Applied Mechanics and Materials Vols. 110-116

Abstract: Small hydropower stations as renewable resources of energy have noticeable potential in the world and with increasing energy demands, using such potentials is a need especially in many developing countries. The major problems of installing the new small hydropower stations are their high specific cost expressed in $/kW installed capacity and maintenance expenses. Part of the solution of these economic problems is to substitute the conventional turbines by simple and inexpensive machines such as reversible pumps. In this present work, an axial pump is simulated in reverse mode by computational fluid dynamics using different turbulence models and Characteristic curves of the reverse pump are obtained for each turbulence model and are compared with experimental data. The results show that Spalart-Allmaras model is preferred for investigation of operation of the axial reverse pump. In the next step, the effects of blades position and impeller size reduction on characteristic curves are considered. The results show that the axial pump can be easily run as a low-head turbine. Also it can be applied in the wide range by combination of blades angle adjustment and impeller size reduction. But the efficiency of turbine mode is low.

Abstract: A mobile robot traversing an uneven terrain can undergo tip over instability when one or more wheels of the mobile robot losses contact with the uneven terrain. In this paper, we study the tip over stability of a three wheeled mobile robot. The three wheeled mobile robot studied in this paper has torus shaped rear wheels and have the ability of lateral tilting – a condition required for slip free motion on uneven terrain. The torus shaped wheels and slip free motion makes the dynamics and tip over stability analysis more difficult and interesting. In this paper, the force-angle stability measure technique is used to analyze and detect tip over instability. Simulation results of the stability analysis shows that the wheeled mobile robot with lateral tilt of rear wheels is capable of moving on certain kinds of rough terrains without tip over.

Abstract: In recent years, ITM 399 series tractor has been manufactured in Iran Tractor Manufacturing Company (ITM), which can be suitable for small farms operations. For big farms operations, minimizing energy consumption, decreasing the time losses and increasing work efficiency, a heavy duty tractor of ITM 8200 series was started to design in the same Company. The gearbox selection, design and analysis for this tractor with the engine power of 154 horse power is studied in this research. The mechanical gearbox equipped with mechanical-hydraulic dynashift system was used in ITM 8200 power transmission system. The dynashift system produces four cases (A, B, C and D) with 8 speeds that produced by main gearbox, which altogether produces 32 forward speeds and 32 reverse speeds for this new tractor. To design the gearbox, with recommended speeds, gearbox ratios and gears ratios was calculated. Then by using the engine torque and slip torque on tractor gearbox, the exerted loads on gears were calculated. After this, by using of American Gear Manufacturing Association (AGMA) method and computer programming design, the gears have been designed. Finally one of the gears in ANSYS software analyzed. The results of this analysis show that: The gears have been designed for tractor gearbox can endure loading and transfer the power requirement of new tractor. The design safety factor of gears has been obtained by ANSYS software approximately equals with safety factor of AGMA methodology. In gear analysis, for applying load to one of gear tooth (unit contact ratio), stress distribution will produce in gear body and especially on neighboring teeth body. For tractor gearbox design, it would be necessary to include slip torque, which will decrease the gear width and gearbox volume.

Abstract: This paper includes project selection problem. Indeed, decision maker wants to select some projects among a group of projects with considering the resource constraints or he/she wants to reach a sequence of projects for doing them. We consider an objective for selecting the projects: minimizing the deviations from optimum solution. We study our models and solution method by a case study from Iran. This solution method is based on goal programming. The results show the efficiency of model and solution method and a chart has been shown for analyzing the results and seeing the sequence of projects. Finally, we propose future researches and generation of problem.

