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.     

Optimal annular plates with respect to their stability under thermal loadings

In the paper the uni- and multimodal optimization problems of elastic annular plates with respect to their stability under thermal loading are investigated. We look for such a distribution of a thickness of a plate (circularly symmetric), which leads to the maximum increment |ΔT| of temperature, causing buckling of the optimal structure under the equality constraint of a constant volume of the material and under inequality constraints imposed on the minimal and maximal values of a plate thickness. The optimal solutions for different modes of supports and different ratio of the inner and outer radius are looked for using the method of moving asymptotes and the simulated annealing.A short version of the paper was presented at WCSMO-6     

Optimal design of elasto-plastic structures subjected to normal and extreme loads

When in the design of structures extreme loadings such as short time, high intensity dynamic pressure (explosion), impact or earthquake have to be taken into consideration then, except for special cases, the plastic reserves of the material can be utilized, but the development of excessive plastic deformations, residual displacements and the collapse have to be prevented. Following this design concept in this paper three appropriate methods are presented for the determination of the optimal layout of material of elasto-plastic structures (beams, frames, trusses and plates) subjected to extreme loading. The investigation is extended also to the case when in the optimal design in addition to one of the extreme loads the normal (working) loads can be separately or simultaneously taken into consideration.     

Optimal design of thin-walled columns for buckling under loadings controlled by displacements

In this paper the problem of the optimal design of thin-walled tubular columns under loadings controlled by displacement is investigated. A radius of cross-sectional circular profile varying along the axis of the shell-column as well as a wall thickness, which lead to the maximal axial displacement caused by compression before the structure buckles are sought. Both global (buckling of a column) and local (wall buckling of a shell) stability of a structure are taken into account. The geometry of the structure is approximated by the convex Bézier polynomial. The results are obtained using numerical optimization method, namely the simulated annealing method.     

Optimal location and sizing of storage units in a drainage system

Adapting urban stormwater drainage systems is essential to handling increased urbanization and climate change. Within an urban area, storage units are an efficient solution to reduce peak runoff, but their implementation involves complex decisions. This paper presents a novel optimization model for defining, in existing sewer drainage systems, the number of storage units, their location, size and the orifice dimensions. The orifice is used to reduce storage unit outflow regulating downstream flows. These components allow an integrated flow control and flooding reduction throughout the network. The desired solution should offer the lowest cost and try to avoid any major flooding impact. The model includes hydraulic, flood and capacity constraints and it is solved through a simulated annealing algorithm that calls upon a dynamic rainfall-runoff simulator for complete evaluation of each solution. The performance of the optimization model is assessed through a case study inspired by a real urban sewer network.     

Analysis of moderately-thick and deep shells subjected to thermal and mechanical loadings

An analytical solution to a boundary value problem of moderately-thick and deep doubly curved shells of rectangular planform subjected to thermal and mechanical loadings is presented. Sanders' kinematic relations that incorporate transverse shear deformations in moderately deep shell theory are considered in the shell formulations, yielding five coupled second order partial differential equations in five unknowns displacements. These are then solved in conjunction with admissible boundary conditions. The numerical results presented herein should serve as bench-mark solutions for future comparisons.     

Introducing a discrete modelling technique for buckling of panels under combined loading

The paper introduces a discrete model to describe the buckling of a stiffened panel beam under a complex loading environment. The study begins by examining the existing load interaction equation for a continuous panel. Experimental and finite element investigations establish the validity of considering the critical panel of a more complex structure in isolation. The paper then devises a discrete model for this critical panel, which was validated for a range of boundary conditions using anti-optimisation. The numerical results show that the discrete model exhibits the buckling behaviour of a continuous panel under combined loading. Recent studies established that the truss-lattice configuration has stable post-buckling behaviour and derived fast analysis technique for such a structure. It is therefore concluded that the truss-lattice model introduced in the present paper can offer a fast analysis formulation for buckling (and potentially post-buckling) of multiple-panel beams suitable for optimisation. Presented at the 7th World Congress on Computational Mechanics, LA, USA, July 2006.     

SAR图像的最优分割方法

根据SAR图像的概率密度函数获得图像的拟然函数,然后将似然函数和边界约束方程结合起来,提出适合于SAR图像分割的代价函数,其中边界约束方程引入邻域结构信息来保证区域边界的规则性,通过使代价函数最小来获得图像的最优分割。算法首先将原图分割成一定大小的块状区域作为初始分割,每一区域代表一个类别;然后随机调整相邻两个区域之间的像素,通过比较代价函数的变化,利用模拟退火算法确定接受该调整的概率。模拟退火是一种求解全局最优的算法,当温度趋向于0时,它可以获得使代价函数最小的SAR图像的分割。最后,利用基于相似性的融合方法对分割进行后期处理,将相似的较小的区域融合成较大的区域,使得分割更合理。我们将该算法应用到一些SAR测试图像上,获得了比较满意的结果。     

