A rigidity theorem for submanifolds in S^(n+p) with constant scalar curvature

Let Mn be a closed submanifold isometrically immersed in a unit sphere Sn . Denote by R, H and S, the normalized +p scalar curvature, the mean curvature, and the square of the length of the second fundamental form of Mn, respectively. Suppose R is constant and ≥1. We study the pinching problem on S and prove a rigidity theorem for Mn immersed in Sn +pwith parallel nor- malized mean curvature vector field. When n≥8 or, n=7 and p≤2, the pinching constant is best.

多重网格加速的LUSGS算法用于喷管流场数值模拟

采用有限体积法,二阶精度插值的Roe格式对三维流场N-S方程进行空间离散;采用LUSGS隐式时间推进法和多重网格技术加快计算收敛速度;采用独特的显式算法克服了两方程湍流模型刚性对流场计算收敛速度的影响,并给出了该方法的理论依据。通过轴对称喷管内流场、二元喷管内外流场的数值模拟验证了采用以上方法在计算效率上的提高。最后将RNG模型计算结果与SA模型计算结果及实验数据做对比分析。

A general method to calculate passive earth pressure on rigid retaining wall for all displacement modes

A general analytical method to calculate the passive rigid retaining wall pressure was deduced considering all displacement modes. First, the general displacement mode function was setup, then the hypotheses were made that the lateral passive pressure is linear to the corresponding horizontal displacement and the soil behind retaining wall is composed of a set of springs and ideal rigid plasticity body, the general analytical method was proposed to calculate the passive rigid retaining wall pressure based on Coulomb theory. The analytical results show that the resultant forces of the passive earth pressure are equal to those of Coulomb＇s theory, but the distribution of the passive pressure and the position of the resultant force depend on the passive displacement mode parameter, and the former is a parabolic function of the soil depth. The analytical results are also in good agreement with the experimental ones.

Active Control of Initial Disturbances for Rockets and Missiles

The active control theory and methods of initial disturbances for rockets and missiles are investigated. The rocket or missile/launcher is simplified as a flexible beam excited by a moving varying velocity rigid body which has two points in contact with the beam. The control force is applied at the supporting point on the beam. Active control strategies based on optimal control theory are proposed and computer simulation is carried out. Simulation results are consistent with the theoretical results, and show that the active control strategies proposed can accomplish the purpose to control the initial disturbances actively. The results show that active control of initial disturbances for rockets and missiles is feasible for application.

Experimental investigation on seismic performance of rigid frame tied-arch bridge with split-piers

A novel seismic design method, namely split-pier seismic design, is proposed. A vertical gap and connect elements are set in split-piers. The lateral stiffness of piers is reduced by cracking of the connect elements under severe earthquake, and the seismic response of bridges is reduced by avoiding the site predominant periods. A model of tied-arch rigid frame bridge with split-piers was designed. Seismic performance was investigated by pseudo-static experimentation on the scale model, The failure process of split-piers, the hysteresis characteristic and the effect of split-piers on the superstructure are presented. Results show that the split-pier has better seismic performance than common ductile piers do.

Numerical analysis of reflective cracking and fatigue lives of semi-rigid pavement structures using ABAQUS and FE-SAFE

In order to compare the impact of thickness of different layers on fatigue lives of different semi-rigid asphalt pavement structures, the mechanical results from finite element models in ABAQUS are incorporated with the fatigue results from fatigue models in FE-SAFE to calculate the mechanical response and fatigue lives of semi-rigid pavement structures under heavy traffic loads. Then the influences on fatigue lives caused by the changes in the thickness of layers in pavement structures are also evaluated. The numerical simulation results show that the aggregated base and the large stone porous mixture （LSPM） base have better anti-cracking performance than the conventional semi-rigid base. The appropriate thickness range for the aggregated layer in the aggregated base is 15 to 18 cm. The thickness of the LSPM layer in the LSPM base is recommended to be less than 15 cm.

