水下爆炸载荷作用下加筋板的动态响应分析

利用Abaqus计算不同水下爆炸载荷作用下加筋板的动态响应,并与RAMAJEYATHILAGAM得出的试验值进行对比,以保证计算分析过程的正确性.计算得到的位移-时间历程曲线可以为加筋板的优化设计提供参考,从而提高其水下爆炸的抗爆能力.     

Minimum cost design of a welded orthogonally stiffened cylindrical shell

In this study the optimal design of a cylindrical orthogonally stiffened shell member of an offshore fixed platform truss, loaded by axial compression and external pressure, is investigated. Ring stiffeners of welded box section and stringers of halved rolled I-section are used. The design variables considered in the optimization are the shell thickness as well as the dimensions and numbers of stiffeners. The design constraints relate to the shell, panel ring and panel stringer buckling, as well as manufacturing limitations. The cost function includes the cost of material, forming of plate elements into cylindrical shape, welding and painting. In the optimization a number of relatively new mathematical optimization methods (leap-frog - LFOPC, Dynamic-Q, ETOPC, and particle swarm - PSO) are used, in order to ensure confidence that the finally computed optimum design is accurately determined, and indeed corresponds to a global minimum. The continuous optimization procedures are adapted to allow for discrete values of the design variables to be used in the final manufacturing of the truss member. A comparison of the computed optimum costs of the stiffened and un-stiffened assemblies, shows that significant cost savings can be achieved by orthogonal stiffening, since the latter allows for considerable reduction of the shell thickness, which results in large material and manufacturing cost savings.     

Optimal design of shells against buckling by means of the simulated annealing method

In this paper, the problem of optimal design of shells against instability under combined state of loadings is considered. We look for the shape of a meridian as well as the thickness of a shell, which ensures the maximal critical value of the loading parameter. The equality constraining the volume of material and the capacity of a shell are considered. The concept of a shell of uniform stability is applied.     

Experiments on interactive buckling in optimized stiffened panels

Five aluminium blade stiffened panels of three different geometries were tested in compression in a displacement controlled loading apparatus. Panel designs were achieved using VICONOPT, a fast-running optimization package based on linear eigenvalue buckling theory, and embrace two different design philosophies. The panels were loaded beyond initial buckling to collapse, and the effects of initial overall imperfections were monitored. In all cases the final failure showed evidence of significant interaction between buckling modes. The tests draw particular attention to a violently unstable and unpredictable form of failure, involving a combination of overall and stiffener buckling, which can occur even when initial buckling in the skin has the effect of pushing the panel in the opposite sense. Received November 14, 2000     

Efficient virtual reality design of quiet underwater shells

Abstract Efficient computational tools are developed to model, visualize, and feel the structural-acoustics of shells in a virtual reality environment. These tools aim at building the structural-acoustic models of shells from an array of basic building blocks including: beams, shells, and stiffeners. The concepts of finite element analysis, sub-structuring, model reduction, meta-modeling, and parallel computations form the main steps to be followed for building simplified computational models of complex shell systems. The resulting models are particularly suitable for the efficient application of multi-criteria optimization techniques in order to select the optimal design parameters of these complex shell systems. The developed integrated analysis tools enable the engineers to design complex systems in a cost effective and a timely manner. Furthermore, engineers will be immersed in an audio-visually coupled tele-operated environment whereby direct interaction and control of the design process can be achieved. In this manner, the behavior of synthetic models of shells can be monitored by literally walking through the shell and adjusting its design parameters as needed to ensure optimal performance while satisfying design and operational requirements. For example, engineers can move electronic wands to vary the number, size, type, and location of stiffeners in the shell, monitor the resulting structural-acoustic visually or by haptic feedback and simultaneously listen to the radiated sound pressure field. Such manipulations of the virtual shells in the scene are carried out while the engineer is navigating through and around the shell to ensure that the vibration and sound levels, at any critical locations, are within the acceptable limits. The developed integrated approach also serves as a means for virtual training of students and engineers on designing and operating complex smart structures on the site as well as through collaborative efforts with other virtual reality sites. Such unique capability will enable engineers to design prototypes of expensive vehicles without building them. Examples of these vehicles include aircraft, submersibles, torpedoes, and others that can share this virtual experience and can be profoundly impacted upon by the proposed approach. The presented optimal design approach is implemented in the Virtual Reality CAVE Laboratory at the University of Maryland that is controlled by an eight parallel processor Silicon Graphics Infinite Reality (ONYX2) computer.     

