Papers by Khoo Boo Cheong
International Journal of Multiphase Flow, 2017
arXiv (Cornell University), Jan 27, 2023
Long Short-Term Memory (LSTM) network-driven Non-Intrusive Reduced Order Model (NROM) for predict... more Long Short-Term Memory (LSTM) network-driven Non-Intrusive Reduced Order Model (NROM) for predicting the dynamics of a floating box on the water surface in a wavemaker basin is addressed in this study. The ground truth or actual data for these wave-structure interactions (WSI) problems, namely box displacements and hydrodynamic forces and moments acting on the box due to wave interaction corresponding to a particular wave profile, are computed using the Smoothed Particle Hydrodynamics (SPH). The dimensionality of the system is first reduced using the Discrete Empirical Interpolation Method (DEIM) and the LSTM is applied to the reduced system resulting in a DEIM-LSTM network for developing a surrogate for prediction. The network is further enhanced by incorporating the physics information into the loss function resulting in a physics-informed LSTM (LSTM-PINN) for predicting the rigid body dynamics of box motion. The performance of predictions for these networks is assessed for the two-dimensional wave basin WSI problem as a proof-of-concept demonstration.
Proceedings of the 4th International Conference of Fluid Flow, Heat and Mass Transfer, Jun 1, 2022
International journal of modern physics., 2014
To generate the hypervelocity (above 5 km/s) test flow for the experimental study of reentry phys... more To generate the hypervelocity (above 5 km/s) test flow for the experimental study of reentry physics, a shock-expansion tube or tunnel is the only qualified test facility by far. In such a facility, the working gas shall be compressed by an extremely strong shock wave, e.g., Ms=27.7 for the 8 km/s test condition. Therefore, thermo-chemical nonequilibrium phenomena may occur in the gas post the shock wave. Such phenomena, consequently, can incur difficulties in diagnostic and measurement to experimental study, and instability problems to numerical analysis on the other hand. The present paper will focus on the numeric-aid diagnostics of the flow conditions.
Flow Measurement and Instrumentation, 2022
Physics of Fluids, 2020
This study investigates the Taylor–Couette flow (TCF) with a longitudinal corrugated surface on a... more This study investigates the Taylor–Couette flow (TCF) with a longitudinal corrugated surface on a stationary outer cylinder and a rotating smooth inner cylinder using large eddy simulation for three values of amplitude to wavelength ratios (A*) (0.1875, 0.2149, and 0.25) to explore the influence of the corrugated surface on the flow structures and the variation of torque for a wider range of Reynolds numbers (Re) (60–650). From the results, four flow regimes are observed. At Re = 60, initially, a pair of secondary vortices appears at the inner wall of the minimum gap region and it evolves to a pair of axisymmetric stationary wall induced vortices (ASSWIVs) in the maximum gap region. As Re increases to 80, 85, and 103 for the three values of A* (0.1875, 0.2149, and 0.25), respectively, another pair of axisymmetric stationary secondary vortices is seen at the minimum gap region of the inner wall. A further increase in Re (Re > 125, 130, and 138 for the three values of A*, respectiv...
Journal of Physics: Conference Series, 2018
Gas-liquid two-phase flow measurement is challenging in comparison to single phase flow measureme... more Gas-liquid two-phase flow measurement is challenging in comparison to single phase flow measurement as their dynamics are more complex. This study aims to investigate the performance of a U shape Coriolis mass flowmeter (CMF) to measure gas liquid two-phase flow via both experimental measurements and numerical simulation. It was observed from both measured and simulation results that the measurement performance of CMF was mainly affected by variation of mixture density and variation of flow pattern associated with gas entrainment. The findings provide fundamental fluidic dynamics of on-line multiphase flow measurements in harsh environments.
The separating characteristics of high performance liquid chromatography (HPLC) columns, measured... more The separating characteristics of high performance liquid chromatography (HPLC) columns, measured in terms of the height equivalent of a theoretical plate (HETP) and skewness of the eluted peak, are investigated using computational fluid dynamics (CFD). Gradually expanding and contracting sections are introduced at the inlet and outlet, respectively, in columns with and without frits and their performance was compared with that of the conventional columns without expanding and contracting regions.
Journal of Rheology, 2013
This paper is concerned with the numerical modelling of a slow (creeping) flow using a particleba... more This paper is concerned with the numerical modelling of a slow (creeping) flow using a particlebased simulation technique, known as dissipative particle dynamics (DPD), in which the particles mass is allowed to approach zero to simultaneously achieve a high sonic speed, a low Reynolds number and a high Schmidt number. This leads to a system of stiff stochastic differential equations, which are solved efficiently by an exponential time differencing (ETD) scheme. The ETD-DPD method is first tested in viscometric flows, where the particle mass is reduced down to 0.001. The method is then applied for the modelling of rigid spheres in a Newtonian fluid by means of two species of DPD particles, one representing the solvent particles and the other, the suspended particle. Calculations are carried out at particle mass of 0.01, with corresponding Mach number of 0.08, Reynolds number of 0.05 and Schmidt number of 6.0 × 10 3. Stokes results are used to determine the DPD parameters for the solvent-sphere interaction forces. The method obeys equipartition and yields smooth flows around the sphere with quite uniform far-field velocities.
