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The failure of mooring lines in net cages could lead to the death or escape of farmed fish, which causes huge economic losses and immeasurable ecological impacts. Therefore, it is very important to ensure the safety of the cage mooring system in practical applications. This study experimentally and numerically investigates the hydrodynamic behaviors of the mooring line failure on a net cage in irregular waves and currents. For the model test, a 1:25 scaled net cage model with eight-point mooring is installed in a wave tank. The two load cells in its upstream mooring lines and a gyroscope on its floating collar are used to measure the mooring force and the rotational motions, respectively. A cutting device equipped with a pneumatic cylinder and a blade is used to cut the line. A self-developed numerical model is specifically established for the model test for cross-validation. Both experimental and numerical results are analyzed and compared in the time and frequency domains. The results show that the mooring load in the remaining line significantly increases as one of the upstream mooring lines is disconnected. Meanwhile, a significant yaw rotation of the floating collar is observed. The results indicate that the maximum tension, drift displacement, and rotational angles significantly increase as the current velocity increases.

At present, the technology of measuring the net volume of a net cage in the real sea is still rare and limited. This study proposes an alternative way of accessing the remaining volume of an aquaculture net cage in both model and full scales. This new approach is called the alternative reduction coefficient (ARC), which is the ratio of the deformed height between a floating collar and a tube sinker to its original height. Its counterpart is the volume reduction coefficient (VRC), which is the ratio of deformed volume to undeformed volume. In the comparison against the existing experimental studies in the model scale, the maximum error of the current-only case is about 11.6%, and that of the wave-current case is about 23%. For the full-scale fish cage subjected to regular waves and current, the simulated results show that the maximum gap of the remaining volume between ARC and VRC is about 13.6% and 15.3% for current-only and wave-current conditions respectively. The results also show that the greater the wave steepness, the larger the error. Finally, in the simulation of the full-scale net cage subjected to irregular waves and current, the results show that the probabilities of the two methods are both a normal distribution and they are very similar, and the Pearson correlation coefficient of the two methods is about 0.937, the bias of the minimum value is only about 0.73%, that of the maximum value is about 7.18%, and that of the standard deviation is about 5.43%. Therefore, we concluded that ARC is an acceptable method of evaluating the remaining volume of fish cages in the real sea.

In 2004, the International Maritime Organization (IMO) adopted the International Convention for the Control and Management of Ships Ballast Water and Sediments (BWM Convention). Taiwan’s government has been in line with the BWM Convention’s obligations by passing several administrative orders and adopted the 3 + 1 Port State Control (PSC) procedure. International trade ports in Taiwan include commercial ports and exclusive industrial harbors. The industrial harbor in Taiwan is unique in the world, so the 3 + 1 PSC procedure cannot be directly applied to the industrial harbor. Based on document analysis, this study discusses the similarities and differences between commercial ports and industrial harbors. The regulations and systems for ballast water management in Taiwan and how they can be applied to industrial harbors are also discussed. Judging from the results of this study of regulations, commercial ports and industrial harbors differ in applicable laws, competent authorities, and construction and management units. However, in operational practice, industrial harbors should be regarded as a commercial port whose use is restricted. Therefore, this study posits that industrial harbors should be classified as commercial ports in Taiwan’s ballast water management system. Classifying industrial harbors as falling outside commercial ports may cause management difficulties and may even cause trouble for international shipping. It is suggested that the Ministry of Economic Affairs (MOEA) first discusses with the Ministry of Transportation and Communications (MOTC) and the Ocean Affairs Council (OAC) to confirm whether industrial harbors are inside or outside the category of commercial ports, and then decide on a management system and suitable laws and regulations for integrating industrial harbors with commercial ports and international affairs.

In this article, a numerical model based on the Morison equation and lump-mass method is developed to simulate the failure of an aquaculture net cage system, by changing an upstream anchor from a fixed node to a free node. Current-only and wave-current conditions are employed to investigate the mooring line tension and volume reduction coefficient of a net cage after a failure. The results show that both mooring line tension and volume reduction coefficient increase after a failure. The failure causes the cage system to drift downstream and move aside. Remaining mooring lines twist to rotate and deform the net cage. The maximum mooring line tension for the current-only cases increases with the current speed. However, the tension ratio only increases up to some certain value, i.e., 1.91 instead of 2. Beyond this, the cage system is completely collapsed resulting in a smaller minimum volume reduction coefficient compared to its counterpart under the normal state. When examined under wave-current conditions, the cage system exhibits oscillatory motion, and a large excitation of the mooring line tension is induced. The corresponding minimum volume reduction coefficient is larger than under the normal state, due to the twisting deformation of the net cage. Different instances of failure time are also examined. It is found that the results at later times (steady-state region), including the mooring line tension, the volume reduction coefficient, and the body motion of the floating collar, are not affected by the failure time. Different wave heights, wave periods, and current speeds are also simulated. The results show that the tension ratio increases with the wave height and the current speed but it decreases with the wave period.

