Mohammad Hasan Shojaeefard; Abolfazl Khalkhali; Pedram Safarpour Erfani
Volume 7, Issue 1 , March 2014
Abstract
The vehicle driving comfort has become one of the important factors of vehicle quality and receives increasing attention. In this paper, optimal points of vehicle suspension parameters are generated using modified non-dominated sorting genetic algorithm (NSGA-II) for Pareto optimization of 5-degree of ...
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The vehicle driving comfort has become one of the important factors of vehicle quality and receives increasing attention. In this paper, optimal points of vehicle suspension parameters are generated using modified non-dominated sorting genetic algorithm (NSGA-II) for Pareto optimization of 5-degree of freedom vehicle vibration model considering three conflicting functions simultaneously. In this way random profile is considered for the road excitation. Objective functions are vertical acceleration of seat, relative displacement between sprung mass and forward tire and relative displacement between sprung mass and rear tire. Results are compared with the previous works. Such comparison shows good behaviour of the optimum design points proposed in this work.
naser esmaeili; S. Hamed Tabatabaei Oreh; Reza Kazemi
Volume 7, Issue 1 , March 2014
Abstract
Abstract: In this work, an optimal control scheme with adaptive weighting coefficients is presented which coordinates different vehicle dynamics control objectives, thus ruling out possible conflicts among them. In a new approach, the weighting coefficients in optimal control are adjusted according to ...
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Abstract: In this work, an optimal control scheme with adaptive weighting coefficients is presented which coordinates different vehicle dynamics control objectives, thus ruling out possible conflicts among them. In a new approach, the weighting coefficients in optimal control are adjusted according to the vehicle state in the phase plane in such a way that a priority is given to each objective of handling and stability in each region. The optimal control acts as a high-level control for the vehicle body, which determines the body lateral force and yaw moment for stable vehicle motion. The body lateral force and yaw moment provide the inputs to the mid-level force (control) distribution module, which works out the desired lateral and longitudinal forces at each wheel. Therefore, the high-level control objectives are allocated to individual tire forces in an optimal manner with the assumption of a 4-wheel-independent car. A low-level control uses the desired individual tire forces to compute the steering angle and applied torque at each wheel. Simulation tests with a nonlinear vehicle model are conducted and comparison with the well-recognized work in the literature is made to show the efficiency of the proposed method.
Karthikeyan Subramanian
Volume 7, Issue 1 , March 2014
Abstract
In the diesel engine Exhaust Gas Recirculation (EGR) components, valve and connecting pipes are the critical components and fails often during new engine development. These components are important for meeting NOx emissions norms. Therefore design of these components should remain robust. But the challenge ...
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In the diesel engine Exhaust Gas Recirculation (EGR) components, valve and connecting pipes are the critical components and fails often during new engine development. These components are important for meeting NOx emissions norms. Therefore design of these components should remain robust. But the challenge in design is compact packaging of complete EGR components on the engine consequently vibration related failure plays a major role. Normally in pneumatic EGR valve, shaft spring stiffness plays a major role for shaft opening and closing. But in this layout during emission testing, shaft is self-opened without feedback signal from sensor this is due to resonance and this problem is solved by increasing the spring stiffness. The next key components is the EGR pipes, the flexible bellows on these pipes are useful for thermal expansion during hot conditions. In this case the bellow crack failure is observed due to vibration. Therefore design improvements were made by proper design of bellow geometry and bracket support for these pipes facilitated prevention of EGR pipe failure. Overall this paper describes the methodology to conduct proper failure investigation to identify the root cause for vibration related failures of EGR system during new product development.
Mohammad Akhondzadeh; Mehrdad Vahdati
Volume 7, Issue 1 , March 2014
Abstract
Air pads are applicable in ultra precision machines very much. Two main components of these machines, spindle and table, use the advantages of such systems. The performance and efficiency of air pads have big influence on the whole machine quality. Parameters affecting pressure distribution of air tables ...
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Air pads are applicable in ultra precision machines very much. Two main components of these machines, spindle and table, use the advantages of such systems. The performance and efficiency of air pads have big influence on the whole machine quality. Parameters affecting pressure distribution of air tables may be considered as, 1) air compressing method, 2) air nozzle diameter, shape, and size, 3) number of air pads, 4) air gap thickness, etc. In this study, effects of air pad shape on pressure distribution in air gap have been investigated using ANSYS. In this simulation, FOTRAN environment have been employed. Investigated shapes for air pads are triangle, rectangle, pentagon, hexagon, ellipse and circle. Pressure distribution-distance from orifice has been plotted for each air pad shape. The results indicate that the rectangle air pad has best pressure distribution.
