Iranian Journal of Science and Technology Transactions of Mechanical Engineering
Volume:38 Issue: 2, 2014

This article deals with a simple Cartesian practical method named blocked-off procedure to study the steady state combined conductive-radiative heat transfer in two dimensional irregular geometries. Using this technique, both straight and curvilinear boundaries can be treated. The finite-volume method is employed to solve the energy equation and the discrete ordinates method (DOM) is used to solve the radiative transfer equation (RTE) to obtain the temperature and radiative-conductive heat flux distributions inside the participating medium. The walls of enclosures are opaque, diffuse and gray with specified temperatures. The medium was considered to be absorbing-emitting and isotropic scattering with variable thermal conductivity. In the case of constant thermal conductivity, results have been compared with those reported in the literature. The major part of this work is to investigate the effects of variable thermal conductivity on the thermal characteristics of radiative-conductive systems.

In this research, the application of response surface methodology (RSM) was highlighted to investigate the effects of biodiesel (from waste cooking oil) in fuel mixture (biodiesel and diesel fuel No.2) and engine operating parameters on performance characteristics (brake power, brake torque and BSFC) of a diesel engine. The experiments were conducted on a four cylinder direct-injection diesel engine based on three-factor five-level central composite rotatable design. The developed mathematical models were helpful to predict the response parameters, and further, to identify the significant interactions between the input factors on the responses. Results showed that the use of biodiesel reduces brake power and brake torque up to 18% and 17% respectively. On the other hand, BSFC increases 18 to 24% by using net biodiesel. Also, results showed that an increase in engine load appeared to cause an increase in the brake power and torque up to 68 and 69% respectively. On the other hand, BSFC is higher at low engine load and increases up to 15% by reducing the engine load.

In this paper, thermal effects in nonlinear buckling analysis of micro beams is investigated. Modified strain gradient theory with nonlinear von-Karman strain displacement relations and small scale parameters are used to derive the buckling behavior of micro beams. The Poisson’s effect is included and its significance is demonstrated. Buckling behavior for two different cases: 1) immovable axial boundary condition 2) movable axial boundary condition, are studied and for each one the results for hinged-hinged and clamped-clamped beams are presented. The analysis shows that modified strain gradient theory leads to a higher critical buckling load in comparison with the classical and couple- stress theories. The results are verified using previous related works.

This article deals with the study of generalized solution for the vibration of functionally graded (FG) microbeam in the context of the dual phase lag model. Numerical results are presented for the FG beam subjected to a ramp-type heating and has exponentially varying material properties through the thickness. The effect of the ramping time parameter is studied on the lateral vibration, temperature, displacement, stress, the moment and the strain energy of the FG microbeam. The influence of the thickness of the beam is also analyzed. A comparison of the results for different theories is presented. The results obtained theoretically have been computed numerically and are presented graphically. Some particular cases are also discussed in the context of the problem.

In this article, mechatronic control of a shell vibration containing fluid (partially filled with a fluid) has been addressed. Simple actuators are utilized to achieve boundary stabilization. These actuators apply linear boundary feedbacks consisting of forces and moments from the boundaries of the shell to dissipate the vibrations. In this research, the fluid has free surface and without attaching any sensors or actuators in the fluid domain, the vibration suppression is obtained. This research utilizes semigroup approach and LaSalle invariant set theorem to prove the boundary stabilization.

Micro and nano-fluidic mixing nowadays is a very important area in research due to its crucial role in new technologies and applications such as biomedical and biochemical synthesis. Due to the low velocities associated with microscale flow, it is often very difficult to mix fluids in a rapid and homogeneous manner. One of the methods of enhancing fluid mixing is to obstruct the fluid flow using vanes or panels known as baffles. In this paper, a Computational Fluid Dynamics (CFD) approach is used to study the effect of baffles on the mixing performance in a passive micromixer. The numerical method is verified by comparing its obtained results with experiments and numerical results published earlier. Rectangular, semi-circular and triangular baffles have been considered for investigating the effects of baffle geometry on mixing performance. Furthermore, the effects of channel inlet angle and baffles offset in mixing performance are studied. As the results show, there is a two-fold increase in mixing performance in the baffled cases as opposed to the simple case.

Hydrodynamic focusing is one of the most utilized techniques in microfluidics. Its applications have been employed in a wide variety of biological analyses including on-chip flow cytometry, single molecule detection, and laminar mixers. In the present study, a new hydrodynamic focusing microdevice for flow cytometry applications is presented and numerically investigated. In the proposed microdevice, the sample fluid is compressed both in vertical and horizontal directions simultaneously by radial sheath flows injected within flow cytometer through one ring. The microdevice configuration is optimized and effective parameters on stream distribution are investigated. In addition, in order to observe hydrodynamic focusing phenomena, particles trajectories are studied. Moreover, results of the proposed model are compared with the previous one in order to verify that the performance of the present model is more efficient.