This numerical simulation determines the wind loads on a stand-alone solar panel in a marine environment. The initial angle of tilt is 20° and 40° and the wind is incident at an angle of 0–180° (in increments of 45°). The wave angle affects the motion of a pontoon. For a wave angle of 0–180° (in increments of 45°), the variation in the surface pressure pattern and the lift coefficient with the angle of incidence of wind and waves in a single period is determined. The lift force is determined by competing the tilt angle for the upper surface with respect to wind and variation in roll angle for a specific wave angle. The data are pertinent to structural design for photovoltaic systems in a marine environment.

This paper investigates the dynamic response of a fully nonlinear model of a DeepCWind floating offshore wind turbine (FOWT) after one of its three-catenary mooring systems is broken. The drift area of the platform, pitch motion of the wind turbine, and tension on the two ends of the mooring line are the main dynamic response foci; in addition, a single mathematical formula is provided in this study to predict the maximum drift in surge direction. After the platform reaches the new equilibrium position maintained by the remaining two mooring lines, the tower pitch exceeds 20 degrees. The tension change is closely related to the drift motion, necessitating an increase in the minimum breaking load (MBL) of the mooring line components. The mathematical forecast of the maximum surge shows good agreement with the numerical results, even with different water depths

In this study, a plucking-driven piezoelectric wave energy harvester (PDPWEH) consisted of a buoy, a gear train frequency up-conversion mechanism, and an array of piezoelectric cantilever beams was developed. The gear train frequency up-conversion mechanism with compact components included a rack, three gears, and a geared cam provide less energy loss to improve electrical output. Six individual piezoelectric composite beams were plucked by geared cam to generate electrical power in the array of piezoelectric cantilever beams. A sol-gel method was used to create the piezoelectric composite beams. To investigate PDPWEH, a mathematical model based on the Euler–Bernoulli beam theory was derived. The developed PDPWEH was tested in a wave flume. The wave heights were set to 100 and 75 mm, the wave periods were set to 1.0, 1.5, and 2.0 s. The maximum output voltage of the measured value was 12.4 V. The maximum RMS voltage was 5.01 V, which was measured by connecting to an external 200 kΩ resistive load. The maximum average electrical power was 125.5 μw.

This study was aimed at investigating a floating solar photovoltaic (FPV) system by numerical and experimental simulations under wave and wind loads to analyze the motion characteristics of the platform, the tension of the mooring line, and the pressure and uplift coefficient of panels at 2.5 m/5 m water depth conditions. The floating platform was installed with four rows of solar panels, each row with five panels, attached with four catenary types of mooring lines at the corner of the platform. The numerical model was based on ANSYS AQWA and ANSYS FLUENT (ANSYS Inc., Canonsburg, PA, USA). The experiment model was a scaled FPV platform with four rows of panels scaled in the 1:4 scale ratio. The results obtained from the experiment and numerical simulation achieved a good agreement. The results show that under normal sea conditions, the FPV system may resonate in a high frequency of wave condition, and a larger lift force occurred at the windward surface. Under extreme sea conditions, the pitch motion of the floating platform changed about ±6° without overturning; however, the wind will cause a large drift of the floating platform and the vortex area formed, which will cause damage to the solar panel.

This paper aims to study the successive mooring line failure (also known as the domino effect) and the collision between floating collars for aquaculture net cages subjected to currents. The numerical model of this study is developed based on the Morison equation and the lumped-mass scheme in the time domain. This model is then applied to see if the domino effect of moorings will happen after releasing the anchor point #1 on the upstream side. In this study, we adopt four different current speeds (0.5, 1.0, 1.5, 2.0 m/s) and three different safety factors (SF, 1.0, 1.5, 2.0) settings to calculate the number of mooring failures, and to see whether it will cause floating collars collision. The results show that in the case of the SF is 2.0, the domino effect will not be triggered, and the floating collar collision will not occur. When the SF is 1.5, and the current speed is up to 1.0 m/s or higher, only the two anchor points on the upstream side will fail and no collision will occur. However, if the SF is not considered (that is, 1.0), the domino effect will occur under all the four current speeds, and the floating collar collision will all occur. Therefore, we suggest that in order to avoid the domino effect of the mooring system of aquaculture net cages from currents, the SF of the mooring system design must be at least 2 times.

