Sharif Digital Repository

By new advancements in vehicle manufacturing, evaluation of vehicle quality assurance has got a more critical issue. Today noise and vibration generated inside and outside the vehicles are more important factors for customers than before. So far several researchers have focused on interior noise transfer path analysis and the results have been published in related papers but each method has its own limitations. In present work, the vibration transfer path analysis and vibration path ranking of a car interior have been performed. As interior vibration is a source of structural borne noise problem, thus, the results of this research can be used to present the structural borne noise state in a... 

High center of mass vehicles are likely to rollover in extreme maneuvers. Available works present control strategies to prevent rollover. In these works, however, other important parameters such as path trajectory tracking are not a main concern. In this paper conflicts between rollover prevention and trajectory tracking is investigated. Model predictive control (MPC) is adopted to predict and avoid rollover while tracking desired trajectory. For this regard a model based future error estimation is introduced. The control framework predicts both rollover and trajectory error simultaneously. It avoids rollover while tries to track the trajectory. Simulation results for two controllers with... 

This article presents a routine for prediction of the crack growth path in gears. Crack simulation helps in determining failure modes and crack detecting by vibration monitoring. To simulate crack propagation an effective method is developed by which the meshing force is calculated based on the compliance of meshing teeth in every stage of crack growth. In this method the compliance matrix of the tooth is calculated using three-dimensional boundary element analysis without the need for simultaneously modelling two meshing gears. The force distribution on the contact area is then calculated using Hertz theory and compliance matrices of meshing teeth. The method is used in prediction of the... 

This paper discusses the effects of substrate motions on the performance of microgyroscopes modeled as ring structures. Using the Extended Hamiltonian Principle, the equations of motion of a ring micro-gyroscope are derived, and the natural frequency equation and response characteristics are extracted in closed form for the case where the substrate undergoes normal rotation. The Galerkin approximation is then used to arrive at the ordinary differential equations of motion for the ring. In these equations, the effects of angular, centripetal and Coriolis accelerations are all apparent. The response of the system to different inputs is studied and the system sensitivity to variation in input... 

This paper discusses the effects of substrate motions on the performance of a microgyroscope modeled as a ring structure. Using Extended Hamilton's Principle, the equations of motion are derived. The natural frequency equation and response of gyroscope are then extracted in closed-form for the case where substrate undergoes normal rotation. The Galerkin approximation is used for discretizing the partial differential equations of motion into ordinary differential equations. In these equations, the effects of angular accelerations, centripetal and coriolis accelerations are well apparent. The response of the system to different inputs is studied and the system sensitivity to input parameter... 

The need for service passenger cars, like taxies and governmental vehicles, to work in central Tehran that can produce less emission has been the main drive behind this research. A series hybrid pneumatic vehicle based on Iran manufactured Samand Passenger car was developed using commercially available components. The idea is to use as much standard parts as possible to reduce the development and manufacturing costs of the developed hybrid car. The vehicle space and weight limitations and the fixed geometry have been the main constraint in adoption of the components. The calculations show that the designed vehicle succeeds to satisfy the requirements set by driving cycle, but requires... 

Development of hybrid cars is the most popular subject among automotive engineers both in production and research. The need for service passenger cars, like taxies and governmental vehicles, to work in central Tehran that produce less emission has been the main drive behind this paper. A parallel hybrid pneumatic vehicle based on Iran manufactured Samand passenger car was developed using commercially available components. The idea is to use as many standard components as possible to reduce development and manufacturing costs. The vehicle space and weight limitations and fixed geometry have been the main constraint in adoption of the components. In this design the 75 kW engine of the Samand... 

This paper presents a mathematical model of laser powder deposition (LPD) to predict temperature field, melt pool depth and dilution. The model validated by experiments is developed using the moving heat source method. In this method, the temperature distribution inside the clad and the substrate is obtained using the superposition principle and the solution of the heat diffusion due to a point heat source. The model, which can be used in real-time applications, predicts the melt pool depth and dilution as a function of clad height and clad width, which in practice can be measured by a vision system. Numerical and experimental analyses show a non-linear behaviour of the melt pool depth as a... 

In this paper vehicle path-following in the presence of rollover risk is investigated. Vehicles with high centre of mass are prone to roll instability. Untripped rollover risk is increased in high centre of gravity vehicles and high-friction road condition. Researches introduce strategies to handle the short-duration rollover condition. In these researches, however, trajectory tracking is affected and not thoroughly investigated. This paper puts stress on tracking error from rollover prevention. A lower level model predictive front steering controller is adopted to deal with rollover and tracking error as a priority sequence. A brake control is included in lower level controller which... 

In this paper, a method for overtaking stationary and moving obstacles will be introduced. The method consists of designing a desired trajectory for lateral motion of the vehicle and then using a lateral motion controller for tracking this desired trajectory. The desired trajectory is a sigmoid exponential function of relative distance between the vehicle and the obstacle and guarantees overtaking the obstacle, if tracked exactly, despite of lateral and longitudinal motions of the obstacle. Lateral acceleration of the vehicle should not exceed safety limits during tracking desired trajectory. This matter has been used as a decision criterion for determining feasible and unfeasible desired... 

