Scientia Iranica
Volume:20 Issue: 6, 2013

This paper presents an integrated vehicle dynamics control which managesto coordinatesteering and braking subsystems using optimal distribution of tire forces (ODF). Specifically,we introduce an ODF scheme which treats thestandard stability conditions of the phase-plane as inequality constraints in the optimization problem. The established scheme works to fulfill the objectives of a higher-level controller as much as possible without violating vehicle dynamics stability conditions. A sliding mode enhanced adaptive high-level control assesses the desired total yaw moment and lateral force for the vehicle control. The proposed controller only requires the online adaptation of control gains without acquiring the knowledge of upper bounds on system uncertainties. An optimization problem incorporating six inequality constraints is solved analytically by Karush-Kuhn-Tucker (KKT) conditions. To coordinate braking and steering subsystems, a phase-plane based adaptation mechanism is suggestedto adjust the weighting coefficients in the considered cost function. The simulation cases show that the vehicle stability can be improved effectively by the suggested scheme

Environmentally benign natural refrigerants have recently attracted a considerable attention due to refrigerant contributions to ozone depletion and global warming.In the groupof natural refrigerants, hydrocarbons are most closely related to the HFCs. In addition to their zero ODP and very low GWP, they are compatible with common materials found in refrigerating systems. Therefore, in this study, the performance simulation of R290 and R600a mixtures (80/20, 70/30, 60/40 and 50/50 proportion by mass, designated by RM1, RM2, RM3 and RM4, respectively) in vapour compression refrigeration system is conducted by thermodynamic calculation of performance parameters using REFPROP software. The results showed that the mixtures exhibited higher refrigerating effect than R134a. The average pressure ratio obtained for RM1, RM2, RM3 and RM4 were 19.5, 16.5, 14.0 and 11.8% lower than that of R134a, respectively. All the mixtures, except RM1, exhibited low discharge pressure which is more desirable in refrigeration systems. The COPs of the mixtures were close to that of R134a with advantage of higher values. Generally, the overall performance of the selected mixtures was better than that of R134a. The performance of RM4 was the best in terms of low compressor work and discharge pressure, and high COP at varying evaporating temperature.

In this study, a numerical model has been developed in AVL FIRE software to perform investigation of direct natural gas injection into the cylinder of spark ignition internal combustion engines. Two main parts have been taken into consideration, aiming to convert an MPFI gasoline engine to direct injection NG engine. In the first part multi-dimensional numerical simulation of transient injection process, mixing and flow field have been performed via different validation cases in order to assure the numerical model validity of results. In all cases, present results were found to have excellent agreement with experimental and numerical results from literature. In the second part the validated model has been applied to methane Injection into the cylinder of a direct injection engine. Five different piston head shapes have been taken into consideration and a centrally mounted inwardly-opening single-hole injector has been adapted to all cases. The effects of injection and combustion chamber geometry have been studied on mixing of air-fuel inside cylinder via quantitative and qualitative representation of results. Furthermore the effect of real engine cylinder head shape on the gas injection has been investigated. Based on the results, suitable geometrical configuration for a NG DI engine has been discussed.

Kinematic control of a special hyper-redundant manipulator with lockable joints is studied. In this manipulator, the extra cables are replaced by a locking system to reduce the weight of the structure and the number of actuators. This manipulator has discrete and continuous variables due to its locking system. Therefore, a hybrid approach has been adopted in control. At first the forward kinematics and velocity kinematics of this manipulator is derived, and then a novel closed-loop control algorithm is presented. This algorithm consists of decision making, inner loop controller, andkinematic calculation blocks. The decision making block is the logical part of the control scheme in which suitable switches will be chosen. The control block usestheend-effector position feedback to generate appropriate commands. The performance of the proposed hybrid control scheme in position tracking is assessed for several trajectories.

