最新刊期
卷 54 ， 期 4 ， 2022
- 摘要：Muck removal at the bottom of tunnel is required before steel arch erection in tunneling boring machine (TBM) construction. With the increasing requirements for quality, efficiency and safety, the traditional manual muck removal is difficult to meet the construction requirements. A muck removal method for the robot was proposed. Firstly, the distribution of muck at the bottom of the tunnel and the characteristics of the environmental structure were analyzed, the design requirements of the robot were obtained, and the new robot structure was designed. Secondly, the link coordinate system was established based on the Denavit–Hartenberg (D–H) parameter method, the forward and inverse kinematics were calculated, the matrix of the end positional and the selection algorithm of the optimal solution of the inverse kinematics were presented, and the workspace was calculated and analyzed. The results showed that the robot could achieve a working depth of 3 830 mm and a working range of ± 45°. Then, taking the single joint position control as an example, the integral separation PID controller was designed. Compared with the traditional PID, the overshoot was reduced by 18.7%, and the problem of joint jitter caused by the accumulation of position error was solved. Finally, the test platform of the muck removal robot was built, and the muck removal experiment was conducted. The results showed that it took 53 seconds to clean muck, which could be used as an effective solution for muck removal at the bottom of the tunnel during open TBM construction.关键词：tunneling boring machine;muck removal robot;structural design;control;experiment
- 811
- |
- 168
- |
- 1
发布时间：2024-01-10
SICHUAN—TIBET RAILWAY ENGINEERING AND ENVIRONMENT
- 摘要：By introducing trapezoidal corrugated steel plates into PEC columns, a new cross-section form of PEC columns was proposed to overcome the disadvantages of flat web steel plates such as low out-of-plane stiffness, easy buckling, and weak bonding with concrete. Five vertical trapezoidal corrugated web PEC columns with different slenderness ratios and different transverse tie bar spacing were tested under axial compression. By studying its bearing capacity under axial compression, the failure mode, load-displacement relationship curve and load-strain relationship curve of the specimen under axial compression load were obtained, and the law of its bearing capacity was further analyzed. The experimental study showed that the failure modes of all specimens were similar, which were compressed flange drum and concrete crushing failure. The restraint form composed of transverse tie bars, flanges and corrugated webs could better restrain concrete, improve its compressive strength, improve the ductility of members, and enhance the deformation capacity. With the increase in slenderness ratio, the initial stiffness and peak bearing capacity of the specimen decreased, but the deformation capacity after the peak increased and the ductility was better. With the decrease of transverse tie bar spacing, the initial stiffness, peak load, and ductility coefficient of the specimen increased, and the specimen had a better axial compressive performance. The finite element model was established by ABAQUS. Additionally, on the basis of verifying the validity of the finite element model and referring to the relevant codes at home and abroad, the superposition principle was used to fit and obtain the bearing capacity calculation formula of vertical trapezoidal corrugated web PEC column under axial compression combined the test results and finite element extended parameter simulation. It was found that the calculated results were in good agreement with the experimental results, which had high reliability and a certain safety reserve.关键词：corrugated web;PEC column;axial compression test;finite element simulation;bearing capacity formula
- 690
- |
- 238
- |
- 0
发布时间：2024-01-10 - 摘要：With the increasing frequency and intensity of extreme rainstorms, the flood management situation has become extremely severe. It is particularly important to study the process of river flood propagation, overflow and inundation and evaluate the risk of flood disaster effectively. To simulate the river flood propagation accurately, a two-dimensional hydrodynamic model using the finite volume method based on unstructured grids was applied, an improved inflow boundary processing method was proposed based on Ghost-Cell Method. The method of profile extraction based on terrain grid data was used to determine the position of thalweg approximately, and thus to calculate the average gradient of the river. The corresponding water level under different discharge was calculated by defining that the flow on the grid of inflow boundary is the uniform flow. The discharge per unit width was distributed reasonably by calculating the weight according to the water depth and inflow boundary length of each grid, and coupled to flux part of the model for calculation by determining the hydraulic elements on the ghost cell outside the boundary . The method was applied to the simulation of the physical model test of the Toce river, and the flow state near the inflow boundary was more reasonable. The water level at gauging points in the river is in good agreement with the measured data. The arrival time and travel time of flood at gauging points is close to the measured values. The NSE (Nash-Sutcliffe efficiency coefficient) is between 0.82 and 0.95, which verifies the feasibility of the method and the accuracy of the model. And it takes 86 s to complete the calculation on the personal computer, which shows that the model can simulate flood propagation process efficiently and accurately. Through the improvement and optimization of the inflow module, this model can be better applied to the simulation, early warning and disaster assessment of flood propagation process, and provides more powerful technical support for flood disaster management and decision.关键词：hydrodynamic model;inflow boundary;flood propagation;Toce river
- 512
- |
- 176
- |
- 0