Kuroshio is one of the ocean currents in the north Pacific, passing through the east of Taiwan. Kuroshio current has a steady flow in which the direction of 75-80% heads the north and the northeast. It is still difficult to harvest Kuroshio energy due to the conditions of deep seabed more than 400m and surface wave of current flow affected by season winds and typhoons. In order to obtain higher efficiency of Kuroshio energy, a power-free underwater vehicle, which works under the sea to carry generation turbines, was developed. This underwater vehicle can move upward and downward by means of changing rudders without applying power supply. In this study, to find the optimal rudder profile for the power-free underwater vehicle several symmetric profiles of the rudder in accordance with National Advisory Committee for Aeronautics (NACA) airfoil designation are selected to investigate the lifting and drag force in the Kuroshio current. Results indicate that the optimum rudder profile is NACA0008-L5 by considering the lift force and mechanical strength of the rudder. The rudder profile NACA0008-L5 at a 30° attack angle in 1.0 m/s uniform flow offers a 19.1% increment of lifting force, more efficient than the other rudder profiles.

Up to date, the mooring system failure of aquaculture net cage remains a continuing problem, especially the domino effect, which often leads to huge economic losses. Thus, this study aims to investigate the domino effect of a mooring system of a net cage under waves and currents. In this study, a time-domain numerical model based on the Morison equation and the lumped mass method is applied. A full-scale net cage system widely used in a local sea area is adopted. A 50 years return period waves with a strong following current is considered to be the design condition. It can be expected that the tension on the remaining upstream anchor increases dramatically when an upstream anchor is lost. Then, the domino effect occurs if the maximum tension on the remaining anchor exceeds its design condition. Therefore, in this simulation, the initial failure is considered to be a man-made event at a preset time, but the rest failures are resulted from exceeding the breaking strength of a rope. Both the current-only condition and the wave-current condition have been examined. The results including mooring line tension, volume reduction coefficient and rigid body motion are discussed. In addition, the results show that the failure sequence of anchor is different between the current-only condition and the wave-current condition.

This study aims to investigate the influence of fishnet mesh size on a floating platform. A self-developed, time-domain numerical model was used for the evaluation. This model is based on potential flow theory, uses the boundary element method (BEM) to solve nonlinear wave-body interactions, and applies the Morison equation to calculate the hydrodynamic forces exerted on fishnets. The mooring system is treated as a linear and symmetric spring. The results near the resonant frequency of the platform indicate that the smaller the fishnet mesh size, the lower the heave, pitch, and sea-side tension response amplitude operators (RAOs), but the higher the reflection coefficient. The results in the lower frequency region reveal that the smaller the fishnet mesh size, the lower the surge and heave RAOs, but the higher the pitch and tension RAOs. Meanwhile, the time-domain results at the resonant frequency of heave motion are shown to indicate the influences of a platform with various fishnets mesh sizes on the rigid body motion, mooring line tension, and transmitted wave heights. In addition, a comparison of nonlinear effects indicates that, after reducing the fishnet mesh size, the second-order RAOs of heave, pitch, and sea-side tension decrease, but the changes are minor against the first-order results.

In this paper, the commercial software Orcaflex is used to simulate the motion behavior of the OC4 floating platform, and the floater stability and mooring line tension after the mooring system failure. In the time domain analysis, the discussion is divided into three phases—the first phase (before the tether failure), the second phase (before the tether failure, before reaching the new steady-state), and the third phase (after reaching the new steady-state). The motion characteristics and tension values at different stages were observed. In this study, only a 50-year return period wave condition is used as an input condition and simulating 11 different incident wind and wave directions. The numerical results are presented in the trajectory map and the table. About the tension of the mooring line, after the mooring system fails, it is notable that the mooring line tension will first decrease and then increase slightly above the initial tension value. In other words, the mooring system may survive after the failure of one mooring line and got a new balance of it. However, the tension amplitude will be higher than the first stage in the new balance and it will likely increase the risk of mooring line fatigue.

