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Paper presented at the The Thirteenth ISOPE Pacific/Asia Offshore Mechanics Symposium, October 14–17, 2018
Paper presented at the The Thirteenth ISOPE Pacific/Asia Offshore Mechanics Symposium, October 14–17, 2018
Paper presented at the The Ninth ISOPE Pacific/Asia Offshore Mechanics Symposium, November 14–17, 2010

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Proceedings Papers

Paper presented at the The Thirteenth ISOPE Pacific/Asia Offshore Mechanics Symposium, October 14–17, 2018

Paper Number: ISOPE-P-18-013

... baroclinic waves in interface (i.e., Internal waves; IWs) due to the different pressure

**variations**. In the ocean, the IWs generation is induced by the interaction between flow and submerged topography (Hsu et. al., 2000); in the lake, the wind plays an important role on producing the surface pressure...
Abstract

ABSTRACT Surface waves (SWs) and internal waves (IWs) are the most common natural phenomena in the ocean. Some oceanographers believe that internal solitary waves have significant influence over the surface waves. In order to observe the interaction between IWs and SWs with different periods over a submerged ridge, laboratory experiments by using plunging wavemaker are run in the study. Laboratory results reveal that the amplitude of SWs decreases as the fluid changes from homogeneous into stratified. At the slow wavemaker speed, the wave period of SWs has a significant decrease when the wave propagates over a ridge; at fast wavemaker speed, the wave period of SWs keep the same value. For the evolution of IWs in strong breaking cases, the wave transmitted amplitude increases as the wave approaches to the ridge. The wave fundamental period of IWs also shorten in slow wavemaker speed but is fixed in fast wavemaker speed. Moreover, the oscillation noises in long period is significant than that in short period. INTRODUCTION In a stratified fluid, external forces (ex., wind or flow etc.,) produce the barotropic waves in surface layer (i.e., Surface waves; SWs) and then induce baroclinic waves in interface (i.e., Internal waves; IWs) due to the different pressure variations. In the ocean, the IWs generation is induced by the interaction between flow and submerged topography (Hsu et. al., 2000); in the lake, the wind plays an important role on producing the surface pressure difference and then internal waves are generated indirectly (Pannard et. al., 2011); at the estuary, the internal waves are generated by the interaction between waves and flow. Internal waves have significant effect on ecology, environment and engineering when they propagate over varied topography (Bourgault et al., 2014; Lamb, 2014). Internal solitary wave (ISW), which is a special type of internal waves, has been studied in previous literature about its generation, transport and dissipation (Grimshaw and Helfrich, 2018; Hsieh et al. 2016, Lamb, 2014). Due to the short flow induced by its larger amplitude of ISW, surface waves becomes small and can be ignored during the interaction.

Proceedings Papers

Paper presented at the The Thirteenth ISOPE Pacific/Asia Offshore Mechanics Symposium, October 14–17, 2018

Paper Number: ISOPE-P-18-039

... true for Darriues turbine. positive pitch angle wind velocity pitch angle different wind velocity

**variation**tip-speed ratio darrieus-type turbine pitch**variation**rotation turbine torque coefficient renewable energy torque wind energy efficiency power coefficient hiraki...
Abstract

ABSTRACT In order to improve the performance of Darrieus turbine, the pitch angles of the blades are varied and tested in a low-speed wind tunnel. First, the pitch angles of the blades are varied with an interval of 15 degrees, to evaluate the possibility of the improvement. The tested tip-speed ratio is ranged from 0.5 to 2.8, which covers the peak of the power, and the generated torque is measured by a torque meter. However, none of the blades exceed the performance of zero-pitched blade. Then, the pitch angles of the blades are varied but with an interval of 2 degrees. As a result, it is found that the blades with pitch angle of 4 and 6 degrees give the highest torque, especially in a tip-speed ratio over 1. By changing the pitch angle of the blade from 0 to 6 degrees, the peak value of the power coefficients is improved by more than 30 percent. INTRODUCTION An ocean current is an attractive renewable energy source for a country surrounded by sea, like Japan. In the ocean currents, a tidal current can reach to a speed above five meters per second, which has an equivalent energy with a wind of typhoon, nearly 47 meters per second. Moreover, the occurrence of a tidal current is highly periodical and easily predicted. A tidal current changes its flow direction by 180 degrees with regular intervals. The Darrieus-type water turbine is suitable for such situation because of its independency to a current direction, as well as simplicity. Actually, the Darrieus turbine is adopted in the demonstration of power generation from a tidal current at Kanmon Strait (Hiraki, et. al. 2010). There are some drawbacks for the Darrieus-type turbine. One of them is the lower efficiency of the power generation, as compared to the horizontal-axis turbines. This is one of the reason why the Darrieus turbine is not commonly used in real situations. The attachment of a device that collects a current into the turbine is an option to enhance the efficiency (Hiraki, et. al. 2013). The incapability of self-starting is also a known problem for a turbine that uses a lift force, which is also true for Darriues turbine.

