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Volume 13, Number 4, December 2023

The present work investigates the wave generation and propagation in a 2-D wave flume to assess the effect of wave reflection for varying beach slopes by using a numerical tool based on computational fluid dynamics. At first, a numerical wave flume (NWF) is created with different mesh sizes to select the optimum mesh size for time efficient simulation. In addition, different beach slope conditions are introduced such as 1:3, 1:5 and numerical beach at the far end of the NWF to optimize the wave reflection solutions. In addition, several parameters are analysed in order to optimize the solutions. The developed numerical model and its key findings are compared with analytical and experimental surface elevation results and it reveals a good correlation. Finally, the recommended numerical solutions are validated with the experimental findings.

Key Words
breakwater; CFD; numerical wave flume; scattering coefficients

V. Kumaran and A.V. Mahalingaiah: Central Water &Power Research Station, (CWPRS), Pune 411 024, India
Manu and Subba Rao: Department of Water Resources and Ocean Engineering, National Institute of Technology, Karnataka, Surathkal, Mangalore-India- 575025

Targeting a floating wave and offshore wind hybrid power generation system (FWWHybrid) designed in the Republic of Korea, this study examines the impact of the interaction, with multiple wave energy converters (WECs) placed on the platform, on platform motion. To investigate how the motion of WECs affects the behavior of the FWWHybrid platform, it was numerically compared with a scenario involving a 'single-body' system, where multiple WECs are constrained to the platform. In the case of FWWHybrid, because the platform and multiple WECs move in response to waves simultaneously as a 'multi-body' system, hydrodynamic interactions between these entities come into play. Additionally, the power take-off (PTO) mechanism between the platform and individual WECs is introduced for power production. First, the hydrostatic/dynamic coefficients required for numerical analysis were calculated in the frequency domain and then used in the time domain analysis. These simulations are performed using the extended HARP/CHARM3D code developed from previous studies. By conducting regular wave simulations, the response amplitude operator (RAO) for the platform of both single-body and multi-body scenarios was derived and subsequently compared. Next, to ascertain the difference in response in the real sea environment, this study also includes an analysis of irregular waves. As the floating body maintains its position through connection to a catenary mooring line, the impact of the slowly varying wave drift load cannot be disregarded. To assess the influence of the 2nd-order wave exciting load, irregular wave simulations were conducted, dividing them into cases where it was not considered and cases where it was included. The analysis of multi-degree-of-freedom behavior confirmed that the action of multiple WECs had a substantial impact on the platform's response.

Key Words
hybrid power generation platform; motion response; multi-degree-of-freedom; numerical analysis; wave energy converter

Dongeun Kim: Multidisciplinary Graduate School Program for Wind Energy, Jeju National University,
102 Jejudaehak-ro, Jeju-si, Jeju-do, 63243, Republic of Korea
Yeonbin Lee: Department of Mechanical Engineering, Hongik University, 94, Wausan-ro, Mapo-gu, Seoul, 04066, Republic of Korea
Yoon Hyeok Bae: Department of Mechanical & System Design Engineering, Hongik University,
94, Wausan-ro, Mapo-gu, Seoul, 04066, Republic of Korea

Herein, we present the design and development of an efficient finite element analysis model for thermal plate forming in shipbuilding. Double curvature shells in the ship building industries are primarily formed through the thermal forming technique. Thermal forming involves heating of steel plates using heat sources like oxy-acetylene gas torch, laser, and induction heating, etc. The differential expansion and contraction across the plate thickness cause plastic deformation and bending of plates. Thermal forming is a complex forming technique as the plastic deformation and bending depends on many factors such as peak temperature, heating and cooling rate, depth of heated zone and many other secondary factors. In this work, we develop an efficient finite element analysis model for the thermo-mechanical analysis of thermal forming. Different simulations are reported to study the effect of various parameters affecting the process. Temperature dependent properties are used in the analysis and the finite element analysis model is used to identify the critical flame velocity to avoid recrystallization of plate material. A spring connected plate is modeled for structural analysis using spring elements and that helps in identifying the resultant shapes of various thermal forming patterns. Finally, detailed simulation results are reported to establish the efficacy, applicability and efficiency of the designed and developed finite element analysis model.