Milad Janbakhsh; S. M. R. Loghmanian; Faramarz Djavanroodi
Volume 7, Issue 1 , March 2014
Abstract
More recently, Titanium and aluminum alloys are gaining more interests to be implemented in hydro-forming applications. It is necessary to predict forming limits for these sheet alloys. Forming limits play an important role in metal forming processes. Forming limit diagrams, present the limit strains ...
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More recently, Titanium and aluminum alloys are gaining more interests to be implemented in hydro-forming applications. It is necessary to predict forming limits for these sheet alloys. Forming limits play an important role in metal forming processes. Forming limit diagrams, present the limit strains for various linear strain paths. In other hand, forming limit curve (FLC), illustrates localized formability for sheet metals under proportional loadings and are known as a powerful tool for trouble-shooting in sheet metal forming processes. In this study, mechanical properties of Ti-6Al-4V titanium sheets, AA7075-T6 and AA2024-T3 aluminum sheets are investigated through the uni-axial tensile test. Anisotropy coefficients as well as work-hardening exponent resulted from tensile test were used to theoretically prediction and numerical simulations of limit strains. For the theoretical prediction of the forming limit curves, several constitutive models were implemented. Several Hill’s yield criteria combined with Swift equation and empirical equation proposed by NADDRG were accomplished to predict the FLDs. Results showed that calculated numerical results are in good agreement with the predicted theoretical data when Hill93-Swift is the instability criteria used.
Mohammad Mehdi Ghaitani; Ali Ghorbanpour Arani; Hasan Khademizadeh
Volume 7, Issue 1 , March 2014
Abstract
In this paper, nonlinear vibration and instability response of an embedded pipe conveying viscose fluid is investigated. The pipe is considered as a Timoshenko beam embedded on an elastic foundation which is simulated by spring constant of the Winkler-model and the shear constant of the Pasternak-model. ...
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In this paper, nonlinear vibration and instability response of an embedded pipe conveying viscose fluid is investigated. The pipe is considered as a Timoshenko beam embedded on an elastic foundation which is simulated by spring constant of the Winkler-model and the shear constant of the Pasternak-model. The external flow force, acting on the beam in the direction of the flexural displacement is described by the well-known Navier-Stokes equation. The corresponding governing equations are obtained using Hamilton's principle considering nonlinear strains and first shear deformation theory. In order to obtain the nonlinear frequency and critical fluid velocity for clamped supported mechanical boundary condition at two ends of the pipe, Differential quadrature method (DQM) is used in conjunction with a program being written in MATLAB. The effect of dimensionless parameters such as aspect ratios of length to radius of the pipe, Winkler and Pasternak modules, fluid velocity and viscosity as well as the material type of the pipe on the frequencies and instability of pipe are investigated. Results indicate that the internal moving fluid plays an important role in the instability of the pipe. Furthermore, the nonlinear frequency and instability increases as the values of the elastic medium constants and viscosity of fluid increases.
Anant Jitendrakumar Sheth
Volume 7, Issue 1 , March 2014
Abstract
With the prolonged use of domestic centrifugal pump, due to erosion, corrosion and an unbalance the sever vibration of the pump are resulted. An erratic sound coming out of pump makes the user uncomfortable. Here, Tuned Vibration Absorber (TVA) is used as a vibration controlling device. It is designed ...
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With the prolonged use of domestic centrifugal pump, due to erosion, corrosion and an unbalance the sever vibration of the pump are resulted. An erratic sound coming out of pump makes the user uncomfortable. Here, Tuned Vibration Absorber (TVA) is used as a vibration controlling device. It is designed to reduce the RMS velocity below 20% of the circumferential speed, at which the impeller is balanced. Natural frequency were found both by analytical and the numerical methods. A fan cover is considered as a TVA, tuned to the operating frequency and the dominating higher frequencies have been tackled by designing new TVA. Here with TVA, the vibration has been reduced to the permissible limit and the amplification factor is within the allowable limit.
sadegh Rahmati; Farid Ghadami
Volume 7, Issue 1 , March 2014
Abstract
Stereolithography process limits wider applications due to low dimensional accuracy comparing with CNC. To improve accuracy and reduce part distortion, understanding the physics involved in the relationship between the setup input parameters and the part dimensional accuracy is prerequisite. In this ...
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Stereolithography process limits wider applications due to low dimensional accuracy comparing with CNC. To improve accuracy and reduce part distortion, understanding the physics involved in the relationship between the setup input parameters and the part dimensional accuracy is prerequisite. In this paper, a model is proposed to find and optimize important parameters to achieve a high accuracy and also, to prediction dimensional accuracy with various values of parameters. For this purpose, the result of a previous study is used. It is found in Stereolithography these factors, respectively, have a most impact on dimensional accuracy in parts built SLA: layer thickness, hatch style, hatch spacing, hatch fill cure depth and hatch overcure. The proposed neural network model in this paper is able to predict dimensional accuracy with about 6 percents error.
