The high-resolution capability is an important development direction for satellite in our country. In this respect, a key technique is the satellite micro-vibration control. This paper reviews the developments of the parallel platform for solving the problem of micro-vibration control in China and abroad, with a comparison of the platform manufacture and the performance conditions. It is shown that the level of the micro-vibration control technology based on the parallel platform in China is still some way behind those of other advanced countries. This paper reviews the typical configuration design, the dynamics modeling, the control system design, the platform optimization and the ground test of the parallel platform. The further research directions for the micro-vibration control technology in our country are suggested.
The widely used corrugated sandwich structures enjoy many advantages over other lightweight porous structures due to their simple configurations, mature manufacturing technologies and low manufacturing cost. This paper presents a comprehensive review of different configurations and representation modes of lightweight corrugated structures, and their fabrication and non-destructive testing technologies. Quasi-static and dynamic mechanical responses of corrugated sandwich structures are reviewed with emphasis on compression, bending, internal pressure, vibration, low velocity impact and blast loading. With respect to multifunctional characteristics, the key developments in engineering applications are summarized.
Based on the comprehensive analysis of the test products, the loading force, the boundary conditions, the measurement practicability, the force transfer test for statically indeterminate rockets is designed, and validated by tests. The test design method can be used to verify the correctness of the calculation of the internal force of the statically indeterminate rocket effectively.
The development of the supersonic mixing layer is an important factor in the supersonic combustion. In this paper, the influence of the chemical reaction on the development of the supersonic mixing layer is analyzed based on results obtained by the high-solution numerical methods with detailed chemical kinetics. The evolvement of the supersonic mixing layer and the mixing layer thickness under the effect of chemical reaction are analyzed in two different combustion modes. The influence of the chemical reaction on the supersonic mixing layer thickness is explained from the aspect of vertex dynamics.
In order to study the buckling and the critical wind speed of the natural draft cooling tower under wind loads, three scale models with different wall thicknesses are built by the 3D printing and then tested in the wind tunnel. The experimental results are compared with those obtained by the finite element method. The results show that the buckling occurs in the elastic region and the ratio of the wall thickness to the throat radius is the key parameter for the critical load. The critical wind pressures obtained by experiments are close to those designed by the current standards, which are about 1/4 of the results obtained by the finite element method, which shows that the design of the wall thickness based on the stability of the cooling tower in the current standard is conservative.
Under the service environment, the structure of metal materials often undergoes a complex process from the micro-damage to the macro-failure. In order to better understand the degeneration mechanism, the CAS wavelet is used to solve the differential equation of the fatigue crack propagation, and the differential equation is transformed into algebraic equations. Then the reliability of a cracked structure in a general environment and a corrosion environment is analyzed with the algebraic equations. At last, by comparing the calculated results with the experiment results, it is shown that the CAS wavelet method can realize a smooth transition from the short crack to the long crack.
The tension force varies significantly in the lifting process of the power catwalk, so, the tension variations and the maximum tensions in the lifting process are important factors in the catwalk's design. In this paper, the geometric equation in four different stages of the catwalk is established according to different boundary conditions, and the dynamics equations are established according to the D'Alembert's principle. A dynamics analysis software of the power catwalks is developed based on the dynamic model in four stages, using the C# to call Matlab functions. The tension variations in the lifting process of the designed power catwalk are analysed through the software, and the calculation results show that the designed power catwalk satisfies the functional requirements. The studies provides an important reference for the power catwalk's field application, a solid foundation for the power catwalk's structural design optimization and the performance improvement.
A plastic accumulative deformation constitutive model of soils under a long term traffic load is very important in the foundation settlement calculation. The existing soil element model can be used to calculate the cumulative strain of the rock and soil body, but without consideration of the cyclic rotation of principal stress axes of the saturated soft clay. For the long-term settlement of subgrade caused by traffic loads, the cyclic principal stress rotation might be important. On the basis of the a series of loading tests with the principal stress rotating under the isotropic consolidation and a series of cyclic torsional tests with anisotropic consolidation, the Newton dashpot is replaced by the Abel dashpot and the fractional order derivative is established. The parameters of the Burgers model and the fractional order derivative Burgers model of the axial plastic cumulative strain are optimized by a genetic algorithm. By analyzing the correlation curve of the calculation value and the test value of the two models, the fractional order derivative Burgers model is found to be more appropriate for calculating the cumulative strain of the soft clay subjected to a cyclic rotation of principal stress axes.
The Flamant solution is improved through a symmetric treatment to obtain accurate displacement fields of a rigid foundation with a frictionless base subjected to uniformly distributed loads. The modified version of the Flamant solution gives results in good agreement with the results obtained by the finite element simulation. It is shown that the original and modified Flamant solutions provide different horizontal and vertical displacements. However, both solutions give similar magnitudes and spatial patterns of the relative settlements when the zero-displacement-point is near the region where the loads are applied.
The shear lag effect, the shear deformation and the self-equilibrium condition for the T-beam with two-ribbed slabs are considered in the present study. Two generalized displacement functions are employed to analyze the mechanical characteristics, and the corresponding four ordinary differential equations with natural boundary conditions are derived. Then, the closed-form solutions for the generalized displacements are obtained. Furthermore, the contributions of the self-equilibrium condition, the shear lag effect to the stress and the deflection of the T-beam with two-ribbed slabs are analyzed in detail. It is concluded that the mechanical analysis of the T-beam with two-ribbed slabs is more accurate. The numerical simulation using the finite element algorithm by the ANSYS validates the proposed approach. Thus, our theoretical analysis provides more insights than the share lag theory of the T-beam with multi-ribbed slabs.