Dissertation•
Hydroelastic Response of Marine Structures to Impact-induced Vibrations. Hydroelastic Reponse of Marine Structures to Impact-induced Vibrations.
01 Jan 2010-
TL;DR: In this paper, a numerical analysis of the hydroelastic behavior of marine vessels under hydrodynamic impact loads, which causes potentially detrimental local flexural vibrations in the vessel, is presented.
Abstract: HYDROELASTIC RESPONSE OF MARINE STRUCTURES TO IMPACT-INDUCED VIBRATIONS by Nabanita Datta Chair : Armin W. Troesch This research deals with the numerical analysis of the hydroelastic behavior of marine vessels under hydrodynamic impact loads, which causes potentially detrimental local flexural vibrations in the vessel. The objective is to provide the dynamic response spectra for transient water-structure dynamics subject to typical impact loads and time scales, using one-way coupling between the fluid and the structure. The hydrodynamic pressure is assumed to be applied on the rigid plate, and then the plate is modelled to respond elastically. The structural vibrations are assumed not to influence the hydrodynamic pressure field. The changing wetted surface is the prime complexity of the problem. The sweeping load sets the plate into small amplitude vibrations, exciting all its natural frequencies (fundamental and overtones). The time-scales of the problem are : (a) the duration of the forcing when sweeping across the plate, and (b) the natural period of the structure. Assuming small deflections of the structure, normal mode summation is used to calculate the vibratory response. The total deflection is assumed to be a series summation of the modal deflections. When the amplitude of the vibrations is small, the dynamic stresses are directly proportional to the flexural displacement. xx Two configurations of the moving load, i.e. (i) uniform stretching load and (ii) impact load, are applied. The coupled system of modal governing differential equation is non-dimensionalized in space and time, and the Dynamic Loading Factor (DLF) of the loading is numerically evaluated by the fourth-order Runge-Kutta method. The corresponding static deflections are calculated by Galerkin’s method. The ratio of the maximum dynamic deflection to the maximum static deflection is the DLF. This analysis provides recommendations to the structural designer, who typically relies on static analysis. The modal participation spectra relative to the dominant fundamental mode for various impact speeds is used to establish modal truncation guidelines. The variation of the response with respect to space and time, and with respect to various parameters like the aspect ratio, damping ratio, boundary conditions, and deadrise angles has been studied. The change in natural frequencies of the structure due to these parameters, and immersion, has also been evaluated.
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01 Jan 2017
Abstract: The concept of using aluminum as the primary construction material for high speed ships and the hydroelastic behavior of the structure is widely gaining importance as a significant research topic in naval architecture. Aluminum is lighter than steel and hence can be predominantly used in high speed crafts which experiences significant slamming. This thesis work is focused on wedge shaped models. Free fall wedge impact is studied and a FORTRAN 90 computer program is developed to estimate the structural response of the wedge experiencing slamming by the use of matrix methods, finite element techniques and Newmark-Beta numerical time integration methods. The numerical solution is validated by comparison with the static solution. The theoretical hydrodynamic pressures which are used as input for this work was originally developed by using a flat cylinder theory [26]. The wedge drop at 0.6096 m (24 inch) drop height with an impact velocity of v=3.05 m/s is based as the premise and the experimental pressure distributions measured by the pressure-transducers and the theoretical pressure predictions are used as inputs and the structural response is derived. Additionally, the response is compared for three different plate thicknesses and the results are compared against each other. The maximum deflection is comparable to the deflection evaluated from the experiment and tends to attain convergence as well. As the plate thickness reduces there tends to be a significant rise in the deflection values for the wedge plate, in the manner that when the plate thickness is halved there is a deviation of more than 75% in the deflection values as such.
3 citations
Cites methods from "Hydroelastic Response of Marine Str..."
...Datta [4] developed a method to provide the dynamic response spectra to study the transient fluid-structure dynamics representative of impact loads and slamming pressures....
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01 Jan 2016
Abstract: The diverse applications of advanced marine craft ascribed to their high speed and technological advancements has led to the use of stronger and lighter metals in such crafts. High speed, in effect also increases slamming loads as higher speed increases frequency of wave encounter while operating in waves. The present study is limited to wedge impact models. Fundamentally, the study is thus about two-dimensional (2D) wedge impact in water. In an attempt to predict the structural response to impact hydrodynamic force, a beam element based finite element (FE) computer program is written and the results of the code are presented in the thesis. A computational tool is developed to predict the transient elastic response of a 2D wedge under impact force using two different numerical methods. Both explicit and implicit numerical schemes have also been studied in order to apply to the present work. Explicit forth order Runge-Kutta (RK4) method and implicit Newmark-β (NB) method have been used in the present work. Coupling effects between excitation and response are ignored in the present numerical computations. Both the numerical schemes are validated using simple static solution and also modal expansion technique. The hydrodynamic pressure distribution along the bottom of a 20◦ deadrise wedge is computed using a flat cylinder theory (Vorus, 1996). An impact velocity of 9.51 ft/sec is used and two different structural boundary conditions are considered in the present analysis. In addition, three different plate thicknesses have been used in the analysis and the results are compared against each other. Stability of the results is tested using node variation test. The results have shown that maximum deflection is around 8 times more for a pinned-pinned beam when compared to clamped-clamped beam. Also, lower plate thickness yielded very significant deflections in both the boundary conditions.
2 citations
Cites background from "Hydroelastic Response of Marine Str..."
