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 >> 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 >> 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.
Subjects: Mechanics >> Other Disciplines of Mechanics submitted time 2024-04-19 Cooperative journals: 《应用力学学报》
Abstract：
Ultrasonic surface rolling(USR)technology combines with the characteristics of high-energy impact and static load rolling.The USR-processed workpiece has the advantages of high surface finish,deep deformation layer,large compressive residual stress and obvious grain refinement.It can greatly improve the fatigue strength of metal materials through appropriately adjusting process parameters,thus it has been widely used in manufacturing industry.Since the invention of USR.a large number of studies on processing technologies and mechanisms have been conducted.It is also extensively applied to important metal materials and key parts.So far,the research on the effect of USR process parameters on the surface integrity and fatigue properties is relatively scattered and lacks systematic summary.Firstly,this paper briefly introduces the working principle and controllability of USR.Then,the residual stress and microstructure induced by different USR parameters,and the relaxation of residual stress during fatigue loading are summarized.The effects of surface integrity induced by USR with different parameters on fatigue properties as well as the potential mechanisms are criticized.The combined strengthening methods related to USR are described,and the application prospect of USR metal materials is forecasted.
Subjects: Mechanics >> Other Disciplines of Mechanics submitted time 2024-02-07 Cooperative journals: 《应用力学学报》
Abstract：
Laying passive constraint layer damping(PCLD)on elastic cavity structure can achieve the effect of vibration and noise reduction.In this paper,an edge-smoothed finite element coupling model for a two-dimensional composite elastic cavity is established.With the PCLD structure discretized by the two nodes and four freedoms PCLD beam element,the sound field adopts the edge smoothed finite element model.Taking the two-dimensional fully layered composite rectangular cavity model as a numerical example,by comparing the three results with the two finite element methods with rough mesh and fine mesh,and with the present method,it is proved that the result obtained by the present method is closer to the one of FEM with fine mesh compared with the result gained by the FEM with the same background mesh.It has higher accuracy and convergence than those of the finite element method,especially in the calculation of intermediate-high frequency.Finally,the noise reduction effect of the PCLD structure on the driving cavity of an automobile and the influence of the thickness parameters of viscoelastic layer and constraint layer on the noise reduction performance of the coupling system are analyzed,and a conclusion is drawn that the thicker viscoelastic layer could bring better damping effect to some extent,while thicker constrained layer could achieve worse damping effect in some peaks
Subjects: Mechanics >> Other Disciplines of Mechanics submitted time 2024-02-07 Cooperative journals: 《应用力学学报》
Abstract：
Based on a functionally graded thin-walled cylindrical microshell model with elastic support,the modal frequency equation was derived by using the modified couple stress theory and the first-order shear deformation theory.The impacts of the elastic support,size effect,temperature gradient,material component index,pore and geometry dimensions on the modal frequencies of the cylindrical microshell were studied.Results indicate that the impacts of elastic stiffness coefficient on the modal frequencies can be neglected in the range of 0 to 105N/m3,but the shear stiffness coefficient has a great influence on the modal frequencies in the range of 0 to 5×104N/m.Moreover,increasing the shear stiffness coefficient is beneficial to increasing the modal frequencies.The modal frequencies obtained by modified couple stress theory are larger than those obtained by classical continuum theory.With or without elastic support and size effect,the modal frequencies decrease with the increase of the temperature gradient and the length of the cylindrical microshell,and increase with the increase of the ceramic volume fraction index.The change laws of the modal frequencies are different with the variation of the pore volume fraction and thickness of the cylindrical microshell.The temperature gradient has a great influence on the modal frequencies of the cylindrical microshell considering size effect or elastic foundation.The influence of pore on the modal frequencies with elastic foundation is especially obvious.
Subjects: Mechanics >> Other Disciplines of Mechanics submitted time 2024-02-07 Cooperative journals: 《应用力学学报》
Abstract：
Natural convection in a horizontal concentric cylindrical annulus with the outer wall temperature higher than the inner wall temperature has received wide engineering applications due to its good thermal insulation effect.The thermal insulation and cooling effect of the horizontal concentric cylindrical annuli is greatly affected by the fluid flow and heat transfer in the annuli,and there is currently a lack of research on the natural convection heat transfer characteristics in the horizontal concentric cylindrical annuli with the outer wall temperature higher than the inner wall temperature.A numerical study of natural convection and heat transfer in horizontal concentric cylindrical annuli with the outer wall temperature higher than the inner wall temperature is performed to investigate the gap ratio and Rayleigh number effect on flow and heat transfer characteristics of air(Pr=0.7).The gap ratio(a ratio of the inner diameter to the gap width of the annulus,namely δ)in the range of 0.1 to 14 and the Rayleigh number over several orders of magnitude(103≤Ra≤107)are considered.The computed flow patterns and temperature fields are shown by means of streamlines and isotherms,respectively,and the effect of gap ratio and Rayleigh number on the average Nusselt number of the inner wall of a cylindrical annulus is also presented.The results show that a two-dimensional stable unicellular flow pattern occurs at low Rayleigh numbers throughout the whole range of gap ratios,and four different flow patterns are also observed,which are a two-dimensional funnel oscillatory flow,a three-dimensional spiral flow,a two-dimensional multicellular flow and a two-dimensional multicellular oscillatory flow.These four flow patterns appear at relatively high Rayleigh numbers depending on the gap ratio.According to the distribution characteristics of flow patterns,the gap ratio can be divided into three parts,namely,wide gap(δ=0.1-2),moderate gap(δ=2-8)and narrow gap(δ=8-14).In each part,correlating equations of the average Nusselt number to the gap ratio and the Rayleigh number are proposed with the coefficient of determination(R2)greater than 0.990 2.