Proceedings Papers

Paper presented at the The Thirteenth ISOPE Pacific/Asia Offshore Mechanics Symposium, October 14–17, 2018

Paper Number: ISOPE-P-18-091

... engineering vertical force wave force numerical model water depth wave-induced force equation element method investigation numerical investigation velocity potential interaction submerged plate wave amplitude hobem

**variation**horizontal force cylinder time series Numerical...
Abstract

ABSTRACT The potential numerical wave flume is applied in this study to estimate the forces and the moment on a submerged plate in the combined wave-current flow by solving the Laplacian equation based on the higher order boundary element method (HOBEM). The free surface motion is tracked by solving the free surface boundary conditions and is advanced in time using the fourth-order Runge-Kutta scheme. The performance of the potential numerical wave flume is assessed by comparing with the published theoretical results and the experimental measurements. The forces and the moment on the submerged plate alternatively increase to the peak value and then decrease to zero with increasing plate breadth, and they are found to increase with increasing water depth. Additionally, it is found that the use of Doppler shifted solutions is not sufficient for considering the effect of depth-uniform current on waves. The generation of higher harmonics due to a sudden change in water depth and the current-induced form drag are found to make significant contributions to the wave loading. INTRODUCTION The submerged plate, used as a breakwater device, is less dependent on the bottom topography, more economical and can assure open scenic views. It allows seawater to exchange freely between the sheltered region and the open sea to prevent stagnation, pollution, transport of sediment to maintain the general partition of the natural seabed. It has been applied as an efficient breakwater in coastal and offshore zones Thus, investigations on submerged plate have been focused on their reflection and transmission characteristics (Stamos and Hajj, 2001.), or the generation of higher order bound and free harmonic waves that affects the sailing conditions (Brossard and Chagdali, 2001; Lin et al., 2014). However, the effects of wave-induced forces and moment on submerged structures are of practical importance as well to assure the strength and stability of the structure over the design life. Extensive researches have shown that the mutual influence of waves and currents is intensified in shallow waters/coastal areas (Isaacson and Cheung, 1993; Chen et al. 1999). Methods that can provide accurate predictions of forces and moment on submerged structures in combined waves and currents are required for the safe and cost efficient design of submerged structures in coastal areas.

Proceedings Papers

Paper Number: ISOPE-P-18-021

... pressure pore pressure submarine pipeline boundary condition flow obliquity equation upstream oil & gas interaction liquefaction saturation pipeline engineering

**variation**soil permeability artificial intelligence offshore pipeline water depth permeability 3D numerical model for...
Abstract

ABSTRACT A precise prediction of seabed stability involving the fluid-pipe-soil interaction can lead to significant cost reductions by optimising design. Unlike previous investigations, a three-dimensional numerical model for the wave-induced soil response around an offshore pipeline is proposed in this paper. The numerical model was first validated with 2-D experimental data available in the literature. Then, a parametric study will be carried out to examine the effects of wave, seabed characteristics and confirmation of pipeline. Numerical examples demonstrate significant influence of wave obliquity on the wave-induced pore pressures and the resultant seabed liquefaction around the pipeline, which cannot be observed in 2-D numerical simulation. INTRODUCTION Nowadays, many offshore structures have been commonly constructed over the last few decades due to the growing engineering resource in the ocean. Submarine pipelines, as one of the popular offshore infrastructures, have been extensively used for transportation of natural gas and oil from offshore platform, and disposal of industrial as well as municipal waste. To ensure the safety of usage of such submarine pipelines, the coastal engineers have to consider the unexpected loads including the wave, current, and anchor dropping/dredging, which might cause the its stability and decrease its life span. Thus, it is customary to bury the pipeline by trenching and refilling soil whose cost is relatively high and time-consuming (FredsØ e, 2016). As reported in the literature, two well-known main mechanisms of dynamic wave-induced seabed liquefactions are the momentary liquefaction and residual liquefaction, based on in the field measurements and laboratory experiments (Zen and Yamazaki, 1991). The fist mechanism, momentary liquefaction, can occur beneath wave troughs when the great seepage flow is upward directly. Since this kind of liquefaction may be happen within a short duration as the passage of wave trough, it is also called instantaneous liquefaction. The other mechanism, residual liquefaction, takes place as a result from a compacted and cyclic shearing process that the build-up of excess pore pressure in the seabed (Seed and Rahman, 1978). As mention previously, the waves also can induce shear stress in the soil when the waves propagate, which has been analytically investigated by Yamamoto et al (1978). Whereas the wave-induced shear stress has less impact on seabed instability compared to that caused by the previous two mechanism above. This study only focuses on the wave-induced seabed liquefaction incorporating both instantaneous mechanism.

