bluuebunny/crossref_metadata_2025 huggingface dataset:
Experimental Verification of Flow-Induced Vibration Fatigue of a Flexible Tube Array With and Without Strakes
Authors: Tognarelli Michael , Gupta Himanshu , Aubault Alexia , Roddier Dominique
Published: October 2016

The flow-induced vibration fatigue of an array of tubes is a complex problem of practical significance in the offshore oil and gas industry. Simple analytical tools for analyzing isolated tubes lack the capability of directly addressing the array problem, so they require some sort of calibration if they are to be used for this application. Computational fluid dynamics (CFD) and coupled computational fluid-structure interaction programs can also be utilized to address the problem in more detail, but at a significant cost in computing time. In either case, understanding of the phenomena is limited, and relatively little relevant data are available to verify the accuracy of these programs for this application. This paper documents a physical model test performed at the University of California-Berkeley Richmond Field Station Tow Basin with the following objectives: to improve confidence in the understanding of the dynamic performance and fatigue demand on both bare and straked tubes in an arrayed configuration; to estimate the influence of an external super-structure (e.g., the truss section of a floating truss spar platform) on the vibrations of the tubes in the array; and, to generate data for verification or calibration of state-of-the-art or emerging analysis tools. The findings provide new, useful information on both the fatigue of tubes in complex configurations and the effectiveness of suppression devices in these scenarios for fatigue mitigation.
Experimental Investigation of Kinematic Flow Field in the Geometric Similar GTT Tanks
Authors: Wei Zhi-Jun , Wu Chui-Jie , Guan Hui
Published: October 2016

In this paper, the kinematic flow field in geometric similar GTT membrane-type floating liquefied natural gas (FLNG) facilities is investigated. The experiments were conducted in three scaled prismatic tanks at scales of 1/20, 1/40 and 1/60 with sway excitation, and the wave elevations near the two vertical sidewalls were measured. The experimental results demonstrate that the kinematic free surface behavior during a single sway wave impact exhibit non-similarity in the three geometric similar tanks with the same experimental media. It is suggested to perform sloshing model test in the large size model tank in order to evaluate the liquid motion in the real LNG tank.
Sloshing Impact Response in LNG Membrane Carriers: A Response Analysis of the Hull Structure Supporting the Membrane Tanks
Authors: Ringsberg Jonas W. , Liljegren André , Lindahl Ola
Published: October 2016

This study presents the determination of structural response due to sloshing impact loads in LNG carriers with membrane type cargo tanks. These loads are characterized by very short durations and are thus likely to inflict a dynamic amplification in the response of the hull. Finite element analyses are presented using a model representing parts of an LNG membrane tank. The objective was to find and quantify the dynamic amplification factor (DAF) for the structural response towards sloshing impact pressures. The influence of variations in the load characteristics such as load duration, extent of the loaded area, load location as well as the influence of the insulation system was evaluated. The study shows that the response in the studied region of the hull structure experiences significant levels of dynamic amplification during impact loads with specific durations. The response sensitivity analysis also shows that the insulation system (MARK III type) has a large effect on the dynamic behaviour of the hull structure. It has been found to alter the magnitude of the stress and deflection response for key structural members. It also changes the load time durations for which the maximum dynamic amplification occurs and increases the magnitude of the corresponding response DAF. Finally, it has been found that dynamic response gives DAF values of up to 2. The effects have been found to be present for temporal load characteristics commonly occurring in sloshing model tests and full-scale measurements and are therefore likely to occur for a vessel in operation.
Challenges in Structural Engineering Design and Analysis of Offshore Plants Under Probabilistic Vapor Cloud Explosion Loads
Authors: Heo YeongAe
Published: October 2016

Hydrocarbon gas explosion is one of the critical hazards resulting in huge environmental impact as well as loss of valuable assets and lives as observed from the historical disasters in the oil and gas industry. In response to these events, stronger international rules and regulations have been made to ensure safety of these structures. Hence, considerable effort has been devoted to quantify accidental design loads for flammable gas based on probabilistic approaches which requires extensive computational fluid dynamic simulations. Also, demand for 3D nonlinear dynamic finite element structural simulations has increased significantly with rapid progress in computer performance. Some of the major issues and difficulties in structural design and evaluation for probabilistic design loads are discussed in this paper. Uncertainties in explosion hazard analysis which cause large variations in probabilistic explosion responses are reviewed. Some gaps between provisions for design load estimation based on probabilistic approaches versus current structural design and analysis schemes are compared. Finally, it is concluded that there is an urgent need for reliable guidelines for risk-based structural design and simulation for probabilistic explosion design loads.
Nonlinear Dynamic Analysis of Deepwater Steel Lazy Wave Riser Subjected to Imposed Top-End Excitations
Authors: Ruan Weidong , Liu Songhua , Li Yanyao , Bai Yong , Yuan Shuai
Published: October 2016

