• Proceedings of the Korean Geotechical Society Conference
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• 2009.09a
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• pp.1338-1345
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• 2009

Although rock excavation is necessary for the effective utilization of urban space, most conventional rock excavation methods, including the blasting method, cause high noise and vibration. Meanwhile, if a high pressure waterjet system is applied to excavate underground spaces in urban areas, the public grievance can be reduced by low noise and vibration. In this study, an abrasive waterjet system is designed and developed to study the influence of various performance parameters such as jet pressure, nozzle traverse speed, stand-off distance, or abrasive feed rate on waterjet excavation performance in laboratory. Using the developed waterjet system, rock drilling characteristics are identified by measuring drilling depths as a function of the jet exposure time. The drilling depth linearly increases with increasing the jet exposure time(under 60sec). Rock cutting characteristics are also obtained with various jet pressures(1600~3200kg/$cm^2$) and nozzle traverse speeds(1.9~14.1mm/s): The cutting depth is nonlinearly related to the jet pressure and traverse speed. Indeed, the cutting depth increases with an increase in the jet pressure and a decrease in the nozzle traverse speed. This trend can be explained by energy transferring/loss mechanism.

• International Journal of Naval Architecture and Ocean Engineering
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• v.13 no.1
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• pp.585-598
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• 2021

The course-keeping stability of a high speed planing boat should be considered at the design stage for its safe operations. The shape of waterjet intake plane is one of important design parameters of a waterjet propelled planing boat. That has significant influences on the stern flow patterns and pressure distributions. In this study, the effects of the waterjet intake shapes of planing boats on the course-keeping stabilities are investigated. Two kinds of designed planing boats have the same dimensions, but there are differences in waterjet intake plane shapes. Captive and free-running model tests, Computational Fluid Dynamics (CFD) analyses are carried out in order to estimate their hydrodynamic performances including course-keeping stabilities. The results show that the flat and wide waterjet intake plane of the initially designed boat makes the course-keeping stability worse. The waterjet intake shape is redesigned to improve the course-keeping stability. The improved performances are confirmed by free-running model tests and full-scale trials.

• Proceedings of the KSME Conference
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• 2004.11a
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• pp.922-927
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• 2004

Abrasive waterjet (AWJ) cutting is an emerging technology for precision cutting of difficult-to-machining materials with the distinct advantages of no thermal effect, high machinability, high flexibility and small cutting forces. This paper investigated theoretical and experimental cutting characteristics associated with abrasive waterjet cutting of quartz GE214. It is shown that the proper variations of several cutting parameters such as waterjet pressure, cutting speed and cutting depth improve the roughness on workpiece surfaces produced by AWJ cutting. From the experimental results by AWJ cutting of quartz GE214, the optimal cutting conditions to improve the surface roughness were proposed and discussed.

• Transactions of the Korean Society of Automotive Engineers
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• v.13 no.2
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• pp.118-126
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• 2005

Abrasive waterjet (AWJ) cutting is an emerging technology for precision cutting of difficult-to-machining materials with the distinct advantages of no thermal effect, high machinability, high flexibility and small cutting forces. This paper investigated theoretical and experimental cutting characteristics associated with abrasive waterjet cutting of quartz GE214. It is shown that the proper variations of several cutting parameters such as waterjet cutting pressure, cutting speed and cutting depth improve the roughness on workpiece surfaces produced by AWJ cutting. From the experimental results by AWJ cutting of quartz GE214, the optimal cutting conditions to improve the surface roughness and precision were proposed and discussed.

• Journal of Korean Tunnelling and Underground Space Association
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• v.24 no.5
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• pp.395-409
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• 2022

To overcome the limitation of conventional rock excavation methods, the excavation with abrasive waterjet has been actively developed. The abrasive waterjet excavation method has the effect of reducing blasting vibration and enhancing the excavation efficiency by forming a continuous free surface on the rock. However, the waterjet cutting performance varies with rock fracturing characteristics. Thus, it is necessary to analyze the cutting performance for various rocks in order to effectively utilize the waterjet excavation. In this study, cutting experiments with the high pressure waterjet system were performed for basalt and granite specimens. Water pressure, standoff distance, and traverse speed were determined as effective parameters for the abrasive waterjet cutting. The cutting depth and width of basalt specimens were analyzed to compare with granite results. The averaged cutting depth of basalt was shown in 41% deeper than granite; in addition, the averaged cutting width of basalt was formed by 18.5% narrower than granite. The results of this study are expected to be useful basic data for applying rock excavation site with low strength and high porosity such as basalt.

