Subjects: Mechanics >> Other Disciplines of Mechanics submitted time 2024-05-07 Cooperative journals: 《应用力学学报》
Abstract：
In order to study the growth of convective disturbance and heat transfer characteristics of rectangular cavity with sinusoidal periodic heating, the hydrodynamic equations were numerically simulated.The results showed that with the increase of Grashof number Gr, the growth rate of maximum amplitude Amax of convective disturbance increases while the time of linear growth phase decreases. For a cavity with aspect ratio A=10 and a width d=2 cm and for the fluid with Prandtl number Pr=6.949, the empirical formula of the growth rate γm of convective disturbance varying with Graschof number is γm=9×10-8Gr1.234 3. For a cavity with A=10 and d=6 cm and for the fluid with Pr=0.703, the empirical formula of the growth rate γmvaring with Graschof number is γm=8×10-4Gr0.52. At Pr=0.027 2, the correlation between the average Nusselt numberNu^- of the hot wall and Graschof number isNu^-=0.000 02Gr1.17; at Pr=6.949,the correlation is Nu^-=0.000 24Gr1.05.The heat transfer capacity of the right wall increases with the increase of Graschof number.
Subjects: Mechanics >> Biomechanics submitted time 2024-04-19 Cooperative journals: 《应用力学学报》
Abstract：
To investigate the effect of lumbar motion chain training system on lumbar function and biomechanics after lumbar disc herniation(LDH)surgery.A total of 122 patients with LDH admitted to the Central Hospital of Xinyang City,Henan Province,were selected and randomly divided into two groups of 61 cases each.Both groups underwent surgical treatment,with the control group receiving conventional training and the observation group receiving lumbar motion chain training system based on the control group.The intervention effects of the two groups were compared.After 12 and 24 weeks of intervention,the average amplitude,stride length,step frequency,AP,and PT of the healthy side and weak chain side in the observation group were higher than those in the control group,while the VAS score and F/E were lower(P<0.05).After 24 weeks of intervention,the SF-36 and BI scores in the observation group were higher than those in the control group(P<0.05).The lumbar spine motion chain training system can alleviate postoperative pain of LDH,improve lower limb gait,restore lumbar spine function and biomechanics,and improve quality of life.
Subjects: Mechanics >> Hydromechanics submitted time 2024-04-19 Cooperative journals: 《应用力学学报》
Abstract：
When the pressure gate valve is closed in the large-span inverted siphon pipeline,it is usually accompanied by the phenomenon of water hammer.At the same time,the coupling effect of the fluid and the solid exists.In order to study the pressure wave under different valve closing time and the dynamic response of the structure with considering the coupling effect,the overall hydraulic calculation is carried out with taking the large-span inverted siphon pipeline and the arch bridge structure as the research objects.Based on the fluid-structure coupling analysis theory,the water hammer pressure wave calculated by the overall hydraulic model is used as the loading condition of the fluid part,and the two-way fluid-structure coupling analysis is carried out on the workbench platform to solve the displacement,internal force,and stress of the bridge structure.The results show that under different valve closing time conditions,the change trend of the water hammer pressure wave curve is roughly the same,and the displacement time history curve of each monitoring point of the structure is basically consistent with the law of the water hammer pressure wave curve.When the valve is closed at a constant speed,increasing the closing time of the gate valve can be an effective measure to reduce the water hammer pressure; the water hammer force has the greatest effect on the bridge pipe,followed by the cover beam,and the arch ring is the smallest,and the dynamic response of the structure mainly occurs along the bridge direction.
Subjects: Mechanics >> Other Disciplines of Mechanics submitted time 2024-04-19 Cooperative journals: 《应用力学学报》
Abstract：
A new form of assembled beam-column joint is proposed,and in order to study the mechanical properties of this joint,the parametric analysis of the assembled new beam-column joint with cantilever beam segment splicing is carried out by ABAQUS software on the basis of the preliminary experimental research.First,the test model of the assembled beam-column joint was established by ABAQUS,and the test results were compared and verified. Then,the parametric analysis of the spliced joint with cantilevered beam segments was carried out and the mechanical properties of the joint under different parameters were obtained by considering the number of stiffening ribs,thickness of cross-plate,thickness of plates,and length of L-shaped angle steel.