发布时间：2024-01-10 - 摘要：The traditional asphalt pavement has strong heat absorption and storage capacity, which is easy to cause rutting and aggravate the development of urban heat island effect. The application of asphalt heat reflective coating can effectively mitigate this problem. At present, most of the research on heat reflective coatings for pavement is focused on the optimization of material composition, and there is less research on the coating structure. Due to the limitation of single-layer structure, the development of cooling performance of asphalt heat reflective coatings is facing continuous challenges. To solve this problem, a three-layer structure cooling coating composed of reflective, radiation and thermal insulation coatings was developed, which can effectively drop the temperature of asphalt pavement. The optimal amounts of composition materials and each layer of coating in the multi-layer structure cooling coatings were studied by cooling experiments, and the structure form of the multi-layer structure cooling coatings was studied. The results showed that the optimal contents of titanium dioxide, mid far infrared ceramic powder and hollow glass beads are 15%, 20% and 15%, respectively, the optimal amounts of reflective, radiative and thermal insulation coatings are 0.6, 0.3 and 0.3 kg/m2, respectively, and the cooling effect of the coatings can be reduced with the addition of pigment. The cooling performance of the coating can be improved by designing three kinds of cooling fillers in different structural layers. The cooling ranges of the coating can be increased by 3.70 ℃ with the addition of radiative layer under the reflective coating, and 1.10 ℃ with the addition of heat insulation layer under the reflective coating. The three-layer structure coatings combining reflective coating as surface layer, radiative coating as middle layer and insulation coating as bottom layer have the best cooling capability. The cooling ranges of surface and interior in the three-layer structure coatings can reach 10.45 ℃ and 9.22 ℃. Compared with single-layer heat reflective coatings, the multi-layer structure cooling coatings has better cooling capability and can effectively reduce the temperature of asphalt pavement.关键词：road engineering;asphalt pavement;multilayer structure coating;cooling effect
- 602
- |
- 197
- |
- 0
发布时间：2024-01-10 - 摘要：In order to improve the span and resistance level of engineering structures, the strengthening mechanism and axial compression performance of the high-strength steel tube confined self-stress concrete (HSTCSC) short column was studied in this paper. Seven large size HSTCSC and one control short columns were tested to investigate their uniaxial compression performance; the confining coefficient of all specimens in the test were greater than three. The influence of the self-stress concrete strengths, the types and hollow rates of the cross section on axial compression performance of the HSTCSC short columns was discussed in detail. Results showed that: 1) the HSTCSC short columns presented obvious waist drum-type failure mode with significant brittle splitting or shear disruption features, and it possessed an high axial bearing capacity and deformation performance. 2) The elastic module and compression strength of the HSTCSC short columns under the confined condition of steel tube were higher than that of the non-confined condition. Moreover, the axial compression properties of HSTCSC short columns were significantly improved by the interaction of self-stress concrete micro-expansion and hoop constraint of high-strength steel tube. 3) The mechanical performance of the HSTCSC short columns was greatly improved with the increase of self-stress concrete compression strength and section hollow rate; however, the influence of the increasing self-stress concrete compression strength on the mechanical performance is limited. The mechanical properties of the HSTCSC short columns with double-layer circular section had a higher reinforcement segment stiffness, which was better than that of the single-layer circular section. 4) The constraint performance of circular sectional high-strength steel tube on self-stress concrete was better than that of the rectangular section, and the effect of the increasement of section hollow rate on the axial compression properties of the HSTCSC short columns was not obvious. Moreover, the deformation performance of the HSTCSC short columns with double-layer circular section will be decreased with the increase of section hollow rate.关键词：high-strength steel tube;self-stress concrete;load-deformation curve;failure mode;bearing capacity
- 521
- |
- 187
- |
- 0
发布时间：2024-01-10 - 摘要：The seismic performance of new type industrial profile steel connecting prefabricated concrete (SPC) frame joint was investigated, and the differences between SPC and traditional monolithic reinforced concrete frame joint were compared. Based on the equality of flexural bearing capacity of beam section, a design method of SPC joint was presented to realize translation of plastic hinge from beam end to the reduction beam section (RBS) of H profile steel without decreasing the flexural bearing capacity. The displacement loading strategy was used and the pseudo static tests were conducted to a monolithic joint and the corresponding SPC joint. Failure characteristic, bearing capacity, deformation capacity, energy dissipation capacity, and strains of key positions were compared between these two specimens. The test results showed that the crack distribution of the SPC joint was similar to that of the monolithic joint, but the maximum crack width of concrete was effectively controlled in the SPC joint. The yielding load of the SPC joint was a little higher than that of the monolithic joint; moreover, the ultimate load and ductility of the SPC joint were significantly increased. Therefore, the SPC joint exhibited better bearing and deformation capacities. The degradation of strength and stiffness of the SPC joint under cyclic loads were both obviously smaller than those of the monolithic joint, and it meant the mechanical behavior of the SPC joint was more stable. The hysteretic curves of the SPC joint were fuller than those of the monolithic joint, and it implied the energy dissipation capacity of the SPC joint was better, especially under a high-intensity earthquake. The realization of the strong column and weak beam mechanism meant that the proposed design method and detail of SPC joint were effective and reasonable. Based on the test results, the seismic performance of the SPC joint was better than that of a traditional reinforced concrete joint. The deformation and damage of SPC joint concentrated on profile steel segment, therefore it can be conveniently repaired and reinforced after an earthquake.关键词：prefabricated construction;beam-column joint;steel-concrete hybrid beam;quasi-static test;seismic response
