Sélim Datoussaïd

Application of Evolutionary Strategies to Optimal Design of Multibody Systems

This paper is concerned with the application of evolutionary strategiesto the optimization of the kinematic or dynamic behaviour of mechanicalsystems. Although slower than classical deterministic, gradient-basedmethods, they represent an interesting alternative: they are global,they should be more robust as they do not rely on continuity andderivability conditions and they can use the simulation software as is.They are inspired from natural evolution: the design variablescorresponding to the genes of an individual mutate from generation togeneration and the ones who survive are those that are the best fittedto their environment, thats to say with the best objective function.The implementation of evolutionary strategies is presented as well assome guidelines to choose the most important parameters. Two examplesare developed for the sake of illustration: the kinematic optimizationof a suspension and the dynamic optimization of the comfort of a railwayvehicle. Finally, the performances are compared with respect todeterministic methods and genetic algorithms.

Optimization design of multibody systems by using genetic algorithms

Abstract The designing step of multibody systems requires in some specific cases an optimization process, where the design parameters have to be determined by taking into account the expected kinematic or dynamic performances. The aim of this paper is to propose an optimal design method adapted to multibody systems containing closed loops and submitted to kinematic and/or dynamic time-dependent criteria. The optimization process is based on genetic algorithms, using a natural evolution concept leading to stochastic optimization techniques that can often overtop classical optimization methods when applied to real-world problems Illustrative examples are given in the context of the optimization of the kinematics of the suspension of a motorcar and the lateral dynamics of an urban railway vehicle.

Computer-Aided Analysis of Urban Railway Vehicles

SUMMARY Computer-aided dynamic simulations are usually employed when designing modern urban railway vehicles. Even if the modeling procedure is similar to the one used for trains, specific features have to be taken into account for tramways: they are designed for low speeds (less than 80 km/h) and narrow curves (less than 20 m of radius). Moreover, in order to improve accessibility, low floor designs have been developed (the floor lying at about 300 mm above the rails level). The simulation procedure has therefore to take account of the occurence of multiple wheel/rail contacts or the modelization of independent wheels. A specific software well adapted to the computer-aided design of urban railway vehicles has been developed by the Faculte Polytechnique de Mons. It performs the following classical analyses: lateral linearization, modal analysis and root locii plots; vertical linearization and comfort prediction; non-linear time simulation in straight track (limit cycles) and in curve (derailment study) pa...

ACIDYM, a Modular Software for Computer-Aided Learning of Kinematic and Dynamic Analysis of Multibody Systems

Computer-aided kinematic and dynamic analysis of mechanical systems can be performed in several ways, differing from each others in the nature of coordinates used as configuration parameters, in the analytical principles leading to the equations of motion, and finally, in the numerical algorithms for solving the non-linear set of differential/algebraic equations.

Development of a Specific Finite Element for Timber Joint Modeling

Widely used for light frame structures or for heavy laminated wood structures, dowel-type fasteners are the most commonly used kind of connectors in timber construction. The purpose of this work is to develop a tool for the semi-rigid analysis and design of such joints. Firstly, interests and approaches described in literature for the semi-rigid modeling of timber plane frames are summarized. Secondly, for a better understanding of the problem, the main characteristics of wood used as a structural material are presented. Finally, a method for an efficient study of joints built with dowel-type fasteners is proposed and developed. This method consists of the introduction of a specific finite element called “Finite Semi-Rigid Element (FSRE)” between the ends of the jointed members. This joint element consists of two nodes, each with three degrees of freedom. These nodes will be tied with common beamelements during the FE analysis. The stiffness of the FSRE is computed from the geometry of the joints and embedding stiffness of all fasteners, along and perpendicular to the grain. The embedding characteristics of fasteners are defined with help of their experimental load-slip curves (fitted with Foschis models) leading finally to the resolution of a FE non-linear problem.

Safety assessment of a high-rise dormitory in case of fire

Purpose This paper aims to focus on the combination of fire- and agent-based modelling approaches to assess the level of safety of a multi-storeyed building case study. Design/methodology/approach For an existing building to be occupied such as the engineering student dormitory of Mons (Belgium), engineers must establish, among the other things, that the building affords a sufficient level of safety during fire incident. This can be verified in accordance with prescriptive- and performance-based methodologies. The performance-based approach consists on using simulation tools such as fire dynamics simulator with evacuation to ensure/verify the level of safety required. In this paper, a model case study was built and then various scenarios have been implemented to answer some safety questions. Findings For this building layout, the results demonstrate that combining different egress components (i.e. stairs and outdoor ladders) has a negative impact on the evacuation process than using only the stairs to evacuate the building; phased evacuation strategy will not necessarily lead to faster evacuation; adding fire doors in the stairs and between the floors has a beneficial effect on the evacuation process. Originality/value This case study proposes some recommendations about adapted evacuation strategy and investments to improve the safety of high-rise student’s dormitory in case of fire.

Structural Behaviour of the Flying-buttresses of the OL-Cathedral of Tournai (Belgium)

Abstract Nowadays, a great number of heritage buildings are affected by structural defects. This paper presents the particular case of the Our Lady Cathedral of Tournai (World Heritage – UNESCO). According to historians and archeologists, the gothic choir of this building shows signs of weaknesses (problems affecting the flying-buttresses, the buttresses and the very slender pillars) since its erection. Over the centuries, several teams of engineers and architects have studied the problem, trying to understand the behaviour of the structure in order to propose a solution to preserve it. Unfortunately, using contemporary theories and calculations (graphostatic approach and limit analysis) these experts have not succeed in finding a convenient solution and the structural problems still exist today. A few years ago, a team from the Polytechnic Faculty of Mons began to study the building using Finite Element Models. From very simplified models, they began to understand the particular behaviour of the flying-buttresses. Then, by coupling their work with a team of archeologists and historians, they advanced their understanding of the building, making models more complicated and more precise. The analysis is based on “2D1/2” models taking into account the superstructure itself. All the materials involved in the study are assumed to be linear elastic. Some non linearities are introduced with a discrete iterative approach to simulate crack propagation. The results obtained confirm the result of preliminary studies but the observed pathologies are much more understood than with previous simplified models. By using FEM the behaviour of the building can be studied at each step of its life and the mistakes made by the engineers of the past can be better understood. Now, the effective behaviour of the flying-buttresses is better known and an effective solution for the future can be planned.