In this study numerical model was developed to solve the unsteady two-dimensional Reynolds Averag... more In this study numerical model was developed to solve the unsteady two-dimensional Reynolds Averaged Navier-Stokes (RANS) equations and the turbulent ε − k equations for simulating the evolution of a breaking solitary wave above a continental shelf. A hybrid particle level set method was adopted to capture the complex free surface evolution, beginning from the steepening of the wave profile to the wave breaking, which was accompanied by the air entrainment, then followed by the successive splash-ups. The governing equations were discretized by the finite-analytic method and the SIMPLER algorithm was used to calculate the coupled velocity and pressure fields. Accuracy of the advection scheme of the level set method was confirmed by solving the Zalesak problem. Before we proceed to investigate the evolution of breaking solitary wave on a continental shelf, our numerical results were compared with the experimental data. After having verified the accuracy of the present numerical scheme,...
Seventeen data buoys were deployed in the Taiwan Sea since 1997. These buoys have made measuremen... more Seventeen data buoys were deployed in the Taiwan Sea since 1997. These buoys have made measurement for more than 100 typhoons. The purpose of this paper is to study the statistical characteristics of the observed typhoon waves. High resolution directional wave spectra are obtained by analyzing the buoy data. The Significant Typhoon Wave Height (SWTH) and the Duration of Large Waves (DLW) are proposed to indicate the sea severity of typhoons. The joint effect of the SWTH and the DLW is used to assess possible impact by the typhoon waves to the coast, using the damage curve calibrated from historical events. In addition analysis on the slope of the equilibrium range on the high-frequency side of the typhoon wave frequency spectra shows that its slope is less than 3.5 in absolute value for coastal water and larger than 3.8 for the deep sea. The JONSWAP spectrum model is then used to fit the mean wave spectra of the largest sea state in typhoons. It is found that the peak-enhancement fa...
The wind effect on the general translational motion of a circular cylinder through an inviscid an... more The wind effect on the general translational motion of a circular cylinder through an inviscid and incompressible fluid, conveyed by a uniform flow at infinity, in the vicinity of another cylinder fixed in space is considered. It is found that the trajectories of the moving cylinder do not change much, if the magnitude of the wind velocity is the same as that of the current velocity, except that they shift slightly in the direction of the wind. However, when the wind velocity is five times the magnitude of the current velocity, the trajectories of the moving cylinder change greatly, particularly when the direction of the wind is perpendicular to the current velocity.
Three-dimensional (3D) computational fluid dynamic (CFD) simulations have gained substantial popu... more Three-dimensional (3D) computational fluid dynamic (CFD) simulations have gained substantial popularity in recent years for stream flow modelling. The complex terrain in streams is usually represented by a 3D mesh conforming to the terrain geometry. Such terrain-conforming meshes are time-consuming to generate. In this work, an immersed boundary method is developed in an existing terrain-conforming CFD model named U2RANS as an alternative, in which terrains are represented implicitly in the Cartesian background mesh. An improved two-layer wall function is proposed in the framework of the k-ε turbulence model, with the aim of producing accurate and smooth wall shear stress distribution and paving the way for future model development on sediment transport and scour modeling. The improvement overcomes the inherent discontinuity and nonlinearity of the two-layer velocity profile, which causes error in the estimation of shear velocity. The new algorithm utilizes a distance control on the...
In this study, we developed a fiber-optic sensing system with an eight-probe array for measuring ... more In this study, we developed a fiber-optic sensing system with an eight-probe array for measuring the spatial distributions of air volume (void) fractions in bubbly flows. Initially, we performed calibration experiments in a cylindrical tank by using a fiber-optic sensing system with a single probe to determine the relationship between the time fraction ratio of bubble signals and void fractions. A high correlation coefficient was obtained between the time fraction ratio and the void fraction, suggesting that the proposed fiber-optic sensing system can measure local void fractions of up to 18%. Subsequently, we used the proposed fiber-optic sensing system with the eight-probe array to measure the spatial distribution of air volume fractions in a bubbly flow caused by breaking waves near a submerged breakwater. The effects of different variables, including the incident wave height, period, and width of the breakwater, on the spatial distribution of the void fraction on the lee side of...