The global wind energy has developed over 30 years. However, as the offshore wind power installed within 50 to 60 meters of water depth is gradually saturated. Offshore wind power installations are progressively shifting from nearshore to offshore. With the increment of water depth, the difficulties and the cost of the offshore wind power installations are also increased, makes the fixed-bottom type of structures less favorable in deep water areas and accelerate the development of the floating type offshore wind platforms. Floating offshore wind platforms can be classified into main three types: spar buoy, semi-submersible, tension-leg platform (TLP) according to reaching stability. In addition to these types, a barge-type floating platform, a new design concept, can reduce the dynamic motion of the platform by its moon pool. In this study, the hydrodynamic performance of a floating barge platform with a moon pool supports an NREL 5MW wind turbine and with a mooring system at a water depth of 50 meters was investigated. This numerical simulation was applied to analyze the hydrodynamic performance of the platform using ANSYS Aqwa software. Experimental tests in a flat water tank were conducted at National Cheng Kung University, Tainan Hydraulics Laboratory (THL). The model is a 1:64 scaled barge platform and the turbine is scaled down from the NREL 5MW. Three tests of the platform were conducted, including the free decay test, regular wave test, irregular wave test with wind operation and parking. The experimental data was analyzed to get the natural period through the free decay test. The numerical simulation results were compared with the 1:64 scaled experiment to observe the motions and Response Amplitude Operator (RAO) of surge, heave and pitch motions on the barge platform with moon pool. The floating barge platform, designed in this study, will be tested in the open sea to ensure it can withstand - extreme wave conditions such as typhoons.

Flexible plates or membranes located on the sea surface can be effective for attenuation waves approaching the beach. The most efficient structures should be found through comprehensive research using developed experiments and theory. Our experimental work was focused on the wave propagation and attenuation passing through floating elastic structures. The experiments were conducted at the wave flume of Tainan Hydraulics Laboratory, National Cheng Kung University, Taiwan. The experiment mainly analyzes the reflection coefficient, transmission coefficient and energy loss of the regular wave of intermediate water depth after passing through the elastic structure under different wave steepness and other different wave conditions. Our experiments also explore the comparison of energy dissipation effects and the differences in motion characteristics between different elastic plates and different plate fixing methods. Three elastic materials were tested in the experiments: Latex, cool cotton and polyvinyl chloride (PVC). A model of a thin elastic plate covering the sea surface was used to evaluate the effectiveness of the structure of the wave barrier. The results of experiments carried out in the wave flume were compared with theoretical predictions in a wide range of generated waves.

The well-known Stokes’ problems are reexamined by applying the Adomian decomposition method (ADM) associated with other mathematical techniques in this paper. Both the finite-depth (bounded) and infinite-depth (unbounded) cases are analyzed. The present paper raises and deals with two major concerns. The first one is that, for Stokes’ problems, it lacks one boundary condition at the expansion point to fully determine all coefficients of the ADM solution in which an unknown function appears. This unknown function which is dependent on the transformed variable will be determined by the boundary condition at the far end. The second concern is that the derived solution begins to deviate from the exact solution as the spatial variable grows for the unbounded problems. This can be greatly improved by introducing the Padé approximant to satisfy the boundary condition at the far end. For the second problems, the derived ADM solution can be easily separated into the steady-state and the transient parts for a deeper comprehension of the flow. The present result shows an excellent agreement with the exact solution. The ADM is therefore verified to be a reliable mathematical method to analyze Stokes’ problems of finite and infinite depths.

Some of the prominent features in later stages of the Benjamin–Feir (BF) instability development are still not well clarified: What are the conditions for a permanent downshifting in the wave energy spectrum, is this process inevitable accompanied by wave breaking dissipation? What is the mechanism of multiple downshifting and discrete energy spreading to higher frequencies, how does it depend on the initial steepness and frequency space of waves? We conducted experimental and theoretical studies on this issue and revealed a number of new features of the development of instability in the late stages of wave’s evolution. We employ the reduced (truncated) version of Zakharov equations, the multi-wave near-neighbor resonance model (NN model), which takes into account the most effective quasi-resonances with minimum detuning from the exact resonance conditions. We show that the near-neighbor model of wave interactions can adequately describe the number of new characteristic features of BF instability. NN model is much simpler than Zakharov equation for computation and analysis. The dissipation version of Zakharov equations based on the Tulin’s semi-empirical model is employed for the description of breaking wave’s propagation. We verify the new characteristic features of BFI for various initial wave conditions by experiments conducted in Tainan Hydraulics Laboratory and confirm the theoretical predictions of NN model. A strong permanent downshifting of the spectral maximum for gentle waves without wave breaking is revealed for initially two-time narrower spectral width in comparison with the most unstable case. For steep waves, a multiple downshifting regime is detected, accompanied by a wave breaking. The discrete energy flow to higher spectral components takes place in the breaking and no-breaking regimes. Results of numerical simulations of Zakharov and NN models reasonably correspond to each other and to our experimental and field observations on wave modulation.

