Pascal Lafon

A COMPARISON OF EVOLUTIONARY ALGORITHMS FOR MECHANICAL DESIGN COMPONENTS

Two evolutionary algorithms - the genetic algorithm and the evolution strategy - are compared in respect of mechanical design problems. Mechanical design problems are real world problems, characterized by a number of inequality constraints, nonlinear equations, mixed discrete-continuous variables and the presence of interdependent discrete parameters whose values are taken from standardized tables. The selection, recombination and mutation operators, and the chosen constraint-handling method are presented for both the genetic algorithm and the evolution strategy. In order to find the best combination of operators for each algorithm which will solve mechanical design problems, a number of selection and recombination operators are compared in respect of these problems. A comparison of these two algorithms with regard to three mechanical design problems extends the results of comparisons presented in the literature for unimodal and multimodal test functions with continuous variables only, and without constraints.

Optimization of mechanical system: Contribution of constraint satisfaction method

In this paper we are studying the application of techniques to solve constraint satisfaction problems (CSP) for designing mechanical systems. After presenting the CSP method and the several ways to solve it, we introduce an optimization point of view for CSP. Then, we propose a quick overview of CSP application in product engineering. An example in mechanical system optimization is given via the case study of the optimal design of a bolt coupling. The case is modelled as a Constraint Satisfaction Problem on real variables. Finally, numerical results illustrate the resolution process with a CSP approach.

Two decompositions for the bicriteria job-shop scheduling problem with discretely controllable processing times

The job-shop scheduling problem with discretely controllable processing times (JSP-DCPT) is a combination of two kinds of sub-problems: the job-shop scheduling problem and the discrete time-cost tradeoff problem. Neither good approximation algorithms nor efficient exact algorithms exist for the bicriteria JSP-DCPT that is to simultaneously minimise the duration and the cost of performing schedules to the problem. An assignment-first decomposition (AFD) and a sequencing-first decomposition (SFD) are proposed for solving the problem. The main difference between the two decompositions lies in the logical sequence for solving the two kinds of sub-problems. The comparison is carried out by evaluating the size of the searching space with respect to each of the two decompositions, and a general conclusion is deduced that for the JSP-DCPT with at least two machines, at least two jobs, and at least two modes for each operation, the efficiency of the searching-based approaches incorporating SFD is superior to that incorporating AFD. Computational studies on JSP-DCPT instances constructed based on a set of well-known JSP benchmarks illustrate the overall superiority of SFD to AFD regarding multiple measure metrics.

Interoperability between a Cooperative Design Modeler and a CAD System: Software Integration versus Data Exchange

The data exchange between Computer-Aided Design (CAD) systems is a crucial issue in concurrent engineering and collaborative design. The paper presents research works and techniques dealing with the interoperability of a Cooperative Design Modeller (CoDeMo), aiming at the integration of product lifecycle knowledge, and a commercial CAD system (CATIA V5). Two kinds of approaches are implemented in the considered case of CAD interoperability for exchanging geometric data, respectively: one is based on a traditional static interface, in which STEP AP203 standard is used; the other is based on a dynamic interface, in which Application Programming Interfaces (API) of the targeted CAD system is adopted. Both approaches should enhance the communication, exchange and sharing of product data between CAD systems for improving concurrent engineering. A comparison between these two approaches is made to show their particular advantages and disadvantages. The development of a translator between the both CAD systems based on each approach has been carried out and evaluated on an assembly case.

Multi-objective optimization based on meta-models of an aeronautical hub including the ductile damage constraint

In forging process, geometric design of initial billet and tools is very important. Traditionally, engineers use their knowledge and experience to design and optimize the geometric model of forging process by using trial-and-error methods. Such methods are time consuming and cost expensive. It is therefore interesting to design an automatic tools builder based on optimization methodology coupled with virtual finite element simulations, thus helping engineers to improve products and reduce cost. In this article we describe a meta-model based multi-objective optimization methodology for forging process designed to build the theoric Pareto optimal front of the mechanical problem. We go through a four-step process: building parametric computer-aided design geometry model, simulating the forging process according to the DOE, fitting meta-models, and optimizing the process by using an advanced algorithm. Two different meta-models, including polynomial and kriging methods, are constructed, based on the simulation values for different responses. Then optimization algorithms NBI-NLPQLP and NSGA-II are applied to find the optimum solutions based on each different meta-model. In order to drive this procedure automatically we use ModeFRONTIER® software. Using this environment, several macro commands are used to connect the geometry modelling (made with CATIA V5™) and numerical simulation process. As an industrial example, a two-step forging of an aeronautic component shows the efficiency of the proposed methodology. That shows contributions of research in dealing with optimization design of die geometry taking into account technological interactions related to the process and the ductile damage inside the deformed part. A set of solutions selected in particular points of the optimal Pareto front are also presented and analysed.

