World Academy of Science, Engineering and Technology, International Journal of Mathematical, Computational, Physical, Electrical and Computer Engineering, Jan 22, 2013
Journal of The Audio Engineering Society, Sep 20, 2016
An Aeolian tone is the whistle-like sound that is generated when air moves past a cylinder or sim... more An Aeolian tone is the whistle-like sound that is generated when air moves past a cylinder or similar object; it is one of the primary aeroacoustic sound sources. A synthesis model of an Aeolian tone has been developed based on empirical formula derived from fundamental fluid dynamics equations. It avoids time consuming computations and allows real-time operation and interaction. Evaluation of the synthesis model shows frequencies produced are close to those measured in a wind tunnel or simulated through traditional offline computations.
Journal of the Acoustical Society of America, Jun 1, 2017
Supersonic crackle, an irritable component of aircraft jet noise, was investigated using model sc... more Supersonic crackle, an irritable component of aircraft jet noise, was investigated using model scale measurements. Near-field results showed Gaussian distribution but far-field had high skewness and even higher in its derivative. Skewness, a measure of asymmetry in the waveform, was compared to screech arising from shock associated noise which was also high but in contrast to crackle its skewness derivative had dropped to a much smaller value than its waveform. Both crackle and screech are nonlinear but their nonlinear properties are entirely different. Crackle is quantified when its derivative skewness becomes larger than its waveform skewness which should exceed 0.3.
The aim of this paper is to propose a method for determining the dispersion relation of a highly ... more The aim of this paper is to propose a method for determining the dispersion relation of a highly stratified medium from measured geometrical patterns of ship-generated internal waves. This is a first step towards devising a practical method for calculating the density distribution of a stratified fluid from the detectable free-surface kinematic signature of the induced internal wake, by using some optical or remote sensing means. We assume that the body which causes the wake moves with a constant velocity along a circular trajectory. By applying the constant-phase method, we derive an explicit solution for the wake crest lines. Then, for an infinitely large ship's turning radius (straight course), a closed-form expression for the dispersion relation versus wake geometry is obtained. A similar approximate form is also obtained for a circular course. Some numerical simulations are presented, and the applicability of the proposed method is demonstrated for several realistic thermocline distributions, measured in lakes and seas.
This paper reports on the numerical investigation of particle saltation in a turbulent channel fl... more This paper reports on the numerical investigation of particle saltation in a turbulent channel flow having a rough bed consisting of 2-3 layers of densely packed spheres. The Shield's Function is 0.065 which is just above the sediment entrainment threshold to give a bed-load regime. The applied methodology is a combination of three technologies, i.e., the direct numerical simulation of turbulent flow, the combined finite-discrete element modelling of the deformation, movement and collision of the particles, and the immersed boundary method for the fluid-solid interaction. It is shown that the presence of entrained particles significantly modifies the profiles of flow velocity and turbulent intensities in the vicinity of a rough-bed. Statistical features of particle translational and angular velocities, together with sediment concentration and volumetric flux density profiles, are presented.
The marine current turbine (MCT) is an exciting proposition for the extraction of renewable tidal... more The marine current turbine (MCT) is an exciting proposition for the extraction of renewable tidal and marine current power. However, the numerical prediction of the performance of the MCT is difficult due to its complex geometry, the surrounding turbulent flow and the free surface. In this paper, the authors have developed a 3D Large Eddy Simulation (LES) numerical code to simulate a three blade MCT under a variety of operating conditions based on the Immersed Boundary Method (IBM) and the Conservative Level Set Method (CLS). The results from the current simulations have shown a great match with the published data and provide a promising potential for more extensive study. Furthermore, the deformation of the MCT blades under operating conditions was modeled by coupling the present code with another in-house Discrete Element Method (DEM) code and clear blade deformation was observed which can be used in future to determine the potential life of a MCT.