The contact force model is one of the important issues in dynamics analysis of mechanical systems with joint clearance. The main objective of this work is to present a computational study on the effects of the contact force models on dynamics characteristics of mechanical system with revolute clearance joints. The intra-joint contact forces that are generated at clearance joints are computed by considering several different elastic and dissipative approaches. A simple review of the constitutive laws utilized in this work is presented and analyzed. Finally, a well-known slider-crank mechanism with a revolute clearance joint is utilized to perform the investigation. The investigation results show that the dynamics characteristics of mechanical system with clearance are obviously shaking and the amplitude increases from the mechanism without clearance. The contact force model of the clearance joint has an important effect on the dynamics responses of mechanical system and the selection of appropriate contact force model of clearance joints plays a significant role in dynamics analysis of multibody mechanical system with revolute clearance joint.

Different from the traditional rigid robots made by hard material such as metal, continuum robots are bionic mechanisms which feature high compliance and continuous shapechanging ability. A full compliant continuum robotic finger is proposed, which is driven by the compressed air inside its silicon rubber chamber and has a certain degree of grasping rigidity. By the moment equilibrium analysis, the mathematical model for the inside compressed air pressure and the bending angle of the finger is established. The kinematic Cartesian coordinates for the proposed continuum robotic finger are constructed based on the D-H method. Then the kinematic model is derived. Simulation and experimental results showed that the proposed full compliant continuum robotic finger has abilities of continuous compliant shape-changing and movement, and the established kinematic model can describe the finger’s movement process and its characteristics.

In the present study, some modifications on the firefly algorithm are presented to improve its performance. The firefly algorithm is a recently developed robust metaheuristic optimization technique which mimics the social behavior of fireflies based on their flashing characteristics. To improve its performance three basic modifications are proposed in the present work. These modifications consist of adding memory, adding newborn fireflies and proposing a new updating formula. To evaluate the applicability of the proposed method, three classical engineering design optimization problems and three sizing optimization of truss structures are solved and results are compared with those available in the literature. It is observed that the proposed method can effectively be used in solution of engineering design optimization problems.

Due to galling with other materials, Ti and its alloys call for solid lubricants during forming. Deforming Ti sheet becomes even more difficult when the forming process involves very low contact area, such as in the novel process single point incremental forming (SPIF). Retaining lubricant at the tool/sheet interface while performing local deformation, as in SPIF, has always been a challenge. One way to satisfy this challenge is to develop a porous surface coating on the sheet and fill its pores with lubricant particles. For SPIF, an electro-chemical deposition process called micro-arc oxidation (MAO) has shown promise to fabricate coatings of desired pore size and thickness to fulfill the said objective. In the present work, the characterization of an MAO coating has been carried out to clarify its role during the incremental forming of pure Ti sheet. The results regarding hardness, bond strength, XRD microstructure and friction co-efficient of the coating under various lubrication conditions are reported.

Welding is one of the usual assembling methods with various applications. The different defects are generated during welding and also in service conditions. After inspection and identifying the defects, the repairs are applied. Welding repair operation causes the mechanical properties and the microstructures of weldment to change. In the present work the variations of yield stress, hardness and microstructures in the A 36 repair butt specimens were investigated by the experimental study. The welding technique was Tungsten Insert Gas method without using filler. The specimens were cut from the welded plates using water jet method for avoiding heat effect during the cutting. The low-carbon steel A 36 thin plate was used to construct the specimens. This material has numerous applications to construct various structures and parts. The specifications of specimens and tests were selected according to the standards. The tensile tests were performed for four numbers of each specimen. The mean of yield stresses in the specimens were reduced after the repairing through half- thickness of the butt welds. Moreover, the mean of yield stresses in the specimens after repairing would be decreased if the welding voltage and current increased. Reduction of the hardness in heat affected zone and variation of the phases and grain size after repairing were other outcomes from testing on the specimens.

The present research investigates improvement of Eddy Current (EC) technique as a nondestructive method for measurement of ductile cast iron microstructural and mechanical characteristics. Six samples of heat treated ductile cast iron have been selected to study the relations between pearlite content and EC outputs. These outputs include voltage and normalized impedance as well as calculated parameters of harmonic analysis. Furthermore, correlation between mechanical properties such as hardness, yield strength and ultimate tensile strength in samples containing different ferrite-pearlite matrices and the magnetic responses has also been found. High correlation coefficients of the relations indicate an acceptable level of accuracy in comparison with destructive method.