Impact Pressure, Void Fraction, and Green Water Velocity due to Plunging Breaking Wave Impingement on a 2D Tension-Leg Structure

2016 ◽  
Author(s):  
Wei-Liang Chuang ◽  
Kuang-An Chang ◽  
Richard Mercier
Keyword(s):  
Void Fraction ◽  
Bubbly Flow ◽  
Vertical Wall ◽  
Pressure Sensors ◽  
Density Variation ◽  
Impact Pressure ◽  
Green Water ◽  
Breaking Wave ◽  
Peak Pressures ◽  
The Impact

Violent impacts due to plunging waves impinging on a 2D tension-leg model structure were experimentally investigated in a laboratory. In the experiment, velocities, pressures, and void fraction were simultaneously measured and the relationship among them was examined. The nonintrusive bubble image velocimetry technique was employed to quantify the instantaneous bubbly flow velocities and structure motion. Pressures on the structure vertical wall above the still water level were measured by four differential pressure sensors. Additionally, four fiber optic reflectometer probes were used to measure the void fraction coincidently with the pressure sensors. With repeated simultaneous, coincident velocity, pressure and void fraction measurements, temporal evolution of the ensemble-averaged velocities, pressures, and void fraction were demonstrated and correlated. Relationship between the peak pressures and their rise time was examined and summarized in dimensionless form. Impact coefficients that relate the impact pressure with flow kinetic energy were obtained from the ensemble-averaged measurements. Finally, the impact coefficients with and without the consideration of the fluid density variation due to bubbles were examined and compared.

Green Water on a Fixed Model in a Large Wave Basin: Flow Velocity, Void Fraction, and Impact Pressure Distributions

2017 ◽  
Author(s):  
Wei-Liang Chuang ◽  
Kuang-An Chang ◽  
Richard Mercier
Keyword(s):  
Flow Velocity ◽  
Void Fraction ◽  
Vertical Wall ◽  
Pressure Sensors ◽  
Impact Pressure ◽  
Green Water ◽  
Breaking Wave ◽  
Large Wave ◽  
Wave Basin ◽  
The Impact

Green water impact due to extreme waves impinging on a fixed, rectangular shaped model structure was investigated experimentally. The experiment was carried out in the large wave basin of the Offshore Technology Research Center at Texas A&M University. In the study, two wave conditions were considered: a plunging breaking wave impinging on the frontal vertical wall (referred as wall impingement) and a breaking wave directly impinging on the deck surface (referred as deck impingement). The aerated flow velocity was measured by employing the bubble image velocimetry (BIV) technique with high speed cameras. The pressure distribution on the deck surface was measured by four differential pressure sensors. The fiber optic reflectometer (FOR) technique was employed to measure the void fraction in front of each pressure sensor end face. The flow velocity, void fraction, and impact pressure, were synchronized and simultaneously measured. Comparisons between an earlier study by Ryu et al. (2007) and the present study were performed to examine the scale effect. Results between Song et al. (2015) and the present results were also compared to investigate the influence of structure geometry on green water flow and impact pressure. To examine the role of air bubbles during the impact, the velocity, pressure, and void fraction were correlated. Correlation between the peak pressure and the aeration level shows a negative trend before the wave impingement but a positive linear relationship after the impingement.

Relation Between Flow Velocity and Impact Pressure in a Green Water Flow

2013 ◽  
Author(s):  
Kusalika Ariyarathne ◽  
Kuang-An Chang ◽  
Richard Mercier
Keyword(s):  
Kinetic Energy ◽  
Void Fraction ◽  
Pressure Rise ◽  
Impact Pressure ◽  
Breaking Wave ◽  
Wave Condition ◽  
Wall Impingement ◽  
Impact Coefficient ◽  
The Impact ◽  
Mean Kinetic Energy

Impact pressure due to plunging breaking waves impinging on a simplified model structure was investigated in the laboratory based on two breaking wave conditions: the wall impingement wave condition and the deck impingement wave condition. Pressure, void fraction, and velocities were measured at various locations on the deck surface. Impact pressure was correlated with the mean kinetic energy calculated based on the measured mean velocities and void fraction to obtain the impact coefficient. For the wall impingement wave condition, the relationship between impact pressure and mean kinetic energy is linear with the impact coefficient close to unity. For the deck impingement wave condition, the above relationship does not show good correlation, whereas the impact coefficient was found to be a function of the rate of pressure rise.