Study on the Dielectric Properties of Chemical Vapor Deposited Diamond Film

Aim To study the dielectric properties of diamond film. Methods Dielectric properties (the frequency dependenCe of conductance, permittivity, and loss factor) of diamond film preped by DC are plasma jet chemical vapor deposition (CVD) were studied. Resuls Dielectric properties of CVD diamond fAn depend mainly on its polycrystalline nature, and the presence of non-diamond disordered graphitic regions and impurities between diamond grains of the film. Annealing at 500℃ leads to the removal of greater part of disordered graphitic regions, but am not remove all disordered graphitic regions and impurities. Conclusion Much work nab to be done tO prepare or post-treat diamond films before using CVD diamond as a substrate for electronic devices.

Analysis of mechanical performance of braided esophageal stent structure and its wires

This paper aims to find the relationship between the structural parameters and the radial stiffness of the braided stent and to understand the stress distribution law of the wires. According to the equation of the space spiral curve, a three-dimensional parametrical geometrical model is constructed. The finite element model is built by using the beam-beam contact elements and 3D beam elements. The constituent nitinol wires are assumed to be linear elastic material. The finite element analysis figures out that the radial stiffness of the stent and the stress distribution of the wires are influenced by all the structural parameters. The helix pitch of the wires is the most important factor. Under the condition of the same load and other structural parameters remaining unchanged, when the number of wires is 24, the stress of the wire crosssection is at the minimum. A comparison between the vitro experimental results and the analytical results is conducted, and the data is consistent, which proves that the current finite element model can be used to appropriately predict the mechanical performance of the braided esophageal stents.

Effect of heat treatment on microstructure and thermophysical properties of diamond/2024 Al composites

50%diamond particle （5μm） reinforced 2024 aluminum matrix （diamond/2024 Al） composites were prepared by pressure infiltration method. Diamond particles were distributed uniformly without any particle clustering, and no apparent porosities or significant casting defects were observed in the composites. The diamond-Al interfaces of as-cast and annealed diamond/2024 Al composites were clean, smooth and free from interfacial reaction product. However, a large number of Al2Cu precipitates were found at diamond-Al interface after aging treatment. Moreover, needle-shaped Al2MgCu precipitates in Al matrix were observed after aging treatment. The coefficient of thermal expansion （CTE） of diamond/2024 Al composites was about 8.5×10-6 °C-1 between 20 and 100 °C, which was compatible with that with chip materials. Annealing treatment showed little effect on thermal expansion behavior, and aging treatment could further decrease the CTE of the composites. The thermal conductivity of obtained diamond/2024 Al composites was about 100 W/（m？K）, and it was slightly increased after annealing while decreased after aging treatment.

Simplified stiffness-based approach for seismic performance evaluation of moment-resisting frame

Based on the concept of stiffness degradation, a damage index of the whole frame and the storey is proposed for the frame seismic performance evaluation. The index is compatible with the non-linear static analysis （e. g. the pushover analysis）, and the structural damage is considered via plastic hinges. Simultaneously, a practical approach is developed to obtain the relationships between the proposed index and earthquake intensities based on the capacity spectrum method. The proposed index is then illustrated through two low-rise reinforced concrete frames, and it is also compared with some other indices. The results indicate that the proposed index is on the safe side and not sensitive to the lateral load pattern. The storey index is helpful to reflect the storey damage and to uncover the position of the weak storey. Finally, the relationship between performance levels and damage index values is also proposed through statistical analysis for the performance-based seismic evaluation.

EARTHQUAKE RESPONSE OF SEMI RIGID FRAME WITH ROTATIONAL DAMPER

The seismic behavior of frames with semi rigid connections and rotational dampers is examined.The ground acceleration due to earthquake is regarded as a stochastic process,and a pseudo excitation algorithm in frequency domain is implemented in a computer program to handle non orthogonal damping properties of the system.The computer program which incorporates detailed connection models and rotational damping models is used to investigate the effect of the connection of the semi rigid frame.It is shown from analytical studies that semi rigid frames with rotational dampers improve the seismic response of the building and may provide an effective and reliable earthquake resistant design solution.

