Author
Vasudevan Rajamohan
Other affiliations: Concordia University
Bio: Vasudevan Rajamohan is an academic researcher from VIT University. The author has contributed to research in topics: Finite element method & Beam (structure). The author has an hindex of 12, co-authored 44 publications receiving 599 citations. Previous affiliations of Vasudevan Rajamohan include Concordia University.
Papers
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TL;DR: This review article highlights the various smart materials, activation mechanisms and the shape-changing techniques employed in the 4D printing process and aims to emphasize the potential and viability of4D printing.
145 citations
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TL;DR: In this paper, the authors investigated the properties of a multi-layered beam with MR fluid as a sandwich layer between the two layers of the continuous elastic structure and formulated the governing equations of a multilayer MR beam in the finite element form and using the Ritz method.
Abstract: Magnetorheological (MR) materials exhibit rapid variations in their rheological properties when subjected to varying magnetic field and thus offer superior potential for applications in smart structures requiring high bandwidth. MR sandwich structures can apply distributed control force to yield variations in stiffness and damping properties of the structure in response to the intensity of the applied magnetic field and could thus provide vibration suppression over a broad range of external excitation frequencies. This study investigates the properties of a multi-layered beam with MR fluid as a sandwich layer between the two layers of the continuous elastic structure. The governing equations of a multi-layer MR beam are formulated in the finite element form and using the Ritz method. A free oscillation experiment is performed to estimate the relationship between the magnetic field and the complex shear modulus of the MR materials in the pre-yield regime. The validity of the finite element and Ritz formulations developed is examined by comparing the results from the two models with those from the experimental investigation. Various parametric studies have been performed in terms of variations of the natural frequencies and loss factor as functions of the applied magnetic field and thickness of the MR fluid layer for various boundary conditions. The forced vibration responses of the MR sandwich beam are also evaluated under harmonic force excitation. The results illustrate that the natural frequencies could be increased by increasing the magnetic field while the magnitudes of the peak deflections could be considerably decreased, which demonstrates the vibration suppression capability of the MR sandwich beam.
122 citations
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TL;DR: In this article, the authors investigated the properties and vibration responses of a partially treated multi-layer magnetorheological (MR) fluid beam and formulated the governing equations of a multi-layered MR beam using finite element method and Ritz formulation.
114 citations
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TL;DR: In this article, a full state and limited state flexible mode shape (FMS) based controller for the suppression of transient and forced vibration of a cantilever beam with full and partial magnetorheological (MR) fluid treatments is presented.
Abstract: This paper presents the synthesis of full state and limited state flexible mode shape (FMS) based controllers for the suppression of transient and forced vibration of a cantilever beam with full and partial magnetorheological (MR) fluid treatments. The governing equations of motion of the three layer MR sandwich beam are expressed in the state variable form comprising a function of the control magnetic field. An optimal control strategy based on the linear quadratic regulator (LQR) and a full state dynamic observer is formulated to suppress the vibration of the beam under limited magnetic field intensity. The lower flexural mode shapes of the passive beam are used to obtain estimates of the deflection states so as to formulate a limited state LQR control synthesis. The transient and forced vibration control performances of both the full state observer-based and the limited state FMS-based LQR control strategies are evaluated for the fully as well as partially treated MR-fluid sandwich beams. The results show that the full state observer-based LQR control can substantially reduce the tip deflection responses and the settling time of free vibration oscillations. The limited state LQR control based on the mode shapes effectively adapts to the deflections of the closed loop beam and thus yields vibration attenuation performance comparable to that of the full state LQR controller. The partially treated beam with MR-fluid concentration near the free end also yields vibration responses comparable to the fully treated beam, while the natural frequencies of the partially treated beams are considerably higher.
55 citations
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TL;DR: In this article, the modal damping characteristics of beams partially treated with magnetorheological (MR) fluid elements were studied using the finite element approach and the finite-element method.