As an effective solution for deepwater oil/gas export, steel lazy wave riser (SLWR) could effectively accommodate large platform offsets, decouple platform motions from the touchdown point and reduce top tension in deepwater marine environment. Since the SLWR dynamic response is very essential for design phase and fatigue analysis, it has already drawn extensive research attention. This paper puts forward a developed mathematical model on the basis of the rod theory and finite element method to predict the static/dynamic response of deepwater lazy wave riser. Newmark-β method combined with Newton–Raphson iterative method is employed for time domain integration of the riser dynamics. Besides, the effects of hydrodynamic loading and internal flow are considered in the mathematical model. The verification of the propose model can be well demonstrated by comparing with OrcaFlex simulation. Finally, parametric analyses about the buoyancy segment are conducted to study the SLWR dynamic response in the critical zones, like the hang-off point and touchdown zone (TDZ).
Time-Domain Analysis of Substructure of a Floating Offshore Wind Turbine in Waves
Authors: Lin Zi , Yang Jianmin , Tao Longbin , Sayer P. , Ning Dezhi
Published: October 2016

This paper aims to analyze the hydrodynamics of a floating offshore wind turbine (FOWT) in waves. Instead of modeling the incident random wave with the traditional wave spectrum and superposition theory, an impulse response function method was used to simulate the incident wave. The incident wave velocity was evaluated by a convolution of the wave elevation at the original point and the impulse response function in the domain. To check the validity of current wave simulation method, the calculated incident wave velocities were compared with analytical solutions; they showed good agreement. The developed method was then used for the hydrodynamic analysis of the substructure of the FOWT. A direct time-domain method was used to calculate the wave-rigid body interaction problem. The proposed numerical scheme offers an effective way of modeling the incident wave by an arbitrary time series.
An Investigation Into the Limitations of the Panel Method and the Gap Effect for a Fixed and a Floating Structure Subject to Waves
Authors: Peña Blanca , McDougall Aaron
Published: October 2016

The wave-induced motions of vessels moored next to a fixed object and open to the sea impact the operability of many offshore operations, and should be assessed in order to avoid accidents and catastrophes. When analysing vessels moored by a fixed object (e.g. quay-side or platform), time domain simulations have shown numeric instabilities resulting in unreliable outcomes. The origin of the numerical instability might lie in the hydrodynamic added mass and wave radiation damping. This is typically calculated using potential flow methods and influenced by the existence of standing waves in the gap between the two bodies. For certain frequencies, these give negative values, potentially causing instabilities in non-linear (coupled) time domain simulations. In these cases, the vessel can behave unexpectedly, generating energy rather than dissipating it. As such, certain simulations have been disregarded as they are unlikely to accurately represent real-life scenarios.

This paper investigates and compares added mass and damping using two different tools and studies the gap effect when conducting diffraction analysis using 3D panel methods. The work covers a literature study into potential theory, multibody analysis, Computational Fluid Dynamics (CFD) and lid techniques.

This is followed by a study conducted using both panel method and CFD analyses. The results from both approaches have been compared, showing interesting information and the necessity of researching more into the problem addressed in this paper.
How to Deal With Basin Modes When Generating Irregular Waves on Shallow Water
Authors: van Essen Sanne , Pauw Willemijn , van den Berg Joris
Published: October 2016

Modeling shallow-water waves in a basin with a finite length and width introduces challenges related to low-frequency (LF) waves, especially for testing of moored vessels with long natural periods. Waves in this frequency range are also present in reality, as for instance bound set-down waves and unbound free waves formed by the geometry bathymetry. In model basins, additional unwanted LF wave components will be formed as a side-product of the wave generation and due to the basin geometry though. Standing waves over the basin length and width (basin modes) can generally be identified, which are difficult to dampen using beaches. This is the case for every wave basin, as they all have finite dimensions.

Moored structures generally have natural frequencies in the LF range, which may be excited by basin modes with similar frequencies. It is therefore important to understand the natural modes of a basin before tests with moored structures in shallow water are done. The energy of these basin modes increases and their natural frequency decreases with decreasing water depth (waves travel slower in shallow water). Generally, it can be said that the issues with basin modes are present on very shallow water (typically ∼15–30 m water depth full-scale for structures with a length around 200 m at a scale around 1 to 40). The smaller the basin for the same water depth, the higher the basin mode frequencies and the higher the likelihood of resonance problems. The energy and frequencies of the basin modes and their relevance for specific tests depend on the effective length and width of the basin, the water depth, wave conditions and the (mooring stiffness of) the structure under consideration. The influence of these variables is evaluated in the current study. Tests were done in MARIN’s Offshore Basin (OB), but most of the results are also expected to be applicable to other basins. The observed basin mode frequencies during these tests were compared to the theoretical values, and an overview of the unwanted LF wave content as a function of water depth, wave height and period is presented. The energy and shape of individual basin modes is also discussed. Considering these results, a practical approach for future basin projects on shallow water is described.
Wrinkling, Fracture, and Necking: The Various Failure Modes in Maritime Crash
Authors: Atli-Veltin B. , Dekker R. , Brunner S. K. , Walters C. L.
Published: October 2016

