Methods for Establishing Governing Deck Impact Loads in Irregular Waves

Volume 3: Structures, Safety and Reliability ◽

10.1115/omae2015-42236 ◽

2015 ◽

Author(s):

Jørn Birknes-Berg ◽

Thomas Berge Johannessen

Keyword(s):

Wave Theory ◽

Order Theory ◽

Irregular Waves ◽

Impact Loads ◽

Wave Impact ◽

Sea State ◽

Simple Method ◽

Weakly Nonlinear ◽

Cfd Method ◽

The Individual

As offshore reservoirs are depleted, the seabed may subside. Bottom fixed installations which previously have had sufficient clearance between the deck and the surface may be in a situation where wave impact with the deck must be considered at relevant probability levels. The accurate calculation of deck impact loads with a prescribed probability of occurrence taking into account the relevant properties of the incident waves, presents a considerable challenge. The ShorTCrest JIP has addressed both the distribution of the crest height in extreme sea states, the properties of the largest crests and the deck impact loading on a closed deck. It has been concluded that the largest waves in the sea may be in the process of breaking and thus have properties which deviate significantly from estimates found from weakly nonlinear irregular or regular wave theory /5/. The present paper investigates a simple method to calculate deck impact loads in irregular waves which take into account the irregularity of the sea state and the possibility of wave breaking. The method is a two-step approach. Firstly, a long duration simulation of surface elevation is carried out using second-order theory in order to identify possible deck impact events. The individual wave events which are capable of impacting the deck is then reproduced using a CFD method and the distribution of the deck impact loads is established. The calculations are compared with model test results for wave impact with a large volume deck box in a single steep sea state and with CFD calculations of deck impact with regular waves.

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A Coupled Potential-Viscous Flow Method for Wave Impact on Semi-Submersible Platform Simulation

Volume 1: Offshore Technology ◽

10.1115/omae2018-78311 ◽

2018 ◽

Author(s):

Kangping Liao ◽

Wenyang Duan ◽

QingWei Ma ◽

Binbin Zhao ◽

Shan Ma ◽

...

Keyword(s):

Viscous Flow ◽

Structural Damage ◽

Impact Loads ◽

Computational Accuracy ◽

Wave Impact ◽

Coupled Method ◽

Flow Method ◽

Impact Simulation ◽

Cfd Method ◽

Rough Sea

In rough sea conditions, Semi-submersible platform often suffers from extreme wave impact loads, which can result in structural damage. It is important to predict the wave impact loads on Semi-submersible platform. A CFD method, based on a fixed regular Cartesian grid system, has been developed by the authors for wave impact loads on semi-submersible platform (Liao et al., 2017). However, time consuming is still the bottleneck of CFD method for industry application. In this study, a coupled potential-viscous flow method is developed for improving computational efficiency. In the present method, our CFD in-house code is coupled with MrNWB dynamic libraries using the Euler Overlay Method (EOM) (Baquet et al., 2017). Comparison of the computational accuracy and efficiency between our original CFD in-house code and the present coupled method will be discussed in detail, and benchmark model test will also be used to validate the present coupled method in wave impact simulation.

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Airgap and Wave in Deck Impact Statistics

Volume 3: Structures, Safety and Reliability ◽

10.1115/omae2016-54927 ◽

2016 ◽

Cited By ~ 2

Author(s):

Øistein Hagen ◽

Thomas B. Johannessen ◽

Jørn Birknes-Berg

Keyword(s):

Structural Reliability ◽

Gap Analysis ◽

Impact Load ◽

Wave Theory ◽

Limit States ◽

Wave Impact ◽

Weakly Nonlinear ◽

Horizontal Wave ◽

Wave Heights ◽

Simple Limit

As offshore reservoirs are depleted, the seabed may subside. Bottom fixed installations which have previously had sufficient clearance between the deck and the sea surface may be in a situation where wave impact with the deck must be considered at relevant probability levels. Some statistical aspects associated with the calculation of a deck impact load with a prescribed probability of occurrence are the subject of the present paper. The Short Crest JIP addressed the distribution of the crest height in extreme sea states, the properties of the largest crests and the deck impact loading on a closed deck. It was concluded that the largest waves in the sea may be in the process of breaking and thus have properties which deviate significantly from estimates found from weakly nonlinear irregular or regular wave theory. The present paper addresses findings from the Short Crest JIP regarding • long-term analysis of wave heights and crest, including the effect of wave breaking • air gap analysis for jacket, TLP and semisubmersible using 2nd order time domain simulations over the platform area • statistics for horizontal wave-in-deck impacts for short crested sea versus for long crested sea • structural reliability analysis of jackets for some simple limit states that are governed by loads caused by impact of extreme crests