This study utilized a two-dimensional numerical viscous wave tank to simulate the run-up and run-... more This study utilized a two-dimensional numerical viscous wave tank to simulate the run-up and run-down processes of non-breaking solitary waves on a steep seawall. The research aimed to investigate the transformation between wave potential energy and kinetic energy, the evolution mechanisms of the wave and flow fields, and the correlation between the dynamic pressure gradient and the reverse flow near the sloping bed. The numerical model results were consistent with laboratory measurements of free surface elevations and flow velocity profiles, demonstrating the accuracy of the numerical model. This study focused on a solitary wave with a wave-height-to-water-depth ratio of 0.15, propagating on a representative seawall with a steep slope of 1:3 along the western coast of Taiwan. The simulation results indicate that the maximum run-up height occurs when the potential energy is at its highest. Undertow is caused by the adverse pressure gradient within the flow field, and the dynamic pre...
In this study, a pressurized, water-filled impedance tube (WFIT) was developed to measure the ref... more In this study, a pressurized, water-filled impedance tube (WFIT) was developed to measure the reflection coefficients of sound-absorbing materials under various hydrostatic pressures. The developed WFIT was calibrated using a two-microphone, three-parameter calibration method (3PCM). The accuracy and repeatability of the measured reflection coefficients for the water–air interface in the WFIT were determined by comparing these coefficients with corresponding theoretical reflection coefficients. The WFIT was then used to measure the acoustic reflection coefficient of a porous rubber specimen on three dates, and the corresponding measurement results exhibited satisfactory repeatability. The aforementioned impedance tube was also used to measure the reflection coefficient of a porous rubber specimen under a hydrostatic pressure of 4 Patm three times on the same day, and one time each on three days, using the same experimental setup and measurement procedure. The results obtained in the...
Unsteady two-dimensional Reynolds Averaged Navier-Stokes (RANS) equations coupled with the k−ε tu... more Unsteady two-dimensional Reynolds Averaged Navier-Stokes (RANS) equations coupled with the k−ε turbulence model was developed to simulate the viscous flow field near seawalls. The complex free-surface configuration was captured using the particle level set method (PLSM). An innovative solid-fluid coupling method was employed to mimic the solid-fluid interaction on fixed Cartesian grids. The proposed numerical model was applied to investigate the viscous flow fields induced by periodic waves propagating on three different seawalls, including vertical and steep seawalls, which are commonly designed in Taiwan with slopes of 1:2 and 1:5. The results reveal that the wave run-up height is closely related to Iribarren number and breaking wave. Partial standing wave or asymmetric recirculating cells in front of a steep seawall lose symmetry with increasing slope. The wave pressure on the seawall face increases as the Ursell number or seawall slope increases. The undertow caused by breaking ...
This study investigates the performance of a passive time-reversal mirror (TRM) combined with aco... more This study investigates the performance of a passive time-reversal mirror (TRM) combined with acoustic ray theory in localizing underwater sound sources with high frequencies (3–7 kHz). The TRM was installed on a floating buoy and comprised four hydrophones. The ray-tracing code BELLHOP was used to determine the transfer function between a sound source and a field point. The transfer function in the frequency domain obtained from BELLHOP was transformed into the time domain. The pressure field was then obtained by taking the convolution of the transfer function in the time domain with the time-reversed signals that were received by the hydrophones in the TRM. The location with the maximum pressure value was designated as the location of the source. The performance of the proposed methodology for source localization was tested in a towing tank and in the ocean. The aforementioned tests revealed that even when the distances between a source and the TRM were up to 1600 m, the distance ...