Abbas Habibalahi; M. S. Safizadeh
Volume 7, Issue 1 , March 2014
Abstract
Stress and residual stress are the main problems in the operating performance of materials. They are the principal causes of material failure and can affect life time of component. However measurement or predictions of them are typically difficult. Two common non-destructive methods, X-ray diffraction ...
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Stress and residual stress are the main problems in the operating performance of materials. They are the principal causes of material failure and can affect life time of component. However measurement or predictions of them are typically difficult. Two common non-destructive methods, X-ray diffraction and ultrasound are not reliable methods for subsurface residual stress measurements and destructive hole-drilling method is not absolutely precise and safe. In this study, the PEC method was applied to the qualitative and quantitative measurements of stress in aluminum alloy specimens. PEC is a high performance non-destructive testing technique but its application in stress and residual measurement is unknown. In this study a qualitative and quantitative approach for measuring residual stress by PEC technique was developed. Results indicated that pulsed eddy current responses are sensitive to stress and showed PEC method is capable of residual stress measurements.
Nariman Ashrafi; Yashar Bashirzadeh
Volume 7, Issue 1 , March 2014
Abstract
The present experimental study reports on enhancement of heat transfer by addition of nanoparticles to the working fluid of commercial swimming pool heat exchangers under laminar flow condition. Three different concentrations of Titanium dioxide nanoparticles were added to the water as working fluid ...
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The present experimental study reports on enhancement of heat transfer by addition of nanoparticles to the working fluid of commercial swimming pool heat exchangers under laminar flow condition. Three different concentrations of Titanium dioxide nanoparticles were added to the water as working fluid of a typical forced convective heat exchanger used to transfer heat to public swimming pools. The experimental setup is capable of measuring velocity, heat transfer rate, and temperature at different points. TiO2 nanoparticles with mean diameter of 20 nm were used. The effects of concentration of suspended nanoparticles and that of Reynolds number on forced convective heat transfer were investigated. It is observed that at 0.1%, 0.5% and 1% weight concentration of suspended TiO2 nanoparticles, the average convective heat transfer coefficient improved by 1.1%, 15.9% and 31.6% respectively. The coefficient is further increased at higher Reynolds numbers. The efficiency of heat exchanger is evaluated for different scenarios.
M. T. Ghorbani
Volume 7, Issue 1 , March 2014
Abstract
In this paper, the problem of optimal path following for a high speed planing boat is addressed. First, a nonlinear mathematical model of the boat’s dynamics is derived and then the Serret-Frenet frame is presented to facilitate the path following control design. To satisfy the constraints on the states ...
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In this paper, the problem of optimal path following for a high speed planing boat is addressed. First, a nonlinear mathematical model of the boat’s dynamics is derived and then the Serret-Frenet frame is presented to facilitate the path following control design. To satisfy the constraints on the states and the input controls of the boat's nonlinear dynamics and minimize both the cross tracking and heading error, a nonlinear optimal controller is formed. To solve the resulted nonlinear constrained optimal control problem, the Gauss pseudospectral method (GPM) is used to transcribe the optimal control problem into a nonlinear programming problem (NLP) by discretization of states and controls. The resulted NLP is then solved by a well-developed algorithm known as SNOPT. The results illustrate the effectiveness of the proposed approach to tackle the boat path following problem.
Reza Alibakhshi
Volume 7, Issue 1 , March 2014
Abstract
This article addresses an efficient and novel method for singularity-free path planning and obstacle avoidance of parallel manipulator based on neural networks. A modified 4-5-6-7 interpolating polynomial is used to plan a trajectory for a spherical parallel manipulator. The polynomial function which ...
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This article addresses an efficient and novel method for singularity-free path planning and obstacle avoidance of parallel manipulator based on neural networks. A modified 4-5-6-7 interpolating polynomial is used to plan a trajectory for a spherical parallel manipulator. The polynomial function which is smooth and continuous in displacement, velocity, acceleration and jerk is used to find a path avoiding obstacles and singularities. The polynomial is further modified to plan a trajectory with minimum passing length through the obstacle and singularity, and the best kinematics conditioning index, as well. An artificial neural network is implemented to solve forward kinematics of the manipulator to estimate the distance between gripper and singularity or obstacle in Euler coordinate. Moreover, the simulation results prove the efficiency of the proposed algorithm.