Development Of A Semi-Swath Craft For Malaysian Waters

Small Waterplane Area Twin Hull (SWATH) and Catamaran vessels are known to have more stable platform as compared to mono-hulls. A further advantage of SWATH as compared to Catamaran is its smaller waterplane area that provides better seakeeping qualities. However, the significant drawback of the SWATH vessel is when encountering head-sea at high forward speed. Due to its low stiffness, it has a tendency for large pitch motions. Consequently, this may lead to excessive trim or even deck wetness. This phenomenon will not only degrade the comfortability but also results in structural damage with greater safety risks. In this research a modified SWATH design is proposed. The proposed design concept represents a combination of Catamaran and SWATH vessel hull features that will lead to reduce in bow-diving but still maintains good seakeeping capabilities. This is then called the Semi- SWATH vessel. In addition, the full-design of this vessel has been equipped by fixed fore fins and controllable aft fins attached on each lower hull. In the development of controllable aft fins, the PID controller system was applied to obtain an optimal vessel’s ride performance at speeds of 15 (medium) and 20 (high) knots. In this research work, the seakeeping performance of Semi-SWATH vessel was evaluated using time-domain simulation approach. The effect of fin stabilizer on the bare hull performance is considered. The validity of numerical evaluation was then compared with model experiments carried out in the Towing Tank at Marine Technology Laboratory, UTM. It is shown that the Semi-SWATH vessel with controllable fin stabilizer can have significantly reduction by about 42.57% of heave motion and 48.80% of pitch motion

COMPUTATIONAL PREDICTION OF A PROPELLER PERFORMANCE IN OPEN WATER CONDITION

In presence of hydrodynamics phenomena occur surrounding propeller evidently affects on accuracy’s prediction of thrust, torque and its efficiency. To achieve the objective, a Computational Fluid Dynamics (CFD) simulations approach is then proposed to obtain a reliable prediction of the thrust (KT), torque (KQ) and efficiency (η) coefficients in open water condition. The effect of various blade numbers associated with constant propeller revolution (RPM=1320) and pitch ratio (P/D=1.0); are performed within the range of advance ratio from 0.1J1.0. The results revealed that the increase of blade number from Z=3 to 5 was proportional with the increase of thrust (KT) and torque (KQ) coefficients; meanwhile, it was reduced the maximum efficiency (η) that possibly lead to downgrade the propeller performance. It should be noted here, the propeller with three blade numbers (Z=3) provide the highest efficiency (η) up to 78.8% at J=0.9. These CFD simulation results are very useful as a preliminary study of propeller characteristics

CFD investigation into seakeeping performance of a training ship

The numerous ship accidents at sea have usually resulted in tremendous loss and casualties. To prevent such disastrous accidents, a comprehensive investigation into reliable prediction of seakeeping performance of a ship is necessarily required. This paper presents computational fluid dynamics (CFD) analysis on seakeeping performance of a training ship (full scale model) quantified through a Response of Amplitude Operators (RAO) for heave and pitch motions. The effects of wavelengths, wave directions and ship forward velocities have been accordingly taken into account. In general, the results revealed that the shorter wavelengths (λ/L ≥ 1.0) have insignificant effect to the heave and pitch motions performance of the training ship, which means that the ship has good seakeeping behavior. However, the further increase of wavelength was proportional with the increase of RAO for her heave and pitch motions; whilst it may lead to degrade her seakeeping quality. In addition, the vertical motions behavior in the following-seas dealt with higher RAO as compared with case of the head-seas condition. Similarly, the subsequent increase of the ship forward velocity was prone to relatively increase of the RAO for her heave and pitch motions especially at λ/L ≥ 2.0. It was merely concluded that this seakeeping prediction using CFD approach provides useful outcomes in the preliminary design stage for safety assessment of the training ship navigation during sailing

SEAKEEPING PREDICTION OF DEEP-V HIGH SPEED CATAMARAN USING COMPUTATIONAL FLUID DYNAMICS APPROACH

Seakeeping is the dynamic response of the ship in waves that may affect to passenger’s uncomfortability due to a harsh environmental condition.  Therefore, an extensive assessment of seakeeping performance in the initial step of ship design is necessarily required. The authors here proposed to analyze the seakeeping performance of ‘deep-V’ high speed catamaran using Computational Fluid Dynamics (CFD) approach. Several effects of Froude number (Fr), wave-length

Buckling criteria for subsea pipeline

Oil and gas production in subsea operation continues to the extreme depth. Harsh environment and severe operation of oil and gas transportation due to high pressure and temperature become crucial for pipeline transportation. Consequently, The pipelines will deform to buckle shape which affect to integrity of pipeline. This phenomenon should be considered in design of pipeline to provide reliability of pipeline operation during time life period. The design result of pipelines is according to DNV F 101 whereas the magnitude of pipeline curvature will validate by ANSYS 14 to ensure pipeline reliability

Seakeeping evaluation of semi-swath vessel in head-seas using time domain simulation