Analysis theory of spatial vibration of high-speed train and slab track system

The motor and trailer cars of a high-speed train were modeled as a multi-rigid body system with two suspensions. According to structural characteristic of a slab track, a new spatial vibration model of track segment element of the slab track was put forward. The spatial vibration equation set of the high-speed train and slab track system was then established on the basis of the principle of total potential energy with stationary value in elastic system dynamics and the rule of ＂set-in-right-position＂ for formulating system matrices. The equation set was solved by the Wilson-θ direct integration method. The contents mentioned above constitute the analysis theory of spatial vibration of high-speed train and slab track system. The theory was then verified by the high-speed running experiment carried out on the slab track in the Qinghuangdao-Shenyang passenger transport line. The results show that the calculated results agree well with the measured rcsults, such as the calculated lateral and vertical rail displacements are 0.82 mm and 0.9 mm and the measured ones 0.75 mm and 0.93 mm, respectively; the calculated lateral and vertical wheel-rail forces are 8.9 kN and 102.3 kN and the measured ones 8.6 kN and 80.2 kN, respectively. The interpolation method, that is, the lateral finite strip and slab segment element, for slab deformation proposed is of simplification and applicability compared with the traditional plate element method. All of these demonstrate the reliability of the theory proposed.

Transient response of a spherical cavity with a partially sealed shell embedded in viscoelastic saturated soil

Based on Biot’s wave equation, this paper discusses the transient response of a spherical cavity with a partially sealed shell embedded in viscoelastic saturated soil. The analytical solution is derived for the transient response to an axisymmetric surface load and fluid pressure in Laplace transform domain. Numerical results are obtained by inverting the Laplace transform presented by Durbin, and are used to analyze the influences of the partial permeable property of boundary and relative rigidity of shell and soil on the transient response of the spherical cavity. It is shown that the influence of these two parameters is remarkable. The available solutions of permeable and impermeable boundary without shell are only two extreme cases of this paper.

Approach for analyzing the ultimate strength of concrete filled steel tubular arch bridges with stiffening girder

A convenient approach is proposed for analyzing the ultimate load carrying capacity of concrete filled steel tubular (CFST) arch bridge with stiffening girders. A fiber model beam element is specially used to simulate the stiffening girder and CFST arch rib. The geometric nonlinearity, material nonlinearity, influence of the construction process and the contribution of prestressing reinforcement are all taken into consideration. The accuracy of this method is validated by comparing its results with experimental results. Finally, the ultimate strength of an abnormal CFST arch bridge with stiffening girders is investigated and the effect of construction method is discussed. It is concluded that the construction process has little effect on the ultimate strength of the bridge.

Numerical evaluation of buckling behavior in space structure considering geometrical parameters with joint rigidity

The buckling behavior of single layer space structure is very sensitive. The joint rigidity, moreover, is one of the main factors of stability which may determine the entire failure behavior. Thus, the reasonable stiffness of joint system, which is neither total pin assumption nor perfect fix condition, is very important to apply to the real single layer space one. Therefore, the purpose of this work was to investigate the buckling behavior of single layer space structure, using the development of the upgraded stiffness matrix for the joint rigidity. To derive tangential stiffness matrix, a displacement function was assumed using translational and rotational displacement at the node. The geometrical nonlinear analysis was simulated not only with perfect model but also with imperfect one. As a result, the one and two free nodal numerical models were investigated using derived stiffness matrix. It was figured out that the buckling load increases in proportion to joint rigidity with rise-span ratio. The stability of numerical model is very sensitive with the initial imperfection, responding of bifurcation in the structure.

Effect of heating time on bonding interface, atom diffusion and mechanical properties of dissimilar titanium joints produced by thermal self-compressing bonding

Solid-state bonding between pure titanium and Ti6Al4V(TC4)alloy was conducted by a new bonding method named as rigid restraint thermal self-compressing bonding.Effects of heating time on bonding interface,atom diffusion and mechanical properties of the joints were studied.Results show that atom diffusion between pure titanium and TC4 alloy significantly takes place during bonding.The diffusion depths of Al and V in pure titanium side are increased with increasing heating time.Due to the enhancement of atom diffusion,bond quality of the bonding interface is improved along with the increase of heating time.The heating time seems to have little effect on microhardness distribution across the joint.However,the tensile strength and ductility of the joint have close relation to heating time.Prolonging heating time can improve the tensile strength and ductility of the joint,especially the latter.When the heating time increases to 450 s,solid-state joint with good combination of strength and ductility is attained.

