The vortex-induced vibration (VIV) of a catenary flexible riser subjected to log-law sheared flows is experimentally investigated in a Reynolds number range of 308–953. The in-plane and out-of-plane responses are captured using the nonintrusive imaging technique. Experimental results illustrate that the mode transition is out of sync in the in-plane and out-of-plane directions, though the excited mode increases with the reduced velocity. Furthermore, the spatial variation of dominant frequency suggests the out-of-sync mode transition along the span. The predominant out-of-plane frequency is also observed in the in-plane response, whereas the in-plane dominant frequency differs when the reduced velocity is sufficiently large. Introduction The dynamic response of a circular cylinder exposed to flows is widely encountered in engineering applications. In particular, in offshore oil and gas engineering, the elongated flexible riser as a result of the increasing water depth experiences more complicated vortex-induced vibration (VIV) with the presence of multiple frequencies and mode competition. The vigorous VIV response is the main reason for structural fatigue damage: 15.8% of the submarine pipeline failures that occurred in the Gulf of Mexico during 1967–2012 were caused by VIV, as statistically reported by the Bureau of Safety and Environmental Enforcement (BSEE). These pipeline fatigue damages resulted in huge economic loss and serious environmental pollution (Marshall, 2021). Thus, a comprehensive understanding of the VIV response of flexible cylinders with a large aspect ratio is urgently required to predict and prevent fatigue failure (Wang et al., 2019). VIVs of flexible cylinders in uniform flows have been extensively investigated in past decades. The considered flexible cylinder in the experiments conducted by Song et al. (2011) has a large aspect ratio of 1,750. Although the cylinder is subject to uniform flow, asymmetric response was observed, with the highest mode reaching the sixth in the cross-flow direction. Whitney et al. (1981) pointed out that higher modes can be excited even at low towing speeds for very long marine pipes of aspect ratios 1,800, 5,400, and 10,800 with a bottom end mass. Sun et al. (2012) reported that the excited mode increased with the incident current velocity.

Vortex-induced vibration (VIV) is one of the main causes of fatigue failure of submarine pipelines under the action of ocean currents. A reasonable evaluation for the allowable (maximum) length of a pipeline span is vital for the avoidance of VIVs. The length of a pipeline span can alter its natural frequency and further influence the corresponding critical reduced velocity for the onset of VIVs. Nevertheless, the experimental observations indicated that the VIV hysteresis could be significant under the natural flows with increasing/decreasing velocity cycles, especially under the wall-proximity conditions. A case study is then performed to examine VIV hysteresis effects on the allowable span length of submarine pipelines. A dimensionless parameter is proposed and derived for characterizing such hysteresis effect on the allowable span length. It is indicated that lower-critical span lengths are much smaller (up to more than 20%) than those estimated with the commonly used upper-critical flow velocity. As such, the VIV hysteresis effect should be taken into account for determining the allowable span length of submarine pipelines. Introduction Submarine pipelines have been widely employed for transporting offshore oil and gas from subsea wells to platforms or onshore processing facilities, thereby being regarded as the lifelines of offshore oil and gas industries. An uneven seabed is always encountered for long-distance laid pipelines, especially while oil and gas exploitation is currently moving toward deep waters. Meanwhile, a partially embedded pipeline could be suspended as a result of tunnel erosion under the action of ocean currents (Sumer et al., 1988; Gao and Luo, 2010; Gao, 2017). As such, free-spanning pipelines—that is, some sections of a long pipeline untouched with the underlying seabed—are frequently occurring and even inevitable in the subsea environments (see Det Norske Veritas and Germanischer Lloyd, 2017).

To determine the mechanism of gravel profile evolution, the spatiotemporal beach profile change was investigated from hydraulic experiments. The temporal profile deformations were obtained by image sampling. Utilizing these results, the scenario experiments were conducted to produce ordinary morphological deformation, such as berm formation, collapse, movement, and growth, under the accretive-type regular wave. As a result, it was found that the incident wave complexly interacts with the downwash and morphological profile shape, and the deformation of the break-point step is affected by the amount of movable sediment. By controlling these factors, we successfully produce the berm collapse under the accretive-type wave.