This study investigates the non-linear propagation of screech noise emitted by supersonic jets. S... more This study investigates the non-linear propagation of screech noise emitted by supersonic jets. Supersonic jet noise consists of three components: mixing, broadband and screech noise. In order to generate broadband and screech noise the jet has to expand imperfectly, meaning shock waves are formed inside the potential core and interact with the surrounding shear layer. The feedback between the generated noise and the nozzle cause the screech noise pattern. It is associated with high frequency (annoying to the human ear). Near field screech noise obtained from Large Eddy Simulation (LES) of circular supersonics jets is investigated using the Burgers equation, taking into account thermo-viscous effects. The Burgers equation is commonly used to investigate non-linear propagation effects. The initial screech signal is found to consist of two main frequency modes. Significant non-linear effects appear during propagation although the pressure amplitude is no more than a few percentages of the ambient pressure. Saw tooth waves are generated and the amplitude is found to decrease as 1/sqrt(t) for low viscous medium according to Lighthill' 'bunching' theory. Further high frequencies are also generated. Finally, geometrical attenuation is discussed by transforming the plane wave propagation to cylindrical form.
Mathematics and Computers in Simulation, Aug 1, 2020
A static and dynamic large deformation analysis of a tapered beam subjected to concentrated and d... more A static and dynamic large deformation analysis of a tapered beam subjected to concentrated and distributed loads is presented in this paper by using a direct integration technique. The bending stiffness of the beam is coordinate dependent. The nonlinear differential equation is numerically solved using an iterative technique without an algebraic equation solver, thus the computational effort can be reduced. A concentrated mass fixed at the free end and suddenly released is studied, and the time-dependent displacements are presented. Comparison has been made with solutions obtained using Finite Element Analysis and excellent agreement is achieved.
This study investigates the hemodynamic responses of the cardiovascular system when a rotary bloo... more This study investigates the hemodynamic responses of the cardiovascular system when a rotary blood pump is operating in the descending aorta, with a focus on the cerebral, coronary and renal autoregulation, using our in-house cardiovascular emulator. Several improvements have been made from our previous studies. A novel coronary system was developed to replicate the native coronary perfusion. Three pinch valves actuated by stepper motors were used to simulate the regional autoregulation systems of the native cerebral, coronary and renal circulations. A rotary pump was installed in the descending aorta, in series with the heart, and the hemodynamic responses of the cardiovascular system were investigated with a focus on cerebral, coronary and renal circulation over a wide range of pump rotor speeds. Experiments were performed twice, once with the autoregulation systems active and once with the autoregulation systems inactive, to reflect that there will be some impairment of autoregulatory systems in a patient with heart failure. It was shown that by increasing the rotor speed to 3000 rpm, the cardiac output was improved from 2.9 to 4.1 L/min as a result of an afterload reduction induced by the pressure drop upstream of the pump. The magnitudes of changes in perfusion in the cerebral, coronary and renal circulations were recorded with regional autoregulation systems active and inactive.
This article is an open access article distributed under the terms and conditions of the Creative... more This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY
Non-linear sound propagation is investigated computationally by simulating compressible time-deve... more Non-linear sound propagation is investigated computationally by simulating compressible time-developing mixing layers using the Large Eddy Simulation (LES) approach and solving the viscous Burgers Equation. The mixing layers are of convective Mach numbers of 0.4, 0.8 and 1.2. The LES results agree qualitatively with known flow behavior. Mach waves are observed in the near sound field of the supersonic mixing layer computed by the LES. These waves show steepening typical to non-linear propagation. Further calculations using the Burgers equation support this finding, where the initial wave slope has a role in kicking them. No visible non-linear propagation effects were found for the subsonic mixing layers. The effects of geometrical spreading and viscosity are also considered.
The behavior of a MVG vane at three different design angles was simulated with LES on an Eppler e... more The behavior of a MVG vane at three different design angles was simulated with LES on an Eppler e387 airfoil that was suffering flow separation. The e387 airfoil was placed at an angle of attack of 12 degrees and at Reynolds number of 200,000 based on the chord length. Different parameters of the generated vortex from the MVG were analyzed to study the behavior of the vortex. The MVG vanes were found to suppress the separation, with the MVG vane placed at 18.5 being the most effective. It was found that turbulence has a strong effect on the instantaneous behavior of the flow field and the easiest measurable characteristic of the MVG’s effect on the flow separation was its effect on the wall shear stress. Recommendations for the optimum placement of the MVG and its zone of influence are discussed.