...In a related work, Nabanita [11] studied the response behavior of flexible rectangular isotropic plate under transient impact loads....
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...In a related work, Nabanita [11] studied the response behavior of flexible rectangular isotropic plate under transient impact loads....
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References
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05 Feb 2001
TL;DR: In this article, a modern treatment of the subject, both the theory of inviscid, incompressible, and irrotational aerodynamics and the computational techniques now available to solve complex problems is presented.
Abstract: Low-speed aerodynamics is important in the design and operation of aircraft flying at low Mach number, and ground and marine vehicles. This 2001 book offers a modern treatment of the subject, both the theory of inviscid, incompressible, and irrotational aerodynamics and the computational techniques now available to solve complex problems. A unique feature of the text is that the computational approach (from a single vortex element to a three-dimensional panel formulation) is interwoven throughout. Thus, the reader can learn about classical methods of the past, while also learning how to use numerical methods to solve real-world aerodynamic problems. This second edition has a new chapter on the laminar boundary layer (emphasis on the viscous-inviscid coupling), the latest versions of computational techniques, and additional coverage of interaction problems. It includes a systematic treatment of two-dimensional panel methods and a detailed presentation of computational techniques for three-dimensional and unsteady flows. With extensive illustrations and examples, this book will be useful for senior and beginning graduate-level courses, as well as a helpful reference tool for practising engineers.
1,810 citations
"Hydroelastic Response of Marine Str..." refers background in this paper
...Kunow-Baumhauer [64] investigated the response of a plate to a transient pressure wave load....
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Book•
01 Jan 1985
TL;DR: The Finite Element Method (FE) is the most widely used method for numerical approximation for partial differential equations defining engineering and scientific problems as mentioned in this paper, and it has been widely used in the field of structural engineering.
Abstract: THE FINITE ELEMENT METHOD : Basic Concepts and ApplicationsDarrell Pepper, Advanced Projects Research, Inc. California, and Dr . JuanHeinrich, University of Arizona, TucsonTh i s introductory textbook is designed for use in undergraduate, graduate, andshort courses in structural engineering and courses devoted specifically to thefinite element method. This method is rapidly becoming the most widely usedstandard for numerical approximation for partial differential equations definingengineering and scientific problems.The authors present a simplified approach to introducing the method and a coherentand easily digestible explanation of detailed mathematical derivations andtheory Example problems are included and can be worked out manually Anaccompanying floppy disk compiling computer codes is included and required forsome of the multi-dimensional homework problems.
391 citations
"Hydroelastic Response of Marine Str..." refers methods in this paper
...7) in the fourth-order partial differential equation of G(x,y) and applying Galerkin’s method (Shames and Dym 1991 [63]) Ajl is calculated as follows : ΣpΣr ∫...
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...Considering a flat surface panel with a constant-strength distribution σ per unit area, bounded by four straight lines, (Katz and Plotkin)[63] the velocity potential at an arbitrary point P(x,y,0) is given as follows:...
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...The maximum static deflection of a square CCCC plate under a uniformly distributed load of 1 N/m(2) can be calculated by several methods as explained in Shames and Dym [63] as given below for the following geometric and material properties: L = 1 m, B = 1 m, h = 0....
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381 citations
"Hydroelastic Response of Marine Str..." refers background or methods in this paper
...Dry vibration analysis is first done to generate the dry natural frequencies (Eigen values) and modeshapes (Eigen vectors) of the plate [35-38]....
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...Young [35] analyzed the free vibration of plates by the Ritz method, with various boundary conditions....
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Book•
29 Feb 1980
TL;DR: In this article, the authors present a survey of ship response to wave excitation in the context of dry hulls and other marine structures to waves, including the characteristics of practical hulls.
Abstract: Preface 1. Ship response 2. The dry hull 3. More accurate analysis of hull dynamics 4. The characteristics of practical hulls 5. Ship distortion in still water 6. Wave theory 7. Symmetric generalised fluid forces 8. Symmetric response 9. Transient loading 10. Antisymmetric response to wave excitation 11. Statistical analysis of ship response 12. Responses of other marine structures to waves Bibliography Index.
338 citations
"Hydroelastic Response of Marine Str..." refers background in this paper
...Pioneering work on hydroelasicity has been done by Bishop and Price [1], beginning with the modal dry and wet analyses of the elastic responses of vessels in rough seaways due to hydrostatic and wave loads, followed by local transient impulsive loading anlaysis in regular and irregular seas....
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TL;DR: In this article, a model for a class of water-entry problems characterized by the geometrical property that the impacting body is nearly parallel to the undisturbed water surface and that the impact is so rapid that gravity can be neglected is presented.
Abstract: This paper summarizes and extends some mathematical results for a model for a class of water-entry problems characterized by the geometrical property that the impacting body is nearly parallel to the undisturbed water surface and that the impact is so rapid that gravity can be neglected. Explicit solutions for the pressure distributions are given in the case of two-dimensional flow and a variational formulation is described which provides a simple numerical algorithm for three-dimensional flows. We also pose some open questions concerning the well-posedness and physical relevance of the model for exit problems or when there is an air gap between the impacting body and the water.
295 citations
"Hydroelastic Response of Marine Str..." refers background or methods in this paper
...Howison et al [7] extended Cointe’s model by using three domains in the fluid, formulating the outer pressure and the stretching inner pressure....
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...The inner pressure Pinner is expressed by Howison et al [7] as a stretching transformation with respect to the moving jet head d(t)....
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