In the North Sea, hydrocarbon release (HCR) from offshore topside piping that is inherently degrading because of vibration-induced fatigue (VIF) has been a significant challenge. This challenge is further exacerbated when the operating assets are located in Arctic environments, especially because of higher temperature gradients and other operational challenges. The result is a significant increase of VIF failure of topside piping, which causes a higher risk of potential HCR in Arctic environments. The “zero oil spill” requirement in the Arctic region requires operators to follow stringent guidelines to mitigate the risk of VIF failure of topside piping. In this regard, this paper demonstrates the application of the Bayesian network (BN) for risk-based fatigue integrity assessment of the topside piping. The value of the calculated risk depends upon the values of likelihood of failure (LoF) and consequence of failure (CoF). The value of LoF in turn depends upon the measured vibrational velocity (coupled with the vibration assessment criteria of the Energy Institute guidelines) and probabilistically estimated remnant fatigue life (RFL) of topside piping. Likewise, the CoF has been assessed from safety, environmental, and business perspectives. The BNs have been modelled using GeNIe and have been utilized to estimate the risk. The outcome of the fatigue integrity assessment using the proposed approach is the categorization of piping into various risk groupings. Piping in the high-risk category is thereby prioritized for inspection, thus preventing HCR in the fragile Arctic region. An illustrative case study, demonstrating the usability of the proposed approach, is presented. INTRODUCTION The rapid growth in demand for hydrocarbons and the decline of production in existing fields have induced the petroleum industry to extend their exploration and production activities to the Arctic regions (Basel et al., 2008; Hasle et al., 2009). The U.S. Geological Survey finds that the Arctic region holds approximately 22% of the world&s undiscovered conventional oil and natural gas resource base, approximately 30% of the world's undiscovered natural gas resources, approximately 13% of the world's undiscovered oil resources, and approximately 20% of the world's natural gas liquid (NGL) resources (Gautier et al., 2009). However, Artic petroleum operations have undergone quite stringent regulatory requirements, due to higher environmental sensitivity (Regjeringen, 2014). Hence, the exploitation of the Arctic reserves depends on the level of technology, as well as assessment and control readiness levels at the design, construction, and operational (i.e., inspection, maintenance, and modification) phases. For instance, compared to non-Artic regions, these regions have higher temperature gradients and increased susceptibility to brittle fracture of metals, human factors, etc. (Basel et al., 2008; Ratnayake, 2017). Hence, it is vital to develop effective methodologies to assess the risk of potential failures.

This paper measures the thermophysical properties of natural methane hydrate (MH)-bearing sediments recovered from the Nankai Trough, Japan. The thermal conductivity, thermal diffusivity, and specific heat of the sample under vertical stress (VS) loading were measured by the hot-disk transient method. The thermal conductivity of the sediments increased with increasing VS. The specific heat and thermal diffusivity have a constant value independent of VS. After MH dissociation, the thermal conductivity and the specific heat dropped significantly, and the thermal diffusivity was increased. In addition, the thermal conductivity, specific heat, and thermal diffusivity were calculated by an estimation model. Introduction Methane hydrate (MH) is expected to be developed as an unconventional natural gas source, replacing existing fossil fuels. MH is a crystalline solid in which cages of hydrogen-bonded water molecules enclose the methane gas molecules. MH is stable in a high-pressure/low-temperature environment. A large amount of MH is known to exist in permafrost on land and in sedimentary layers beneath the seabed (Sloan and Koh, 2007). The collected seismic data for oil and gas exploration show a wide distribution of bottom-simulating reflections (BSRs) under the seafloor in the Nankai Trough region near the Japan Sea coast. BSRs indicate the lower limit of gas hydrate stability zone in a vertical profile. In 1999, the first Nankai Trough methane hydrate exploration well was drilled. In early 2004, the Japan Ministry of Economy, Trade, and Industry drilled a multiwell from Tokaioki to Kumano-nada (Tsuji et al., 2009). The core was recovered using a pressure-temperature core sampler, which maintained the in-situ condition of 16 excavation sites at water depths ranging from 720 to 2,030 m in the same year. Recovered core analysis confirmed that the MH-bearing sediments in the Nankai Trough area are pore-filling-type hydrates (Fujii, Nakamizu, et al., 2009; Fujii, Saeki, et al., 2009).