Depending on the state of stress, material can fail in a number of different modes during a collision. Three modes are identified here as material separation in the absence of necking, material separation after the onset of necking, and localized buckling/wrinkling. Through a series of case studies, the states of stress present in a collision are analyzed. Of particular interest is leakage in a scaled fuel tank that could not have been predicted by FEA due to resolution and may have been ignored even with sufficient resolution because it was in a region of generally compressive stresses. Following the review of case studies, the aforementioned failure mechanisms are reviewed, and the corresponding states of stress are summarized. It is shown that the current state of technology for failure after the onset of necking is insufficient but quickly improving. Concepts are taken from the sheet metal industry to understand the onset of buckling/wrinkling, but there is little readily available to simulate failure after the initial onset.
Experimental Verification Analysis of Propane Pre-Cooling and Dual Nitrogen Expansion Liquefaction Process Adaptable for Floating Liquid Natural Gas (FLNG) in South China Sea Deep Water Gas Field
Authors: Yu Xichong , Xie Bin , Li Yuxing , Li Yan , Wang Qing , Cheng Bing , Wang Chunsheng
Published: October 2016

Liquefaction process is one of the key technologies of offshore FLNG device and is charged by a few of the company’s patent protection. Due to the special offshore operating environment, the choice of FLNG liquefaction process is different from that of onshore. It is very important that FLNG liquefaction process suitable for the marine environment and the oil and gas properties of the South China Sea. In this paper, the static and dynamic performance of propane pre-cooling and dual nitrogen expansion liquefaction process with independent intellectual property rights have been verified by experiment loop simulation with small scale 2000m3/d and middle scale 20000m3/d. Dynamic simulation experimental measures for liquefying key devices such as cold box placed on the swing experiment platform and propane separation tank and the cold box between difference of liquid level changes, are used to verify offshore adaptability of the liquefaction process. Through the static experiments of a small experimental loop with the scale of 2000m3/d simulation considers the liquefaction rate of 93%, energy consumption 0.42kw.h/m3; Dynamic experimental results through the cold box placed on the swinging platform shows that the heat transfer performance of cold box is not affected when FLNG hull roll wave reached 3.6 degrees. The mid-scale experimental simulation of 20000m3/d show that the liquefaction process has the advantages of simple debugging process, convenient operation, quick shutdown and restart, flexible operation, good adaptability to offshore operating parameters, and can realize 3 sets of refrigeration cycles simulation. The propane pre-cooling and dual nitrogen expansion liquefaction process with independent intellectual property rights through the static and dynamic experiments of small and middle scale experimental loop, is verified to the characteristics of high liquefaction rate, low energy consumption and good offshore adaptability. The liquefaction process with independent intellectual property rights can be used to as one of FLNG facility key technologies to develop offshore gas field and faraway from onshore of the South China Sea.
A Hybrid Numerical Model to Address Fluid Elastic Structure Interaction
Authors: Gangadharan Manoj Kumar , Venkatachalam Sriram
Published: October 2016

Hydroelasticity is an important problem in the field of ocean engineering. It can be noted from most of the works published as well as theories proposed earlier that this particular problem was addressed based on the time independent/ frequency domain approach. In this paper, we propose a novel numerical method to address the fluid-structure interaction problem in time domain simulations. The hybrid numerical model proposed earlier for hydro-elasticity (Sriram and Ma, 2012) as well as for breaking waves (Sriram et al 2014) has been extended to study the problem of breaking wave-elastic structure interaction. The method involves strong coupling of Fully Nonlinear Potential Flow Theory (FNPT) and Navier Stokes (NS) equation using a moving overlapping zone in space and Runge kutta 2nd order with a predictor corrector scheme in time. The fluid structure interaction is achieved by a near strongly coupled partitioned procedure. The simulation was performed using Finite Element method (FEM) in the FNPT domain, Particle based method (Improved Meshless Local Petrov Galerkin based on Rankine source, IMPLG_R) in the NS domain and FEM for the structural dynamics part. The advantage of using this approach is due to high computational efficiency. The method has been applied to study the interaction between breaking waves and elastic wall.
Probabilistic Estimation of Shale Gas Reserves Implementing Fast Marching Method and Monte Carlo Simulation
Authors: Kim Jaejun , Kang Joe M. , Park Yongjun , Lim Seojin , Park Changhyup , Park Jihye
Published: October 2016

