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CONTENTS
Volume 16, Number 3, September 2026
 

Abstract
This paper presents a quantitative Safety Index (SI) for tug-assisted berthing operations by integrating environmental and manoeuvring demand with the available transverse control capacity from assisting tugs and shipboard thrusters. The proposed framework combines transverse wind force, current force, and dynamic stopping demand into a total required control force, while the effective tug and thruster contributions are represented as the available supply force. The resulting capacity-demand ratio is mapped to a bounded SI between 0 and 1, with SI>0.80 adopted as the acceptable operating criterion. The framework was evaluated retrospectively using three actual LNG-carrier berthing operations at LNG Jetty No. 3, Bintulu Port, representing light, medium, and high environmental-load conditions. These findings demonstrate that the SI can support preliminary tug-allocation and berthing-control decisions by providing a consistent measure of available control margin. The index is intended as a first-level operational screening tool to complement pilot judgement, port operating limits, and detailed manoeuvring assessment.

Key Words
controllability margin; safety Index; tug allocation; tug-assisted berthing; wind and current load

Address
Amir Syawal Kamis: Ahmad Faizal Ahmad Fuad, Tamim Ahmed: Faculty of Maritime Studies, Universiti Malaysia Terengganu, 21030 Kuala Nerus, Terengganu, Malaysia
Azmirul Ashaari:Azman Hashim Business School, Universiti Teknologi Malaysia, 81310 Johor Bahru, Johor, Malaysia
Azman Mohamad Noor, Mohd Sabri Amin,
Mohd Norafham Che Rus: Bintulu Port Sdn Bhd, 97008 Bintulu, Sarawak, Malaysia

Abstract
This study numerically investigates the vortex-induced vibration (VIV) responses of an elastically mounted rigid cylinder (EMRC) near a plane boundary using the physics-guided neural network (PGNN) approach. The proposed model integrates governing structural dynamics and experimental data to predict the dimensionless vibration response of an EMRC for different reduced velocities, mass ratios, damping ratios, surface roughness, and gap ratios. The PGNN predictions are validated against experimental and wake oscillator model (WOM) results for various gap ratios, including 0.06, 0.14, 0.5, 0.7, and 1.09. The results indicate that the proposed model has higher prediction accuracy, with an R2 value of approximately 0.95, and it also performs better compared to the conventional machine learning approaches. The present PGNN approach is computationally efficient and a physically reliable alternative to traditional numerical methods for near-wall VIV analysis.

Key Words
elastically mounted rigid cylinder; gap ratio; physics-guided neural network; reduced velocity; vortex-induced vibration

Address
Ankitha Miyyapuram, R. Prethiv Kumar: Department of Civil Engineering, National Institute of Technology Calicut, Kozhikode, India

Abstract
Semi-submersible platforms are one of the most promising floating structures, that have excellent stability, adaptability and highly suitable in deep water zones. This study presents the influence of pontoon on the hydrodynamic response of a four-column (4C) semi-submersible platform that supports a 2 MW Vertical Axis Wind Turbine (VAWT). The base geometry platform was adopted from a validated reference model, modeled and analysed using Ansys AQWA based on linear potential flow theory, to evaluate motion responses under regular waves. The numerical model was verified with published results, showing good agreement in the heave, pitch and surge Response Amplitude Operators (RAOs) after providing appropriate damping. Following, modifying the base hexagonal pontoon geometry into 4 configurations: inverted frustum shaped, frustum shaped, connected pontoon for base model and inverted frustum shaped connected pontoon. The hydrodynamic responses were evaluated under 0

Key Words
ansys aqwa; hydrodynamic response; response amplitude operators (RAOs); semisubmersible; vertical axis wind turbine (VAWT)

Address
N.M. Fousal, K. Nivetha, M. Abdul Akbar: Department of Civil Engineering, National Institute of Technology Calicut
NIT Campus P.O., Kozhikode, Kerala, India