Proceedings Papers

Paper Number: ISOPE-P-18-029

... midstream oil & gas anchor weight anchor dnv method strength pipeline geometry limit state equation offshore pipeline impact energy pipeline concentric ring reliability theory probability pipeline failure probability drop point material property

**variation**failure probability...
Abstract

ABSTRACT With the increase of human activities at sea, it is inevitable that anchors drop into the water due to operating errors, which may lead to failure of pipelines and cause economic damage and environmental pollution. Previous methods of related analysis are mostly based on the DNV-RP-F107 recommended method (hereinafter referred as DNV method). DNV method hardly considers the variation of anchor's size and weight. And it is insensitive to the pipeline geometry and material properties. Based on reliability theory, DNV method is improved to calculate failure probability under the consideration of the above relevant factors. The efficiency of the proposed method is verified by a practical case. Besides, analysis of the influence of various factors on pipeline failure probability is completed in this paper, including anchor weight, size, pipeline geometry and material properties, the distance from the anchor drop point. Meanwhile, considering the variability, the sensitivities of variables to the failure probability are discussed. Study results indicate that the failure probability calculated by DNV method is underestimated in some situations, which can probably cause a loss for pipeline projects. Whereas the proposed method is able to consider much more influences and leads to reasonable results consistent with the actual situation. INTRODUCTION Submarine pipeline is seen as the ‘lifeline’ for offshore oil and gas industry. Pipeline safety is one of the most important problems for engineering practice. Recently, anchors dropping into the sea becomes more frequent due to the increasing human activities at sea. The dropped anchors are likely to impact on pipelines and lead to pipeline failures, which can cause economic damage and environmental pollution. In order to reduce the risk and provide safe design, considerable research efforts have been devoted to risk assessment and reliability analysis of pipelines. In general, methods of the relevant research mainly consist of two categories: one is qualitative analysis, which can study the main influence factors on pipeline failures. Among them, fault tree analysis (FTA) is the most popular methodology and has been extensively applied to pipeline failure analysis. (Wang et al., 2007; Dong et al., 2005; Lavasani et al., 2011). The other one is quantitative analysis, which can determine pipeline failure probability and provide reliable reference for safe design. Katteland et al. (1995) developed a model for risk calculation, and applied it to evaluate the risk of all the installations in the North Sea. Det Norske Veritas (2010) proposed a ubiquitously used method for pipeline risk assessment and failure probability calculation (DNV method). Based on statistics of crane accidents, Det Norske Veritas (2013) also gave the falling probability for typical loads and various objects, which provided abundant references for pipeline risk assessment. On the basic of the above research, Liu et al. (2005) proposed a model to calculate the probability of pipeline being impacted under various anchorage conditions. Ding et al. (2010) modified DNV method and made a risk assessment of pipelines due to third-party activities. Yan et al. (2014) proposed a procedure to estimate the pipeline failure probability caused by anchoring activities. Up to now, to the best of the author's knowledge, quantitative analysis methods are mainly based on DNV method. In some situations, this method is hardly to consider the effect of anchor size and weight on pipeline failure probability. What's more, it is insensitive to the effect of pipeline geometry and material properties, which is not consistent with practice and may cause errors. In order to give an insight into those effects, a method based on reliability theory to calculate pipeline failure probability is proposed.

Proceedings Papers

Paper presented at the The Twelfth ISOPE Pacific/Asia Offshore Mechanics Symposium, October 4–7, 2016

Paper Number: ISOPE-P-16-055

... induced by the fluctuating lift. wire arrangement cylinder reservoir surveillance vortex rms strouhal number cylinder case hydrodynamic force diameter ratio reynolds number production control production monitoring coefficient

**variation**shear parameter upstream oil & gas...
Abstract

Abstract Two-dimensional numerical simulations are conducted to examine the effects of tripping wires on the hydrodynamic properties of a stationary cylinder in uniform and shear flows at a fixed Reynolds number of 100. Three sets of numerical tests are carried out: symmetric and asymmetric tripping wire arrangements in a shear flow; symmetric arrangement of tripping wires of various diameters in a uniform flow; and symmetric arrangement of tripping wires placed at a range of distances from the cylinder in a uniform flow. The results of each test are described in terms of hydrodynamic forces and vortex shedding frequency. Introduction Vortex induced vibration (VIV) takes place when a fluid flow passes an elastically mounted bluff body. Earlier studies of VIV focused primarily on the suppression of this phenomenon to minimize its damage caused to engineering structures such as bridges and offshore pipelines. In recent years, a shift towards developing viable renewable energy technologies has led to a technology that harnesses energy from the typically harmful phenomenon of VIV (Raghavan, 2007; Bernitsas et al ., 2008; Nishi et al ., 2012). Since the amount of energy produced by a VIV energy harnessing system is directly related to the amplitude of the transverse oscillations associated with VIV, which in turn depends on the lift force acting on the bluff body, recent research has been focusing on maximizing the amplitude of lift fluctuation and enhancing the motion induced by the fluctuating lift.

