scholarly journals Dynamic Analysis of Suction Stabilized Floating Platforms

2020 ◽  
Vol 8 (8) ◽  
pp. 587
Author(s):  
Susheelkumar C. Subramanian ◽  
Michaela Dye ◽  
Sangram Redkar
Keyword(s):  
Floquet Theory ◽  
Normal Forms ◽  
Ocean Waves ◽  
Offshore Structures ◽  
Harsh Environment ◽  
Time Varying ◽  
Floating Platform ◽  
Dynamical Characteristics ◽  
Floating Platforms ◽  
Generic Design

The occurrence of parametric resonance due to the time varying behavior of ocean waves could lead to catastrophic damages to offshore structures. A stable structure that could withstand the wave perturbations is quintessential to operate in such a harsh environment. In this work, the authors detail the relevance of a Suction Stabilized Float (SSF) or a Suction Stabilized Floating platform towards such an application. A generic design of a symmetrically shaped float structure along with its inherent stabilization behavior is discussed. Furthermore, the authors extend their prior research on this topic towards modelling the dynamics of SSF and perform stability analysis. The authors demonstrate the dynamical characteristics of SSF analytically using Floquet theory and Normal Forms technique, in this work. Additionally, the simulation results are verified and validated with the numerical methods.

scholarly journals Wave interaction with Floating platform of different shapes and supports using BEM approach

2017 ◽  
Vol 14 (2) ◽  
pp. 115-133
Author(s):  
Anoop I. Shirkol ◽  
Nasar Thuvanismail
Keyword(s):  
Numerical Model ◽  
Elastic Plate ◽  
Wave Interaction ◽  
Wave Force ◽  
Ocean Waves ◽  
Wave Forces ◽  
Thin Elastic Plate ◽  
Floating Platform ◽  
Floating Elastic Plate ◽  
Different Shapes

Wave interaction with a floating thin elastic plate which can be used as floating platform is analyzed using Boundary Element Method (BEM) for different shapes such as rectangular, circular and triangular. Different support conditions are considered and the performance of the floating platform under the action of ocean waves is explored. The study is performed under the assumption of linearized water wave theory and the floating elastic plate is modelled based on the Euler-Bernoulli beam theory. Using Galerkin’s approach, a numerical model has been developed and the hydrodynamic loading on the floating elastic plate of shallow draft (thickness) is investigated. The wave forces are generated by the numerical model for the analysis of the floating plate. The resulting bending moment and optimal deflection due to encountering wave force is analysed. The present study will be helpful in design and analysis of the large floating platform in ocean waves.

Conditional Short-Crested Second Order Waves in Shallow Water and With Superimposed Current

2004 ◽  
Author(s):  
Jo̸rgen Juncher Jensen
Keyword(s):  
Shallow Water ◽  
Wave Spectrum ◽  
Ocean Waves ◽  
Offshore Structures ◽  
Second Order ◽  
Stokes Wave ◽  
Wave Crest ◽  
Wave Kinematics ◽  
Wave Approach ◽  
Non Linear

For bottom-supported offshore structures like oil drilling rigs and oil production platforms, a deterministic design wave approach is often applied using a regular non-linear Stokes’ wave. Thereby, the procedure accounts for non-linear effects in the wave loading but the randomness of the ocean waves is poorly represented, as the shape of the wave spectrum does not enter the wave kinematics. To overcome this problem and still keep the simplicity of a deterministic approach, Tromans, Anaturk and Hagemeijer (1991) suggested the use of a deterministic wave, defined as the expected linear Airy wave, given the value of the wave crest at a specific point in time or space. In the present paper a derivation of the expected second order short-crested wave riding on a uniform current is given. The analysis is based on the second order Sharma and Dean shallow water wave theory and the direction of the main wind direction can make any direction with the current. Numerical results showing the importance of the water depth, the directional spreading and the current on the conditional mean wave profile and the associated wave kinematics are presented. A discussion of the use of the conditional wave approach as design waves is given.

