最新刊期
卷 53 ， 期 5 ， 2021
- 摘要：A water–soil coupling model of channel fluid movement is established considering the interaction of gully bed erosion, slope confluence, and rainfall, which can provide theoretical basis for watershed risk assessment, disaster prevention and mitigation, and identification of potential debris flow gully. By analyzing the erosion process of the channel fluid on the movable solid source of the gully bed, and coupling it with the slope confluence and the rainfall over the channel with temporal and spatial variability, the water–soil coupling model of the channel fluid movement in the small watershed can be established. The finite difference method was used to discretize the water–soil coupling model of fluid movement in time and space. A computer code for the coupling model of fluid motion was written in MATLAB. Meanwhile, laboratory experiments were carried out with varying flow rates and groove slopes to observe the evolution of fluid flow depth, flow velocity and fluid bulk density under different working conditions. By analyzing the results of the 12 sets of experiments, it was found that under the condition that the slope of the groove remains unchanged, the fluid flow depth and the fluid velocity were positively correlated with the flow and the bulk density was negatively correlated with the flow. At the same time, the numerical simulation results of the fluid flow depth, flow velocity and fluid bulk density at the control point of the groove were compared to and analyzed with the experimental results. It was found that the simulation accuracy of the fluid flow velocity and fluid bulk density were higher than 90%, and the simulation accuracy of the fluid flow depth was higher than 80%. The results revealed that the established water–soil coupling model of the channel fluid movement in the small watershed is accurate.关键词：gully bed start;fluid movement model;water–soil coupling;finite difference method;numerical discrete
- 977
- |
- 487
- |
- 0
发布时间：2024-01-10 -
Flow Separation and Vortical Structure Around Submerged Breakwater Subject to Nonlinear Water Waves AI导读
摘要：Flow separation and vortical dynamics generated by second-order Stokes waves propagating over a submerged rectangular breakwater supported on a rubble mound were investigated using particle image velocimetry (PIV) technology and numerical model based on Reynolds–averaged-Navier–Stokes equations (RANS). Experimental wave surfaces show nonlinear deformation before and after the structure. The asymmetry and skewness of the weatherside wave profile are –0.21 and 0.04, respectively, which indicates a steep front face and gentle rear face. The asymmetry and skewness of the leeside wave profile are –0.39 and 0.99, respectively, which indicates more significant lack of symmetry relative to vertical and horizontal axes. Phase-averaged velocity and vortex fields calculated from PIV data show that clockwise and counterclockwise vortices are generated periodically on the weatherside and leeside of the structure. However, these vortices are not fully developed. The subsequent flow reversal moves the vortices towards the free surface or the structure to make them dissipated. The weatherside vortex pair is confined within a relatively narrow region of about 0.5 times Keulegan–Carpenter number from the weatherside of the structure, which implies smaller wave energy dissipation. Meanwhile, the leeside vortex pair is confined within a relatively wide region of about 1.0 times Keulegan–Carpenter number from the leeside of the structure, which indicates greater dissipation of wave energy. In addition, a small circulation system is found above the upstream shoulder of the rubble mound and its movement is confined within two times the unperturbed wave particle trajectory, which may lead to local scouring. A numerical wave flume was established based on RANS–VOF mode and then verified by experimental results. The applicability of different wave-making methods and the effect of energy dissipation by sponge layer were analyzed. The RANS–VOF model was then used to further study the flow separation of shear boundary layers. Numerical results show that the supply of vorticity mainly comes from the shear boundary layers at the surface of the structure. The adverse vorticity in the shear boundary layers is induced by the adverse pressure gradient imposed by the movement of the vortices previously shed from the structure. The generation, shedding, stretching, advection and dissipation of vortices is expected to significantly change the local flow around submerged structures and hence cause local scour as well as additional loading. Therefore, the effect of the complex flow induced by vortices should be taken into account in engineering design.关键词：nonlinear water wave;submerged rectangular breakwater;velocity field;vorticity field;flow separation- 1019
- |
- 421
- |
- 1
发布时间：2024-01-10 - 摘要：To meet the demand for green construction of power grids in the new era, it is urgent to develop and apply a new type of environment-friendly foundation for power grid projects. For this purpose, an improved thin-walled tapered-end grouted miniature steel pipe pile was proposed, and the uplift bearing characteristics of this pile were studied through field tests. With the project background of the 220 kV line Shuanglou—Jiaohe Dongguang north substation, 18 steel pipe piles with two pile diameters of 159 mm and 203 mm, two burial depths of 5 m and 8 m were designed under two conditions of grouting and no grouting. The effects of grouting on the load–displacement curves, uplift bearing capacities, and soil failure modes for different test piles were analyzed through on-site uplift bearing characteristic tests. Based on the failure mechanism of pile–soil interface obtained through the field tests, a finite element model incorporated the pile–soil interaction for the tests was established, and the uplift deformation and failure process of the steel pipe pile was numerically simulated and analyzed. The simulation results showed that the failure modes of the pile–soil interface were consistent with the field tests. By comparing the shear strength parameters and microstructure of the soil around the pile before and after grouting, the macroscopic and microscopic mechanism of the influence of grouting on the soil around the pile was analyzed. The test results are as follows: 1) The load–displacement curve of steel pipe pile changed from steep drop type to slow change type after grouting, and the grouting enhanced the ability of the pile foundation to resist plastic deformation. 2) The uplift capacity of steel pipe pile increased by 59%～148% after grouting, and the increase range was negatively related to the slenderness ratio of test pile. 3) There were few cracks in the surface soil at the failure state of uplift tests for the non-grouting steel pipe piles. The pile body was almost extracted, and the surface soil appeared radial and circumferential cracks at the failure state of the grouting steel pipe piles. 4) Many voids in soil were filled in the process of grouting, which improved the soil strength around the pile. Cement consolidation was formed around the steel pipe pile after grouting, and a shear surface was formed between the cement consolidation and soil. This conclusion was also supported by the numerical simulation results. The influence mechanism of grouting on the uplift bearing capacity of steel pipe pile was mainly reflected in the increase of shear area and side friction of soil around the pile. The engineering application showed that the proposed steel pipe pile had a short construction period, a high bearing capacity, and a low impact on the surrounding environment. These steel pipe piles have been well popularized and applied in the 220 kV line project Shuanglou—Jiaohe Dongguang north substation.关键词：transmission line;grouting steel pipe pile;field test;CT scanning;numerical simulation;uplift bearing capacity
