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 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.

Pressure Gage Measurements in a Dry to Wet Environment

2009 ◽  
Author(s):  
Anne M. Fullerton ◽  
Thomas C. Fu
Keyword(s):  
Gate Valve ◽  
Water Drop ◽  
Water Pressure ◽  
Pressure Sensors ◽  
Pressure Rise ◽  
Thermal Drift ◽  
Wave Impact ◽  
Unique Problem ◽  
Pressure Gage ◽  
The Impact

Pressure gages are used in many fluid measurements applications. One such application is the measurement of wave impact pressures on structures. This application poses a unique problem of measuring pressures in a “wet to dry” environment. Often there is a thermal drift component in the pressure readings that makes it difficult to extract the actual pressure rise due to wave loading. These types of measurements also require high response rates to measure the detail of the short duration impacts, usually on the order of one to twenty kilohertz. Several bench tests were carried out in at the Naval Surface Warfare Center, Carderock Division, in 2008 to investigate various types of gages to find a robust gage that could withstand this type of application. Three different gages were used in this investigation. The first sensor (gage 1) is a dynamics general purpose ICP (integrated circuit piezoelectric) pressure sensor, capable of making very high frequency dynamic pressure measurements, rated to 200 psi. The second sensor (gage 2) is a voltage compensated, media isolated piezoresistive sensor, rated to 15 psi. This gage had a pressure port which was filled with water during testing to eliminate air compression effects. The third sensor (gage 3) is a semiconductor pressure gage rated to 25 psi (172.4 kPa). A water “drop” test setup was constructed of 2 inch (5.1 cm) PVC pipe. The pressure gages were mounted to the bottom of the setup facing up, and the pipe was filled from the top, with a quick acting gate valve located 2 feet (0.61 m) from the pressure sensors. Once the pipe was filled with the desired amount of water, the gate valve was opened as quickly as possible, and the impact force was measured. Vent pipes were mounted to a “cross” fitting in the vertical pipe which allowed for the air to escape. Several water “drop” tests were performed with this setup. From these tests, the thermal drift of gage 1 is evident. Gage 3 exhibits similar behavior. Gage 2 captures the water pressure impact, and then returns to a small positive static pressure as a result of the water that is sitting above it. Of the three sensors, gage 2 appears to be the most temperature stable.

Investigation of Material Deformation by the High-Speed Water Slugs

2002 ◽  
Author(s):  
O. Petrenko ◽  
E. S. Geskin ◽  
G. A. Atanov ◽  
B. Goldenberg ◽  
A. Semko
Keyword(s):  
Shock Waves ◽  
Nozzle Exit ◽  
High Speed ◽  
Numerical Models ◽  
Water Pressure ◽  
Experimental Studies ◽  
Surface Cleaning ◽  
Water Velocity ◽  
Material Deformation ◽  
The Impact

Water constitutes an attractive manufacturing tool It is readily available and clean. The waterjets are conventionally used for surface cleaning, material removal, and surface modification. The intrinsic shortcomings of such an application are the need in the use of expensive and heavy pumping facilities and, what are more important, peculiarities of the waterjet-substrate interaction which limit material deformation by the incoming jet. These shortcomings are eliminated if the workpiece is impacted by the array of the water slugs, generated by the direct injection of high-intensity energy pulses into the water vessel (barrel) and ejection the portion of the water via the nozzle attached into the barrel. Such a device (barrel-nozzle combination) will constitute an effective and versatile manufacturing tool. Understanding of the phenomena that occur in the course of the energy injection into the water is necessary for the design of the desired device. The phenomena in question are determined by the ratio between the speed of the water in the barrel in the course of the energy injection and the speed of the shock waves in the water. If this ratio is much less than unity, the exit velocity is determined by the ratio between the cross section areas of the nozzle exit and the barrel. If the ratio in question approaches the unity, the water velocity at the nozzle exit is determined by the impact pressure. The device utilizing this principle is termed the water extruder. If however, the ratio is much more than unity the exit water velocity is determined by the superposition of shock waves developed in the fluid. This device termed the water cannon is able to accelerate the water slug to the speed far exceeding 1,000 m/sec. The numerical and experimental studies of water extruder were carried out. The numerical models were constructed and the variation of the water velocity and the water pressure in the barrel were investigated. Experimental setup for the study of the water extruder was constructed by the modification of Remington power tool. The experiments involved the piercing of metal strips. The effect of operational conditions on the maximal depth of the piecing was determined. Another series of experiments involved the study of the slug impact on plastic (lead) and brittle (concrete) materials. The effect of the stand off distance on the removal of both kinds of material was investigated. As the result the suggestions about the way of construction of the water extruders and their practical applications were made.