Beyond geometric CAD system: implementation of STEP translator for multiple-views product modeller

A new kind of Computer-Aided Design (CAD) system is proposed to support the integration and collaboration in Concurrent Engineering (CE). The kernel of the system is the Co-operative Design Modeller (CoDeMo), which supports the multiple-views knowledge integration in the product definition. The enhancement of CoDeMo and CAx systems interoperability is required for achieving a consistent design support environment. This paper mainly deals with CoDeMo interoperability capabilities based on STEP AP203 Edition 2 standard. The aim is to show the benefit and efficiency of STEP-based application in the integration approach of CoDeMo and CAx systems. The architecture, development and application of the STEP pre-processor are described, respectively. A case study is given to illustrate the translation process of product data and to demonstrate the interest of the STEP translator.

Design optimization of floating breakwaters with an interdisciplinary fluid–solid structural problem

The design optimization of floating breakwaters implicates solving an interdisciplinary problem consisting of three models. The first one arises from the interaction of linear waves with a moored floating breakwater with a leeward boundary that is composed of a vertical sidewall representing the quay wall in ports. The second covers the dynamical behaviour of the oscillating structure caused by the incoming waves. These two assemble the hydrodynamic performance of the floating breakwater; while the third concerns its structural mechanics subject to hydrostatic and hydrodynamic forces. The goal of the optimization problem is to design an optimal floating breakwater that can attenuate the waves to the minimum height inside the port and fulfill several constraints related to floating, stability, and structural resistance. The objective function and constraints are expressed in terms of geometrical parameters of the breakwater as mathematical expressions assembled in an optimization algorithm based on the seq...

Parametrical and Motion Analysis of a Moored Rectangular Floating Breakwater

Moored floating breakwaters with a leeward boundary, assimilating the port quay walls are described by a large number of coupled variables. This complicates their design and requires a detailed parametrical and motion analysis to assess their hydrodynamic performance. A diffraction-radiation boundary value problem is developed. It arises from the interaction of linear waves on a moored floating breakwater with a leeward boundary described by a partial reflective sidewall. The effects of the sidewall clearance, structural parameters, mooring lines stiffness, and their angle of inclination on the transmission coefficient and the dynamic motion of the floating breakwater are considered. The transmission coefficient is strongly affected by the motion itself and the allowable length change in the mooring lines.

Optimization of Forging Preforms by Using Pseudo Inverse Approach

A simplified method called “Pseudo Inverse Approach” (PIA) has been developed for axi-symmetrical cold forging modelling. The approach is based on the knowledge of the final part shape. Some intermediate configurations are introduced and corrected by using a free surface method to consider the deformation paths without classical contact treatment. A new direct algorithm of plasticity is developed using the notion of equivalent stress and the tensile curve, which leads to a very fast and robust plastic integration procedure. Numerical tests have shown that the Pseudo Inverse Approach is very fast compared to the incremental approach. In this paper, the PIA will be used in an optimization loop for the preliminary preform design in multi-stage forging processes. The optimization problem is to minimize the effective strain variation in the final part and the maximum forging force during the forging process. The numerical results of the optimization method using the PIA are compared to those using the classical incremental approaches to show the efficiency and limitations of the PIA.

Numerical Modelling of Floating Breakwaters and Shape Optimization Using a Nonlinear Programming Method

In this paper, shape optimization is addressed through sequential quadratic programming (SQP). The recent increase in information technologies dedicated to optimal design, associated with the progress of the numerical tools, allows significant improvement in the design optimization of floating breakwaters. First of all, the physical and mechanical constraints, related to the environment of floating breakwaters, are expressed in terms of the geometrical dimensions of the latter in form of mathematical expressions. Then, the optimization procedure is developed based on SQP method and satisfactory results are obtained demonstrating the capability of this work.Copyright