The Experts below are selected from a list of 288 Experts worldwide ranked by ideXlab platform
Matjaž Skrinar - One of the best experts on this subject based on the ideXlab platform.
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On the derivation of symbolic form of stiffness matrix and Load Vector of a beam with an arbitrary number of transverse cracks
Computational Materials Science, 2012Co-Authors: Matjaž Skrinar, Tomaž PliberšekAbstract:Abstract This paper considers derivation of the stiffness matrix and the Load Vector due to a uniform transverse Load for an already-known simplified computational model of a slender beam having an arbitrary number of transverse cracks. The principle of virtual work allows for the coefficients of the stiffness matrix and the Load Vector to be given in clear and closed analytical forms which enable faster and straightforward evaluation. However, since the derivation approach excludes information about the transverse displacement distributions between the nodes the alternatives for the determination of transverse displacements within the finite element are thus further discussed to complete the analysis of multi-cracked beams. Also these results are given in clear and closed analytical forms. The presented stiffness matrix is ideal for modeling any flexural cracks of beams and columns near supports and joints with other structural elements which is, for example, required in earthquake engineering, where the European earthquake engineering design code EC8 requires the cracks to be included in the analysis of concrete elements. Furthermore, as the newly-presented form of stiffness matrix makes the influence of the depths and locations of the cracks to the flexural bending deformation more recognizable that may also open new possibilities in the identification of cracks.
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Elastic beam finite element with an arbitrary number of transverse cracks
Finite Elements in Analysis and Design, 2009Co-Authors: Matjaž SkrinarAbstract:This paper formulates the finite element of a beam with an arbitrary number of transverse cracks. The derivations are based on a simplified computational model, where each crack is replaced by a corresponding linear rotational spring, connecting two adjacent elastic parts. The stiffness and geometrical stiffness matrices thus take into account the effect of flexural bending deformation caused by the presence of the cracks. The expressions for calculating the coefficients of stiffness and geometrical stiffness matrices, as well as the Load Vector of the element, are presented in closed forms. Since the corresponding interpolation functions were implemented in the derivations, transverse displacements within the finite element can also be obtained. Due to the fact that the number of parameters describing the cracked beam's structure is thus reduced to its minimum, it can be expected that this element could be efficiently implemented, not only in static and stability analysis, but also in inverse identification of cracks in beam-like structures.
Søren Nielsen - One of the best experts on this subject based on the ideXlab platform.
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Identification of aerodynamic damping in wind turbines using time-frequency analysis
Mechanical Systems and Signal Processing, 2017Co-Authors: Bei Chen, Zili Zhang, Xugang Hua, Biswajit Basu, Søren NielsenAbstract:Abstract The paper presents a wavelet-based linearization method for evaluating aerodynamic damping of a wind turbine during operation. The method is used to estimate the aerodynamic damping solely from actual measurements of the dynamic response of the operating wind turbine due to ambient excitation from air turbulence and control forces. Based on the response measurements the generalised displacement, velocity and acceleration Vectors related to a given aeroelastic model and an available aeroelastic code are estimated by a state observer. Then, the external generalised Load Vector, depending on the generalised velocity Vector, is obtained from the aeroelastic code. Next, the external generalised Load Vector is linearized into two parts: a quasi-static Load Vector independent on the generalised velocity Vector and a first order term linearly proportional to the velocity Vector indicating the aerodynamic damping matrix. Filtering technique is applied to evaluate the quasi-static Load Vector from the actual measurements of the structural stiffness force, made up as a product of the time-dependent stiffness matrix and the estimated generalised displacement Vector. Finally, the time-dependent aerodynamic damping matrix has been evaluated by wavelet analysis at each time step. Unlike other inverse-based approaches, this wavelet-based method can avoid calculating the inverse of the velocity Vector covariance matrix, which is singular. The proposed method has been illustrated by a reduced 13-DOF aeroelastic model, which is used to mimic the in situ response measured on the wind turbine.
Dario J Aristizabalochoa - One of the best experts on this subject based on the ideXlab platform.
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second order stiffness matrix and Load Vector of an imperfect beam column with generalized end conditions on a two parameter elastic foundation
Engineering Structures, 2014Co-Authors: Gabriel J Coloradourrea, Dario J AristizabalochoaAbstract:The stiffness matrix and Load Vector for an imperfect Euler–Bernoulli beam-column with generalized end conditions subjected to axial and transverse Loads are presented. The proposed method includes the effects of initial imperfections (i.e., out-of-straightness, out-of-plumbness, and axial Load eccentricities at both ends), a two-parameter elastic foundation, partially restrained sidesway and rotational semirigid connections at both ends, and transverse and end axial Loads (tension or compression) on the stiffness matrix and Load Vector. The proposed method is capable of solving the second-order response and lateral stability, and capturing the phenomenon of deflection reversals in 2D framed structures by using a single segment per element. The effects of shear deformations and torsion along the member are not included in the present research. Three comprehensive examples are provided to show the effectiveness and validity of the proposed matrix method.