This paper evaluates the estimated ultimate recovery for 10-year operation at a shale gas reservoir, implementing FMM (Fast Marching Method) as a surrogate model of full-scale numerical simulation and Monte Carlo simulation as a tool for accessing the uncertainty of FMM-based proxy parameters. Sensitivity analysis shows the significant properties affecting the gas recovery that are enhanced permeability, matrix permeability, and porosity in sequence. Using the statistical distributions of these parameters, this study determines P10, P50, and P90 of the 10-year cumulative gas production and compares them with the values from full-physics simulations. The computing time based on the proxy model is much smaller than that of the full-scale simulations while the prediction accuracy is acceptable. FMM can forecast the production profiles reliably without time-consuming simulation and the integration of Monte-Carlo simulation is able to evaluate the uncertainty of gas recovery, quantitatively.
Fatigue Strength and Angular Distortion of the Full-Penetration Tee Type Joint Fabricated by One-Side Single-Pass Laser-Arc Hybrid Welding
Authors: Gotoh Koji , Tsumura Shuichi
Published: October 2016

Laser-arc hybrid welding is a high-quality welding technology and is expected to improve the productivity of manufacturing hull and offshore structures. Application of this technology allows the replacement of fillet-welded joints in structures with full-penetration welded joints. The fatigue performance and deformation caused by welding will be improved by this replacement. The present study experimentally investigates the fatigue performance and deformation due to welding. Two types of tee joints, which penetrate from one side and both sides, were applied. The investigations confirm the superiority of full-penetration tee joints fabricated by laser-arc hybrid welding over conventional fillet-welded joints.
Simulations of the Response of Coated Circular Plates Subjected to Near-Field Underwater Explosion Using RKDG-FEM
Authors: Jin Zeyu , Yin Caiyu , Chen Yong , Hua Hongxing
Published: October 2016

The early response of coated circular plates subjected to near-field underwater explosion in the experiment (Chen et al., 2015, Marine Structures, 40, pp. 247–266) is simulated using a numerical solver that coupling the Runge-Kutta discontinuous Galerkin method to the finite element method (RKDG-FEM), in which the interactions of the gas bubble, shock waves, deformable structures and cavitation are taken into account. The coupling procedure is based on the modified ghost fluid method with special treatments for the RKDG method. Good agreements are observed between the numerical results and the experimental results of the bare steel plate, the steel plate coated with rubber and the steel plate coated with foam. The calculations show that the soft coating material can reduce the pulse width of the pressure load and the foam coating has a superior protective performance.
Experimental Study on Bubble Collapse Near a Solid Boundary
Authors: Zhang Shuai , Wang Shiping , Liu Yunlong
Published: October 2016

In this paper, we present a high-voltage electric-spark bubble-generating method which can generate a bubble with its maximum radius reaching up to ∼35 mm at a room pressure. Vertical migration and clear liquid jet inside the bubble are captured by a high speed photography. With this method, a series of experiments on bubbles collapse above a solid boundary are carried out under different non-dimensional standoff distances γ (= s/Rm, where s is the vertical distance from the bubble center to the solid boundary and Rm denotes the maximum bubble radius). It is found when bubble is extremely close to the solid boundary (γ < 0.6), the lower surface of the bubble will cling to the solid boundary, which causes the cone-shaped liquid jet to impact on solid boundary directly without buffering of the water layer. With the increase of γ, the bottom of the bubble is gradually away from the solid boundary with an increasing curvature, but the jet inside the bubble remains conical all along. The speed of the jet tip and the migration of the bubble top are also discussed subsequently, aiming to provide a reference for the numerical study. Finally, the critical value of γ is investigated, at which the effect of the buoyancy will compensate the attraction of the solid boundary when the buoyancy parameter of bubble is bout 0.06.
Prediction of Offshore Structural Response Extreme Values by Modified Finite-Memory Nonlinear System Modeling
Authors: Mohd Zaki N. I. , Abu Husain M. K. , Mukhlas N. A. , Najafian G.
Published: October 2016

Offshore structures are exposed to random wave loading in the ocean environment, and hence the probability distribution of the extreme values of their response to wave loading is of great value in the design of these structures. Due to nonlinearity of the drag component of Morison’s wave loading and also due to intermittency of wave loading on members in the splash zone, the response is often non-Gaussian; therefore, simple techniques for derivation of the probability distribution of extreme responses are not available. However, it has recently been shown that the short-term response of an offshore structure exposed to Morison wave loading can be approximated by the response of an equivalent finite-memory nonlinear system (FMNS). Previous investigation has shown that the developed FMNS models perform better for high Hs values and that their performance for low Hs value is not particularly good. In this paper, MFMNS technique, a modified version of FMNS models is discussed. The improvement in MFMNS model is simply achieved by dividing the structure into two zones (Zones 1 and 2) so that the horizontal distance between the nodes in each zone is relatively small compared to the wavelengths. It is shown that MFMNS technique can be used to determine the short-term probability distribution of the extreme responses accurately with great efficiency.
Reliability-Based Design and Assessment for Lifetime Extension of Ageing Offshore Structures
Authors: Mat Soom E. , Abu Husain M. K. , Mohd Zaki N. I. , Azman N. U. , Najafian G.
Published: October 2016

