Numerical modelling of multiple tuned mass damper equipped with magneto rheological damper for attenuation of building seismic responses

TMD is basically designed to be tuned to the dominant frequency of a structure which the excitation frequency will resonate the structural motion out of phase to reduce unwanted vibration. However, a single unit TMD is only capable of suppressing the fundamental structural mode and for multimode control, more than one TMD is needed. In this study, a 3-storey benchmark reinforced structural building subjected to El Centro seismic ground motion is modelled as uncontrolled Primary Structure (PS) by including properties such as stiffness and damping. For the case of controlled PS which the passive mechanism is included to the system, optimum parameters of both TMD and Multiple TMD (MTMD) are designed to be tuned to the dedicated structural modes where the performance is dependent on parameters such as mass ratio, optimum damping ratio, and optimum frequency ratio. The input and output components of structural system arrangements are then characterized in the transfer function manner and then converted into state space function. For enhancement of the passive system, Magneto-Rheological (MR) damper is added to both single TMD and MTMD passive system. The response analysis is executed using both time history and frequency response analysis. From the analysis, semi-active case is the most effective mechanism with 99% displacement reduction for the third and second floors, and 98% for the first floor, compared to the uncontrolled case. It is concluded that the MR damper significantly contributed to the enhancement of the passive system to mitigate structural seismic vibration

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

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 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

Sloshing in a closed domain under unidirectional excitation

1145-1153Sloshing is a phenomenon where a partially filled tank is exerted into various environmental sea conditions, such as wave and wind. Sloshing in a tank of liquefied natural gas carrier can lead to structural damage of tank structures and motion instability of the carrier. Thus, sloshing analysis needs to be conducted beforehand to minimize the risk of damages. This paper presents experimental and numerical study on sloshing phenomenon in a prismatic membrane tank model under unidirectional excitation with 30% water filling condition. A regular wave motion stimulated by the linear actuator was applied to the model tank and recorded by a video camera. Meanwhile, OpenFoam software was used to simulate the sloshing numerically in a volume of fluid method based on Navier-Stokes theorem. The sloshing patterns and free surface elevation in the prismatic membrane model tank, with the same input amplitude and frequency, were investigated for both cases. Both experimental and simulation results showed reasonable agreement on the sloshing profile, while the internal free surface elevation in the closed domain indicated a deviation with maximum absolute error of 4.9 cm

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

Dynamic behaviours of damaged stability for floating energy storage unit after accidental collision

The transient dynamic behaviour of floating energy storage unit (FESU) is a result of coupling between three non-linear effects, which are sloshing of floodwater, wave loading, and FESU dynamics. The coupling of these effects would result in the catastrophic failure of the FESU in extreme conditions. Computational Fluid Dynamics (CFD) has shown that it holds great potential in solving the problem in the time domain, which is suitable for the transient stage. In this study, CFD simulation of damaged stability was conducted by using OpenFOAM to determine the dynamic response of FESU under the effects of floodwater and wave in transient flooding. OpenFOAM CFD simulation was conducted for the flooding of barge shaped FESU with different water inlet and air outlet sizes in still water condition followed by damaged stability in Stokes’ fifth-order beam wave and head wave condition. Dynamic responses of FESU, such as roll, pitch, heave, and floodwater volume flow rates were determined using the dynamic meshing solver of OpenFOAM. Simulation results showed similarity to experimental results within the time frame of 16 seconds. Reduction in water inlet area and air outlet area decreased the flooding time and flow rate of flood water. The amplitude of vibration of roll and pitch motion increased as the flood water volume was increased due to the force of floodwater exerted on the wall. Sloshing effects also caused the model to roll and pitch in secondary vibrational motion. Due to the coupling effect of the three non-linear criteria, the inflow and outflow of floodwater changed with time, which concludes that transient effects should not be ignored in the damaged stability assessment of FESU

Numerical analysis of point absorber for wave energy conversion in Malaysian seas

Wave energy conversion by using point absorber has recently gained intensive research in renewable energy. However, a majority of research works only focused on the regions with high wave heights, which may not be readily achievable in Malaysian seas condition. As the technology of point absorber facing the concern on less-applicability in low wave height conditions in Malaysia, a numerical modeling to understand the maximum potential power output to be generated by point absorber is now in demand to predict the power capture ability of point absorber in Malaysian waters. In order to complete this research gap, this paper is aiming to determine the sensitivity of different configurations of power take-off system in point absorber and to numerically analyze the potential maximum power output to be generated by the point absorber in Malaysian water, under regular wave motion. The significance of this study leads to a better understanding of the envelope of power output generated by point absorber in Malaysian seas. The methodology is conducted with theoretical modeling of point absorber, developing a numerical model of power take-off system to identify the maximum magnetic flux density of different stator-translator configuration, and simulating the power output of point absorber in time-domain under regular wave condition based on Malaysia seas data. The results show that power output of point absorber can be increased by a double-sided stator. The envelope of maximum power output to be generated has been identified. This research provides a further understanding of the development of point absorber technologies in Malaysian seas condition

Principal component analysis on meteorological data in UTM KL

The high usage of fossil fuel to produce energy for the increasing demand of energy has been the primary culprit behind global warming. Renewable energies such as solar energy can be a solution in preventing the situation from worsening. Solar energy can be harnessed using available system such as solar thermal cogeneration systems. However, for the system to function smoothly and continuously, knowledge on solar radiation’s intensity several minutes in advance are required. Though there exist various solar radiation forecast models, most of the existing models requires high computational time. In this research, principal component analysis were applied on the meteorological data collected in Universiti Teknologi Malaysia Kuala Lumpur to reduce the dimension of the data. Dominant factors obtained from the analysis is expected to be useful for the development of solar radiation forecast model