A new fractal model of elastic,elastoplastic and plastic normal contact stiffness for slow sliding interface considering dynamic friction and strain hardening

The deflection properties of elastic stage, elastoplastic stage and plastic stage of elastomer were analyzed. Taking account of the kinetic friction force in friction interface and strain hardening in slow sliding interface, the elastic, elastoplastic and plastic normal contact stiffness model for harsh surface was established, which revised the Majumdar-Bhushan fractal model and made it more perfect. In the combination of macro and micro perspective, the effects of coarse surface fractal variables, kinetic friction force in the friction interface, material characters of the friction couples on the contact status and contact property were discussed by the study of digital analysis. Results imply that the normal contact stiffness improves with the increasing real contact area and normal contact load, and reduces with the augment of kinetic friction coefficient. When the kinetic friction coefficient is smaller than 0.3, the normal contact stiffness comprises a linear decrease with the increment of kinetic friction coefficient. When the kinetic friction coefficient is bigger than 0.3, the normal contact stiffness has an exponential decrease with the increasing kinetic friction coefficient.     

Substructuring technique for dynamics analysis of flexible beams with large deformation

In this paper, the substructuring technique is extended for the dynamics simulation of flexible beams with large deformation. The dynamics equation of a spatial straight beam undergoing large displacement and small deformation is deduced by using the Jourdain variation principle and the model synthesis method. The longitudinal shortening effect due to the transversal deformation is taken into consideration in the dynamics equation. In this way, the geometric stiffening effect, which is also called stress stiffening effect, is accounted for in the dynamics equation. The transfer equation of the flexible beam is obtained by assembling the dynamics equation and the kinematic relationship between the two connection points of the flexible beam. Treating a flexible beam with small deformation as a substructure, one can solve the dynamics of a flexible beam with large deformation by using the substructuring technique and the transfer matrix method. The dynamics simulation of a flexible beam with large deformation is carried out by using the proposed approach and the results are verified by comparing with those obtained from Abaqus software.     

Minimum resistance ship hull uncertainty optimization design based on simulation-based design method

In the ship hull optimization design based on simulation-based design (SBD) technology, low precision of the approximate model leads to an uncertainty form of optimization model. In order to enable the approximate model with finite precision to maximize the effectiveness, uncertainty optimization method is introduced here. Wave resistance coefficient approximation model, built by back propagation (BP) neural network, is represented as a form of interval. Afterwards, a minimum resistance optimization model is established with the design space constituted by principal dimensions and ship form coefficients. Double-level nested optimization architecture is proposed: for outer layer, improved particle swarm optimization (IPSO) algorithm with learning factor improvement strategy is used to generate design variables, and for inner layer, modified very fast simulated annealing (MVFSA) algorithm is used to solve the objective function interval with uncertainty region. Cases calculation proves the effectiveness and superiority of uncertainty optimization method for ship hull SBD optimization design, thus providing a good way for finding optimal designs.     

A new functional optimization method applied to the pitch distribution of a marine propeller

Based on Hilbert space theory, an infinite-dimensional optimization method to find the optimal pitch distribution of marine propellers was developed. Thereby, the three-dimensional effect of induced velocity could effectively be controlled in an optimal way; i.e., an investigation was carried out to learn whether the present method is applicable to the design of marine propellers, especially pitch distributions, by maximizing the propeller efficiency functional. In addition, with the help of Hilbert space theory, it was successfully shown that the optimization method developed has a unique mathematical solution. In this work, only the pitch distribution was optimized, while other parameters such as the camber and thickness of the trial propeller remained as in the original. With a numerical study, it is shown that the present optimization method gives an optimal pitch distribution, the open-water characteristic curve being superior to the original curve. Received: August 24, 2000 / Accepted: July 16, 2001     