Computational fluid dynamics (CFD) modeling of breaking waves over a slope and the resulting erosion in the case of an Arctic coastline is presented in this study. The study is performed with the open-source numerical model REEF3D. First, the numerical model is validated for the simulation of incident waves, wave breaking on a slope, and the sediment transport process. The numerical results show good agreement with wave theory and experimental data. The validated numerical model for the hydrodynamics and the sediment transport process is then used to simulate the coastal erosion process under the breaking wave impact on a vertical bluff. An Arctic coastline at Bjørndalen region at Isfjorden, Svalbard, is chosen, where a significant coastal erosion was observed during a storm event in September 2015. Introduction Most of the Arctic coastline is susceptible to climate change. Because of global warming and the transfer of additional heat fluxes, the frozen period of the upper active layers in the Arctic coastline is reduced. Consequently, coastline stability decreases during the extended warmer period. The average thickness of the active sediment layer in Svalbard, Norway, varies between 1.0 and 10.0 m and consists of coarse-grained sandy soil (Fromreide, 2014). Climate change can affect this Arctic coastline in two ways. First, the extended warmer period results in the formation of deeper and weaker active sediment layers (IPCC, 2007). Second, the melting of the Arctic ice sheets increases the sea level, resulting in higher tides. In combination, the higher tides approach the Arctic coastline (Thompson et al., 2016) and erode the weaker active sediment layer. A recent example of this change has been experienced in the Bjørndalen region in Isfjorden, Svalbard, where significant coastal erosion occurred during a storm event in September 2015. The waves reached the cabins built near Isfjorden and resulted in an almost 1.0-m-deep scour hole (Barstein, 2015). Therefore, in order to better understand the coastal erosion phenomenon in the Arctic regions, the processes of wave breaking and the resulting sediment transport have to be investigated in detail. The study is also important for the design of new coastal structures and suitable mitigation measures at the Arctic coastline.

Disk-shaped oceanographic buoys are commonly deployed with instrumentation to monitor and store localized environmental conditions for later transmission to passing oceanographic vessels or orbiting satellites for analysis and interpretation. The instrumentation and beacons are powered by battery packs and may utilize solar panels for recharging. Unfortunately, both the solar panels and instrumentation are too often vandalized. This research study investigates a SEAREV buoy design concept that features a pendulum wave energy conversion system inside an enclosure beneath the standard buoy hull. In this research study, a Lagrange formulation is used to develop equations of motion that are coupled with a hydraulic power take-off system. An in-house simulation model was selected to predict the buoy surge and pitch motions needed to estimate the electrical energy generated from a design seas. An iterative computational scheme was developed that utilizes an equivalent damping model of the power take-off system. The illustrative examples consider two four-meter disk buoys modified with a SEAREV wave energy conversion device, and they are subjected to relatively benign sea conditions using field measurements obtained by the National Oceanic and Atmospheric Administration (NOAA) in the Gulf of Mexico. A scatter diagram of the data was developed and used as the basis to estimate the buoy surge and pitch response and the resulting power generated. Bounded power estimates are presented and based on a limited survey of disk buoy power requirements; the predicted results for the system without optimization can provide four to five watts of power, and the findings are quite promising.