- 483
- |
- 181
- |
- 0
发布时间：2024-01-10 - 摘要：Due to the superposition of convection heat transfer of water flow and heat conduction of freezing pipes, the shape of the artificial frozen wall was obviously asymmetrical under the action of the seepage field. To solve the difficulty in the calculation of the freezing temperature field caused by the irregular shape of a frozen wall under the action of a seepage field, the freezing temperature field of three pipes arranged in a straight line was taken as the research object, the shape of the freezing front was simplified by the method of subsection equivalence. The analytical solution of steady-state temperature field of asymmetric frozen wall induced by directional seepage, the calculation formulas of thickness and average temperature of the frozen wall were derived based on the solution theory of steady-state temperature field. To verify the rationality of the formulas, the evolution law of the freezing temperature field of three pipes under the action of the seepage field was experimentally studied by using the self-constructed hydrothermal coupling physical model test system. The following conclusions were drawn from the research: the calculation results of freezing temperature on the key axis agreed well with the experimental results, the rationality of the analytical solution was verified by the model test; the closure time and asymmetry coefficient of the frozen wall were increased sharply with the increase of flow velocity under the action of the seepage field. When there was seepage in the formation, the temperature change process of the frozen wall was complicated, however, there was still a law that the average temperature decreased with the increase of thickness of the frozen wall. The formulas obtained in this paper could achieve an accurate mathematical description of the artificial freezing temperature field under the action of the seepage field, and it would provide a reference for the calculation of the artificial freezing temperature field of high-velocity permeation formation.关键词：artificial ground freezing;seepage;freezing temperature;analytical solution;similar model test
- 592
- |
- 153
- |
- 1
发布时间：2024-01-10 - 摘要：With the implementation of national networking projects, power transmission towers will inevitably be built in areas prone to geological disasters such as steep slopes, ridges, and landslides. Under the influence of rainfall, the deformation and even instability of the landslide will directly affect the safety of the towers, which has a massive impact on the development of the power system and social economy. The Yanzi landslide and the tower foundation were taken as the research object. Based on the physical model test, the instability process of the tower foundation landslide with cracks in different relative positions under rainfall was studied firstly, and a physical model test plan for the tower foundation landslide was designed. Then, the macroscopic phenomenon of the tower foundation landslide and the change process of the deformation and mechanical characteristics of the landslide and the tower foundation during the rainfall process were analyzed. Finally, the analysis process of the disaster model of the tower foundation landslide under rainfall was summarized. The results showed that the prefabricated cracks provided advantageous seepage paths for rainwater, and rainfall gradually expanded the depth and width of the prefabricated cracks, and gradually extended and penetrated to the right end of the landslide, causing local instability of the toe at the right end of the landslide, and resulting in multi-level local traction and sliding failure. The tower foundation on the landslide and the upper tower foundation outside the landslide both slide down along with the landslide and fall backwards, and the latter occurred later than the former. But the bottom tower foundation outside the landslide did not damage during the whole process. Further, when there were cracks in the Yanzi landslide, the deformation and stability of the local landslide should be used to analyze the disaster mode of the tower foundation under rainfall. The research findings can provide an intuitive understanding and technical support for the actual project of the tower foundation landslide.关键词：rainfall;tower foundation;landslide;cracks;physical model;instability process;disaster mode
- 527
- |
- 185
- |
- 0
发布时间：2024-01-10 -
Model Tests on Bearing Characteristics of High-strength Steel Tube Grid and Lattice Girder in Tunnel
摘要：Strengthening the primary support to quickly intervene in the stress state of surrounding rock was one of the effective ways to ensure the safety and stability of the tunnel during construction and operation periods. Following the concept of “timely support and strong support”, the mechanism of high-strength seamless steel tube replacing threaded reinforcement to enhance the bearing capacity of initial support structure was studied. The laboratory loading tests of steel tube grids and lattice girders under the conditions of single load and common load with concrete were carried out. The failure forms, deformation characteristics, ultimate bearing capacity, complete stress process, and crack development laws of the above structures were systematically analyzed. The results showed that steel consumption of the two supporting structures was basically the same, the maximum allowable deformation and ultimate bearing capacity of the steel tube grid were 1.6 times and 1.8 times than that of the lattice girder, respectively, which verified that the high-strength steel tubes could effectively improve the bearing performance of this structure. The lattice girder exhibited broken-line bending failure, but the steel tube grid represented smooth curve failure, and the rebound deformation was greater after unloading. The flexural rigidity of the steel tube grid concrete member was essentially the same as that of the lattice girder member, and the ultimate bearing capacity was 22.5% higher than that of the lattice girder concrete member. The bearing capacity of the lattice girder itself was limited, and it had a higher bearing capacity after forming a composite structure with concrete. The steel tube grid had the characteristics of high strength and high toughness, and the structural force was reasonable. Additionally, it could provide radial support to the surrounding rock in a timely and effective manner, and it was more suitable for weak and broken surrounding rock conditions with rapid early deformation.关键词：high-strength steel tube grid;lattice girder;bearing characteristic;failure mode- 741