The development of studying flexible pipe bend reinforced by Kevlar fibers

The flexible pipe bend can not only reduce the structural vibration and fluid noise in pipeline, but also realize the flexible connection of a horizontal line and a vertical line and compensate the displacement of three dimensions produced by the shock or vibration of pipeline in the special situations. Up to now, little attention has been paid to study the flexible pipe bend applied in the pipeline of medium or high pressure, because no appropriate framework materials can be used to reinforce it which must endure the burst pressure higher than 10 MPa. The investigation shows that it is possible to produce the flexible pipe bend of medium or high pressure if such fibers with high performance as Kevlar fibers are used to be its reinforced materials. However, its structural designing theory, manufacturing technology and measuring techniques aren‘t yet perfect and systematic, which leads to the instability of the performance of products. Furthermore, few references about its research can be seen. Therefore, it is necessary to systematically and thoroughly develop the structural designing theory, manufacture technology and measuring techniques of flexible pipe bend.     

A new model for soil consolidation based on microstructure

This paper introduces a new means to predict consolidation deformation of soil from its microstructure. Based on a kind of pore-size distribution density function, a fractal model for soil consolidation is established. Through this model, the relation between macroscopic deformation and microcosmic pore property of soil is founded. In order to justify this proposed model for soil consolidation, consolidation experiments of soft clay are performed. Afterward, the microstructure of soft clay unconsolidated and consolidated under every pressure is studied by a scanning electron microscope (SEM). The results show that the proposed model for soil consolidation is valid in predicting consolidation deformation.     

Numerical simulation of non-destructive testing of stainless steel composites plate by infrared thermography

The non-destructive testing (NDT) of debonding in stainless steel composites plate (SSCP) is performed by infrared thermography, finite element analysis (FEA) software ANSYS is taken as the simulative tool, and 2D simulative model has been set up to investigate effect of the thickness of coating and/or substrate on the detectibility of debonging in SSCPs. Two parameters, namely the maximum defect temperature difference and defect appearing index, are defined to evaluate the detectivity of defects, and their computational methods and formulas are given respectively. The preliminary changing tendency of the maximum defect temperature difference and defect appearing index with the thickness of coating and/or substrate is found by numerical simulation.     

基于μC/OS-Ⅱ的汽车CAN总线智能节点的设计

在将嵌入式操作系统μC/OS-Ⅱ成功移植到LPC2129的基础上,给出了基于ARM7内核的LPC2129汽车CAN总线硬件电路,详细阐述了基于嵌入式操作系统μC/OS-Ⅱ的智能节点软件设计方法.     

Interaction of two three-dimensional explosion bubbles

The interaction of two underwater explosion bubbles was mathematically analyzed in this paper. Based on the assumption of potential flow, high-order curved elements were used to discretize the boundary integral equation and solve it. Assuming that gas inside the bubble follows the isentropic rule, the Euler-Lagrange method was used to trace the evolution of the bubble, and when calculating the singular integral, the singularity of the double-layer singular integral was eliminated by reconstructing a principal-value integral of double-layer potential so that a more precise result could be obtained. Elastic mesh technique (EMT) was also used when tracing the evolution of the bubble interface, and numerical smoothing wasn't needed. A comparison of calculations using this three-dimensional model with results of the Reyleigh-Plesset bubble model shows that the three-dimensional model and calculation method in this paper is practical. This three-dimensional model was applied to simulate the interaction of two bubbles under the action of gravity, and the dynamic characteristics of two bubbles near the surface was also analyzed. Bubbles influenced by surface effects and gravity present severe non-linearity. This paper provides a reference for research into the dynamics of multi-bubbles.     

Multiple sub-array beamspace CAATI algorithm for multi-beam bathymetry system

This paper extends CAATI (Computed Angle-of-Arrival Transient Imaging) technique of Multi-angle Swath Bathymetry Sidescan Sonar (MSBSS) into Multi-Beam Bathymetry Sonar (MBBS) and presents a new Multiple Sub-array Beamspace-CAATI (MSB-CAATI) algorithm. The method not only can achieve high resolution seafloor mapping in the whole wide swath, but also can work well in complex acoustic environments or geometries. Simulation results and processing results of sea-experiment data prove the validity and superiority of the algorithm.