Scientia Iranica
Year:2014 | Volume:21 | Issue:3 (TRANSACTIONS B: MECHANICAL ENGINEERING)|Papers Count:10

In the following investigation, a submerged-type Wet Soot Absorber (WSA) is studied, and its capability to reduce the soot emission level of a four cylinder, Direct Injection (DI) diesel engine is evaluated. The WSA can provide a large contact area between water and exhaust flow, which increases the soot capturing probability. Hence, the system can be more compact and suitable for vehicle engine applications. The ECE-R49 standard test is followed to assess the effect of the WSA on engine performance and soot emission. The experiments revealed that a soot removal efficiency of 70% is attained under full-load engine operating conditions, due to the high momentum of exhaust gas flow entering the chamber of the unit and providing more flow penetration into the water. Also, further bubble break-up in high gas velocity results in a larger liquid-gas interface and contributes to better soot removal. The minor negative effects of utilizing the WSA on Brake Specific Fuel Consumption (BSFC) are also compared with those of conventional DPFs, and the advantages of WSA are discussed.

A linear analysis of the temporal instability of a viscoelastic liquid jet with axisymmetric and asymmetric disturbances moving in an innite viscous fluid is investigated. The cause of the instability in the liquid jet is Kelvin-Helmholtz instability, due to the velocity difference and capillary instability, due to surface tension. The dispersion relation for viscoelastic potential flow is cubic in nature. The stability analysis shows that viscoelastic liquid jets are less unstable than inviscid jets and more unstable than viscous liquid jets for both axisymmetric and asymmetric disturbances. Stability analysis has been undertaken in terms of various parameters, such as Weber number, Reynolds number, Deborah number etc.

A theoretical solution of the mechanical behavior of thick piezoelectric cylinders subjected to dynamic pressures is presented in this paper. The five governing equations in terms of resultant forces and resultant moments with respect to basic displacement vector components, and are used. The First-order Shear Deformation Theory (FSDT) is employed to consider the effects of shear forces on the shell structure. The effects of transverse shear deformation and rotary inertia are included into the analysis. The formulation is based on the thick-shell equations. Navier-type solutions are obtained and used for simply supported circular cylindrical shells. Finally, the New mark family of methods is used to numerically time integration of the system of coupled second order ODEs. Results obtained with the present analysis are found to be in good agreement with those available in the literature. The results of this paper can serve as a reference for future study in the design of smart engineering structures.

In common catamaran vessels, demihulls are parallel to each other. In this paper, the total resistance of a catamaran vessel with non-parallel demihulls is investigated experimentally and numerically. Experiments are carried out at different Separation Ratios (S.R.), that is the ratio of fore to aft separation of the catamaran demihulls; and also in two ratios of length to separation in amidships (L/Sm). The FLUENT solver, based on the Finite Volume Method (FVM), was used for numerical solution. Applying the VOF model, the free surface around the catamaran vessel and total resistance are calculated and compared with experimental results. Finally, the frictional resistance of the catamaran from the ITTC 1957 correlation line is calculated and compared with CFD frictional resistance. The results show that non-parallel demihulls cause total resistance to increase at Froude numbers below 0.8, and decrease at Froude Numbers over 0.8. In the numerical part, at low Froude numbers, numerical results have an error up to 10% relative to model test results, but error increases at high Froude numbers up to 25%.

In this paper, a damage mechanics approach is used to investigate the effect of crash and damage caused by impact in a steel cylinder filled by Compressed Natural Gas (CNG). The Canadian Standard Association (CSA) for CNG cylinders is used as a damage detection criterion, and the cylinders' capability of reuse. The Johnson-Cook damage model is used to compute cylinder failures. Simulations are carried out in different impact directions, and the effect of cylinder internal pressure, collision velocity and fall height are analyzed. Also, failure due to collisions in various situations is studied and discussed. Investigations for cases including crash and drop tests showed that the maximum damage in a cylinder is created in the case of normal impact and, by changing impact direction from normal to the side, the amount of damage will be decreased. Also, by eliminating failed elements and comparing the damage depth caused by collision using the CSA standard, it was observed that in most cases of normal accidents and drop tests, damaged cylinders lose their ability for reuse. However, in the case of side impact, the cylinder remains intact or can be reused after repair.