Multi-fidelity optimization of laminated conical shells for buckling

Optimum laminate configuration for minimum weight of filament-wound laminated conical shells is investigated subject to a buckling load constraint. In the case of a composite laminated conical shell, due to the manufacturing process, the thickness and the ply orientation are functions of the shell coordinates, which ultimately results in coordinate dependence of the stiffness matrices (A,B,D). These effects influence both the buckling load and the weight of the structure and complicate the optimization problem considerably. High computational cost is involved in calculating the buckling load by means of a high-fidelity analysis, e.g. using the computer code STAGS-A. In order to simplify the optimization procedure, a low-fidelity model based on the assumption of constant material properties throughout the shell is adopted, and buckling loads are calculated by means of a low-fidelity analysis, e.g. using the computer code BOCS. This work proposes combining the high-fidelity analysis model (based on exact material properties) with the low-fidelity model (based on nominal material properties) by using correction response surfaces, which approximate the discrepancy between buckling loads determined from different fidelity analyses. The results indicate that the proposed multi-fidelity approaches using correction response surfaces can be used to improve the computational efficiency of structural optimization problems.     

A simulated annealing approach to the traveling tournament problem

Automating the scheduling of sport leagues has received considerable attention in recent years, as these applications involve significant revenues and generate challenging combinatorial optimization problems. This paper considers the traveling tournament problem (TTP) which abstracts the salient features of major league baseball (MLB) in the United States. It proposes a simulated annealing algorithm (TTSA) for the TTP that explores both feasible and infeasible schedules, uses a large neighborhood with complex moves, and includes advanced techniques such as strategic oscillation and reheats to balance the exploration of the feasible and infeasible regions and to escape local minima at very low temperatures. TTSA matches the best-known solutions on the small instances of the TTP and produces significant improvements over previous approaches on the larger instances. Moreover, TTSA is shown to be robust, because its worst solution quality over 50 runs is always smaller or equal to the best-known solutions. A Preliminary version of this paper was presented at the CP'AI'OR'03 Workshop.     

Optimal design of underwater stiffened shells

The optimal design parameters of stiffened shells are determined using a rational multicriteria optimization approach. The adopted approach aims at simultaneously minimizing the shell vibration, associated sound radiation, weight of the stiffening rings as well as the cost of the stiffened shell. A finite element model is developed to determine the vibration and noise radiation from cylindrical shells into the surrounding fluid domain. The production cost as well as the life cycle and maintenance costs of the stiffened shells are computed using the Parametric Review of Information for Costing and Evaluation (PRICE) model. A Pareto/min-max multicriteria optimization approach is then utilized to select the optimal dimensions and spacing of the stiffeners. Numerical examples are presented to compare the vibration and noise radiation characteristics of optimally designed stiffened shells with the corresponding characteristics of plain un-stiffened shells. The obtained results emphasis the importance of the adopted multicriteria optimization approach in the design of quiet, low weight and low cost underwater shells which are suitable for various critical applications. Received September 14, 2000 Communicated by J. Sobieski     

Optimal design of rigid-plastic beams subjected to dynamical loading

In the present paper the optimization problem of dynamically loaded simply supported beams is handled. The concept of a rigid-plastic body is used. The shape of the beam is sought, for which the integral residual deflection for a given time-instant and load is minimal. Two numerical methods for solving the problem are proposed. The numerical results are compared with those obtained by Lepik (1982).     

Floorplan design of VLSI circuits

In this paper we present two algorithms for the floorplan design problem. The algorithms are quite similar in spirit. They both use Polish expressions to represent floorplans and employ the search method of simulated annealing. The first algorithm is for the case where all modules are rectangular, and the second one is for the case where the modules are either rectangular or L-shaped. Our algorithms consider simultaneously the interconnection information as well as the area and shape information for the modules. Experimental results indicate that our algorithms perform well for many test problems.This work was partially supported by the Semiconductor Research Corporation under Contract 86-12-109, by the National Science Foundation under Grant MIP 8703273, and by a grant from the General Electric Company.     

Optimal design of interference fit assemblies subjected to fatigue loads

This paper presents a methodology for an optimal design of interference fit subjected to fatigue loads. Optimization consists in finding a trade-off between mass and competing safety factors at hub and shaft contact zone as well as in shaft fillet. Developing an effective calculation method for fatigue strength of an interference fitted assembly using the finite element method is one of the main steps of the procedure. Meanwhile, coupling the finite elements model of interference fit with an optimization algorithm is not adequate considering the computing time and the significant number of calculations necessary to portrait the assembly behavior. Therefore, a sequential approximate multi-objective optimization algorithm (SAMOO) is presented. The method involves Design Of Experiments (DOE), interpolation with kriging functions, and multi-objective optimization. Preliminary study of parameter variance, and advanced post-processing of multi-objective optimization, provide engineers with valuable information for identifying an optimal design of interference fit assembly using fewer finite element calculations.     