This paper proposes an Age-Dependent Clustering (ADC) structure to be used for prognostics. To achieve this aim, a step-by-step methodology is introduced, that includes clustering, reproduction, mapping, and finally estimation of Remaining Useful Life (RUL). In the mapping step, a neural fitting tool is used. To clarify the age-based clustering concept, the main elements of the ADC model is discussed. A Genetic algorithm (GA) is used to find the elements of the optimal model. Lastly, the fuzzy technique is applied to modify the clustering. By investigating a case study on the health monitoring of some turbofan engines, the efficacy of the proposed method is demonstrated. The results showed... 

In this paper an experimental/numerical technique is developed for engine mount optimization. The method is general and can be applied to optimize active and passive vibration isolators or absorbers in any mechanical systems or civil structures. Engine mount optimization techniques mostly rely on an accurate mathematical model of the whole vehicle, which in most cases is not available or is too difficult to develop. As a result, the current approach for selecting engine mounts for a vehicle is based upon trial and error which is very time-consuming and expensive. The proposed technique counts upon experimental data for optimization and does not require any mathematical model of the vehicle... 

Modern sensors consist of arrays of detectors specially arranged to enhance precision, capabilities, and field of view (FOV). Sensor arrays can have multiple functionalities, such as the simultaneous detection of position and motion. We use a linear sensor model and develop an optimization method to design an array of photodiodes. Our objective function minimizes bias and variance estimations. We introduce a maximum likelihood technique to approximate and determine the bias caused by measurement errors, and verify our theory by statistically complete simulations. We apply our theory to design an optimal sun sensor. The sensor has a predefined conical FOV, and its accuracy is controlled by a... 

Design and optimization of centrifugal compressors, based on main blades configuration of impeller have been vastly discussed in open literature, but less researches have addressed splitters. In this research, the impeller of a commercial turbocharger compressor is investigated. Here, profiles of main blades are not changed while the effect of changing the configuration of splitters is studied. An optimization study is performed to find the best configuration using genetic algorithm over a complete operating curve of the compressor. CFD codes with experimental support are used to predict the compressor performance. Quantumetric tests beside destructive analysis of two impellers are... 

In this research, multi-level optimization of the profile of the splitter blades of a turbocharger compressor is performed using genetic algorithm in order to improve its performance. Successive corrections of the profile at hub, mid-span, and shroud of the splitter blades, with the objective of decreasing the incidence losses at the leading edge and adjustment of the blade loading at the shroud, result in an impeller having improved splitter blades. The impeller flow field analysis shows that the optimization has been successful in reducing the flow leakage at the shroud region as well as the losses in the leading edge region. Although numerical simulations predict a decrease by 0.5% in... 

This paper discusses the effects of substrate motions on the performance of a microgyroscope modeled as a suspended beam with a tip mass. These motions can be either along or around the three axes. Using the Extended Hamilton's Principle, the equations of motion are derived. In these equations, the effects of beam distributed mass, tip mass, angular accelerations, centripetal and coriolis accelerations are well apparent. The effect of electrostatic forces inducing the excitation vibrations are considered as linear functions of beam displacement. The response of the system to different inputs is studied and the system sensitivity to input parameter changes are examined. Finally, the sources... 

In this research, the centrifugal compressor of a turbocharger is investigated experimentally and numerically. Performance characteristics of the compressor were obtained experimentally by measurements of rotor speed and flow parameters at the inlet and outlet of the compressor. Three dimensional flow field in the impeller and diffuser was analyzed numerically using a full Navier-Stokes program with SST turbulence model. The performance characteristics of the compressor were obtained numerically, which were then compared with the experimental results. The comparison shows good agreement. Furthermore, the effect of area ratio and tip clearance on the performance parameters and flow field was... 

A manipulator mounted on a moving vehicle is called a mobile manipulator. A mobile manipulator with an appropriate suspension system can pass over uneven surfaces, thus having an infinite workspace. If the manipulator could operate while the vehicle is traveling, the efficiency concerning with the time and energy used for stopping and starting will be increased. This paper presents the kinematic and dynamic modeling of a one degree of freedom manipulator attached to a vehicle with a two degrees of freedom suspension system. The vehicle is considered to move with a constant linear speed over an uneven surface while the end effector tracks a desired trajectory in a fixed reference frame. In... 

This paper presents a closed-loop laser cladding process used in nonplanar deposition of desired metallic materials. In the proposed system, the deposited layer geometry is continuously controlled via a sliding mode controller (SMC). The controller, which uses the scanning speed as the control input, is designed based on a parametric Hammerstein model. The model is a parametric dynamic model with several unknown parameters, which are identified experimentally using the recursive least squares method. The designed SMC is robust to all model parameters' uncertainties and disturbances. The results showed that the tracking accuracy improves and the chattering effect reduces if an integrator on... 

We report the design, fabrication and error analysis of a sun sensor array composed of six photodiodes. The sensor estimates the direction of the sun using a linear least squares method. The performance of the sensor is deteriorated by three major sources: fabrication errors, scattered environmental light, and inexact modeling of photodiodes. Using a calibration procedure and modeling the uniform component of the environmental light, we mitigate the first two errors and significantly reduce root mean squared error from 2.63° to 0.83°. For a Field of View (FOV) of 110°, the maximum estimation error also drops from 3.8° to 1.6°. Through exact mathematical modeling of photodiodes, we...