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.

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.

Optical Observation of the Supercavitation Induced by High-Speed Water Entry

2000 ◽  
Vol 122 (4) ◽  
pp. 806-810 ◽  
Author(s):  
Hong-Hui Shi ◽  
Motoyuki Itoh ◽  
Takuya Takami
Keyword(s):  
Experimental Investigation ◽  
Free Surface ◽  
Shock Waves ◽  
High Speed ◽  
Bubbly Flow ◽  
Water Entry ◽  
Gas Pressure ◽  
Optical Observation ◽  
Water Tank ◽  
Experimental Facility

When a high-speed projectile penetrates into water, a cavity is formed behind the projectile. The gas enclosed in the cavity experiences a nonequilibrium process, i.e., the gas pressure decreases as the projectile moves more deeply into water. As a result, the cavity is sealed near the free surface (surface closure) and subsequently the cavity breaks up in water (deep closure). Accompanying the break-up of the cavity, secondary shock waves appear. This is the so-called supercavitation in water entry. This paper describes an experimental investigation into the water entry phenomenon. Projectiles of 342 m/s were generated from a small-bore rifle that was fixed vertically in the experimental facility. The projectiles were fired into a windowed water tank. A shadowgraph optical observation was performed to observe the entry process of the projectile and the formation and collapse of the cavity behind the projectile. A number of interesting observations relating to the motion of the free surface, the splash, the underwater bubbly flow and so on were found. [S0098-2202(00)00204-2]

Air entrapment by a falling water mass

1995 ◽  
Vol 294 ◽  
pp. 181-207 ◽  
Author(s):  
Hasan N. Oguz ◽  
Andrea Prosperetti ◽  
Ali R. Kolaini
Keyword(s):  
High Speed ◽  
Water Mass ◽  
Boundary Integral ◽  
Surface Shape ◽  
Water Tank ◽  
Air Entrapment ◽  
Free Surface Shape ◽  
Large Water ◽  
The Impact ◽  
Good Agreement

The impact of a nearly cylindrical water mass on a water surface is studied both experimentally and theoretically. The experiments consist of the rapid release of water from the bottom of a cylindrical container suspended above a large water tank and of the recording of the free-surface shape of the resulting crater with a high-speed camera. A bubble with a diameter of about twice that of the initial cylinder remains entrapped at the bottom of the crater when the aspect ratio and the energy of the falling water mass are sufficiently large. Many of the salient features of the phenomenon are explained on the basis of simple physical arguments. Boundary-integral potential-flow simulations of the process are also described. These numerical results are in fair to good agreement with the observations.

