Semi-Active Magneto-Rheological Damper and Applications in Tension Leg Platform / Semi-Submersible

A reliable and cost-effective way to protect the hydrocarbon production modules in harsher environments has been crucial to the success of offshore oil and gas projects. Nevertheless, the excessive tension variations in the top-tensioned risers (TTRs) can lead to catastrophic structural integrity issues. Magneto-rheological (MR) damper is a controllable device which can reduce the tension variations. However, the integration and behaviors of MR damper are remained as significant challenge for floating platforms. The main purpose of this research is to develop numerical analysis tool to analyze the specific characteristics of MR damper in offshore structural dynamics and interactively changing the structural behaviors correspond to various external loadings. The research methodologies were initiated by modeling the hydro-pneumatic tensioner (HPT) of TTR in component-level, which included hydro-pneumatic components and viscous fluid frictional effect. The HPT model was numerically incorporated with MR damper. This numerical tool combined with CHARM3D, a fully-coupled time-domain dynamic analysis program for floating bodies, mooring lines, and risers. The responses of combined numerical model were simulated by coupling with tension leg platform (TLP) and dry-tree semi-submersibles (DTS), respectively, under 100-year extreme condition and 1000-year survival condition of central Gulf of Mexico (GOM). The MR damper was controlled by using semi-active controllers that were developed in fuzzy-logic and skyhook schemes. Mathieu’s stability analysis was utilized to predict TTR’s parametric stability. The results manifested that total required stroke length in DTS can be reduced by as much as 0.963 meter in the studied case after MR damper was incorporated with semi-active fuzzy logic controller. By providing damped and deformed contact surface, MR damper was able to redistribute the excessive tension in the tensioner cylinders during extreme bottom-out motion. Moreover, the dynamic tension variations of TTR can be suppressed by 94 percent in the case of TLP. In conclusion, these results are beneficial to assure service life span of TTR’s tensioner and moderate the relevant operational expenditure (OPEX). In addition, the reductions of the total required stroke length and tension variations in DTS have enabled the platform designer to be more flexible in the sizing of the DTS and TTR tensioners

Numerical modelling of convective wave using fractional-step method

Wave equation is often solved independently without involving Continuity and momentum equations and this implies that the numerical simulation is restricted to wave phenomenon in static fluid. Meanwhile the available wave models are more suitable for the case in which the convective effect outweighs the local wave fluctuation. However, there are many fluid dynamics phenomena which involves equally significant effect of convective flow and wave disturbance, such as mountain waves, strong aeroacoustics wave and strong ocean waves. These flows need to be simulated by computational coupling. We have developed a solver using fractional step method for the construction of convective wave coupling algorithm. In our implementation, we model a flow across the wave-excited lid driven cavity as our case study, in which the model is to imitate the aerodynamic mountain wave. We found that the convective wave ratio plays a great role in affecting the velocity field of the fluid domain

Performance of the lightning air terminal for the macro model of buildings

"Lightning is a natural occurring phenomenon having a very high voltage and current. Building protection from the effect of lightning stroke is one of the most important features. Lightning flash, nature changes with increasing the clearance between the ground structure and the cloud. Providing proper protection to the building, Frankling rod/Lightning air terminal is an essential element to receive the lightning flashes in order to make sure the protection of building. In this paper a down scaled building with four lightning rods has been chosen to see how the lightning rods with different air gap and view of the building perform, in lightning flash. The building is tested with three different views which are front, back and side views. The lightning rods provided different air gaps/clearance between the plain and the top plate. Single stage impulse generator is used. A voltage up to 90 kV is applied to analyze the lightning flash receiving ability of lightning rods. Through experimental work the lightning flash receiving ability is studied in detail for three views of the down scaled building.

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

Advanced automation and robotics for high volume labour-intensive manufacturing

High volume, labour-intensive manufacturing operations pose several challenges for successful operations. It is an even bigger challenge to move away from manual dependency and shift towards automation of production processes. There seems to be no general agreement among researchers on what are the critical success factors (CSFs) on the implementation of advanced automation and robotics processes in the manufacturing environment. Success factors vary across the manufacturing industry and also organizational units. This paper attempts to elicit the opinion and perception of academic professionals with links to high volume labour-intensive manufacturing industry. A systematic literature search was conducted on the topic and semi-structured interviews were conducted with experts to gather their views on CSFs. Results from the literature search and interviews revealed that factors related to Organization Strategy, Culture, and Structure; Top management support; Past experience, staffing, and learning; Project management, planning, and control; Finance, and resource availability; Technology maturity and vendor support; to be critical for the success of the production process automation project initiatives. Findings from this study can be used as guidelines to ascertain CSFs for organizations and strategy planning. Manufacturing organizations can also use this study to evaluate their organizational readiness and enhance the level of automation further

On stability of time marching in numerical solutions of rayleigh-plesset equation for ultrasonic cavitation