Proceedings Papers

Paper presented at the The Twelfth ISOPE Pacific/Asia Offshore Mechanics Symposium, October 4–7, 2016

Paper Number: ISOPE-P-16-024

... layer interaction kinematic pressure

**variation**pressure difference vorticity numerical simulation upper layer plane obstacle cylinder spatiotemporal**variation**interface Numerical tudy on the 3D nteraction between an nternal olitary ave and ertical ylinder Chih-Min Hsieh 1 Ming-Hung...
Abstract

Abstract A finite volume method based Cartesian grids is adopted to solve the Navier-Stokes equations using Improved Delayed Detached Eddy Simulation turbulence model with OpenFOAM for the study the 3D evolution as a large depression internal solitary wave propagates across a vertical cylinder. Numerical results reveal that these significant differences of density and kinematic pressure are found at both sides of the cylinder and the complex vortex is occurred around the cylinder because of partially transmission and reflection effect. Moreover, the kinematic pressure difference may maintain a maximum as the radius is over the critical value in the same physical condition. Introduction Internal solitary waves (ISWs) exist in a density stratified flow and are usually generated by the tide-topography interaction, especially in South China Sea (SCS) (Alford et al., 2015). Due to its large amplitudes up to 170m and strong velocity difference exceeding 2.4 ms-1 between its upper and lower water layer (Chang et al., 2008), an ISW has significant ramification not only in marine ecology but also engineering works in the ocean (Bourgault et al., 2014; Lamb, 2014; Wang et al., 2007). Reports (Lamb, 2014; Reeder et al., 2008) also concludes that (1) self-generation of the vortices with strong turbulent mixing within the water column and (2) waveform inversion across a continental shelf are two of the highlights of an ISW across a slope-shelf topography. As an ISW propagates around large vertical cylinders (i.e., an Island), wave diffraction can be observed significantly in some previous studies (Lynett and Liu, 2002; Tang et al., 2015). For small vertical cylinders, such as deep-sea oil drilling rigs or pipelines, the strong velocity difference induced by an ISW propagation causes the threat to these structures (Cai et al., 2008; Song et al., 2011; Xie et al., 2011). The interaction between surface wave and small cylinder has been vigorously studied in several decades, however, the investigations about discussing that between an ISW and the obstacle has less references, especially at small cylinder. Although some researchers (Cai et al., 2008; Song et al., 2011; Xie et al., 2011) used numerical simulation to discuss the responses between ISWs and the small vertical cylinder, they almost simplified the problem and did not discuss the turbulent effect. In order to further study the 3D interaction between a depression ISW and small vertical cylinder, a series of numerical modeling about a depression ISW propagating across a small vertical cylinder are employed and revealed in this paper.

Proceedings Papers

Paper presented at the The Eleventh ISOPE Pacific/Asia Offshore Mechanics Symposium, October 12–14, 2014

Paper Number: ISOPE-P-14-080

... coefficient shed insights on the mechanism of energy dissipation. Semi-analytical results with calibrated damping coefficient are presented and good agreements with experimental data are obtained. body draft narrow gap fluid resonance potential flow model resonant wave height

**variation**laboratory...
Abstract

Abstract Laboratory tests and semi-analytical analysis are carried out to investigate the wave resonance in a narrow gap between a fixed floating box and a vertical wall. The mechanical energy dissipation involved in the fluid resonance is concerned. The experimental tests confirmed that the resonant wave height increases slowly with the incident wave height, which is lower than a linear function. The reflection coefficient shows complex non-linear dependence on the body draft, gap width and incident wave height. The experimental results associated with resonant wave height and reflection coefficient shed insights on the mechanism of energy dissipation. Semi-analytical results with calibrated damping coefficient are presented and good agreements with experimental data are obtained.

Proceedings Papers

Paper presented at the The Eleventh ISOPE Pacific/Asia Offshore Mechanics Symposium, October 12–14, 2014

Paper Number: ISOPE-P-14-058

... that tidal asymmetry has a profound effect on geomorphology. harmonic analysis yangtze estuary cross-section area constituent tidal asymmetry amplitude parameter

**variation**period 1993 2008 deformation coefficient lianxinggang station zhang qinglonggang station geomorphology tide...
Abstract

Abstract Harmonic analysis was carried out on tide data of Lianxinggang and Qinglonggang station, which are located in the downstream and upstream of the north branch of the Yangtze Estuary, respectively. Some appropriate parameters are selected to characterize the geomorphology features of the north branch of the Yangtze Estuary from the perspective of tidal asymmetry. It shows that tides in the north branch are flood-dominant, and tidal asymmetry of upstream is more dominant than that of downstream. The offshore tide deforms strongly as it approaches the narrowing mouth. It indicates that tidal asymmetry has a profound effect on geomorphology.

Proceedings Papers

Paper presented at the The Eleventh ISOPE Pacific/Asia Offshore Mechanics Symposium, October 12–14, 2014

Paper Number: ISOPE-P-14-054

... spar wind turbine heave motion turbine incident wave subsea system

**variation**tlp sustainability wind speed surge renewable energy foundation semi heave fowt wind energy coefficient Dynamic Response Analysis for Floating Offshore Wind Turbine Structures Zhenya Liu1, Min Zhang1*, Bin...
Abstract

Abstract In this paper, three typical floating offshore wind turbines (FOWTs) were studied, with the generic 5MW wind turbine. The dynamic responses of three FOWTs are calculated in both frequency and time domain in operational and survival case under the same environmental conditions. During the calculation, the coupled load effects of aerodynamic and hydrodynamic loads are considered as well as the structure and mooring lines. By comparing the motions and mooring line tensions of three FOWTs to conclude that Semi-submersible shows better dynamic response and safer factor of strength of the mooring systems. And the sensitivities of three FOWTs to the environmental conditions as wave height and wind speed are also studied.