The methodology for Reliability-Based Design and Assessment (RBDA) of an ageing fixed steel offshore structure was established to support detailed re-assessment applied to the management of the structure’s safety, integrity analysis and reliability by evaluating the loading acting on the structure. It is a tool for the high-end analysis of the structure for risk-based design assessment and has been succesfully implemented in the North Sea under Shell operating company. The main purposes of RBDA are to manage a structure’s risk level over its remaining service life and to initiate the cost-efficient inspection or mitigation actions (if required). This method consists of Type I and II uncertainties used to determine the probability of failure for the structure over its remaining service life. However, limited work has been done so far on its application at many different regions, particularly in the South East Asia. Therefore, this paper investigates the robustness of the RBDA methodology applied to fixed offshore structures at shallow waters of Malaysia by considering the native environmental criteria, local authorities’ obligation and company requirements. It is shown that this procedure can efficiently assist in understanding the structure’s failure mechanism and correctly define the relevant type of mitigations required.
A Finite Element Model of 18650 Lithium-Ion Battery for Explosion Caused by Internal Short Circuit
Authors: Wang Lubing , Liu Binghe , Xu Jun
Published: October 2016

The lithium-ion battery (LIB) is widely used in portable devices, power tools and electric vehicles, which becomes one of the most important moving power sources. However, inevitable internal short circuits may cause the pressure inside the battery rising, leading to fire or intensive explosion. In this paper, a finite element (FE) model is established to reasonably capture the major explosion behavior of 18650 battery, one of the most prevailing battery models in electric vehicles, caused by internal short circuit. An explosive load is applied to the 18650 battery FE model based on ABAQUS platform to simulate the internal short circuit. The FE model includes key components such as anode part, cathode part, multi-layered separator and the outside shell. Mechanical parameters are taken from previous studies [1] as well as current mechanical testing, with the consideration of temperature, strain rate and anisotropy effect. Result may provide future in-depth studies to study the lithium-ion battery explosion which are not available from the real-world experiment such to guide the optimal design for safe battery manufacturing.
Experimental Simulation of Self-Trapping Mechanism of CO2 Hydrates in Marine Sediments
Authors: Kim Hak-Sung , Cho Gye-Chun
Published: October 2016

CO2 hydrate-bearing sediments imply that the formation of CO2 hydrates in unconsolidated sediments decreases permeability and increases the stiffness of the sediment system significantly. Therefore, CO2 hydrate-bearing sediments act as cap-rocks which prevent the CO2 leakage from CO2-stored layer. In this study, an experimental simulation of CO2 geological storage into marine unconsolidated sediments was performed. CO2 hydrates were formed during CO2 liquid injection process, resulting in prevention of CO2 upward flow. Temperature, pressure, P-wave velocity, and electrical resistance were measured during the experiment, and their measurement results verify the occurrence of self-trapping effect induced by CO2 hydrate formation.
Design and Construction of an Active Wave Absorber in a Wave Channel
Authors: de Barros Passos Rafael , Fernandes Antonio Carlos , Costa Ramon Romankevicius
Published: October 2016

An important step in the development of new ocean structures is to conduct tests on reduced scale models in tanks that reproduce the environmental conditions of their operation. For the wave modeling in a 2D channel, waves are generated in one of its end by the wave-maker and they should not be reflected back to the tested vessel. If these reflected waves were not absorbed they would interfere into the wave field and consequently interact with the body or structure under investigation, which can reduce considerably the experiment duration and the quality of its results. The simplest solution is the use of a passive beach to absorb the reflected waves, composed by a long ramp at the far end of the channel. As an alternative to these conventional beaches, wave-makers equipped with a designed control system can be used as active absorbers. These so-called active beaches have the advantage that they do not extend into the experimental domain of the basin and, at least in linear theory, low or zero reflection could be achieved. The objective of the present work is to design and construct an active wave absorption system into LOC, Laboratory of Waves and Currents, at COPPE/UFRJ, considering a wave field over the channel with no body or structure interaction. First results showed an absorption level comparable with the passive beach, however a careful tuning process is necessary to minimize the reflection coefficient.
Updating Failure Probability of a Welded Joint in Offshore Wind Turbine Substructures
Authors: Mai Quang A. , Sørensen John D. , Rigo Philippe
Published: October 2016

The operation and maintenance cost of offshore wind turbine substructures contributes significantly in the cost of a kWh. That cost may be lowered by application of reliability- and risk-based maintenance strategies and reliability updating based on inspections performed during the design lifetime. Updating the reliability of a welded joint can theoretically be done using Bayesian updating. However, for tubular joints in offshore wind turbine substructures when considering a two dimensional crack growth and a failure criterion combining brittle fracture and material strength, the updating is quite complex due to the wind turbine loading obtained during operation. This paper solves that updating problem by using the Failure Assessment Diagram as a limit state function. It is discussed how application of the updating procedure can be used for inspection planning for offshore wind turbine substructures, and thus also for reducing the required safety factors at the design stage.
Long-Term Extreme Response of a Vessel Rolling in Random Seas
Authors: Chai Wei , Naess Arvid , Leira Bernt J.
Published: October 2016

