DYNAMIC RESPONSES OF FLOATING OFFSHORE PLATFORMS WITH LARGE HULLS

Spar and semi-submersible are the most common types of floating offshore platforms used for deepwater operations. The spar consists of a hollow cylindrical deep-draft floating hull that provides buoyancy, with strake surrounding the hull to reduce vortex induce vibration and to held in place by mooring lines. To remain stable, it is important to maintain the centre of gravity always below the centre of buoyancy. The semi-submersible comprises of two horizontal water tight pontoons and number of column units that stand on the pontoons to provide support to the deck structure. It is held in place by mooring lines and dynamic positioning system. Both these types of platforms are made up of large-sized hull for providing buoyancy. As the ratio of the diameter of these structures to the wave length is above 0.2, the wave diffraction theory is the correct theory to be applied for the calculation of wave forces and wave damping, according to the literature. However, the application of diffraction theory, even linear one, is very much complicated and requires very costly commercial software. Hence, many research papers have reported results of dynamic analysis, using Morison equation for such cases, reasoning that for a considerable part of the frequency range, the ratio of diameter to wave length is still below 0.2. This is because of the ease of using Morison equation in programming and the possibility of incorporating the various non-linearity in the analysis. Yet, it has been established that the consultants are using only diffraction analysis for the analysis and design of such platforms. The aim of this study was to determine and compare the responses by both Morison equation and diffraction theory to the model test responses, and to suggest nonlinear multiple regression curves to estimate the structure responses. Model tests were conducted for spar and semi-submersible platform models in the wave tank at the Offshore Engineering Laboratory of Universiti Teknologi PETRONAS and the responses were measured. The respective prototypes were analyzed using a numerical Newmark Beta time domain integration method that was developed by using Matlab program. The platforms were designed as rigid bodies and three degree of freedom; surge, heave and pitch were considered. Linear wave theory and Morison equation were used for wave force determination in time domain analysis. A commercial software was employed to determine responses of the structures by Linear Wave Diffraction module. These results proved that the diffraction theory results were much closer to the actual model test results, thereby proving that using Morison equation for such platforms is not justified. Using the results of the diffraction analysis for a large number of platforms and conducting a non-linear multiple regression analysis, this thesis also suggests formulae to obtain suitable regression curves for predicting the diffraction responses of the spar and semi-submersible for any dimension and draft within the range suggested

COMPARATIVE STUDY OF THE DYNAMIC RESPONSE OF FLOATING PLATFORMS SUBJECTED TO LONG-CRESTED AND SHORT-CRESTED WAVES

Spar and semi-submersible platforms are the common types of large floating offshore platforms operating in deepwater regions. Due to lack of sufficient analytical, experimental and statistical data regarding the performances of such platforms subjected to the real sea condition based on short-crested waves. These types of platforms are normally designed for long-crested waves. In the real sea condition, generally short-crested waves exist

Parametric Study for the Critical Tubular Joint of the Jacket Structure

The final year project titled 'Parametric Study for the Critical Tubular Joints of the Jacket Structure' was carried out with the aim of studying the trends of the joint of the submerged jacket structure accordingly to its conditions. To achieve the aim of the project, several objectives been designed. Firstly is to study different load case of the jacket and to determine the critical joint trends of the jacket when the jacket subjected to several different loading conditions. Extensive literature review was conducted in order to come up with ideas about the offshore structure, joint of the jacket structure, environmental forces and the SACS program review, which the software been used to run the analysis. The research been carried out for the five fixed jacket models with various loading conditions, as all the data been input to the SACS program, analysis been carried out on the jacket structure. The result of the joint can with the maximum unity check been focused and been analyzed. The results then been presented in the graphical form, which shows the relationship between depth of the critical joint and total weight of the model; and depth of the critical joint and the water depth. Environmental and the model weight were the significant elements that contribute to the depth of the critical joint. From the graphical results presented the trends of the critical joints been determined

