• The KSFM Journal of Fluid Machinery
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• v.10 no.4
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• pp.61-70
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• 2007

Numerical analysis of three dimensional incompressible turbulent flows in LNG marine high pressure drop control valves was carried out by using the CFD-ACE from ESI-Group. In this study, flow characteristics of control valves with complex flow fields including cavitation effect were investigated. Simulation was performed on five models of control valve that had different orifice diameters of anti-trim and the size of valve. Comparing newly designed control valves for controling the occurrence of cavitation with the conventional valve, new valves showed a improved flow pattern with almost no cavitation.

• Proceedings of the KOSOMBE Conference
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• v.1998 no.11
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• pp.311-312
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• 1998

It is an important issue that cavitation is always deal with shock wave. During operation with ESWL(Extracorporeal Shock Wave Lithotriptor), the cavitation bubbles are generated at the focal region. This phenomenon is an important problem because the cavitation bubbles have a harmful effect on the disintegration ability and the human body. In this paper, therefore, we investigate the relation between the cavitation and the radiated sound due to the ESWL.

• Journal of the Korean institute of surface engineering
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• v.45 no.6
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• pp.278-283
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• 2012

This investigation evaluated the effect of cavitation condition on electrochemical characteristics of 304 stainless steel, which is widely used for marine environment. The cavitation test with time were conducted on 304 stainless steel in seawater solution. Surface morphologies of specimen were observed by scanning electron microscope (SEM) and 3D microscope. Pitting depth, weight loss and damage rate were analyzed after each cavitation experiment. The surface damage was more severe as the current density increased. A dramatical increase in the damage depth and weight loss was observed after 7 hours of cavitation experiment.

• Journal of the Society of Naval Architects of Korea
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• v.52 no.3
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• pp.236-247
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• 2015

In this paper, the experimental equipments for ventilated supercavitation in cavitation tunnel is constructed and the basic data of ventilated supercavitation regard to the entrainment coefficient and Froude number is fulfilled. The experiments are conducted for the disk cavitator with injecting air and the pressure inside cavity and the shape of cavity are measured. As the entrainment coefficient increases while the Froude number is kept constant, the ventilated cavitation number decreases to a minimum value which decreases no more even with increasing the air entrainment. The minimum value of ventilated cavitation number, caused by the blockage effect, decreases according to increasing the diameter ratio of test section to cavitator. The cavity length is rapidly enlarged near the minimum cavitation number. In low Froude numbers, the cavity tail is floating up due to buoyancy and the air inside the cavity is evacuated from its rear end with twin-vortex hollow tubes. However, in high Froude numbers, the buoyancy effect is almost negligible and there is no more twin-vortex tubes so that the cavity shape becomes close to axisymmetric. In order to measure the cavity length and width, the two methods, which are to be based on the cavity shapes and the maximum width of cavity, are applied. As the entrainment coefficient increases after the ventilated cavitation number gets down to the minimum cavitation number, the cavity length still increases gradually. These phenomenon can be confirmed by the measurement using the method based on the cavity shapes. On the other hand, when the method based on the maximum width of cavity is used, the length and width of the cavity agree well with a semi-empirical formular of natural cavity. So the method based on the maximum width of cavity can be a valid method for cavitator design.

• Journal of Advanced Marine Engineering and Technology
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• v.37 no.5
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• pp.484-492
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• 2013

With the industrial acceleration in a lot of countries of the world, the demand for anti-corrosion and anti-abrasion material increases continuously. Particularly, stainless steel with the fine surface and excellent corrosion resistance is widely used in various industrial fields including ship, offshore structures tidal power plant, and etc. In marine environment, however, it is easy to generate by the corrosion damage by $Cl^-$ ion and cavitation damage due to high rotation speed on stainless steel. Therefore, in this research, the cavitation erosion-corrosion test (Hybrid test) was performed for 304 stainless steel specimen used in the high flow rate seawater environment. And the cavitation damage behavior in the corrosive environment was analyzed overall. The high hardness was shown due to the formation of compressive residual stress by the water cavitation peening effect in cavitation condition. However, high current density in the potentiodynamic polarization experiment presented with the breakdown of the passive film caused by physical impact. Therefore, both electrochemical characteristics and mechanical properties must be taken into account to improve the cavitation resistance in seawater.

