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CONTENTS
Volume 11, Number 3, September 2021
 


Abstract
This research proposes an improved mathematical model which can be used to calculate wheel over point (WOP) for a ship's route optimisation. WOP is a marking made on the charted course to demonstrate where the ship must initiate the course alteration to guarantee that it follows the route. The advance transfer technique (ATT) was used to determine WOP. Through practical exercise, two gaps were identified in ATT. From there, an improved mathematical model, namely ATMM, were developed. A preliminary manoeuvring analysis was then carried out in this study using a ship simulator for ATMM and the existing ATT. Then, the cross-track distance produced by both methods were compared to verify the difference. It was found that the ATMM produced better result in maintaining a ship on its course. This research's mathematical model is expected to be used onboard ship and used in the Electronic Chart Display and Information System to aid navigator in making more effective course alteration.

Key Words
cross track distance; manoeuvring analysis; passage planning; ship simulation; wheel over point

Address
Amir Syawal Kamis: Rating Programs, Akademi Laut Malaysia, BT 30 Kg Tg Dahan, 78200 Kuala Sungai Baru Melaka, Malaysia;
Faculty of Maritime Studies, Universiti Malaysia Terengganu,
21030 Kuala Terengganu, Terengganu, Malaysia
Ahmad Faizal Ahmad Fuad: Faculty of Maritime Studies, Universiti Malaysia Terengganu,
21030 Kuala Terengganu, Terengganu, Malaysia
Azmirul Ashaari: Azman Hashim International Business School, Universiti Teknologi Malaysia, Jalan Bertingkat Skudai,
81310 Johor Bahru, Johor, Malaysia
Che Wan Mohd Noor: Faculty of Ocean Engineering Technology and Informatics, Universiti Malaysia Terengganu, 21030 Kuala Terengganu, Terengganu, Malaysia


Abstract
In this study, the three dimensional numerical simulation of a seawater exchange breakwater using the Helmholtz resonator has been carried out in OpenFOAM. When the frequency of the incident wave coincides with one of the natural frequencies of a closed semi-circular resonator, resonance occurs in the resonator. The amplified water elevation in a resonator pushes the seawater periodically into the ocean/port side through the water channel and consequently improves the water quality of the port. The numerical model is based on Reynolds Averaged Navier Stokes equations with SST turbulence model. The VOF (Volume of Fluid) method is used to capture the free surface behavior. The numerical model is validated with model experiments conducted by Cho (2001) in a two-dimensional wave tank for regular waves. Numerical simulations for the prototype model in irregular waves based on the JONSWAP spectrum are also conducted to show whether the proposed seawater exchange breakwater can be feasible to the real seas. It is found that the seawater exchanging rate is greatly enhanced in the low-frequency wave region where the frequency of the Helmholtz resonance situates. If designing the Helmholtz resonator properly, it can supply the clean seawater sustainedly into the port side without additional electric power.

Key Words
CFD; Helmholtz resonator; irregular waves; seawater exchange breakwater; OpenFOAM

Address
Arun George and Il-Hyoung Cho: Department of Ocean System Engineering, Jeju National University, Jeju 690-756, Republic of Korea

Abstract
Experimental investigations were carried out to assess the global wave forces and wave induced moments on slotted vertical barriers (SVB). Fourty two different wave barrier configurations (5%, 10%, 20%, 30%, 40%, 50% and 60% porosities and 1 to 6 number of slotted walls) were tested in random wave fields of JONSWAP spectra for wide range of significant wave heights and peak periods. It is found that the wave force is very sensitive to the change in porosity of the SVB. It is also found that relatively long waves and low porosity on SVB results in the highest wave force and short waves and high porosity on the SVB results in the lowest wave force. For most of the conditions, the wave force on SVB is less than the wave force on a single impervious vertical wall and force reduction to an extent of 20% to 80% is possible for the range of porosity and number of porous walls studied. A predictive equation to estimate the wave induced significant moment is provided with high regression coefficient. The average lever arm for assessing the wave induced moment is 0.6145 times the local water depth.

Key Words
breakwater; experimental investigation; fluid structure interaction; stability; wave forces

Address
Subramaniam Neelamani: Coastal Management Program, Kuwait Institute for Scientific Research,
P.O. Box: 24885, Safat 13109, Kuwait
Noor Al-Anjari: Department of Civil Engineering, College of Engg and Petroleum, Kuwait University, Kuwait


Abstract
The main objective of the present research was investigating the effects of a floating wave barrier with square cross section installed in front of an offshore jacket structure on the wave height, base shear, and overturning moment. A jacket model with the height of 4.55 m was fabricated and tested in the 402 m-long wave flume of NIMALA marine laboratory. The jacket was tested at the water depth of 4m subjected to the random waves with a JONSWAP energy spectrum. Three input wave heights were chosen for the tests: 20 cm, 23 cm, and 28 cm. Results showed that the average decrease in the jacket' s base shear due to the presence of a floating wave barrier with square cross section was 18.97%. The use of wave barriers with square cross section also resulted in 19.78% decrease in the jacket' s overturning moment. Hence, it can be concluded that a floating wave barrier can significantly reduce the base shear and overturning moment in an offshore jacket structure.

Key Words
base shear; floating wave barrier; jacket structure; NIMALA wave flume; overturning moment; random waves

Address
Arash Dalili Osgouei and Arash Dalili Osgouei: Department of Civil Engineering, Maragheh Branch, Islamic Azad University, Maragheh, Iran
Ramin Vafaei Poursorkhabi: Department of Civil Engineering, Tabriz Branch, Islamic Azad University, Tabriz, Iran
Hamid Ahmadi: Faculty of Civil Engineering, University of Tabriz, Tabriz 5166616471, Iran;
Center of Excellence in Hydroinformatics, Faculty of Civil Engineering, University of Tabriz, Tabriz, Iran


Abstract
The present work focuses on the development of a numerical body nonlinear time-domain method for estimating the effect of active roll fin stabilizers on ship roll motion in both regular and irregular seaway. The time-domain analysis aims at providing fast and accurate ship responses that will be useful during the design process through accurate estimation of the environmental loads. A strip theory-based approach is followed where the Froude-Krylov and hydrostatic forces are calculated for the exact wetted surface area for every time step. The equations of motions are formulated in the body frame and consider the six degrees of coupled motions. The active fin, rudder, and propeller modules are included in the simulation. This leads to accurate modeling of the system dynamics. The numerical unstabilized roll motion is validated with experimental seakeeping simulations conducted on a Coastal Research Vessel (CRV). The phenomena of Parametric Rolling (PR) is identified during the numerical investigation of the candidate vessel. Besides, a nonlinear PID (NPID) control technique and LQR method is implemented for active roll motion control and its performance is observed in regular as well as irregular waves. The proposed numerical approach proves to be an effective and realistic method in evaluating the 6-DoF coupled ship motion responses.

Key Words
CRV; fin controller; irregular waves; non-linear seakeeping; NPID Controller; oll motion stabilization; parametric rolling

Address
Neha Patil and Suresh Rajendran: Department of Ocean Engineering, Indian Institute of Technology, Chennai – 600036, India


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