Dynamic Stability and Protection Design of a Submarined Floater Platform Avoiding Typhoon Wave Impact

This research proposes the design of a mooring system that allows the floating platform to stably dive deep enough to prevent damage induced by typhoon waves. The design principle of the mechanism is that the submarined floating platform with negative buoyancy is connected to a pontoon with positive buoyancy. The diving depth of the floating platform is determined by the rope length. If the static equilibrium of the two forces is satisfied, the diving depth will be kept. If the diving depth of the floating platform is enough, the platform will not be directly damaged by the wave impact. In reality, the system will be greatly subjected to the typhoon wave and the ocean current. The stability of the system and the dynamic tension of the rope must be significantly concerned. In this study, the linear elastic model of the mooring system composed of a floater platform, towed parachute, pontoon, traction rope, and mooring foundation is derived. The theoretical solution of the static and dynamic stability analysis of the mooring system is proposed. The dynamic behaviors of the floating platform and pontoon, and the tension of the rope under the effects of waves and ocean currents, are investigated. It is discovered that the buffer spring helps reduce the tension of the rope. The proposed protection procedure can avoid the damage of the floating platform and the mooring line, due to Typhoon wave impact.

A new approach of implementation of Wave Boundary Layer in OpenIFS

<p>Despite of significant improvement in modelling of the atmosphere after years of research, the accuracy of predicting cyclone/typhoon waves still remains highly challenging. Evidence shows that the air-sea-waves interaction over the ocean surface can significantly impact on the coupled atmosphere-ocean systems, through momentum, mass, and energy exchanges. In particular, the momentum exchanges have been found to affect both the structure of the wave boundary layer and the sea state, through the wave dissipation and wave breaking. For many decades, studies suggested different parameterizations of the momentum fluxes, through drag coefficient (C<sub>d</sub>) and the roughness length (z<sub>0</sub>). In recent years, research has been focused on the theoretical approaches of the momentum parameterization within the Wave Boundary Layer (WBL) in order to obtain the best C<sub>d</sub> and z<sub>0</sub> (Hara and Belcher 2002,2004; Moon et al. 2004; Du et al. 2017,2019). In this study, based on the works of Du et al. (2017, 2019), we introduce a new approach of the parameterization of the momentum flux using the roughness length. The potential of the scheme is analysed with extreme wind and wave events and the results are validated against buoy observations.</p>

RECOVERY OF SANDY BEACH AFTER TYPHOON WAVES - CASE STUDY ON CHIGASAKI COAST

Beach topography quickly changes in response to the action of storm waves, resulting in erosion of the foreshore with accretion under a calm wave condition after a storm. These seasonal beach changes may occur on beaches with protective measures or artificial beaches produced by beach nourishment. On these beaches, the shore protection function of a sandy beach is reduced when a trough is formed immediately offshore of the shoreline and the foreshore slope increases, indicating the importance of the study on topographic changes. Moreover, the time required for a beach recovery in response to wave conditions has not been sufficiently studied, along with the 3-D topographic changes associated with beach cycles. In this study, we aim to investigate these issues using the Narrow Multi-Beam survey data, wave data, and seabed materials data, taking the Chigasaki coast as an example. It was found that a seabed shallower than 2 and 3 m depths was eroded by rapid offshore sand transport during a storm event with the deposition of sand in a zone between 3 and 5 m depths, and then the beach recovered within 1-2 years after the storm. It was also confirmed that a bar and trough disappeared in 1-2 months under the conditions of HE = 0.5 m, TE = 8 s, and H/L = 0.005 when the crown depth of the bar was smaller than approximately 2 m. Thus, the topography after the storm waves recovers within several months or 1-2 years depending on wave conditions and the crown depth of the bar.Recorded Presentation from the vICCE (YouTube Link): https://youtu.be/W_P_3p_xd8U

An Efficient Method for Simulating Typhoon Waves Based on a Modified Holland Vortex Model

A combination of the WAVEWATCH III (WW3) model and a modified Holland vortex model is developed and studied in the present work. The Holland 2010 model is modified with two improvements: the first is a new scaling parameter, bs, that is formulated with information about the maximum wind speed (vms) and the typhoon’s forward movement velocity (vt); the second is the introduction of an asymmetric typhoon structure. In order to convert the wind speed, as reconstructed by the modified Holland model, from 1-min averaged wind inputs into 10-min averaged wind inputs to force the WW3 model, a gust factor (gf) is fitted in accordance with practical test cases. Validation against wave buoy data proves that the combination of the two models through the gust factor is robust for the estimation of typhoon waves. The proposed method can simulate typhoon waves efficiently based on easily accessible data sources.