In this paper, the long-term extreme response of a vessel rolling in random beam seas is addressed. The long-term response analysis is based on the upcrossing rates of the roll motion under different sea states. However, the nonlinear effects associated with the restoring and damping terms have a significant influence on the high-level response, assessing the corresponding statistics, such as the upcrossing rate, with low probability levels is difficult and time-consuming. In this work, the Markov theory is introduced in order to tackle this problem. Specifically, the random roll excitation moment is approximated as a filtered white noise process by applying a linear filter technique and an efficient four-dimensional (4D) path integration (PI) procedure is applied in order to calculate the response statistics. The long-term analysis of nonlinear roll motion in random seas that takes into considerations of the response statistics obtained by the 4D PI method as well as the variation of the sea states could be a valuable reference for ship stability research.
Assimilating a Time-Domain Representation of a Wave Energy Converter Into a Spectral Wave Model
Authors: Luczko Ewelina , Bailey Helen , Robertson Bryson , Hiles Clayton , Buckham Bradley
Published: October 2016

To accommodate future power demands, wave energy converters (WECs) will be deployed in arrays, but largely unanswered questions of the annual energy production and environmental impact of such installations present regulatory dilemmas. In recent years, Sandia National Laboratories (SNL) has developed a modified version of the Simulating Waves Nearshore (SWAN) wave model to simulate WEC energy extraction in a propagating wave field. The SNL source code modifications to SWAN have facilitated a way to characterize the frequency dependent power absorption of a device in a spectral model using standard WEC parameterizations. The work presented in this paper seeks to build on source code modifications previously made by SNL. A new WEC meta-model, alters the incident wave spectrum based on power extracted from the sea and dissipated by hydrodynamic losses experienced at the WEC. These losses are calculated in an external six degree of freedom (DOF) time domain WEC simulation. The two WEC models were compared in terms of significant wave height reduction in the WEC’s lee and annual power production. The new model reduced the estimated distance required for the waves to recover 95% of the incident wave height by 50% for the same sea state. A 4.5% difference in annual power production was observed for a WEC operating in the lee of another device when deployed off the west coast of Canada.
DNV GL-ST-F101 Combined Loading Criterion: Background and Derivation
Authors: Collberg Leif , Levold Erik
Published: October 2016

The local buckling criterion for combined loading in DNV GL-ST-F101 (DNV-OS-F101) [1] was introduced in its present format in the 2007 revision. The formulation is based on a plasticity theory, modified for strain hardening and, finally, finite element calculations. Derivation of this formula has not been published before and is given in the paper. Further, there is some confusion in the industry with respect to the use of effective force in the formulation which will be explained. This paper is supported by a paper that compares this formulation with tests and other criteria, Fyrileiv et al [2].
Predicting Welding Residual Stress Distributions in P92 Steel Joints Considering the Influence of Solid-State Phase Transformation
Authors: Deng Dean , Murakawa Hidekazu
Published: October 2016

In this study, an advanced computational approach based on SYSWELD software was developed to simulate welding residual stress distributions in P92 steel joints with the consideration of solid-state phase transformation. Using the developed numerical method, we calculated the welding residual stress distribution in a single-pass weld joint, and clarified the influences of volume change, variation of yield strength and phase transformation induced plasticity on the formation of residual stress. Meanwhile, experiment was carried out to measure the welding residual stress distributions in the single-pass joint. The effectiveness of the developed computational approach was verified by the experimental results. In addition, the features of welding residual stress distribution in multi-pass P92 steel joint were discussed based on the results obtained by numerical simulation, and some new viewpoints on welding residual stress in multi-pass P92 steel joints were obtained.
Failure Behavior of RC Slabs Subjected to Medium Velocity Impact
Authors: Beppu Masuhiro , Kataoka Shinnosuke
Published: October 2016

This study is intended to investigate failure mechanism of plain concrete and reinforced concrete slabs subjected to a medium-velocity impact by conducting impact tests. In a series of tests, a steel projectile with a mass of 8.3kg collided a concrete slab with a thickness of 18cm. In order to examine impact response of the concrete specimen, impact load and reaction force were measured. Test results revealed that the impact velocity corresponding to the scabbing limit was about 40m/s and the failure mode of the concrete specimen subjected to the medium-velocity was similar to the punching shear failure.
Hydrodynamic Behavior of an Ultra-Deep Water Decoupled Buoy Supporting Risers
Authors: Claro Cláudia , Cruz Ivan , Karunakaran Daniel , Hepener Gustavo , Ji Chunqun , Ding Yun , Wu Chunfa , Scharnke Jule , de Wilde Jaap , Franciss Ricardo
Published: October 2016

Hybrid risers systems used in recent offshore oil & gas projects to decouple large platform motions from main body of the risers can only support a single riser or a small number of risers. In the Sapinhoa Lula NE FPSO project, the challenge was how to design a riser system comprised of over forty risers and umbilical for each of the two FPSOs in 2,200 meter of deep water. The solution is large submerged Buoys with a unique hull form, each of them capable of supporting twenty plus risers and umbilical. The system is called Buoy Supported Riser system, or BSR system.

