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All Journal Jurnal Rekayasa Mesin Mekanika: Majalah Ilmiah Mekanika
Aldias Bahatmaka
Department of Mechanical Engineering, Universitas Negeri Semarang
Mechanical Engineering

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Analysis of Variations in Bow Design and Vessel Speed on the Response Amplitude Operator (RAO) of a Crew Boat Using Computational Fluid Dynamics (CFD) Arnova Chandra Cahya Kirana; Aldias Bahatmaka; Dina Malsyage; Joung Hyung Cho; Seo Ou Ttum
Mekanika: Majalah Ilmiah Mekanika Vol 24, No 2 (2025): MEKANIKA : Majalah Ilmiah Mekanika
Publisher : Universitas Sebelas Maret

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.20961/mekanika.v24i2.106779

Abstract

The performance and stability of crew boats in dynamic maritime environments are significantly influenced by hull geometry, particularly the design of the bow. This study investigates the influence of various elliptical bulbous bow configurations and vessel speeds on the Response Amplitude Operator (RAO) in heave and pitch motions. Using Computational Fluid Dynamics (CFD) simulations via ANSYS AQWA, four bow configurations, including a bare hull and three bulbous bow variants, were analyzed at speeds of 6, 12, and 18 knots under regular wave conditions defined by the Joint North Sea Wave Project (JONSWAP) spectrum. To validate the accuracy and reliability of the simulation method employed in this study, a comprehensive validation procedure was undertaken. For heave motion, the RAO deviation was 3.71%, and for pitch, 4.59%, both within acceptable CFD validation standards. Results indicate a minimal impact at lower speeds; however, at 18 knots, Bow 3 achieved the most significant reduction in RAO, with reductions of up to 9% in heave and 22.4% in pitch. These findings confirm the importance of optimized bow geometry in enhancing seakeeping performance.
Finite Element-Based Evaluation of Double-Hull Midsection Performance under Oblique Collision Dina Malsyage; Aldias Bahatmaka; Arnova Chandra Cahya Kirana; Lee Sang Won; Song Yeon Hee
Mekanika: Majalah Ilmiah Mekanika Vol 24, No 2 (2025): MEKANIKA : Majalah Ilmiah Mekanika
Publisher : Universitas Sebelas Maret

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.20961/mekanika.v24i2.106778

Abstract

Ship collisions pose a significant concern in maritime safety, particularly for double hull vessels operating in confined or high-risk areas. Understanding the structural response to collision is essential for improving crashworthiness. This study investigates the safety limits of a double-hull midsection ship under oblique impacts. Finite Element Analysis (FEA) was used to simulate three collision angles (45°, 60°, 90°) and four velocities (1, 3, 5, and 7 m/s). A benchmark study confirmed simulation accuracy with an error of less than 2%. The study reveals that impact angle and velocity significantly affect the ship's structural response. Perpendicular impacts (90°) with varying velocities produce the highest internal energy, reaching up to 28.99 MJ. In oblique impacts at 45°, the highest crushing force was generated, which reached 51.05 MN. Safety factor analysis indicates that impacts exceeding 3 m/s, especially those approaching perpendicular, lead to a decrease in structural integrity, falling below the acceptable limit. At 7 m/s and 90°, the stress on the inner hull exceeds the material's ultimate strength, indicating a potential for failure. To ensure structural safety, operational speeds should be limited to below 3 m/s. Findings highlight the importance of managing collision risks and guiding future ship design optimization.
Analysis of Stern Flap Application on Planing Hulls to Reduce Resistance Using CFD Indra Nurul Hidayat; Aldias Bahatmaka; Fedrik Immanuel Rumapea; Dandi Exada
Mekanika: Majalah Ilmiah Mekanika Vol 25, No 1 (2026): MEKANIKA : Majalah Ilmiah Mekanika
Publisher : Universitas Sebelas Maret

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.20961/mekanika.v25i1.114603

Abstract

Planing hulls exhibit complex hydrodynamic characteristics at high speeds due to two-phase flow interactions, variations in wetted surface area, and nonlinear pressure distributions, making resistance prediction challenging. This study evaluates the effect of stern flap angle and span width on the total resistance of a planing hull under calm-water conditions. Numerical simulations were conducted using a Reynolds-Averaged Navier–Stokes (RANS)-based Computational Fluid Dynamics approach with a k–ε turbulence model and the Volume of Fluid (VOF) method in ANSYS Fluent. The numerical model was validated against a benchmark CFD study previously verified with Fridsma's experimental data, showing deviations below 5% across the investigated Froude number range. Parametric simulations were performed for stern flap angles of 2°, 4°, and 6° with span widths of 43%, 48%, and 53% of the hull breadth. The results indicate that stern flap configuration significantly affects resistance, particularly under full planing conditions. The optimal configuration was obtained at a span of 53% of the hull breadth with a 2° flap angle, reducing the non-dimensional resistance (R/Δ) from 0.186 to 0.1699 (9.69%) at Fr = 1.8. Trim analysis shows an average reduction of 1.16°, contributing to the observed decrease in resistance.
Numerical Analysis of Oblique Collision on Ship Bow Structure Using the Finite Element Method Juan Abiegnail Sianipar; Aldias Bahatmaka; Song Yeon Hee; Haris Nubli
Jurnal Rekayasa Mesin Vol. 21 No. 2 (2026): Volume 21, Nomor 2, Agustus 2026
Publisher : Mechanical Engineering Department - Semarang State Polytechnic

Show Abstract | Download Original | Original Source | Check in Google Scholar

Abstract

Oblique bow collision is a complex maritime accident scenario, as the angled impact produces a non-uniform distribution of force and deformation, making the resulting damage substantially harder to predict than perpendicular collisions. Although numerous finite element studies have examined ship collision behavior, most have isolated a single parameter, leaving the combined effect of collision position and angle insufficiently characterized within a single validated numerical approach. This study addresses that gap by evaluating, for the first time within one validated numerical approach, the combined influence of collision position and angle on the structural response of a ferry-to-LPG carrier collision, using Explicit Dynamic Finite Element Method analysis in ANSYS Workbench 2024 R2 (LS-DYNA solver), with two collision positions (P1: main deck; P2: mid-body/bulbous bow) and three angles (90°, 120°, 135°) at 5 m/s across six scenarios, validated against experimental data with a crushing force error of 1.07%. Results show collision position more decisively affects structural resistance than angle, with P2 producing a peak force of 31.44 MN at 90°, over 60% higher than P1. Peak force and internal energy absorption were also found decoupled, with the highest energy absorbed at P2-120° (9.85 MJ) rather than the highest-force case, indicating that the P2-90° zone is structurally critical and warrants priority reinforcement, such as additional transverse framing or localized plate thickening. These findings support treating energy absorption as equally critical to peak force in ship collision safety assessment, in line with Sustainable Development Goal 9 (Industry, Innovation and Infrastructure), and future work is recommended to develop this numerical approach further through variations in collision velocity and distance.
Co-Authors Arnova Chandra Cahya Kirana Dandi Exada Dina Malsyage Fedrik Immanuel Rumapea Haris Nubli Indra Nurul Hidayat Juan Abiegnail Sianipar Song Yeon Hee