Impulsive Loads on Interconnected Floating Bodies

2009 ◽  
Author(s):  
Luca Martinelli ◽  
Piero Ruol ◽  
Barbara Zanuttigh
Keyword(s):  
Laboratory Tests ◽  
Scaling Laws ◽  
Floating Body ◽  
Floating Bodies ◽  
Lumped Mass ◽  
Mass System ◽  
Wave Energy Converters ◽  
Impulsive Loads ◽  
Proper Scaling ◽  
Tie Rods

Aim of this contribution is to examine the load on the mooring and on the tie rods of a set of interconnected floating bodies under extreme waves, with particular attention to the layout obliquity. Tests carried out at the IMAGE department of Padova University are briefly presented. It is doubtful how to scale the laboratory tests in the presence of impulsive loads on semi-taught moorings. In order to find proper scaling laws, a numerical model is presented where the chain and the floating body are studied as a lumped mass system. Results, compared to available laboratory tests are encouraging and it appears that the main processes in presence of impulses are correctly represented by the model. Model calibration will be carried out shortly, on the basis of specific ongoing tests on floating Wave Energy Converters.

Torsional Vibrations of a Boiler Feed Pump

1978 ◽  
Vol 100 (4) ◽  
pp. 637-643 ◽  
Author(s):  
A. W. Lees ◽  
K. A. Haines
Keyword(s):  
Flexural Vibration ◽  
Feed Pump ◽  
Lumped Mass ◽  
High Pressure Pump ◽  
Mass System ◽  
Order Of Magnitude ◽  
Vibration Pattern ◽  
Suitable Combination ◽  
Element Technique ◽  
Analytic Models

The paper describes an investigation into the dynamic behavior of a large steam turbine-driven boiler feed pump, following the failure of gearboxes, couplings and bearings. The line consists of a 17 MW turbine driving a four-stage high pressure pump directly and a single-stage booster pump via a 2:1 single-reduction gearbox. Flexural vibration was measured using accelerometers at the bearings and eddy current proximity transducers. The torque transmitted to the gearbox was measured using a four-arm strain gauge bridge mounted in a coupling spacer shaft, the signals being obtained via a telemetry system. The observations showed a complex vibration pattern which was compared with predictions from simple analytic models. A lumped mass system accurately predicted the order of magnitude of oscillatory torque as a function of frequency, given the inevitable errors in gear manufacture. It was shown that the choice of flexible coupling has a crucial effect on the response. The methods of calculation have been generalized to give an accurate model of a system with distributed mass. This is achieved formally using the dynamic Green’s function approach or, for detailed results by a finite-element technique. It was shown that a change of coupling alters the dynamic torque of the system. Hence the effects of a number of changes were calculated and a suitable combination of couplings and gearbox were chosen to implement the practical solution to the problem. The basis for the choice is described and the implications for more general design criteria are discussed.

Seismic response and retrofit of industrial brick masonry chimneys

1992 ◽  
Vol 19 (1) ◽  
pp. 117-128 ◽  
Author(s):  
A. Ghobarah ◽  
T. Baumber
Keyword(s):  
Seismic Response ◽  
Ground Motion ◽  
Strong Motion ◽  
Brick Masonry ◽  
Wind Loading ◽  
Earthquake Ground Motion ◽  
Lumped Mass ◽  
Mass System ◽  
Higher Modes ◽  
Recent Earthquakes

During recent earthquakes, the documented cases of collapsed unreinforced brick masonry industrial chimneys are numerous. Observed modes of structural failure are either total collapse or sometimes collapse or damage of the top third of the structure. The objective of this study is to analyze and explain the modes of observed failure of masonry chimneys during earthquake events, and to evaluate two retrofit systems for existing chimneys in areas of high seismicity. The behaviour of the masonry chimney, when subjected to earthquake ground motion, was modelled using a lumped mass system. Several actual strong motion records were used as input to the model. The shear, moment, and displacement responses to the earthquake ground motion were evaluated for various chimney configurations. It was found that the failure of the chimney at its base is the result of the fundamental mode of vibration. Failure at the top third of the structure due to the higher modes of vibration is possible when the chimney is subjected to high frequency content earthquakes. Higher modes, which are normally not of concern under wind loading, were shown to be critical in seismic design. Post-tensioning and the reinforcing steel cage were found to be effective retrofit systems. Key words: masonry, chimneys, behaviour, analysis, design, retrofit, dynamic, earthquakes, seismic response.