- 1066
- |
- 405
- |
- 0
发布时间：2024-01-10 -
Analysis on Seismic Behavior of a New Frame Joint of Isolation Layer in PC Base-isolated Structure AI导读
摘要：The base isolation structure has a high requirement for integrity of the isolation layer, and the connection behavior of the isolation layer members affects the integrity and the seismic behavior of the isolation layer directly. In this paper, the welding connection mode between longitudinal reinforcements at the bottom of the beam was improved, the tensile tests were also carried out, and a new frame joint was proposed of the isolation layer for prefabricated concrete base isolation structure. Then, the finite element models of the new frame joint and traditional cast-in-place joint were established to simulate the seismic behavior and the structural integrity under the lateral repeated loads in ABAQUS. Finally, an improved connection mode for the new frame joint was proposed by comparing the difference of seismic behavior between the two kinds of joints. The results showed that the tensile strength of the specimen which connected by grooving and welding on the steel plate was close to that of the complete reinforcement, and could significantly reduce the bending deformation of the connecting steel plate. The bearing capacity, stiffness and energy dissipation capacity of the prefabricated frame joint were lower than that of the cast-in-place joint, but the deformation capacity was stronger. The bearing capacity, stiffness, and deformation capacity of the new frame joint on the prefabricated isolation layer increased when some anchored rebars were added to the ends of the prefabricated beam, the reinforcement ratio at the end of beams also increased, at the same time, the plastic development of the longitudinal reinforcement was delayed by the anchored rebars, so the energy dissipation capacity decreased. The load-bearing capacity, stiffness and deformation capacity of the improved prefabricated frame joint were all stronger than that of cast-in-place joint, so the improved new frame joint had an excellent structural integrity, and it could be used in practical engineering widely.关键词：prefabricated concrete (PC);welding;tensile testing;integrity;numerical simulation- 751
- |
- 466
- |
- 1
发布时间：2024-01-10 - 摘要：To study the dynamic performance of C-type cold-formed thin-walled steel members under transverse impact loading, two groups of 12 members were selected for impact test. The deformation modes and displacement extremum of the test members were compared with the results of ANSYS/LS–DYNA finite element simulation and the results showed that the deformation modes of the two members were similar, and the difference of displacement extremum was less than 8.0%, which indicated that ANSYS/LS–DYNA finite element model could accurately and effectively simulate the dynamic response of the steel member. Then, the numerical model was used to analyze the influence of different impact parameters (density, velocity and angle) on the deformation mode and dynamic performance of C-type cold-formed thin-walled steel members successively. The results showed that the maximum impact force of members increased by 25.5%, the maximum vertical displacement was 20.30 mm, and the proportion of stable strain energy in the peak value was basically maintained at 60.0%, when the density of impactor increased by 2000 kg/m3 in the range of 2000～8000 kg/m3; when the velocity of the impactor increased by 3 m/s in the range of 3～9 m/s, the maximum impact force of the member increased by 79.1%, the maximum vertical displacement was 26.78 mm, and the proportion of the stable strain energy in the peak value basically remained at 60.0%; when the impact angle of the impactor increased from 30° to 90°, the maximum amplification of impact force was 41.4%, the maximum vertical displacement was 20.09 mm, and the proportion of stable strain energy in the peak value was between 60.0% and 70.0%. Eventually, the deformation and degree of damage of the member were affected by the change of impactor density, velocity and impact angle, and the impact velocity had the most outstanding influence on the deformation of the member.关键词：thin-walled members;dynamic loads;plastic deformation;dynamic response
- 882
- |
- 431
- |
- 0
发布时间：2024-01-10 - 摘要：The failure mode analysis of surrounding rock is the basis of stability analysis, control, and support design of surrounding rock in underground engineering. The excavation of surrounding rock is a complex loading and unloading process with radial stress decreasing and axial stress increasing, but the failure mode of surrounding rock of tunnels is often studied by overloading tests. As an important factor affecting its failure mode, the stress path of surrounding rock in overload test is different from that of confining pressure unloading with axial compression. To compare the failure modes of tunnel surrounding rock under different stress states, the strain evolution law and failure surface development process of tunnel surrounding rock during overload and excavation unloading process were studied by utilizing the WE–600B hydraulic universal testing machine and self-designed tunnel model tester. In terms of strain evolution law, both conditions produced a certain tensile strain at the bottom of the arch, while the strain growth rate of the side wall and arch waist in the excavation and unloading mode was higher than that in the overload mode, and the deformation speed of surrounding rock towards the blank surface was faster and the failure was more severe in the excavation and unloading mode. In the development of the failure surface, the surrounding rock on both sides of the straight wall was peeled off under tunnel overloading, and the peeled body remains intact, however it was extruding and crushing to free space and the integrity was very poor during excavation unloading, indicating that the crushing degree of surrounding rocks under the excavation and unloading path was greater. During overloading condition, the failure process from the tensile cracks of arch bottom under low stress state transits into the tensile-shear coupling “V” shape peeling failure of the side walls under high stress state. The failure model was wedge failure and vertical tension fracture coupling “V” shape splitting failure when the tunnel was under two kinds (60%