• Corrosion Science and Technology
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• v.19 no.5
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• pp.239-249
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• 2020

The characteristics of cavitation-erosion damage with changes in the amplitude of 5052-O aluminum alloy for ships were investigated in a seawater environment. In the cavitation-erosion experiment, the cavitation environment was created using a vibration-generating device with a piezo-electric effect. The amplitudes of 5 ㎛, 10 ㎛, and 30 ㎛ were created by changing the geometric shape of the cavitation horn. The resistance characteristics of cavitation-erosion damage were evaluated by weight loss and pitting area. The damaged surface was analyzed using scanning electron microscopy (SEM) and 3D optical microscopy. As the amplitude increased, the amount of damage and the area of the damaged surface increased, and the damage was concentrated at the center and edge of the specimen. The pit was created after the initial incubation period with increasing experimental time, and then the pits were merged to grow and propagate into craters, and eventually, the surface was detached and damaged. The cavitation-erosion damage after 30 minutes with amplitude of 10 ㎛ and 30 ㎛ was 1.48 and 2.21 times compared to 5 ㎛, respectively.

• Journal of computational fluids engineering
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• v.17 no.3
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• pp.25-32
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• 2012

This work was devoted to compare two different cavitation models to study the dependency of model constants. The cavitation model of Merkle et al.(2006) and Kunz et al.(2000) were used for the present computational study. The cavitation models were coupled with the incompressible unsteady Reynolds-Averaged Navier-Stokes solver to indicate the vaporization and condensation processes. For this purpose, a preconditioning method was added as the pseudo-time term to solve the unsteady stiffness problems. For the validation of the numerical simulation, the computation was performed for the cavitating flow in a converging-diverging channel. The present results show that Merkle's cavitation model is independent to the model constants, and the higher numerical accuracy over Kunz's cavitation model.

• Tribology and Lubricants
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• v.19 no.5
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• pp.285-291
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• 2003

Ultrasonic vibrator is an equipment which atomizes and homogenization the oils by breaking the oil particles with ultrasonic cavitation, and would improve the properties. The present study deal with the ultrasonic breaking systems which recycle the shipborne waste oil into usable oil to be burnt. The first place, experimental studies were carried out to investigate the homogenizing effect of the waste oils by ultrasonic cavitation. Variation of the properties(viscosity, specific gravity and pH) and the matrix structures for the various shipborne waste oils were interpreted to analyse the breaking, dispersion effects by ultrasonic cavitation. The experimental results can be useful to the development of waste oil disposing systems.

• International Journal of Naval Architecture and Ocean Engineering
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• v.9 no.2
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• pp.227-237
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• 2017

In this paper, we investigated physical characteristics of an artificial supercavity generated behind an axisymmetric cavitator. Experiments for the same model were carried out at two different cavitation tunnels of the Chungnam National University and the University of Minnesota, and the results were compared and verified with each other. We measured pressures inside the cavity and observed the cavity formation by using a high-speed camera. Cavitation parameters were evaluated in considering blockage effects of the tunnel, and gravitational effects on supercavity dimensions were examined. Cavity dimensions corresponding to the unbounded cavitation number were compared. In addition, we investigated how artificial supercavitation develops according to the combination of injection positions and direction.

• Journal of Soil and Groundwater Environment
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• v.21 no.1
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• pp.80-85
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• 2016

Acoustic cavitation can induce various sonochemical effects including pyrolysis and radical reactions and sonophysical effects including microjets and shockwave. In environmental engineering field, ultrasound technology using sonochemical effects can be useful for the removal and mineralization of recalcitrant trace pollutants in aqueous phase as one of emerging advanced oxidation processes (AOPs). In this study, the effect of liquid height, the distance from the transducer to the water surface, on sonochemical oxidation reactions was investigated using KI dosimetry. As the liquid height/volume increased (40~400 mm), the cavitation yield steadily increased even though the power density drastically decreased. It was found that the enhancement at higher liquid height conditions was due to the formation of standing wave field, where cavitation events could stably occur and a large amount of oxidizing radicals such as OH radicals could be continuously provided.