Velocity, Pressure, and Dam-Break Similarity of Green Water Flow on a 3D Structure

2011 ◽  
Author(s):  
Kuang-An Chang ◽  
Kusalika Ariyarathne ◽  
Richard Mercier
Keyword(s):  
Vertical Wall ◽  
Three Dimensional ◽  
Dam Break ◽  
Green Water ◽  
Breaking Wave ◽  
Dimensional Model ◽  
Three Dimensional Model ◽  
Wave Condition ◽  
Wall Impingement ◽  
The Impact

Flow dynamics of green water due to plunging breaking waves interacting with a simplified, three-dimensional model structure was investigated in laboratory. Two breaking wave conditions were tested: one with waves impinging and breaking on the vertical wall of the model at the still water level (referred as wall impingement) and the other with waves impinging and breaking on the horizontal deck surface (referred as deck impingement). The bubble image velocimetry (BIV) technique was used to measure the flow velocity. Measurements were taken on a vertical plane located at the center of the deck surface and a horizontal plane located slightly above the deck surface. The applicability of dam-break theory on green water velocity prediction for the three-dimensional model was also investigated. Furthermore, pressure measurements were performed at several locations above the horizontal deck surface for the wall impingement wave condition. Predictions of maximum impact pressure based on the measured pressure and flow velocities were investigated using the impact coefficient approach that links pressure with kinetic energy.

scholarly journals Sources of the Measurement Error of the Impact Pressure in Sloshing Experiments

2019 ◽  
Vol 7 (7) ◽  
pp. 207
Author(s):  
Dong Hwi Kim ◽  
Eun Soo Kim ◽  
Sung-chul Shin ◽  
Sun Hong Kwon
Keyword(s):  
Integrated Circuit ◽  
Measurement Errors ◽  
High Speed ◽  
Pressure Sensors ◽  
Pressure Measurements ◽  
Sensor Surface ◽  
Experimental Conditions ◽  
Surface Conditions ◽  
Peak Pressures ◽  
The Impact

Sloshing experiments have increasingly received academic attention. Understanding the measurement errors in the sloshing impact pressures is an important parts of the sloshing experiments since these errors, which arise from experimental conditions, affect the subsequent results. As part of the research on the sources of the measurement errors, focused on the effects of surface conditions of pressure sensors on the measurement of impact pressures. Thirty-six integrated circuit piezoelectric pressure sensors were placed on the upper surfaces of a two-dimensional tank to measure the sloshing impact pressures under surge or pitch motions. For each motion, the experimental conditions were divided in two based on whether the surfaces of the sensors were dry or wet. The peak pressures of each test were measured as twenty repeated experiments to ensure reliability. The flow in the tank was visualized using a high-speed camera to observe and analyze macroscopic and microscopic phenomena along the sensor surface. Thermal shock effects were confirmed by varying the experimental temperature and that of the sensor surface. The effects of the wet surface and droplets formed on the sensor surface on pressure measurements are discussed.

Effects of Obstacle’s Curvature on Shock Waves in Gravity-Driven Experimental Flows Impacting a Circular Cylinder or a Wall

2020 ◽  
Author(s):  
Zheng Chen ◽  
Siming He ◽  
Dieter Rickenmann
Keyword(s):  
Shock Wave ◽  
Circular Cylinder ◽  
Pressure Sensors ◽  
Granular Flows ◽  
Impact Pressure ◽  
Small Scale ◽  
Cylinder Surface ◽  
Seismic Signals ◽  
Dynamic Impact ◽  
The Impact

<p>Geophysical granular flows such as rock and snow avalanches, flow-like landslides, debris flows, and pyroclastic flows are driven by gravity and often impact on engineering structures located in gullies and slopes as they flow down, generating dynamic impact pressures and causing a major threat to infrastructures. It is necessary to understand the physical mechanism of such granular flows impacting obstacles to improve the design of protective structures and the hazard assessment related to such structures. In this study, the small-scale laboratory experiments were performed to investigate the dynamic impact caused by granular flow around a circular cylinder with variable radius of curvatures and the dynamic impact against a flat wall. Pressure sensors were used to measure the impact pressure of granular flows at both the upstream cylinder surface and at the bottom of the channel. Accelerometers were mounted on the underside of channel to record the seismic signals generated by the granular flows before and during the impact with the obstacle. Flow velocities and flow depths were determined by using high-precision cameras. The results show that a bow shock wave is generated upstream of the cylinder, causing dynamic pressures on both the obstacle and the bottom of the channel. The dimensionless standoff distance of the granular shock wave decreases nonlinearly or almost exponentially with increasing Froude number (Fr) in the range of 5.5 to 11.0. The dimensionless pinch-off distance and dimensionless run-up height grow linearly with increasing Fr, and they were significantly influenced by the radius of curvature of the structure at the stagnation point (RCSSP). The dimensionless impact pressure on the structure surface is sensitive to the RCSSP, while the differences decrease as Fr increases; Seismic signals generated at the underside of the channel and at the top of the cylinder were also recorded to assist in analyzing the effects of RCSSP.</p>

Spatial and temporal variability of snow avalanche impact pressure and its importance for structural design

2020 ◽  
Author(s):  
Betty Sovilla ◽  
Michael Kyburz ◽  
Camille Ligneau ◽  
Jan-Thomas Fischer ◽  
Mark Schaer
Keyword(s):  
Structural Design ◽  
Temporal Variability ◽  
Pressure Sensors ◽  
Flow Regimes ◽  
Test Site ◽  
Impact Pressure ◽  
Snow Avalanche ◽  
Small Cells ◽  
Hazard Mapping ◽  
The Impact