- |
- 297
- |
- 1
发布时间：2024-01-10 - 摘要：Cementitious grout is the crucial part of the grouted sleeve connection, and its constitutive relationship under loading is the technical support to form the fire safety design method for grouted sleeve connections. The tests with 36 small prism specimens were conducted to study the uniaxial compressive behaviors of heat-damaged cementitious grout under static or dynamic loading strain rates after the specimens were exposed to elevated temperatures up to 600 ℃. It was found that explosive spalling was inhibited by the combined measures of pre-drying temperature with 105 ℃ in 120 min and the heating rate with 5 ℃/min. There were other findings after the specimens being loaded as follows: all specimens were failed to several vertical fractures with full-length along the height, and there were obvious spalling occurring to the specimens under the dynamic strain rate loadings; the compressive strength of heat-damaged specimens under dynamic loading strain rate with 0.067 s–1 were higher than that under static loading, which was up to 29.6%; the elastic modulus and the peak strains of heat-damaged specimens under the dynamic loading strain rate with 0.001 s–1 decreased and increased along with the increasing of elevated temperatures, respectively; compared to these of specimens at ambient temperature, the declining range of elastic modulus was up to 57.0% and ascending range of the peak strain was beyond 13.2%; the normalized curves between stress and strain of heat-damaged specimens contained ascending and declining segments, both of which were nonlinear curves; based on the experimental data, a combined static and dynamic uniaxial compression model of heat-damaged cementitious grout was built and used for the finite element simulation of heat-damaged grouted sleeve connections under high-stress cyclic loading. It was found that the peak loads and load-displacement curves from the simulation were consistent with the test results. In addition, the failure pattern of heat-damaged grouted sleeve connections under high-stress cyclic loading with rebar fracture outside the sleeve was firstly demonstrated in the simulation and 400 ℃ was the critical temperature that failure pattern of rebar fracture outside the sleeve converted into the bond-slip failure between cementitious grout and rebar after the connections were exposed to elevated temperatures.关键词：cementitious grout;elevated temperature;uniaxial compression;constitution model;grouted sleeve connection;finite element simulation
- 872
- |
- 341
- |
- 1
发布时间：2024-01-10 - 摘要：The backfill formed by the solidification of the filling slurry contains a large number of pores, and the influence of pores on the mechanical properties of the backfill is not clear. In order to explore the correlation mechanism between the pore structure and the uniaxial compressive strength (UCS) of the backfill, sodium dodecyl sulfate (SDS) was used to adjust the pore content of the backfill. Low-field nuclear magnetic resonance (NMR) technology was used to test the transverse relaxation time of the internal pores, the UCS was tested by a press, and the microscopic image of the damaged surface pore structure was obtained by scanning electron microscope (SEM). The pore size distribution was analyzed, and the fractal characteristics of the pore size were studied. The results showed that the total pores in the backfill gradually decrease with the increase of curing age, and the higher the SDS content, the closer the total pores of the sample at 14 and 28 d. The proportion of multi-damaging pores decrease significantly with the increase of the curing age, and it is negatively correlated with the UCS of the sample. The proportions of non-damaging pores, less-damaging pores, and damaging pores change little during each age. When the SDS content is 0.2% of the quality of the cement used, the UCS of the sample is the highest. The number of pores with pore diameters in the range of 5~130 nm has obvious fractal characteristics, while the number of pores with pore sizes outside this range do not have fractal characteristics. The ettringite in the hydration products is clustered, and the clustered ettringite squeezes the pore space due to growth, development, and extension. This is the microscopic reason why the total number of pores and the number of multi-damaging pores decrease with the increase of curing age. The research results can provide theoretical support for a more comprehensive understanding of the strength of the backfill.关键词：backfill;NMR;pore structure;UCS;correlation mechanism
- 464
- |
- 219
- |
- 0
发布时间：2024-01-10 - 摘要：The effect of P-wave (longitudinal wave) on soil under strong earthquake motions cannot be ignored. However, the traditional method of analyzing the dynamic behavior of soil under cyclic loading by unidirectional vibration often ignores the influence of P-wave on the dynamic stability of the soil. To study the dynamic characteristics of tailing sands under high stress, a series of bidirectional vibration triaxial tests under different confining pressures, dynamic shear stress ratios, and consolidation stress ratios were carried out adopting bidirectional cyclic loads to simulate seismic loads. The result showed that under bidirectionally excited cyclic loading, the saturated tailing sands had a cumulative plastic deformation εtp when isobaric consolidation and anisotropic consolidation. With the increase of dynamic stress amplitude, εtp had a linear negative correlation with the vibration’s times during isobaric consolidation, and a linear positive correlation with the vibration’s times during anisotropic consolidation; the cumulative pore-pressure curves of tailing sands were characteristic of stages. Confining pressure had a significant effect on the characteristic of the cumulative pore-pressure curves of tailing sands. When the confining