In this study, stress distribution in the aneurismal wall of the abdominal aortic is addressed. Full equilibrium equations derived from the thick-wall theory are solved using the well-known Finite Element Method (FEM). Nine-node quadratic rectangular plane elements are employed for the spatial discretization of the computational domain. Nonlinear constitutive equations and non-uniform wall properties are taken into consideration. The results of this investigation show that in addition to the aneurysm size, some other factors may significantly affect stress distribution in aneurismal wall. Factors such as wall thickness, blood pressure and longitudinal tension have been identified for both uniform and non-uniform wall properties. Having numerically simulated different cases, it is demonstrated that longitudinal stress is the maximum stress in the wall, and it is not significantly affected by the uniformity of wall stiffness.

This paper is concerned with the problem of delay-dependent passive analysis and control for interval stochastic time-delay systems. The system matrices are assumed to be uncertain within given intervals, the time delay is a time-varying continuous function belonging to a given range, and the stochastic perturbation is in the form of a Brownian motion. By using ItO's differential formula and the Lyapunov stability theory, delay-dependent stochastic passive control criteria are proposed without ignoring any useful terms by considering the information of the lower bound and upper bound for the time delay. Based on the criteria obtained, a delay-dependent passive controller that ensures the stochastic passivity of the closed-loop system is presented. Then, the controller gain is characterized in terms of LMIs, which can be easily checked by resorting to available software packages. Numerical examples are given to demonstrate the effectiveness of the method.

This study investigates the dynamic response of an electrostatically defected capacitive cantilever Functionally Graded (FG) micro-beam subjected to a harmonically varying thermal load, which incites vibration due to the different material properties of the beam constituents and the thermo-elastic coupling effect. The FG beam is made of a mixture of metal and ceramic, where the material properties vary continuously through the thickness according to an exponential distribution law (E-FGM). Assuming the Euler- Bernoulli beam theory and the infinite speed of heat transportation, the equation of motion and the conventional coupled energy equation are derived. Applying Galerkin formulation and then using the Rung-kutta method as an efficient numerical tool, these equations are simultaneously solved. Changing the ceramic constituent percentage of the bottom surface, five different types of FGM micro-beams are investigated and the results are presented for all types. Numerical results show the response of a cantilever FG microbeam subjected to a harmonically varying temperature input. Moreover, the influences of the beam ceramic constituent percentage on stability, vibrational behavior and natural frequency are presented.

This paper presents a Graphical User Interface (GUI) and simulator, which is designed for a cable suspended robot (ICaSbot), in Lab VIEW environment. This interface is designed to be used for training users in a virtual environment and also controlling the cable robot in an on-line manner. The proposed GUI consists of kinematics, dynamics and on-line control sections. All the mentioned sections are involved in the simulator of the robot employed to display the motion of the end-effector in a virtual environment. Using the proposed GUI, the user is able to exert the desired commands and study the end-effector motion and all of its kinematics and kinetics output in a virtual environment. Afterward, this motion can be applied to the real robot in the part called "hardware control", while six different control methodologies can be selected. The controlling commands, such as driving the motors and monitoring the actual data received from the sensors, can be managed in this part of the GUI. The efficiency and applicability of the designed GUI are proved by conducting some ISO and experimental tests on the cable robot of IUST, called ICaSbot, and comparing the results with simulation, including repeatability and accuracy tests and tracking a predefined trajectory.

The effects of heat and mass transfer on two-dimensional magnetohydro-dynamic (MHD) flow of Maxwell fluid over a stretching surface are discussed. The stretching surface satisfies the convective boundary conditions. In addition, the analysis has been carried out in the presence of Joule heating, thermal radiation and thermophoresis. Governing partial differential equations are first reduced into ordinary differential equations and then computed for series solutions. Numerical values of local Nusselt and Sherwood numbers are presented and examined.