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Wave Impact Loads Prediction With Compressible Air Effects Using CFD

Volume 2: CFD and FSI ◽

10.1115/omae2019-96026 ◽

2019 ◽

Author(s):

I. Gatin ◽

S. Liu ◽

N. Vladimir ◽

H. Jasak

Keyword(s):

Vertical Wall ◽

Wave Theory ◽

Ideal Gas ◽

Computational Method ◽

Green Water ◽

Impact Loads ◽

Wave Impact ◽

Trapped Air ◽

Air Pockets ◽

Air Compression

Abstract A computational method for predicting wave impact loads where compressible air effects might be present is presented in this paper. The method is a Finite Volume based Computational Fluid Dynamics method where air is modelled as a compressible ideal gas while water is treated as incompressible. Special numerical treatment of the interface based on the Ghost Fluid Method enables capturing the sharp transition in compressible properties of air and water across the free surface, making the method accurate for predicting trapped air pockets during wave impacts or slamming. The approach enables predicting impacts where trapped air pockets play an important role in the loading of the structure due to the capacity to absorb and redistribute wave impact energy. The present approach is validated on a falling water slamming case where trapped air compression is present. Next, a full scale wave breaking impact on a vertical wall is simulated and the results compared to experimental measurements, with trapped air compression effects. Finally, the method is applied on a breakwater green water loading calculation of an Ultra Large Container Ship in an extreme focused wave impact based on the Response Conditioned Wave theory. Motion of the container vessel is calculated directly during the simulation. The calculation is shown to be computed with limited computer resources in reasonable amount of time. Overall the approach proved to be accurate, robust and efficient, providing a tool for assessing wave impact loads with or without compressible air effects.

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A Simple Method for the Evaluation of Internal Doses in Nuclear Medicine

Nuklearmedizin ◽

10.1055/s-0038-1624857 ◽

1974 ◽

Vol 13 (02) ◽

pp. 193-206

Author(s):

L. Conte ◽

L. Mombelli ◽

A. Vanoli

Keyword(s):

Nuclear Medicine ◽

Close Agreement ◽

Whole Body ◽

Simple Method ◽

Rapid Estimation ◽

Absorbed Doses ◽

The Mean ◽

The Individual ◽

Estimation Of Risk

SummaryWe have put forward a method to be used in the field of nuclear medicine, for calculating internally absorbed doses in patients. The simplicity and flexibility of this method allow one to make a rapid estimation of risk both to the individual and to the population. In order to calculate the absorbed doses we based our procedure on the concept of the mean absorbed fraction, taking into account anatomical and functional variability which is highly important in the calculation of internal doses in children. With this aim in mind we prepared tables which take into consideration anatomical differences and which permit the calculation of the mean absorbed doses in the whole body, in the organs accumulating radioactivity, in the gonads and in the marrow; all this for those radionuclides most widely used in nuclear medicine. By comparing our results with dose obtained from the use of M.I.R.D.'s method it can be seen that when the errors inherent in these types of calculation are taken into account, the results of both methods are in close agreement.

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A CFD Study of Focused Extreme Wave Impact on Decks of Offshore Structures

Volume 2: CFD and VIV ◽

10.1115/omae2014-23804 ◽

2014 ◽

Cited By ~ 2

Author(s):

Xin Lu ◽

Pankaj Kumar ◽

Anand Bahuguni ◽

Yanling Wu

Keyword(s):