Given a large block of fine-grained sediment that overlies a 1° continental slope, if the entire sediment deposit is shaken by an earthquake to slide down the slope with an initial velocity (referred to as "submarine landslide" hereinafter), our block model showed that the whole deposit can continuously slide downslope with the “help” of basal frictional heating. In theory, basal Coulomb friction can generate a thermal internal energy in the basal shear zone of landslides (called "frictional heating"), the increasing temperature activating two mechanisms. One mainly decreases the Ter­zaghi effective normal stress of the landslides and the other decreases the Coulomb friction coefficient. Combining these two mechanisms can effectively decrease the basal frictional resistance of the landslides increasing the mobility of the landslides on gentle slopes (entitled as "frictional heating lubrication"). As shown in our calcu­lations, frictional heating increases with the increase of the initial downslope velocity but decreases with the increase of the shear zone thickness.

This study investigates the impact of a mooring line failure on an aquaculture net cage through a laboratory experiment and numerical simulations. An eight-point mooring net-cage model with two load cells in its upstream mooring lines was installed in a water flume. An experiment was conducted to measure the upstream mooring force acting on the net cage exposed to currents in the intact and failed mooring conditions. A device equipped with a pneumatic cylinder and a blade was designed to cut the mooring line. The obtained results revealed that as one of the upstream mooring lines was cut, the mooring load in the other line increased greatly. However, the net-cage system reached a new force equilibrium within a few seconds. The mooring line tension ratios between the failed and intact states observed in this study were between 1.5 and 2.0. In addition to the strong mooring tension response, a significant yaw rotation of the floating collar of the net-cage system was also observed, but the motion stopped within a second after the failure occurred. In addition, a comparison of mooring forces between the experiment and numerical simulations exhibited good agreement for current velocities less than 25 cm/s. The simulated results showed that after the failure of one upstream line, the mooring load in selected lateral mooring lines increased substantially, and the net-volume change showed a sharp peak at the time of failure. Moreover, when the cage system regained balance after failure, the net-cage volume returned to its pre-failure value. Finally, the reduction in the safety factor resulted from the mooring line failure was discussed for practical engineering applications.

In this study, a floating barge moon pool platform model equipped with an NREL 5 MW wind turbine and mooring systems was numerically and experimentally tested under wave and wind loads to analyze the hydrodynamic performance and stability of the barge platform and the mooring system in a 50 m water depth condition. The numerical model was based on ANSYS AQWA, and this hydrodynamic model included nonlinear hydrostatic and Froude–Krylov forces, diffraction/radiation forces obtained from the linear potential theory, and Morison forces to consider viscous effects on the heave plates. The experiment model was a 1:64 scaled barge platform with an NREL 5 MW wind turbine scaled in the same ratio. Both full coupling platform were simulated under three conditions, namely free decay test, regular wave test, and irregular wave test, including a typhoon extreme case, with wind operation and parking. First, the hydrodynamic model was calibrated against the free decay test results. Consequently, a good agreement was achieved by calibrating the mooring properties of the experiment model. A comparison of the regular wave cases was then performed, with the same trend of results observed for the surge, heave, and pitch motions of the floating barge system. Finally, irregular model tests, which aimed to measure the dynamics of the barge platform and the mooring system in a 50-year sea state in Taiwan offshore, were conducted. The motion responses of the barge platform and the mooring tensions were recorded and compared with full coupled dynamic analysis results. The DNV GL standards were used to check the reliability of the mooring system and the stability of the barge platform.

Development of Benjamin−Feir instability is investigated under laboratory conditions and by analytical modeling. Nonlinear properties of the wave train with discrete spectrum are also investigated. The mechanically generated waves are composed of several discrete waves, while the newly generated harmonics are still combined into discrete spectra with the same frequency step. The technique proposed in this study allows us to study accurately the nonlinear variations in main properties of each harmonic with fixed frequency, such as amplitude, phase speed, and wavenumber along the wave tank together with velocities of wave packet crests, especially for the large transient waves. The phase speeds of short waves increase near large transient waves, and the velocities of longer waves are close to the values determined by the linear theory of waves. The relative long wave accompanied by short waves can dramatically change the local kurtosis and skewness of the wave field. They may play an important role for the generation of large transient wave and provide an opportunity for triggering of the freak waves.