The aim of this study is to create a computational model of the human ureteral system that accura... more The aim of this study is to create a computational model of the human ureteral system that accurately replicates the peristaltic movement of the ureter for a variety of physiological and pathological functions. The objectives of this research are met using our in-house fluid-structural dynamics code (CgLes-Ycode). A realistic peristaltic motion of the ureter is modelled using a novel piecewise linear force model. The urodynamic responses are investigated under two conditions of a healthy and a depressed contraction force. A ureteral pressure during the contraction shows a very good agreement with the corresponding clinical data. The results also show a dependency of the wall shear stresses on the contraction velocity. It confirms the presence of high shear stress at the proximal part of the ureter. Additionally, it is shown that an inefficient lumen contraction can increase the possibility of a continuous reflux during the propagation of peristalsis.
International Journal of Numerical Methods for Heat & Fluid Flow, Feb 2, 2023
Purpose-The paper aims to investigate the influence of smooth curvature distributions on the self... more Purpose-The paper aims to investigate the influence of smooth curvature distributions on the self-noise of a low Reynolds number aerofoil and to unveil the flow mechanisms in the phenomenon. Design/methodology/approach-The paper performed Large Eddy Simulation (LES) approach to investigate the unsteady aerodynamic performance of both the original aerofoil E387 and the redesigned aerofoil A7 in a time-dependent study of boundary layer characteristics at Reynolds number 100,000 and Angle of Attack 4-degree. The aerofoil A7 is redesigned from E387 by removing the irregularities in the surface curvature distributions and keeping a nearly identical geometry. Flow vorticity magnitude of both aerofoils, along with the spectra of the vertical fluctuating velocity component and noise level, are analysed to demonstrate the bubble flapping process near the trailing edge and the vortex shedding phenomenon. Findings-The paper provides quantitative insights about how the flapping process of the laminar separation bubble within the boundary layer near the trailing edge affects the aerofoil self-noise. It is found that the aerofoil A7 with smooth curvature distributions presents a 10% smaller laminar separation bubble compared to the aerofoil E387 at Reynolds number 100,000 and Angle of Attack 4-degree. The LES results also suggests that curvature distribution smoothing leads to a 6.5% reduction in overall broadband noise level. Originality/value-This paper fulfils an identified need to reveal the unknown flow structure and the boundary layer characteristics that resulted in the self-noise reduction phenomenon yielded by curvature distribution smoothing.
World Academy of Science, Engineering and Technology, International Journal of Mathematical, Computational, Physical, Electrical and Computer Engineering, Jan 22, 2013
Journal of The Audio Engineering Society, Sep 20, 2016
An Aeolian tone is the whistle-like sound that is generated when air moves past a cylinder or sim... more An Aeolian tone is the whistle-like sound that is generated when air moves past a cylinder or similar object; it is one of the primary aeroacoustic sound sources. A synthesis model of an Aeolian tone has been developed based on empirical formula derived from fundamental fluid dynamics equations. It avoids time consuming computations and allows real-time operation and interaction. Evaluation of the synthesis model shows frequencies produced are close to those measured in a wind tunnel or simulated through traditional offline computations.
Journal of the Acoustical Society of America, Jun 1, 2017
Supersonic crackle, an irritable component of aircraft jet noise, was investigated using model sc... more Supersonic crackle, an irritable component of aircraft jet noise, was investigated using model scale measurements. Near-field results showed Gaussian distribution but far-field had high skewness and even higher in its derivative. Skewness, a measure of asymmetry in the waveform, was compared to screech arising from shock associated noise which was also high but in contrast to crackle its skewness derivative had dropped to a much smaller value than its waveform. Both crackle and screech are nonlinear but their nonlinear properties are entirely different. Crackle is quantified when its derivative skewness becomes larger than its waveform skewness which should exceed 0.3.
The aim of this paper is to propose a method for determining the dispersion relation of a highly ... more The aim of this paper is to propose a method for determining the dispersion relation of a highly stratified medium from measured geometrical patterns of ship-generated internal waves. This is a first step towards devising a practical method for calculating the density distribution of a stratified fluid from the detectable free-surface kinematic signature of the induced internal wake, by using some optical or remote sensing means. We assume that the body which causes the wake moves with a constant velocity along a circular trajectory. By applying the constant-phase method, we derive an explicit solution for the wake crest lines. Then, for an infinitely large ship's turning radius (straight course), a closed-form expression for the dispersion relation versus wake geometry is obtained. A similar approximate form is also obtained for a circular course. Some numerical simulations are presented, and the applicability of the proposed method is demonstrated for several realistic thermocline distributions, measured in lakes and seas.