Measured post-storm beach recovery and swash velocities were simulated using the process-based, depth-averaged 1-D cross-shore numerical model CSHORE over 30 tide cycles. The field data were collected during a three-week experiment along the Delaware coast of the United States following a nor'easter storm. A pronounced ridge formed immediately after the storm and rapidly grew in height and shoreward extent. The model was able to capture the ridge accretion process (crest location, elevation, and ridge slope) and time-averaged swash flows accurately once sediment transport related parameters were calibrated. In addition to sensitivity analyses of the most important numerical parameters, profile evolution and swash velocity results are presented. Introduction Intertidal sand bars are a common morphological feature often observed along sandy coasts with micro- and mesotidal beaches. The formation and dynamic behavior of bars, or bar and trough systems, located in the surf and swash zones of the beach are controlled by a variety of morphological and hydrodynamic characteristics of the surrounding environment. The dynamic evolution of these features is thought to play a critical role in beach recovery mechanisms after erosive storm events. In particular, the ridge and runnel (RR) type of swash bar is a single bar and trough system, asymmetric in shape and generally found in the upper intertidal zone on sandy beaches subject to relatively small tidal ranges (<3 m; Kroon and Masselink, 2002). Wave runup coinciding with the rising storm tide carries a large amount of sediment landward that is left in the inner swash zone, building a pronounced berm face, or a ridge, followed by the landward slip-faced dipping, or runnel (King and Williams, 1949). The formation and onshore migration of RR-type bars is linked to beach recovery processes since the onshore migration of a (partially) submerged nearshore bar during low-energy wave conditions following a storm can carry large amounts of sediment back up on the subaerial portion of the beach.

Recently, the deterioration of reservoir embankments has progressed severely; thus, a more efficient design and construction method for deteriorated reservoir structures is required. For a fill-type reservoir embankment, a method that employs intervals between the horizontal filter and the embankment has been used and shown to achieve an efficient design. Since the horizontal filter is an important structure that provides stable drainage during an earthquake or concentrated leak, it is necessary to examine any change in the seepage characteristics depending on the filter intervals. In this study, the seepage characteristics of a reservoir embankment were examined according to the filter interval range via 3-D finite element analysis; additionally, potential risks such as those from piping were reviewed relative to the design interval of structurally stable filters. Consequently, results showed that the maximum filter intervals to yield efficient seepage characteristics were within 0–20.5 m for the pore water pressure of the core and the height of the seepage line. The piping evaluation results, as based on the range of the critical hydraulic gradient ( I cr : 0.8–1.4), demonstrated that the piping maintained stability within the filter interval range of 0–20.5 m; applying this range, stability was maintained when filters were installed throughout the embankment. However, when the filter interval exceeded 20.5 m, the piping was observed to fluctuate between stable and unstable conditions according to the range of the critical hydraulic gradient. Thus, to ensure structural stability, this study has proposed a decision method for the interval of horizontal filters based on the results of 3-D seepage analysis and the theoretical range of critical hydraulic gradient. Introduction Recently, because of the effects of climate change, concerns for functional degradation are rising for soil reservoirs vulnerable to seepage; moreover, the risk of disaster is expected to increase because risk factors for the collapse of embankment still exist. At present, 99.3% of all agricultural dams and reservoirs in South Korea are fill dams with the cross-sectional horizontal filter zone designed downstream of the embankment according to the relevant specifications (MAFRA, 2002). The interval of horizontal filters is designed to range between 10 and 40 m, and these filters regulate water drainage from the collected water inside the embankment.