Real World ◽

Offshore Structures ◽

Air Gap ◽

Irregular Waves ◽

Linear Wave ◽

Extreme Wave ◽

Wave Impact ◽

Loading Test ◽

Wide Range ◽

Wave Maker

The design of offshore structures for extreme/abnormal waves assumes that there is sufficient air gap such that waves will not hit the platform deck. Due to inaccuracies in the predictions of extreme wave crests in addition to settlement or sea-level increases, the required air gap between the crest of the extreme wave and the deck is often inadequate in existing platforms and therefore wave-in-deck loads need to be considered when assessing the integrity of such platforms. The problem of wave-in-deck loading involves very complex physics and demands intensive study. In the Computational Fluid Mechanics (CFD) approach, two critical issues must be addressed, namely the efficient, realistic numerical wave maker and the accurate free surface capturing methodology. Most reported CFD research on wave-in-deck loads consider regular waves only, for instance the Stokes fifth-order waves. They are, however, recognized by designers as approximate approaches since “real world” sea states consist of random irregular waves. In our work, we report a recently developed focused extreme wave maker based on the NewWave theory. This model can better approximate the “real world” conditions, and is more efficient than conventional random wave makers. It is able to efficiently generate targeted waves at a prescribed time and location. The work is implemented and integrated with OpenFOAM, an open source platform that receives more and more attention in a wide range of industrial applications. We will describe the developed numerical method of predicting highly non-linear wave-in-deck loads in the time domain. The model’s capability is firstly demonstrated against 3D model testing experiments on a fixed block with various deck orientations under random waves. A detailed loading analysis is conducted and compared with available numerical and measurement data. It is then applied to an extreme wave loading test on a selected bridge with multiple under-deck girders. The waves are focused extreme irregular waves derived from NewWave theory and JONSWAP spectra.

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Multi-Objective Multidisciplinary Design Optimization of a Robotic Fish System

Journal of Marine Science and Engineering ◽

10.3390/jmse9050478 ◽

2021 ◽

Vol 9 (5) ◽

pp. 478

Author(s):

Hao Chen ◽

Weikun Li ◽

Weicheng Cui ◽

Ping Yang ◽

Linke Chen

Keyword(s):

Design Optimization ◽

Optimization Algorithm ◽

Multidisciplinary Design Optimization ◽

Robotic Fish ◽

Multidisciplinary Design ◽

Optimization Approach ◽

Multi Objective Optimization ◽

Multi Objective ◽

Cfd Method ◽

The Individual

Biomimetic robotic fish systems have attracted huge attention due to the advantages of flexibility and adaptability. They are typically complex systems that involve many disciplines. The design of robotic fish is a multi-objective multidisciplinary design optimization problem. However, the research on the design optimization of robotic fish is rare. In this paper, by combining an efficient multidisciplinary design optimization approach and a novel multi-objective optimization algorithm, a multi-objective multidisciplinary design optimization (MMDO) strategy named IDF-DMOEOA is proposed for the conceptual design of a three-joint robotic fish system. In the proposed IDF-DMOEOA strategy, the individual discipline feasible (IDF) approach is adopted. A novel multi-objective optimization algorithm, disruption-based multi-objective equilibrium optimization algorithm (DMOEOA), is utilized as the optimizer. The proposed MMDO strategy is first applied to the design optimization of the robotic fish system, and the robotic fish system is decomposed into four disciplines: hydrodynamics, propulsion, weight and equilibrium, and energy. The computational fluid dynamics (CFD) method is employed to predict the robotic fish’s hydrodynamics characteristics, and the backpropagation neural network is adopted as the surrogate model to reduce the CFD method’s computational expense. The optimization results indicate that the optimized robotic fish shows better performance than the initial design, proving the proposed IDF-DMOEOA strategy’s effectiveness.

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Focusing of long waves with finite crest over constant depth

Proceedings of The Royal Society A Mathematical Physical and Engineering Sciences ◽

10.1098/rspa.2013.0015 ◽

2013 ◽

Vol 469 (2153) ◽

pp. 20130015 ◽

Cited By ~ 18

Author(s):

Utku Kânoğlu ◽

Vasily V. Titov ◽

Baran Aydın ◽

Christopher Moore ◽

Themistoklis S. Stefanakis ◽

...

Keyword(s):

Source Region ◽

Wave Theory ◽

Long Waves ◽

Constant Depth ◽

Large Wave ◽

Weakly Nonlinear ◽

Scaling Relationships ◽

2011 Japan Tsunami ◽

Wave Heights ◽

Run Up

Tsunamis are long waves that evolve substantially, through spatial and temporal spreading from their source region. Here, we introduce a new analytical solution to study the propagation of a finite strip source over constant depth using linear shallow-water wave theory. This solution is not only exact, but also general and allows the use of realistic initial waveforms such as N -waves. We show the existence of focusing points for N -wave-type initial displacements, i.e. points where unexpectedly large wave heights may be observed. We explain the effect of focusing from a strip source analytically, and explore it numerically. We observe focusing points using linear non-dispersive and linear dispersive theories, analytically; and nonlinear non-dispersive and weakly nonlinear weakly dispersive theories, numerically. We discuss geophysical implications of our solutions using the 17 July 1998 Papua New Guinea and the 17 July 2006 Java tsunamis as examples. Our results may also help to explain high run-up values observed during the 11 March 2011 Japan tsunami, which are otherwise not consistent with existing scaling relationships. We conclude that N -waves generated by tectonic displacements feature focusing points, which may significantly amplify run-up beyond what is often assumed from widely used scaling relationships.