Chemical Engineering Science, 2012
We employed dissipative particle dynamics simulations to explore the phase behavior of T-shaped t... more We employed dissipative particle dynamics simulations to explore the phase behavior of T-shaped ternary amphiphiles composed of rodlike cores connected by two incompatible end chains and side grafted segments. By fine-tuning the number of terminal and lateral beads, three phase diagrams for the model systems with different terminal chain lengths are constructed in terms of temperature and lateral chain length, which have some common features and mostly compare favorably with experimental studies with the exception a couple of new phases. It is worthwhile to highlight that the mixed cylindrical phase and the perforated layer phase, as the experimentally observed mesophases exclusive for facial amphiphilies, are found in simulations for the first time. Also, a novel gyroid structure is observed in series of T-shaped ternary amphiphiles for the first time. Furthermore, by evaluating the effective volume fraction of lateral chains, the phase sequence spanning from conventional smectic layer phase via perforated layer structures and polygonal cylindrical arrays to novel lamellar mesophase is established, which is not just qualitatively consistent with the related experimental findings but even the stability windows of some mesophases quantitatively correspond well to experimental results. The success of reproducing the in-plane ordering of rods in the lamellar phase as well as the generic phase diagram of such T-shaped ternary amphiphiles in great detail implies that our genetic model qualitatively captures many of the characteristics of the phase behavior of real T-shaped molecules and could serve as a satisfactory basis for further exploration of self-organization in other related soft matter systems.
Applied Mechanics and Materials, 2011
In this paper, the convex distortion and transient distortion characteristics of TIG welding for ... more In this paper, the convex distortion and transient distortion characteristics of TIG welding for a titanium alloy with finite dimensional thin plate were investigated experimentally and numerically. A three dimensional thermal-mechanical finite element method (FEM) was adopted to predict the characteristics of Transient distortion by taking the initial shape, gravity loading and restriction conditions into account. The simulation results were validated by the experimental results. The results show that the numerical simulations could provide accurate prediction on the Transient temperature and distortion processing. The temperature gradient through thickness, the dimension of plate and the clamping were main factors governing the distortion during welding.
Ultrasound in Medicine & Biology, 2013
In this study, the effect of high-intensity focused ultrasound (HIFU) on Enterococcus faecalis on... more In this study, the effect of high-intensity focused ultrasound (HIFU) on Enterococcus faecalis on both planktonic suspensions and biofilms was investigated. E. faecalis persist in secondary dental infections as biofilms. Glass-bottom Petri dishes with biofilms were centered at the focal point of the HIFU wave generated by a 250-kHz transducer. Specimens were subjected to HIFU exposure at different periods of 30, 60 and 120 s. The viable bacteria, removal effect and bacterial viability of biofilms attached to the Petri dish surface were studied by colony-forming units (CFUs), scanning electron microscopy and confocal microscopy, respectively. The removal and bactericidal effects of HIFU are dependent on the exposure time. A significant reduction in biofilm thickness and CFU was found with the increase in HIFU exposure. The removal or bactericidal effect of HIFU was more significant starting from 60 s of exposure. This study highlighted the potential application of HIFU as a novel method for root canal disinfection.
AIAA Scitech 2019 Forum, 2019
Physics of Fluids, 2017
A rheological constitutive law is developed for a suspension of rigid rods in a Bingham fluid for... more A rheological constitutive law is developed for a suspension of rigid rods in a Bingham fluid for volume fractions ranging up to the semiconcentrated regime. Based on a cell model approach, which allows expressing the shear stress on the particle surface, the particle stress contribution is derived and involves additional yield stress terms related to an ensemble average orientation distribution of the rods. As a first approach, a von Mises criterion is used to describe the composite flow threshold, which is found to be anisotropic in the sense that it depends on the rod orientation. A rod dynamics equation is also proposed and incorporates some diffusion/perturbation due to yielded regions encountered throughout the suspension. In parallel, an equivalent kinetic theory is also developed. The model provides good agreement with shear stress experiments for kaolin pastes filled with steel fibers of two different aspect ratios.
This paper is concerned with the use of oscillating particles instead of the usual frozen particl... more This paper is concerned with the use of oscillating particles instead of the usual frozen particles to model a suspended particle (solid body) in a Dissipative Particle Dynamics (DPD) particle-based simulation method. A suspended particle is represented by a set of basic DPD particles connected to reference sites by linear springs. The reference sites are moved as a whole with the imposed displacement that is calculated using data from the previous time step, while the velocities of their associated DPD particles are found by solving the DPD equations at the current time step. In this way, a specified Boltzmann temperature can also be maintained in the region occupied by the suspended particles and this parameter can be utilised to control the size of suspended particles. Several numerical results in two dimensions are presented to demonstrate attractiveness of the proposed model.
Langmuir : the ACS journal of surfaces and colloids, Jan 16, 2015
The concentration dependence of yield stress and dynamic moduli of kaolinite suspensions is studi... more The concentration dependence of yield stress and dynamic moduli of kaolinite suspensions is studied. Complex electrostatic interactions between kaolinite platelets promote a more liquid-like behavior, with clay particles changing from attractive interactions to a face-face repulsive interaction as the mass fraction of clay particles increases. A yield stress model is developed based on the repulsive interaction between disk-shaped particles, which yields a good prediction of experimental observations when repulsive face-face interaction is dominant. The critical concentration when attractive interaction changes completely to face-face repulsive interaction is estimated from the theory. Four regions are identified in the variation of yield stress as a function of the concentration.
Inverse Problems in Science and Engineering, 2013
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Papers by Khoo Boo Cheong