Influence of Wave Group Characteristics on the Motion of a Semisubmersible in Freak Waves

2014 ◽  
Author(s):  
Yanfei Deng ◽  
Jianmin Yang ◽  
Longfei Xiao
Keyword(s):  
Time Lag ◽  
Ocean Waves ◽  
Offshore Structures ◽  
Hydrodynamic Performance ◽  
Wave Crest ◽  
Time Lags ◽  
Wave Group ◽  
Freak Waves ◽  
Motion Responses ◽  
Group Characteristics

In the last few decades, the hydrodynamic performance of offshore structures has been widely studied to ensure their safety as well as to achieve an economical design. However, an increasing number of reported accidents due to rough ocean waves call for in-depth investigations on the loads and motions of offshore structures, particularly the effect of freak waves. The aim of this paper is to determine the sea conditions that may cause the maximum motion responses of offshore structures, which have a significant effect on the loads of mooring systems because of their tight relationship. As a preliminary step, the response amplitude operators (RAOs) of a semisubmersible platform of 500 meters operating depth are obtained with the frequency-domain analysis method. Subsequently, a series of predetermined extreme wave sequences with different wave group characteristics, such as the maximum crest amplitude and the time lag between successive high waves, are adopted to calculate the hydrodynamic performance of the semisubmersible with mooring systems in time-domain. The paper shows that the maximum motion responses not only depend on the largest wave crest amplitude but also the time lags between successive giant waves. This paper will provide an important reference for future designs which could consider the most dangerous wave environment.

scholarly journals Time-Varying Ocean-Like Surface Scattering at Grazing Incidence: Numerical Analysis of Doppler Spectrum at HF/VHF/UHF Bands

2019 ◽  
Vol 2019 ◽  
pp. 1-15 ◽  
Author(s):  
Yidong Hou ◽  
Biyang Wen ◽  
Caijun Wang ◽  
Yonghuai Yang
Keyword(s):  
Incident Angle ◽  
Grazing Incidence ◽  
Ocean Waves ◽  
Incoherent Scattering ◽  
Doppler Spectrum ◽  
Local Perturbation ◽  
Time Varying ◽  
Surface Integral ◽  
Application Range ◽  
Small Perturbation Method

This paper numerically analyzes the characteristics of the Doppler spectrum at HF/VHF/UHF bands from 1D time-varying ocean-like surfaces at grazing incidence in vertical polarization mode. The rough surface is transformed into a local perturbation plane which has its roughness flattened at the edges. The scattering waves include coherent reflected wave and incoherent scattering waves. The surface currents exciting the incoherent scattering waves are regarded as the unknowns which can be solved from the improved surface integral equation using the method of moments (MoM). The incident plane wave allows the incident angle to reach up to 90° (grazing incidence). Then the backscattering wave in the far field can be calculated, and the Doppler spectrum is obtained by coherent Monte-Carlo simulation. Firstly, the validity of the method is verified by comparing with the mature small perturbation method at the HF band. Then the incident wave frequency is asymptotically increased from HF to UHF, and the application range of the SPM is quantitatively evaluated in the Doppler spectrum domain. Finally, the paper focuses on analyzing the characteristics of Doppler spectrum in different bands and different sea states and comparing the influence of nonlinear ocean waves on the Doppler spectrum at different frequencies.

scholarly journals Harnessing the Energy of Tidal Currents: State-of-the-Art and Proposal of Use in EV Charging Points

Proceedings ◽  
2018 ◽  
Vol 2 (23) ◽  
pp. 1504
Author(s):  
Aitor Fernández-Jiménez ◽  
Daniel Fernández-de la Cruz ◽  
Jesús Ruiz-Torres ◽  
Jose Luis Perrino-Blanco ◽  
Raúl Jimeno-Almeida
Keyword(s):  
Electric Vehicles ◽  
State Of The Art ◽  
Tidal Currents ◽  
The State ◽  
Floating Platform ◽  
Charging Station ◽  
Floating Platforms ◽  
Ev Charging ◽  
State Of Art

The implantation of floating platforms for the generation of electricity from tidal currents is possible due to the development of new hydrokinetic microturbines. This article presents an analysis of the situation in which the exploitation of tidal currents is nowadays, the state of art of the existing technologies and the principal projects that are currently underway. In addition, it focuses on the different aspects and criteria to consider for building one of these plants. Finally, an installation by floating platform is proposed to supply electricity to a charging station for electric vehicles near the Nalon river (Spain) with a description of it and an analysis of feasibility.

Nonlinear System Identification in Offshore Structural Reliability

1995 ◽  
Vol 117 (3) ◽  
pp. 171-177 ◽  
Author(s):  
P. D. Spanos ◽  
R. Lu
Keyword(s):  
System Identification ◽  
Nonlinear System ◽  
Structural Reliability ◽  
Transfer Functions ◽  
Nonlinear System Identification ◽  
Simulated Data ◽  
Wave Force ◽  
Ocean Waves ◽  
Offshore Structures ◽  
Analysis And Design