In this article, the effects of volute cross section shape and centroid profile of a radial flow compressor volute were investigated. The performance characteristics of a turbocharger compressor were obtained experimentally by measuring rotor speed and flow parameters at the inlet and outlet of the compressor. The three-dimensional flow field model of the compressor was obtained numerically solving Navier-Stokes equations with SST turbulence model. The compressor characteristic curves were plotted. For model verification, the results were compared with experimental data, showing good agreement.Modification of a volute was performed by introducing a shape factor for volute cross section geometry. By varying this parameter, new external volutes were generated and modeled while the original volute was intermediate volute. The effect of volute cross section shape on compressor pressure ratio and isentropic efficiency at design rotational speed were investigated.Also pressure non-uniformity around compressor impeller was investigated using pressure taps around the impeller outlet to verify numerical results. This effect was considered and reported for new cases using numerical results.The results show how the shape and centroid profile of volute circumferential cross sections can influence the compressor characteristics and circumferential static pressure non-uniformity.

This paper considers the problem of constructing an evolution family for the linear non autonomous Cauchy problem u(t) 􀀀 A(t)u(t) = 0; u(􀀀1) = x 2 RN;where A 2 C([􀀀1; 1];RNN): The essence of the method is that the evolution family is sought in the form of a series of Chebyshev polynomials. Then, by de ning appropriate weighted sequence spaces and matrices of linear operators, we are able to obtain a suf- cient condition - based only in the given data - for the representation of the solution of the initial value problem (). The method is motivated for practical considerations in the context of Magnetic Resonance Imaging.

Welding process plays a major role in ship production. As welding process can be performed in less time, ship fabrication can be completed in a shorter time. Therefore, it is a significant issue that welding time is able to be ended as soon as possible. For this, operator factor, which is a component of welding time calculation, could be increased. If this is done, welding time could be decreased. The purpose of this study is to determine the effects of operator factor on the production quantity of panel line. In the work, panel line of a shipyard situated in Turkey was illustrated as an example. Whole workstations of panel line were taken into consideration and modeled in SIMIO simulation environment. Changing operator factor in web welding work station on panel line, different welding time values were achieved. These welding time values were then inserted in simulation model and model was run along a specified period and finally production quantities of panel line were obtained as an output. So, the effects of operator factor changing on panel line throughput were determined.

Organic dust flames deal with a field of science in which many complicated phenomena like pyrolysis or devolatization of solid particles and combustion of volatile and char particles take place. One-dimensional flame propagation in the cloud of fuel mixture has been analyzed in which flame structure is divided into three zones: preheat zone, reaction zone and post flame zone.It is assumed that particles pyrolyze first to yield a fuel mixture consisting of gaseous and charry fuel. In this research, the effect of char content on pyrolysis process has taken into account and a novel non-linear burning velocity correlation is obtained. Our results are in a reasonable agreement with experimental data.

In this paper, we used the Picard successive iteration method and behind the new Modified Krasnoselskii iteration method in order to solve the different type of the ordinary linear differential equation having initial condition.By applying the new Modified Krasnoselskii iteration method not only we obtain the approximate solutions for the problem, but also establish the corresponding iterative schemes. Finally, it is shown that the accuracy of the new iteration method (which is called new Modified Krasnoselskii iteration method) is substantially improved by employing variable steps which adjust themselves to the solution of the differential equation.

In this paper, a stable finite volume formulation of lattice Boltzmann method is used to study time dependent flows. For simulation purpose, a cell-centered scheme is implemented to discretize the convection operator and weighting factors are used as flux correctors to enhance the stability. Also, additional lattices at the edge of each boundary cell are used, which allow a much better description of the actual geometrical shape. Compared with previous finite volume formulations, the proposed approach resulted in a wider domain of stability and faster convergence. The scheme is validated through simulations on flow over circular cylinder and mixing layer flow. The results show that the method is a promising scheme in simulating time dependent flows.

A closed-loop control methodology is investigated for stabilization of a vibrating non-classical micro-scale Euler-Bernoulli beam with nonlinear electrostatic actuation. The dimensionless form of governing nonlinear partial differential equation (PDE) of the system is introduced. The Galerkin projection method is used to reduce the PDE of system to a set of nonlinear ordinary differential equations (ODE). In non-classical micro-beams، the constitutive equations are obtained based on the non-classical continuum mechanics. In this work، proper control laws are constructed to stabilize the free vibration of non-classical micro-beams whose governing PDE is derived based on the modified strain gradient theory as one of the most inclusive non-classical continuum theories. Numerical simulations are provided to illustrate the effectiveness and performance of the designed control scheme. Also، the results have been compared with those obtained by the classical model of micro-beam.