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Calibri 83ffff̙̙3f3fff3f3f33333f33333.rTU Delft Repositoryg Puuidrepository linktitleauthorcontributorpublication yearabstract
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departmentresearch group programmeprojectcoordinates)uuid:3b9572dd-090a-4d95-9ccb-e5d41edfa11aDhttp://resolver.tudelft.nl/uuid:3b9572dd-090a-4d95-9ccb-e5d41edfa11a=An effective fluid model for the bending failure of level iceKeijdener, C. (TU Delft Offshore Engineering); Hendrikse, H. (TU Delft Offshore Engineering); Metrikine, A. (TU Delft Offshore Engineering; TU Delft Engineering Structures)In this paper, the efficacy of an effective fluid model (EFM) is studied for replicating the effects that hydrodynamics has on the interaction between level ice, modeled as a semi-infinite Kirchhoff-Love plate, and a downward sloping structure, modeled as a rigid and immobile body. The proposed EFM is based on a distributed frequency-independent added mass and damping coefficient, as well as a damper located at the point of contact with the structure. The optimal value of the three coefficients of the EFM is obtained by minimizing the error of the predicted breaking length and maximum contact force over a range of ice velocities when compared to a true hydrodynamics ISI model that is based on incompressible potential flow. The resulting effective hydrodynamic ISI model has greatly improved performance compared to an ISI model that only accounts for hydrostatics, even when the parameters of the system are changed. Moreover, it is much easier to implement and has significantly faster calculation times than the true hydrodynamic ISI model.8Ice crushing; offshore wind; frequency lock-in; ice floeenconference paper)uuid:d45ddd1f-a57a-4b44-9a9f-19ac61fa289fDhttp://resolver.tudelft.nl/uuid:d45ddd1f-a57a-4b44-9a9f-19ac61fa289f?The effect of hydrodynamics on the bending failure of level ice
In this paper, the bending failure of level ice caused by the interaction with a downward sloping structure is studied in 2D. The focus is on the effect of hydrodynamics on the interaction. This study is done by comparing the predictions of a model that includes both hydrostatics and hydrodynamics with one that only includes hydrostatics.<br/>For both models, the ice is modeled as a semi-infinite Kirchhoff-Love plate that is assumed to float on an infinitely wide fluid layer of finite depth. The fluid pressure exerted on the ice is governed by the nonlinear Bernoulli equation. The ice moves towards the structure, impacts with its downward sloping hull, slides down the structure and ultimately fails in downward bending. Validation of this model shows good agreement with experimental data.<br/>It is shown that the nonlinear term in the Bernoulli equation has a negligible effect on the interaction and can be ignored. The effect of hydrodynamics can thus be attributed to the linear part of the hydrodynamic pressure.<br/>The effect of the rotational inertia of the ice and axial compression is negligible as well. At low velocities, ice fails in a quasi-static manner, while at higher velocities, the failure takes place shortly after the contact initiation. The<br/>transition between these two regimes is marked by a transition velocity that is significantly lower for the hydrodynamic model than for the hydrostatic one. Because of this, it is not desirable to use the hydrostatic model for velocities above the transition velocity.UIce-structure interaction; Level ice; Hydrodynamics; Bending failure; Breaking lengthjournal article:)
2020-06-01Engineering StructuresOffshore Engineering)uuid:0cc4c1e5-bbc9-4305-a66f-c8621ec74085Dhttp://resolver.tudelft.nl/uuid:0cc4c1e5-bbc9-4305-a66f-c8621ec74085Initial results of a study into the estimation of the development of frequency lock-in for offshore structures subjected to ice loading=Hendrikse, H. (TU Delft Offshore Engineering; Norwegian University of Science and Technology); Seidel, Marc (Siemens Wind Power); Metrikine, A. (TU Delft Offshore Engineering; TU Delft Applied Mechanics; Norwegi< an University of Science and Technology); Loset, Sveinung (Norwegian University of Science and Technology)Ice-induced vibrations have to be considered in design of vertically sided offshore structures subjected to loading by sea ice, such as offshore wind turbines and oil- and gas platforms. The interaction between ice and structure may result in high global peak loads and the occurring structural vibrations can contribute significantly to the