Peyman Khosravi

Vibration control of Timoshenko beam traversed by moving vehicle using optimized tuned mass damper

The dynamic behavior of a combined bridge–vehicle system in which the bridge is modeled as a Timoshenko beam and the vehicle as a half-car planar model is investigated using the finite element method. The governing equations of motion of the Timoshenko beam with the attached tuned mass damper (TMD) traversed by a moving vehicle are obtained. Adesign optimization algorithm is developed in which the analysis module based on the derived finite element formulation has been combined with the optimization module using the sequential programming technique. The objective is to determine the optimum values of the parameters (frequency and damping ratios) of a TMD, in order to minimize the maximum frequency response of the beam midspan when traversed by a moving vehicle. Results obtained illustrate that by attaching an optimally TMD to the Timoshenko beam a significantly faster vibration control can be achieved.

Local Buckling and Mode Switching in the Optimum Design of Stiffened Panels

Local buckling can significantly affect the strength of stiffened panels. Most studies on the optimization of stiffened panels consider only one or two forms of buckling (buckling modes), because considering all possible mode shapes in nonlinear analysis of stiffened panels, particularly during the iterative process of optimization, is a complex and time-consuming task. This study presents an approach for optimization of stiffened panels considering geometric nonlinearity and local buckling. A method is presented to efficiently incorporate the effects of local buckling and mode switching during the optimization process.

Optimization of Geometrically Nonlinear Thin Shells Subject to Displacement and Stability Constraints

A methodology is developed for shape optimization of thin plate and shell structures undergoing large deflections subject to displacement and system stability constraints. The optimization method considers shape parameters and overall thickness of the structure as the design variables and aims to minimize the total mass of the structure subject to stability or displacement constraint Two optimality criteria based on Karush-Kuhn-Tucker conditions are developed for mass minimization problems. Optimality criteria are combined with nonlinear corotational analysis to optimize structures with geometric nonlinearity. The method is applied to plate and shallow shell structures. The efficiency of the developed design optimization methodology is compared with that of the gradient-based method of optimization (sequential quadratic programming).

Finite element analysis of a Timoshenko beam traversed by a moving vehicle

Abstract In this study the finite element formulation for the dynamics of a bridge traversed by moving vehicles is presented. The vehicle including the driver and the passenger is modelled as a half-car planner model with six degree of freedom, travelling on the bridge with constant velocity. The bridge is modelled as a uniform beam with simply supported end conditions that obeys the Timoshenko beam theory. The governing equations of motion are derived using the extended Hamilton principle and then transformed into the finite element format by using the weak-form formulation. The Newmark-β method is utilized to solve the governing equations and the results are compared with those reported in the literature. Furthermore, the maximum values of deflection for the Timoshenko and Euler—Bernoulli beams have been compared. The results illustrated that as the velocity of the vehicle increases, the difference between the maximum beam deflections in the two beam models becomes more significant.

Finite Element Approach for Vehicle-Structure Interaction of a Uniform Timoshenko Bridge

In this study the finite element formulation for the dynamics of a bridge traversed by moving vehicles is presented. The vehicle including the driver and the passenger is modeled as a half-car-planner model with six degrees of freedom, traveling on the bridge with constant velocity. The bridge is a uniform with simply supported end conditions, and it obeys the Timoshenko beam theory. The equations of motion are derived using the extended Hamilton’s principle, and transformed to the finite element form using the weak-form formulation. Newmark’s method is applied to solve the governing equations and the results are compared with those available in the literature. Also, the maximum deflections in Timoshenko and Euler-Bernoulli beams have been compared. The results illustrated that as the velocity of the vehicle increases, the difference between the maximum beam deflection in two beam models becomes more significant.

Non-Linear Analysis of Composite Plates and Shells Using a New Shell Element

One of the most popular approaches in the finite element analysis of plates and shells is using an assemblage of facet triangular elements built by combining a membrane and a plate bending element to model the curved surface. Due to the lack of a drilling degree of freedom in most triangular membrane elements, these elements may cause rotational singularity in the stiffness matrix. One approach to overcome this problem is using membrane elements with in-plane (or drilling) rotational degree of freedom. Although some elements with drilling degree of freedom have been derived, most of them suffer from aspect ratio locking. Recently, Felippa [1] developed an optimal membrane element with drilling degree of freedom. Its response for in-plane pure bending is not dependent on the aspect ratio. There are several triangular plate bending elements to combine with a membrane element. Batoz et al. [2] studied several triangular Kirchhoff plate bending elements and showed that Discrete Kirchhoff Triangle (DKT) [3], is the most reliable triangular element for analysis of thin plates. Katili [4] developed a discrete Kirchhoff-Mindlin triangular plate bending element called DKMT which is capable to include the transverse shear effects in thick plates, and coincides with the DKT element in case of thin plates. As a result, both thin and thick plates can be modeled with this element.

Limit Load Analysis of Thin Geometrically Nonlinear Structures Using a New Shell Element

In this study, limit load analysis of thin geometrically nonlinear structures is performed using a new shell element. The element is developed by combining the discrete kirchhofi triangle (DKT) plate bending element, and the optimal membrane triangle (OPT). Inconsistent stress stifiness matrix is formulated using appropriate approximations for displacements. Using co-rotational approach combined with arc-length method, nonlinear analysis is performed and the limit load is found for shallow thin shells. The results are compared with those found by other membrane elements combined with the same plate bending element. It is shown that analysis using other membrane elements may overestimate the stifiness and consequently the limit load of the structure signiflcantly.