• Journal of Korean Tunnelling and Underground Space Association
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• v.17 no.5
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• pp.533-551
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• 2015

The rock fracturing during waterjet cutting is very complicated because rock is inhomogeneous and anisotropic, compared with artificial materials (e.g., metal or glass). Thus, it is very important to verify the effects of rock properties on waterjet rock cutting performance. Properties affecting the rock cutting efficiency have been variously described in the literature, depending on the experimental conditions (e.g., water pressure, abrasive feed rate, or standoff distance) and rock-types studied. In this study, a rock-property-related literature review was performed to determine the key properties important for waterjet rock cutting. Porosity, uniaxial compressive strength, and hardness of the rock were determined to be the key properties affecting waterjet rock cutting. The results of this analysis can provide the basic knowledge to determine the cutting efficiency of waterjet rock cutting technology for rock excavation-related construction.

• Transactions of the Korean Society of Machine Tool Engineers
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• v.16 no.5
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• pp.183-190
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• 2007

It is well known that abrasive waterjet(AWJ) was developed as a kind of high-density energy processing technologies. AWJ is used to obtain the better cutting quality of various materials such as metals, ceramics, glass and composite materials within a short manufacturing time because of the characteristics of heatless and noncontact processing. However, AWJ device still has some problems to obtain the high quality of thin workpiece. In this paper, we investigated the optimal microcutting conditions of AWJ, such as maximum pressure, cutting speed and standoff distance of thin multi-layered materials. The experimental results show that AWJ has possibilities and potential to apply to the microcutting of thin multi-layered materials for IT industrial applications.

• Journal of the Korean Society of Industry Convergence
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• v.23 no.5
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• pp.817-823
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• 2020

In recent, the machining of difficult-to-cut materials such as titanium alloys, stainless steel, Inconel, ceramic, glass, and carbon fiber reinforced plastics (CFRP) used in aerospace, automobile, medical industry is actively researched. Abrasive waterjet is a non-traditional processing method in which ultra-high pressure water and abrasive particles are mixed in a mixing chamber and shoot out jet through a nozzle, and removed by erosion due to collision with a material. In particular, the nozzle of the abrasive waterjet is one of the most important parts that affect the machining quality as with a cutting tool in general machining. It is very important to monitor the condition of the nozzle because the workpiece is uncut or the surface quality deteriorates due to wear, expanding of the bore, damage of the nozzle and clogging of the abrasive, etc. Therefore, in this paper, we propose a monitoring system based on Acoustic Emission(AE) sensor that can detect nozzle condition in real time during AWJ processing.

• Journal of the Society of Naval Architects of Korea
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• v.33 no.1
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• pp.65-76
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• 1996

A screw propeller is usually accepted as a propulsor of many kinds of ships. However, for high speed vessels, screw propeller has large cavitation area on the blades so propeller efficiency is decreased and erosion can be happened. To avoid this problem, supercavitating propeller and waterjet are generally used for high speed vessels. In this paper, we introduced the self-propulsion test procedure which has been developed for high speed vessels in Hyundai Maritime Research Institute. The model ship used in experiment represents catamaran about 5.3 m in length. To minimize the experimental errors, two impellers were driven by a single motor. Thrust was calculated by converting the measured pressure to flow rates at the nozzle exit. The test procedure is composed of resistance test, self propulsion test and analysis. In order to measure the pressure, pressure tabs were installed around the nozzle exit and connected to the pressure sensor by vinyl tube.

• Journal of the Society of Naval Architects of Korea
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• v.36 no.2
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• pp.9-21
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• 1999

The waterjet is very widely used today in propulsion system of high speed vessel but manufacturer is limited because of an efficiency and a difficulty of a manufacture on the inlet configuration of the waterjet. The importancy in designing the inlet configuration of the waterjet lies on the minimization of the cavitation which is largely affecting the efficiency. In this paper, the configuration analysis is carried out to find a optimum shape which is minimizing the cavitation using a two dimensional potential-based panel method with an inlet configuration of a flush type. Also, it is developed a direct design method finding an inlet configuration by a given pressure distributions. The numerically obtained optimum shape using this configuration analysis method show a good agreement compared to the Kashiwadani's results. It is carried out a direct design method over a lip and a ramp of an inlet configuration wish pressure distributions obtained a result of the configuration analysis and the results show a good agreement compared to original configuration.