Journal of Waterway, Port, Coastal, and Ocean Engineering

In order to realize the utilization of wave energy on ships, this study proposes a wave energy utilization system mounted on ships. The wave energy utilization system can transform wave energy into electric energy. The working principle and installation mode of the system are introduced in detail, and the motion model of the system on the ship is established. The motion equation of the system is solved by the Newmark-β method, and the influence of different slider masses (150–500 kg) and different radius of sliding rail (7–15 m) on the energy recovery performance of the system is studied. The data simulation shows that under a certain radius of the sliding rail, there is a slider mass that makes the system achieve the best energy collection effect. With the increase of the radius of the sliding rail, the slider mass corresponding to the best energy recovery performance of the system also increases. In addition, the energy recovery performance of the system under actual sea conditions is simulated, and the research shows that the system can continuously output power.

In offshore engineering, objects, e.g., drill pipes, anchor chains, and some small components, may accidentally fall into the water from ships or offshore platforms, which can cause casualties on decks or damage underwater equipment. The damaged equipment may further harm the environment, such as oil leaking from a damaged wellhead. Therefore, for economic and environmental reasons, a requirement for predicting the trajectory of dropped objects is needed. In this paper, we first propose the state–space motion model of dropped cylinders based on three-degree-of-freedom equations. Instead of being deterministic, the trajectory of the falling cylinder is described as a stochastic process by adding a small perturbation, being Gaussian distributed, to the initial state. Second, three probabilistic methods for state estimation, i.e., the Monte Carlo (MC) method, the unscented method, and the Cubature method, are employed in the envelope prediction of the dropped objects and provide reliable results. The MC method is a classic method for solving stochastic problems and has been applied to study the motion of falling objects. However, it always requires a sufficiently large sample, which results in large computation loads and is not applicable in practical utilization, especially in real-time applications. Simulation results show that the accuracy of the unscented method and the Cubature method are comparable to the MC method, while the computation time is only 0.5% of the MC method. Therefore, the two alternatives other than the MC method significantly improve their application possibilities and provide an effective way for the envelop prediction of dropped cylindrical objects in marine transportation or offshore operations. Furthermore, compared with the unscented method, the Cubature method is a density-assumed method, making itself handy for dynamic and real-time risk assessment of falling objects transported and installed at sea.

Ranking among the most threatening and challenging marine geological disasters, submarine landslides of different magnitudes have destroyed various pipelines, attracting widespread attention from the scientific and engineering communities. However, the relative size and spatial relation of landslides and pipelines, especially the landslide cover thickness above the pipeline, have not been explored in previous studies. As a result, the conventional analysis methods continue to change, and the practical application of these methods is difficult when a general criterion is lacking. In this study, three parameters, namely, the landslide cover thickness H_C, pipeline diameter D, and span height H_S, are first proposed to clarify this problem, and a unified standard analysis model is established. Second, the drag forces on pipelines with five values of H_C and two values of H_S under four typical Reynolds numbers are systematically analyzed using a validated computational fluid dynamic method. These analyses indicate that with increasing H_C, the drag force gradually increases; however, the growth law of the drag force deviates under different H_S conditions. Notably, considering the effect of H_C, the maximum drag force can be increased to as much as five times the original value, and therefore, this effect cannot be ignored. Furthermore, the cause of the drag force variation is revealed by the evolution of the flow fields (e.g., streamlines, velocity vectors, and pressure). Finally, a reference value of the drag force coefficient and an adjustment factor $f_{{\psi }_C}$ are proposed, and a standard chart methodology is established to evaluate the drag forces.

