Block-separable linking constraints in augmented Lagrangian coordination

Augmented Lagrangian coordination (ALC) is a provably convergent coordination method for multidisciplinary design optimization (MDO) that is able to treat both linking variables and linking functions (i.e. system-wide objectives and constraints). Contrary to quasi-separable problems with only linking variables, the presence of linking functions may hinder the parallel solution of subproblems and the use of the efficient alternating directions method of multipliers. We show that this unfortunate situation is not the case for MDO problems with block-separable linking constraints. We derive a centralized formulation of ALC for block-separable constraints, which does allow parallel solution of subproblems. Similarly, we derive a distributed coordination variant for which subproblems cannot be solved in parallel, but that still enables the use of the alternating direction method of multipliers. The approach can also be used for other existing MDO coordination strategies such that they can include block-separable linking constraints.     

A specification language for problem partitioning in decomposition-based design optimization

Decomposition-based design optimization consists of two steps: partitioning of a system design problem into a number of subproblems, and coordination of the design of the decomposed system. Although several generic frameworks for coordination method implementation are available (the second step), generic approaches for specification of the partitioned problem (the first step) are rare. Available specification methods are often based on matrix or graph representations of the entire system. For larger systems these representations become intractable due to the large number of design variables and functions. This article presents a new linguistic approach for specification of partitioned problems in decomposition-based design optimization. With the elements of the proposed specification language, called Ψ (the Greek letter “Psi”), a designer can define subproblems, and assemble these into larger systems in a bottom-up fashion. The assembly process allows the system designer to control the complexity and tractability of the problem partitioning task. To facilitate coupling to generic coordination frameworks, a compiler has been developed for Ψ that generates an interchange file in the INI format. This INI-definition of the partitioned problem can easily be interpreted by programs written in other languages. The flexibility provided by the Ψ language and the automated generation of input files for computational frameworks is demonstrated on a vehicle chassis design problem. The developed tools, including user manuals and examples, are made publicly available.     

Azo disperse dyes for synthetic fibres. I: 2-Methyl- and 2-phenylquinazolone derivatives

Ten variously substituted derivatives ( IVa – j ) of 4′(quinazol-4-on-3-yl) azobenzene were prepared. The effects of the nature and orientation of the substituents on the colour and dyeing properties of these dyes on polyester and acrylic fibres were evaluated.     

Incomplete series expansion for function approximation

We present an incomplete series expansion (ISE) as a basis for function approximation. The ISE is expressed in terms of an approximate Hessian matrix, which may contain second, third, and even higher order “main” or diagonal terms, but which excludes “interaction” or off-diagonal terms. From the ISE, a family of approximation functions may be derived. The approximation functions may be based on an arbitrary number of previously sampled points, and any of the function and gradient values at suitable previously sampled points may be enforced when deriving the approximation functions. When function values only are enforced, the storage requirements are minimal. However, irrespective of the conditions enforced, the approximate Hessian matrix is a sparse diagonal matrix. In addition, the resultant approximations are separable. Hence, the proposed approximation functions are very well-suited for use in gradient-based sequential approximate optimization requiring computationally expensive simulations; a typical example is structural design problems with many design variables and constraints. We derived a wide selection of approximations from the family of ISE approximating functions; these include approximations based on the substitution of reciprocal and exponential intervening variables. A comparison with popular approximating functions previously proposed illustrates the accuracy and flexibility of the new family of approximation functions. In fact, a number of popular approximating functions previously proposed for structural optimization applications derive from our ISE. Based on the similarly named paper presented at the Sixth World Congress on Structural and Multidisciplinary Optimization, Rio de Janeiro, Brazil, May 2005     

Influence of some organic compounds on the corrosion mechanism of carbon steel (XC38) in 3% NaCl II. Orthoaminothiophenol (C6H7NS) and surfactant dodecyl sodium phosphate (C10H21PO4Na2)

This paper presents an investigation of the influence of added organic compounds on the electrochemical behaviour of the carbon steel (XC38) in stirred and aerated 3% NaCl. Steady-state and transient measurements have been made using a rotating disc electrode. The influence of dodecyl sodium phosphate (C₁₀H₂₁PO₄Na₂) and orthoaminothiophenol (C₆H₇NS) have been studied. Results obtained allowed corrosion inhibition mechanism to be established. The nature of the electrode process has been elucidated.     

Decomposition analysis of the multidisciplinary coupling in LED System-in-Package design using a DSM and a specification language

LED System-in-Package (SiP) aims to reduce manufacturing and material costs of LED lighting products through integration of components into one single package, based on semiconductor technology. This introduces multidisciplinary coupling in the system behavior which requires reconsideration of the existing LED design decomposition practice. This paper presents our method to do a decomposition analysis of the multidisciplinary coupling structure for an industry scale LED SiP design problem. The innovative aspect of our method is the use of a specification language to specify the input-output (binary) relationships between design variables, behavioral responses, objective and constraint responses. A design structure matrix, representing the mutual linkage, is automatically generated from the specification. The rows and columns of the DSM are subsequently re-ordered using partitioning and sequencing algorithms to provide insight in the coupling structure. The method is illustrated by means of a simplified example. Subsequently, the results for a recently manufactured LED SiP design prototype are presented.     

Effective process times for multi-server flowlines with finite buffers

An Effective Process Time (EPT) approach is proposed for the building of aggregate models to represent multi-server tandem queues with finite buffers. EPT distributions of the workstations in the flow line are measured without identifying the contributing factors. A sample path equation is used to compute the EPT realizations from arrival and departure events of lots at the respective workstations. If the amount of blocking in the line is high, the goodness of fits of the EPT distribution determines the accuracy of the EPT-based aggregate model. Otherwise, an aggregate model based on just the first two moments of the EPT distributions is sufficient to obtain accurate predictions. The approach is illustrated in an industrial case study using both simulation and analytical queueing approximations as aggregate models.     

Use of Design Sensitivity Information in Response Surface and Kriging Metamodels

Metamodels based on responses from designed (numerical) experiments may form efficient approximations to functions in structural analysis. They can improve the efficiency of Engineering Optimization substantially by uncoupling computationally expensive analysis models and (iterative) optimization procedures. In this paper we focus on two strategies for building metamodels, namely Response Surface Methods (RSM) and kriging. We discuss key-concepts for both approaches, present strategies for model training and indicate ways to enhance these metamodeling approaches by including design sensitivity data. The latter may be advantageous in situations where information on design sensitivities is readily available, as is the case with e.g. Finite Element Models. Furthermore, we illustrate the use of RSM and kriging in a numerical model study and conclude with some remarks on their practical value.