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.     

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     

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.     

Dynamic analysis of box girders with tee-stiffening using unconstrained optimization techniques

The paper presents a numerical procedure for dynamic analysis of box girders with tee-stiffeners utilizing unconstrained optimization techniques. Unlike the finite element or finite strip methods, the procedure does not require discretization to the whole structure, thus resulting in great savings in computational time. The potential and kinetic energy of the assembled structure is expressed in terms generalized functions that describe the longitudinal and transverse displacement profiles. The problem is then converted into uunconstrained optimization problem to determine the magnitude of the lowest natural frequency and the associated mode shape. Results are presented showing the sensitivity the natural frequency to the stiffener depth (d) and the flange width (b). It is shown that the number of longitudinal and transverse stiffeners largely influence the magnitude of the natural frequency (λ) of the box girder. Design guidelines are also provided to optimize the dynamic response of the structure. The procedure is very practical and can be utilized in the industry for the analysis of box girders.     

Reliability-based optimum design of a welded stringer-stiffened steel cylindrical shell subject to axial compression and bending

The economy of stiffened shells vs the unstiffened version depends on loading, type of stiffening and stiffener profile. The stiffening is economic when the shell thickness can be decreased in such a measure that the cost savings caused by this decreasing is higher than the additional cost of stiffening material and welding. The present work deals with cylindrical shell columns fixed at the bottom and free at the top subject to axial compression and horizontal force acting on the top of the column. The shell is stiffened outside with stringers welded by longitudinal fillet welds. Half rolled I-section (UB) stiffeners are used to reduce welding cost. The cost function to be minimized includes the costs of the materials, forming of shell elements into the cylindrical shape, assembly, welding and painting. The design variables are the shell thickness, number and profile of stiffeners for the stiffened shell, but only the first type of variable in the unstiffened case. Randomness is considered both in loading and material properties. A level II reliability method (first-order reliability method) is employed. Individual reliability constraints related with shell buckling, stringer panel buckling and the limitation of the horizontal displacement of the column top are considered. The overall structural reliability is obtained by using Ditlevsen's method of conditional bounding. The costs of both the stiffened and unstiffened shells designed to ensure a stipulated probability of failure will be compared with the solutions obtained for a code-based method, which employs partial safety factors. Results are given illustrating the influence of the constraint on the horizontal displacement.     

Minimum cost design of a cellular plate loaded by uniaxial compression

Cellular plates are constructed from two base plates and an orthogonal grid of stiffeners welded between them. Halved rolled I-section stiffeners are used for fabrication aspects. The torsional stiffness of cells makes the plate very stiff. In the case of uniaxial compression the buckling constraint is formulated on the basis of the classic critical stress derived from the Huber’s equation for orthotropic plates. The cost function contains the cost of material, assembly and welding and is formulated according to the fabrication sequence. The unknown variables are the base plate thicknesses, height of stiffeners and numbers of stiffeners in both directions. The cellular plate is lighter and cheaper than the plate stiffened on one side. The Particle Swarm Optimization and the IOSO techniques are used to find the optimum. PSO contains crazy bird and dynamic inertia reduction criteria, IOSO is based on a response surface technology.     

Global minimum cost design of a welded square stiffened plate supported at four corners

This paper presents the application of a refined version of the original Snyman–Fatti (SF) global continuous optimization algorithm (Snyman and Fatti, J Optimiz Theory Appl 54:121–141, 1987) to the optimal design of welded square stiffened plates. In particular we investigate square plates of square symmetry subjected to uniformly distributed normal static loads, supported at four corners, and stiffened by a square symmetrical orthogonal grid of ribs. Halved rolled I-section stiffeners are used welded to the base plate by double fillet welds. Profiles of different size are used for internal and edge stiffeners. A cost calculation method, developed by the first two authors and mainly used for welded structures (Farkas and Jármai 2003), allows for the computation of cost for different proposed designs of the welded stiffened plates. The cost function includes material, welding as well as painting costs, and is formulated according to the fabrication sequence. Design variables include base plate thickness as well as the dimensions of the edge and internal stiffeners. Constraints on stress in the base plate and in stiffeners, as well as on deflection of edge stiffeners and of internal stiffeners are considered. For this purpose the Snyman–Fatti (SF) global unconstrained trajectory method is adapted to handle constraints of this type. For control purposes a particle swarm optimization (PSO) algorithm is also applied to confirm the results given by the SF algorithm. Since the torsional stiffness of open section stiffeners is very small, the stiffened plates are modelled as a torsionless gridwork. We present an algorithm for calculating the moments and deflections for torsionless gridworks with different number of internal stiffeners, using the force method.     

