,SVI value was below 95 mL/gMLSS,and the percentage of denitrifying phosphorus accumulating organisms (DNPAOs) accounted for phosphorus accumulating organisms (PAOs) increased from 10.87% in inoculation sludge to 25.46%.During the start-up process,COD removal was basically stable and A2/O reactor achieved the efficient utilization of carbon sources.Nitrification process provided electron acceptors for denitrifying phosphorusremoval,and the high-efficiency removal of TN should build on the complete NH4-N oxidation.A close correlation between NO3--N and PO43--P removals was revealed.In addition to the simultaneous nitrogen and phosphorus removals in anoxic zone,aerobic phosphorus absorption played an important role in keeping stable effluent PO43--P under the operation condition with average influent C/N ratio of 3.44,COD,TN and PO43--P removals reached to 82.23%,74.72% and 96.80%,respectively,and the effluent concentrations of COD,NH4+-N,TN and PO43--P were 38.5,1.15,14.2,0.15 mg/L during the stable operation stage,which showed that the A2/O+MBBR system achieved high-efficient removals of organic matter,nitrogen and phosphorus simultaneously.Where.The variations of real-time control parameters of DO,pH and ORP exhibited quantitative relationship with nitrogen and phosphorus removals.During the stable operation,anaerobic ORP value was -398~-336 mV,pH increased by 0.55 and ORP increased to -300~-175 mV in denitrification process,and pH decreased by 0.37 in nitrification process.ORP and pH intuitively reflected the denitrification process,and pH sensitively revealed the nitrification process.Real-time control parameters were beneficial to promote the rapid start-up and stable operation.
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发布时间：2023-11-14 - 摘要：Abstract:It has been showed directly or indirectly that the lubricant is possible to be sucked back into the mechanical seal with dimples or grooves in the existing studies.This phenomenon,termed "outlet suctio" in this paper,may decrease the leakage.Further studies are still required for this phenomenon and its mechanism.A three-dimensional fluid numerical simulation,based on the multiphase flow cavitation model in Fluent,was developed for the mechanical seal with inclined elliptical dimples.The causes of outlet suction and the influence of the outlet suction on leakage were studied by changing the differential pressure between the inner and outer diameter and the rotation rate.Firstly,in order to ensure the accuracy of calculation model,the fluid factor was calculated for the flow pattern check,the grid independence was tested for the grid size,and the simulation result was compared with the reference.Secondly,in the numerical simulation experiments,the phenomenon of outlet suction was observed directly in the streamline plots on the r-θ section of calculation unit beside the outlet section and the velocity distribution contours in radial direction on the outlet section.Thirdly,the pressure and radial velocity distribution on r-θ section was discussed.The results showed that the outlet suction occurs because the pressure close to the seal outlet falls below the external atmospheric pressure.This pressure decrease is caused by the hydrodynamic effect near the divergence gaps of dimples.The increase of hydrodynamic effect enhances the outlet suction.When the decreased pressure reaches the cavitation pressure,the cavitation occurs.The cavitation effect hinders the increase of outlet suction.Finally,the effect of Δp and n on outlet suction,and the effect of outlet suction on the leakage decrease were studied based on the analysis of the out flow rates and outlet suction flow rates.The leakage decreases because of the outlet suction,even to zero.The outlet suction caused by inclined elliptical dimples can be employed to decrease the leakage of mechanic seals.关键词：mechanical seal;inclined elliptical dimple;outlet suction;leakage
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发布时间：2023-11-14 - 摘要：Abstract:The dry gas seals have wide applications in the conditions of high temperature,high pressure and a variety of corrosive media,but it has been not enough to understand the effects of high pressure and high temperature on dry gas seals,especially the problems in the numerical simulation.Both pressure and temperature of end-face gas film field in dry gas seals change greatly,especially at the working condition of high pressure.The density and viscosity of sealing medium or nitrogen change with varying pressure and temperature.Especially,the effect of pressure on the former is greater.In usual numerical simulation for dry gas seals,the density of sealing medium is determined according to the given temperature and pressure,which does not take into account the influences of physical parameters of sealing medium on seal performance so that the results might have errors.A new way used for the simulation of flow field of high pressure dry gas seals was proposed with the consideration of the effects of the changes of flow field and temperature field on the density of sealing medium in order to decrease the errors.Firstly,ANSYS Workbench software was used to make a thermal analysis for sealing rings to obtain the temperature field.The temperature distribution in the gas film field was then estimated by CFD.Then,user defined functions(UDFs) were created to relate the density of nitrogen (sealing medium) to pressure and temperature.Fluent software was used to complete the simulation with UDF loaded.Pressure distribution of end-face gas field and the opening force of the seal were obtained after continuous iteration.The flow fields of high pressure dry gas seals were reflected more truly.The flow fields of a dry gas seal were simulated using Fluent soft ware by the methods of variable-density (to define the density as a function of pressure and temperature) and the given density (to take density as the given directly),respectively.The grid size independent verification was carried out.The comparison of simulation results showed that the variable-density method could make the results closer to the conditions of the actual situation.It is feasible to use UDFs of Fluent to describe the variable-density of gas film between the sealing faces of a dry gas seal,which provides a new method to more accurately simulate gap flow field between sealing faces.The effect of pressure on the density of sealing gas is great under high pressure.The flow fields of high pressure dry gas seals are reflected more truly by the methods of variable-density.Moreover,the influence of temperature change on the density of sealing gas should be taken into account.关键词：dry gas seal;density;fluid field;spiral groove;numerical simulation
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- 1974
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发布时间：2023-11-14
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