Subjects: Mechanics >> Other Disciplines of Mechanics submitted time 2024-04-19 Cooperative journals: 《应用力学学报》
Abstract：
The existence of complex microscopic features in the bolted structure leads to inevitable uncertainty in the numerical model.Aiming at the quantification of parameter uncertainty in bolt design,this paper proposes a stochastic model updating method for assembled structures with bolted joints based on a high-precision modal synthesis method.First,considering the influence of higher-order residual modes,a high-precision modal synthesis method suitable for the elastic interface of bolted joints is derived.Then,under the framework of Bayesian inference,using the natural frequency and mode shape probability distribution of the assembled structure,the posterior probability density function of the bolt parameters is established,and the parameter uncertainty is quantified with delayed rejection adaptive metropolis(DRAM)sampling method.The numerical examples indicate that for structures with large differences in natural frequencies among the substructures,compared with the general modal synthesis methods,the method proposed in this paper can ensure good model updating performance in the case of using a small number of substructure modes.
Subjects: Mechanics >> Other Disciplines of Mechanics submitted time 2024-04-19 Cooperative journals: 《应用力学学报》
Abstract：
In order to study the dynamic mechanical characteristics and stress wave propagation law of filled joint rocks under different confinement angles and different confining pressures,the impact test was carried out on sandstone specimens with a filling joint thickness of 8 mm by using the modified dynamic and static combination loading(split hopkinson pressure bar,SHPB)device.The dynamic mechanical characteristics and stress wave propagation laws of filled joints under different confining pressure grades(0,4,6 and 8 MPa)and different joint inclination angles(0°,15°,30° and 45°)were studied,and the stress wave oblique emission theory was used and verified.The experimental results show that ①The reflected amplitude of intact sandstone is the smallest.Taking 0 MPa as an example,the reflected amplitude increases from 0.194×10-3 to 0.299×10-3,which is positively correlated with the inclination,and the transmission amplitude is negatively correlated with the inclination angle from 0.169×10-3 to 0.053×10-3.Taking 0° as an example,the reflected amplitude is negatively correlated with the confining voltage,which decreases from 0.194×10-3 to 0.074×10-3 and the transmitted amplitude increases from 0.169×10-3 to 0.257×10-3.②Under the action of impact dynamic load,a certain degree of confining pressure can limit deformation,inhibit cementation surface separation,and improve bearing capacity.The larger the inclination angle of the joint,the greater the deformation of the filling joint,and the worse the bearing state.③With the increase of confining pressure,the reflectivity decreases and the transmission capacity increases.The reflection coefficient of the 0° inclination specimen decreases from 0.603 to 0.147,and the transmission coefficient increases uniformly from 0.569 to 0.789.With the increase of inclination angle,the reflection capacity of the confining pressure specimen increases,while the transmission capacity decreases,which is consistent with the theoretical analysis law.④The joint inclination angle is negatively correlated with the absorption energy density of the sample,but the confining pressure is positively correlated with the absorption energy density of the sample,which is consistent with the transmission reflection law under the action of confining pressure.
Subjects: Mechanics >> Other Disciplines of Mechanics submitted time 2024-04-19 Cooperative journals: 《应用力学学报》
Abstract：
In order to obtain the tri-dimensional seismic ground motion time histories which are compatible with the corresponding floor response spectra,the eigenfunctions of the sixth order ordinary differential equation are used as the basis functions to decompose and reconstruct the real recorded earthquake ground motion.By constructing the influence matrix,the amplitude coefficient of the eigenfunction is gradually adjusted through iterative calculation,and the preset fitting accuracy threshold is finally achieved.The orthogonalization procedure is introduced to ensure the statistical independence between the tri-directional time histories,and two sets of numerical examples are provided.The examples show that it is capable of achieving high matching accuracy between the response spectra of generated time histories and the target spectra.During the iteration,the time history response spectrum uniformly approaches the target spectra.The iterative process converges; the generated seismic time histories are drift-free and satisfy the code requirements.