Sudden snap events on mooring lines and hanging cables can cause spikes in tension, resulting in reduced safety factors during extreme events. For example, the mooring system of a floating offshore wind turbine (FOWT) can be exposed to wave-induced motions making the former vulnerable to snap type impact. Suitable criteria to define snap events are still largely unclear, making current design practices overly conservative. To understand the underlying physics of snap loads on a mooring line system, this paper presents a theoretical development and an experimental parametric study of snap events. The effects of the nonlinearity of bilinear line stiffness and hydrodynamic drag force, as well as the weight of payload on snap events are investigated using the vertical hanging cable model. This cable model includes two springs in series and a payload. The bilinear spring model is designed to create nonlinear dynamic tension. A total of 108 tests were conducted in the wave tank of Tainan Hydraulic Laboratory. The excitation amplitude ranges from 0.01 to 0.04m; excitation time period ranges from 0.5 to 2s; the weight of payload ranges from 6.13 to 18.95N. The tests carried out in water are compared to those conducted in air. It is seen that the hydrodynamic drag force together with the small pretension could result in larger normalized tension ranges.

This study aims to investigate the performance changes resulted from a mooring line failure of a marine fish cage exposed to irregular waves and current. A numerical model based on the lumped mass method and Morison equation was extended to simulate the mooring line failure scenario. In this study, the failed resulting changes were compared with its normal counterpart in both the time domain and the frequency domain. After one upstream anchor loss, the maximum tension on the remaining anchor has increased significantly, as well as the drift distance of the rearing part (net chamber, floating collar, and tube-sinker) of the fish cage. The resulting changes can also be seen in both the wave-frequency and the low-frequency region in the spectra, including mooring tensions and body motions.

This study experimentally determines the wind loads on a stand-alone solar array (length-to-width ratio of 0.19, 1/10-scale commercial modules). The freestream velocity in a uniform flow is 14.5 &plusmn, 0.1 m/s, and the turbulence intensity is 0.3%. The angle of tilt ranges from 10&deg, to 80&deg, and the wind is incident at angle of 0&deg, &ndash, 180&deg, Mean surface pressure measurements on the upper and the lower surface of the inclined solar panels are used to calculate the lift coefficient. For the angle of incidence of 0&deg, 60&deg, for the wind, the variation in the lift coefficient with the angle of tilt is U-shaped. The formation of a strong windward corner vortex results in greater lift force on the right half of the inclined plate for the angle of incidence of 30&deg, 45&deg, for the wind.

The aim of this paper is to establish a simple approach to experimentally study the mooring line damping in shallow water, where snap loading may occur more frequently. Experimental measurements were conducted in a wave basin at a scale of 1:50, which corresponds to a full scale of 28 m water depth. A chain made by stainless steel was used, and the tension force at the fairlead was measured by tension gages. Moreover, the line geometry, touchdown point speed, and mooring line velocity were derived from image processing techniques. Surge motions at fairlead were driven from a programmable wavemaker. Regular surge motions with different frequencies and pretensions were tested in this system in order to investigate the quasi-static and dynamic behaviors of the mooring chain. In the quasi-static test, the mooring line keeps a typical catenary shape, and its indicator diagram exhibits a smooth-closed curve. In the dynamic test, the mooring line is fully lifted from the seabed, and it cyclically goes through the stage of semitaut and fully taut. We successfully reproduced a snap event in the laboratory scale, and the resulting mooring line damping can considerably increase in this manner. Two criteria for snap event were examined, and both of them were verified by the experiments.

The objective of this paper was to present the modeling and optimization of mooring lines for floating offshore wind turbines (FOWT) located in various water depths from 50 m to 100 m in Taiwan western offshore areas. A semi-submersible floating wind turbine system is considered based on Offshore Code Comparison Collaborative Continuation (OC4) DeepCwind platform with the National Renewable Energy Laboratory (NREL) offshore 5-MW baseline wind turbine. The mooring lines proposed consist of a catenary mooring with studless chains. Three nominal sizes of the mooring chain links are taken into account with diameters of 95 mm, 115 mm and 135 mm. According to this configuration, a total of five mooring designs for different water depths (i.e., 50 m, 60 m, 70 m, 80 m, 100 m) are analyzed according to the rules and regulations of the two certification institutions, Det Norske Veritas (DNV) and American Petroleum Institute (API). Considering ultimate limit state (ULS), fatigue limit state (FLS) and maximum operating sea state (MOSS) based on a typhoon with a 50-year return period and current with a 10-year return period, 25-year design life, as well as 1-year return period, respectively, long-term predictions of breaking strength, fatigue and stability are performed. The software OrcaFlex version 10.3 d is used to simulate and design the mooring lines. The obtained results show that the shallow mooring design of 50 m water depth case presents the heaviest chains among the other water depths, increasing their mooring costs. On the other hand, the 100 m water design has much longer mooring lines, making this parameter the cost driving one. Thus, the minimum mooring cost range is from 60 m to 80 m water depth.