Proceedings Papers

Paper presented at the The Tenth ISOPE Pacific/Asia Offshore Mechanics Symposium, October 3–5, 2012

Paper Number: ISOPE-P-12-063

..., water depth

**variation**and scour-and-fill feature of Hechangzhou Braided Channel were analyzed. The evolution mechanism was also concerned through the points of incoming water & sediment conditions and geologic-geomorphic feature of Hechangzhou Channel. Finally, some suggestions were provided for the...
Abstract

ABSTRACT: The Hechangzhou Braided Channel in Zhenyang (Zhenjiang-Yangzhou) Reach is one of the severely changing sections in the lower reaches of Yangtze River. To effectively forecast the evolution trend of this reach and prevent disaster, this paper is mainly based on the concepts and methods of GIS. Using the noted geographic information software MapInfo 9.5 and Surfer 8.0, we digitized the scanned river survey maps (1:10000) of Hechangzhou in 1974, 1978, 1997, respectively, and established the Digital Elevation Model (DEM) for this river section. Then the recent plane deformation, water depth variation and scour-and-fill feature of Hechangzhou Braided Channel were analyzed. The evolution mechanism was also concerned through the points of incoming water & sediment conditions and geologic-geomorphic feature of Hechangzhou Channel. Finally, some suggestions were provided for the third phase project in Zhenyang Reach and following regulations. INTRODUCTION Located in the middle of Jiangsu Province, the Zhenyang Reach of Yangtze River starts from Siyuan Channel and ends at Wufeng Mountain, with a length of 56km. It includes five major segments: Yizheng Channel, Shiyezhou Braided Channel, Liuwei Channel, Hechangzhou Braided Channel and Dagang Channel. Because of the combined action of geologic structures, riverbed landforms, incoming water & sediment conditions and other factors, the Zhenyang Reach has severe evolution all the time, and it is considered as one of the 14 reaches which are most difficult to be regulated in the lower reaches of Yangtze River (Lv et al., 2009). Meanwhile, the south branch which was former main channel experiences a progressive decline. It seriously influences the functions of constructions along the river such as ports, factories and intakes. Therefore, doing a deep analysis on evolution process and mechanism of Hechangzhou Braided Channel is significative to forecast the evolution trend of this reach, reduce disasters and direct regulation measures.

Proceedings Papers

Paper presented at the The Ninth ISOPE Pacific/Asia Offshore Mechanics Symposium, November 14–17, 2010

Paper Number: ISOPE-P-10-023

... stationary and non-stationary processes in the NWP. Results show that the non-stationary extreme wind speed of 50-year return periods is 3.2% higher than the stationary one in the NWP. As a result, it is proposed that the non-stationary effects of long-term

**variation**in atmospheric general circulation should...
Abstract

ABSTRACT: In this paper, 64-year tropical cyclone (TC) data in the Northwest Pacific (NWP) were analyzed to predict extreme wind speed under the background of climate change. The extreme value theory is presented in order to obtain extreme wind speed with different return periods in both stationary and non-stationary processes in the NWP. Results show that the non-stationary extreme wind speed of 50-year return periods is 3.2% higher than the stationary one in the NWP. As a result, it is proposed that the non-stationary effects of long-term variation in atmospheric general circulation should be considered in the offshore engineering standard or criterion revision. INTRODUCTION The NWP is the place where the most frequent and intense TCs occur among the global sea areas, and the reliability of offshore structures in this area are heavily affected by TCs, which may bring strong winds and corresponding huge destructive waves inducing great damage of social property and economic. On the other hand, with the development of the human economy, the climate change induced by greenhouse gases (e.g. CO2 and CH4 et.al.) emission has become an unchangeable fact. The annual report released by IPCC (Intergovernmental Panel on Climate Change) in 2007 persuasively confirmed that the global temperature has risen by 0.74°C in the past one hundred years (1906–2005). For example, when the hurricanes of Katrina which is the most destructive natural disaster in American history (Demirbilek, 2010; D.H. Levinso et al., 2010)and Rita were haunting about the Mexico gulf in 2005, the 167 offshore platforms and 183 oil pipelines were destroyed, resulting in 40 percent oil production of Gulf of Mexico interruption. In the South China Sea (SCS), a great many of offshore structures were also threatened by super strong typhoons such as Zhenzhu in 2006.

Proceedings Papers

Paper presented at the The Ninth ISOPE Pacific/Asia Offshore Mechanics Symposium, November 14–17, 2010

Paper Number: ISOPE-P-10-028

... advantages of perforated caissons are the lower reflection coefficient and smaller wave force (Li, 2007).