scholarly journals Viscous-flow-based investigation of Cloaking phenomenon among multi-floating bodies and experimental verification

2019 ◽  
Vol 272 ◽  
pp. 01016
Author(s):  
Z K Wang ◽  
G H He ◽  
Z G Zhang ◽  
Y H Meng
Keyword(s):  
Experimental Research ◽  
Scattered Wave ◽  
Floating Body ◽  
Offshore Platforms ◽  
Floating Bodies ◽  
Cfd Simulations ◽  
Wave Drift ◽  
Real Coded Genetic Algorithm ◽  
Drift Force ◽  
Interaction Problem

The safety of mooring systems on offshore platforms seems more and more significant with the utilization of offshore space and resources, so the reduction of wave drift force is the key issue in this wave-body interaction problem. The wave drift force acting on the inner floating body surrounded by multiple small floating bodies can be reduced obviously with the occurrence of a phenomenon, which is called the Cloaking phenomenon. The Cloaking phenomenon refers to the reduction or complete elimination in amplitude of the scattered waves. In this paper, a real-coded genetic algorithm was used to optimize the parameters of outer floating bodies to minimize the scattered wave energy, and then the wave drift force acting on the inner body can be reduced. Furthermore, associated CFD simulations and experimental research were conducted with the above optimized parameters to investigate and verify the Cloaking phenomenon more systemically. It is shown that the wave drift force acting on the inner floating body in the Cloaking configuration can be reduced obviously both in numerical and experimental research, and the reduction of the wave drift force is closely related to the change of wave field around the structure.

scholarly journals Generalized eigenfunction method for floating bodies

2011 ◽  
Vol 667 ◽  
pp. 544-554 ◽  
Author(s):  
COLM J. FITZGERALD ◽  
MICHAEL H. MEYLAN
Keyword(s):  
Time Domain ◽  
Water Waves ◽  
Equations Of Motion ◽  
Linear Equations ◽  
Two Dimensions ◽  
Floating Body ◽  
Floating Bodies ◽  
Abstract Wave Equation ◽  
Generalized Eigenfunction ◽  
The Time Domain

We consider the time domain problem of a floating body in two dimensions, constrained to move in heave and pitch only, subject to the linear equations of water waves. We show that using the acceleration potential, we can write the equations of motion as an abstract wave equation. From this we derive a generalized eigenfunction solution in which the time domain problem is solved using the frequency-domain solutions. We present numerical results for two simple cases and compare our results with an alternative time domain method.

3D SPH Simulation of Wave Interaction Between Wave Energy Converters: Towards Optimum Wave Power Absorption in Wave Farms

2020 ◽  
Author(s):  
N. Sasikala ◽  
S. A. Sannasiraj ◽  
Richard Manasseh
Keyword(s):  
Wave Energy ◽  
Oscillation Amplitude ◽  
Excitation Frequency ◽  
Ocean Waves ◽  
Dynamic Responses ◽  
Q Factor ◽  
Floating Bodies ◽  
Sustainable Resources ◽  
Wave Energy Converters ◽  
Energy Converters

Abstract Ocean waves are one of the sustainable resources of renewable energy for carbon-free electricity. For cost-effective commercial-scale projects, Wave Energy Converters (WECs) are deployed in arrays with optimum spacing as an alternative for a large (oscillatory) device in isolation. It has been found that when the wave excitation frequency is close to the resonant frequency of the WEC, the efficiency factor of energy farms, called q-factor, increases with the oscillation amplitude of the device. It has been found that the maximum absorbed energy of WECs depends directly on array configuration as that the radiated and incident wave fields interfere to direct the energy flux in the ocean towards the floating bodies. In this paper, the fully nonlinear interaction between two 3D floating bodies in close proximity and excited near its’ resonance is studied using Weakly Compressible Smoothed Particle Hydrodynamics (WCSPH). Apart from the calculations of q factor, hydrodynamic forces acting on the floating bodies and their dynamic responses are also calculated. An optimum array of WECs is proposed.