pressure was the same, changes in the dynamic shear stress ratio and consolidation stress ratio had little effect on the characteristic of the cumulative pore-pressure curves. With the increase of confining pressure, the cumulative pore-pressure curves of tailing sands under isobaric consolidation and anisotropic consolidation had two development modes of 3 or 4 development stages. When the cumulative pore-pressure curves had three stages, the characteristic of the cumulative pore-pressure curves of tailing sands under isobaric consolidation and anisotropic consolidation had a significant difference. However, when the cumulative pore-pressure curves had four stages, the characteristics of the cumulative pore-pressure curves of tailing sands under isobaric consolidation and anisotropic consolidation were the same. Besides, through the analysis of the test results, the cumulative pore-pressure growth model of tailing sands under high-stress considering multiple factors was derived, and two forms of this model were obtained under isobaric consolidation and anisotropic consolidation. Thus, the research findings can provide a reference for the seismic reinforcement design of the tailings dam.关键词：high-stress;tailing sand;dynamic behavior;bidirectional cyclic load;plastic deformation;pore-pressure growth model
- 696
- |
- 190
- |
- 0
发布时间：2024-01-10
HYDRAULIC & CIVIL ENGINEERING
- 摘要：Based on the characteristics of sandstorm environment in midwest of Inner Mongolia, the ultraviolet aging tests were carried out on the polyurethane coating in UV aging test chamber. The aeolian erosion tests were carried out on the aged coating through a simulated sandstorm experiment system. Nanoindenter and Paint Film Elasticity Tester were used to analyze the basic mechanical properties of steel structure polyurethane coating. Fourier Transform Infrared Spectroscopy and Scanning Electron Microscopy were used to analyze the aging behavior of polyurethane coating under ultraviolet light. Study on the erosion resistance of aged coating by aeolian erosion. The results showed that the hardness of the polyurethane coating of unaged steel structure is 16.41 MPa, and the flexibility is 0.5 mm. UV aging causes a significant decrease in the hardness and flexibility of the steel structure coating. After three years of UV aging, the hardness of the steel structure coating decreases to 55.63%; UV aging effect breaks the chemical bond of polyurethane coating on steel structure, among which C-O and C-N bond break and finally generate amino radicals, release CO2, and the coating has obvious cracks, peeling, chapped, aging residue and white crystalline substances, and the roughness of the coating increases; After the steel structure coating is subjected to ultraviolet aging, the erosion rate increases, and the erosion resistance performance is significantly reduced. The main reason for the damage of the steel structure coating during low-angle erosion is the horizontal direction The main reason for the damage of the steel structure coating during high-angle erosion is the vertical extrusion deformation. The ultraviolet aging effect changes the maximum erosion rate angle of the steel structure coating from 38° to 30°～35°. The ultraviolet aging effect causes the maximum erosion rate angle of the steel structure coating to decrease.关键词：sand erosion;UV aging;steel structure polyurethane coating;erosion mechanism
- 545
- |
- 173
- |
- 1
发布时间：2024-01-10 - 摘要：Aiming at the problem of stable high-efficiency underwater drag reduction for the vehicle surface, an experimental study on the flow drag reduction performance of autostable electrolyzed microbubble array was carried out. The test piece of electrode-wall micropore array capable of forming the stable microbubble array air film through electrolysis was prepared, revealing the mechanism of electrolysis voltage, micropore size, flow velocity affecting the growth behavior and resident stability of electrolyzed microbubbles, and the flow drag reduction performance and mechanism of microbubble array were investigated by the experimental and numerical methods. The research results indicated that the electrode-wall micropore could realize the self-adaptive start-stop control of microbubble electrolysis; the time for the microbubble to reach stable diameter was shorter, but the resident time and rate of the microbubble array would decrease under the higher electrolysis voltage; the resident time and rate of the microbubble array were greater, and the time for the microbubble to reach stable diameter was shorter for the 250 μm micropore; the microbubble array’s average drag reduction rate was about 23%, and the maximum resident time and rate were 420 s, 95.46%, respectively, for the 250 μm micropore when the voltage was 20 V; the resident microbubble deformation and the air/water interfacial force jointly caused a large amount of upward throwing high-speed flow above microbubbles, which suppressed the down-sweep flow burst of flow direction vortices, and significantly reduced the near-wall Reynolds shear stress; the microbubble array near-wall numerical average kinetic energy was about 0.010 m2/s2 less than that of pure flat plate (about 0.021 m2/s2), the microbubble array numerical average wall shear was about 30 Pa less than that of pure flat plate (about 55 Pa), thus the high-efficiency turbulent drag reduction was achieved.关键词：electrolysis;microbubble array;drag reduction;resident rate;burst
- 555
- |
- 147
- |
- 1