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timoshenko beam column with generalized end conditions on elastic foundation dynamic stiffness matrix and Load Vector
Journal of Sound and Vibration, 2008Co-Authors: Luis G Arboledamonsalve, David G Zapatamedina, Dario J AristizabalochoaAbstract:Abstract The dynamic-stiffness matrix and Load Vector of a Timoshenko beam-column resting on a two-parameter elastic foundation with generalized end conditions are presented. The proposed model includes the frequency effects on the stiffness matrix and Load Vector as well as the coupling effects of: (1) bending and shear deformations along the member; (2) translational and rotational lumped masses at both ends; (3) translational and rotational masses uniformly distributed along its span; (3) axial Load (tension or compression) applied at both ends; and (4) shear forces along the span induced by the applied axial Load as the beam deforms according to the “modified shear equation” proposed by Timoshenko. The dynamic analyses of framed structures can be performed by including the effects of the imposed frequency ( ω >0) on the dynamic-stiffness matrix and Load Vector while the static and stability analyses can be carried out by making the frequency ω =0. The proposed model and corresponding dynamic-stiffness matrix and Load Vector represent a general solution capable to solve, just by using a single segment per element, the static, dynamic and stability analyses of any elastic framed structure made of prismatic beam-columns with semi-rigid connections resting on two-parameter elastic foundations. Analytical results indicate that the elastic behavior of framed structures made of beam-columns is frequency dependent and highly sensitive to the coupling effects just mentioned. Three comprehensive examples are presented to show the capacities and validity of the proposed method and the obtained results are compared with the finite element method and other analytical approaches.
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first and second order stiffness matrices and Load Vector of beam columns with semirigid connections
Journal of Structural Engineering-asce, 1997Co-Authors: Dario J AristizabalochoaAbstract:The firstand second-order stiffness matrices and Load Vector of a prismatic beam-column of double symmetrical cross section with semirigid end connections including the effects of end axial Loads (tension or compression) and shear deformations are derived in a classical manner. The derived matrices can be used in the stability, firstand second-order elastic analyses of framed structures with rigid, semirigid, and simple connections. The classical stability functions are utilized in the stiffness matrix and in the Load Vector. The proposed stiffness matrices can also be utilized in the inelastic analysis of frames whose members suffer from flexural degradation or, on the contrary, stiffening at their end connections. The validity of both matrices is verified against available solutions of stability analysis and nonlinear geometric elastic analysis of framed structures. Three examples are included that demonstrate the effectiveness of the proposed matrices.
Michael Muskulus - One of the best experts on this subject based on the ideXlab platform.
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Pareto-Optimal Evaluation of Ultimate Limit States in Offshore Wind Turbine Structural Analysis
Energies, 2015Co-Authors: Michael MuskulusAbstract:The ultimate capacity of support structures is checked with extreme Loads. This is straightforward when the limit state equations depend on a single Load component, and it has become common to report maxima for each Load component. However, if more than one Load component is influential, e.g., both axial force and bending moments, it is not straightforward how to define an extreme Load. The combination of univariate maxima can be too conservative, and many different combinations of Load components can result in the worst value of the limit state equations. The use of contemporaneous Load Vectors is typically non-conservative. Therefore, in practice, limit state checks are done for each possible Load Vector, from each time step of a simulation. This is not feasible when performing reliability assessments and structural optimization, where additional, time-consuming computations are involved for each Load Vector. We therefore propose to use Pareto-optimal Loads, which are a small set of Loads that together represent all possible worst case scenarios. Simulations with two reference wind turbines show that this approach can be very useful for jacket structures, whereas the design of monopiles is often governed by the bending moment only. Even in this case, the approach might be useful when approaching the structural limits during optimization.
Tomaž Pliberšek - One of the best experts on this subject based on the ideXlab platform.
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On the derivation of symbolic form of stiffness matrix and Load Vector of a beam with an arbitrary number of transverse cracks
Computational Materials Science, 2012Co-Authors: Matjaž Skrinar, Tomaž PliberšekAbstract:Abstract This paper considers derivation of the stiffness matrix and the Load Vector due to a uniform transverse Load for an already-known simplified computational model of a slender beam having an arbitrary number of transverse cracks. The principle of virtual work allows for the coefficients of the stiffness matrix and the Load Vector to be given in clear and closed analytical forms which enable faster and straightforward evaluation. However, since the derivation approach excludes information about the transverse displacement distributions between the nodes the alternatives for the determination of transverse displacements within the finite element are thus further discussed to complete the analysis of multi-cracked beams. Also these results are given in clear and closed analytical forms. The presented stiffness matrix is ideal for modeling any flexural cracks of beams and columns near supports and joints with other structural elements which is, for example, required in earthquake engineering, where the European earthquake engineering design code EC8 requires the cracks to be included in the analysis of concrete elements. Furthermore, as the newly-presented form of stiffness matrix makes the influence of the depths and locations of the cracks to the flexural bending deformation more recognizable that may also open new possibilities in the identification of cracks.