We summarize the studies of two dynamical problems arising from harbor engineering. The first is on the long-period oscillations in a harbor forced by short and random incident waves. The second is on the unexpected oscillations of the mobile storm barrier designed for the Venice lagoon. In both problems nonlinearity plays a crucial role in the mathematical analysis. Part I. Long-Period Harbor Oscillations Excited By Random Wind Waves Introduction Harbors are designed to protect ships from storm-induced sea waves. Long-period oscillations inside a harbor are hazardous to ship operations in general and to loading and unloading of cargos in particular. They can cause excessive straining and breakage of mooring lines as well as collision of ships against piers, etc. During strong oscillations, the swift current at the entrance hammers the passing of small vessels. Early studies of harbor oscillations were focussed on the linear mechanism of synchronous resonance, which is appropriate for treating the effects of long-period tsunamis (Miles and Munk, 1961; Lee, 1971; Chen and Mei, 1974). However, many harbors in the world are troubled more often by the short incident waves generated by storms. An example is the case of Barbers Point Harbor in Hawaii (Okihiro, 1993). The wave gauge at an inside station recorded a sharp peak at the frequency of f = 0.001 Hz corresponding to the wave period of T = 100 s, which is ten times the typical wind wave period of O (10) s (see Fig. 1). Hualien Harbor is located on the eastern (Pacific) coast of Taiwan, which is invaded by typhoons several times each year. During Typhoon Longwang on October 2, 2005, a 7000-ton cargo ship broke loose from its dock at the northern end of the basin, drifted southward for 1 km, ran aground outside the harbor, and broke in half. Figure 2 displays the wave height spectra recorded at several stations during Typhoon Tim of 1994. Those spectra at outside stations # 2 and # 5 show high peaks at quite short periods O (15) s. However, at stations #8 and #10 inside the basin, high peaks appear instead at quite long periods O (140) s.

The motion response of a moored semi-submersible-type single module (SMOD) of a Very Large Floating Structure (VLFS) is significantly influenced by the seabed topography and shallow water effects. To investigate the motion response of a moored SMOD that is located near islands, both numerical and experimental studies have been conducted. The hydrodynamic parameters of the SMOD were acquired by the use of the panel method. A finite-element model was adopted to calculate the tension forces of the mooring lines. It was found that the moored SMOD exhibited low-frequency characteristics in shallow water. As the seabed became more inclined, the roll motion became larger, while the sway and heave motions hardly changed. As the water depth became shallower, the heave and roll motions were mitigated; however, the sway motion was aggravated. Introduction As a key technology, the study of the positioning capacity of a Very Large Floating Structure (VLFS) is always a research focus in the field of ocean engineering, and many studies have been carried out and reported (Ohmatsu, 2005). Normally VLFSs can be classified into two types according to their geometry: pontoons and semi-submersibles (Lamas-Pardo et al., 2015). The pontoon-type VLFS is a very large floating pontoon structure. Mooring systems are often equipped for this kind of VLFS to keep the floating structures on site. The Mega-Float program in Japan is a typical pontoon-type VLFS research program, and many relevant studies have been addressed (Ohmatsu, 2005; Watanabe et al., 2004; Wang and Tay, 2011). The semi-submersible-type VLFS consists of an upper deck, some columns, and submerged pontoons. Because of the small waterline-area geometry, the semisubmersible-type VLFS is suitable for deep water in a harsh marine environment. The Dynamic Positioning (DP) system is thus regarded as being more appropriate for this kind of VLFS due to the requirement of mobility as well as the ability to resist the harsh sea condition. The Mobile Offshore Base (MOB) concept proposed by the U.S. Navy is a typical semi-submersible VLFS project that is still under research (Palo, 2005).

Given the freezing index contour and the cross-sectional conditions of the field pavement, a field monitoring system is built with a total of 45 cross sections. The frost penetration depth is then calculated using the internal temperature data collected through the system. By estimating the temperature change of the asphalt pavement depending on the air temperature change by using a thermal equilibrium equation with both variables of the measured air temperature and the internal temperature by pavement layer and by analyzing the change of frost penetration depth according to the surface temperature change, a frost penetration depth prediction model is presented that is thought to be most appropriate and rational for Korea's climate and environmental conditions. Introduction Climatic conditions such as freezing temperatures and rainfall are important factors affecting road pavement serviceability. Because of the climatic characteristics of Korea, exemplified by seasonal frozen ground, the pavement freezes up to a certain depth in the winter season, while it thaws in the spring season. To reduce the damage caused by the freezing and thawing of the pavement (a dominant environmental factor), an antifrost layer needs to be incorporated in the pavement design to prevent freezing of the pavement. The frost penetration depth, calculated based on the freezing index, is reflected in current asphalt pavement design. The current calculation of frost penetration depth, however, does not appropriately reflect the internal temperature change of the pavement layer according to air temperature or the freezing index created based on the changed weather conditions and air temperature due to climate warming. To address these problems, the temperature distribution according to the pavement layer needs to be analyzed by measuring not only the air temperature by region, cross section, and season, but also the internal temperature of the field pavement.

