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All Journal Mekanika: Majalah Ilmiah Mekanika Makara Journal of Technology
Adiputra, Ristiyanto
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Chemical Engineering, Chemistry & Bioengineering Civil Engineering, Building, Construction & Architecture Electrical & Electronics Engineering Engineering Materials Science & Nanotechnology Mechanical Engineering

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Investigation of Ship Hull Girder Strength with Grounding Damage Alie, Muhammad Zubair Muis; Adiputra, Ristiyanto
Makara Journal of Technology Vol. 22, No. 2
Publisher : UI Scholars Hub

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Abstract

The objective of the present study is to investigate ship hull girder strength as a result of grounding damage upon longitudinal bending. A bulk carrier and tanker are analyzed and Smith’s Method is adopted and implemented in the analysis program. An efficient solution procedure is performed by assuming the cross-section remains plane and the vertical bending moment is applied to the cross section. As a fundamental case, the damage is simply created by removing the elements from the cross section. Welding residual stress, initial imperfections, and crack extensions are not considered. The grounding damage is made by two conditions, namely those are placed at the center part of the cross section and those located at an asymmetric position. To determine the ultimate strength, which includes the progressive collapse behavior of ship hull with damage, the simply supported scenario is imposed to the cross section and hogging and sagging conditions are taken into account. The results obtained for intact and damage conditions by the in-house program are compared with one another to observe the collapse behavior in advance.
Effects of Collision Damage on the Ultimate Strength of FPSO Vessels Alie, Muhammad Zubair Muis; Ramasari, Dian; Rachman, Taufiqur; Adiputra, Ristiyanto
Makara Journal of Technology Vol. 24, No. 1
Publisher : UI Scholars Hub

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Floating production storage offloading (FPSO) vessels are movable offshore structures. These structures are designed with large dimensions, and their decks are loaded with several types of equipment. During collision damage, the hull and deck parts loaded with equipment are severely affected. Therefore, the ultimate strength of FPSO vessels should be thoroughly checked and evaluated. The objective of the present study is to analyze the ultimate strength of FPSO vessels against collision damage characterized by hogging and sagging under longitudinal bending. The cross section of an FPSO vessel is modeled with elements composed of stiffened and unstiffened plates. The vessel length is assumed to occupy one frame space. The ultimate strength of FPSO vessels against collision damage is determined by performing a numerical analysis under hogging and sagging conditions. Multipoint constraint is applied to both sides of the cross section, and the material properties are set to be constant. Collision damage is represented by the loss of element stiffness, and it represents the percentage of the ship’s depth. For the extent of transversal damage, B/16 is set to be constant. The minimum and maximum collision damages are taken as 10% and 60% of the ship’s depth, respectively. Numerical results show that the ultimate strength of FPSO vessels and their bending stiffness decrease under collision.
Recent Advancements in Ocean Current Turbine Blade Design: A Review of Geometrical Shape, Performance and Potential Development Using CAE Fajri, Aprianur; Jurkovič, Martin; Kandimba, Enock Michael; Lutanto, Agus; Falah, Fajrul; Adiputra, Ristiyanto; Firdaus, Nurman
Mekanika: Majalah Ilmiah Mekanika Vol 23, No 2 (2024): MEKANIKA : Majalah Ilmiah Mekanika
Publisher : Universitas Sebelas Maret

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.20961/mekanika.v23i2.87374

Abstract

The global energy demand is experiencing a significant surge, reaching 442 exajoules in 2023. The urgency to develop renewable energy sources intensifies as global energy needs continue to escalate, coupled with the detrimental impact of fossil fuel consumption on climate change. Ocean current energy has emerged as a promising renewable energy source due to its predictability and minimal environmental impact. However, the efficiency and reliability of Ocean Current Turbines (OCTs) depend highly on their blades' design and performance. This review provides a comprehensive overview of recent advancements in ocean current and tidal current turbine blade design and the challenges and issues associated with their operation and maintenance. The paper discusses various design aspects, including blade geometry, material selection, hydrodynamic performance optimization, and bio-inspired designs. Additionally, it highlights the common failures and degradation mechanisms of turbine blades, such as fatigue, erosion, and cavitation. Furthermore, the review explores the challenges faced in developing and deploying OCTs, such as improved blade durability, cost-effectiveness, and environmental compatibility.
Finite Element Modeling of Thickness Reduction and Displacement Behavior in 316L Stainless Steel Plates Under Corrosion States Melnyk, Oleksiy; Islami, Daffa Putra; Adiputra, Ristiyanto
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.v24i2.102853

Abstract

Structural steel corrosion is a critical engineering problem that can lead to catastrophic failures, resulting in loss of life, environmental harm, and substantial economic damage. Notable incidents, such as offshore platform collapses and ship hull breaches, have demonstrated the severe consequences of undetected or underestimated corrosion. In marine environments, crevice corrosion presents a particularly challenging case, as confined chemical conditions and the presence of barnacles promote localized degradation. Barnacles generate microcracks that accelerate the deterioration process. However, finite element modeling of crevice corrosion remains scarce and often relies on oversimplified geometries, which limits the accuracy in capturing actual corrosion volume, depth, and affected area. This study develops a 3D finite element model of barnacle-induced crevice corrosion on 316L stainless steel plates, based on long-term immersion data. Corrosion geometries were analyzed using laser scanning microscopy, with the analytical mapped field feature applied under transverse loading and random pit positions for exposure durations of 6, 12, and 36 months. The results reveal progressive increases in displacement (up to 17.27%), strain (30.8%), and stress (20.12%) compared to uncorroded plates, underscoring the substantial impact of localized corrosion on structural performance.
Seakeeping Analysis of Floating Structures with Pipe Integration Based on the Boundary Element Method Onyshchenko, Svitlana; Faizatama, Alfido Marchandi; Firdaus, Nurman; Adiputra, Ristiyanto
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.v24i2.103847

Abstract

Floating structures are key components in offshore renewable energy systems. In the development of energy conversion, several integrated components are required, one of which is the Cold-Water Pipe (CWP). This integration will affect the interaction of the structure with environmental loads such as waves and currents, which influence the stability and seakeeping of the structure. This study employs computational analysis based on the Boundary Element Method (BEM) to more efficiently evaluate the hydrodynamic response of full-scale structures. Response Amplitude Operator (RAO), additional mass, motion response, and mooring line tension are identified as the main parameters. It was found that all these parameters are sensitive to mesh discretization. A mesh convergence study was conducted using mesh sizes of 1.8, 2.1, 2.2, and 2.3 m, which produced consistent RAO and additional mass values. Conversely, mesh sizes of 1.9, 2.0, 2.4, and 2.5 m showed inconsistencies in stability results at sea. The coarsest net (2.5 m) produced errors of up to 33% in swing, heave, and roll motions, with greater deviations in heave motion. However, tension on the mooring line remained relatively stable, indicating reduced sensitivity to variations in net size.
Co-Authors Faizatama, Alfido Marchandi Fajri, Aprianur Falah, Fajrul Firdaus, Nurman Islami, Daffa Putra Jurkovič, Martin Kandimba, Enock Michael Lutanto, Agus Melnyk, Oleksiy Muhammad Zubair Muis Alie Onyshchenko, Svitlana Ramasari, Dian Taufiqur Rachman