Subjects: Mechanics >> Other Disciplines of Mechanics submitted time 2024-04-19 Cooperative journals: 《应用力学学报》
Abstract：
This article studies the free vibration of a functionally graded piezoelectric porous cylindrical microshell resting on elastic foundation under thermo-electro-mechanical loads.First,the dynamic model of the functionally graded piezoelectric porous cylindrical microshell resting on elastic foundation was established.Then the analytical solution of modal frequencies of the functionally graded piezoelectric porous cylindrical microshell resting on elastic foundation was derived using the third-order shear deformation shell theory and the modified couple stress theory.Last the factors affecting model frequency were discussed by numerical case studies.The results show that the Pasternak foundation is preferred to improve the modal frequencies of the shell to the Winkler foundation.The modal frequencies of the cylindrical microshell could be adjusted via changing the stiffness coefficients of the elastic foundation,axial load,applied voltage,porosity distribution,material volume fraction indexes,and structure dimensions.The larger the porosity volume fraction,the greater the influence of temperature and axial load on the modal frequency,and the smaller the influence of applied voltage on the modal frequency.The change trends of modal frequency with increasing porosity volume fraction are obviously different with different material volume fraction indexes.The elastic foundation can weaken the influence of temperature,axial load and applied voltage on the modal frequency,and its influence on the modal frequency of thin or short cylindrical shell is more significant.
Subjects: Mechanics >> Other Disciplines of Mechanics submitted time 2024-04-19 Cooperative journals: 《应用力学学报》
Abstract：
The damage of transmission and transformation tower system under wind-rain coupling often attributes to wind load, ignoring the amplification effect of rain load coupling excitation. Based on the tensioning tower system model of a transmission line, the time-history loads of wind and rain in a normal weather field and a wet downburst field are simulated. The dynamic response analysis of the tower-line system is carried out. The results show that the rainfall has a significant impact on the response of the transmission tower-line system. With the increase of rainfall intensity, the response of the tower-line system increases obviously. Under the condition of extreme rainfall, the displacement of tower top in wet downburst field increased by 31.30% in X direction and 33.93% in Y direction, respectively. The displacement and acceleration power spectral density of the tower top increased significantly in both wind and rain fields,and the resonance response of the system was enhanced. The stress of the main material at the key position of the tower increased by 11.64% and 37.07%,respectively. In different wind fields, the increasing incentive effect of raindrop impact on tower-line system during heavy rainfall cannot be ignored.
Subjects: Mechanics >> Other Disciplines of Mechanics submitted time 2024-04-19 Cooperative journals: 《应用力学学报》
Abstract：
This paper innovatively provides a coherence function model,specially adapted for water-covered canyon-hill composite topography and for simulating the multi-support seismic motions.First,a new coherence function model considering the soil filtering effect and vertical distance is proposed and derived.The characteristics of coherence and physical meaning of the proposed model are further investigated and summarized.Then,the multi-support underground seismic motions are generated by decomposing the underground power spectral density matrix,which is formed by combining the coherence function based on the derived model with the transfer function.Subsequently,the reasonability and rationality of the simulated results are verified by comparing the simulated power spectrum and the coherence function to the theoretical ones.Finally,the influence of the presented coherence function model on the differential effect of multi-support seismic motions and the dynamic response of a continuous rigid frame bridge is specially analyzed,respectively.The results show that the coherence among the simulated variable seismic motions is relatively reduced,but the variability of seismic motions at each foundation is increased,which leads to the enlargement of the structural responses.
