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10 December 2006, Volume 28 Issue 6
Mechanicist
2006, 28(6):  0-0.  doi:10.6052/1000-0992-2005-371
Abstract ( 1370 )   PDF (888KB) ( 586 )
The model of the stationary and rotating isolated wheels is studied with numerical methods under fixed ground boundary conditions. Based on the $k$-$\varepsilon$ two-equation high Reynolds number model, the 3D steady incompressible N-S equations are solved numerically with the CFD software STAR-CD. The drag coefficients of three different breadth stationary and rotating isolated wheels are calculated in an appropriate computational domain, then the relationship between breadth, velocity of the flow and drag coefficient is discussed. In addition, from the calculated results and test results, the paper also discusses the velocity field and the pressure field around the wheels.
Application study
2006, 28(6):  0-0.  doi:10.6052/1000-0992-2005-388
Abstract ( 1656 )   PDF (882KB) ( 862 )
The paper presents a mathematical modeling study on the gait stability control of a 17 degrees of freedom biped robot, based on ZMP theory and the Pose Transformation Matrix, with the mathematical description of relative center of gravity and relative reference frame. The proposed mathematical model can describe the stability control of robots. It is shown, by Matlab mathematical computation and emulation study, that this model can describe the walking rules of biped robots, which means that gait stability control of biped robots can be achieved. The whole model is encapsulated into a visual system by VC++ so that the model can be brought under a practical control, thus providing a technical support for the study of real-time control of future robots.
Mechanicist
2006, 28(6):  0-0.  doi:10.6052/1000-0992-2005-389
Abstract ( 1315 )   PDF (709KB) ( 646 )
Based on the small deflection plate theory, the equilibrium differential equation of isotropic thin slab with a temperature variation perpendicular to surface is deduced, by assuming a deflection function which satisfies the equilibrium differential equation and using the Levy method. An analytical solution is obtained for the case with four simply supported edges, which provides a basis for subsequent engineering calculations.
2006, 28(6):  0-0.  doi:10.6052/1000-0992-2005-409
Abstract ( 1408 )   PDF (618KB) ( 2040 )
Original Cam-clay model, modified Cam-clay model and a new unified constitutive model for both clay and sand are widely used in both research and engineering applications. Within the classic elastoplastic theory, those constitutive models for geomaterials are deduced afresh in this paper. Comparisons between those constitutive models within the classic elastoplastic theory and the practical geotechnical engineering are made. The relationships between the corresponding variables and parameters are obtained.
2006, 28(6):  0-0.  doi:10.6052/1000-0992-2005-453
Abstract ( 1301 )   PDF (612KB) ( 562 )
The optimization mathematical model for discrete cross-sections is established with the constraints of strength, rigidity, stability, minimum cross-section and the structural deflection of double-layer space grids members and solutions are obtained by using the genetic algorithm. A example indicates that the genetic algorithm can be applied in the optimal design of double-layer space grids and reliable results can be obtained.
2006, 28(6):  0-0.  doi:10.6052/1000-0992-2005-457
Abstract ( 1191 )   PDF (903KB) ( 690 )
The calculation formulas for the wave velocities of P$_{1}$ wave (fast compressional wave), P$_{2}$ wave (slow compressional wave) and S wave were derived from continuity of deformation and equilibrium conditions and considering the compression of soil grains and pore fluid. According to Snell theorem, the reflection and transmission of incident plane P$_{1}$ wave from the nearly saturated soil at the interface of elastic soil was studied, and curves of reflection coefficients, transmission coefficients, stresses and displacements of the interface were numerically obtained. The results show that the saturated degree is an important factor that affects the reflection and transmission. The reflection coefficients, transmission coefficients, stresses and displacements change little when the saturated degree increases by 4% from 95{\%} to 99%, but they change obviously when the saturated degree increases by only 1% from 99{\%} to 100%
2006, 28(6):  0-0.  doi:10.6052/1000-0992-2005-484
Abstract ( 1205 )   PDF (1380KB) ( 579 )
construction technology and is the main demanding object in the future space activities. The inflatable structure is mainly made up of membrane; therefore, the maintenance of the structural surface accuracy is one of the most important problems. Wrinkling is the unique characteristic of the flexible membranes, and the wrinkles degrade the surface accuracy and the structural performance, so, the study on wrinkles in membrane structures is desirable and essential. In this paper, a prediction model of wrinkles is proposed, based on the buckling theory, and the wrinkles, including the wrinkle amplitude, wrinkle wavelength and the critical compressive stress, in a rectangular membrane subjected to in-plane horizontal shearing loads are predicted using the method proposed in the present paper. The predicted results show good agreement with our recent experiments and the reported data.