This Special Issue concentrates on the problems of interactions between water waves and ocean structures [...]

In this paper, a piezoelectric wave-energy converter (PWEC), consisting of a buoy, a frequency up-conversion mechanism, and a piezoelectric power-generator component, is developed. The frequency up-conversion mechanism consists of a gear train and geared-linkage mechanism, which converted lower frequencies of wave motion into higher frequencies of mechanical motion. The slider had a six-period displacement compared to the wave motion and was used to excite the piezoelectric power-generation component. Therefore, the operating frequency of the piezoelectric power-generation component was six times the frequency of the wave motion. The developed, flexible piezoelectric composite films of the generator component were used to generate electrical voltage. The piezoelectric film was composed of a copper/nickel foil as the substrate, lead&ndash, zirconium&ndash, titanium (PZT) material as the piezoelectric layer, and silver material as an upper-electrode layer. The sol-gel process was used to fabricate the PZT layer. The developed PWEC was tested in the wave flume at the Tainan Hydraulics Laboratory, Taiwan (THL). The maximum height and the minimum period were set to 100 mm and 1 s, respectively. The maximum voltage of the measured value was 2.8 V. The root-mean-square (RMS) voltage was 824 mV, which was measured through connection to an external 495 k&Omega, resistive load. The average electric power was 1.37 &mu, W.

When a block of dense sandy soil moves downhill, the shear-induced soil dilatancy along the basal shear boundary produces a negative value of excess pore pressure that increases the basal frictional resistance. Dilatancy angle, , the degree to which the basal soil dilates due to the shear, normally evolves during slope failure. A study by other researchers shows that if is constant, the block of dense soil will remain stable (or unstable) sliding when the velocity-weakening rate of the basal friction coefficient of the block is small (or large) enough. Moreover, during unstable sliding processes, the block of dense soil exhibits "periodic" patterns of intermittent slipping. Here, we used a more efficient and accurate numerical scheme to revisit that study. We expanded their model by assuming evolves during slope failure. Consequently, we acquired completely different results. For instance, even though the velocity-weakening rate of the friction coefficient is fixed at the same smaller (or larger) value that those researchers use, the stable (or unstable) steady states of landslide they predict will inversely change to unstable (or stable) when decreases (or increases) with the increase of slide displacement to a value small (or large) enough. Particularly, in unstable processes, the soil block exhibits "aperiodic" styles of intermittent slipping, instead of "periodic". We found out that the stick states appearing later last longer (or shorter) in the case of decreasing (or increasing) . Moreover, because the basic states of landslides with impacts of dilatancy evolution are not steady nor periodic, traditional stability-analysis methods cannot be "directly" used to analyze the stability of such landslides. Here, we broke through this technical problem to a degree. We showed that combining a concept called "quasi-steady-state approximation" with a traditional stability-analysis technique can qualitatively predict the instability onset of the landslides. Through this study, we demonstrated that the combination of Chebyshev collocation (CC) and 4th-order Runge-Kutta methods is more accurate and efficient than the numerical scheme those researchers use.

The development of offshore wind power in Taiwan is moving toward to the next step: to establish the demonstration wind farm before 2016. The aim of this study is to investigate the dynamic motion of the floating platform (semi-submersible type) in a wind-wave-current flume using a 1:50 scale model. The thrust force on the wind turbine was simulated by a solid disk with a diameter of 0.66 m at present stage. Compared to the prototype, the elaborate scale model has only 2% error in geometric dimension, total weights and gravity position. The natural frequency and damping coefficient of floating offshore wind turbine (FOWT) was obtained from the free decay test. Different wave directions, wave environments, drafts, wind intensities, current speeds and combined wind/wave/current were applied to study the instability of FOWT and operating conditions. The six-degree-of freedom (DOF), accelerations and drift forces were measured to compare with model result and improve the existing design.

The focus of present study is on how to generate solitary waves in a wave flume using a piston type wave maker. Experimental observations are implemented to evaluate the stability of the generated solitary waves. A better “stability” implies that the generated solitary wave can travel a longer distance without an obvious decay. Another discovery of this study is the imperfect fitness of wave paddle to the flume could degenerate the solitary wave heights in a great amount. Numerical simulations are carried out to verify this. This study concludes that the method proposed by Wu et al. (2014) is effective for generating solitary waves, even if the wave paddle fits the wave flume imperfectly.