**variation**renewable energy porosity vertical flux radiation problem water column ocean energy breakwater potential use perforated caisson yong liu diffraction problem vertical flux...
Abstract

ABSTRACT: This study proposes a potential use of an oscillating water column (OWC) located inside a perforated caisson breakwater. Based on the linear potential theory, the interaction of water wave with the OWC is decomposed as a diffraction problem and a radiation problem as usual. This study only gives the analytical solution of the diffraction problem by means of the matched eigenfunction expansion method. Three parameters of engineering interest, the reflection coefficient, the vertical flux inside the OWC and the wave force acting on the whole structure, are examined. Some useful results are presented. The present study may provide an alternative low reflection OWC for engineers. INTRODUCTION Recently, various technologies of sea wave energy utilization have been extensively studied all over the world. A latest review on this topic has been given by Falcão (2010). The oscillating water column (OWC) is one of widely used wave power extraction devices. It generally includes a partially-immersed chamber with bottom open and with one or several Wells turbines. The incident wave induced oscillating motion of water surface inside the OWC can push the air through the Wells turbines, and then an electrical generator is driven by the turbines. In practice, the OWC devices are often installed on the coast or coastal structures rather than offshore, for reducing the costs of construction, maintenance, storage and so on. Especially, installing OWC devices on breakwaters seems to be a fine idea (e.g., Boccotti, 2007; Martins-Rivas and Mei, 2009). Perforated caisson breakwater is often used as a new type structure. It is initially proposed by Jarlan (1961) and consists of a perforated front wall, a solid rear wall and a wave absorbing chamber between the two walls. The advantages of perforated caissons are the lower reflection coefficient and smaller wave force (Li, 2007).

Proceedings Papers

Paper presented at the The Ninth ISOPE Pacific/Asia Offshore Mechanics Symposium, November 14–17, 2010

Paper Number: ISOPE-P-10-047

... ABSTRACT: This study presents the result of investigation of gap effect in slamming experiment. The transverse gap, longitudinal gap, and vertical air gap effects were investigated. The pressure at the center was measured to estimate the

**variation**of pressures. It was found that the smaller...
Abstract

ABSTRACT: This study presents the result of investigation of gap effect in slamming experiment. The transverse gap, longitudinal gap, and vertical air gap effects were investigated. The pressure at the center was measured to estimate the variation of pressures. It was found that the smaller the transverse and longitudinal gaps, the larger the pressure is. As the vertical air gap increases, the magnitude of peak pressure increases. It can be concluded that the measured pressure can be very dependent on those gaps. INTRODUCTION When it comes to the slamming experiment there are many factors which affect the time history of the impact pressures. They are impact velocity, deadrise angle of the model, length of the model. Not many researchers in this community speak about the effect of the ratio of the water plane area and area of the model bottom. It is anybody's guess that when this ratio gets small, the pressure time history might be affected by the disturbance caused by the nearby wall of the tank. To consider the effect of this ratio, two definitions are introduced in this study. They are transverse and longitudinal gaps. Two different transverse gaps were tested to see its effect. Another gap introduced is the vertical air gap. Therefore horizontal and vertical gap effects were investigated at this investigation. Chuang(1966) carried out slamming experiment at the model basin whose dimension is 7620mm 4572mm ⅹ ⅹ2590.8mm(Length ⅹ Width ⅹ Depth). The size of his model was 508mmⅹ673.1ⅹ12.7mm (LⅹBⅹD). Chung et al. (2006) carried out an experiment to test the LNG insulation system at the tank size of 5000mmⅹ5000mmⅹ3000mm (LⅹWⅹD) while the size of the model was 1655mmⅹ1655mmⅹ500mm (LⅹBⅹT).

Proceedings Papers

Paper Number: ISOPE-P-10-062

... temperature power spectrum

**variation**cross correlation renewable energy working fluid flow rate Spectrum Analysis of OTEC System Outputs Using Ammonia/water Mixture as Working Fluid by Continuous Operation Takafumi Morisaki*1, Satoru Goto*2, Yasuyuki Ikegami*3 *1Graduate School of Science and...
Abstract

ABSTRACT: Though the power generation system using ammonia/water mixture (AWM) as working fluid has been put into practical use in the wasteheat power generation systems at high heat source temperatures, power generation using ocean thermal energy conversion (OTEC) system at low heat source temperatures is not verified thoroughly. Therefore, this paper reports on two weeks continuous operation of an OTEC experimental device. The influence of cold source temperature is clarified on the turbine inlet and outlet temperatures and pressures in this paper. INTRODUCTION In the current century, energy and environmental problems are becoming critical, and the need for the development of renewable energy has become urgent. The Ocean Thermal Energy Conversion (OTEC) power plant is a system for generating electric power using the temperature difference between the shallow and the deep water of the ocean. It is an environment-friendly source of energy. Unlike most of the renewable energy resources which are weather dependents, OTEC system provides a stable source of electricity along the year because the shallow and the deep water temperatures are constant. In addition, the seawater used for electricity generation can be further used in many fields, such as desalination of seawater, agriculture, and Lithium recovery. As the temperature difference between the heat source and the heat sink of the ocean is much smaller than that in the conventional and in the nuclear power systems, the cycle efficiency of the OTEC systems is much lower and a huge amount of warm and cold water should be drawn from the ocean in order to drive the cycle; subsequently, the pumping power is huge. As it is a great importance for the practical design of the system, this paper reports on the spectrum characteristic of the OTEC system outputs.

