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A New Method for Multi-objective Optimal Design of Milling Parameters by Considering Chatter Vibrations

Sharif University of Technology-E. Jafarzadeh, S. Khodaygan
K.N.Toosi University of Technology-A. Sohani
Published 2019-05-13 by SAE International in United States
The desired milling process with high material removal rate (MRR) and low surface roughness of the product can be achieved only if machining chatter is absent. Incorporating chatter into the optimal selection of the machining parameters leads to a complex problem. Therefore, the approach of selecting conservative intervals for the machining parameters is usually employed instead. In this paper, a practical approach is proposed to specify the optimal machining parameters (depth of cut and spindle speed) in order to maximize MRR and minimize forced vibrations by considering machining chatter. Firstly, the worst-case scenario-based optimization problem in terms of the surface quality is solved to find the critical time at which maximal amplitude vibrations occur. Then, the time dependency of the problem is eliminated. Secondly, the multi-objective optimization is conducted to achieve the Pareto Optimal Front (POF). The Stability Lobe Diagram (SLD) is obtained independently through well-established analytical methods. Optimal machining parameters on the obtained POF are mapped into the SLD to represent optimal results for the cases at which machining chatter is absent. Finally, these…
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A Method for System Identification in the Presence of Unknown Harmonic Excitations Based on Operational Modal Analysis

Sharif University of Technology-S. Khodaygan
Published 2019-01-23 by SAE International in United States
Operational modal analysis techniques classically have been developed based on the assumption that the input to the system is a stationary white noise. While, in many practical cases, the systems are excited by combination of white noise and colored noises (harmonic excitations). Consequently, in conditions where non-white noises are present, the existing OMA methods cannot completely distinguish between the system poles and the induced poles due to colored noises. In order to overcome this weakness of OMA methods, some researches have been conducted in the field. In this paper, a new method is proposed for identifying the modal parameters of the system under the unknown colored noises, based on the Power Spectral Density Transmissibility (PSDT) function. In this work, the proposed methodology is established upon applying the auxiliary force, which can re-excite the system under operational conditions. In order to identify the modal parameters through the PSDT function, an appropriate parametric identification method such as the Poly-reference Least Squares Complex Frequency-domain method (PLSCF), or Poly-Max method, is utilized. Thus, modal parameters of the system poles…
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Multi-Objective Optimal Tolerance Allocation of the Mechanical Systems under the Thermal Gradients

Sharif University of Technology-S. Khodaygan, Javad Hemati-Nik
Published 2018-04-03 by SAE International in United States
Tolerance allocation is a key tool to reach a product with the minimum cost and the maximum performance. Since the thermal effects can cause the dimensional and geometrical variations in the components of mechanical assemblies, the tolerance allocation may be inefficient in the optimal tolerance design at the nominal conditions without including the thermal impacts. In this paper, a new optimal tolerance design of mechanical assemblies with the thermal effects is proposed. According to the proposed method, the tolerance allocation procedure is modeled as a multi-objective optimization problem. The functional objective, the manufacturing cost, and the quality loss function are considered as the corresponding objectives multi-objective optimal tolerance design problem. Using the computational results from the finite element simulations and based on the Artificial Neural Network (ANN) method, the design function as functional objective can be modeled. The optimal tolerance design problem in a multi-objective optimization form can be solved using Non-dominated Sorting Genetic Algorithm-II (NSGA-II). The Pareto optimal front (POF) of the proposed multi-objective optimization problem can be obtained. Finally, to illustrate the efficiency…
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A New Approach for the Reliability-Based Robust Design Optimization of Mechanical Systems under the Uncertain Conditions

Sharif University of Technology-S. Khodaygan, M. H. Sharafi
Published 2018-04-03 by SAE International in United States
A mechanical system inherently affected by the conditions, factors, and parameters of uncertainties. Without including the uncertainty effects in the design procedure, the designs may not be robust and reliable. Robust design optimization (RDO) method is a procedure to find the insensitive design with respect to the variations. On the other hand, reliability is measured by the probability of satisfying a specific design criterion. Therefore, a reliable design is a design that satisfies the specified criteria even with some uncertainties in variables and parameters. Reliability-based design optimization (RBDO) is an optimization procedure that incorporates reliability requirements to find the proper design. Since RDO and RBDO are usually the expensive computational approaches, the Reliability-Based Robust Design Optimization (RBRDO) may be difficult to apply. In this paper, a new model for the reliability based robust design optimization is introduced. First, two new factors that are called “chance - penalty function” and “reliability multiplier” are introduced. Based on these new factors, the optimality, the robustness, and the reliability functions as three objective functions are modeled. Then, a combined…
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Modal Parameter Identification of Rotary Systems Based on Power Spectral Density Transmissibility Functions

Sharif University of Technology-S. Khodaygan
Published 2018-04-03 by SAE International in United States
Operational modal analysis based on power spectral density transmissibility functions (PSDT) is a powerful tool to identify the modal parameters with low sensitivity to excitations. The rotor systems may have the asymmetric damping or stiffness matrices which can lead to increase the difficulties of the identification procedure. In this paper, a new method is proposed to identify the modal parameters of the asymmetric rotary systems by the operational modal analysis based on the power spectral density transmissibility functions. For pole extraction from the PSDT function, a proper parametric identification method such as the Poly-reference Least Squares Complex Frequency-domain method (PLSCF) or poly-Max method can be used. Then, the rotary system poles can be identified from a Stabilization Diagram (SD) with overestimating the system model order. The proposed algorithm is validated by a computer simulation.
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Experimental Investigation of Waste Gate Effects on Performance and NOx Emissions in a Turbocharged Aftercooled CNG SI Engine and its Turbocharger