Subjects: Mechanics >> Solid Mechanics submitted time 2024-04-19 Cooperative journals: 《应用力学学报》
Abstract： Considering that research of circumferential horizontal shear wave(SH wave)has been published on the solid cylinders and cylindrical shell structures,aiming to discuss the existence of SH surface waves on the cylindrical cavity.Since it is impossible to directly obtain the analytical solution of SH surface wave propagating in cylindrical cavity,we compare the tendency of wave structures,strain energy density varying along thickness of SH waves on the surface of cylinders and various cylindrical shells.The governing equation of SH wave of homogeneous elastic material and functionally graded material in cylindrical coordinate system is established.The Bessel functions solution and the power series asymptotic solution of the governing equations of homogeneous elastic materials and functionally graded materials are obtained,respectively.Furthermore,the dispersion curves,the wave structures and the strain energy density are calculated.The results show that the power series method can be employed for solving wave governing equations with variable coefficients with high accuracy,the energy of circumferential SH waves in cylindrical structures is concentrated on the outer surface or subsurface,and the phenomenon of energy concentration is more obvious along thickness.It can be deduced from the distribution of strain energy density that the circumferential SH surface wave cannot propagate in the cylindrical cavity.Finally,for homogeneous material structure and functionally graded material structure,the inverse method is used to prove that any analytical solution cannot satisfy the attenuation condition of SH surface wave in the cavity.
Subjects: Mechanics >> Solid Mechanics submitted time 2024-04-19 Cooperative journals: 《应用力学学报》
Abstract：
The autoclaved aerated concrete block developed by desert sand is a new type of masonry material.A pseudo-static test considering the different vertical compressive stresses and constraints of structural columns is carried out on four pieces of desert sand wall made of autoclaved aerated concrete block in order to study the application of this new block in village buildings.The failure characteristics i.e.,force-displacement curve,skeleton curve,stiffness degradation curve and ductility of the four walls under low cyclic loading arecompared and analyzed. The test results show:1)The wall is mainly shear failure.The main crack of the wall without structural columns runs through the entire wall is about 45°,and the main crack of the wall with structural columns is in the shape of “inverted eight”.And when the vertical compressive stress increases,the seismic capacity of the wall increases,the lateral stiffness improves,but the ductility decreases. 2)Under the same vertical compressive stress,comparative analysis shows that the ultimate bearing capacity of the wall with structural columns is increased by about 2.22 times that of plain wall,ductility increased by about 60%,and the stiffness is also improved. 3)Based on the principal tensile stress theory and Coulomb failure theory,the calculation formulas for the seismic bearing capacity of the new block wall are established, and the calculation formula of seismic bearing capacity established by Coulomb failure theory is more reasonable in application. 4)The skeleton curve of the established restoring force model can reflect the experimental characteristics of the desert sand autoclaved aerated concrete block wall well.
Subjects: Mechanics >> Solid Mechanics submitted time 2024-04-19 Cooperative journals: 《应用力学学报》
Abstract：
In order to study the propagation characteristics of type Ⅰ fractures of concrete with different aggregate sizes,concrete three-point bending beam fracture tests with the maximum aggregate size of 10,20,30,40 mm were carried out,and the data of full-field strain and displacement changes in the calculated area on the specimen surface were measured by using digital image correlation techniques to investigate the changes and development of fracture energy,fracture toughness and fracture process zone of concrete with different aggregate sizes.The relationship between the FPZ extension process and the post-peak loading was investigated.The results show that with the increase of the aggregate size,the compressive strength,peak load and fracture parameters of the specimens show a trend ofincreasing first and then decreasing,and the change of FPZ length of M20 specimens has a strong correlation with post-peak load,and the aggregate has the best restraint effect on microcracks,In addition,by analyzing the development law of FPZ of concrete specimens with different aggregate sizes,it can be learned that specimens with the aggregate size of 20 mm have an improved local deformation capacity after peaking,enhanced fracture energy and fracture toughness,higher bearing capacity and smaller FPZ in the fracture process than other aggregate sizes concrete; therefore,the suitable aggregate size is 20 mm.
