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CONTENTS
Volume 12, Number 4, December25 2022
 


Abstract
This paper deals with the study of hydrodynamic pressure in reservoir adjacent to the concrete gravity dam subjected to dynamic excitation. Widely famous finite element method is used to discretize the reservoir domain for modelling purpose. Pressure is considered as nodal variable following Eulerian approach. A suitable nonreflecting boundary condition is applied at truncated face of reservoir to make the infinite reservoir to finite one for saving the computational cost. Thorough studies have been done on generation of hydrodynamic pressure in reservoir with variation of different geometrical properties. Velocity profile and hydrodynamic pressure are observed due to harmonic excitation for variation of inclination angle of dam reservoir interface. Effect of bottom slope angle and inclined length of reservoir bottom on hydrodynamic pressure coefficient of reservoir are also observed. There is significant increase in hydrodynamic pressure and distinct changes in velocity profile of reservoir are noticeable for change in inclination angle of dam reservoir interface. Change of bottom slope and inclined length of reservoir bottom are also governing factor for variation of hydrodynamic pressure in reservoir subjected to dynamic excitation.

Key Words
earthquake excitation; Eulerian approach; finite element; hydrodynamic pressure; infinite reservoir

Address
Santosh Kumar Das, Kalyan Kumar Mandal and Arup Guha Niyogi: Department of Civil Engineering, Jadavpur University, Kolkata-32, India

Abstract
Annually, about 48-60% of sediment discharge of the Mekong River is delivered near the mouths of the Mekong River branches which is mostly coinciding with the southwest (SW) monsoon. This sediment budget in turn will be southwestwardly transported along the coast of the Mekong Delta (MD) during the northeast (NE) monsoon. Analysis of monsoonal changes in grain-size distribution (GSD) of surface sediment contributes to a better understanding of erosion and deposition processes along the MD. This study aims to figure out changes in GSD and sediment textures along the MD between SW and NE monsoons based on 183 surficial sediment samples collected along the MD during two field surveys carried-out in October 2016 and February—March 2017. Compared to the GSD during the SW and NE monsoon, the GSD along the MD changed significantly, especially in the estuary areas and along the coast of Bac Lieu and Ganh Hao. Whereas, in the west coast of the MD, GSD seem no changes between the two seasons. These changes in seabed sediment suggest that sediment with grain-sizes ranging from silt to fine sand can be transported during only a NE season.

Key Words
bathymetry; eroding; fine sand; grain-size distribution; Mekong Delta

Address
Thanh C. Nguyen, An T. Dang and Khuong N.T. Tran: University of Science, Ho Chi Minh City, Vietnam;
Vietnam National University- Ho Chi Minh City, Vietnam, 227 Nguyen Van Cu Str.,
Dist. 5, Ho Chi Minh City, Vietnam

Abstract
An innovative concept for wet-transportation and stepwise installation of mono-bucket foundation for 15 MW offshore wind turbine is proposed. Case studies for two different mono-bucket and wrap-buoy dimensions are conducted and their hydrostatic and hydrodynamic performances are compared for both wet-towing and lowering operations. The intact stability and transient responses are analyzed in detail for various stages of lowering operation. Wave-induced motion statistics during wet tow in sea state 4 (highest operational window) are checked. The proposed concept is found to be feasible and can be an alternative cost-effective solution without using heavy-lift crane vessel in practice.

Key Words
acoustic shackle; intact stability; segmented wrap buoy; stepwise installation; transient response; vertical wet tow; without crane vessel

Address
Ikjae Lee and Moohyun Kim: Department of Ocean Engineering, Texas A&M University, College Station, TX, 77845, USA

Abstract
This paper describes experimental studies of impact pressure generated by breaking regular waves in shallow water on a vertical cylinder. Experimental work was carried out in a shallow water flume using a 1:30 - scale model of a vertical rigid circular hollow cylinder with a diameter 0.2 m. This represents a monopile for shallow water offshore wind turbines, subjected to depth induced breaking regular waves of frequencies of 0.8 Hz. The experimental setup included a 1 in 10 sloping bed followed by horizontal bed with a constant 0.8 m water depth. To determine the breaking characteristics, plunging breaking waves were generated. Free surface elevations were recorded at different locations between the wave paddle to the cylinder. Wave impact pressures on the cylinder at a number of elevations along its height were measured under breaking regular waves. The depth-induced wave breaking characteristics, impact pressures, and wave run-up during impact for various cylinder locations are presented and discussed.

Key Words
breaking characteristics; depth induced wave breaking; impact pressure; monopile substructure; wave runup

Address
Vipin Chakkurunnipalliyalil, Panneer Selvam Rajamanickam and Sannasiraj Annamalaisamy Sannasiraj: Department of Ocean Engineering, IIT Madras, Chennai, India

Abstract
Dynamic Positioning (DP) is a system that uses computer-controlled thrusters, propellers, and other propulsion devices to automatically maintain a vessel's position and heading. In this study, a wind turbine installation vessel with DP capabilities was proposed for use in mild environmental conditions in the Yellow Sea. The thruster arrangements of the vessel were analyzed in relation to wind and current loads, and it was found that a four-corner arrangement of thrusters provided the best position-keeping performance. The vessel's DP control performance was also analyzed in relation to the increased environmental load caused by the presence of a wind turbine, using a capability plot. The vessel's performance was evaluated in three different states: floating with no load, during the loading of a wind turbine and suction buckets, and after the wind turbine has been installed. The use of 750 kW and 1,000 kW thrusters was also considered, and the environmental loads in the Saemangeum coastal area and the environmental load when a 5-Megawatt wind turbine is on board were assessed. The study concluded that at least four thrusters should be used for DP to safely manage the installation process of wind turbines.

Key Words
capability plot; computational fluid dynamics; dynamic positioning; wind turbine installation vessel

Address
Daeseong Lim, Jeong-Hyun Yoon and Seo-ho Lee: Intelligent Mechatronics Engineering, Sejong University, 209, Neungdong-ro, Gwangjin-gu,
Seoul, Republic of Korea
S.W. Kim: Intelligent Mechatronics Engineering, Sejong University, 209,
Neungdong-ro, Gwangjin-gu, Seoul, Republic of Korea



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