Small Waterplane Area Twin Hull (SWATH) and Catamaran vessels are known to have more stable platform as compared to mono-hulls. A further advantage of SWATH as compared to Catamaran is its smaller waterplane area that provides better seakeeping qualities. However, the significant drawback of the SWATH vessel is when encountering head-sea at high forward speed. Due to its low stiffness, it has a tendency for large pitch motions. Consequently, this may lead to excessive trim or even deck wetness. This phenomenon will not only degrade the comfortability but also results in structural damage with greater safety risks. In this research a modified SWATH design is proposed. The proposed design concept represents a combination of Catamaran and SWATH hull features that will lead to reduce in bow diving but still maintains good seakeeping capabilities. This is then called the Semi-SWATH vessel. In addition, the full-design of this vessel has been equipped by fixed fore fins and controllable aft fins attached on each lower hull. In the development of controllable aft fins, the PID controller system was applied to obtain an optimal vessel’s ride performance at speeds of 15 (medium) and 20 (high) knots. In this research work, the seakeeping performance of Semi-SWATH vessel was evaluated using time-domain simulation approach. The effect of fin stabilizer on the bare hull performance is considered. The validity of numerical evaluation was then compared with model experiments carried out in the Towing Tank at Marine Technology Laboratory, UTM. It was shown that the Semi-SWATH vessel with controllable fin stabilizer can have significantly reduction by about 42.57% of heave motion and 48.80% of pitch motion

Prediction of an optimum total resistance coefficient on catamaran using Design of Experiment (DOE) incorporated with CFD approach

In presence of complex hydrodynamic interferences between two demihulls on a catamaran ship has been prone to have a reliable prediction to her optimum total resistance. To achieve this, the author presents a Computational Fluid Dynamic (CFD) modelling incorporated with Design of Experiment (DOE) approach. Several parameters such as effect of Froude number ( ) with respect to various lateral separation ratios (S/L) of the catamaran have been taken into account. Here, the optimum total resistance coefficient (CT) has been mainly set within the range of S/L ratio 0.2 = S/L = 0.4 associated with Froude number 0.56 = = 0.66. The primary objective function of this optimization model has led towards minimizing a drag force and increased a lift force with respect to the above S/L ratios. In general, the simulation results had seemed quantitative similarity values for the optimum of 0.6589, 0.6599 and 0.6596 with S/L ratios of 0.2, 0.3 and 0.4, respectively. In the case of = 0.56, the optimum S/L ratios of 0.2993 and 0.3988 have resulted in insignificant reduction of CT by 0.62% and 0.32% as compared to S/L of 0.3 and 0.4, respectively. Similarly, the optimum S/L ratios of 0.2750 and 0.3750 with = 0.66 have led to reduce by 0.14% and 0.46% as compared to S/L of 0.3 and 0.4, respectively. This CFD simulation results are very useful as preliminary data for the optimised ship resistance, which is mainly required to predict a ship powering in the early design stage

A fundamental CFD investigation of offshore structures for artificial coral reef development

Rigs-to-Reefs (R2R) is an alternative for oil and gas industry for decommissioning purpose. The program will benefit marine life as an artificial reef for a sustainable solution to promote ecosystem growth. For any oil platform considered for reefing, an extensive study on the suitability and performance of the artificial reef is essential. These studies will evaluate the stability and relevance of the structure as an artificial reef when deployed on the seabed. This paper presents the research on dynamic response and flow characteristics of a conceptual proposed R2R platform. The Computational Fluid Dynamics (CFD) simulation is intended to study the dynamic responses and flow characteristics analysis of a jacket oil platform for optimal settlement and growth of corals. Artificial reef performances were evaluated by calculating the performance indices of the upwelling and back eddy profile. It was found that the upwelling efficiency index is higher at current direction normal to the platform due to the higher frontal area exposed to the incoming flow. Meanwhile, back eddy efficiency index shows a significant low value for all directions. The CFD results presented will be discussed in terms of the possibility of better performance of an artificial reef which considering engineering and biological aspects

Theoretical and experimental analysis of a slack towline motion on tug-towed ship during turning

Concerning the safety of towing, a slack towline condition on tug-towed ship motions interaction during turning is necessary to be studied. This paper presents a fundamental investigation aimed at gaining a more comprehensive insight into the basic mechanism of the slack towline condition identified via several towing parameters affecting its occurrence. Through applying steady turning theory of the tug-towed ship presented by Fitriadhy and Yasukawa (2011a), a slack towline formula is derived, which is capable of defining a boundary limit of their turning ability before the towline falls into the slack condition. Several criteria of the slack towline are described and the reason behind its proposed formula explained. A comprehensive theoretical clarification is presented here using nonlinear analysis for a better prediction of their turning ability including capturing the slack towline condition, where effects of towline length and deflection-rudder angle are discussed. The results revealed that the tug was vulnerable to lose handling of towing with respect to the towed ship that led to the towline falling into the slack condition. For validation, a series of turning tests for the towed ship model were carried out at Towing-Tank in which the theoretical approaches agreed qualitatively with the experimental results

Mooring pattern optimization using a genetic algorithm

In this paper, a constraint Genetic Algorithm is used for the purpose of mooring pattern optimization. The Genetic Algorithm is applied through a mathematical formulation which is introduced to define a typical mooring system optimization problem. The mathematical formulation is used in a case study on a spread moored crane barge, operating in the vicinity of a jacket type platform, in order to minimize its surge motions towards the platform. For this purpose, a set of criteria regarding clearances between anchors and seabed preinstalled facilities (pipelines), and also between the crane barge and the jacket platform are presented and considered. An automatic process of repetitive analyses implementing a MATLAB code as an interface between the Genetic Algorithm and a mooring system analysis program is used, and an optimum solution is resulted by performing 4000 quasi-dynamic analyses in time domain. The effectiveness of the Genetic Algorithm in leading to an optimum mooring system pattern is studied and it is shown that using a proper formulation of the problem, the Genetic Algorithm can be a very useful tool for finding an optimum pattern for mooring systems in fields with constraints on anchor locations and vessel motion