Development of Chinese large-scale space end-effector

In order to achieve large tolerance capture and high stiffness connection for space payload operations,a Chinese large-scale space end-effector (EER) was developed.Three flexible steel cables were adopted to capture the payload with large capture allowance.Ball screw transmission mechanism and plane shape-constraint four bar linkage mechanism were utilized to connect the payload with high stiffness.The experiments show that capture tolerances in X,Y,Z,Pitch,Yaw,Roll directions are 100 mm,100 mm,120 mm,10.5°,10.5°,12°,respectively.The maximum connection stiffness is 4 800 N·m.The end-effector could meet the requirements for space large tolerance capture and high stiffness connection in the future.

Rigid-Plastic Dynamic Response of Reinforced Concrete Bridge Pier Impacted by Automobile

Bridge piers are impacted by autos sometimes. The pier usually has not been destroyed after once impact by auto. But there are few research on damage which will affect pier's capability, and most relative studies have focused the problems on piers impacted by vessels. The methods involve mainly sutra experience theory, numerical analysis, and experimental method. Owing to the complicacy of the bridge pier impacted by a vessel, there are few research derived with the sutra mechanics model and the piers impacted by autos. The dynamic response is studied here under the assumption of the rigid-plastic small-deformation for the pier impacted by auto. According to the Parkes beam model, the rigid-plastic theoretical solution is deduced. The final deformation is calculated by a practical example for the pier impacted by auto.

Critical embedment depth of a rigid retaining wall against overturning in unsaturated soils considering intermediate principal stress and strength nonlinearity

The overturning stability is vital for the retaining wall design of foundation pits, where the surrounding soils are usually unsaturated due to water draining. Moreover, the intermediate principal stress does affect the unsaturated soil strength; meanwhile, the relationship between the unsaturated soil strength and matric suction is nonlinear. This work is to present closed-form equations of critical embedment depth for a rigid retaining wall against overturning by means of moment equilibrium. Matric suction is considered to be distributed uniformly and linearly with depth. The unified shear strength formulation for unsaturated soils under the plane strain condition is adopted to characterize the intermediate principal stress effect, and strength nonlinearity is described by a hyperbolic model of suction angle. The result obtained is orderly series solutions rather than one specific answer; thus, it has wide theoretical significance and good applicability. The validity of this present work is demonstrated by comparing it with a lower bound solution. The traditional overturning designs for rigid retaining walls, in which the saturated soil mechanics neglecting matric suction or the unsaturated soil mechanics based on the Mohr-Coulomb criterion are employed, are special cases of the proposed result. Parametric studies about the intermediate principal stress, matric suction and its distributions along with two strength nonlinearity methods on a new defined critical buried coefficient are discussed.

Construction of improved rigid blocks failure mechanism for ultimate bearing capacity calculation based on slip-line field theory

Based on the slip-line field theory, a two-dimensional slip failure mechanism with mesh-like rigid block system was constructed to analyze the ultimate bearing capacity problems of rough foundation within the framework of the upper bound limit analysis theorem. In the velocity discontinuities in transition area, the velocity changes in radial and tangent directions are allowed. The objective functions of the stability problems of geotechnical structures are obtained by equating the work rate of external force to internal dissipation along the velocity discontinuities, and then the objective functions are transformed as an upper-bound mathematic optimization model. The upper bound solutions for the objective functions are obtained by use of the nonlinear sequential quadratic programming and interior point method. From the numerical results and comparative analysis, it can be seen that the method presented in this work gives better calculation results than existing upper bound methods and can be used to establish the more accurate plastic collapse load for the ultimate bearing capacity of rough foundation.