Comprehensive analyses have been performed during the design of the BSR system. In-depth study of the BRS’ hydrodynamic behavior has been performed to ensure that it meets all design requirements for a 30 year operation life and can be installed safely. Model tests including VIM tests have been conducted to verify hydrodynamic coefficients for the in-place and installation conditions.

The main objective of this paper is to present the hydrodynamic analysis methodology for the design of BSR system.
Stochastic Characterisation of Ship Hull Damage in Collisions
Authors: Obisesan Abayomi , Sriramula Srinivas , Harrigan John
Published: October 2016

This paper presents the probabilistic characterisation of basic variables of ship structures and their application in characterising ship hull response during collisions. 83 dog-bone samples from mild steel are tested until fracture by axial displacement and basic strength variable data are collected from their resulting stress-strain relations. The data are fitted with suitable probability density functions (PDFs), with the two best PDFs identified from Goodness-of-Fit (GoF) test results. In order to analyse response variability from ship hull collisions, indentation tests are done on six hull plate models by penetrating them with two bulbous bow models. A sampling technique is then used to select probable input design sets from the probabilistic characteristics derived for basic variables. These design sets are propagated through an automated nonlinear finite element (FE) simulation of the hull plate indentation to characterise hull plate response at the onset of rupture.
Numerical Investigation on the Influence of Froude Number on the Hydrodynamic Derivatives of a Container Ship
Authors: Thayale Veedu Rameesha , Krishnankutty Parameswaran
Published: October 2016

Evaluation of maneuverability of a ship at the early design stages is necessary for ensuring safety of its voyage. IMO recommends the test speed or approach speed for the maneuvering predictions as 90–100% of the service speed of the vessel. The confined model tests for ship maneuvering assessment are usually conducted at low speeds and the hydrodynamic derivatives obtained from these tests are used in the equation of motion even when vessel operates at much higher speeds. But the hydrodynamic derivatives and consequently the trajectory predicted using these derivatives differ substantially from the actual maneuvering conditions. Hence the dependency of the derivatives on vessel speed needs to be understood properly to get the correct estimate of the vessel trajectory prediction. This paper investigates the effect of vessel speed (Fn) on hydrodynamic characteristics of a container ship. Straightline test and horizontal planar motion mechanism (HPMM) tests are conducted for a container ship model for different speeds in a CFD environment.
SVR-Based Parametric Identification for Parametric Roll Resonance of Ships in Longitudinal Regular Waves
Authors: Hou Xian-Rui , Zou Zao-Jian
Published: October 2016

Parametric roll resonance, as a nonlinear phenomenon related to ship stability, is particularly apt to happen when a ship is sailing in longitudinal waves. It can generate sudden oscillation with large amplitude up to 30–40 degrees of roll and put the ship and crew in danger. To predict the parametric roll resonance of ships, a suitable model for describing this phenomenon is needed. In this paper, a nonlinear mathematical model considering the strong nonlinear coupling among the heave, roll, and pitch motions of ships is established, and support vector regression (SVR) is applied to identify the unknown damping and restoring coefficients in the mathematical model. To verify the accuracy and validity of SVR in parametric identification, a container ship is considered, and the coupled heave, roll, and pitch motions of the ship in longitudinal regular waves are simulated. Based on the simulated responses, the unknown coefficients in the mathematical model are identified by SVR. Then the coupled heave-roll-pitch motion of the container ship in regular waves is predicted by using the identified coefficients in comparison with the simulated data, and satisfactory agreement is achieved. From this study, it is concluded that SVR can be applied to identify the unknown coefficients in the nonlinear mathematical model for predicting the parametric roll resonance of ships in longitudinal regular waves.
A Review of VIV Responses of Steel Lazy Wave Riser
Authors: Felisita Airindy , Gudmestad Ove T. , Karunakaran Daniel , Martinsen Lars Olav
Published: October 2016

The Steel Lazy Wave Riser (SLWR) configuration is considered as one of the favorable solutions for deepwater applications. This is due to the SLWR’s capability to effectively absorb the dynamic motions from the vessel and the relatively lower cost that it offers. However, the application of SLWRs has its own challenges when it comes to fatigue due to Vortex-Induced Vibrations (VIV). The buoyancy section and the touchdown area may be critical to VIV due to curvature and current exposure onto the area. Furthermore, there is only limited previous research on VIV responses of a SLWR configuration.