发布时间：2024-01-10 - 摘要：The content of active SiO2 in the highland barley straw ash (HBSA) prepared under certain conditions is high, which could be used as a new type of cement cementitious materials. In order to study the preparation conditions of HBSA as a new active mixing material and its effect on the mechanical properties and water resistance of magnesium oxychloride cement mortar (MOCM), the activity of HBSA under different conditions of calcination and grinding was studied by scanning electron microscopy (SEM), X-Ray diffractometer (XRD), Fourier transform infrared spectroscopy (FTIR), and laser particle size analyzer (LPSA). The water resistance of MOCM with different mixing methods and HBSA contents was analyzed by mechanical property test. The pore structure of MOCM was measured by Nuclear Magnetic Resonance (NMR), and the microstructure of MOCM was characterized by FTIR and SEM. Finally, the influence mechanism of HBSA on mechanical properties and water resistance of MOCM was revealed. The results showed that the HBSA obtained by calcination at 600 ℃ for 2 h and grinding for 2 h has the highest activity. The way of external mixing of appropriate amount of HBSA into MOCM could obtain better water resistance compared with the way of internal mixing. With the increase of the contents of HBSA, the compressive strength under dry and saturated conditions increases first and then decreases in the way of external mixing. The compressive strength in dry state increases first and then decreases, and the compressive strength in saturated state decreases continuously in the way of internal mixing. Mechanical property is the best when the addition of HBSA was 5% in the way of external mixing, and the water resistance is the best when the addition of HBSA was 10% in the way of external mixing. When the HBSA content is up to 10% in the way of external mixing, MOCM could generate a lot of hydrated magnesium silicate (M—S—H) gels. The proportion of harmful pores and more harmful pores are significantly reduced, so as to optimize the pore structure and improve the water resistance.关键词：active mixed materials;magnesium oxychloride cement mortar;highland barley straw ash;mechanical properties;water resistance;influence mechanism
- 508
- |
- 206
- |
- 4
发布时间：2024-01-10
CHEMICAL ENGINEERING & MATERIAL ENGINEERING
- 摘要：Under extreme working conditions, the lubricating oil film in the clearance of hydrostatic bearing is subjected to the combined action of strong extrusion pressure and strong shear force. Therefore, the temperature of lubricating oil increased, and the viscosity decreased, resulted in the oil film becomes thinner. During the operation, the hydrostatic support is prone to tribological failure and the lubrication state is difficult to obtain under extreme conditions. In order to solve this technical problem, the new inclined oil pad of hydrostatic support structure was designed to form a static and dynamic pressure hybrid thrust bearing, and an idea that use the micro-gap oil film morphology to characterize the lubrication state of the hydrostatic support was proposed. The equations such as temperature rise, power consumption, thermal-solid coupling deformation, fluid-solid coupling deformation and oil film shape were derived for the new double rectangular cavity hydrostatic bearing with tilting oil pad. In the first, Solidworks software was used to establish the three-dimensional geometric model of hydrostatic support oil film, ANSYS ICEM software was used to carry out high-quality gap oil film structured mesh division, oil film mesh was introduced into ANSYS CFX to set the corresponding boundary conditions, and MATLAB was used to fit the viscose-temperature relation curve of 46# lubricating oil for variable viscosity simulation. The distribution characteristics of the oil film temperature and oil film pressure fields under extreme operating conditions were solved and analyzed. In the second, the thermal-mechanical coupling deformation of the friction pairs and the three-dimensional oil film shape were obtained by data processing in MATLAB to judge the lubrication status of hydrostatic support. In the end, an oil film thickness measuring device was set up to obtain the oil film thickness state and verify the correctness of the oil film morphology that obtained by theoretical analysis and numerical simulation. The results showed that the lubricating performance of the structure is improved significantly under extreme working conditions. In the light load and high speed situation, the thermal deformation plays a leading role and the oil film thickness is uneven. Correspondingly, and the oil film is smoother when the force deformation dominates at low speed and heavy load situation. The greatest deformation appeared at the corners of the sealing oil edges on the outside of the oil cavity, where the oil film is the thinnest, which is prone to tribological failure.关键词：hydrostatic and dynamic pressure hybrid support;tilting oil pad;lubrication state;thermal-mechanical coupling deformation;morphology characterization of micro-clearance oil film
- 605
- |
- 227
- |
- 0
发布时间：2024-01-10 - 摘要：In view of the influence of tool setting position on the accuracy of a machine tool and the evaluation of its final accuracy and performance, a method of geometric accuracy prediction for a five axis CNC machine tool (FACMT) considering tool setting position is proposed. Firstly, the kinematics equation of the FACMT based on a NAS979 inclined cone frustum is established by using multi-body system theory. On this basis, the solving equations for the actual machining position and NC machining instructions of the test piece based on tool setting position are built, the prediction model of geometric accuracy for the FACMT is established and the accuracy indexes such as roundness, angularity and concentricity of the cone frustum are predicted. Then, the simulation prediction for accuracy of the FACMT is carried out. The predicted values of roundness, angularity and concentricity are 0.0251 mm,
$\phi $ $\phi $ $\phi $ $\phi $ $\phi $ 关键词：tool setting position;CNC machine tool;geometric accuracy;prediction model;cone frustum- 481
- |
- 177
- |
- 0
发布时间：2024-01-10 - 摘要：Parallel sliders textured with oriented dimples have different frictional performances when moving in different directions. However, the anisotropy of dimples is hardly studied to adopt the different working conditions at bidirectional movements. Therefore, based on the multiphase flow cavitation model in Fluent, a three-dimensional numerical model of the lubricant between the parallel sliders with equilateral triangular dimples was developed for reducing the friction coefficient with the anisotropy of triangle dimples. Firstly, the fluid factor was calculated for checking the flow pattern, and the grid independence test was done for determining the grid size. The calculation result was also compared with the reference in order to ensure the accuracy of the model. Secondly, the anisotropy of triangle dimples was described. The reason of anisotropy is the different wedge effects at different moving direction. Thirdly, the influences of the velocity and the depth of dimples on the anisotropy were studied. Finally, the average friction coefficient of the sliders with triangular dimples was compared with that with circular dimples under different bidirectional movement conditions. The results showed that the anisotropy of sliders with triangular dimples is obvious in the low pressure region, with a maximal friction coefficient difference 31.68%. The increase of velocity widens the pressure range where obvious anisotropy appeared. The effect of dimple depth on the anisotropy depends on the effect of the dimple depth on the dynamic pressure, and the best depth for friction performance is 3 μm. The friction coefficient of sliders with circular dimples is between that with triangular dimples moving forward and backward, and the maximum difference is 17.96%. When the working conditions of the two directions are different, the friction coefficient of sliders with triangular dimples can be reduced by 13.3%.