A two-phase storm surge study is presented, documenting both a deterministic screening followed by a probabilistic approach for storm surge analysis. The analysis considers extreme storm surge events at a location on the eastern shore of Lake Huron. The deterministic screening considers a suite of conservative scenarios developed to determine the maximum credible surge level. The probabilistic analysis develops a hazard curve, relating water levels to quantified annual exceedance probabilities, with consideration of both aleatory and epistemic uncertainty. Together the two approaches provide a robust framework for addressing uncertainty in the flooding risk due to extreme storm surges. Introduction Extreme historic storm surge events have been observed in the Great Lakes. This study evaluates extreme storm surge levels and associated probabilities for a site on the eastern shoreline of Lake Huron (see Fig. 1). In order to provide a robust understanding of the storm surge hazard, a Probabilistic Flood Hazard Assessment (PFHA) was performed for storm surge. There is a significant gap in scholarly publications regarding storm surge flooding on the Great Lakes. However, the United States Army Corps of Engineers and the United States Federal Emergency Management Agency provide informative resources in their various publications and guidelines. Previous studies (e.g., USACE, 1988) have computed storm surge effects for events with an annual exceedance probability on the order of 10 −2 . However, this particular study is interested in lower probability events, such as the 10 −6 event, that require a much more careful treatment of the aleatory and epistemic uncertainties in PFHA. This paper provides a high-level approach for performing a PFHA for storm surge by illustrating its main components in a case study. The initial step in the PFHA was a qualitative screening evaluation consisting primarily of a literature review. The qualitative evaluation indicated that storm surge was a potential hazard on the shoreline of Lake Huron. This warranted a bounding deterministic screening analysis to determine whether a quantitative PFHA was warranted. The deterministic bounding screening analysis involved computing a maximum credible surge level for the shoreline area of interest. This analysis was based on conservative hydrodynamic modeling with sensitivity analyses for various atmospheric parameters.

This paper presents computational and experimental studies of an Autonomous Underwater Vehicle (AUV) undergoing prescribed lateral and angular acceleration manoeuvres (pure sway and pure yaw). The Computational Fluid Dynamics (CFD) modelling is based on the Unsteady Reynolds-averaged Navier-Stokes (URANS) equations with the use of a hybrid meshing scheme through systematic grid refinement. The obtained CFD predictions were validated through Experimental Fluid Dynamics (EFD) utilising a captive model fitted to a Horizontal Planar Motion Mechanism (HPMM). The present investigation will contribute to the identification of force and moment coefficients for the development of control system algorithms for underwater vehicles.

The oil and gas industry has demonstrated the ability to drill and develop offshore oil and gas resources in first-year sub-Arctic ice and in shallow-water high-Arctic environments. However, development in deep water (water depths exceeding 100 m) remains a formidable challenge due to small, unpredictable open-water windows and large environmental loads from multi-year ice features. This paper provides an overview of recent projections of undiscovered Arctic hydrocarbon resource potential and the geographical distribution of the resource potential thought to lie in deep water. The unique environmental conditions are summarized along with their impact on the cost of supply outlook for Arctic resources relative to other hydrocarbon supplies. The key technical challenges facing deep-water high-Arctic development are reviewed along with the current industry efforts aimed at meeting the challenges. INTRODUCTION According to a 2008 Circum-Arctic Resource Assessment by the U.S. Geological Survey (USGS) (Bird et al., 2008), the Arctic could hold about 22% of the world's remaining undiscovered hydrocarbons. Resource projections such as these, coupled with diminishing supplies of conventional oil resources and higher oil prices, have resulted in intensified acreage acquisition and exploration activities in the Arctic. Arctic exploration is expanding well beyond the shallow-water depths of current industry production experience, which is limited to bottom-founded structures and gravel islands in depths less than 40 m. In fact, much of the undrilled prospective acreage lies in socalled deep water, that is, beyond the 100-m water-depth contour). The expanding search into the deep-water Arctic is to some extent underpinned by industry confidence that the necessary enabling technology will emerge if the prize is large enough. Such confidence is supported by industry's long-standing record of overcoming major technological hurdles to safely and economically produce large hydrocarbon accumulations in harsh environmental conditions around the globe.