Debris impact has an important role in structural damage during extreme coastal events. Understanding the transport of debris and the characteristic of its motion is crucial because the debris impact depends on debris motion. This study investigated floating debris dispersion and motion by conducting laboratory experiments that considered the effects of a structural array, or a gridded layout of city-like buildings. Physical model experiments were conducted for two different hydrodynamic conditions: (1) current only; and (2) current + wave combined cases. Debris was released from a certain height in a repeatable way. Visual data were collected by four overhead video cameras and a particle tracking algorithm was implemented to track debris motion. Onshore debris spreading was much larger in the current + wave combined cases than in the current only trials. The results indicated that the structural array restricted the lateral spreading of debris onshore, and between the buildings, the spread of the particles approached a Gaussian distribution as the particles move inland. The offshore dispersion of debris particles was slightly higher when structures were present due to the additional turbulence that was created by the reflected waves. Debris spreading angles (θs) were calculated for each case and compared with the angles used in the current engineering practice. The presented results aimed to increase the current knowledge on debris motion and spreading during extreme events, such that engineers might build more resilient coastal communities.

Typhoons and other extreme weather events frequently strike offshore fishing ports. Therefore, an objective and realistic assessment of the berthing capacity of fishing ports are critical to offshore production safety and the safe management of fishing ports to minimize typhoon effects. We integrated the MIKE 21 spectral wave (SW) and Holland wind models to recreate typhoon wave characteristics during the transit of Typhoon In-Fa and further analyzed the berthing capacity of the Shengsi fishing port (SFP) under different recurrence periods and route impacts. We planned the mooring area realistically and upgraded the marine fisheries production safety and security system. The model’s major wave heights and water levels are consistent with the actual observations, and the d-trend model evaluation demonstrates that our model performs well. The berthing capacity of the SFP was accurately calculated based on the significant wave height and stable mooring conditions for fishing vessels. The effective berthing area within SFP reached 5.88 km² during the typhoon transit, accounting for 89.3% of the harbor area. A total of 5,154 fishing vessels, comprising 492 large-sized fishing vessels, 2,334 medium-sized fishing vessels, and 1,328 small-sized fishing vessels, could be moored. The berthing capacity under the impact of typhoons with varying recurrence periods is boosted by 10% compared with that of a 100a typhoon. When under the influence of typhoons with distinct trajectories, the wider the sheltered area of SFP is due to the topography sheltering effect, the more southerly the typhoon path is. This article examines the impact of alternative typhoon routes and return periods on fishing port sheltering capacity. The MIKE 21 SW wave and the Holland typhoon models are adopted to simulate the wave characteristics of the waters surrounding the fishing ports during the occurrence of the typhoon to analyze the fishing ports’ berthing capability. This report can be a reference for disaster reduction and offshore fishing port berthing management.

The Zhuoshui River has one of the highest sediment yields in the world. The riverine sediment may have been transported away from the river mouth by strong tidal currents and deposited in a navigational channel and a harbor basin south of the Zhuoshui River. This study describes the dispersal of riverine sediments in mesotidal conditions, including transport processes of sediments via river plumes, initial deposition, resuspension, and long-term net accumulation. Our results revealed that the distribution of suspended sediment concentration (SSC) and the transport process of the river plume was markedly modulated by tidal currents in a north–south direction. Under high-discharge conditions, energetic winds and ocean currents interrupted the offshore propagation of the sediment-laden river plume with a high SSC to the ocean. The plume, induced by typhoon floods, was either propagated northward due to the Coriolis effect or was deposited near the river mouth. The sediments deposited within the inner shelf were resuspended by intensive tidal currents and transported through southward residual circulations to the navigation channel south of the river mouth.

To reduce the local scour around pier-type structures, a “porous plate method” was proposed, aiming at effectiveness in multidirectional horizontal flows. The porous plates installed on the pier surface near the bed play two important roles in the reduction of the local scour. One is “breaking down or weakening” of the horseshoe vortex by a decline in vorticity. In the neighborhood (just upstream region), the local scour depth greatly decreases due to suppression of picking up sediment grains from the bed. Another is the resultant “flow regulation” in the boundary layer on the pier surface. In the downstream side, the wake separated from the pier surface behaves as “semi-homogeneous turbulence” without a Kármán vortex street, then the scour area drastically decreases.