A method to optimize the scope of a software product platform based on end-user features

ContextDue to increased competition and the advent of mass customization, many software firms are utilizing product families – groups of related products derived from a product platform – to provide product variety in a cost-effective manner. The key to designing a successful software product family is the product platform, so it is important to determine the most appropriate product platform scope related to business objectives, for product line development.AimThis paper proposes a novel method to find the optimized scope of a software product platform based on end-user features.MethodThe proposed method, PPSMS (Product Platform Scoping Method for Software Product Lines), mathematically formulates the product platform scope selection as an optimization problem. The problem formulation targets identification of an optimized product platform scope that will maximize life cycle cost savings and the amount of commonality, while meeting the goals and needs of the envisioned customers’ segments. A simulated annealing based algorithm that can solve problems heuristically is then used to help the decision maker in selecting a scope for the product platform, by performing tradeoff analysis of the commonality and cost savings objectives.ResultsIn a case study, PPSMS helped in identifying 5 non-dominated solutions considered to be of highest preference for decision making, taking into account both cost savings and commonality objectives. A quantitative and qualitative analysis indicated that human experts perceived value in adopting the method in practice, and that it was effective in identifying appropriate product platform scope.     

单台批处理机生产运输协调合作博弈调度问题

研究单台批处理机生产与生产前运输的协调调度问题,目标函数为最小化与完成时间相关的生产总成本.以工件为博弈方,以联盟的最大成本节省为特征函数,将调度问题转换为合作博弈模型.针对相同运输时间与加工时间的情形,证明该合作博弈具有非空核,beta规则可得一个核分配.针对一般问题,设计Q-learning算法求解联盟最优调度,并利用beta规则对节省的成本进行分配.数值算例验证了合作博弈模型的可行性以及Q-learning算法与beta规则对节省成本分配的有效性.     

Analysis and optimum design of fibre-reinforced composite structures

The optimal design of a carbon-fibre-reinforced plastic (CFRP) sandwich-like structure with aluminium (Al) webs is addressed. The material parameters are determined using tensile tests, whereafter the results of an analytical model, a numerical model and an experimental setup are compared. The analytical and numerical approximations are then used to optimize the structure in a multi-algorithm approach for minimum cost and maximum stiffness. The selected algorithm and approximation are motivated by their accuracy and computational efficiency. The CFRP plates are optimized with respect to ply arrangement, while the complete sandwich-like structure is optimized with respect to the combination of manufacturing and material cost. Design constraints on maximum deflection of the total structure, buckling of the CFRP composite plates, buckling of the Al webs, stress in the composite plates and stress in the Al stiffeners are included in the formulation. For the different phases in the optimization process, we use the recently proposed particle swarm optimization algorithm, a dynamic search technique and a continuous-discrete optimization technique .     

飞机线缆自动检测系统布局优化设计研究

针对大型飞机约40000测试点的线缆自动检测系统中测试箱点数、测试箱位置和测试设备间控制电缆连接路径进行优化设计。利用近邻交换法实现机载插头自动分类,并基于0-1背包求解方法提升测试箱可接入点数利用率;利用分步遗传粒子群算法,以转接电缆总长最短为目标,优化测试箱可接入点数和测试箱位置;将控制电缆连接路径抽象为多支路无返回旅行商问题,取测试箱空间位置为节点,测试箱之间的控制线缆为边,测试箱内的对接点数量为权重,构建无向加权网络模型,并以支路总长最短、支路均衡为目标,采用混合离散粒子群算法搜索最佳连接路径,实现测试系统多支路优化设计。与原设计结果相比,测试箱可接入点数利用率从89.7%提高到100%,减少转接电缆10%、控制电缆18%。对线缆自动检测系统测试方案中待优化项目进行数学建模,涵盖了转接电缆的插头分类模型建立、转接电缆长度计算模型建立和控制电缆长度计算模型建立,并基于粒子群智能优化算法,优化线缆自动检测系统布局,从而达到了飞机线缆自动检测系统轻量化设计及最优成本实现。     

Improved trust‐region gradient‐search algorithm for accelerated optimization of wideband antenna input characteristics

Full‐wave electromagnetic (EM) simulation models are ubiquitous in carrying out design closure of antenna structures. Yet, EM‐based design is expensive due to a large number of analyses necessary to yield an optimized design. Computational savings can be achieved using, for example, adjoint sensitivities, surrogate‐assisted procedures, design space dimensionality reduction, or similar sophisticated means. In this article, a simple modification of a rudimentary trust‐region‐embedded gradient search with numerical derivatives is proposed for reduced‐cost optimization of input characteristics of wideband antennas. The approach exploits information and history of relative changes of the design (as compared with the trust region size) during algorithm iterations to control the updates of components of the antenna response Jacobian, specifically, to execute them only if necessary. It is demonstrated that the proposed framework may lead to over 50% savings over the reference algorithm with only minor degradation of the design quality, specifically, up to 0.3 dB (or <3%). Numerical results are supported by experimental validation of the optimized antenna designs. The presented algorithm can be utilized as a stand‐alone optimization routine or as a building block of surrogate‐assisted procedures.     

双效精馏结构的运行成本核算与比较

应用商业模拟软件Aspen Plus模拟计算甲醇/水溶液分离体系的单塔精馏和三种双效精馏,并以全年运行总成本费用最低为目标函数,对模拟结果核算成本.从节能和成本两方面考虑,双效精馏比单塔精馏具有明显的优势.对所研究的甲醇/水分离体系,双效顺流精馏是最佳的精馏结构,全年总成本比单塔精馏约节约29.9%.     

