Dr. Seyed M. Hashemi,
Department of Aerospace Engineering,
Ryerson University, Toronto (ON),
Canada
Dr. Seyed M. Hashemi is a Professor at Ryerson University, Department of Aerospace Engineering. His research revolves around developing novel analytical, semi-analytical and numerical models and mesh-reduction techniques in order to achieve higher convergence rates in the dynamic analysis of intact and defective, flexible, composite/sandwich structural elements.
Dr. Hashemi has a Bachelor of Science in Mechanical Engineering from Sharif University of Technology (SUT), Tehran/Iran (1990), and a Diplôme D’Études Profondis (DEA) en Mécanique from the Université de Lille I, Flandre Androit, Lille (1992), France. He received his Doctor of Philosophy in 1998 from Laval University, studying numerical modelling of blades and rotating beam-structures. In particular, this work focused on developing a highly convergent Dynamic Finite Element (DFE) method, with applications to the vibration analysis of rotary blades and beam-structures.
Later, he worked as a research associate in the Department of Mechanical Eng., Laval University, and subsequently joined the University of Waterloo, where he worked on a variety of topics related to structural vibration analysis/ modelling/ control, including vibration control of a turbo-Prop engine, tall buildings, … . Dr. Hashemi also collaborated with the Kinesiology Department of the University of Waterloo on several projects, namely passive/active vibration control of Parkinson tremors.
Dr. Hashemi joined Ryerson University in September 2001, where he continues his research work on Finite Elements, Dynamic Finite Element (DFE) and other numerical methods in structural vibration, design, analysis and modelling. To date, he has (co-)authored over 160 publications, including some fifty journal papers, 12 chapters in books and edited volumes, and over 100 conference papers on DFE applications in the areas of structural dynamics, vibration, composites/sandwich structures, and the modeling of MEMS devices, Morphing Wings, Hyperloop Deployable Wheel Subsystem, etc.
Dr. Hashemi is also:
- A licensed Professional Engineer (P.Eng.) in Ontario, Canada,
- Adjunct Professor at the Department of Mechanical and Mechatronics Eng., University of Waterloo, Waterloo (ON), Canada,
- Member of the Centre of Excellence in Smart Structures and Dynamical Systems; Amirkabir University of Technology, I-R-Iran (since July 2013),
- Associate Member of Ryerson Institute for Aerospace Design and Innovation, (RIADI),
- Member of Professional Engineers Ontario (PEO), and OSPE
- Senior member of American Institute of Aeronautics and Astronautics (AIAA), and AIAA Student Branch’s Faculty Advisor (Ryerson University),
- Member of International Institute of Acoustics and Vibration (IIAV), Canadian Aeronautics and Space Institute (CASI), Iranian Society of Acoustics and Vibration (ISAV), Int. Association of Comp. Science and Information Tech (IACSIT), ...
Home page: http://www.ryerson.ca/aerospace/research/Research%20profiles/hashemi.html
E-mail address: smhashem@ryerson.ca
Dynamic Finite Element (DFE) Formulation for Vibration Modelling and Analysis of Structural Elements: Past, Present, and Future Directions
Department of Aerospace Eng., Ryerson University, in general, and recent
research and developments the within the speaker’s research group, in
particular, will be first briefly presented. The speaker’s research mainly
revolves around developing novel analytical, semi-analytical and numerical
models and mesh-reduction techniques in order to achieve higher convergence
rates in the dynamic analysis of intact and defective, flexible structural
elements, made of conventional and advanced materials.
The development of a highly convergent, frequency-dependent, Dynamic Finite
Element (DFE) formulation and its application to vibration analysis of
various structural elements will be presented. The hybrid DFE method is a
fusion of the Galerkin weighted residual formulation and the so-called
‘exact’ Dynamic Stiffness Matrix (DSM) method, where the basis functions of
approximation space are assumed to be the closed form solutions of the
differential equations governing uncoupled vibrations of the system. The use
of resulting (dynamic) trigonometric interpolation (shape) functions leads to
a frequency dependent stiffness matrix, representing both mass and stiffness
properties of the element. Assembly of the element matrices and the
application of the boundary conditions then leads to a frequency dependent
nonlinear eigenproblem. A Wittrick-Williams (W-W) algorithm, based on a Sturm
sequence root counting technique, is then used to extract the system natural
frequencies and modes.
The DFE formulation, developed by the presenter in mid-nineties, was
originally applied to the free vibration analysis of rotating (i.e.,
centrifugally stiffened) beams. Incorporating different accelerations, due to
the presence of gyroscopic, or Coriolis forces, has been possible considering
the fact that the resulting stiffness matrix, in this case, is Hermitian. It
has been demonstrated that the DFE can be advantageously used when the
multiple and/or higher modes of vibrations have to be evaluated. The DFE
formulation was then applied to the free vibration analysis of
(geometrically) coupled bending-torsion beam-structures, without and with
warping, and was later further extended to triply coupled
bending-bending-torsion vibration of centrifugally stiffened, nonuniform
beams and blades. The effects of variable geometric parameters were taken
into account by introducing the so-called ‘deviator terms”, leading to a
Refined formulation (RDFE), which results in very high convergence rates; it
can be justifiably called a “Mesh Reduction Method (MRM)”.
Coupled extension-torsion vibration analysis of such structural elements as
helical springs, braided/twisted wire ropes and cables were also
investigated. The same procedure is equally applicable to the dynamic
analysis of flexible, Circumferentially Uniform Stiffness (CUS), laminated
composite box beams and tubes, exhibiting materially coupled
extension-torsion behavior.
The bending-extension vibrations of both straight and curved
symmetric/asymmetric sandwich beams have also been investigated, where the
face layers follow the Rayleigh beam assumptions, while the core is governed
by Timoshenko beam theory. The first four natural frequencies of an
asymmetric soft-core sandwich beam, obtained using a single-element DFE
model, were found to match with ‘exact’ Dynamic Stiffness Matrix (DSM) data;
a Quasi-Exact (QE-DFE) method.
The DFE has also been applied to the vibration and aeroelastic analysis of
intact and defective laminated composite wing configurations, exhibiting both
material and geometric bending-torsion couplings. The effects of single and
multiple crack and delamination defects on the vibration response of
sandwich/composite and various prestressed beam configurations, subjected to
combined axial load and end moments, have also been investigated. In all case
studies, the comparison between the DFE, exact DSM and FEM results, and those
available in literature has validated the proposed formulation and confirmed
its practical applicability and general superiority over the conventional
FEM.
Finally, the preliminary results for the Dynamic Finite Element (DFE)
formulation, and its application to the free vibration analysis of isotropic
thin (Kirchhoff) rectangular plate configurations are promising. Further
research is presently underway to extend the DFE formulation to the
dynamic/stability analysis of general (i.e., non-rectangular) and multilayer
plates, as well as thick and anisotropic plate/shell elements.
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