International Journal of Engineering
Volume:24 Issue: 3, Sep 2011

One of the important issues in the study of steel frames is to find a suitable formulationfor semi-rigid connections. In this paper, the explicit stiffness matrix for a two-dimensional beamcolumn element having end-flexibilities is derived. The effects of the lateral uniformly distributed load on the deflection are considered. Both the tensile and compressive axial loads are also taken into account by one formula. Using the proposed stiffness matrix, some first-order, second-order, buckling, and dynamic analyses for semi-rigid frames are performed. The plastic analysis is also carried out using the plastic hinge approach. Comparing the calculated results with other references shows the accuracy and capabilities of the utilized element. Furthermore, the influences of the semirigid connections on the static and dynamic responses are investigated.

Sensitivity analysis of structures considering their nonlinear behavior has recently beenan important process in optimal design of them based on new design concepts such as Performance- Based Design (PBD). The main objective of this research is to develop an efficient and applicable method for nonlinear sensitivity analysis of Reinforcement Concrete Moment Resisting Frames (RCMRF) considering both axial and flexure effects under seismic loading. For this purpose, sensitivity equations are firstly derived based on pushover method, which is a powerful tool for nonlinear analysis of structures in the PBD context, and then a procedure for nonlinear sensitivity analysis is proposed. The results of the method are compared with nonlinear sensitivity results considering only flexural effect and those of Finite Difference Method (FDM). It is shown that existence of axial forces can affect sensitivity coefficients with respect to the design variables.

The present paper discusses the development of a performance model of power generation system of a thermal plant for performance evaluation using Markov technique and probabilistic approach. The study covers two areas: development of a predictive model and evaluation of performance with the help of developed model. The present system of thermal plant under study consists of four subsystems with three possible states: full working, reduced capacity working and failed. Failure and repair rates for all the subsystems are assumed to be constant. A transition diagram represents the operational behavior of the system. A probabilistic model has been developed, considering some assumptions. Data in feasible range are selected from a survey of thermal plant and the effect of each subsystem on the system availability is tabulated in the form of availability matrix, which provides various erformance/availability levels for different combinations of failure and repair rates of all subsystems. On the basis of this study, performance of power generation system is evaluated.

Mathematical programming and artificial intelligence (AI) methods are known as the mosteffective and applicable procedures to form manufacturing cells in designing a cellular manufacturing system (CMS). In this paper, a bi -objective programming model is presented to consider the cell formation problem that is solved by multi-objective particle swarm optimization (MOPSO) algorithm.The model contains two conflicting objectives, namely optimal labor allocation and maximization of cell utilization. In order to verify its effectiveness of the MOPSO algorithm, the results are compared with those obtained from a well-known evolutionary procedure, called NSGA-II.

In the new competitive environment, selecting and planning of the supply chain is verycrucial and involves evaluation of many factors. Different approaches have been applied to assess the supplier/s. Most of these studies are based upon the supplier/'s capabilities. It may be neither rational nor economical to deal with each item via a generic material control system. Furthermore, supplier/s selection not only depends on supplier/'s capability, but also depends on the nature and characteristics of the parts. Little attention is given to decisions on the appropriate selecting of supplier/s, and assigning order quantities to them, especially, in case of multiple sources considering their performance and material's characteristics. In this paper two models are presented which locate the optimal supplier/s regarding supplier/'s capabilities and material's characteristics for leverage items based on references 1 and 2. The first one is a G.P. model which considers constraints of lead-time, quality, demand, supplier/s capacity and budgets in a dynamic condition. The second one considers the problem in a contingent environment and considers criteria with normal distributions. Each model is followed an illustrative numerical example and sensitivity analysis which demonstrate the effectiveness and validation of the model.

The beneficial effects of shot peening on fatigue life of mechanical components are wellknown. However, there are some reports in the literature that indicate inappropriate shot peening parameters tend to reduce the fatigue life. It is therefore, the purpose of this study to find a logical quantitative justification for these observations. Using finite element method, a dynamic elasticplastic simulation of shot peening was presented. Effect of shot velocity and size on surface morphology after shot peening were examined. Fatigue crack initiation life calculation of shot peened specimens revealed that beneficial effect of shot peening significantly vanishes in the case of high velocities and bigger shots.

In this paper, the nonlinear free and forced axisymmetric vibration of a thin circular platemade of functionally graded material (FGM) with rigid core has been studied. This plate is formulated in terms of von-Karman’s dynamic equation. In this study a semi-analytical approach is developed. For harmonic vibrations, by using assumed-time-mode method and Kantorovich time averaging technique, the governing equations are solved. This problem is solved using MATLAB code. FGM properties vary through the thickness of the plate. FGMs are spatial composites in which material properties vary continuously as well as non-homogeneity. The mass of the core respect to the mass of plate is negligible. For verification, a coreless FGM circular plate has been solved using this code.The results show a good approximation. The results reveal that the vibration amplitude and volume fraction have significant effects on the resultant stresses in large amplitude vibration of the functionally graded plate with rigid core.

The primary function of the suspension system of a vehicle is to isolate the road excitations experienced by the tires and prevent them from being transmitted to the passengers. In this paper, we formulate an optimal vehicle suspension design problem with the quarter-car vehicle dynamic model. A new multi-objective genetic algorithm is used for Pareto optimization of a two-degree of freedom vehicle vibration model considering the two conflicting functions simultaneously. The important conflicting objective functions that have been considered in this work are, namely, sprung massacceleration and relative displacement between sprung mass and tire. Comparison of the results with those reported in literature demonstrates the superiority of the presented method. It is shown that the results of 2-objective optimization provide more non-dominated choices for designers for optimal design of a product to select appropriate choices regarding the condition and purpose of using a vehicle.

This paper deals with the hydrodynamic and thermal analysis of a new type of porousheat exchanger (PHE). This system operates based on energy conversion between gas enthalpy and thermal radiation. The proposed PHE has one high temperature (HT) and two heat recovery (HR1 and HR2) sections. In HT section, the enthalpy of flowing high temperature gas that is converted to thermal radiation to gas enthalpy takes place. In each section, a 2-D rectangular porous segment which is assumed to be absorbing, emitting and scattering is present. For theoretical analysis of the PHE, the gas and solid are considered in non-local thermal equilibrium and separate energy equations are used for the two phases. Besides, in the gas flow simulation, the lattice Boltzmann method (LBM) is applied to obtain the velocity distribution through the porous segments. For the purpose of thermal analysis of the proposed PHE, volume-averaged velocities through the porous matrix obtained by LBM are used in the gas energy equation, and then the coupled energy equations for gas and porous medium of each section are numerically solved using finite difference method. The radiative transfer equation is solved by discrete ordinates method to calculate the distribution of radiative heat flux in the porous medium. The numerical results consist of the gas and porous media temperature distributions. The variation of radiative heat flux are also presented. Furthermore, the effects of scattering albedo, optical thickness and inlet gas temperature on the efficiency of the proposed PHE are investigated. It is revealed that this type of heat exchanger has high efficiency in comparison to conventional one. Also, the present numerical results for a porous radiant burner are compared with theoretical finding by the other investigator and good agreement is found.