${\sigma _{{{{\textit{z}}\max}}}}$ ${\sigma _{{{{\textit{z}}\max}}}}$ 关键词：surrounding rock of tunnel;overloading test;excavation unloading test;strain evolution;development of failure surface;failure patterns- 1178
- |
- 394
- |
- 2
发布时间：2024-01-10 - 摘要：Creep deformation and stress relaxation are two properties of rock mass in underground engineering, but in many construction practices, rock mass is neither pure creep deformation nor pure stress relaxation, with stress and strain of rock masses simultaneously changed with time, which is time-dependent, and may ultimately cause failure. It’s hard to explain the phenomenon simply by creep deformation and stress relaxation, so it is a challenge for rock mechanics researchers. To ensure the long-term stability of underground engineering and its structures, it is necessary to further study the properties of rock mass in the generalized theory of rheological mechanics. In the linear viscoelastic theory, the creep compliance was obtained by creep deformation test while the relaxation modulus by stress relaxation test, and the two values were showing linear rheological features, in a reciprocal relationship with each other, and could be converted in each other under certain conditions, so they were no essential difference. But in non-linear viscoelastic theory, their relationship was not clear, and the generalized rheological theory by the stress-feedback controlling method provided the possibility to study mutual relationship. The generalized rheological tests of Tage tuff at 50%, 85% of the peak stress level, Sanjome andesite at 50%, 65% and 80% of the peak stress level were carried out by using the stress-feedback testing method, the generalized rheological direction coefficient for two rocks were 3.0, ±∞, –3.0, –1.0, –0.3, 0, 0.3, respectively. The experimental results showed that the generalized rheological law for two rocks was similar, and the variation of stress and strain obeyed the logarithms law. Based on the definitions of creep compliance and relaxation modulus in the linear viscoelastic theory, the generalized related strain and stress were defined, the calculating method for generalized rheological-compliance (GRC) and generalized rheological-modulus (GRM) was proposed. According to the testing results analyses, the proposed method was general, and creep compliance and relaxation modulus were two special forms of generalized rheological properties. It was found that GRC and GRM were relevant to viscoelastic deformation, had obvious characteristics of time-dependence, direction coefficient-dependence and non-linear rheology, and the ratio between GRC and GRM slightly decreased with time, which showed that the rock rigidity gradually reduced, and deformation quickly increased in pre-failure region. Consequently, the proposed method in this paper can further analyze the quantitative relationship between rock rigidity and plastic deformation, it is very valuable for further investigation of time effect and assessing the long-term stability of underground structures.关键词：generalized rheological-compliance;generalized rheological-modulus;nonlinear-viscoelasticity;rigidity;plastic deformation
- 940
- |
- 488
- |
- 0
发布时间：2024-01-10 - 摘要：The double steel plate composite shear wall structure is widely used in the high-rise buildings due to its advantages of good integrity, high rigidity and high shear bearing capacity. In this paper, the mechanical characteristics of L-shaped section double steel plate composite shear wall structure were analyzed. The finite element software ABAQUS was used to model and analyze the L-shaped section double steel plate composite shear wall, and the results were compared with the experimental results, through the finite element parametric modeling, the influence and characteristics of the main parameters such as axial compression ratio, steel plate thickness, steel plate strength grade, concrete strength grade, end H-beam size and other parameters on the hysteretic performance of the shear wall were studied. Results showed that the finite element model fit well with the test results; the bearing capacity of specimens increased with decreasing height–width ratio; increasing the thickness of the steel plate and the size of the H-beam at the end, increasing the strength grade of the steel plate and the strength grade of the concrete would increase the bearing capacity of the L-shaped section double steel plate composite shear wall; the strength of the concrete and the addition of H-shaped steel at the flangeless web were the main factors affecting the bearing capacity. It is recommended that the design axial compression ratio of the L-shaped section double steel plate composite shear wall should be restricted under 0.4.关键词：L-shaped double steel plate composite shear wall;finite element analysis;parametric analysis;end strengthening;pseudo-static test
- 886
- |
- 341
- |
- 2
发布时间：2024-01-10 - 摘要：Hysteresis is one of the important characteristics of automatic adjustment of river system, while there are few studies on the law of sediment delayed response in the Three Gorges Reservoir (TGR). Based on the delayed response model, the measured data were analyzed and the delayed response model was modified by considering the sediment concentration and sediment particle size in order to construct the delayed response model in accordance with the characteristic of sediment deposition in TGR. Firstly, the changes of water and sediment conditions and sediment deposition characteristics since the impoundment of TGR were counted, and the influence of cascade reservoirs in the upper Yangtze River was analyzed. In order to simulate and analyze the sedimentation delayed response law in different periods of TGR, the existing model was used and modified. Based on the existing and modified response model simulation results, it can be seen that: 1) The modified response model can better simulate the sediment deposition process of TGR after the impoundment of cascade reservoirs because of the consideration of sediment concentration and sediment particle size. 2) After the impoundment of cascade reservoirs, the fluctuation range of inflow and sediment decreases, the sediment inflow of TGR is more concentrated in flood season, both of which make the channel adjustment rate increase, the delayed response time of sediment deposition in TGR is shortened from the early 4 years to the early 3 years. 3) After the impoundment of cascade reservoirs, the influence weight of sediment concentration on the sediment deposition process increases, while the influence weight of flow and water level in front of dam decreases. By using the modified model, it can be seen that the inflow of sediment concentrates more in the flood season, which make the delayed response time of sedimentation in TGR shorten, and the influence weight of sediment on the sediment deposition increases.关键词：Three Gorges Reservoir;delayed response model;sedimentation