关键词：equilateral triangular dimples;numerical calculation;anisotropy;friction coefficient;asymmetric pressure difference
- 541
- |
- 168
- |
- 0
发布时间：2024-01-10
MECHANICAL ENGINEERING
- 摘要：Due to its simplicity, efficiency and safety, image velocimetry has gained widespread attention and is beginning to be used in domestic and international hydrographic stations. At present, the mainstream image-based flow measurement techniques mainly include large-scale particle image velocimetry (LSPIV) and spatio-temporal image velocimetry (STIV), etc. While the LSPIV method uses natural particles as tracers and uses the spatial correlation method to process the image to obtain the flow field vector, the STIV method sets the velocity line according to the main flow direction of the river, samples the grey scale of the velocity line in the video image to form the spatio-temporal image, and uses the texture angle in the spatio-temporal image to obtain the flow velocity. Generally, the LSPIV method has disadvantages such as poor stability due to its reliance on the visibility of the tracer, and the STIV method has disadvantages such as high requirements for the stability of the cross-sectional flow regime and the ability to measure only one-dimensional flow velocities. In this paper, a grouping flow measurement method based on the combination of inter-frame difference and fast optical flow using dense inverse search (FD-DIS-G) was proposed. In the method, the frame difference method was used to calculate a kinematic saliency map that captures subtle water surface motions to deal with the problem that river motions are not evident in the video, which reduces the reliance on natural tracers. Then, the fast optical flow is used to calculate the dense optical flow displacements between small areas of the kinematic prominence map, improving the accuracy and timeliness of flow measurements and effectively overcoming the flow instability. Meanwhile, a method of grouping processing abnormal values was designed, which improves the overall accuracy of the algorithm and enhances the stability of the algorithm. The results of the experiments showed that the accuracy of the mean flow velocity and cross-sectional flow rate is significantly improved compared with the widely-used image flow measurement methods, and the proposed mean flow velocity measurement methods achieves real-time performance and its stability of is significantly enhanced.关键词：video flow measurement;dense optical flow;frame difference method
- 608
- |
- 260
- |
- 0
发布时间：2024-01-10 - 摘要：Optical fibre sensing techniques have been applied in security engineering to detect disturbances. However, most of the conventional single-mode-fibre based distributed security monitoring systems fail to simultaneously implement important functions such as recognizing intrusion patterns, quantifying the intensities and warning early fire. In this study, a monolithic multi-parameter sensing system using a multicore fibre based on spatial-division-multiplex sensing was developed to meet the expanding demands in security engineering. In the system, the local strains and temperatures were monitored by the core with fibre Bragg gratings (FBG), the external disturbances were localized and quantified by the phase-sensitive core, and the temperature field was measured and the overheated was identified by the Raman core. In the post-process, 4 intrusion localization methods were adopted for multi-level intrusion identification, namely the high-degree central moment, signal range, spatial average kurtosis and eigen-frequency method. The multi-index disturbance quantitative evaluation method was proposed, the strain field was calculated according to the signal patterns by the subsidiary disturbance quantification algorithm for Rayleigh backscattering signal, and the strain histories of FBG core were considered as well, such that the quantitative disturbance indices could be derived and utilized to quantify intrusion intensities as well as recognize the patterns; the fire alarms were released based on the real-time temperature field that also contributed to compensating strain measurement. The performance of the proposed system was evaluated by 7 practical tests on a steel fence structure. The results demonstrated that features of each intrusion event were acquired in time, space and frequency domain through 4 localization methods, intrusions were localized accurately (errors <1 m), and the moderate ground vibration could be identified through the eigen-frequency method; in the weight-impact test, 15 disturbance intensities were correctly quantified and the quantitative indices presented positive correlation with impact intensities; the temperature field along the fibre was synchronously obtained with the heated region localized, and the result of FBG agreed well with that of Raman core. The developed system serves as a novel method to overcome drawbacks of conventional systems, including monitoring parameter deficiency and poor reliability, and solves typical problems in security monitoring such as temperature-strain cross-sensitivity and disturbance quantification.关键词：multicore fibre;security engineering;multi-parameter sensing;spatial division multiplexing;disturbance quantification
- 722
- |
- 218
- |
- 0