Spike and Modal Stall Inception in an Advanced Turbocharger Centrifugal Compressor

2009 ◽  
Vol 131 (3) ◽  
Author(s):  
Z. S. Spakovszky ◽  
C. H. Roduner
Keyword(s):  
Centrifugal Compressor ◽  
High Speed ◽  
Pressure Ratio ◽  
Pressure Sensors ◽  
Rotating Stall ◽  
Vaned Diffuser ◽  
Stall Inception ◽  
Compression System ◽  
The Impact ◽  
Highly Loaded

In turbocharger applications, bleed air near the impeller exit is often used for secondary flow systems to seal bearing compartments and to balance the thrust load on the bearings. There is experimental evidence that the performance and operability of highly-loaded centrifugal compressor designs can be sensitive to the amount of bleed air. To investigate the underlying mechanisms and to assess the impact of bleed air on the compressor dynamic behavior, a research program was carried out on a preproduction, 5.0 pressure ratio, high-speed centrifugal compressor stage of advanced design. The investigations showed that bleed air can significantly reduce the stable flow range. Compressor rig experiments, using an array of unsteady pressure sensors and a bleed valve to simulate a typical turbocharger environment, suggest that the path into compression system instability is altered by the bleed flow. Without the bleed flow, the prestall behavior is dominated by short-wavelength disturbances, or so called “spikes,” in the vaneless space between the impeller and the vaned diffuser. Introducing bleed flow at the impeller exit reduces endwall blockage in the vaneless space and destabilizes the highly-loaded vaned diffuser. The impact is a 50% reduction in stable operating range. The altered diffuser characteristic reduces the compression system damping responsible for long-wavelength modal prestall behavior. A four-lobed backward traveling rotating stall wave is experimentally measured in agreement with calculations obtained from a previously developed dynamic compressor model. In addition, a self-contained endwall blockage control strategy was employed, successfully recovering 75% of the loss in surge-margin due to the bleed flow and yielding a one point increase in adiabatic compressor efficiency.

scholarly journals Experimental investigation of size effects in colliding droplet

2017 ◽  
Author(s):  
Lars Pasternak ◽  
Martin Sommerfeld
Keyword(s):  
Experimental Investigation ◽  
Size Effects ◽  
Relative Velocity ◽  
High Speed ◽  
Droplet Generator ◽  
Collision Process ◽  
Droplet Collisions ◽  
Process And Outcome ◽  
Binary Collisions ◽  
The Impact

The present work focuses on the size effect of binary collisions of PVP droplets (viscosity 5.5 mPas). The aim was the identification of the boundaries between bouncing, coalescence, stretching and reflexive separation.These boundaries are necessary for numerical simulations of droplet collisions in spray drying processes. Therefore, droplet chains were generated by droplet generators with oscillating membrane and directed towards each other at different angles for producing binary collisions. In the experiments two droplet properties (i.e. droplet size and size ratio) were varied. Two synchronised high-speed cameras were used to observe the collision process and outcome perpendicularly and parallelly to the collision plane. The variation of the impact parameter B was performed by a frequency offset for one droplet generator. The relative velocity (i. e. 0.5 to 4.7 m/s) was set by changing the collision angle.DOI: http://dx.doi.org/10.4995/ILASS2017.2017.4781

Experimental Investigation of Water Entry Impact on Hydrophobic Surfaces

2015 ◽  
Author(s):  
Bulent Guzel ◽  
Fatih C. Korkmaz
Keyword(s):  
Experimental Investigation ◽  
Flow Separation ◽  
High Speed ◽  
Water Entry ◽  
Air Entrapment ◽  
Hydrophobic Surfaces ◽  
Blunt Bodies ◽  
Drop Tests ◽  
Set Up ◽  
The Impact

The results of an experimental investigation on hull bottom slamming of three different geometries, sphere, cylinder and wedge, with hydrophobic surfaces are presented. In water entry of blunt bodies, different fluid dynamics phenomena like jet formation, cavity formation, water splashing, flow separation on solid surfaces and air entrapment between solid and liquid surface have been studied for decades. Our study is aimed at understanding and modeling the dynamics of slamming under an extended range of parameters including hydrophobic surfaces. In this study, drop tests have been set up for hull bottom slamming by dropping a body from various heights toward water surface. From digital images captured using a high speed camera, flow separation and water splashing at different velocities are observed and spreading diameters and entrance characteristics are measured during the impact process. At the same time, we measure the pressure distribution on the surface of the bodies during impact via strain gages.

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