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K. Shankar

Bio: K. Shankar is an academic researcher from Indian Institute of Technology Madras. The author has contributed to research in topics: State vector & Transfer matrix. The author has an hindex of 5, co-authored 9 publications receiving 65 citations.

Papers
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TL;DR: In this paper, the stiffness parameters of structural members are identified by a novel inverse scheme based on consistent mass transfer matrix (TM), and the results are experimentally verified using a beam element.
Abstract: The stiffness parameters of structural members are identified by a novel inverse scheme based on consistent mass transfer matrix (TM), and the results are experimentally verified. The parameters are identified from the measurement of the state vector at a starting point, and displacements at few other locations. A new consistent mass-based TM is derived from the dynamic stiffness matrix of a beam element. The state vector at a location is the sum of the internal and external contributions of displacements, forces and moments at that point. When these are multiplied with the TM we obtain the state vector at the adjacent node. The identification algorithm proposed in this inverse problem involves predicting the displacements at certain locations using the TM, and comparing them with the measured displacements at those locations. The mean square deviations between the measured and predicted responses at all locations are minimized using an optimization algorithm, and the optimization variables are th...

15 citations

Journal ArticleDOI
TL;DR: In this paper, a damage detection scheme for multiple crack detection in beams is presented, based on a transfer matrix derived from beam element with two cracks, where a crack is modelled as a hinge, which provides an additional flexibility to the element.
Abstract: A damage detection scheme for multiple crack detection in beams is presented, based on a transfer matrix derived from beam element with two cracks. Based on fracture mechanics principles, a crack is modelled as a hinge, which provides an additional flexibility to the element. Each element is assumed to have two open-edge cracks and a new transfer matrix called two crack transfer matrix is developed using finite element method. Using an inverse approach, the transfer matrix is used to predict cracks in a beam. The state vector at a node includes displacements, forces and moments at that node; when it is multiplied with the transfer matrix, the state vector at the adjacent node can be obtained. The state vector formed at the starting node, known as initial state vector, needs to be estimated, from which state vectors at adjacent nodes are predicted using the transfer matrix. Displacement responses are measured at a few adjacent nodes in the structure. The mean square error between measured and predicted res...

13 citations

Journal ArticleDOI
TL;DR: In this paper, a structural damage detection scheme using Transfer Matrix (TM) is presented, which is suitable for local crack identification in large structures, by different measurement strategies for the initial state vector near the zone of interest.

10 citations

Journal ArticleDOI
TL;DR: In this article, a new method for identification of structural parameters using Damped Transfer Matrices (DTM) and state vectors is proposed, which can be used for the local identification in a zone in a structure without modeling the entire global structure.
Abstract: A new method for identification of structural parameters is proposed using Damped Transfer Matrices (DTM) and state vectors. A new transfer matrix is derived for continuous mass systems including the damping parameters. The state vector at a location is the sum of the internal and external contributions of displacements, forces, and moments at that point, when it is multiplied with the transfer matrix, state vector at the adjacent location is obtained. The structural identification algorithm proposed here involves prediction of displacement responses at selected locations of the structure using DTM and compares them with the measured responses at the respective locations. The mean square deviations between the measured and predicted responses at all locations are minimized using a nonclassical optimization algorithm, and the optimization variables are the unknown stiffness and damping parameters in the DTM. A nonclassical heuristic Particle Swarm Optimization algorithm (PSO) is used, since it is especially suited for global search. This DTM algorithm with successive identification strategy is applied on one element or sub-structure of a structure at a time and identifies all the parameters of adjacent elements successively. The algorithm is applied on numerically simulated experiments of two structures such as ten degrees of freedom lumped mass system and a cantilever with seven finite elements and one sub-structure of a nine member frame structure. Also this algorithm is verified experimentally on a sub-structure of a fixed beam. The main advantage of this algorithm is that it can be used for the local identification in a zone in a structure without modeling the entire global structure.