Subjects: Mechanics >> Solid Mechanics submitted time 2024-04-19 Cooperative journals: 《应用力学学报》
Abstract：
Basalt fiber reinforced composite(BFRP)has the advantages of strong corrosion resistance,high specific strength and environmental protection.The correct evaluation of the reliability and bearing capacity of BFRP pipeline is the basis for its application in the field of high value-added oil and gas transportation.For composite pipes wound by the basalt fiber(BF),the strength of impregnated fiber bundles is obtained on a meso scale firstly.Then,both axial and circumferential specimens were cut from a pipe and the tensile strength of the two kinds of specimens were measured.Based on both experimental measurement and finite element simulation,damage evolution of structure layers of the pipe wall was studied under conditions of tension,compression and shearing,and the constitutive model of the structure layer is obtained.Finally,a finite element model of the BF-wound composite pipe was established,and influences of fiber performances on the pipe’s carrying capacity were studied.It is shown that the effective fiber content exerts a great influence on the bearing capacity of the pipe.It is important to reduce the dispersion of fiber reinforcement from aspects such as fiber production and pipe forming process for predicting load-bearing reliability accurately and promoting BF composites application in oil and gas pipeline field.
Subjects: Mechanics >> Solid Mechanics submitted time 2024-04-19 Cooperative journals: 《应用力学学报》
Abstract：
Blind bolted T-shaped plate joints with good force transfer performance and high seismic performance,can make full use of the section characteristics of double steel tubes in composite concrete-filled steel tubular columns.Cyclic loading tests and numerical simulations on five blind bolted joints were conducted.There were three types of deformation characteristics of the T-shaped plate due to its different ribbed forms,but all the failure modes of the joints were plastic deformation of steel beams after T-shaped plates yielded.Numerical simulation results agreed well with the experimental results.A tensile model of the T-shaped plate was established according to the force-transferring mechanism based on the results of experiments and simulations.The bending bearing capacity of T-shaped plate flanges and stiffeners was calculated respectively,and the ultimate bearing capacity of the joint was calculated.The error between the calculated results and the experimental results is very small,and they are very close to the numerical simulation results.The results show that the calculation formula based on the tensile model of a T-shaped plate is suitable for the case of strength matching between T-shaped plates and blind bolts.The rib form of T-shaped plates has the greatest influence on the ultimate bearing capacity of the joint,followed by the flange thickness of T-shaped plates,and the web thickness of T-shaped plates has little influence.The maximum critical value and the best matching value between the diameter of the blind bolt and the flange thickness of T-shaped plates are obtained,which provides a theoretical reference and design basis for the application of this type of joint in composite structures.
Subjects: Mechanics >> Solid Mechanics submitted time 2024-04-19 Cooperative journals: 《应用力学学报》
Abstract：
To explore the influences of section types(rectangular,1/4 arch,1/2 arch)and the groove-width ratio(B/b=1.5:1,2:1,3:1,4:1)on the earth pressure of the hill-filled cut-and-cover tunnel(HFCCT),this paper used the discrete element software PFC2D to simulate and analyze the evolution laws of the average vertical earth pressure(VEP)on the top of the cut-and-cover tunnel(CCT),the settlement difference between inner and outer soil columns,and the contact force chains among particles.Moreover,the paper analyzed the correlation between the settlement difference and the earth pressure based on the earth pressure theory of culvert and pipe,which was put forward by Gu Anquan,and further modified the function of the above-mentioned theory so as to make it applicable to the different section types and groove-width ratio (B/b).The results show that ①when the B/b is determined,the contact force chains will distribute on the top of the CCT and the average vertical earth pressure(VEP)is greater if the CCT adopts a rectangular section.The average VEP will decrease if the CCT adopts an arched section.However,there is partly stress concentration at the top of the arched section.② When the section is determined,the average VEP and settlement difference on the top of CCT both increase with the increase of B/b.As the B/b decreases,the slope effect is enhanced,the settlement of the outer soil column reduces gradually,and the interaction between the inner and outer soil columns declines,which makes the VEP on the top of the CCT decrease.③ The settlement difference between the inner and outer soil columns is linearly related to the additional earth pressure.Compared with the rectangular section,the same additional earth pressure under the arched section is generated by a smaller differential settlement,which benefits the stability of the structure.