Nonlinear Normal Modes and Localization in Elastic Vibro-Impact Systems With Multiple Constraints

2007 ◽  
Author(s):  
David Wagg
Keyword(s):  
Mathematical Formulation ◽  
Normal Modes ◽  
Nonlinear Normal Modes ◽  
Degree Of Freedom ◽  
Lumped Mass ◽  
Localized Modes ◽  
Impact Oscillator ◽  
Mass System ◽  
Nonlinear Normal ◽  
Two Degree Of Freedom

In this paper we consider the dynamics of compliant mechanical systems subject to combined vibration and impact forcing. Two specific systems are considered; a two degree of freedom impact oscillator and a clamped-clamped beam. Both systems are subject to multiple motion limiting constraints. A mathematical formulation for modelling such systems is developed using a modal approach including a modal form of the coefficient of restitution rule. The possible impact configurations for an N degree of freedom lumped mass system are considered. We then consider sticking motions which occur when a single mass in the system becomes stuck to an impact stop, which is a form of periodic localization. Then using the example of a two degree of freedom system with two constraints we describe exact modal solutions for the free flight and sticking motions which occur in this system. A numerical example of a sticking orbit for this system is shown and we discuss identifying a nonlinear normal modal basis for the system. This is achieved by extending the normal modal basis to include localized modes. Finally preliminary experimental results from a clamped-clamped vibroimpacting beam are considered and a simplified model discussed which uses an extended modal basis including localized modes.

Aspects of Novelty Detection

2007 ◽  
Vol 347 ◽  
pp. 3-16 ◽  
Author(s):  
Keith Worden ◽  
Graeme Manson ◽  
Cecilia Surace
Keyword(s):  
Experimental Study ◽  
Structural Health Monitoring ◽  
Health Monitoring ◽  
Novelty Detection ◽  
Fe Model ◽  
Offshore Structure ◽  
Lumped Mass ◽  
Aircraft Wing ◽  
Mass System ◽  
Detection Techniques

The object of this paper is to illustrate the use of novelty detection techniques in Structural Health Monitoring (SHM) by the consideration of a number of case studies of varying complexity, from a simple lumped-mass system to an FE model of an offshore structure to an experimental study of an aircraft wing.

scholarly journals Experimental dataset and numerical simulation of floating bodies transport in open-channel flow

2020 ◽  
Vol 22 (5) ◽  
pp. 1161-1181
Author(s):  
Elisabetta Persi ◽  
Gabriella Petaccia ◽  
Stefano Sibilla ◽  
Pilar Brufau ◽  
José Ignacio García-Palacin
Keyword(s):  
Channel Flow ◽  
Water Surface ◽  
Open Channel ◽  
Numerical Models ◽  
Rectangular Channel ◽  
Open Channel Flow ◽  
Body Motion ◽  
Lagrangian Model ◽  
Floating Body ◽  
Floating Bodies

Abstract Numerical models trying to faithfully represent the movement of floating bodies transport in open-channel flow require experimental data for validation. In order to provide an adequate dataset, flume experiments were carried out to analyse the transport of singular and grouped rigid bodies floating on the water surface. Both cylindrical and spherical samples were employed: they were released in a rectangular channel under steady conditions in one-dimensional (plain channel) and two-dimensional (2D) configurations using one rectangular side obstacle, one smooth side obstacle or two rectangular alternate obstacles. The outcomes of the experiments are the planar displacement and the rotation of the samples, which are related to the flow field in the different configurations. The detailed experimental analysis of the floating body motion provides information for the calibration of numerical models simulating floating bodies transport. This dataset is thus employed for the validation of the Eulerian–Lagrangian model ORSA2D_WT, highlighting its strengths and improvable aspects. Similar applications could be carried out with any 2D model which performs the simulation of discrete elements moving on the water surface.

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