overall fatigue of the structure. A regime of particular interest is the frequency lock-in regime in which the interaction causes the structure to oscillate at high amplitude with a frequency close to one of its natural frequencies. Assessment of frequency lock-in in the design phase can be done based on simple approaches once for given ice conditions the natural modes to experience frequency lock-in and the range of ice drift velocities for which lock-in develops are known. Determining those modes and velocities is however challenging due to the nonlinear nature of the interaction between ice and structure and limited available reference data. In this paper two methods are applied to determine the structural modes and ice drift velocities required as an input for simplified design approaches. The first method is the application of design standards and estimation formulas available from literature. The second method is the application of a recently developed numerical model for simulation of the interaction. The methods are applied to two existing structures which have experienced frequency lock-in and an offshore wind turbine designed to be employed at a location with mild ice conditions. Results show that the estimation formulas do not match with full-scale observations of the existing structures and can therefore not be applied to obtain input for the simplified design approaches. The second method shows to give simulation results consistent with the full-scale observations. Application to the offshore wind turbine reveals that it is most susceptible to frequency lock-in in the second mode.IceIceIce-induced vibrations induced vibrationsinduced vibrationsinduced vibrations induced vibrations induced vibrations; frequency lock -in; Offshore wind; structural design)uuid:ca5f3a2a-111c-4f6f-91a6-7e4239025cd0Dhttp://resolver.tudelft.nl/uuid:ca5f3a2a-111c-4f6f-91a6-7e4239025cd0'Ice-induced vibrations and ice bucklingHendrikse, H. (TU Delft Applied Mechanics; Norwegian University of Science and Technology); Metrikine, A. (TU Delft Offshore Engineering; TU Delft Applied Mechanics; Norwegian University of Science and Technology)Ice-induced vibrations can occur when flexible, vertically-sided offshore structures are subject to level ice such that the failure mode of ice is predominantly crushing. When the ice is relatively thin, or when the width of the structure is much larger than the ice thickness, the ice tends to buckle and subsequently fail as soon as the stress caused by the buckling exceeds the bending strength of the ice sheet. This type of failure is referred to in this paper as buckling failure. The buckling failure can limit the global load on the structure but not necessarily prevents the development of ice-induced vibrations. Study of the latter in cases when ice fails by mixed crushing and buckling is of interest for the design of offshore structures as well as for the interpretation of model-scale tests which often show buckling as a consequence of the use of relatively thin ice. In this study a phenomenological approach for ice crushing and a model of a wedge beam on elastic foundation are combined, thereby composing a simplified model which incorporates both crushing and flexural motion of the ice sheet. Typical load signals and a failure mode map generated with the model correspond well with model-scale observations in a qualitative sense. The model predicts that ice-induced vibrations of limited duration can develop as long as the buckling failure does not occur within at least one period of intermittent crushing or frequency lock-in. A specific case is discussed for which buck< ling failure would be expected to occur, but sustained intermittent crushing is observed instead, illustrating that buckling does not necessarily limit the development and duration of ice-induced vibrations, but even the opposite could happen. The possibility for ice-induced vibrations to develop in the regime of mixed crushing and buckling failure is further discussed focusing on the effects of the boundary conditions, structural shape and structural and ice properties.[Ice buckling; Ice engineering; Ice loads; Ice-induced vibrations; Ice-structure interaction
2018-11-01Applied Mechanics)uuid:78c5857b-b183-4f41-9621-1aa396809702Dhttp://resolver.tudelft.nl/uuid:78c5857b-b183-4f41-9621-1aa396809702The completeness of the set of modes for various waveguides and its significance for the near-field interaction with vibrating structures+Tsouvalas, A.; Hendrikse, H.; Metrikine, A.