- 1077
- |
- 697
- |
- 4
发布时间：2024-01-10 - 摘要：Land subsidence is mainly caused by excessive exploration of groundwater resource, which has been a common and serious geological hazard. Land subsidence has the characteristics of the long-term development of soil deformation, in which one of the main reasons for the phenomenon is the rheology of clay in aquitard and sand in aquifer. Therefore, based on the generalized Kelvin viscoelastic model used to simulate the rheological properties of aquitard and aquifer, combined with Terzaghi’s one-dimensional consolidation theory and continuity condition, the equation governing rheological consolidation and definite solution condition of long-term deformation of the aquitard–aquifer foundation owing to groundwater level variation are obtained. Using Laplace transform, based on traditional matrix transfer method and boundary transform technique, the calculation formulas of the pore water pressure and settlement of the two-layer system in Laplace space are derived, respectively. In order to obtain the solutions in time domain, the Stehfest method is used to calculate numerical inverse transformation and the computation program has been developed. Compared with the existing analytical solutions of single-layer soil, the experimental results and numerical simulation results of two-layer system, the two methods and computation program are verified. In contrast to the traditional matrix method, the boundary transformation technique can transform the involved mixed-type boundary conditions into more tractable uniform boundary conditions; in the meanwhile, it has higher computational accuracy and efficiency. Finally, based on the boundary transformation technique and average consolidation degree defined by the total settlement, more numerical examples have been conducted to investigate the influences of viscosity of skeleton, soil layer permeability and water head falling rate on the long-term deformation of two-layer soil. The results show that the influences of permeability coefficient and drawdown rate on consolidation progress are mainly reflected in the early and middle stage, and the consolidation progress develops more slowly with the decrease of the permeability and drawdown rate. However, the viscosity coefficient exhibits a significant effect on the later stage of soil deformation, and the time needed to complete the deformation is longer with the increase of viscosity under the same groundwater drawdown.关键词：groundwater level variation;land subsidence;double-layered ground;viscoelastic model;semi-analytical solution
- 1666
- |
- 496
- |
- 1
发布时间：2024-01-10 - 摘要：The dual effects of climate change and human activities have caused significant changes in the hydrological process of a river basin. The variation diagnosis of hydrological sequence has important scientific significance and application value for flood control, disaster reduction, and ecological environment protection. The traditional hydrological variation diagnosis methods have shortcomings such as insufficient multi-point detection ability, strong subjectivity, and low accuracy. A hydrological variation diagnosis coupling model based on heuristic segmentation algorithm and approximate entropy was established in this paper. The main modeling steps are as follows: Firstly, use approximate entropy to describe the dynamic state of each point in the hydrological sequence, and fully obtain the approximate entropy sequence that changes with the movement of the sliding window based on the data sliding technology; Secondly, use the heuristic segmentation algorithm to sequentially divide each point into two iterative calculations and comparisons, and then obtain the test statistics sequence and the confidence probability sequence of each point; Finally, judge whether to divide the hydrodynamic state of the approximate entropy sequence according to the confidence probability result, and determine the number and location of the mutation point. The present coupling model was used to diagnose the variation of the annual runoff sequence of the Wenjiachuan Station of the Kuye River from 1956 to 2018. The results show that the annual runoff sequence of the Kuye River changed in 1983 and 1996, which is consistent with the actual situation. Through a large number of simulations, it is proven that the coupling model has the following potentials: 1) It has excellent detection performance for strong trend mutations, and has good performance under certain sliding step lengths for weak trend mutations. 2) Under different parameters, the coupling model has better performance for the detection of weak trend dynamic structure mutations, and the detection error is small. 3) When the sample size is high (4000～8000), the weight error is small, and the mutation interval detected by the coupling model contains the set ideal mutation point; the larger the sample size is, the more accurate the detection will be; When the sample size is low (60～3000), the detected mutation interval is closer to the true mutation point, and the detection effect is acceptable.关键词：variation diagnosis;approximate entropy;heuristic segmentation algorithm;coupling model;Kuye River
- 860
- |
- 422
- |
- 1
发布时间：2024-01-10 - 摘要：Pipe jacking synchronous grouting is an important method to reduce formation disturbance and final settlement. In order to obtain the relationship between the grouting pressure and the final settlement, find out the reasonable grouting pressure and grouting amount in the actual project to reduce the disturbance of the surrounding stratum, and provide theoretical and experimental supports for the improvements of the synchronous grouting technology, the stratum–mud interaction and the mechanism of settlement from the perspective of the structural characteristics of soil particles and bentonite molecules were analyzed, theoretical assumptions for the four stages of settlement were put forward. Then, the geotechnical engineering centrifuges and self-developed pipe jacking projects were used to simulate the pipe jacking under different grouting pressures on-site. Through the comparative analyses of the settlement curves, the conclusions of the theoretical analysis part were verified. Finally, the relevant parameters such as the grouting pressure in the experiment were applied to the pipe jacking project in Suzhou Donghui Park and the settlement measurement points were arranged on-site, further verified the conclusions. Researches showed that the settlement after grouting can be divided into four stages: soil collapse stage, seepage loss stage, mud skin formation stage and grout uplift stage. The soil collapse stage was short and the settlement speed was fast. Seepage loss stage lasted for a long time and the total settlement was large, which was the main part of the formation settlement. At the mud skin formation stage, the bentonite molecules accumulated on the mud–stratum contact surface to form mud skin, and the slurry was not permeated into the stratum and the settlement of the stratum slowed down. Finally, at the grout uplift stage, the grouting pressure of the mud acted on the mud skin to push the overlying soil and produce settlement compensation. The size of grouting pressure and grouting amount had a great influence on the final settlement. Small grouting pressure and grouting amount would increase the settlement caused by soil collapse and seepage loss, while large grouting pressure would cause excessive settlement compensation effect, even could cause surface uplift. Selecting a reasonable grouting pressure and grouting amount was very important and effective for controlling stratum settlement. It could be used in various pipe jacking projects on-site.