We simulate 2 cases to examine the effect of horizontal grid resolution on simulation of the semidiurnal internal tide in Monterey Bay: a coarse grid (∼2900-m resolution) and a fine grid (∼290-m resolution). All other inputs—barotropic M2 tidal velocity boundary conditions, initial conditions, and other physical and numerical parameters—remain constant between the 2 runs. The results show that the choice of grid resolution and the associated interpolated bathymetry are crucial to properly simulate the internal tides. The coarse grid acts like a filter to remove critical locations where internal tides are generated, and this grid loses the ability to capture energetic small-scale motions. The fine grid yields results consistent with field measurements. INTRODUCTION Munk (1966) suggested that the ocean mixes largely at its boundaries. More recently, Müller and Briscoe (1999) refined that view by hypothesizing that internal tides and internal waves (nontidal) propagating near coastal boundaries maybe important players in the global energy budgets, mixing, and dissipation. Lien and Gregg (2001) and Carter et al. (2002) observe highly concentrated intermittent patches of turbulence coincident with computed linear internal wave characteristics over ridges and within canyons. Within the proximity of such bathymetric features, Petruncio et al. (1998) observe currents due to internal tides that are an order of magnitude larger than those in the surrounding area. This suggests a connection between enhanced mixing, elevated dissipation, and internal tides and internal waves in coastal locations. Numerical simulations provide a tool to investigate this possible relationship. Results need to be accurate to assess this connection, and the accuracy of the results partly relies on the choice of grid resolution. A poor choice of grid resolution can lead to unrealistically low measures of velocities and scalar quantities, leading to inaccurate estimates of energy flux and conclusions about dissipation due to internal tides and waves.

An analytical solution has been developed to simulate the suction pile installation in sand based on small-scale laboratory model tests. The analytical solution includes the concept of the mobilized effective soil friction angle ratio to describe the reduction in the soil strength and interface friction between pile and soil during the suction pile installation. To validate the analytical solution, 3 suction piles 1.5 m in diameter were tested in the field. During the pile installation, the relationships between the applied suction pressure and the resulting pile penetration were obtained and used for validation. INTRODUCTION Based on small-scale laboratory model test results, an analytical solution was developed to help install suction piles successfully in the field (Bang et al., 1999, 2000b). The analytical solution is capable of estimating the correct suction pressure so that the pile can safely penetrate the sandy seafloor without creating any soil instability at a given pile penetration depth. The correct suction pressure value is provided as a range. The lower bound value corresponds to the suction pressure inside the pile that can barely overcome the pile's bearing capacity so that the pile can penetrate the soil. The upper bound suction pressure is the value that initiates the soil instability state, i.e., boiling, at which time the soil becomes unstable and starts to flow into the pile. Eventually the pile inside will be filled with sand, keeping the pile installation from completion. The analytical solution adopted the concept of the mobilized effective soil friction angle ratio to simulate the soil strength reduction due to the water flow caused by the applied suction pressure during installation. The mobilized effective soil friction angle ratio is the ratio between the mobilized effective friction coefficient and the available effective friction coefficient of the soil.