Abstract
This study presents a region-specific comparative and design-selection framework for FPSO mooring systems operating in tropical, moderate-water-depth environments, with emphasis on Indonesian offshore conditions in the Natuna Sea (water depth 94–100 m). A representative 250,000 DWT ship-shaped FPSO was modeled in OrcaFlex 11.2b through coupled time-domain simulation (time step 0.1 s, duration 10,800 s) under operational, survival (1-year) and extreme (100-year) metocean conditions derived from BMKG long-term observations. Wind and current loads were applied through OCIMF force coefficients and Morison line drag with the empirical values stated explicitly. Three spread-mooring configurations were compared: a conventional 3xarrangement (A, six lines), a 4x3 arrangement with increased redundancy (B, twelve lines), and a 4xchain–polyester hybrid (C, twelve lines). The 6-DOF natural periods and RAOs were verified against target ranges for comparable FPSOs, and intact response, single-line-failure robustness (with representative 6-DOF and tension time series), fatigue and installation were assessed. The methodology deliberately separates the effect of line topology (A-B) from the effect of line material (B-C), so that lower tension in the 4x3 arrangement is not, by itself, interpreted as mathematical optimization. Relative to the baseline, configuration B reduced peak line tension by 18.7% and configuration C by 27.5%; the safety factor increased from 1.52 (A) to 1.87 (B) and 2.10 (C). For configuration B under the 100-year extreme state, a single-line failure raised the worst-neighbour peak tension to about 5,420 kN (safety factor 1.63), which remains above the API RP 2SK damaged requirement of 1.25. Fatigue life of the critical top-chain segment improved by approximately 47% (B) and more than 100% (C). Significant wave height and pretension were the dominant parameters, with an operating pretension range of 15–20% of minimum breaking load. Staged tensioning reduced peak installation loads by up to 35%, and a first-order lifecycle estimate indicates total-cost savings of up to 13.8%. The framework supports transparent, reproducible design selection for moderate-depth tropical FPSO applications.

Key Words
fatigue life; FPSO; Indonesian waters; mooring system; metocean conditions; moderate water depth; OrcaFlex; RAO; single-line failure; polyester rope

Address
Mutadi, Munaji: Universitas 17 Agustus 1945 (UNTAG) Cirebon, Indonesia

Abstract
The strumming of flexible cables is an undesirable phenomenon caused due to vortex-induced vibrations (VIV). The strumming phenomenon can be observed in tow cables, mooring lines, umbilical cables, risers, etc. This phenomenon causes the fatigue failure of flexible cables which is a major challenge faced by the offshore industries. To suppress this strumming phenomenon there are several passive flow control devices that exist. In this study it is proposed to use a passive and flexible flow control device called fairings. We conducted an experimental study to investigate the strumming behavior of a cable with and without fairings. A parametric investigation is also carried out by changing the length of the fairings. The study is compared with a flexnose fairing cable which is a wellestablished work. The experiments are carried out for the bare cable, wrap-around cable and wrap around fairings, for three various tensions and for the Reynolds number (Re) ranging from 1600 to 25000. The responses obtained from the measurements are non-dimensional acceleration, which are converted to non-dimensional amplitude using HHT method. We observe that the strumming of cable and stream wise forces are reduced by 95% and 12 to 35%, respectively.

Key Words
cable strumming; fairings; HHT method; inline force VIV; passive suppression

Address
K.V.K. Vinay, K. Murali: Department of Ocean Engineering, IIT Madras, Chennai, India

Abstract
This study investigates the effect of hull taper on the heave added mass of axisymmetric point absorbers using a systematic numerical framework. Simulations were conducted using linear potential flow theory via the boundary element method in AQWA. A structured set of geometries, spanning taper ratios from cylinder to cone, was analyzed under fixed wetted surface area and draft to isolate the influence of taper. Results show that displaced mass normalized added mass exhibits a shallow minimum near moderate taper ratios, especially for large diameters and long wave periods. Analysis of variance identifies taper ratio as the primary contributor to added mass variation, followed by wave period and diameter-period interaction. Additional comparisons under fixed draft and top diameter reveal that moderately tapered frustums consistently exceed matched cylinders in normalized added mass at long periods, while low taper geometries show crossover behavior. Surface based normalization reinforces this trend, highlighting stronger period dependence in frustums. RAO analysis links these added mass trends to a shift in resonance toward shorter wave periods for tapered hulls. The findings establish taper as a key design parameter for tuning hydrodynamic inertia and optimizing point absorber performance across diverse wave climates.

Key Words
heave added mass; hull tapering; hydrodynamic modeling; point absorber; wave energy conversion

Address
Faheem Ijaz, Masri Bin Baharom, Khurram Altaf: Department of Mechanical Engineering, Universiti Teknologi PETRONAS, Perak, Malaysia
Hee Min Teh: Department of Civil and Environmental Engineering, Universiti Teknologi PETRONAS, Perak, Malaysia

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