Nonlinear forces acting on offshore structures are examined from a system identification perspective. The nonlinearities are induced by ocean waves and may become significant in many situations. They are not necessarily in the form of Morison’s equation. Various wave force models are examined. The force function is either decomposed into a set of base functions or it is expanded in terms of the wave and structural kinematics. The resulting nonlinear system is decomposed into a number of parallel no-memory nonlinear systems, each followed by a finite-memory linear system. A conditioning procedure is applied to decouple these linear sub-systems; a frequency domain technique involving autospectra and cross-spectra is employed to identify the linear transfer functions. The structural properties and the force transfer parameters are determined with the aid of the coherence functions. The method is verified using simulated data. It provides a versatile and noniterative approach for dealing with nonlinear interaction problems encountered in offshore structural analysis and design.

scholarly journals Wave intensities and slopes in Lagrangian seas

2007 ◽  
Vol 39 (04) ◽  
pp. 1020-1035 ◽  
Author(s):  
Sofia Åberg
Keyword(s):  
Gaussian Random Field ◽  
Gaussian Model ◽  
Wave Model ◽  
Ocean Waves ◽  
Offshore Structures ◽  
Sea Surface ◽  
Lagrangian Model ◽  
Level Crossing ◽  
Wave Slamming ◽  
Wave Slope

In many applications, such as remote sensing or wave slamming on ships and offshore structures, it is important to have a good model for wave slope. Today, most models are based on the assumption that the sea surface is well described by a Gaussian random field. However, since the Gaussian model does not capture several important features of real ocean waves, e.g. the asymmetry of crests and troughs, it may lead to unconservative safety estimates. An alternative is to use a stochastic Lagrangian wave model. Few studies have been carried out on the Lagrangian model; in particular, very little is known about its probabilistic properties. Therefore, in this paper we derive expressions for the level-crossing intensity of the Lagrangian sea surface, which has the interpretation of wave intensity, as well as the distribution of the wave slope at an arbitrary crossing. These results are then compared to the corresponding intensity and distribution of slope for the Gaussian model.

scholarly journals Towards the Rapid Design of Engineered Systems Through Deep Neural Networks

2018 ◽  
Author(s):  
Christopher McComb
Keyword(s):  
Fluid Dynamics ◽  
Neural Networks ◽  
Deep Neural Networks ◽  
Ocean Waves ◽  
Offshore Structures ◽  
Computational Approaches ◽  
Oil Platforms ◽  
Analysis And Synthesis ◽  
Engineered Systems ◽  
Computationally Intensive

The design of a system commits a significant portion of the final cost of that system. Many computational approaches have been developed to assist designers in the analysis (e.g., computational fluid dynamics) and synthesis (e.g., topology optimization) of engineered systems. However, many of these approaches are computationally intensive, taking significant time to complete an analysis and even longer to iteratively synthesize a solution. The current work proposes a methodology for rapidly evaluating and syn- thesizing engineered systems through the use of deep neural networks. The proposed methodology is applied to the analysis and synthesis of offshore structures such as oil platforms. These structures are constructed in a ma- rine environment and are typically designed to achieve specific dynamics in response to a known spectrum of ocean waves. Results show that deep learning can be used to accurately and rapidly synthesize and analyze off- shore structure.

scholarly journals Effects of Time-Varying Fluid on Dynamical Characteristics of Cantilever Beams: Numerical Simulations and Experimental Measurements

2020 ◽  
Vol 2020 ◽  
pp. 1-18
Author(s):  
Mingyu Shao ◽  
Chicheng Ma ◽  
Shuaizhao Hu ◽  
Chuansong Sun ◽  
Dong Jing
Keyword(s):  
Numerical Simulations ◽  
Beam Theory ◽  
Mass Effect ◽  
Added Mass ◽  
Experimental Measurements ◽  
Time Varying ◽  
Cantilever Beams ◽  
Dynamical Characteristics ◽  
The Mathematical Model ◽  
Euler Bernoulli Beam

In order to obtain the effects of time-varying fluid on dynamical characteristics of cantilever beams, this paper gives a comprehensive study of cantilever beams vibrating in a fluid with variable depth. The mathematical model of the cantilever beams in time-varying fluid is derived by combining Euler–Bernoulli beam theory and velocity potential theory, and the influence of the time-varying fluid is discussed. Then, a two-way fluid-structure interaction (FSI) numerical simulation procedure is proposed to calculate the transient responses of the beam. The validity and accuracy are verified according to the comparison among theoretical analysis, numerical simulations, and experimental measurements. Results show that, besides the added mass effect, a damping-like term is also induced due to the motion of the fluid, which is proportional to the moving velocity of the fluid. Both the added mass and the added damping increase with the increment of the width of the beam. The surrounding fluid near the free end affects the beam more significantly. As a negative damping is caused while the fluid decreases, resulting in a much slower decay of the time responses. Therefore, the added damping should not be neglected in the analysis of the FSI problems with time-varying fluid.

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