Proceedings Papers

Paper presented at the The Eighth ISOPE Pacific/Asia Offshore Mechanics Symposium, November 10–14, 2008

Paper Number: ISOPE-P-08-018

... with some parameters of uncertainties such as the significant wave height and the maximum acceleration of seismic motion. equation

**variation**coefficient wind energy production offshore platform upstream oil & gas reservoir characterization seismic force seismic motion evaluation...
Abstract

ABSTRACT: The dynamic response evaluation of the idealized offshore platform model on wind energy production subjected to wave force and seismic force is carried out in the present study. It is expected that development of the offshore wind energy production would be very effective to encourage the reduction of greenhouse gas emissions. The safety evaluation of the offshore platform would be carried out with the available estimation of the dynamic response to the wave force and seismic force with uncertainty. It is suggested that the evaluation with the MCS simulation gives important roles on the reliable performance based evaluations for the offshore platform with wind energy production subjected to dynamic forces with considerably different characteristics INTRODUCTION It is expected that development of the offshore wind energy production would play important roles on the reduction of greenhouse gas emissions (Otsuka, 2002). The dynamic response evaluation of the idealized offshore platform model on offshore wind energy production subjected to wave force and seismic force is carried out in the present study. The steady wind force, which can be provided to generate the wind energy production, would be obtained in the coastal area with water depth about 50m (Hendersons, 2002). The offshore structure is expected to have important roles on development of wind energy production system. The environmental condition of the offshore structure is more severe than the land structure. If the offshore structure is located in the seismic activity area, it is essential to perform the dynamic response estimation on the wave force as well as seismic force in order to carry out the reliable design of the structure. The wave and seismic force are usually estimated by relevant expressions with some parameters of uncertainties such as the significant wave height and the maximum acceleration of seismic motion.

Proceedings Papers

Paper presented at the The Eighth ISOPE Pacific/Asia Offshore Mechanics Symposium, November 10–14, 2008

Paper Number: ISOPE-P-08-040

... mathematical formulation for non-linear

**variation**of hydrodynamic inertia coefficient (Cm) along the water depth to yield optimum force on TLPs as well as influence of wave directionality on their geometric configuration while discussing the method of solution. Responses are obtained for two configuration of...
Abstract

ABSTRACT: Response behavior of TLP under hydro-dynamic loading is nonlinear due to large structural displacements and fluid-structure interaction. This study focuses on influence of two imperative parameters namely inertia coefficient and wave directionality on its geometry. Paper develops a mathematical formulation for non-linear variation of hydrodynamic inertia coefficient (Cm) along the water depth to yield optimum force on TLPs as well as influence of wave directionality on their geometric configuration while discussing the method of solution. Responses are obtained for two configuration of TLPs namely square and equivalent triangular TLP with total initial pretension same as that of square. INTRODUCTION Offshore TLPs are vertically moored compliant structures built for petroleum extraction in deep sea. Their compliant mechanism extends high degree of mobility to alleviate destructive loads, enabling early oil production and reduced field installation costs. Inertia forces become predominant when they are dynamically excited. Researchers (Chandrasekaran et al., 2002b) studied the complexities arising from various nonlinearities namely: change in tether tension; buoyancy; as well as hydrodynamic drag forces and discussed appropriate solution procedures. They showed that calculation of wave forces on displaced position of the platform introduces a steady offset component in structural response. Water particle kinematics based on Navier- Stokes' equation is nonlinear with respect to the transverse velocity (see for example, Drobyshevski, 2004). Therefore influence of hydrodynamic coefficients on response behavior of compliant structures like TLPs showed the importance of including first order terms while computing the wave forces. (Sabuncu and Sander, 1981); however, these variations do not influence heave response much. (see for example, Spyros 2005). Chaplin & Subbiah (1994) presented results for probability distribution of peak forces and Morison coefficients based on experimental investigation on a rigid vertical cylinder under multidirectional waves.

Proceedings Papers

Paper presented at the The Sixth ISOPE Pacific/Asia Offshore Mechanics Symposium, September 12–16, 2004

Paper Number: ISOPE-P-04-037

... airflow into duct. wave energy device heave amp duct nondimensional hong reaction force orifice diameter spring coefficient frequency amplitude coefficient heave amplitude diameter equation