Iterative improvement to solve the parcel hub scheduling problem

This paper presents iterative improvement algorithms to solve the parcel hub scheduling problem (PHSP). The PHSP is combinatorial optimization problem that consists of scheduling a set of inbound trailers to a small number of unload docks. At the unload docks, the inbound trailers must be unloaded and the parcel sorted and loaded onto outbound trailers. Because the transfer operation is labor intensive, the transfer of parcels must be done in such a way as to minimize the timespan of the transfer operation. Local search (LS) and simulated annealing (SA) algorithms are developed and evaluated to solve the problem. The performances of the algorithms are compared to the performance of an existing genetic algorithm (GA). The computational results show that the LS and SA algorithms offer solutions that are superior to those offered by the GA.     

Fuzzy hybrid simulated annealing algorithms for topology design of switched local area networks

Topology design of switched local area networks (SLAN) is classified as an NP-hard problem since a number of objectives, such as monetary cost, network delay, hop count between communicating pairs, and reliability need to be simultaneously optimized under a set of constraints. This paper presents a multiobjective heuristic based on a simulated annealing (SA) algorithm for topology design of SLAN. Fuzzy logic has been incorporated in the SA algorithm to handle the imprecise multiobjective nature of the SLAN topology design problem, since the logic provides a suitable mathematical framework to address the multiobjective aspects of the problem. To enhance the performance of the proposed fuzzy simulated annealing (FSA) algorithm, two variants of FSA are also proposed. These variants incorporate characteristics of tabu search (TS) and simulated evolution (SimE) algorithms. The three proposed fuzzy heuristics are mutually compared with each other. Furthermore, two fuzzy operators, namely, ordered weighted average (OWA) and unified AND–OR (UAO) are also applied in certain steps of these algorithms. Results show that in general, the variant which embeds characteristics of SimE and TS into the fuzzy SA algorithm exhibits more intelligent search of the solution subspace and was able to find better solutions than the other two variants of the fuzzy SA. Also, the OWA and UAO operators exhibited relatively similar performance.     

Sensitivity of buckling loads of anisotropic shells of revolution to geometric imperfections and design changes

Buckling load sensitivity calculations in the shell-of-revolution program FASOR are discussed. This development is based on Koiter's initial postbuckling theory, which has been generalized to include the effect of stiffness changes, as well as geometric imperfections. The implementation in FASOR is valid for anisotropic, as well as orthotropic, shells. Examples are presented for cylindrical panels under axial compression, complete cylindrical shells in torsion, and antisymmetric angle-ply cylindrical panels under edge shear.     

恶劣天气因素下最优车辆路线调度路径选择

考虑恶劣天气因素下的最优车辆路线调度关系到灾害环境下的货物运输效率。由于在较为恶劣的天气环境下,车辆路径的属性特征会发现不可预估的变化。上述属性变化无法通过设定权值进行程度的描述。利用传统算法进行车辆路线调度,没有充分考虑天气因素给车辆路径选择带来的影响。往往通过经验设定固定的影响权值,没有考虑对不同路径选择属性数据影响的差异性,调度过程缺陷明显。提出采用模拟退火遗传算法的最优车辆路线调度方法。依据相关理论构建车辆调度优化模型,结合在恶劣天气环境下,车辆行驶路径所需时间、交叉路口密度、通行能力等因素综合变化,根据模拟退火算法模拟差异化的天气影响因素,利用遗传算法求取模型最优解,实现考虑恶劣天气因素的最优车辆路线调度的路径选择。实验结果表明,利用改进算法进行车辆路线调度,能够有效的获取车辆当前的最佳路线,提高了车辆调度的效率。     

A robust design of simulated annealing approach for mixed-model sequencing

The effectiveness of the solution method based on simulated annealing (SA) mainly depends on how to determine the SA-related parameters. A scheme as well as parameter values for defining an annealing schedule should be appropriately determined, since various schemes and their corresponding parameter values have a significant impact on the performance of SA algorithms. In this paper, based on robust design we propose a new annealing parameter design method for the mixed-model sequencing problem which is known to be NP-hard. To show the effectiveness of the proposed method, extensive computation experiments are conducted. It was found that the robust designed method outperforms the SA algorithm by McMullen and Frazier [McMullen, P.R., & Frazier, G.V. (2000). A simulated annealing approach to mixed-model sequencing with multiple objectives on a just-in-time line. IIE Transactions, 32, 679–686].     

Optimal design of conical springs

Mechanical systems often use springs to store energy though their axial length must sometimes be significantly reduced. This leads to the use of conical springs as they are able to telescope. Designers of mechanical systems can call on a large number of tools to assist them though most of these are merely validation tools requiring concomitant trial and error strategies. Optimization strategies can be applied to provide synthesis assistance tools for which the designer simply specifies his requirement. Thus the tool directly indicates the spring best suited to standards and requirements. Recent advances in the study of constant pitch conical springs have provided analytical expressions of their behavior even in the non-linear phase. Considering this, we have used optimization strategies to provide a synthesis tool for conical spring design. An example of application is presented. The tool introduced here is thus a synthesis assistance tool that can be of considerable interest for designers who require a conical spring in their design.