This paper reports on the numerical investigation of particle saltation in a turbulent channel fl... more This paper reports on the numerical investigation of particle saltation in a turbulent channel flow having a rough bed consisting of 2-3 layers of densely packed spheres. The Shield's Function is 0.065 which is just above the sediment entrainment threshold to give a bed-load regime. The applied methodology is a combination of three technologies, i.e., the direct numerical simulation of turbulent flow, the combined finite-discrete element modelling of the deformation, movement and collision of the particles, and the immersed boundary method for the fluid-solid interaction. It is shown that the presence of entrained particles significantly modifies the profiles of flow velocity and turbulent intensities in the vicinity of a rough-bed. Statistical features of particle translational and angular velocities, together with sediment concentration and volumetric flux density profiles, are presented.
The marine current turbine (MCT) is an exciting proposition for the extraction of renewable tidal... more The marine current turbine (MCT) is an exciting proposition for the extraction of renewable tidal and marine current power. However, the numerical prediction of the performance of the MCT is difficult due to its complex geometry, the surrounding turbulent flow and the free surface. In this paper, the authors have developed a 3D Large Eddy Simulation (LES) numerical code to simulate a three blade MCT under a variety of operating conditions based on the Immersed Boundary Method (IBM) and the Conservative Level Set Method (CLS). The results from the current simulations have shown a great match with the published data and provide a promising potential for more extensive study. Furthermore, the deformation of the MCT blades under operating conditions was modeled by coupling the present code with another in-house Discrete Element Method (DEM) code and clear blade deformation was observed which can be used in future to determine the potential life of a MCT.
This study investigates the non-linear propagation of screech noise emitted by supersonic jets. S... more This study investigates the non-linear propagation of screech noise emitted by supersonic jets. Supersonic jet noise consists of three components: mixing, broadband and screech noise. In order to generate broadband and screech noise the jet has to expand imperfectly, meaning shock waves are formed inside the potential core and interact with the surrounding shear layer. The feedback between the generated noise and the nozzle cause the screech noise pattern. It is associated with high frequency (annoying to the human ear). Near field screech noise obtained from Large Eddy Simulation (LES) of circular supersonics jets is investigated using the Burgers equation, taking into account thermo-viscous effects. The Burgers equation is commonly used to investigate non-linear propagation effects. The initial screech signal is found to consist of two main frequency modes. Significant non-linear effects appear during propagation although the pressure amplitude is no more than a few percentages of the ambient pressure. Saw tooth waves are generated and the amplitude is found to decrease as 1/sqrt(t) for low viscous medium according to Lighthill' 'bunching' theory. Further high frequencies are also generated. Finally, geometrical attenuation is discussed by transforming the plane wave propagation to cylindrical form.
Mathematics and Computers in Simulation, Aug 1, 2020
A static and dynamic large deformation analysis of a tapered beam subjected to concentrated and d... more A static and dynamic large deformation analysis of a tapered beam subjected to concentrated and distributed loads is presented in this paper by using a direct integration technique. The bending stiffness of the beam is coordinate dependent. The nonlinear differential equation is numerically solved using an iterative technique without an algebraic equation solver, thus the computational effort can be reduced. A concentrated mass fixed at the free end and suddenly released is studied, and the time-dependent displacements are presented. Comparison has been made with solutions obtained using Finite Element Analysis and excellent agreement is achieved.
This study investigates the hemodynamic responses of the cardiovascular system when a rotary bloo... more This study investigates the hemodynamic responses of the cardiovascular system when a rotary blood pump is operating in the descending aorta, with a focus on the cerebral, coronary and renal autoregulation, using our in-house cardiovascular emulator. Several improvements have been made from our previous studies. A novel coronary system was developed to replicate the native coronary perfusion. Three pinch valves actuated by stepper motors were used to simulate the regional autoregulation systems of the native cerebral, coronary and renal circulations. A rotary pump was installed in the descending aorta, in series with the heart, and the hemodynamic responses of the cardiovascular system were investigated with a focus on cerebral, coronary and renal circulation over a wide range of pump rotor speeds. Experiments were performed twice, once with the autoregulation systems active and once with the autoregulation systems inactive, to reflect that there will be some impairment of autoregulatory systems in a patient with heart failure. It was shown that by increasing the rotor speed to 3000 rpm, the cardiac output was improved from 2.9 to 4.1 L/min as a result of an afterload reduction induced by the pressure drop upstream of the pump. The magnitudes of changes in perfusion in the cerebral, coronary and renal circulations were recorded with regional autoregulation systems active and inactive.