Minimum cost design of a welded stiffened square plate loaded by biaxial compression

The optimized plate structure consists of a simply supported square base plate stiffened with an orthogonal grid of flat stiffeners welded to the base plate by fillet welds. The uniformly distributed compressive load acts biaxially in the plane determined by the centre of gravity of T-sections, which consist of a part of the base plate and of a stiffener. In the optimization process the number of stiffeners as well as the thicknesses of the base plate and flat stiffeners, which minimize the cost function and fulfil the design constraints, as sought. The cost function includes the cost of material, assembly, welding and painting. Constraints relate to the global buckling, local buckling of base plate parts and stiffeners as well as to the deflection due to shrinkage of welds. To illustrate the effectiveness of the mathematical methods, the problem is solved by the Rosenbrocks hill-climb algorithm as well as by entropy-based unconstrained minimization.     

Optimization of conical shells of Mises material

Conical shells made of a von Mises material are considered. The shells are subjected to unifromly distributed lateral loading and are simply supported at outer edges whereas inner edges are absolutely free. The shell wall is assumed to be of piece-wise constant thickness. Resorting to the lower bound theorem of limit analysis, optimal designs of shells are established under given weight (material volume of a shell) which corresponds to the maximum load carrying capacity. Received May 15, 2000     

Design optimization of stiffened storage tank for spacecraft

Stiffened storage tank is an important structural component in spacecraft. Its structural weight is one of the key criterions in the design phase. This paper focuses on the design optimization of the structure by using finite element method, structural sensitivity analysis techniques, and sequential linear/quadratic programming aimed to reduce the structural weight. Design variables include the numbers of stiffeners, stiffeners’ section dimensions, and shell thickness distribution. Detailed finite element modeling processes are presented, which are the ways to construct the stiffener (beam orientation and offset) and shell elements and the ways to determine the analysis model and structural boundary conditions. A brief introduction to sensitivity analysis and optimization solution algorithm is also given. Main attention is paid to the studies of design optimization of the tank structure, including the selection of design cases, evaluation, and comparison of the optimal results. There are six design cases considered in the design procedures. Numerical results show that by using the above computational techniques, the structural weight is effectively reduced. In this work, MSC.Patran/Nastran is employed to construct the Finite Element Model (FEM), and JIFEX, which is developed in our group, is used to conduct the structural design optimization. JIFEX is a structural analysis and optimization software package developed by Gu and colleagues in the Dalian University of Technology Department of Engineering Mechanics. Among its many functions is the ability to analyze and optimize piezoelectric smart structures.     

Optimization of plastic spherical shells with a central hole

An optimization method for plastic spherical shells is presented. The shells under consideration are clamped at the outer edge and contain a central hole. The material of the shells obeys the generalized square yield condition and the associated flow rule. The problem of maximization of the load carrying capacity under the condition that the weight (material volume) of the shell is fixed is transformed into a problem of nonlinear programming. The latter is solved with the aid of Lagrangian multipliers. The solution obtained is compared with the optimal solution of the minimum weight problem for given load carrying capacity. Received September 9, 1999     

Optimum design of welded stiffened plates loaded by hydrostatic normal pressure

The optimal positions of horizontal stiffeners are computed considering the condition that the base plate parts, having equal thicknesses and loaded by bending moments, should be stressed to yield strength. The trapezoidal stiffeners are designed for bending using the stress and local buckling constraints. The optimal number of stiffeners is determined on the basis of material and fabrication cost calculations. It is shown by a numerical example that the nonequidistant stiffener arrangement gives 22% weight and 16–18% cost savings. Received June 30, 1999     