Subjects: Mechanics >> Other Disciplines of Mechanics submitted time 2023-12-18 Cooperative journals: 《应用力学学报》
Abstract：
Abstract:Based on the relevant theoretical research on bionic creatures,the diamond surface of the shark and the pit features of the dung beetle were extracted.Moreover,a composite structure coupling bionic fan was designed.In order to study the influence of bionic composite structure on aerodynamic performance and noise of engine cooling fan,a CFD simulation model corresponding to the test bench was established.A method calculating aerodynamic performance and noise of fan was given.And the calculated values of the two types of fans were compared.The results show that in the large flow range,the power capacity of the composite structure coupled bionic fan is significantly improved.The static pressure is increased by 13.11%,and the power is reduced by 6.01%.And it can be found that the bionic composite structure is able to separate the large and chaotic vortexes nearby into numerous small vortexes.The vortex noise which is caused by irregular collision is reduced.At the same time,it can also allocate the peak value of A-weighted sound pressure level to the frequency band on both sides to achieve the purpose of noise reduction.The noise value is reduced by 1.38 dB.
Subjects: Mechanics >> Other Disciplines of Mechanics submitted time 2023-12-18 Cooperative journals: 《应用力学学报》
Abstract：
The extended finite element method(XFEM)has a great advantage over the finite element method(FEM)in dealing with strong and weak discontinuities by introducing enrichment function into discontinuities.In this paper,bimaterial interface craks have been simulated using extended finite element method(XFEM).The displacement approximation equation of bimaterial interface crack is given.The integral method of the interaction integral and the integral strategy of element stiffness matrix are presented.Material discontinuity has been modeled by modified extended finite element method,and the crack penetration is simulated by Heaviside function,the crack tip is simulated by two different asymptotic crack tip enrichment functions,and the corresponding propagation extended finite element program is compiled by Matlab.Good agreement between the numerical results and the reference solutions for bimaterial interface cracks problems is realized.
Subjects: Mechanics >> Other Disciplines of Mechanics submitted time 2023-12-18 Cooperative journals: 《应用力学学报》
Abstract：
To study the dynamic response of single-layer cylindrical latticed shell under impact and examine the accuracy of finite particle method(FPM)in simulating the dynamic response of latticed shell structure,7 FPM models were established based on 7 impact conditions,which were adopted contact model of double ball deriving from symmetrical penalty function and were introduced Cowper-Symonds constitutive model.The law of energy conservation was used for obtaining impact stiffness coefficients in contact model.The results of simulation were used to reveal the dynamic response of structure and were compared with experimental ones.The results show that 1)time history curves of impact force were close those of experimental ones,2)node displacements got in FPM were smaller than those of experiment due to failure of considering damage factors of latticed shell,but its destabilizing momentum was the same as that of experiment,3)strain energy which was generated from impact had a tendency to transfer through the braces.Meanwhile,members in impact area and high stiffness area,such as adjacent supports area,were the main forced components.In total,FPM is an accurate method to simulate dynamic response of single-layer cylindrical latticed shell under impact,which can provide theoretical basis for improving impact resistance of similar structures.
Subjects: Mechanics >> Other Disciplines of Mechanics submitted time 2023-12-18 Cooperative journals: 《应用力学学报》
Abstract：
In this paper,a 3D discrete element model of 1×7 wire rope with local contact deformation is established to solve the mechanical response problem of complex twisted structure under tensile deformation.First,a single continuous wire is discretized into multiple spheres by cohesive bond model between spheres based on the discretization method of continuum.Then,3D discrete element model of 1×7 wire rope is constructed by helix equation and rotation matrix,which is compared with the classical experimental results.Finally,the influence of helical angles on mechanical behavior of 1×7 wire rope is analyzed by the discrete element model.The results show that the increase of helical angle will increase the equivalent Young’s modulus of rope and the axial deformation of the outer wire,and reduce the contact force between the outer wire and the center wire.
Hits
Hits
Downloads
Comment