Key Words
finite element analysis; flame bending; numerical techniques; ship building; thermal plate forming; transient thermal analysis

S.L. Arun Kumar and R. Sharma: Design and Simulation Laboratory, Department of Ocean Engineering, IIT Madras,
Chennai (TN) - 600036, India
S.K. Bhattacharyya: Department of Naval Architecture and Offshore Engineering, AMET University, Kanathur (TN) - 603112, India

A collision between a ship and an offshore platform may result in structural damage and closure; therefore, damage analysis is required to ensure the platform's integrity. This paper presents a damage assessment of a three-legged jacket platform subjected to ship collisions using the industrial finite element program Bentley SACS. This study considers two ships with displacements of 2,000 and 5,000 tons and forward speeds of 2 and 6.17 meters per second. Ship collision loads are applied as a simplified point load on the center of the platform's legs at inclinations of 1/7 and 1/8; diagonal bracing is also included. The jacket platform is modelled as beam elements, with the exception of the impacted jacket members, which are modelled as nonlinear shell elements with elasto-plastic material and constant isotropic hardening to provide realistic dented behavior due to ship collision load. The structural response is investigated, including kinetic energy transfer, stress distribution, and denting damage. The simulation results revealed that the difference in leg inclination has no effect on the level of localized denting damage. However, it was discovered that a leg with a greater inclination (1/8) resists structural displacement more effectively and absorbs less kinetic energy. In this instance, the three-legged platform collapses due to the absorption of 27.30 MJ of energy. These results provide crucial insights for enhancing offshore platform resilience and safety in high-traffic maritime regions, with implications for design and collision mitigation strategies.

Key Words
damage; displacement; failure; local denting; offshore platforms; ship collisions

Jeremy Gunawan;Ocean Engineering Program, Institut Teknologi Bandung, Indonesia
Jessica Rikanti Tawekal,
Ricky Lukman Tawekal and Eko Charnius Ilman: Ocean Engineering Program, Institut Teknologi Bandung, Indonesia;
Offshore Engineering Research Group, Institut Teknologi Bandung, Indonesia

Reducing hawser line tensions and dynamic responses to a certain level is of paramount importance as the hawser lines provide important structural linkage between 2 body TLP-TAD system. The objective of this paper is to demonstrate how MR Damper can be utilized to achieve this. Hydrodynamic coefficients and wave forces for two bodies including second-order effects are obtained by 3D diffraction/radiation panel program by potential theory. Then, multi-hull-riser-mooring-hawser fully-coupled time-domain dynamic simulation program is applied to solve the complex two-body system's dynamics with the Magneto-Rheological (MR) Damper modeled on one end of hawser. Since the damping level of MR Damper can be changed by inputting different electric currents, various simulations are conducted for various electric currents. The results show the reductions in maximum hawser tensions with MR Damper even for passive control cases. The results also show that the hawser tensions and MR Damper strokes are affected not only by input electric currents but also by initial mooring design. Further optimization of hawser design with MR Damper can be done by active MR-Damper control with changing electric currents, which is the subject of the next study.

Key Words
hawsers; hawser tension; magnetorheological damper; MR damper; multi-body system; station keeping

Muhammad Zaid Zainuddin, Moo-Hyun Kim and Chungkuk Jin: Department of Ocean Engineering, Texas A&M University,
727 Ross Street, College Station, TX 77843, United States of America
Shankar Bhat: Offshore Structures, Hull, Riser & Mooring (OHR&M) Deepwater Projects Shell Petroleum Development Company, 21/22 Marina, Lagos, Nigeria

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