水下滑翔机垂直面运动优化控制

水下滑翔机是一种依靠水动力和净浮力驱动的新型水下机器人. 本文分析了滑翔机在垂直面滑翔时, 浮力变化和内置可动质量块位置变化对滑翔机运动状态的影响．针对滑翔机在潜浮切换时, 由于机翼受力不对称产生的无升力现象而导致的切换过程不稳定的问题, 采用两点边值的优化控制方法, 规划了内置质量块的位量, 以消除滑翔机在潜浮切换过程中各个时刻产生的不对称无升力现象．最后给出了滑翔机实际机械系统可接受的最优控制 方案. 仿真表明了这种优化方法的有效性.     

Optimal Design of a 6-DOF Parallel Manipulator Using Particle Swarm Optimization

Performance indices of parallel manipulators (PMs) vary widely with the variation of geometric properties. Improvement of one parameter often leads to worsen the other parameters. Therefore, getting into an optimum design for the PMs has been subject of much recent research. In this paper, we optimize three performance parameters of a PM simultaneously including workspace, condition number, and stiffness. In addition, a new performance index is introduced for stiffness evaluation of the PMs. The index is invariant under similarities. Because of complexity of cost function and number of variables, choosing an optimization method that can converge to the optimum point is very important. We select particle swarm optimization (PSO) method and show that this algorithm is perfect for performance optimization of PMs. Furthermore, we propose a new subroutine added to PSO algorithm to improve its convergence.     

压电加筋壁板结构的多模态自抗扰振动控制

针对压电加筋壁板结构多模态主动控制时存在振动模型和外界干扰难以确定等问题, 提出一种不依赖结构数学模型的多模态自抗扰振动控制方法. 首先,采用多回路的扩张状态观测器实时估计其他模态的输出叠加、输入耦合、高次谐波以及外界激励等组成的集总干扰, 并将估计值通过前馈补偿的方式消除干扰对整个控制系统的影响. 然后, 针对每个控制模态设计独立的PD反馈控制器. 为了提高整个控制系统的振动抑制性能, 结合多模态振动控制的特点, 引入一种具有实际意义的性能指标函数. 并基于此性能函数, 提出基于logistic映射的自抗扰振动控制器参数自动优化方法. 最后, 利用dSPACE半实物仿真平台, 搭建了四面固支壁板结构的压电振动控制实验系统.最后, 多模态干扰激励的实验结果表明了所提的多模态自抗扰振动主动控制方法的有效性.     

On the design optimization of built-up stiffened steel beams with buckling and frequency constraints

The literature on the structural design optimization of steel-plate girders indicates a need for more refined research studies to obtain optimal designs by formulating and solving the design problem that combines structural sizing and shape parameters in one unified, constrained problem. For this purpose, the structural optimization design problem of stiffened steel-plate girders is formulated with specified loading conditions and constraints on strength and serviceability considerations including limits on fundamental frequency and buckling modes. The finite-element method-based model is used to define the objective function and the structural/geometric response functions, while the geometric domain elements are used to systematically perturb the structural shape during the search for an optimal shape of the structure. The mathematical statement of the gradient-based-design problem is solved for an optimal structural size and shape with buckling and frequency constraints in addition to the traditional strength constraints. The numerical results obtained are compared with results obtained from a less formal ad hoc design procedure, and some conclusions are drawn to emphasize the design benefits obtained from solving the design problem for optimal structural size and shape.     

Optimal design of plastic cylindrical shells of von Mises material

Optimal design of plastic circular cylindrical shells of von Mises material is studied. The optimization problem is stated as the maximization problem of the load carrying capacity for given weight of the shell. Shells with constant and piecewise-constant thickness are considered. The maximization problem is performed under the requirement that the material volume of the stepped shell is equal to the case of the reference shell of constant thickness. The material of the shell is assumed to be an ideal rigid plastic obeying von Mises yield criterion. The considered nonlinear problems are solved by using the CASes method.     