Abstract: Gas metal arc welding is a fusion welding process which has got wide applications in industry. In order to obtain a good quality weld, it is therefore, necessary to control the input welding parameters. In other words proper selection of input welding parameters in this process contribute to weld productivity. One of the important welding output parameters in this process is weld dilution affecting the quality and productivity of weldment. In this research paper using Taguchi method of design of experiments a mathematical model was developed using parameters such as, wire feed rate (W), welding voltage (V), nozzle-to-plate distance (N), welding speed (S) and gas flow rate (G) on weld dilution. After collecting data, signal-to-noise ratios (S/N) were calculated and used in order to obtain the optimum levels for every input parameter. Subsequently, using analysis of variance the significant coefficients for each input factor on the weld dilution were determined and validated. Finally a mathematical model based on regression analysis for predicting the weld dilution was obtained. Results show that wire feed rate (W),arc voltage (V) have increasing effect while Nozzle-to-plate distance (N) and welding speed (S) have decreasing effect on the dilution whereas gas Flow rate alone has almost no effect on dilution but its interaction with other parameters makes it quite significant in increasing the weld dilution

Abstract: Failure Mode and Effect Analysis (FMEA) has a well deserved reputation for systematic and thorough evaluation of failures at the system, sub-system or component level in all manufacturing and processing sectors. These organizations are looking for the final product to be “safe and reliable”. FMEA helps designers to identify and eliminate/control dangerous failure modes, minimizing damage to the system and its users. This paper, as an extension to the prior research work, introduces an insight into the reasons of failure and its effects in a thermal power plant opted for the case study, based on conceptual designs in context of FMEA. The analysis takes into account preparation of appropriate diagnostic and maintenance procedures with the aim of enhancement of thermal plant reliability. The FMEA technique used may be helpful for the design and maintenance departments to curtail the downtime of the plant.

Abstract: Thermal errors of CNC machines have significant effects on precision of a workpiece. One of the approaches to reduce these errors is modeling and on-line compensating them. In this study, thermal errors of an axis of the machine are modeled by means of artificial neural networks along with fuzzy logic. Models are created using experimental data. In neural networks modeling, MLP type which has 2 hidden layers is chosen and it is trained by backpropagation algorithm. Finally, the model is validated with the aid of calculating mean squared error and correlation coefficients between outputs of the model and a checking data set. On the other hand, an adaptive neuro-fuzzy inference system is utilized in fuzzy modeling which uses neural network to develop membership functions as fuzzifiers and defuzzifiers. This network is trained by hybrid algorithm. At the end, model validation is done by mean squared error like previous method. The results show that the errors of both modeling techniques are acceptable and models can predict thermal errors reliably.

Abstract: Electromagnetic coils are used in a wide variety of engineering applications. The magnitude of current (and hence magnetic field strength) is inherently frequency-dependent; above the coil’s breakpoint frequency current reduces in proportion to frequency. This effect often limits the high-frequency performance of devices. A magnetically-coupled conducting loop (“shorted-turn”) may produce beneficial effects of reducing the primary coil’s electrical impedance at high frequencies. This shorted turn effect was modelled using linear transfer function analysis and shown to have close agreement to experimental frequency-response measurements. Parameter sensitivity analysis was conducted to identify the effect of individual shorted-turn variables on the frequency response of a primary coil. Experimental variation of shorted-turn parameters confirmed the theoretical analysis, with thicker-walled, lower-resistance loops providing a more pronounced modification of primary coil response. These results and analysis provide a framework to design shorted-turns within electrical devices to optimise high-frequency behaviour.

Abstract: In this paper, the free vibration of moderately thick annular sector plates made of functionally graded materials is studied using the Differential Quadrature Method (DQM). The material properties of the functionally graded plate are assumed to vary continuously through the thickness, according to a power-law distribution. The governing differential equations of motion are derived based on the First order Shear Deformation plate Theory (FSDT) and then solved numerically using DQM under different boundary conditions. The results for the isotropic plates which are derivable with this approach are presented and compared with the literature and they are in good agreement. The natural frequencies of the functionally graded moderately thick annular sector plates under various combinations of clamped, simple supported and free boundary conditions are presented for the first time. The effects of boundary conditions, sector angle, radius ratio, thickness to outer radius ratio, volume fraction exponent and variation of the Poisson’s ratio on the free vibration behavior of the plate are studied

Abstract: Transient radiative heat transfer of turbid tissues with a focused short-pulsed laser is studied. To investigate radiation transfer phenomenon during ultra short time regime, transient radiative transfer equation is adopted and it is solved by TDOM (Transient Discrete Ordinate Method). The nonuniform grid system is considered to capture abrupt change of radiation energy absorption. The hyperbolic conduction model is considered to predict temperature increment of turbid tissues.