Luís Sousa

OPTIMAL DESIGN OF NONLINEAR STRUCTURES AND MECHANICAL SYSTEMS

This paper presents an optimal structural design system based on a variational theory of design sensitivity analysis for linear and nonlinear structures and mechanical systems. So called flexible systems and structures, as well as design and control variables, are treated within a unified frame. The concept of an auxiliary system, the principle of virtual work, and a Lagrangean-Eulerian description of the deformations and design variations, are used to develop the unified viewpoint. Finite element and finite difference methods are used for spatial and time discretization of the sensitivity equations. The isoparametric concept of the finite element formulation is related to the concept of control volume. The concept of a design element is used for the design modeling of the structure and to generate the analysis model from the design model. Structural analysis and optimization codes are combined to create an optimal design capability. Optimalily criteria methods and nonlinear programming are applied as opt...

Optimal design of elastic-plastic structures with post-critical behaviour

This work deals with the optimal design of nonlinear structures where both geometric and path-dependent material nonlinearities are considered. Postcritical behaviour is allowed. Critical and postcritical constraints are considered. Constraints on local and global stability have been introduced. The classical critical load constraint against global instability is given with numerical advantage by a new method using a displacement constraint. The total Lagrangian description and a continuum variational formulation are used for the response and design sensitivity analysis. A continuation algorithm is used to implement the postcritical path. The path-dependent sensitivity problem is addressed by an incremental strategy. A direct differentiation approach is used to derive the response sensitivities with respect to both cross-section and configuration design. A finite element technique models the structure. A mathematical programming approach is used for the optimization process. Numerical examples are performed on three-dimensional truss structures.

Optimal cross-section and configuration design of elastic-plastic structures subject to dynamic cyclic loading

This paper shows an optimal design problem with continuum variational formulation, applied to nonlinear elasticplastic structures subject to dynamic loading. The total Lagrangian procedure is used to describe the response of the structure. The direct differentiation method is used to obtain the sensitivities of the structural response that are needed to solve the optimization problem. Since unloading and reloading of the structure are allowed, the structural response is path-dependent and an additional step is needed to integrate the constitutive equations. It can be shown, consequently, that design sensitivity analysis is also path-dependent. A finite element method with implicit time integration is used to discretize the state and sensitivity equations.A mathematical programming approach is used for the optimization process. Numerical applications are performed on a 3-D truss structure, where cross-sectional areas and nodal point coordinates are treated as design variables. Optimal designs have been obtained and compared by using two different strategies: a twolevel strategy where the levels are defined according to the type of design variables, cross sectional areas or node coordinates, and optimizing simultaneously with respect to both types of design variables. Comparisons have also been made between optimal designs obtained by considering or not considering the inertial term of the structural equilibrium.

A New Concept for a Wheel-Embedded Assembly for Electric Vehicles

The present research focuses on the development of a multifunctional wheel-embedded assembly for electrically powered vehicles. It must perform the core functions of a road-going vehicle—propulsion, braking, steering, and suspension—with all functional mechanical elements within the wheel envelope. The originality of the research lies in the integration of all aforementioned functions at once. The proposed concept exhibits two off-center electric motors, sliding pillar-type suspension with direct-drive steering at the top, and braking is achieved by means of a conventional disk and caliper assembly, but servohydraulically actuated with magnetically actuated parking brake. It makes extensive use of geometric nesting and function sharing—the large transmission gear doubles as hub and wheel carrier, the suspension pillar is also used for steering torque transmission. Finally, the advantages and disadvantages of the proposed concept are addressed, as well as practical applications.

Development of Validated Generic Road Vehicles for Crashworthiness Through Optimization Procedures

The development of passive safety devices for vehicles or setup of virtual tests requires that detailed numerical models are available. Generally, the vehicle manufacturers are unable to release the detailed data for their models due to commercial and legal restrictions. Since finite element models for road vehicles suitable for crashworthiness analysis are very detailed, their complexity involve computations that require long time to perform analysis involving large deformations with plasticity and contact. With the actual computer technology the computational time for these models is measured in terms of days. However, during the design of a new vehicle, the redesign of a component or of a particular safety device, many simulations must be performed to appraise different design solutions. An alternative approach to the use of detailed FEM models is important to reduce calculations time. Multibody models of road vehicles are shown here to be suited for early design phases of such vehicles, components or devices, being the computational time required for any specific crash analysis being measured in same number of minutes than the hours required for FEM models. This work presents a methodology for modeling generic road vehicle models for multibody dynamic analysis that have all the characteristics of a real cars, have crash responses for front and side impact similar to the top of line vehicle of its class for the Euro NCAP test but still are not the exact model of any existing vehicle. The multibody modeling work is based on a previously existing finite elements model of the vehicle. First a strategy to convert the finite element to a multibody system model is presented so that the structural features of the MB model are correlated with those of the complex of the FEM model. The responses of the two models are correlated through selected responses extracted from results of impact simulations regarding occupant safety and energy absorption. The crash scenarios used, according to standards for crash tests, are the same for finite element and multibody models. Selected responses, obtained from the results of the simulations in representative points of the car and the barrier, are used to compare the performance of the models in terms of displacements, velocities and accelerations. The plastic hinge characteristics of the multibody model are redefined, using an optimization procedure to ensure that the selected responses of the multibody and finite element models are similar, thus leading to validated multibody models.