Effect of boundary conditions on natural frequencies for rotating composite cylindrical shells with orthogonal stiffeners

The effect of the boundary conditions on the natural frequencies for rotating composite cylindrical shells with the orthogonal stiffeners is investigated using Love’s shell theory and the discrete stiffener theory. The frequency equation is derived using the Rayleigh–Ritz procedure based on the energy method. The considered boundary conditions are four sets, namely: (1) clamped–clamped; (2) clamped–simply supported; (3) clamped–sliding; and (4) clamped–free. The beam modal function is used for the axial vibration mode and the trigonometric functions are used for the circumferential vibration mode. The composite shells are stiffened with uniform intervals and the stiffeners have the same material. By comparison with the previously published analytical results for the rotating composite shell without stiffeners and the orthogonally stiffened isotropic cylindrical shells, it is shown that natural frequencies can be determined with adequate precision.     

双通道云数据存储安全方案研究

为了改善解决云计算中热点问题之一～数据存储安全,该文在研究现有经典云数据存储体系架构的基础上,根据云本身的超强计算能力和代价低廉等特性,提出了一种优化的双通道并行云存储架构,配以非对称数据加密手段,在硬件与架构层面直接针对安全问题作出优化部署。在大量的节约成本、提高效率、精简架构的情况下保证了云环境下数据存储安全性的提升。模拟部署表明,双通道并行云架构及非对称数据加密能有效的提高云数据存储的安全性。     

Cost–Performance Optimization of Application- and Context-Aware Distributed Infrastructures

Application- and context-aware infrastructures involve the network in the execution of distributed applications through special devices, namely, the application cards, placed in network nodes. The sharp separation of applications and network is smoothed, and by performing part of the distributed application inside the network, it is possible to reduce costs and improve performance with a better optimization of the whole distributed information and communication technology (ICT) infrastructure. This optimization is allowed by the additional degrees of freedom of placing cards in nodes and of assigning applications to such cards. In this paper, we provide an optimization algorithm that minimizes the total cost of the entire distributed ICT infrastructure, given a target performance objective defined as the end-to-end delay for the completion of the distributed application tasks. We focus on two sample applications that are well suited for application- and context-aware infrastructures: caching and protocol translation. The joint optimization of computing and communication resources is an innovative contribution of this paper, as, in the literature, hardware and network components are typically optimized separately. Results show that the total infrastructural cost savings are in the range of 15%-20%. However, savings can be obtained only if cards satisfy a cost-performance curve that is also analyzed.     

Organizational Factors Affecting Capacity Planning Practices

Because of the high cost of most major equipment acquisitions, even a small improvement in the computer capacity planning (CCP— process can result in significant cost savings. The survey results presented here assess the effects of computing organization characteristics on various aspects of CCP practices. The results also should help MIS managers and analysts broaden their understanding of how this function can be conducted and what factors significantly affect its practice.     

Organizational Factors Affecting Capacity Planning Practices

Because of the high cost of most major equipment acquisitions, even a small improvement in the computer capacity planning (CCP— process can result in significant cost savings. The survey results presented here assess the effects of computing organization characteristics on various aspects of CCP practices. The results also should help MIS managers and analysts broaden their understanding of how this function can be conducted and what factors significantly affect its practice.     

目标检测中框回归损失函数的研究

在目标检测中,框回归损失函数的设定直接影响预测框的定位准确性。预测框与目标框的交并比（IOU）被设定为优化预测框的损失函数,但是当两框无重叠面积时无法进行梯度回传。广义的交并比（GIOU）在IOU损失函数的基础上增加非重叠面积部分,将两部分优化项作为损失函数调整预测框位置,解决了无法梯度回传的情况。但当两框是包含关系时,GIOU的第二部分优化项消失,损失函数退化为IOU。为了解决以上问题,提出了一种重新定义的广义交并比损失函数（RGIOU）,将非重叠部分面积定义为两框之并减去两框之交,再除以两框形成的最小闭包面积作为第一部分,除以最小闭包面积的平方作为第二部分,利用权重阈值进行加和形成新的损失函数。避免了两框是包含关系时存在的问题,提升了目标检测算法的精度。上述算法在PASCAL VOC 2007以及MS COCO 2014数据集上加以验证。     

Parameter-free optimum design method of stiffeners on thin-walled structures

In this paper, we present a shape optimization method for designing stiffeners on thin-walled or shell structures. Solutions are proposed to deal with a stiffness maximization problem and a volume minimization problem, which are subject to a volume constraint and a compliance constraint, respectively. The boundary shapes of the stiffeners are determined under a condition where the stiffeners are movable in the in-plane direction to the surface. Both problems are formulated as distributed-parameter shape optimization problems, and the shape gradient functions are derived using a material derivative method and an adjoint variable method. The optimal free-boundary shapes of the stiffeners are obtained by applying the derived shape gradient function to the $H^{1}$ gradient method for shells, which is a parameter-free shape optimization method proposed by one of the authors. Several stiffener design examples are presented to validate the proposed method and demonstrate its practical utility.