Abstract: The modal damping characteristics of beams partially treated with magnetorheological (MR) fluid elements are studied using the modal strain energy approach and the finite element method. Different configurations of a sandwich beam partially treated with MR fluid are considered, including a beam with a cluster of MR fluid segments and a beam with arbitrarily located MR fluid segments. The significance of the location of the MR fluid segments on the modal damping factor is investigated under different end conditions. An optimization problem is formulated by combining finite element analysis with optimization algorithms based on sequential quadratic programming (SQP) and the genetic algorithm (GA) to identify optimal locations for MR fluid treatment to achieve maximum modal damping corresponding to the first five modes of flexural vibration, individually and simultaneously. The solutions of the optimization problem revealed that the GA converges to the global solutions rapidly compared to the SQP method, which in some modal configurations usually entraps in the local optimum. The results suggest that the optimal location of the MR fluid treatment is strongly related to the end conditions and also the mode of vibration. Furthermore, partial treatments with MR fluid can significantly alter the deflection modes of the beam. It has also been demonstrated that optimal locations of the MR fluid segments based on linear combination of the modal damping factors of the first five modes are identical to those obtained based on the first mode, irrespective of the end conditions. However, the optimal locations of the MR fluid segments, identified based on the logarithmic summation of the modal damping factors of the first five modes, would yield a more uniform shear energy distribution compared to that attained by considering individual modes or a linear summation of the individual modes.
47 citations
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TL;DR: This paper presents an update to the authors' previous review paper by summarizing the notable developments in the field of piezoelectric energy harvesting through the past decade.
Abstract: Energy harvesting technologies have been explored by researchers for more than two decades as an alternative to conventional power sources (e.g. batteries) for small-sized and low-power electronic devices. The limited life-time and necessity for periodic recharging or replacement of batteries has been a consistent issue in portable, remote, and implantable devices. Ambient energy can usually be found in the form of solar energy, thermal energy, and vibration energy. Amongst these energy sources, vibration energy presents a persistent presence in nature and manmade structures. Various materials and transduction mechanisms have the ability to convert vibratory energy to useful electrical energy, such as piezoelectric, electromagnetic, and electrostatic generators. Piezoelectric transducers, with their inherent electromechanical coupling and high power density compared to electromagnetic and electrostatic transducers, have been widely explored to generate power from vibration energy sources. A topical review of piezoelectric energy harvesting methods was carried out and published in this journal by the authors in 2007. Since 2007, countless researchers have introduced novel materials, transduction mechanisms, electrical circuits, and analytical models to improve various aspects of piezoelectric energy harvesting devices. Additionally, many researchers have also reported novel applications of piezoelectric energy harvesting technology in the past decade. While the body of literature in the field of piezoelectric energy harvesting has grown significantly since 2007, this paper presents an update to the authors' previous review paper by summarizing the notable developments in the field of piezoelectric energy harvesting through the past decade.
471 citations
01 Aug 2010
TL;DR: Stereolithography is a solid freeform technique (SFF) that was introduced in the late 1980s as discussed by the authors, which has the highest fabrication accuracy and an increasing number of materials that can be processed is becoming available.
Abstract: Stereolithography is a solid freeform technique (SFF) that was introduced in the late 1980s Although many other techniques have been developed since then, stereolithography remains one of the most powerful and versatile of all SFF techniques It has the highest fabrication accuracy and an increasing number of materials that can be processed is becoming available In this paper we discuss the characteristic features of the stereolithography technique and compare it to other SFF techniques The biomedical applications of stereolithography are reviewed, as well as the biodegradable resin materials that have been developed for use with stereolithography Finally, an overview of the application of stereolithography in preparing porous structures for tissue engineering is given
319 citations
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TL;DR: The need for attention directed to the variable stiffness strategy is recognised and the significance of intensive research activities in a highly integrated and multidisciplinary environment emphasised if higher maturity stages of the concepts are to be reached.
244 citations
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TL;DR: An active structure is an engineering structure containing sensors and actuators that, when active, modify the response of the structure to its environment as discussed by the authors, and it is a type of structural control that can be used in extreme environments (space, undersea, polar), contaminated contexts (nuclear, chemical, biological).
239 citations
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TL;DR: A good overview of existing additive manufacturing techniques can be found in this paper, with more focus on the extrusion-based technologies (fused deposition modeling and direct ink writing) due to their scalability, cost efficiency and wider range of material processability.
233 citations