This paper presents a parametric study of VIV responses of various SLWR systems. The study location is the deeper area of the Norwegian Continental Shelf. The main parametric variations are water depth, the length of the buoyancy section, the dimension of the buoyancy modules and the hydrocarbon content. These variations result in different lazy wave configurations, which give different trends of VIV responses. The analysis works are performed using the computer programs Riflex and VIVANA.

The observation results show that, for the type of current used in this study, riser configurations at the same water depth tend to have the same level of fatigue life. In addition, risers in shallower water have a lower fatigue life compared to risers in deeper water due to the current profiles used in this study and the higher system stiffness of the risers at shallower water.

The results also show that the buoyant section has only little to modest influence on the VIV-fatigue life. The influence will only become apparent when the buoyancy section creates a sufficiently high arch shape in the lazy wave configuration.

The riser’s selfweight mainly affects the riser’s fatigue life at the upper catenary part of the riser. Although the upper catenary part of the riser generally has sufficient VIV-fatigue lifetime, a riser with lighter content has a lower fatigue life at this part compared to a riser with heavier content.
Radiative Damping of Offshore Wind Turbine Gravity Base Foundations at Low Frequencies
Authors: He Rui , Huang Ting
Published: October 2016

With the fast increasing need of clean energy, more and more offshore wind turbines (OWTs) are being planned or constructed. Some offshore wind turbines are supported on Gravity Base Foundations (GBFs). As tall and slender offshore wind turbines are very sensitivity to the dynamic loadings at low frequencies, if designed improperly, it is likely to cause resonances. On the other hand, most of the designs ignore the radiative damping of GBFs, which will lead to a conservative solution and a cost of more money. In this paper, by referring to three different models, the corresponding vertical, horizontal and rocking damping ratios for a typical GBF at low frequencies are obtained and compared, respectively. With these damping ratios obtained, one can develop a more realistic and economic model to calculate the dynamic responses of offshore wind turbines on GBFs under both vertical and horizontal forces at low frequencies.
A New Flapping-Hydrofoil Wave Power Generating Unmanned Ocean Vehicle
Authors: Sun Tao , Zhao Jiangbin , Yan Xinping , Xu Pengpeng
Published: October 2016

To solve the issue of the energy supply for unmanned ocean vehicles, the ocean wave energy as an abundant and widely distributed renewable clean energy, provides a feasible way. This paper proposes a flapping-hydrofoil method applied to unmanned ocean vehicles, harnessing the ocean wave energy to generate power. The structure of the flapping-hydrofoil wave energy harvester is presented, including the internal transmission device and the design of the hydrofoil. Then the operation modes (buoyancy drive and electric drive) and the application prospects (operating on and under the sea surface) of the flapping-hydrofoil wave energy ocean vehicle are also discussed, with the sincere expectations of further development of the ocean science and technology as well as offshore engineering.
Suspension Design of a Semi-Submersible Platform
Authors: Zhu Hongzhong , Hu Changhong , Liu Yingyi , Liao Kangping
Published: October 2016

With the development of ocean energy exploration, reliable and low cost semi-submersible platforms are expected to develop. The maximum pitching amplitude of a floater for floating offshore wind turbine should be less than a few degrees to avoid fatigue failure. In this paper, a novel conceptual design of a new type semi-submersible with suspensions for suppressing the pitch motion is presented. Many wave energy dissipation devices, such as add-on wave energy converters to a floating platform, could be regarded as the suspension system in our design. Firstly, linear models are applied to approximate the radiation forces and wave exciting forces so that the whole motion system is represented by a state-space model. Then, we show that design of suspensions leads to synthesize a controller via solving a constrained H∞ optimization problem. Finally, numerical examples are performed to verify the design and it can be shown that the pitch motion of the semi-submersible platform is remarkably reduced.
Simulations of Extreme Wave Runup on a Vertical Wall by Analytic Boussinesq Model
Authors: Kurnia R.
Published: October 2016

Wave runup on a vertical wall has both fundamental and practical interest. The wave impact on a structure is an important aspect that must be taken into account in the design of coastal structures. From linear wave theory, it is known that the wave amplitude on a vertical fully reflecting wall is twice the amplitude of the incoming wave. The result may be different for nonlinear dispersive waves. Following [1], we show that the propagation of a short wave group of very long nonlinear monochromatic waves above a flat bottom, can increase the amplitude nonlinearly in the travel to a wall, and produce much higher amplitudes on the wall compared to the initial amplitude: the amplification of such a wave can reach six times the initial amplitude. The strong amplification due to the combined action of nonlinear steepening and dispersion before the wall leads to waves that resemble undular bores. Using the same principles, we show that the propagation of a focusing wave group to a wall that is located at the focusing point of the wave can produce an extreme runup with 11 times amplification of the maximum initial amplitude. The simulations are done by HAWASSI-AB, a spatial-spectral implementation of Analytic Boussinesq model [2].