<p>Measurements of snow avalanche impact pressures are performed at the Vallée de la Sionne test site since winter 1999. In these years of operation, we recorded the impact pressure of around 60 avalanches characterized by different flow regimes and dimensions.</p><p>Pressure measurements were performed, simultaneously, on three different structures which are spatially distributed with a maximum distance of 30 m, in the run-out zone of the Vallée de la Sionne test site. The structure widths range from 0.25 to 1 m. On these structures pressure sensors ranging from small cells with 0.10 to 0.25 m in diameter to large pressure plates with area of 1m<sup>2 </sup>are mounted at different heights.</p><p>A systematic analysis of all 60 avalanche data sets shows that the pressure measured at the different obstacles varies considerably, even within the same avalanche, both in space and time. Part of these differences can be attributed to different drag coefficients and dependence on obstacle size, but a large part of these differences can only be explained by the spatial variability of the flow properties and the temporal variability of the physical processes governing the interaction of the avalanche and the structures.</p><p>In this contribution we show how spatial and temporal impact pressure variabilities correlate to avalanche dimension and flow regimes and we discuss the implication of such variations for structural design and hazard mapping.</p>

Green water void fraction due to breaking wave impinging and overtopping

2008 ◽  
Vol 45 (5) ◽  
pp. 883-898 ◽  
Author(s):  
Yonguk Ryu ◽  
Kuang-An Chang
Keyword(s):  
Void Fraction ◽  
Green Water ◽  
Breaking Wave

Investigations of Reduction Effect of Vertical Wall on Dam-Break-Simulated Tsunami Surge Exerted on Wharf Piles

2018 ◽  
Vol 12 (02) ◽  
pp. 1840006 ◽  
Author(s):  
Cheng Chen ◽  
Bruce W. Melville ◽  
N. A. K. Nandasena
Keyword(s):  
High Speed ◽  
Preliminary Investigation ◽  
Vertical Wall ◽  
Pressure Sensors ◽  
Time History ◽  
Dam Break ◽  
Reservoir System ◽  
Reduction Effect ◽  
The Impact ◽  
Surge Height

For a preliminary investigation of the impact of a tsunami surge on wharf piles, a tsunami flume was built in a laboratory, and a dam break flow was generated by a gate-reservoir system to simulate a tsunami surge. In addition, a vertical wall was installed in front of the wharf model so that its effect in reducing tsunami load could be studied. Five different tsunami surge strengths were generated by this gate-reservoir system. Wave transducers were used in the test flume to capture surge heights and velocities, and hence the surge front profiles, for different surge strengths. High-speed video cameras (210 frames per second) were used to record the flow motion of the tsunami surge, and pressure sensors (1000[Formula: see text]Hz in frequency) were used to capture the time histories of the tsunami pressure on the wharf piles. Four stages of tsunami surge motions were observed by this high-speed camera. Accordingly, the pressure time history can be divided into three phases. In our experimental range, pressures were influenced by surge height and wall height, but not by the wall position. Based on the dimensionless experimental data (pile heights, surge heights, vertical wall heights, and surge pressures), equations for estimating tsunami loads on wharf pile are proposed, expressing surge front (peak impact) pressure and quasi-steady pressure as functions of surge height, wall height, and pile height.

Experimental Investigation of the Green Water Loads on a Wave-Piercing Tumblehome Ship

2017 ◽  
Author(s):  
Hui Li ◽  
Bao-Li Deng ◽  
Shu-Zheng Sun ◽  
Wen-Lei Du ◽  
Hao-Dong Zhao
Keyword(s):  
Experimental Investigation ◽  
High Speed ◽  
Water Pressure ◽  
Pressure Sensors ◽  
Green Water ◽  
Strong Nonlinearity ◽  
Water Tank ◽  
Water Tank Experiment ◽  
The Impact ◽  
Ship Speed

This paper presents the results of an experimental investigation of green water loads on a wave-piercing tumblehome ship. A water tank experiment was carried out in head regular waves by using a self-propelling segmented ship model. Wave probes and pressure sensors were arranged on the bow deck along the longitudinal and transverse directions. The height of water and the impact pressure on the deck were measured and their distributions in different wave conditions studied. The motion of the water flowing on the deck was recorded by a high-speed video system. Based on the experimental results, it was found that the green water is more serious with the increase of incident wave height and ship speed. The bow shape has little effects on the occurrence of green water, but it influences the green water loads to some extent. The distribution of green water pressure is different from that of green water height due to the strong nonlinearity of green water pressure.

scholarly journals Breaking Wave Impact Pressure on a Vertical Wall

2010 ◽  
Vol 1 (3-4) ◽  
pp. 155-166 ◽  
Author(s):  
C. Rajasekaran ◽  
S.A. Sannasiraj ◽  
V. Sundar
Keyword(s):  
Vertical Wall ◽  
Impact Pressure ◽  
Breaking Wave ◽  
Wave Impact
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