Iranian Journal of Science and Technology Transactions of Mechanical Engineering
Volume:39 Issue: 1, 2015

Based on the notion of micro-structure in linear elasticity presented by Mindlin, a new extended continuum mechanics (ECM) formulation is derived which can be utilized to model the material behavior at atomic scale. An attempt has been made to present a formulation capable of producing the molecular dynamics (MD) simulation results with less computational effort. To this end, some new kinematical variables are defined and some constitutive relations are obtained from MD. To validate the proposed ECM formulation, it is applied to a properly defined sample problem and the response is compared with the MD simulation result and the classical continuum mechanics (CCM) solution.

In this article, an analytical solution is developed to study the free vibration analysis of functionally graded rectangular nanoplates. The governing equations of motion are derived based on second order shear deformation theory using nonlocal elasticity theory. It is assumed that the material properties of nanoplate vary through the thickness according to the power law distribution. Our numerical results are compared with the results of isotropic nanoplates and functionally graded macro plates. The effects of various parameters such as nonlocal parameter and power law indexes are also investigated.

The objective of this experimental work was to assess the drop impact damage on Woven Glass Fibre Reinforced Polymer composite laminate through online method and offline method. Online monitoring of drop impact damage was carried out by Acoustic Emission (AE) technique and AE signals during the drop impact test were captured. From the analysis of AE signals, it was observed that as the impact energy increases the AE parameters such as counts, counts to peak, signal strength and root mean square (RMS) values also increase. Offline assessment of impact damage on composite laminate was also observed by ultrasonic technique and it was inferred that ultrasonic parameters, namely amplitude and attenuation ratio were decreased with increase in impact energy of test. But attenuation coefficient had an indirect relationship with impact energy. During online/offline monitoring of composite laminate the AE/UT parameters which were obtained from real time monitoring are used to predict Impact Damage Tolerance (IDT) using a separate trained artificial neural network model. Based on the IDT value of composite, the component should be continued in-service or replaced.

In this paper, a connecting rod was modeled and analyzed by finite element method. By using genetic algorithm (GA) and modified cuckoo optimization algorithm (MCOA), the material properties and some geometrical specifications were optimized. Cost function was a combination of weight and stress. The connecting rod was under a load of 21.8 kN which obtained 36 o crank angle at 5700 rev/min. The reduction percentages of weight in 2-D analysis were 45.47% and 50.34% based on GA and MCOA, respectively. The reduction percentages of stress were also 1.26% and 2.20% based on GA and MCOA, respectively. The values of reduction percentages in 3-D analysis showed the same trends. The results showed that applying each of the algorithms was efficient. Meanwhile, the results of MCOA were better than GA, because of the smaller number of iterations and the initial population, which resulted in increasing the rate of convergence (i.e. decreasing computational time) and accuracy of answers. It can be mentioned that MCOA is an efficient and reliable algorithm and can be used as a benchmark for future works.

The increase of cell temperature with increased irradiance is probably the most significant disadvantage of using Photovoltaic modules equipped with booster reflectors. The aim of this study is to investigate the possibility of improving the performance of a photovoltaic water pumping system by using a booster reflector and to keep the temperature of PV panels at a low level by cooling PV panels with a film of water. The water required for covering the cells is fed by the pump itself. By applying the modifications on the photovoltaic water pump system, significant improvement in the output power from PV panels, and therefore in the pump flow rate, is displayed in the experimental results.

Diesel fuel has a limited resource and concerns over environmental pollution are leading to the use of ‘bio-origin fuels’ as they are renewable and environmentally benign. Jatropha methyl ester, an esterified biofuel, has an excellent cetane number and a reasonable calorific value. It closely resembles the behaviour of diesel. However, being a fuel of different origin, the standard design limits of a diesel engine is not suitable for Jatropha methyl ester. Therefore, in this work, operational parameters are studied to find out the optimum performance of Jatropha methyl ester run diesel engine. The parameters varied are the compression ratio (CR) and injection timing (IT) along with load in a diesel engine. This work targets finding the effects of the engine operating parameters on the performance of the engine with regard to specific fuel consumption (SFC) and brake thermal efficiency (BTHE) with Jatropha methyl ester(J20) as fuel. Further exhaust emissions of the engine for the above conditions are also studied.Thus J20 can be effectively used in a diesel engine without any modification. At compression ratio of 19.5 along with injection timing of 30obTDC (before top dead centre) will give better performance and lower emission which is very close to diesel. Comparison of performance and emission was done for different values of compression ratio along with injection timing to find the best possible combination for operating engine with J20. It is found that the combined increase of compression ratio and injection timing increases the BTE and reduces SFC while having lower emissions. Diesel 20%) saved, will greatly meet the demand of fuel in railways.