关键词：grouting pressure;stratum settlement;settlement mechanism;geotechnical centrifuge experiment;grouting simulation system
- 1585
- |
- 664
- |
- 0
发布时间：2024-01-10 - 摘要：To effectively improve the durability of welded rectangular section members (WRSM) with tubular flange in long-span bridges, the use of weathering steel instead of ordinary steel was proposed. At the same time, to study the axial bearing capacity of WRSM of weathering steel tube flange under full weld penetration and partial weld penetration, the axial compression short columns with welded rectangular section under three different weld penetration depths were studied. Tests of the static strain, dynamic strain, vertical displacement, and lateral displacement of each specimen under uniaxial compression were conducted. By comparing the test results and theoretical analysis results, the bearing capacity of WRSM with different penetration depths was obtained. The results showed that: 1) the bearing capacity of full penetration weld of WRSM was higher than that of partial penetration weld of WRSM. 2)The vertical displacement of full penetration member was larger than that of partial penetration member. For the lateral displacement of members under different penetration depths, the test point L4 increases with the rise of axial compression load, and the test point L3 first increases and then decreases with the rise of axial compression load. 3) For the internal concrete strain value of the member, the abrupt change of the full penetration member was smaller than that of the partial penetration member when it cracks. The vertical strain of the steel on the surface of the member was compressed as a whole and increases with the rise of the load; the lateral strain of the steel on the surface of the member was tensioned as a whole, and locally compressed at the top four corners.关键词：weathering steel;welded rectangular section members with tubular flange;axial bearing capacity;weld penetration depths;concrete-filled steel tubes
- 808
- |
- 472
- |
- 1
发布时间：2024-01-10 - 摘要：Onshore ground motions were widely used for seismic analysis of sea-crossing bridges, and the difference between the onshore and offshore ground motions were ignored. Due to soil loss around piles scoured by water for a long time, the stability of substructure of bridge in marine environment was reduced. Taking an approach part of a sea-crossing bridge as an example, a finite element model for this approach part was built by using the ABAQUS software. The pile-soil effect and hydro dynamic force were considered in the model. The probabilistic seismic demand analysis method was used with the fragility analysis of bridge piers under onshore and offshore ground motions with different scour conditions. By drawing the transcendence probability vulnerability curves and the transcendence probability increase diagrams of piers and bearings, the damage regularities of bridges under the onshore and offshore ground motions and different scour depths of bridges key components were studied. The results showed that the bridge piers were more vulnerable under offshore motions than that under onshore motions. With the increase of the local soil scour depth, the failure probability of the bridge piers and bearings increased. The effect of scour depth had a more obvious effect on the failure exceeding probability of the piers. The failure exceeding probability of the piers in bridge longitudinal direction was higher than that in bridge transverse direction under the same intensity of ground motion. The bearings were more vulnerable than bridge piers under the same working conditions. The increase of failure exceeding probability of the bearings under the offshore motions was also generally higher than that under the onshore. As the scour depth increased, the failure exceeding probability of the bearing gradually increased. Comparing with the onshore motions, the scour depth had a more obvious influence on the failure exceeding probability of bridge piers under the offshore motions with the increase of the ground motion intensity.关键词：seismic prevention for bridge;onshore and offshore ground motion;local scour depth;pile-soil interaction;fragility analysis
- 983
- |
- 460
- |
- 0
发布时间：2024-01-10 - 摘要：The resistance measurement methods in the electroosmotic model were modified. The series method was proposed to replace the current electric potential measurement and fixture method, and the wiring method suitable for measuring the resistance of EKG electrode was proposed. The method of measuring contact resistance between electrode and soil with electroosmotic soil of different lengths in series eliminated the error influence of resistance of a section of soil between the measuring needle and electrode in electric potential measurement and avoided the influence on current distribution because of inserting the potentiometric needle in the soil. The method of measuring electrode resistivity with electrodes of different lengths in series eliminated the error influence of contact resistance between electrode and fixture in fixture method. The experimental results showed that the ratio of contact resistance obtained by electric potential measurement to that obtained by series method was mostly between 1.3～1.4, which verified that the contact resistance measured by electric potential measurement was larger because resistance of a section of soil between the needle and electrode was included in the contact resistance. The ratio depended on the resistance value of the soil between the needle and electrode. Series method for EKG electrode was not applicable. The wiring method was presented to measure EKG electrode resistivity to eliminate the influence of uneven current distribution in the electrode plate due to embedded copper wire. The measurement results of wiring method were basically not affected by the length of the electrode, with good reliability and stability. The wiring method was convenient and applied in EKG electrode in the production process. There is a broad application prospect. The ratio of resistivity of EKG electrode obtained by wiring method to that obtained by the fixture method was mostly between 0.08～0.10. The ratio was mainly related to the contact resistance between electrode and fixture which just depended on the fixture and electrode. Therefore, the ratio could be used to modify previous results obtained by fixture method. The EKG electrodes have been used in many laboratory tests and projects. Considering the influence of the resistivity of EKG electrode on the energy consumption of the whole test and project, the resistivity ratio of 0.08～0.10 could be adopted for correction.关键词：electroosmosis;electrode resistance;contact resistance;EKG electrode