Modal decomposition is often used in geophysics and acoustics for the solution of problems related to wave propagation in elastic or acousto-elastic waveguides. One of the key elements of this method is the solution of an eigenvalue problem for obtaining the roots of the characteristic equation, which may signify either frequencies or wavenumbers. The nature of the roots for the majority of the elastic systems allows for a line search along the real or the imaginary axis in the complex plane. Nonetheless, there exist cases in which eigenvalues become complex-valued requiring thus the use of more advanced algorithms. Most up-to-date algorithms for the solution of complex eigenvalue problems are based on the principle of the argument method for a first gross estimation of the location and the number of the roots within a predefined region, followed by a bisection or steepest descent method for a refinement of the final root position. These techniques are shown to be efficient when the roots are located distinctly apart. In the case of elastic or acousto-elastic waveguides, complex roots do exist and often lie close to each other, thereby not allowing for an efficient application of such algorithms. In this study, an approach is presented in which the real and the imaginary parts of the characteristic equation of several types of waveguides are treated separately in order to define the locus of points in the complex plane where roots may lie. It is shown that next to the real-valued roots, which correspond to propagating modes in the medium, infinitely many imaginary and complex-valued ones do exist which complete the eigenvalue spectrum. The contribution of the latter is rather significant in the vicinity of a load and is very essential for the source-waveguide interaction.jcharacteristic equation; complex eigenvalues; acousto-elastic waveguides; principle of the argument methodLUniversity of Porto, Faculty of Engineering, Department of Civil Engineering!Civil Engineering and GeosciencesStructural Engineering)uuid:8e6d9572-6b1f-4b97-9681-9356cefd3156Dhttp://resolver.tudelft.nl/uuid:8e6d9572-6b1f-4b97-9681-9356cefd3156RThe influence of friction at the ice-structure interface on the induced vibrationsHendrikse, H.; Metrikine, A.V.5Vertically-sided offshore structures occasionally experience sustained vibration due to drifting ice sheets crushing against them. These vibrations may lead to problems associated with structural integrity and safety. Traditionally, three regimes of interaction are distinguished: intermittent crushing, frequency lock-in and continuous brittle crushing. These regimes correspond to the dynamic ice-structure interaction at low-, intermediate- and high ice sheet velocities respectively. In this paper the effect of friction at the ice-structure interface on the frequency lock-in regime is studied. This investigation is a follow-up of a comparison between prediction models and full-scale data for ice induced vibrations which has been carried out in the framework of an Ice Induced Vibrations JIP (IIV JIP). This comparison showed that no simultaneous match could be found for both the structural acceleration of and ice force on cylindrical<U structures. This raised the question of whether or not the neglected in the models frictional interaction at the ice-structure interface could be a reason for such an inconsistency. In order to answer this question the interaction at the ice-structure interface is implemented, in a simplified manner, according to the Coulomb friction law in one of the models tested in the framework of the IIV JIP. In this model it is assumed that the three regimes of the dynamic ice-structure interaction can be described based on the distribution of ice strength in the ice sheet. It is concluded that friction alone cannot explain the large inconsistency in case of cylindrical shaped structures. It is suggested that the way the current models translate the available measurement data to input might be worth further investigation. Effects of friction on the range of velocities for which frequency lock-in might occur are expected to be minimal when a fully confined scenario is considered, although an overall increase in loads is predicted. The influence of friction for scenarios with marginal confinement needs further investigation with a more advanced model.Unigrafia Oy)uuid:588dc546-89f7-4296-bb24-257cab17c7f5Dhttp://resolver.tudelft.nl/uuid:588dc546-89f7-4296-bb24-257cab17c7f5iNovel ice induced vibration testing in a large-scale facility: Deciphering ice induced vibrations, part 1uMaatanen, M.; Loset, S.; Metrikine, A.; Evers, K.U.; Hendrikse, H.; Lonoy, C.; Metrikin, I.; Nord, T.; Sukhorukov, S.%Dalian University of Technology Press)uuid:5ae00145-3038-47b8-ab2f-4a5cdebb4039Dhttp://resolver.tudelft.nl/uuid:5ae00145-3038-47b8-ab2f-4a5cdebb4039A method to measure the added mass and added damping in dynamic ice-structure interation: Deciphering ice induced vibrations, part 3)Hendrikse, H.; Metrikine, A.; Evers, K.U.
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