This article is an open access article distributed under the terms and conditions of the Creative... more This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY
Non-linear sound propagation is investigated computationally by simulating compressible time-deve... more Non-linear sound propagation is investigated computationally by simulating compressible time-developing mixing layers using the Large Eddy Simulation (LES) approach and solving the viscous Burgers Equation. The mixing layers are of convective Mach numbers of 0.4, 0.8 and 1.2. The LES results agree qualitatively with known flow behavior. Mach waves are observed in the near sound field of the supersonic mixing layer computed by the LES. These waves show steepening typical to non-linear propagation. Further calculations using the Burgers equation support this finding, where the initial wave slope has a role in kicking them. No visible non-linear propagation effects were found for the subsonic mixing layers. The effects of geometrical spreading and viscosity are also considered.
The behavior of a MVG vane at three different design angles was simulated with LES on an Eppler e... more The behavior of a MVG vane at three different design angles was simulated with LES on an Eppler e387 airfoil that was suffering flow separation. The e387 airfoil was placed at an angle of attack of 12 degrees and at Reynolds number of 200,000 based on the chord length. Different parameters of the generated vortex from the MVG were analyzed to study the behavior of the vortex. The MVG vanes were found to suppress the separation, with the MVG vane placed at 18.5 being the most effective. It was found that turbulence has a strong effect on the instantaneous behavior of the flow field and the easiest measurable characteristic of the MVG’s effect on the flow separation was its effect on the wall shear stress. Recommendations for the optimum placement of the MVG and its zone of influence are discussed.
The aim of this study is to create a computational model of the human ureteral system that accura... more The aim of this study is to create a computational model of the human ureteral system that accurately replicates the peristaltic movement of the ureter for a variety of physiological and pathological functions. The objectives of this research are met using our in-house fluid-structural dynamics code (CgLes-Ycode). A realistic peristaltic motion of the ureter is modelled using a novel piecewise linear force model. The urodynamic responses are investigated under two conditions of a healthy and a depressed contraction force. A ureteral pressure during the contraction shows a very good agreement with the corresponding clinical data. The results also show a dependency of the wall shear stresses on the contraction velocity. It confirms the presence of high shear stress at the proximal part of the ureter. Additionally, it is shown that an inefficient lumen contraction can increase the possibility of a continuous reflux during the propagation of peristalsis.
International Journal of Numerical Methods for Heat & Fluid Flow, Feb 2, 2023
Purpose-The paper aims to investigate the influence of smooth curvature distributions on the self... more Purpose-The paper aims to investigate the influence of smooth curvature distributions on the self-noise of a low Reynolds number aerofoil and to unveil the flow mechanisms in the phenomenon. Design/methodology/approach-The paper performed Large Eddy Simulation (LES) approach to investigate the unsteady aerodynamic performance of both the original aerofoil E387 and the redesigned aerofoil A7 in a time-dependent study of boundary layer characteristics at Reynolds number 100,000 and Angle of Attack 4-degree. The aerofoil A7 is redesigned from E387 by removing the irregularities in the surface curvature distributions and keeping a nearly identical geometry. Flow vorticity magnitude of both aerofoils, along with the spectra of the vertical fluctuating velocity component and noise level, are analysed to demonstrate the bubble flapping process near the trailing edge and the vortex shedding phenomenon. Findings-The paper provides quantitative insights about how the flapping process of the laminar separation bubble within the boundary layer near the trailing edge affects the aerofoil self-noise. It is found that the aerofoil A7 with smooth curvature distributions presents a 10% smaller laminar separation bubble compared to the aerofoil E387 at Reynolds number 100,000 and Angle of Attack 4-degree. The LES results also suggests that curvature distribution smoothing leads to a 6.5% reduction in overall broadband noise level. Originality/value-This paper fulfils an identified need to reveal the unknown flow structure and the boundary layer characteristics that resulted in the self-noise reduction phenomenon yielded by curvature distribution smoothing.
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