**variation**spring force orifice dia upstream oil & gas Study of Oscillatory...
Abstract

ABSTRACT: The effect of frequency and amplitude of the OWC (Oscillating Water Column) motion on the nonlinear reaction forces in an air duct are studied experimentally. Experimental OWC model is idealized as a simple circular cylinder with an orifice type air duct located at the middle of the top rid. Reaction forces due to forced heave oscillation are measured and analyzed. By subtracting the effect of inertia forces and restoring forces, pneumatic damping force and added spring force are deduced. The effects of the frequency and amplitude of the heave motion are discussed. Also, the effects of solidity of the duct on the reaction forces are discussed. INTRODUCTION During last two decades various ideas have been proposed to utilize wave energy, and the system based on OWC(Oscillating Water Column) concept has turned out to be the most probable candidate for commercialization(McCormick, 1981; Masuda, 1986) because its simplicity of operational principle and easiness of construction. The key component of OWC type wave energy device is the air chamber, which converts the wave energy into kinetic energy of the oscillating airflow by the pumping action of inner free surface. The air flow is driven through a duct to a turbine generator as shown in Fig. 1. A special turbine is usually introduced to pick-up mechanical energy from kinetic energy of oscillating airflow (Hong, 2001). Efficiency of the OWC type wave energy device is determined by the shape of air chamber, the shape of the duct and the type of turbine. In order to design an optimal air chamber, the reaction force induced by the oscillating airflow into the duct should be modeled correctly. The reaction force is considered to be a damping force for a fixed OWC case, because it is in-phase with the velocity of the airflow into duct.

Proceedings Papers

Paper presented at the The Sixth ISOPE Pacific/Asia Offshore Mechanics Symposium, September 12–16, 2004

Paper Number: ISOPE-P-04-008

... is necessary to clarify the probability features of the strength. truskov ice temperature drift ice eastern coast saeki okhotsk coast strength sakhalin brine uniaxial compressive strength

**variation**coefficient saroma lagoon sea ice salinity compressive strength hokkaido...
Abstract

ABSTRACT: Uniaxial compressive strength is one of the main parameters that determines the ice load acting on structures. The properties of sea ice vary according to the maritime and weather conditions, and they strongly depend on regionality. This paper aims to clarify the characteristics of uniaxial compressive strength of sea ice along the coast of Hokkaido and Sakhalin through the comparative study of existing formula of Weeks and Assur's, Timco and Frederking's, Truskov's and experimental results of the authors. INTRODUCTION More than 30 different ice load formula have been proposed for designing offshore and maritime structures in ice-infested sea. However, these properties of sea ice depend on its consolidation process and history, which vary according to regional conditions such as maritime and weather conditions. So, the proposed formula were for Arctic ice and could not be applied to the calculation of ice load in other region without first confirming their applicability. Off the northeastern coast of Sakhalin Island in the Okhotsk Sea, exploitation of oil and natural gas is currently underway. This project is the first-ever, full-scale exploitation in the offshore of the Okhotsk Sea, which requires the facilities and structures in ice-infested water. Therefore, it is necessary to determine the applicability of the formula and parameters on uniaxial compressive strength of sea ice in the Okhotsk Sea. On the other hand, in the calculation of ice load, the average value of uniaxial compressive strength is used for ice load formula, in general. However, it is known that the strength of natural sea ice varies widely for sea ice grown under similar conditions. In order to take into account the dispersion of uniaxial compressive strength of sea ice for calculating ice load, it is necessary to clarify the probability features of the strength.

Proceedings Papers

Paper presented at the The Sixth ISOPE Pacific/Asia Offshore Mechanics Symposium, September 12–16, 2004

Paper Number: ISOPE-P-04-025

... that freeze-thaw coefficient (kmrz) describes qualitative

**variations**in concrete system by way of quantity. Thus we may measure constructive/destructive processes at kinetic destruction of investigated material. It is suggested to implement method of Maximum Permissible Strains (MPS) by designed...
Abstract

ABSTRACT: This study presents an analysis of maximum concrete strength retrogression under the effect of variable-polarity thermal fields (VPTF). Absence of reasonable freeze-thaw resistance criterion causes necessity to specify maximum strength retrogression, which is understood invariable for structure of every investigated material. It is proved that though concrete freeze-thaw process is a thermodynamic one, it is impossible to apply the first law of thermodynamics in explicit form for material freeze-thaw resistance. This study explains why it is impossible to use specific potential energy at volume expansion/compression of the material when such energy transforms to deformation energy according to the Hooke's law. By application of thermodynamic physical-mathematical justifications there is given a method, which considers specificity of every created material structure. It is shown that freeze-thaw coefficient (kmrz) describes qualitative variations in concrete system by way of quantity. Thus we may measure constructive/destructive processes at kinetic destruction of investigated material. It is suggested to implement method of Maximum Permissible Strains (MPS) by designed computerized multifunctional information system for assessment of material quality and durability (CMISQD). INTRODUCTION Analysis of stressed concrete condition under the effect of variablepolarity thermal fields (VPTF) and variation of some calculated concrete properties show that freeze-thaw resistance criterion is insufficiently reasonable from the physical point of view. Stressed concrete condition at freeze-thaw cycle may be compared with long-term loading. Available experimental data show that the concrete strength under long-term effect of statistic loading is lower than the concrete strength under short-term loading. Such a difference ranges 0~30%, and it increases with the time of loading the sample. Further improvement of test methods, study of the destruction process and solution of the problem of the construction material durability under VPTF effect are mainly defined by application of various factors (technologic, structural, thermodynamic, etc) to concrete resistance.