- 1029
- |
- 510
- |
- 0
发布时间：2024-01-10 -
Calculation of Axial Compressive Bearing Capacity of Composite Strengthened Circular Timber Column AI导读
摘要：The composite strengthening method with near surface mounted steel bars and wrapped fiber reinforced polymer strips can improve the bearing capacity and deformation behavior of timber columns effectively, and enhance their working performance greatly. To propose the load-bearing capacity formula of short timber columns strengthened with near surface mounted steel bars and wrapped carbon fiber reinforced polymer (CFRP) strips, a total of 42 reinforced specimens (12 groups) were tested under axial compression. The test results indicated that the failure of timber columns mainly occurred where the initial defects concentrated, and the bearing capacity and deformation performance of timber columns could be improved through the composite strengthening, showing significant strengthening effectiveness. Based on the typical strength model of concrete columns wrapped with fiber reinforced polymer strips, three strength models of timber columns with wrapped CFRP strips by analyzing and fitting the relevant experiment data were proposed. Through the comparison between theoretical and test values, the feasible strength model for the calculation of timber columns confined by CFRP strips was selected, and then the calculation formula of bearing capacity for the circular timber columns with composite reinforcement method was obtained. According to the additional experiment results and the comparison calculation for test data in existed research, it can be obtained that the theoretical calculation was able to predict the test results, which verified the reliability of the formula for the calculation of the strengthened timber columns’ load-bearing capacity.关键词：composite strengthening;mounted steel bar;CFRP strips;circular timber column;compressive bearing capacity- 898
- |
- 520
- |
- 0
发布时间：2024-01-10
HYDRAULIC & CIVIL ENGINEERING
- 摘要：Aiming at improving the modeling accuracy of conical enveloping worm and double-enveloping worm wheel, the digitization modeling and solving algorithm of these complicate tooth surface were proposed. The coordinate frame and modeling systems of cone generator, worm and worm wheel were constructed based on the enveloping process, the meshing equation of worm working tooth profile were derived by appling vector representation, differential geometry and kinematics method, and the digital representation models of the worm working tooth were established according to matrix transformation. The meshing equation and digital models of double-enveloping worm wheel working profile were established while taking the generated worm as new generator. The generatrix of the addendum and bottom for the worm and worm wheel were presented combing the enveloping conditions and tooth profile boundary, and the constraints of the digital models for the worm wheel pair were also worked out, in addition, the solving algorithm for the complicate digital models was designed. The MATLAB calculation programme was developed, the contact sample lines of worm and worm wheel in different coordinate systems were presented, the calculation results showed that the contact lines of worm and worm wheel maintain complex nonlinearity. All of the meshing point clouds for the worm and worm wheel surfaces were calculated based on the designed solving algorithm. The calculation accuracy were analyzed by appling reverse envelope method. The three-dimensional digital models of worm and worm wheel were obtained by fitting the meshing points in Creo, and modeling method and driving performance of the worm wheel pair was verified by virtual assemble. The experiment results indicated the calculation accuracy at level of 10–9 to 10–8, the driving effect was consistent with the theoretical expectation, which demonstrated the effectiveness and precision of the proposed modeling method and solving algorithm.关键词：conical enveloping;double-enveloping worm wheel pair;digital model;solving algorithm
- 1111
- |
- 466
- |
- 0
发布时间：2024-01-10 - 摘要：An active control method of trailing edge flap is investigated for suppressing high frequency vibration of wind turbine blades. The structure is modeled as composite blade beam with circumferentially asymmetric stiffness (CAS) configuration, which is based on the analysis of the elastic flap-wise/twist displacements and incorporates the angle control of trailing-edge flap driven by a stepping motor. Aerodynamic expressions of the aeroelastic system are based on a novel quasi-steady model suitable for trailing-edge flap. The partial differential aeroelastic equations of the aeroelastic system are solved based on the discretization function of Galerkin method. The high-frequency vibration of the blade is successfully suppressed by the active control based on the swing angle of the trailing-edge flap. The active control is realized by H∞ algorithm using linear matrix inequality (LMI) design and state observer design. Time-domain stability analysis and robust control method is investigated to realize displacement response analysis and robust performance analysis, and input signal display of trailing-edge flap angle. The optimization is investigated to mechanism of LMI is to optimize uncertain robust performance parameters based on the selection of robust control parameters, so that the controlled displacement and control input are kept within reasonable ranges. In order to reduce the influence of state variable detection error in full state feedback, state reconstruction and state observer are used to improve the control performance. At the same time, the reliability and robustness of H∞ control algorithm based on LMI are verified by comparisons of the results of high-frequency vibration control using different robust performance parameters and different wind speeds. Based on a real-time OPC technology of S7–300 PLC and WinCC configuration software, a process control experiment is adopted to verify the feasibility of the control algorithm in the engineering application. A real-time engineering application feasibility scheme is provided for the control method that cannot be conventionally implemented in the controller hardware due to the complexity of the intelligent control algorithm.关键词：wind turbine;high-frequency vibration of blade;trailing-edge flap;active control;H∞ control