Ultrasonic irradiation approach has become one of the most popular methods applied in chemical processing including lignocellulosic biomass pretreatment and industrial cleansing. The phenomenon of ultrasonic cavitation can be indeed delineated via the Rayleigh-Plesset equation (RPE), which governs the transient radius of the bubble. Nonetheless, the time marching in the numerical solutions for RPE is highly unstable, which cannot be assured using von Neumann analysis. High sensitivity of RPE to time step may lead to extremely long computational time. The lack of numerical investigation into the time stepping issue of RPE has hindered in-depth simulation of ultrasonic cavitation. Therefore, the purpose of this paper is to investigate the stability criterion of time stepping for RPE in different time progression schemes, namely Euler explicit, 2nd order Taylor’s method, 4th order Runge-Kutta, Runge-Kutta Fehlberg and Cash-Karp Runge-Kutta method. A simple modified adaptive time step method and a independence study has been introduced in this paper for fast, stable and accurate computation of RPE. Compared with the traditional constant time marching method, the new model is able to improve the computational cost significantly without affecting the time marching stability and resolution of the results. Among the investigated method, Runge-Kutta family solvers have higher computational accuracy, with the cost of higher critical a value. The model is also applied to compute the pressure and temperature hike during bubble collapse due to different sonication power. The simulation results show that the ultrasonic irradiation with higher sonication power could produce a higher energy to break the lignocellulose wall

Suppression of sloshing in liquefied natural gas during ocean-going transportation by using spherical floaters and blanket

Malaysia National Key Economic Area (NKEA) is endeavouring to promote the liquefied natural gas (LNG) as one of the dominant greener energy resources which significantly benefits Malaysia as the world's third-largest exporter of LNG. However, safer sea transportation of LNG is in high demands because sloshing of liquid bulks can cause structural damage and disastrous safety issue towards the LNG carrier. Conventional methods, such as baffle inside the liquid tank still has major problems as it could be damaged by very violent liquid sloshing and require regular inspection. On the other hand, floaters and blanket have been proven as a more effective solution. However, a better understanding of the behaviours of floaters and blanket is needed to design more effective anti-sloshing devices, which have huge potential benefits to Malaysian LNG transporters. In this paper, sloshing experiment under random unidirectional excitations was conducted to investigate the effectiveness of liquid surface suppression by using floaters and blanket. The results of the liquid free surface without suppressors, liquid surface covered by scattered floaters and liquid surface covered by blanket were analysed and discussed. The findings are expected to contribute to the design of anti-sloshing devices towards safer sea transportation of LNG which could largely benefit our nation

Challenges and opportunities of marine propulsion with alternative fuels

The increasingly stringent shipping emissions regulations and global decarbonisation movement have prompted the adoption of alternative fuels in the shipping industry. This review presents the performance results and evaluation of alternative fuel engines under low-medium speed operation that has not been considered by existing reviews. This operating regime is typically used in marine propulsion. Relevant articles published by reputable journals were retrieved from scholarly databases and analysed. The evaluated alternative fuels were waste plastic oil (WPO), tyre pyrolysis oil (TPO), biodiesel, ammonia, vegetable oil (VO), and waste lubricant oil (WLO). Neat WPO and TPO demonstrated poorer emissions performances than diesel; alternatively, retarding the fuel injection timing of the WPO engine and blending the TPO with biodiesel had elevated engine performances substantially. As compared to VO degum and blending VO with diesel, VO preheating was a more promising approach to augment engine performance. Ammonia is an attractive candidate owing to its carbon-free chemical composition, but novel technologies are needed to address its terribly high NOx emission. Diesel-like fuel (DLF) derived from WLO produced notably better engine performance than fossil diesel. This review provides insight into liquid alternative fuels performances for low-medium speed engine operation, whose combustion physics is considerably different from high-speed operation. Such understandings are vital to address the current issues regarding marine engine systems, promoting the development of combustion technologies and alternative fuels uptake in marine propulsion

Preliminary investigation on the disruption of microalgae cell wall using vortex induced vibration (VIV)

Scenedesmus sp. is industrially known for its high lipids content that can be used in biofuels production. Most of the conventional mechanical methods to disrupt the microalgae cell wall use high frequency approaches. The conventional high frequency methods have few disadvantages which are high energy consumption, high cost and application of solvents which are the cause of environmental pollution. In this paper, a low frequency method called vortex induced vibration (VIV) is proposed to replace the conventional mechanical methods to disrupt microalgae cell wall. An experimental rig has been designed and fabricated for this experiment. Based on the experiment, the result shows that VIV method has the possibility to break microalgae cell wall since the turbidity decrease throughout the days

Suppression of vortex-induced vibration of a rigid cylinder using flexible shrouding

Experimental investigations were conducted to address the reduction of vortex-induced vibration (VIV) and mean drag coefficient (Cd mean) acting on the oscillating cylinder fitted with a shroud of various parameters. The effectiveness of the shrouds in suppressing the VIV of a short rigid cylinder was investigated by varying the mesh size (B) and mesh thickness (H). The experiments were performed in water flume in NAHRIM and data analysis of Cross-Flow (CF) and In-Line (IL) vibration amplitudes, IL and CF frequencies, mean drag coefficient responses were carried out. Calculation of the laminar boundary layer thickness around a circular cylinder was carried out as a benchmark in deciding the thickness of the mesh. The effect of mesh size and mesh thickness of shrouds was also addressed in this article. From the results obtained, it can be observed that the shroud with mesh size B = 0.2D and mesh thickness H = 0.03D achieved an optimum condition where it was able to suppress the amplitude without increasing Cd mean, with 76.62% of amplitude reduction and 48.40% of Cd mean reduction