In this study, the dynamic responses of a net-cage system were investigated through a time-domain numerical model based on the Morison equation and lumped-mass scheme. Then, the tension of the mooring lines and the motion of the net cage were studied after the failure of its mooring system. The results showed that the maximum tension in the remaining anchor increased, with large peak spectral values corresponding to the wave principal frequency and a lower frequency corresponding to the mooring force. Although additional sway, yaw, and roll motions of the cage were induced, the floating cage reached a new equilibrium position after several waves with a larger and stronger vibrating characteristic. With an increase in the current velocity, the tension ratio relative to that under the normal condition increased to 1.5. The trace of the cage after the failure showed that the longitudinal drift increased with the current velocity, whereas the lateral shift only reached a certain extent as it was constrained by lateral anchors. With the same number of cages attached, the mooring failure led to an increase in tension. As the number of cages increased, the maximum line tension also increased; however, the tension ratio remained almost constant. Finally, the safety factor of the mooring line tension for engineering applications was found to be substantially reduced after the failure.

Experimental results are presented regarding the free-surface elevations, velocity fields, and horizontal pressure gradients of dambreak-generated undular bores propagating over a horizontal bottom. Ultrasonic wave gauges, high-speed particle image velocimetry, and a flow visualization method are used to investigate the flow fields. Features of the full-depth velocity field and pressure gradient (equal to minus the sum of the local and convective accelerations) in the free stream over the boundary layer are elucidated with respect to the phase of the free-surface elevation and are categorized into four temporal stages. For stage I with rising free-surface elevations, a successive increase in the magnitude of the pressure gradient (with a negative value) corresponds to a favorable pressure gradient in the free stream. Around the zero-up/down-crossing phase of each leading wave evolving in stage II, the pressure gradient has a negative/positive maximum, revealing the maximum favorable/adverse pressure gradient in the free stream. However, the pressure gradient is zero at each crest or trough phase, showing an instantaneous zero pressure gradient. Within stage III characterized by a constant free-surface elevation, the pressure gradient is almost zero. In stage IV with descending free-surface elevations, the pressure gradient first increases from nearly zero to a positive maximum (representing the maximum adverse pressure gradient), then keeps this value for a period of time, and eventually decreases to zero. Subsequently, flow reversal with an increase in thickness over the bottom and free-stream velocity equal to zero takes place.

Positive proximal resection margins are strongly associated with anastomotic recurrence in esophageal cancer. However, the prognostic significance of dysplastic proximal resection margins remains unclear. The aim of this study is to investigate whether the dysplastic proximal resection margin can predict anastomotic recurrence and overall survival in patients with esophageal squamous cell carcinoma. Between 2000 and 2014, patients with esophageal squamous cell carcinoma who received a nonpalliative resection and survived the perioperative period were included. Two expert pathologists independently reviewed the proximal resection margin status, which was classified as negative, dysplastic, or positive. The kappa statistic was used to test interobserver reliability. Anastomotic recurrence and overall survival served as the main outcome measures. The study cohort consisted of 469 patients (445 males and 27 females). There was an excellent interobserver agreement for negative (kappa = 0.88), dysplastic (kappa = 0.88), and positive (kappa = 1) proximal resection margins-which were identified in 418 (89.1%), 37 (7.9%), and 14 (3.0%) patients, respectively. After a median follow-up of 21.6 months, 30 (6.4%) patients developed an anastomotic recurrence. Compared with patients with negative proximal resection margins (24/418, 5.7%), the occurrence of anastomotic recurrence was more commonly observed in those with positive proximal resection margins (3/14, 21.4%, P = 0.017) but not in those with dysplastic proximal resection margins (3/37, 8.1%, P = 0.56). Multivariable Cox regression analysis identified positive proximal resection margins (hazard ratio: 5.93, P = 0.010) and advanced clinical stage (hazard ratio: 12.04, P = 0.023) as independent risk factors for anastomotic recurrence. Dysplastic proximal resection margins were not retained in the model as an independent predictor (hazard ratio: 1.38, P = 0.602). The 5-year overall survival rates of patients with negative (38.2%) and dysplastic margins (27.0%) were similar (P = 0.814), and significantly higher than that observed in those with positive proximal resection margins (9.5%, P = 0.015). In conclusion, dysplastic proximal resection margins can be identified in at least 7.9% of patients with esophageal squamous cell carcinoma, but neither they are associated with an increased risk of anastomotic recurrence nor they portend a poor overall survival.