This work is an attempt towards employing ductile damage criterion and finite element simulations for prediction of fracture initiation and evolution in deep drawing of copper/stainless steel clad sheets. The material mechanical properties and ductile damage parameters were determined through standard and notched tensile tests. The effect of some important process parameters on damage evolution were examined through numerical modeling and the acceptable range of variations for each parameter were introduced in order to prevent tearing of the blank during the process. The numerical predictions of deformation and fracture behavior were in a good agreement with experimental observations.

In this paper, based on the slab method of analysis, a novel and general approach is developed for studying the radial forging process with curved profile dies. The presented approach is not only more general with respect to previous studies, but it is also easier to understand and use and can be efficiently used for optimization of the die profile depending on the forging geometry and conditions. The obtained general equations reduce to those obtained in previous studies for the special case of linear dies. The process is also simulated by the finite element method to further enhance the results of the study. The obtained results provide useful information for the optimal design of the radial forging die.

Double bridge girder overhead cranes are used for heavy duty applications in the industry. In this paper a detailed parametric design optimization of the main girder of box type is performed for a 150Ton capacity and 32m long span crane, after its basic design using available design rules. Design optimization is performed using detailed 3D finite element analysis by changing the number, shape and location of horizontal stiffeners along the length of the girder and number and location of stiffeners along the vertical direction to control any possible buckling, with minimum possible weight and for safe stress and deflection. Optimization is performed in two steps. In the first step, keeping plates thickness constant different types and number of stiffeners are added and optimized geometry is found. In the second step, the best geometry of the first step is further optimized for maximum allowable bending stress by changing thickness, height and width of the box girder with minimum possible weight. Effect of added stiffeners is highlighted in controlling its buckling.

A novel technique is investigated for PID controller adaptation in order to control the temperature of a liquid-phase reactor tank by using a heat exchanger system. As for nonlinearity, time delay problems and model uncertainties introduced by the heat exchanger, an interval type-2 fuzzy system (IT2FS) is implemented to enhance and improve the total control performance. Moreover, the fuzzy inference rules which enable the adaptive adjustment of PID parameters are established based on error and error variations. Target tracking, oscillation control and error evaluation for the proposed controller are compared with previously performed control strategies on the mentioned heat exchanger system. The results show that the adaptive technique for PID gain based on IT2FS has lower error and strengthened capacity for external oscillation control and also an acceptable tracking capability.

In this paper, the Quantitative Feedback Theory (QFT) is proposed to design a controller for feed drive of Virtual Computer Numerical Control (VCNC) systems. The designed robust QFT controller is also compared to two commonly used controller design methods, i. e. Fuzzy Control (FC) and Sliding Mode Control (SMC), for contour tracking problem. The position commands required for contour following task are evaluated by the Non-Uniform Rational BSpline (NURBS) curve interpolator with the S-shape feedrate profile for two contours, i. e. «heart» and «omega» as the case studies. After modeling the feed drive of the VCNC system, the robust QFT controller and also FC and SMC controllers are designed to achieve the allowable tolerance contour error. The simulation results for the «heart» and «omega» contour following tasks with the aforementioned controllers were analyzed and discussed. It is found that the designed QFT controller not only achieves the tight contour error but also yields better satisfactory performance, especially at the corners of the tool path, compared to the other controllers used in contour following applications in VCNC systems.

In this literature, a combined method has been employed to simultaneously reduce smoke (Soot) and oxide of nitrogen (Nox) and maintain the performance parameters of diesel engine. This includes creating an air jet by designing an air-cell inside the piston body, advanced injection timing and using cold exhaust gas recirculation. The tested engine was an M 4.244 engine that worked as natural aspiration. The air-cell causes reduction in both Soot and NOx emissions. Furthermore, applying cold EGR had a noticeable effect on NOx emission reduction. Advancing injection timing, the performance parameters of the engine could be improved. The tests were done in 25%, 50%, 75% and 100% load conditions, for the engine speed of 2000 rpm. The results showed that by simultaneous reduction of Soot and NOx emissions, performance parameters can be kept in a suitable range. The greatest reductions in NOx and Soot emissions have been observed in 100% load. There have been no considerable changes in BSFC (Brake Specific Fuel Consumption and power) while injection timing advances have been applied for 5° CA and 5% EGR.