- 855
- |
- 445
- |
- 1
发布时间：2024-01-10 - 摘要：Rotary vane steering gear has the advantages of compact structure, high mechanical efficiency, and easy installation, and is widely used in ships. The existing rotary vane steering gear is a single-layer hydraulic swing cylinder, and the rotation range of the rudder blade is restricted by the structure of the swing cylinder and has saturated nonlinearity. In addition, the phenomena of rudder impingement, lag and running caused by hydrodynamic interference seriously affect the ship’s course control and rudder anti-roll effect. Aiming at the above problems, a new steering principle of compound structure swing cylinder is proposed based on the mathematical model of direct drive electro-hydraulic servo rotary vane actuator and the analysis of the interference of hydrodynamic force on rudder angle. The double-layer structure is adopted for the compound swing cylinder, the inner layer is rudder driving cylinder, the outer layer is torque decoupling cylinder. The inner and outer rotors rotate in the same direction, which can increase the working range of the rudder blade. Meanwhile, the torque decoupling cylinder rotor outputs boost torque acting on the rudder drive cylinder rotor, which can offset the load torque generated by the hydrodynamic force on the drive cylinder rotor. Improve the rotation accuracy of the rudder blade and solve the problem of force-position coupling in the movement of the rudder. The reverse rotation of the inner and outer rotors can make the steering gear brake and change direction in time, and improve the steering performance. The compound swing cylinder is used for the vane steering gear. The steering gear system has a large stability margin, with amplitude margin of 45.3 dB and phase margin of 99.2°, which meets the design index of servo system. Simulation analysis shows that, compared with the single-layer swing cylinder plus control strategy, the compound swing cylinder has faster response speed and no overshoot, the speed of reaching steady state increased by about 36%, the steady-state error is maintained within ±0.05° under external load interference. When tracking a slope signal with a slope of 0.01°/s, the steering accuracy can be maintained within the ±0.03° position error band, which has high position control accuracy.关键词：rotary vane steering gear;compound swing cylinder;torque decoupling;position control
- 933
- |
- 436
- |
- 0
发布时间：2024-01-10 - 摘要：As the basic part of motion of humanoid robots, human-like motion planning of the anthropomorphic arm is always one of the research hotspots and difficulties. A novel human-like motion planning method based on movement primitives was proposed. This method can satisfy the feature of arm motion and improve the accuracy. Firstly, the arm structure was decoupled and the arm model was built to express different arm movements. The methods of extraction and connection about movement primitives were established. The mapping relations between the arm models and inverse kinematic (IK) solutions were established. Meanwhile, a motion framework was proposed. The joint trajectories of a certain platform can be generated to accomplish required tasks with this motion framework. Secondly, according to the motion features of different movement primitives, the associated Human Performance Measures for different movement primitives were constructed to solve the IK problem. Finally, the proposed method was verified by the similarity experiment and the human-like movement experiment for the general motion of humanoid robot NAO. In the similarity experiment, the robot NAO generated the human-like movements with the proposed method. The motion data were compared with the real data generated by humans. All the errors were less than 1 cm, which satisfied the accuracy requirements of human-like movements. In the human-like movement experiment, the robot NAO performed a human-like arm movement with the proposed method. The proposed method was also compared with the minimum total potential energy method and the last norm algorithm. Using the proposed method, 7% and 58 % increase in similarity were achieved respectively, compared with those two methods. With the proposed method, the complex motion models were decoupled into different simple sub-movements and the classification of the movements reduced the calculation amount. The experiments proved that the anthropomorphic arm can generate human-like movements accurately.关键词：anthropomorphic arm;human-like motion planning;movement primitive;posture prediction
- 1264
- |
- 570
- |
- 0
发布时间：2024-01-10
MECHANICAL ENGINEERING
- 摘要：In order to study the effect of test load and speed on the tribological properties of Nano–SiC modified ultra high molecular weight polyethylene (UHMWPE)–rubber composites under water lubrication condition, Nano–SiC and Polytetrafluoroethylene (PTFE) filled UHMWPE–rubber composites were prepared by high temperature mixing and hot pressing.The friction and wear properties of the composites under four different loading conditions were investigated by MRH–3 ring block friction tester. The micro wear surface morphology of the samples was analyzed by optical microscope (OM), scanning electron microscope (SEM) and non-contact optical three-dimensional profilometer, and the friction mechanism of the modified composites was explored from the micro layer surface. The experimental results show that when the speed increases from 0.005 m/s to 0.541 m/s, the dynamic and static friction coefficients of the modified composites show a significant downward trend, the fluctuation of the friction coefficient is stable, and the stick–slip phenomenon gradually weakens until it disappears. The change of test load and nano particle content are negatively related to the friction and wear degree. Under the condition of water lubrication, the friction coefficient and wear rate decrease obviously with the increase of nano particle content. The composite with 5% filling ratio has the best tribological performance. The friction coefficient and wear rate decrease 35% and 46.6% respectively compared with UHMWPE–rubber, and the worn surface morphology also changes; The wear rate of the composite decreases from 1.25 × 10–6 mm3/(N·m) to 0.40 × 10–6 mm3/(N·m). The results showed that both the content of Nano–SiC and the load pressure have a certain influence on the friction and wear, that is, UHMWPE–rubber composite filled with appropriate amount of Nano–SiC can reduce the stick–slip phenomenon, and the friction pair composed of the dual steel ring under a certain load pressure can effectively improve the friction performance, which is conducive to reducing the wear of water lubricated bearing and enhancing the service life of ship transmission system.关键词：water lubricated bearing;UHMWPE;stick–slip phenomenon
- 1039
- |
- 477
- |
- 0