Subjects: Mechanics >> Other Disciplines of Mechanics submitted time 2024-04-19 Cooperative journals: 《应用力学学报》
Abstract：
Aiming at the problem that it is difficult for the existing modeling and analysis methods of soft finger based on fin ray effect to meet the requirements of high precision and small amounts of calculation,we proposed approximately regarding the soft finger as concatenated four-bar mechanisms by observing the soft finger deformation.The theoretical model to solve contact force and actuating torque was established based on the principle of virtual work when the deformation state is given.The deformation recovery torque was modeled using linearly elastic torsional spring,and then an improved particle swarm algorithm was programmed to solve the stiffness coefficient of the torsional spring of each phalanx.Based on the Abaqus finite element model and combined with the secondary development,the relationship between actuating torque and pressure,joint angle was obtained,and then fitted with the aid of BP neural network.Last,an experiment platform was built to measure the grip force of the soft robotic picking hand.The results showed that the absolute relative error of the model was less than 8.6%,which was equivalent to that of the finite element model.The values of actuating torque calculated by BP neural network shared the same trend with the values measured and the relative error was under 12.7%.
Subjects: Mechanics >> Other Disciplines of Mechanics submitted time 2024-04-19 Cooperative journals: 《应用力学学报》
Abstract：
An experimental study on the dynamic mechanical properties of polyurea was carried out by using a low impedance split Hopkinson pressure bar and pull rod test device.The dynamic compression and dynamic tensile tests of polyurea 8380 at room temperature(T=18 ℃)and high temperature(50,80 ℃)and low temperature(-40,-20 ℃)were carried out respectively.The dynamic compression and dynamic tensile properties of the material were studied,and the effects of strain rate and temperature on the dynamic mechanical properties of the material were studied.The results show that:the dynamic mechanical properties of polyurea 8380 have significant strain rate effect at different temperatures.With the increase of loading strain rate,the strength,deformation capacity and energy dissipation capacity of the material are improved to varying degrees.The dynamic mechanical properties of polyurea 8380 have obvious temperature dependence.The dynamic compressive properties of polyurea 8380 show different changes at high and low temperatures.The dynamic compressive strength of polyurea 8380 is much lower than that at room temperature.With the increase of temperature,the dynamic compressive strength of the material decreases.At a low temperature,the dynamic compressive strength and energy dissipation capacity of polyurea 8380 are significantly improved compared with those at room temperature.With the decrease of temperature,the dynamic compressive strength of the material increases.
Subjects: Mechanics >> Other Disciplines of Mechanics submitted time 2024-04-19 Cooperative journals: 《应用力学学报》
Abstract：
In order to obtain large damping composite material structure,the dynamic properties of the co-cured multi-layer damping films embedded composite beam are studied.Based on the first-order shear deformation theory and Hamilton’s principle,a dynamic equation of the structure is presented,the theoretical solution of free vibration characteristics under the fixed-support boundary condition are derived and solved by using the variational principle and Galerkin method,by simulation and test to verify the feasibility of the theory,and the relationships of parameter change on the fundamental frequency and damping ratio are revealed.Conclusions provide a theoretical basis for the optimal design of multi-layer damping membranes in composite structures.
Subjects: Mechanics >> Other Disciplines of Mechanics submitted time 2024-04-19 Cooperative journals: 《应用力学学报》
Abstract：
The two-dimensional two-axis braided SiC/SiC composite braided tubes are taken as the research object,and their thermal shock resistance and failure mechanism are studied.A thermal shock test platform based on quartz lamp irradiation heating was built,on which the thermal shock test of SiC/SiC composite braided tubes was carried out,and then the diametral compression test of the braided tubes after thermal shock was also performed.The mechanical properties and failure mechanism of the braided tube were investigated,and the empirical formula of thermal shock strength degradation was obtained by fitting.The results showed that the thermal shock test platform can simulate the service environment with rapid temperature rise and drop,and the maximum heating and cooling rates can reach about 40 and 60 ℃/s,respectively,during the thermal shock test.With the increase of thermal shock cycle number,the circumferential tensile strength of SiC/SiC composite braided tubes decreases quickly at an increasing rate.The thermal stress caused by thermal shock leads to the appearance of microcracks in the matrix around the fiber and weakens the adhesion between the fiber bundle and matrix,which is one of the main causes of the strength degradation of braided tube.The fitting algorithm can well describe the strength degradation caused by cyclic thermal shock and has the value of engineering applications.
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