In this study numerical model was developed to solve the unsteady two-dimensional Reynolds Averag... more In this study numerical model was developed to solve the unsteady two-dimensional Reynolds Averaged Navier-Stokes (RANS) equations and the turbulent ε − k equations for simulating the evolution of a breaking solitary wave above a continental shelf. A hybrid particle level set method was adopted to capture the complex free surface evolution, beginning from the steepening of the wave profile to the wave breaking, which was accompanied by the air entrainment, then followed by the successive splash-ups. The governing equations were discretized by the finite-analytic method and the SIMPLER algorithm was used to calculate the coupled velocity and pressure fields. Accuracy of the advection scheme of the level set method was confirmed by solving the Zalesak problem. Before we proceed to investigate the evolution of breaking solitary wave on a continental shelf, our numerical results were compared with the experimental data. After having verified the accuracy of the present numerical scheme,...
Seventeen data buoys were deployed in the Taiwan Sea since 1997. These buoys have made measuremen... more Seventeen data buoys were deployed in the Taiwan Sea since 1997. These buoys have made measurement for more than 100 typhoons. The purpose of this paper is to study the statistical characteristics of the observed typhoon waves. High resolution directional wave spectra are obtained by analyzing the buoy data. The Significant Typhoon Wave Height (SWTH) and the Duration of Large Waves (DLW) are proposed to indicate the sea severity of typhoons. The joint effect of the SWTH and the DLW is used to assess possible impact by the typhoon waves to the coast, using the damage curve calibrated from historical events. In addition analysis on the slope of the equilibrium range on the high-frequency side of the typhoon wave frequency spectra shows that its slope is less than 3.5 in absolute value for coastal water and larger than 3.8 for the deep sea. The JONSWAP spectrum model is then used to fit the mean wave spectra of the largest sea state in typhoons. It is found that the peak-enhancement fa...
The wind effect on the general translational motion of a circular cylinder through an inviscid an... more The wind effect on the general translational motion of a circular cylinder through an inviscid and incompressible fluid, conveyed by a uniform flow at infinity, in the vicinity of another cylinder fixed in space is considered. It is found that the trajectories of the moving cylinder do not change much, if the magnitude of the wind velocity is the same as that of the current velocity, except that they shift slightly in the direction of the wind. However, when the wind velocity is five times the magnitude of the current velocity, the trajectories of the moving cylinder change greatly, particularly when the direction of the wind is perpendicular to the current velocity.
Three-dimensional (3D) computational fluid dynamic (CFD) simulations have gained substantial popu... more Three-dimensional (3D) computational fluid dynamic (CFD) simulations have gained substantial popularity in recent years for stream flow modelling. The complex terrain in streams is usually represented by a 3D mesh conforming to the terrain geometry. Such terrain-conforming meshes are time-consuming to generate. In this work, an immersed boundary method is developed in an existing terrain-conforming CFD model named U2RANS as an alternative, in which terrains are represented implicitly in the Cartesian background mesh. An improved two-layer wall function is proposed in the framework of the k-ε turbulence model, with the aim of producing accurate and smooth wall shear stress distribution and paving the way for future model development on sediment transport and scour modeling. The improvement overcomes the inherent discontinuity and nonlinearity of the two-layer velocity profile, which causes error in the estimation of shear velocity. The new algorithm utilizes a distance control on the...
In this study, we developed a fiber-optic sensing system with an eight-probe array for measuring ... more In this study, we developed a fiber-optic sensing system with an eight-probe array for measuring the spatial distributions of air volume (void) fractions in bubbly flows. Initially, we performed calibration experiments in a cylindrical tank by using a fiber-optic sensing system with a single probe to determine the relationship between the time fraction ratio of bubble signals and void fractions. A high correlation coefficient was obtained between the time fraction ratio and the void fraction, suggesting that the proposed fiber-optic sensing system can measure local void fractions of up to 18%. Subsequently, we used the proposed fiber-optic sensing system with the eight-probe array to measure the spatial distribution of air volume fractions in a bubbly flow caused by breaking waves near a submerged breakwater. The effects of different variables, including the incident wave height, period, and width of the breakwater, on the spatial distribution of the void fraction on the lee side of...