发布时间：2024-01-10 - 摘要：To solve the problems that the identification accuracy and stability of the single-layer identification scheme are deteriorated due to the increase in the number of cryptographic algorithms, the complexity of ciphertext data and the increase of interference between data, a hybrid gradient boosting decision tree and logistic regression (HGBDTLR) model were proposed, and a block cipher algorithm identification scheme based on this model (HGLBIS) was constructed. In this scheme, 15 NIST randomness testing methods were used as the ciphertext feature extraction methods to extract features from the ciphertext files, and 10 meaningful feature values were selected as the input to the classifier; then these 10 feature values were used to train a gradient boosting decision tree model, and the trees generated from its learning were used to construct new features; finally, the new features were one-hot encoded, and added to the original features to train the logistic regression model. In the ciphertext only scenario, nine different cryptographic algorithm identification schemes were constructed based on nine different classifier models. Then, these nine schemes were used to perform binary classification of block ciphers experiments on ciphertext files of different sizes encrypted by two typical block cipher algorithms AES and 3DES, and five classification of block ciphers experiments on ciphertext files of different sizes encrypted by five commonly-used block cipher algorithms AES, 3DES, Blowfish, CAST and RC2. The experimental results showed that, compared with the existing identification schemes, when the size of ciphertext files is the same, the scheme proposed in this paper has almost the highest identification accuracy on both the binary classification and five classifications of block ciphers. At the same time, with the change of the size of ciphertext files, the identification accuracy shows a fluctuating change. In conclusion, the proposed scheme has the smallest fluctuation range, the smallest degree of influence and the highest stability.关键词：cryptographic algorithm identification;machine learning;ensemble learning;gradient boosting decision tree;logistic regression
- 643
- |
- 188
- |
- 1
发布时间：2024-01-10 - 摘要：Wireless sensor networks have the characteristics of large scale, self-organization, reliability, data-centricity, integration, etc., and are widely used in military, medical, mine monitoring, safety production and other fields. However, the existing non-ranging positioning algorithms for wireless sensor networks suffer from large positioning errors. Aiming at this problem, a DV-Hop (distance vector-hop) localization algorithm based on the global artificial fish swarm algorithm optimization was proposed, namely DEWF-D localization algorithm. In the algorithm, the error-prone steps of the DV-Hop algorithm were optimized in the non-ranging positioning algorithm, and finally more accurate positioning coordinates were obtained by reducing the errors in the algorithm process. First, messages were transmitted by the beacon nodes with two different communication radii, and the number of hops was precisely processed to reduce the error caused by the number of hops; then, the average distance per hop was calculated using the minimum mean square error criterion and the error weighting method; Finally, the global artificial fish swarm algorithm was used to replace the trilateration method for coordinate calculation. Simulation results showed that, compared with the DV-Hop algorithm and other algorithms, the positioning accuracy of the proposed algorithm is respectively improved by 28.3%, 6.9%, and 12.5% under different beacon node densities; and under different communication radii, the positioning accuracy is improved by 24.4%, 7.6%, 14.8%, respectively. It was demonstrated that the DEWF-D algorithm can effectively improve the positioning accuracy and solve the problem of large positioning errors in previous positioning algorithms.关键词：wireless sensor network;DV-Hop localization algorithm;dual communication radius;global artificial fish swarm
- 640
- |
- 170
- |
- 2
发布时间：2024-01-10 - 摘要：The multi-intensity phase retrieval methods obtain different coded diffraction patterns by changing the physical parameters in the optical imaging system, which can achieve the best convergence of phase and high-precision reconstruction without additional prior knowledge. However, the existing multi-intensity phase retrieval methods often need to constantly change the physical structure of the imaging system and accurately move or adjust the spatial position of some optical elements in the process of obtaining different measurements. The repeated alignment and calibration significantly increase the workload, resulting in more complex imaging structure. To solve the above problems, a real-time acquisition method of Fresnel field coded diffraction pattern based on high-speed phase modulation was proposed in this paper. In the method, two pure phase spatial light modulators: electrically tunable lens (ETL) and pure phase silicon-based liquid crystal (PLCoS) were mainly used to perform the fast dynamic phase modulation. The phase was transmitted to the recording plane through free space, and the intensity information was obtained by the detector without using a lens or changing the physical structure of the imaging system. The WF algorithm was used to simultaneously reconstruct the amplitude and phase of the light field from multiple coded diffraction patterns. In the paper, the effectiveness and robustness of the proposed method were verified by the contrast experiments of farfield (FF) and Fresnel field (FrF) under different iteration times, different mask numbers, different noise levels and different algorithms. Compared with the traditional multi-intensity phase retrieval methods, the proposed imaging system is more compact and simple. It avoids the workload of repeated alignment and calibration, and has important application potentials. Especially, the electrically tunable lens (ETL) modulation scheme can be applied to high-speed recording of high-resolution scenes.关键词：multiple intensity;phase modulation;Fresnel field;phase retrieval
- 715
- |
- 195
- |
- 0
发布时间：2024-01-10
INFORMATION ENGINEERING
- Technical support is provided by Beijing Founder electronics co., LTD 京ICP备09064830号-19
京公网安备11010802024621 - It is recommended to read the content of this site in Chrome&IE9+. Please switch to extreme mode in browser 360.
- Cookies We use cookies to help provide and enhance our service and tailor content. By continuing, you agree to the use of cookies.
0