Parametric Study for the Critical Tubular Joint of the Jacket Structure

The final year project titled 'Parametric Study for the Critical Tubular Joints of the Jacket Structure' was carried out with the aim of studying the trends of the joint of the submerged jacket structure accordingly to its conditions. To achieve the aim of the project, several objectives been designed. Firstly is to study different load case of the jacket and to determine the critical joint trends of the jacket when the jacket subjected to several different loading conditions. Extensive literature review was conducted in order to come up with ideas about the offshore structure, joint of the jacket structure, environmental forces and the SACS program review, which the software been used to run the analysis. The research been carried out for the five fixed jacket models with various loading conditions, as all the data been input to the SACS program, analysis been carried out on the jacket structure. The result of the joint can with the maximum unity check been focused and been analyzed. The results then been presented in the graphical form, which shows the relationship between depth of the critical joint and total weight of the model; and depth of the critical joint and the water depth. Environmental and the model weight were the significant elements that contribute to the depth of the critical joint. From the graphical results presented the trends of the critical joints been determined

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

Numerical investigation of the effect of ocean depth variations on the dynamics of a ship mounted two-DoF manipulator system

The dynamics of a ship need to be considered in the development of a manipulator system that will be applied to the ocean-based operation. This paper aims to investigate the effect of ocean depth variations on the ship motion as disturbances to a ship-mounted two-DoF (Degrees of Freedom) manipulator joint torque using an inverse dynamics model. Realization is conducted by deriving the mathematical model of a two-DoF manipulator system subject to six-DoF ship motion, which is derived by using Lagrange-Euler method. It is then combined with numerical hydrodynamic simulation to obtain the ship motions under ocean depth variations, such as shallow (50 m), intermediate (750 m), and deep (3,000 m) waters. Finding results show that randomness of the ship motions appears on the manipulator joint torque. In the azimuth link, maximum joint torque is found in shallow water depth with an increment of 8.271 N.m (285.69 %) from the undisturbed manipulator. Meanwhile, the maximum joint torque of the elevation link is found in intermediate water depth with an increment of 53.321 N.m (6.63 %). However, the difference between depth variations is relatively small. This result can be used as a baseline for sizing the electrical motor and developing the robust control system for the manipulator that is mounted on the ship by considering all ocean depth conditions

Anti-IL-17A antibody-associated de novo vitiligo: Case report and review of literature

Interleukin (IL)-17 inhibitor is a biological therapy approved for moderate to severe psoriasis and psoriatic arthritis. The common adverse events of IL-17 inhibitor include injection site reaction, infections, nasopharyngitis, and headache. However, vitiligo associated with the use of IL-17 inhibitors was rarely reported in the previous literature. Here we described a woman who developed de novo vitiligo after 4 months of IL-17A inhibitor treatment for psoriasis and psoriatic arthritis. Upon discontinuation of IL-17A inhibitor and shifting to a broader T cell inhibitor—cyclosporine, our patient had control of both psoriasis and vitiligo and achieved 75% repigmentation after 3 months of oral cyclosporine without phototherapy. Due to the increasing use of anti-IL-17 biologics in psoriasis patients, clinicians should inquire about vitiligo’s history before treatment and inform patients of the possible adverse effects

A study on Malaysia consumer perception towards buying an automobile

This study is to conduct the research to examine the relationships of the factors, particularly perceived quality, perceived value and perceived risk that will affect on Malaysia consumer purchase decision towards cars. Survey using convenience sampling was done at Klang Valley to customers’ age between 23 to 65 years old and above. This study showed significant results and the association between the three factors mentioned previously with purchase decision

Effect of pretreatment process on bioconversion of kenaf (hibiscus cannabinus l.) core to glucose.

Kenaf (Hibiscus cannabinus L.) is a renewable carbon-rich lignocellulosic resource for fermentable sugars. In this study, kenaf cores cultivar V36 from four-month-old stems were pretreated by i) physical, ii) physical and thermal, and iii) physical and chemical methods. The celluloses of pretreated kenaf core particles were then hydrolyzed into fermentable sugars by cellulase from Trichoderma reesei (C2730). The pretreated kenaf core particles were incubated for 48 h at 37 °C. The efficiency of bioconversion was mainly dependent on the pretreatments applied prior to the hydrolysis process. The effects of the pretreatments on kenaf core’s lignin, holocellulose, and cellulose contents were also determined. Kenaf cores without pretreatment had 19.4% lignin, 86.2% holocellulose, and 47.4% alpha-cellulose. The combination of physical and chemical pretreatment on kenaf cores cultivar V36 resulted in a higher cellulose content (92.49%) and produced 50 times higher sugar concentration than the physical pretreatment