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Haider, Syed F.
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New Method for Decoupling the Powertrain Roll Mode to Improve Idle Vibration

FCA US LLC-Syed F. Haider, Ahmad Abbas, Francisco Sturla
Published 2019-06-05 by SAE International in United States
Modern engines have high torque outputs and have low RPM due to increased demand for fuel efficiency. Vibrations caused by such engines have to be mitigated. Decoupling the roll mode from the remaining five rigid body modes results in a response which is predominantly about the torque roll axis (TRA) and helps reduce vibrations. Therefore, placing the mounts on the TRA early in the design phase is crucial. Best NVH performance can be obtained by optimizing the powertrain mount parameters viz; Position, Orientation and Stiffness. Many times, packaging restricts the mounts to be placed about the TRA resulting in degradation in NVH performance. Assuming that the line through the engine mount (Body side) centers is the desired TRA, we propose a novel method of shifting the TRA by adding mass modifying the powertrain inertia such that the new TRA is parallel to and on top to the desired TRA. This in turn will decouple the roll mode and reduce vibrations. This problem is formulated as an optimization problem. The numerical examples presented in this paper…
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An Improved Reanalysis Method Using Parametric Reduced Order Modeling for Linear Dynamic Systems

SAE International Journal of Passenger Cars - Mechanical Systems

Oakland University-Syed F. Haider, Zissimos Mourelatos
  • Journal Article
  • 2016-01-1318
Published 2016-04-05 by SAE International in United States
Finite element analysis is a standard tool for deterministic or probabilistic design optimization of dynamic systems. The optimization process requires repeated eigenvalue analyses which can be computationally expensive. Several reanalysis techniques have been proposed to reduce the computational cost including Parametric Reduced Order Modeling (PROM), Combined Approximations (CA), and the Modified Combined Approximations (MCA) method. Although the cost of reanalysis is substantially reduced, it can still be high for models with a large number of degrees of freedom and a large number of design variables. Reanalysis methods use a basis composed of eigenvectors from both the baseline and the modified designs which are in general linearly dependent. To eliminate the linear dependency and improve accuracy, Gram Schmidt orthonormalization is employed which is costly itself. In this paper, we propose a method to reduce the orthonormalization cost and improve the computational efficiency of the PROM reanalysis method. Our method eliminates non-important design variables and/or reduces the basis size by eliminating redundant modes. A vibratory analysis of an automotive door demonstrates the efficiency and accuracy of the…
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Computational Efficiency Improvements in Topography Optimization Using Reanalysis

SAE International Journal of Materials and Manufacturing

Oakland University-Syed F. Haider, Zissimos Mourelatos
  • Journal Article
  • 2016-01-1395
Published 2016-04-05 by SAE International in United States
To improve fuel economy, there is a trend in automotive industry to use light weight, high strength materials. Automotive body structures are composed of several panels which must be downsized to reduce weight. Because this affects NVH (Noise, Vibration and Harshness) performance, engineers are challenged to recover the lost panel stiffness from down-gaging in order to improve the structure borne noise transmitted through the lightweight panels in the frequency range of 100-300 Hz where most of the booming and low medium frequency noise occurs. The loss in performance can be recovered by optimized panel geometry using beading or damping treatment. Topography optimization is a special class of shape optimization for changing sheet metal shapes by introducing beads. A large number of design variables can be handled and the process is easy to setup in commercial codes. However, optimization methods are computationally intensive because of repeated full-order analyses. In this paper, we propose using a Modified Combined Approximations (MCA) reanalysis method integrated with topography optimization to improve the computational efficiency. Using a tire tub example, we…
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Reanalysis of Linear Dynamic Systems using Modified Combined Approximations with Frequency Shifts

SAE International Journal of Passenger Cars - Mechanical Systems

Oakland University-Zissimos Mourelatos
Oakland Universtiy-Syed F. Haider
  • Journal Article
  • 2016-01-1338
Published 2016-04-05 by SAE International in United States
Weight reduction is very important in automotive design because of stringent demand on fuel economy. Structural optimization of dynamic systems using finite element (FE) analysis plays an important role in reducing weight while simultaneously delivering a product that meets all functional requirements for durability, crash and NVH. With advancing computer technology, the demand for solving large FE models has grown. Optimization is however costly due to repeated full-order analyses. Reanalysis methods can be used in structural vibrations to reduce the analysis cost from repeated eigenvalue analyses for both deterministic and probabilistic problems. Several reanalysis techniques have been introduced over the years including Parametric Reduced Order Modeling (PROM), Combined Approximations (CA) and the Epsilon algorithm, among others. It has been shown that the Modified Combined Approximations (MCA) method - an improvement over CA - is the most efficient reanalysis technique for problems with a large number of degrees of freedom. This paper proposes an improvement of the MCA method using frequency shifts. Numerical examples are presented and results are compared with existing methods.
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