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Wave Impact Loads on the Bottom of Flat Decks

10.1115/omae2021-62990 ◽

2021 ◽

Author(s):

Daniel de Oliveira Costa ◽

Julia Araújo Perim ◽

Bruno Guedes Camargo ◽

Joel Sena Sales Junior ◽

Antonio Carlos Fernandes ◽

...

Keyword(s):

Scale Effects ◽

Offshore Structures ◽

Model Tests ◽

Analytical Models ◽

Navier Stokes ◽

Impact Loads ◽

Wave Impact ◽

Wave Channel ◽

Waves And Currents ◽

The Impact

Abstract Slamming events due to wave impact on the underside of decks might lead to severe and potentially harmful local and/or global loads in offshore structures. The strong nonlinearities during the impact require a robust method for accessing the loads and hinder the use of analytical models. The use of computation fluid dynamics (CFD) is an interesting alternative to estimate the impact loads, but validation through experimental data is still essential. The present work focuses on a flat-bottomed model fixed over the mean free surface level submitted to regular incoming waves. The proposal is to reproduce previous studies through CFD and model tests in a different reduced scale to provide extra validation and to identify possible non-potential scale effects such as air compressibility. Numerical simulations are performed in both experiments’ scales. The numerical analysis is performed with a marine dedicated flow solver, FINE™/Marine from NUMECA, which features an unsteady Reynolds-averaged Navier-Stokes (URANS) solver and a finite volume method to build spatial discretization. The multiphase flow is represented through the Volume of Fluid (VOF) method for incompressible and nonmiscible fluids. The new model tests were performed at the wave channel of the Laboratory of Waves and Currents (LOC/COPPE – UFRJ), at the Federal University of Rio de Janeiro.

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Distribution of Wave Impact Forces From Breaking and Non-Breaking Waves

Volume 4: Ocean Engineering; Ocean Renewable Energy; Ocean Space Utilization, Parts A and B ◽

10.1115/omae2009-79978 ◽

2009 ◽

Cited By ~ 2

Author(s):

Anne M. Fullerton ◽

Thomas C. Fu ◽

Edward S. Ammeen

Keyword(s):

Free Surface ◽

Wave Height ◽

Breaking Waves ◽

Qualitative Assessment ◽

Total Force ◽

Impact Loads ◽

Wave Impact ◽

Data Set ◽

Wave Characteristics ◽

Wide Range

Impact loads from waves on vessels and coastal structures are highly complex and may involve wave breaking, making these changes difficult to estimate numerically or empirically. Results from previous experiments have shown a wide range of forces and pressures measured from breaking and non-breaking waves, with no clear trend between wave characteristics and the localized forces and pressures that they generate. In 2008, a canonical breaking wave impact data set was obtained at the Naval Surface Warfare Center, Carderock Division, by measuring the distribution of impact pressures of incident non-breaking and breaking waves on one face of a cube. The effects of wave height, wavelength, face orientation, face angle, and submergence depth were investigated. A limited number of runs were made at low forward speeds, ranging from about 0.5 to 2 knots (0.26 to 1.03 m/s). The measurement cube was outfitted with a removable instrumented plate measuring 1 ft2 (0.09 m2), and the wave heights tested ranged from 8–14 inches (20.3 to 35.6 cm). The instrumented plate had 9 slam panels of varying sizes made from polyvinyl chloride (PVC) and 11 pressure gages; this data was collected at 5 kHz to capture the dynamic response of the gages and panels and fully resolve the shapes of the impacts. A Kistler gage was used to measure the total force averaged over the cube face. A bottom mounted acoustic Doppler current profiler (ADCP) was used to obtain measurements of velocity through the water column to provide incoming velocity boundary conditions. A Light Detecting and Ranging (LiDAR) system was also used above the basin to obtain a surface mapping of the free surface over a distance of approximately 15 feet (4.6 m). Additional point measurements of the free surface were made using acoustic distance sensors. Standard and high-speed video cameras were used to capture a qualitative assessment of the impacts. Impact loads on the plate tend to increase with wave height, as well as with plate inclination toward incoming waves. Further trends of the pressures and forces with wave characteristics, cube orientation, draft and face angle are investigated and presented in this paper, and are also compared with previous test results.

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