Robust control of variable speed autonomous underwater vehicle

Set point tracking control of autonomous underwater vehicle (AUV) via robust model predictive control (RMPC) is considered. Input-constrained RMPC with integral action, which has been developed in our previous work, is used to control the AUV in this study. In order to derive a RMPC control rule, non-linear dynamics of AUV with six degree of freedom is linearized at certain operating points. So, horizontal and vertical plane dynamics of system are represented by linear models which have polytopic uncertainties. Since the derived control rule will be used in real time, the computation time should be reduced. To overcome this computational time problem and get rid of trial–error step of Algorithm 1, a new algorithm is proposed here. The simulations are carried out using the control rule based on this algorithm and these results are presented.     

飞机座舱减振降噪优化设计方法

采用结构拓扑优化的变密度法和形貌优化法,对模拟飞机座舱的四角固支声音箱体,进行了减振降噪的研究.比较优化前后结构固有频率的变化和对声压的影响,得出了结构拓扑优化对减振降噪作用的高效性.     

Experiments in the coordinated control of an underwater arm/vehicle system

The addition of manipulators to small autonomous underwater vehicles (AUVs) can pose significant control challenges due to hydrodynamic interactions between the arm and the vehicle. Experiments conducted at the Monterey Bay Aquarium Research Institute (MBARI) using the OTTER vehicle have shown that dynamical interactions between an arm and a vehicle can be very significant. For the experiments reported in this paper, a single-link arm was mounted on OTTER. Tests showed that for 90-degree, two-second repetitive slews of the arm, the vehicle would move as much as 18 degrees in roll and 14 degrees in yaw when no vehicle control was applied.Using a new, highly accurate model of the arm/vehicle hydrodynamic interaction forces, which was developed as part of this research, a coordinated arm/vehicle control strategy was implemented. Under this model-based approach, interaction forces acting on the vehicle due to arm motion were predicted and fed into the vehicle controller. Using this method, station-keeping capability was greatly enhanced. Errors at the manipulator end point were reduced by over a factor of six when compared to results when no control was applied to the vehicle and by a factor of 2.5 when compared to results from a standard independent arm and vehicle feedback control approach. Using the coordinated-control strategy, arm end-point settling times were reduced by a factor three when compared to those obtained with arm and vehicle feedback control alone. These dramatic performance improvements were obtained with only a five-percent increase in total applied thrust.     

Constrained adaptive topology optimization for vibrating shell structures

This paper describes an algorithm for structural topology optimization entitled Constrained Adaptive Topology Optimization or CATO which is applied here to produce the optimum design of shell structures under free vibration conditions. The algorithm, based on an artificial material model and an updating scheme, combines ideas from the more mathematically rigorous homogenization (h) methods and the more intuitive evolutionary (e) methods. Thus, CATO can be seen as a hybrid h/e method. The optimization problem is defined as maximizing or minimizing a chosen frequency with a constraint on the structural volume/mass by redistributing the material through the structure. The efficiency of the proposed algorithm is illustrated through several numerical examples. Received February 17, 2000     

功能梯度薄壁圆柱壳的自由振动

研究了由功能梯度材料制成的薄壁圆柱壳的自由振动.采用幂律分布规律描述功能梯度材料沿厚度的梯度性质,根据Donnell壳体理论,导出了功能梯度材料薄壁圆柱壳线性振动的简化控制方程.基于此理论分析了功能梯度圆柱壳的自由振动特性,给出了两端简支功能梯度材料薄壁圆柱壳小挠度固有振动的频率公式.以简支圆柱壳作为算例,与前人结果及有限元法对比验证了该简化功能梯度薄壁圆柱壳理论的正确性,同时讨论了周向波数及梯度指数对其频率的影响.