发布时间：2024-01-10 - 摘要：In order to study the effect of Nano–particles on the low organic waste activated sludge fermentation performance. The WAS were fermented in the nanometer CuO (Nano–CuO) and nanometer ZnO (Nano–ZnO) fermentation systems. The results showed that the hydrolytic acidizing property of Nano–ZnO fermentation system was significantly higher than Nano–CuO fermentation system. Protease increased with the addition of Nano–ZnO and Nano–CuO, and the maximal value was 25.15 EU/mg VSS (Nano–CuO) and 46.71 EU/mg VSS (Nano–ZnO), respectively. The α–glucosidase increased firstly and then decreased with the addition of Nano–ZnO and Nano–CuO, the maximal value were 0.0037 EU/mg VSS of 10 mg/L (Nano–CuO) and 0.0039 EU/mg VSS of 1 mg/L (Nano–ZnO), respectively. Alkaline phosphatase and acid phosphatase declined with the Nano–ZnO and Nano–CuO addition however the Nano–ZnO system was higher than Nano–CuO system. The coenzyme 420 declined with the increase of Nano–ZnO but increased with the increase of Nano–CuO. Theterrimonas, chryseolinea and ferruginibacter were enriched in Nano–ZnO fermentation system which resulted in the higher SCFAs production.关键词：sludge anaerobic fermentation;Nano–CuO;Nano–ZnO;hydrolytic acidification;short volatile fatty acids;biological enzyme
- 1044
- |
- 373
- |
- 1
发布时间：2024-01-10 - 摘要：Industrial and agricultural activities lead to increasing soil cadmium (Cd) pollution. As an important functional component of soil colloid, both montmorillonite (Me) and humic acid (HA) have good adsorption properties for Cd. Four molecular weight grades of HA were obtained by tangential flow ultrafiltration. FTIR, element determination, functional group titration were used to study the effect of HA with different molecular weight on the adsorption of Cd on montmorillonite and the mechanism of action. The results showed that with the increase of molecular weight of HA, the content of hydroxyl and carboxyl groups decreased while the phenolic hydroxyl group and methyl group increased, the aromaticity increased, the hydrophobicity became stronger, and the pH value increased. The contents of Cd and HA adsorbed by montmorillonite in the ternary system increased with the increase of molecular weight. When the initial concentration of Cd was 50 mg/L, the adsorption capacity of HA, HA1, HA2, HA3, HA4 montmorillonite system for Cd was 1.99, 2.11, 2.46, 4.12, 4.88 mg/g, respectirely. And the Cd adsorbed under the action of each molecular weight HA was mainly reducible state. The smaller HA was easier to compete for the adsorption of the Cd already bound on the surface of montmorillonite, and due to its strong hydrophilicity, the Cd adsorbed by small HA would be brought into the solution, reducing the content of Cd absorbed by the system. With the increase of molecular weight, its competition effect with montmorillonite was reduced, and the HA was difficult to enter into the montmorillonite layers. At this time, under the hydrophobic effect, the large molecule HA adsorbed Cd would cover the surface of montmorillonite, thus increasing the adsorption amount of Cd in the system.关键词：humic acid;montmorillonite;cadmium;molecular weight;adsorption
- 880
- |
- 445
- |
- 2
发布时间：2024-01-10
CHEMICAL ENGINEERING & MATERIAL ENGINEERING
- 摘要：Generally, the noise transmitted in the optical path mainly includes the influence of optical power, external vibration interference, the intrinsic noise of the optical path, and the influence of thermal motion caused by environmental temperature changes. The optical fiber is extremely sensitive to environmental interference, and any environmental disturbance will bring corresponding phase errors. At the same time, if the signal is preprocessed and filtered, it is easy to cause some small information to be lost and increase reconstruction errors. Aiming at the problem of internal common mode noise affecting measurement accuracy and increasing reconstruction error in micron-level vibration measurement, a differential measurement system based on all-fiber Fabry–Perot (F–P) interference is established. Firstly, according to the phase equation of the F–P interference principle and the 2×2 single-mode fiber coupler during the transmission process, the through arm and the coupling arm have a phase difference of 90°. It is deduced that the signals received by the two output detectors are equal in amplitude and opposite in direct. Then the difference between the two signals can increase the overall signal amplitude, weaken the influence of common mode noise on the signal, and enhance the signal quality. Through the reconstruction displacement analysis of the interference signal, the experimental results show that the reconstruction error of the synthesized signal is reduced by 0.4% in the 2 μm sinusoidal vibration of the mirror. Under 1.4 μm vibration measurement on rough surface, the reconstruction error is reduced by 2.8%. The experimental results also show that the differential structure can reduce the vibration measurement reconstruction error, and the reconstructed waveform is smoother.关键词：laser vibration measurement;Fabry–Perot interference;differential system;de-noising
- 968
- |
- 415
- |
- 0
发布时间：2024-01-10 - 摘要：The main purpose of video foreground-background separation is to extract interesting objects from video, but it is still one of the most challenging tasks in the field of computer vision due to the influence of noise and illumination changes. Truncated nuclear norm (TNN) algorithm is a classical robust principal component analysis (RPCA) algorithm, which is widely used in video foreground-background separation. However, the TNN in this algorithm does not approach the rank function of the traditional robust principal component analysis better, resulting in weak stability and low accuracy of video foreground-background separation in some complex scenes. To solve this problem, an improved ITNN method is proposed. Firstly, the method adopts the nonconvex γ norm to replace the nuclear norm of TNN method. The problem that the nonconvex γ norm approaches the rank function more closely than the nuclear norm is analyzed, and the corresponding model of ITNN is proposed. Secondly, in order to solve the proposed ITNN model, the generalized alternating direction method of multipliers (GADMM) is introduced. Finally, the proposed ITNN is applied to the experiments of video foreground-background separation for different public videos. The foreground which is extracted from different videos by different methods verifies the effect of our proposed ITNN methods. Meanwhile, the F-measure values and running time are also recorded for extracting foreground from different videos by different methods. These all verify the effect of the proposed ITNN method. In summary, experiments show that the proposed ITNN algorithm is effective and superior in video foreground and background separation.关键词：robust principal component analysis;truncated nuclear norm;generalized alternating direction method of multipliers;non-convex γnorm;foreground-background separation
- 924
- |
- 493
- |
- 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