Numerical analysis on seismic performance of underground structures in liquefiable interlayer sites from centrifuge shaking table test

When an underground structure passes through a liquefiable soil layer,the soil liquefaction may pose a significant threat to the structure.A centrifuge shaking table test was performed to research the seismic response of underground structures in liquefiable interlayer sites,and a valid numerical model was obtained through simulation model test.Finally,the calibrated numerical model was used to perform further research on the influence of various distribution characteristics of liquefiable interlayers on the seismic reaction of underground structures.The key findings are as follows.The structure faces the most unfavorable condition once a liquefiable layer is located in the middle of the underground structure.When a liquefiable layer exists in the middle of the structure,the seismic reactions of both the underground structure and model site will increase with the rise of the thickness of the liquefiable interlayer.The inter-story drift of the structure in the non-liquefiable site is much smaller than that in the liquefiable interlayer site.The inter-story drift of the structure is not only associated with the site displacement and the soil-structure stiffness ratio but also closely associated with the slippage of the soil-structure contact interface under the condition of large deformation of the site.

Numerical simulation on conjugate heat transfer of turbine cascade

Numerical simulation on conjugate heat transfer of an internal cooled turbine vane was carried out. Numerical techniques employed included the third-order accuracy TVD scheme, multi-block structured grids and the technique of arbitrary curved mesh. Comparison between results of commercial CFD codes with several turbulence models and those of this code shows that it is incorrect of commercial CFD codes to predict the thermal boundary layer with traditional turbulence models, and that turbulence models considering transition lead to more accurate heat transfer in thermal boundary layer with some reliability and deficiency yet. The results of this code are close to those of CFX with transition model.

Design of a continuously variable Mach-number nozzle

A design method was developed to specify the profile of the continuously variable Mach-number nozzle for the supersonic wind tunnel. The controllable contour design technique was applied to obtaining the original nozzle profile, while other Machnumbers were derived from the transformation of the original profile. A design scheme, covering a Mach-number range of3.0<Ma<4.0, was shown to illustrate the present design technique. To fully validate the present design method, computational fluid dynamics(CFD) analyses were carried out to study the flow quality in the test area of the nozzle. The computed results indicate that exit uniform flow is obtained with 1.19% of the maximal Mach-number deviation at the nozzle exit. The present design method achieves the continuously variable Mach-number flow during a wind tunnel running.

Application of consistent geometric decomposition theorem to dynamic finite element of 3D composite beam based on experimental and numerical analyses

Analyzing static and dynamic problems including composite structures has been of high significance in research efforts and industrial applications.In this article,equivalent single layer approach is utilized for dynamic finite element procedures of 3D composite beam as the building block of numerous composite structures.In this model,both displacement and strain fields are decomposed into cross-sectional and longitudinal components,called consistent geometric decomposition theorem.Then,the model is discretized using finite clement procedures.Two local coordinate systems and a global one are defined to decouple mechanical degrees of freedom.Furthermore,from the viewpoint of consistent geometric decomposition theorem,the transformation and element mass matrices for those systems are introduced here for the first time.The same decomposition idea can be used for developing element stiffiness matrix.Finally,comprehensive validations are conducted for the theory against experimental and numerical results in two case studies and for various conditions.

A thermo-viscoelastic model for particle-reinforced composites based on micromechanical modeling

Micromechanics-based constitutive models offer superior ability to estimate the effective mechanical properties for the composites,which greatly promote the computational efficiency in the multiscale analysis for composite structures.In this work,a thermo-viscoelastic model for particle-reinforced composites is proposed to estimate their thermal-mechanical coupling behaviors in terms of a micromechanics-based homogenization method in the time domain.The matrix and particles of the composites are modeled as“thermo-rheologically complex”viscoelastic materials.The temperature-dependent effective elastic strain energy ratios of particle to composite are proposed to evaluate the contributions of the matrix and particles.The thermo-viscoelastic model for the composites is then formulated by superposing the matrix and particle’s contributions.Finite element simulations based on the representative volume element models are employed to validate the constitutive model under various thermal-mechanical coupling loads.The effects of the loading rate,viscous parameter and particle content on the effective thermal-mechanical responses of the composites are also comprehensively discussed.The experimental data from literature are also employed to verify the constitutive model.The findings show that the proposed thermo-viscoelastic model can accurately predict the thermal-mechanical coupling behaviors for the particle-reinforced composites.

A NOVEL DRIVING STRATEGY FOR DYNAMIC SIMULATION OF HOISTING ROPE WITH TIME-VARYING LENGTH

A simulation method for investigating the vibration behavior of hoisting rope with time-varying length is improved.By previously creating markers in the MSC.ADAMS software package,the parametric model of the rope wound along helix is established based on the concentrated-mass theory with multi-degree of freedom(multi-DOF).A novel driving strategy,cooperating fixed joints with angle sensors under the control of driving script,is proposed to substitute conventional contact force.Researching on the hoisting rope in the sinking winch mechanism,an equivalent discretization model is obtained with complicated boundary conditions considered.The differential equations of motion of the hoisting system are formulated employing Lagrange’s equation and numerically solved using Runge–Kutta method.The simulation indicates that the horizontal swing is decreased in principle and the simulation with 800 discrete ropes is not performed more than 61 min.Therefore,this feasible strategy could not only guarantee the accuracy but also promote simulation efficiency and stability.The motion curves exported from ADAMS simulation coincide with one in numerical simulation,which validates both the numerical model and the driving strategy.

Piezoelectric d_(15) shear-response-based torsion actuation mechanism:An exact 3D Saint-Venant type solution

This paper is concerned with the detailed analysis of the behavior of a piezoceramic bi-morph torsion actuator using the d_(15)-effect.The bi-morph actuator is made of two oppositely polarized adjacent piezoceramic prismatic beams.The mathematical analysis is based on the Saint-Venant torsion theory;a formulation of the electromechanically coupled problem in terms of a stress function and of the electric potential is derived,which represents an exact solution of a specific three-dimensional problem;in particular,for the case when the axial stress and the axial component of the electric displacement vector are independent of the axial coordinate.The resulting boundary-value problem in the cross-section is solved using the method of finite differences.Solutions for the actuated rate of twist are presented and compared to three-dimensional electromechanically coupled finite element solutions using ABAQUS®for the case of a cantilevered bi-morph actuator.A very good agreement is found.

Experimental evidence of photonic crystal waveguides with wide bandwidth in two-dimensional Al2O3 rods array

A cross-shaped photonic crystal waveguide formed by a square lattice Al_2O_3 rods array is numerically and experimentally investigated. The band gap of the TE mode for the photonic crystals and transmission characteristics of waveguides are calculated by the plane wave expansion method and the finite element method.We perform the experiments in the microwave regime to validate the numerical results. The measured reflection and transmission characteristics of the photonic crystals show a large band gap between 8.62 and 11.554 GHz（relative bandwidth is 29.34%）. The electromagnetic waves are transmitted stably in the waveguides, and the transmission characteristics maintain a high level in the band gap.