Dr. Mehdi Ahmadian Profile

Dr. Mehdi Ahmadian

Professor and Director at Virginia Polytechnic Institute and State Univ

SPIE Involvement:

Author

Publications (24)

Proceedings Article | 27 April 2011 Paper

Active control of structures with adaptive modified positive position feedback

S. Nima Mahmoodi, Mehdi Ahmadian

Proceedings Volume 7977, 79770E (2011) https://doi.org/10.1117/12.880820

KEYWORDS: Actuators, Control systems, Sensors, Vibration control, Feedback control, Adaptive control, Active vibration control, Signal processing, Fourier transforms, Aerospace engineering

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Proceedings Article | 10 April 2010 Paper

Shim stack deflection analysis in hydraulic dampers using energy methods

Alireza Farjoud, Mehdi Ahmadian

Proceedings Volume 7643, 764325 (2010) https://doi.org/10.1117/12.847893

KEYWORDS: Mathematical modeling, Error analysis, Analytical research, Stress analysis, Resistance, MATLAB, Safety, Smart structures, System integration, Current controlled current source

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This paper presents a detailed analysis of the deflection of the shim stacks used in hydraulic dampers. In hydraulic dampers, a stack of circular disks (shims) is mounted on each side of the main piston to create a pressure drop as the hydraulic oil is passed through the piston from one side to the other. A stiff shim stack creates a high pressure drop across the piston, resulting in high damping. A softer shim stack creates less pressure drop and smaller damping. In practice, shims can be added or removed from the shim stack assembly to tune the damper and generate the desired damping force characteristics as a function of velocity. Tuning a damper requires taking the damper apart, making the changes to the shim stack assembly, and putting the damper back together. This takes a considerable amount of time and effort. Therefore, mathematical modeling of the shim stack assembly becomes a crucial part of the analysis of hydraulic dampers. The goal of the study presented here is to provide a model of the shim stack assembly in order to accurately predict the level of damping for different configurations of the shim stack. The shims that are stacked on each other will deflect under the pressure created by the hydraulic oil, and at the same time, slide against each other. This important characteristic of the shim stack needs to be accounted for in the mathematical model and makes the analysis complicated. For the sake of simplicity, in past studies the shim stack is approximated by the deflection of a single disk and formulas for a single disk are used. This, however, introduces a significant amount of error in the damper hydraulic model. In this paper, the deflection of shim stacks is analyzed and compared with the single disk approximation. It is found that this approximation fails to agree with the more accurate model of representing the shims individually. Therefore, a more detailed and accurate model is necessary for better simulating the damping characteristics of hydraulic dampers as a function of relative velocity across the damper.

Proceedings Article | 10 April 2010 Paper

Force characteristics of a modular squeeze mode magneto-rheological element

Michael Craft, Mehdi Ahmadian, Alireza Farjoud, William Burke, Clement Nagode

Proceedings Volume 7643, 764313 (2010) https://doi.org/10.1117/12.848856

KEYWORDS: Data modeling, Surface finishing, Fluid dynamics, Magnetism, Silicon, Vibration isolation, Magnetic resonance imaging, Manufacturing, Microelectromechanical systems, Safety

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Proceedings Article | 10 April 2010 Paper

Effective energy harvesting devices for railroad applications

C. Nagode, M. Ahmadian, S. Taheri

Proceedings Volume 7643, 76430X (2010) https://doi.org/10.1117/12.847866

KEYWORDS: Magnetism, Prototyping, Energy harvesting, Finite element methods, Electromagnetism, Motion models, Energy efficiency, Electromechanical design, Neodymium, Computer simulations

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Proceedings Article | 9 April 2010 Paper

Active vibration control with optimized modified acceleration feedback equipped with adaptive line enhancer

S. Nima Mahmoodi, Michael Craft, Mehdi Ahmadian

Proceedings Volume 7643, 76430Q (2010) https://doi.org/10.1117/12.847881

KEYWORDS: Feedback control, Actuators, Focus stacking software, Active vibration control, Sensors, Control systems, Vibration control, Signal processing, Smart materials, Shape memory alloys

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Proceedings Article | 9 April 2010 Paper

Ultrasonic acoustic health monitoring of ball bearings using neural network pattern classification of power spectral density

William Kirchner, Steve Southward, Mehdi Ahmadian

Proceedings Volume 7650, 765024 (2010) https://doi.org/10.1117/12.847105

KEYWORDS: Neural networks, Ultrasonics, Acoustics, Statistical analysis, Image classification, Acoustic emission, Data acquisition, Visualization, Classification systems, Artificial neural networks

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Proceedings Article | 7 April 2009 Paper

Nonlinear MR model inversion for semi-active control enhancement

Daniel Reader, Steve Southward, Mehdi Ahmadian

Proceedings Volume 7288, 72880P (2009) https://doi.org/10.1117/12.817631

KEYWORDS: Control systems, Data modeling, Amplifiers, Systems modeling, Device simulation, Instrument modeling, Control systems design, Algorithm development, Performance modeling, Mathematical modeling

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Proceedings Article | 7 April 2009 Paper

Active vibration cancellation of tonal disturbance using orthogonal eigenstructure control

M. Rastgaar, M. Ahmadian, S. Southward

Proceedings Volume 7288, 728823 (2009) https://doi.org/10.1117/12.815639

KEYWORDS: Actuators, Control systems, Electromagnetism, Active vibration control, Data modeling, Vibration control, Matrices, Feedback control, Sensors, Amplifiers

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Proceedings Article | 7 April 2009 Paper

Vibration control of piezoelectrically actuated microcantilevers

S. Nima Mahmoodi, Mehdi Ahmadian

Proceedings Volume 7288, 72881F (2009) https://doi.org/10.1117/12.820071

KEYWORDS: Vibration control, Control systems, Feedback control, Active vibration control, Actuators, Control systems design, Solids, Safety, Microelectromechanical systems, Micromirrors

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Proceedings Article | 7 April 2009 Paper

Rheometer characterization of MR fluids in squeeze mode

Alireza Farjoud, Mehdi Ahmadian, Ryan Cavey

Proceedings Volume 7288, 72880R (2009) https://doi.org/10.1117/12.820068

KEYWORDS: Magnetism, Particles, Iron, Mathematical modeling, Resistance, Amplifiers, Microfluidics, Control systems, Data modeling, Safety

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Proceedings Article | 18 April 2008 Paper

Application of orthogonal eigenstructure control to flight control design

M. Rastgaar Aagaah, M. Ahmadian, S. Southward

Proceedings Volume 6928, 69280P (2008) https://doi.org/10.1117/12.775261

KEYWORDS: Control systems, Actuators, Control systems design, Sensors, Beam guidance systems, Feedback control, Matrices, Aerospace engineering, Error analysis, Vehicle control

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