10 citations

Journal ArticleDOI
TL;DR: In this paper, a line crack in an element and oriented at an arbitrary angle is detected using an inverse time domain formulation, which minimizes the difference between the measured and theoretically predicted accelerations.
Abstract: Damage in a plate in the form of a line crack contained in an element, and oriented at an arbitrary angle is detected using an inverse time domain formulation. The time domain acceleration responses need to be measured at certain locations. The crack damage is modeled using an equivalent orthotropic finite element scheme based on the strain energy equivalence principle. The principle is to minimize the difference between the measured and theoretically predicted accelerations. Since the computational effort of identification using the global finite element model of the plate proved prohibitive, the substructure method was used. The substructure was further condensed of the rotary DOF's for increased computational improvement. In order to identify the location and magnitude of the damage variables, acceleration responses at the substructure interfaces and also a few selected points inside the substructure are required. Using numerically simulated experiments the crack was reliably detected using this method. The damage is identified with the addition of noise as well as at different forcing frequencies. The Genetic Algorithm (GA) and Particle Swarm Optimization (PSO) were used to solve the inverse problem. The PSO algorithm proved superior to GA in convergence and accuracy.

9 citations


Cited by
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Journal ArticleDOI

1,604 citations

01 Dec 2013

185 citations

Journal ArticleDOI
TL;DR: In this paper, the authors considered the high-order vibration characteristics of structures with multi-cracks and established finite element models for concrete steel beam and bridge with cracks under three different conditions and obtained vibration frequency and three order modes through simulation.
Abstract: Complex bridges will inevitably have cracks in operation. Dynamic characteristics with crack structures have been researched central issues. In the past, few researches were conducted from the whole structure of bridges with multi-cracks. In the meanwhile, related experimental research and systematic numerical simulation were lacking. In addition, researches on cracks seldom considered the high-order vibration characteristics of structures with multi-cracks. Aimed at this problem, this paper selected the whole bridge structure which was widely applied in engineering to study dynamic characteristics. For the concrete steel bridge with two cracks, this paper established finite element models for concrete steel beam and bridge with cracks under three different conditions and obtained vibration frequency and three order modes through simulation. Then, this paper analyzed and verified the correctness of numerical simulation result through experiment. Based on the verified model, this paper conducted a systematic analysis and summary, and obtained the following findings: The vibration frequency of concrete steel beams with cracks was obviously affected by cracks. The higher the order was, the greater the impact of cracks on frequency would be and the smaller the impact of cracks on the amplitude of modes would be. With the increased crack depth, the impact on the vibration frequency of concrete steel beams was more obvious. Additionally, crack distance also had some impacts on the dynamic characteristics of concrete steel beams. Numerical simulation model and method in this paper provided foundation and reference for continuing to analyze concrete steel beams with other crack forms or other structural forms. In the meanwhile, the three-dimensional analytical contour in this paper could help engineers to more intuitively understand and valuably apply the change rule of impact of crack depth and position on concrete steel beams.

35 citations

Journal ArticleDOI
TL;DR: In this paper, a new method is devised for locating a single crack in a frame using natural frequency degradations, which is based on simulated noise free and contaminated natural frequency measurements.

32 citations

Journal ArticleDOI
01 Sep 2015
TL;DR: In this work the inverse problem of identification of structural stiffness coefficients of a damped spring-mass system is tackled by using different versions of Ant Colony Optimization (ACO) metaheuristic solely or coupled with the Hooke-Jeeves local search algorithm.
Abstract: In this work the inverse problem of identification of structural stiffness coefficients of a damped spring-mass system is tackled. The problem is solved by using different versions of Ant Colony Optimization (ACO) metaheuristic solely or coupled with the Hooke-Jeeves (HJ) local search algorithm. The evaluated versions of ACO are based on a discretization procedure to deal with the continuous domain design variables together with different pheromone evaporation and deposit strategies and also on the frequency of calling the local search algorithm. The damage estimation is evaluated using noiseless and noisy synthetic experimental data assuming a damage configuration throughout the structure. The reported results show the hybrid method as the best choice when both rank-based pheromone deposit and a new heuristic information based on the search history are used.

23 citations