Essam A. Al-Bahkali

Nonlinear Steady State Solution for a Thermoelastic Sliding System Using Finite Element Method

ABSTRACT A two-dimensional finite element model is developed for determining the non-linear steady-state configuration of a two-dimensional thermoelastic system involving sliding in the plane with frictional heat generation. Above a certain critical speed, this causes the uniform pressure solution to be unstable and the final steady-state configuration involves regions of separation at the interface and associated temperature and displacement fields that migrate over the contacting bodies in the direction of sliding. A major challenge in the development of a suitable algorithm is to determine this migration speed by iteration to be able to use a reference frame in which the fields are stationary. The results of the algorithm were validated by comparison with the long-time behaviour of a previously published (but very time consuming) transient simulation algorithm.

On the vibration and control of a flexible rotor mounted on fluid film bearings

Abstract In this paper, an active vibration controller for controlling the dynamics of a flexible rotor running in flexibly-mounted journal bearings is addressed. The control effort consists of two components. The first is a state feedback controller designed to stabilize the system and to achieve desirable transient response. The second is a feed-forward controller, based on the state of the excitation model, designed to counteract the effect of the external excitations on the system. The results have shown that a significant improvement in the system response is achieved by a stationary compensation of the selected set of excitation frequencies.

Multiobjective Optimization of Turning Cutting Parameters for J-Steel Material

This paper presents a multiobjective optimization study of cutting parameters in turning operation for a heat-treated alloy steel material (J-Steel) with Vickers hardness in the range of HV 365–395 using uncoated, unlubricated Tungsten-Carbide tools. The primary aim is to identify proper settings of the cutting parameters (cutting speed, feed rate, and depth of cut) that lead to reasonable compromises between good surface quality and high material removal rate. Thorough exploration of the range of cutting parameters was conducted via a five-level full-factorial experimental matrix of samples and the Pareto trade-off frontier is identified. The trade-off among the objectives was observed to have a “knee” shape, in which certain settings for the cutting parameters can achieve both good surface quality and high material removal rate within certain limits. However, improving one of the objectives beyond these limits can only happen at the expense of a large compromise in the other objective. An alternative approach for identifying the trade-off frontier was also tested via multiobjective implementation of the Efficient Global Optimization (m-EGO) algorithm. The m-EGO algorithm was successful in identifying two points within the good range of the trade-off frontier with 36% fewer experimental samples.

Fatigue life estimate of landing Gear's leg using modal analysis

The present work concerns solving Noise, Vibration and Harshness (NVH) and fatigue based on Power Spectrum Density (PSD) analysis of a landing gears leg for an Un-Manned Aerial Vehicle (UAV). This analysis includes random vibration and high-cycle fatigue analysis in a random vibration environment. In this analysis, the cumulative damage ratio is computed using material S-N (Stress-Number of cycles) fatigue curve. Dirlik method is used for the analysis of lifetime as it is proven to provide accurate results for large number of applications, both in automotive and aerospace industry. It is also compared to other methods that have been developed in LS-DYNA® as well. The input acceleration PSD data are provided through measurements. The obtained analysis results shows that although the landing gear design is safe according to dynamic and static load, its service life is about 3037 hours due to random vibration effect.

Deployment of a Neo-Hookean membrane: experimental and numerical analysis

The aim of this research is to assess the response of a thin membrane subjected to high-pressure gas loading for inflation. This procedure is applied during the design process of the membrane structure to allow the product to resist high-pressure loading and to further characterize the hyper-elastic material. The simulation in this work considers the standard procedures used in the LS-DYNA software, which applies such assumptions as a uniform airbag pressure and temperature in addition to a more recently developed procedure that takes into account the fluid-structure interaction between the inflation gas source and the hyper-elastic membrane; this approach is referred to as the Arbitrary Lagrangian Eulerian (ALE) formulation. Until recently, to simulate the inflation of the hyperelastic membrane, a uniform pressure based on a thermodynamic model or experimental test has been applied to the structure as the boundary conditions. To conserve CPU time, this work combines both methods; the fluid structure coupling method is used at an earlier stage in which the fluid is modeled using full hydrodynamic equations, and at the later stage, the uniform pressure procedure is applied, and the fluid mesh and analysis are removed from the computation. Both simulations were compared to test data, indicating satisfactory correlation with the more recently developed procedure, the ALE theory, which showed the greatest accuracy both in terms of graphical and schematic comparison, particularly in the early stages of the inflation process. As a result, the new simulation procedure model can be applied to research on the effects of design changes in the new membrane.

Lagrangian and ALE Formulations For Soil Structure Coupling with Explosive Detonation

Simulation of Soil-Structure Interaction becomes more and more the focus of computational engineering in civil and mechanical engineering, where FEM (Finite element Methods) for structural and soil mechanics and Finite Volume for CFD are dominant. New formulations have been developed for FSI applications using ALE (Arbitrary Lagrangian Eulerian) and mesh free methods as SPH method, (Smooth Particle Hydrodynamic). In defence industry, engineers have been developing protection systems for many years to reduce the vulnerability of light armoured vehicles (LAV) against mine blast using classical Lagrangian FEM methods. To improve simulations and assist in the development of these protections, experimental tests, and new numerical techniques are performed. To carry out these numerical calculations, initial conditions such as the loading prescribed by a mine on a structure need to be simulated adequately. The effects of blast on structures depend often on how these initial conditions are estimated and applied. In this report, two methods were used to simulate a mine blast: the classical Lagrangian and the ALE formulations. The comparative study was done for a simple and a more complex target. Particle methods as SPH method can also be used for soil structure interaction.

Numerical investigation of vibration and dynamic pressure of a vertical axis wind turbine

In the environmental field, the problems of noise reduction have become a major preoccupation, particularly on the noise generated by the acoustic radiation pressure produced by wind turbines. This paper is aimed at presenting the investigation on the application of variational indirect boundary element method for study the acoustic radiation pressure produced by vertical-axis wind turbine. For this initiative, we considered Neumann boundary condition. The formulation has two advantages: the first one is to avoid the meshing of the fluid domain; the second advantage is to treat the singular integral of the Greens function, solution of fundamental solution of the wave equation in frequency domain.

The effect of adhesive thickness on spot weld-bonded joints of dissimilar materials using finite element model

In present work, the bonded and spot weld-bonded of dissimilar materials joints for three dimensional models using the finite element technique were studied for different adhesive thicknesses. The results show that the stresses in adhesive bonded joints are concentrated at the ends of the overlapped area. When the spot-welding is combined with the adhesive bonding, the stresses are concentrated at the adhesive bond ends and at both ends of the weld nugget. The results show also that the stresses are more concentrated towards the material of the lowest melting point. Changing the thickness of the adhesive layer for various dissimilar material models give us the optimal thickness for each case that one can use in designing lap joints of two dissimilar materials. The results in general show that the thinner the adhesive is, the higher is the peak stresses developed in the weld-bonded joint.