2006, 28(6):  0-0.  doi:10.6052/1000-0992-2005-497
Abstract ( 1323 )   PDF (597KB) ( 693 )
The half-plane antiplane multiple-edge crack problems are solved by using complex variable function and singular integral equation approach. The fundamental solution of a single-edge crack in half-plane is proposed, which is obtained by distributing the dislocation density along the crack configuration, and considering the traction-free condition along the boundary of the half-plane. The fundamental solution is a function of the distributed dislocation density and is composed of the principal part and the complementary part. The half-plane multiple-edge crack problem can be considered as a superposition of many single-edge crack problems. Thus, a system of Cauchy singular integral equations can be formulated. By using a semi-open quadrature rule, the singular integral equations are solved. And the stress intensity factors at the crack tips can be calculated. Finally, some numerical examples are given.
2006, 28(6):  0-0.  doi:10.6052/1000-0992-2005-500
Abstract ( 1111 )   PDF (935KB) ( 528 )
In this paper, the current status about the tests on swelling strains of expansive soils is analyzed. Formulas are derived, which can be used to calculate the linear swelling ratio between moisture content and upper load for expansive soils by adopting lateral restricted swelling experimental data for expansive soils in Ningming section of Nanning-Youyiguan road,in case of lateral confinment and upper loads, based on the relationship between upper loads and linear swelling ratio, the relationship between upper loads and end moisture content and the relationship between process moisture content and water absorption content. Some comments are put forward about embankment construction of expressway from Nanning to Youyi gate.
2006, 28(6):  0-0.  doi:10.6052/1000-0992-2005-502
Abstract ( 1114 )   PDF (784KB) ( 458 )
Wind flow around twin-tower tall buildings is generally complicated and there is no simple method or laws for determination of the induced surface pressures on such buildings. Therefore study and prediction of wind effect on this type of buildings are necessary. Based on the wind tunnel test of surface pressures on a twin-tower tall building, the wind flow around the building was predicted using the time-averaged numerical simulation technique. The wind-flow characteristics and the law of pressure distributions were summarized accordingly. Through comparison of the computed wind pressures with the corresponding wind tunnel test data, it indicates that the numerical simulation technique is accurate and feasible in prediction of the wind flow involving strong aerodynamic interference.
2006, 28(6):  0-0.  doi:10.6052/1000-0992-2005-515
Abstract ( 1141 )   PDF (1098KB) ( 561 )
Mixed-model fracture is a prevailing phenomena in concrete. At present, there are two main approaches in describing the fracture behavior of concrete structures: One using stress intensity factor(SIF) as the main fracture parameter, and the other being energy based. Theoretically, these two methods should be consistent with each other. The basic assumptions, standards and application ranges of different fracture criteria are discussed. Furthermore, by comparing results in tests, the merits and demerits of different fracture criteria are discussed.
2006, 28(6):  0-0.  doi:10.6052/1000-0992-2006-015
Abstract ( 1155 )   PDF (411KB) ( 635 )
A general equation is established to calculate the deformation of continuous beams on many supports taking into consideration the stepped cross sections and unequal spans. From the differential equation of the deflection and by using singular functions, the boundary parametric equation, in which a certain number of undetermined initial parameters and the reactions of supports are contained, is derived for analyzing the displacements of the continuous beams. And further, the recurrence formula is developed for calculating the displacements of the continuous beams with variable stiffness and unequal spans. Finally, in consideration of the compatible conditions of displacements and equilibrium conditions as well , the system of algebraic equations is obtained for solving the reaction of support. A numerical example indicates that the present method may be adapted for programming.
2006, 28(6):  0-0.  doi:10.6052/1000-0992-2006-142
Abstract ( 1145 )   PDF (854KB) ( 789 )
Qualitative analysis of current density distribution in a thin conductive plate containing cracks is the first problem to be solved for the crack-preventing technology based on the electromagnetic heating effect. To investigate the singular distribution of the current density at the crack tips, most of the existing solutions are complicated or are only valid for a specific arrangement of the cracks. In this paper it is found that there exists a close analogy between the current density distribution and the anti-plane shear problem. Hence the solution to the current density distribution in a cracked conductive plate can be deduced by considering a corresponding mode III crack problem. The current density factor is defined in a similar way as the stress intensity factor, as its counterpart in the mode III crack problem. The consequent crack problem can be solved efficiently by the distributed dislocation technique, which is a widely applied tool in fracture mechanics. A numerical example is provided to demonstrate that the proposed numerical method is convenient and accurate and also helps to the understanding of the singularity of the current density distribution at the crack tip.
2006, 28(6):  0-0.  doi:10.6052/1000-0992-2006-305
Abstract ( 1150 )   PDF (2460KB) ( 841 )
The relationship between protection of historical cultural buildings and mechanics, and the problems of mechanics in the protection of ancient relics are reviewed in this paper. A brief introduction to the history of the protection of cultural relics in China and all over the world is followed by a discussion on problems of mechanics modeling. Particularly, the achievements made, and the opportunity and challenge confronted by the researchers are emphasized. Finally, some comments and suggestions for the future research and protection of ancient buildings are proposed.