Sharif University of Technology-Shahaboddin Kharazmi, Ali Hajilouy-Benisi, Aliasghar Mozafari
Published 2015-09-01 by SAE International in United States
In this paper a turbocharged aftercooled NG SI engine was experimentally investigated at Sharif University turbocharging lab at WOT. The engine torque, boost pressure, air consumption and volumetric efficiency were assessed experimentally at WOT in view point of waste-gate. Waste-gate opening effects on turbine and compressor characteristics were also evaluated experimentally at Sharif University turbocharger lab. The engine was also experimentally investigated at four different waste-gate opening pressure thresholds under ECE-R49 test cycle. It is also experimentally found that changing waste-gate opening pressure threshold from 165 mmHg to 200 and 265 mmHg decreases total bsNOx at a rate of 6% and 12% respectively. Increase of the pressure threshold to 323 mmHg augmented total bsNOx. Therefore, to minimize the bsNOx, the threshold of 265 mmHg was the optimum pressure threshold. Waste-gate not only had substantial effects on turbocharged CNG SI engine, but also significantly affected on NOx emissions.
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Error Reduction in Spatial Robots Based on the Statistical Uncertainty Analysis

SAE International Journal of Materials and Manufacturing

Sharif University of Technology-S. Khodaygan
K.N. Toosi University of Technology-M. Hafezipour
  • Journal Article
  • 2015-01-0435
Published 2015-04-14 by SAE International in United States
Kinematic accuracy of the robot end-effector is decreased by many uncertainties. In order to design and manufacture robots with high accuracy, it is essential to know the effects of these uncertainties on the motion of robots. Uncertainty analysis is a useful method which can estimate deviations from desired path in robots caused by uncertainties. This paper presents an applied formulation based on Direct Linearization Method (DLM), for 3D statistical uncertainty analysis of open- loop mechanisms and robots. The maximum normal and parallel components of the position error on the end-effector path are introduced. In this paper, uncertainty effects of both linear and angular variations in performance of spatial open-loop mechanisms and robots are considered. Based on the relations for the percent contributions of manufacturing variables, for the position error reduction, the tolerances that have the most significant effects on the commutated uncertainty zone of the end-effector position can be modified. The proposed method is illustrated using a spatial manipulator with three-revolute joints and verified with a Monte Carlo simulation method. Finally, normal and parallel distances…
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Sliding Mode Observers to Detect and Isolate Faults in a Turbocharged Gasoline Engine

SAE International Journal of Engines

Sharif University of Technology-Rasoul Salehi, Aria Alasty, Gholam-Reza Vossoughi
  • Journal Article
  • 2015-01-0227
Published 2015-04-14 by SAE International in United States
This paper presents a novel model-based algorithm which is able to detect and isolate major faults assigned to the gas exchange path of a gasoline engine both in the intake and exhaust sides. The diagnostics system is developed for detection and isolation of these faults: air leakage fault between the compressor and the air throttle, exhaust manifold pressure sensor fault, wastegate stuck-closed fault and wastegate stuck-open fault. Sliding mode observers (SMOs) are the core detection algorithms utilized in this work. A first order SMO is designed to estimate the turbocharger rotational dynamics. The wastegate displacement dynamics coupled to the exhaust manifold pressure dynamics is estimated using a second order SMO. Verified with experimental data from a modern TC gasoline engine running in a test cell, the two sliding mode observers are then used in a strategy to detect the faults in the gas exchange path. The proposed diagnostics system shows successful results in isolation of the four faults for gasoline engines without requiring a hot-film air-flow meter (HFM).
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Air Leak Detection for a Turbocharged SI Engine using Robust Estimation of the Turbocharger Dynamics

SAE International Journal of Passenger Cars - Electronic and Electrical Systems

Sharif University of Technology-Rasoul Salehi, Aria Alasty, Gholam-Reza Vossoughi
  • Journal Article
  • 2014-01-0279
Published 2014-04-01 by SAE International in United States
Proper operation of an internal combustion engine is required by demands of a vehicle driver and governmental legislations. Therefore it is necessary to monitor, within an online technique, the engine and detect any fault which disrupts its normal operation. In this paper, the air-charge path, as a key element in a turbocharged engine, is monitored for an air leakage fault. At first, a robust algorithm to estimate unmeasured turbocharger rotational speed is presented. The sliding mode methodology is used to design the estimator which is shown to be robust to the compressor modeling uncertainties. The estimation error from the sliding mode observer (SMO) is then used to detect abnormal behavior of the turbocharger along with the engine due to a leakage fault in the air-charge path. Experimental results from a modern turbocharged SI engine indicate the designed monitoring technique is able to detect a leakage fault, of 7 mm or higher sizes, in the air-charge path.
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Robust Tolerance Design of Mechanical Assemblies Using a Multi-Objective Optimization Formulation

Sharif University of Technology-S. Khodaygan, Mohammad R. Movahhedy
Published 2014-04-01 by SAE International in United States
The design process always has some known or unknown uncertainties in the design variables and parameters. The aim of robust design is minimization of performance sensitivity to uncertainties. Tolerance allocation process can significantly affect quality and robustness of the product. In this paper, a methodology to minimize a product's sensitivity to uncertainties by allocating manufacturing tolerances is presented. The robust tolerance design problem is formulated as a multi-objective optimization based on the combined function-uncertainty-cost model. Genetic algorithm is utilized to solve the multi-objective optimization and a case study is presented to illustrate the methodology.
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