An analytical solution method capable of determining the geometric configuration and tensile forces of the mooring lines associated with fixed plate/pile or drag anchors has been proposed. The solution method is capable of analyzing multisegmented mooring lines that can consist of either chains, cables, or wires embedded in layered seafloor soils. It utilizes a systematic iterative search method based on specific boundary conditions. This paper describes the principles associated with the solution for the mooring line analysis. Calibration of input data has been made through the centrifuge model tests on mooring lines. Comparisons between the analytical predictions and the results from a series of field tests of mooring lines have then been made for various types of drag anchors. The comparisons of the tension at the anchor shank, the length of the mooring line on the bottom, and the angle of the mooring line at the water surface buoy indicate that the analytical solution method is capable of predicting the behavior of mooring lines with a high degree of accuracy. INTRODUCTION The U.S. Navy has developed an analytical solution method that can analyze offshore and deepwater mooring lines associated with embedded drag and fixed anchors (Bang, 1996). Mooring lines may be comprised of multisegments with different material and/or geometric properties and embedded in a general seafloor soil having either cohesion or friction or both. Any number of sinkers can also be added to the suspended portion of the mooring line in water. Solutions can be obtained with a fixed total length of the mooring line, a fixed horizontal length of the mooring line, or a fixed exit angle of the mooring line at the seafloor surface. The calibration of input data for the solution method of analyzing mooring lines embedded in cohesive seafloor soils was made through laboratory centrifuge model tests (Bang et al., 1996; Bang et al., 1999).

Single segmented mooring lines were tested in a geotechnical centrifuge for the purpose of calibrating the analytical solution developed for the analysis and design of various mooring lines associated with underwater drag/permanent anchors. The model mooring lines included steel ball chains and wire cables placed at various depths within the soft clayey seafloor soil. The mooring lines were loaded to preset tensions at the water surface under an elevated acceleration inside the centrifuge to simulate the field stress conditions experienced by the prototype mooring lines. This paper describes the calibration of 2 factors used as part of the input parameters in the analytical solution of mooring lines and considers the effect of chasing wires used in the experiment to determine the locations of the mooring lines. INTRODUCTION The U.S. Naval Facilities Engineering Service Center (NFESC) conducted a series of centrifuge model tests (Law et al., 1994) on buried mooring lines in order to validate the analytical model developed by Bang (1996). During the centrifuge model tests a set of chasing wires was attached to the mooring chains and cables. Fig. 1 shows a schematic sketch of the layout of the mooring line and chasing wires. The chasing wires were used to locate the exact geometries of the mooring chains/cable during transition from the initial to the final position due to the applied load. However, it was found later that the chasing wires had a rather significant effect on the mooring line geometry and tension, particularly on the mooring cable because of its thin cross-section. This paper studies the effect of the chasing wires on the performance of the mooring line and the soil in calibrating the material and geometric parameters necessary for the validation of the analytical model.

Forces on vertical breakwaters exerted by standing waves with water overtopping were studied in this paper. In experiments, vertical breakwaters with various heights under the action of a set of incident wave conditions were conducted in a two-dimensional wave channel. The relationship between the height of the breakwater and the wave crest height in overtopping waves was first examined. The standing-wave pressure due to water overtopping was then analyzed based on the experimental results. The theoretical Fourier solution for the nonovertopping standing-wave pressure was also presented and compared with the experiment. Experimental results showed that the standing-wave force on the seaside wall due to water overtopping was reducible about 18% maximum, when compared with the situation of a nonovertopping wave on the breakwater. The empirical formula for estimating the force on the seaside of the breakwater by the overtopping wave was proposed in this study. This paper also presented an example for estimating the net maximum wave force on a vertical breakwater when the transmitted wave in the harbor due to overtopping was considered. INTRODUCTION Wave overtopping occurs when the crest of the breakwater is lowered below the maximum water surface elevation. This phenomenon is allowable for the design of maritime structures that reduce the wave force on the wall and save construction costs. Thus the estimation of the quantity of wave overtopping has become an essential part of the design of breakwaters. Most previous studies paid attention only to the volume rate of wave overtopping, rather than its influence on wave forces in breakwaters. Wave overtopping is a complicated phenomenon arising from the interaction of the incident wave and the structure. Most studies of the features of wave overtopping were examined by means of experiments, such as Saville and Caldwell (1953) for a vertical wall, Sibul (1955) for an inclined wall, and Iwagaki et al. (1965) for effects of incident waves and mean water level on wave overtopping.