This study utilized a two-dimensional numerical viscous wave tank to simulate the run-up and run-... more This study utilized a two-dimensional numerical viscous wave tank to simulate the run-up and run-down processes of non-breaking solitary waves on a steep seawall. The research aimed to investigate the transformation between wave potential energy and kinetic energy, the evolution mechanisms of the wave and flow fields, and the correlation between the dynamic pressure gradient and the reverse flow near the sloping bed. The numerical model results were consistent with laboratory measurements of free surface elevations and flow velocity profiles, demonstrating the accuracy of the numerical model. This study focused on a solitary wave with a wave-height-to-water-depth ratio of 0.15, propagating on a representative seawall with a steep slope of 1:3 along the western coast of Taiwan. The simulation results indicate that the maximum run-up height occurs when the potential energy is at its highest. Undertow is caused by the adverse pressure gradient within the flow field, and the dynamic pre...
In this study, a pressurized, water-filled impedance tube (WFIT) was developed to measure the ref... more In this study, a pressurized, water-filled impedance tube (WFIT) was developed to measure the reflection coefficients of sound-absorbing materials under various hydrostatic pressures. The developed WFIT was calibrated using a two-microphone, three-parameter calibration method (3PCM). The accuracy and repeatability of the measured reflection coefficients for the water–air interface in the WFIT were determined by comparing these coefficients with corresponding theoretical reflection coefficients. The WFIT was then used to measure the acoustic reflection coefficient of a porous rubber specimen on three dates, and the corresponding measurement results exhibited satisfactory repeatability. The aforementioned impedance tube was also used to measure the reflection coefficient of a porous rubber specimen under a hydrostatic pressure of 4 Patm three times on the same day, and one time each on three days, using the same experimental setup and measurement procedure. The results obtained in the...
Unsteady two-dimensional Reynolds Averaged Navier-Stokes (RANS) equations coupled with the k−ε tu... more Unsteady two-dimensional Reynolds Averaged Navier-Stokes (RANS) equations coupled with the k−ε turbulence model was developed to simulate the viscous flow field near seawalls. The complex free-surface configuration was captured using the particle level set method (PLSM). An innovative solid-fluid coupling method was employed to mimic the solid-fluid interaction on fixed Cartesian grids. The proposed numerical model was applied to investigate the viscous flow fields induced by periodic waves propagating on three different seawalls, including vertical and steep seawalls, which are commonly designed in Taiwan with slopes of 1:2 and 1:5. The results reveal that the wave run-up height is closely related to Iribarren number and breaking wave. Partial standing wave or asymmetric recirculating cells in front of a steep seawall lose symmetry with increasing slope. The wave pressure on the seawall face increases as the Ursell number or seawall slope increases. The undertow caused by breaking ...
This study investigates the performance of a passive time-reversal mirror (TRM) combined with aco... more This study investigates the performance of a passive time-reversal mirror (TRM) combined with acoustic ray theory in localizing underwater sound sources with high frequencies (3–7 kHz). The TRM was installed on a floating buoy and comprised four hydrophones. The ray-tracing code BELLHOP was used to determine the transfer function between a sound source and a field point. The transfer function in the frequency domain obtained from BELLHOP was transformed into the time domain. The pressure field was then obtained by taking the convolution of the transfer function in the time domain with the time-reversed signals that were received by the hydrophones in the TRM. The location with the maximum pressure value was designated as the location of the source. The performance of the proposed methodology for source localization was tested in a towing tank and in the ocean. The aforementioned tests revealed that even when the distances between a source and the TRM were up to 1600 m, the distance ...
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