• Geomechanics and Engineering
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• v.17 no.6
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• pp.535-541
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• 2019

Combining the radial well drilling and hydraulic fracturing technique, the production capacity of the reservoirs with low-permeability can be improved effectively. Due to the existence of radial holes, the stress around the well is redistributed, and the initiation and propagation of hydraulic fractures are different with those in traditional hydraulic fracturing. Therefore, it is necessary to study the influences of radial horizontal wells on hydraulic fracturing. The laboratory experiment was conducted to simulate the hydraulic fracturing on the physical model with radial holes. The experimental results showed that, compared with the borehole without radial holes, the sample with radial hole in the direction of maximum horizontal stress was fractured with significantly lower pressure. As the angle between direction of the horizontal hole and the maximum horizontal stress increased, the breakdown pressure grew. While when the radial hole was drilled towards the direction of the minimum horizontal stress, the breakdown pressure increased to that needed in the borehole without radial holes. When the angle between the radial hole and the maximum horizontal stress increase, the pressure required to propagate the fractures grew apparently, and the fracture become complex. Meanwhile, the deeper the radial hole drilled, the less the pressure was needed for fracturing.

• Journal of the Korean Society for Precision Engineering
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• v.20 no.7
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• pp.227-232
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• 2003

In order to make a deep and precise micro-hole, electrode wear and clearance between the electrode and the workpiece are important parameters using micro-electrical discharge machining. In this study, experiments were carried out to show the characteristics of electrode wear and radial clearance with respect to the depth of machined hole. Electrode wear varied with respect to the depth of hole. With deeper machined hole, bigger clearance was observed. Also it was found that the diameter of electrode influences machining characteristics of deep holes.

• The KSFM Journal of Fluid Machinery
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• v.12 no.4
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• pp.44-53
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• 2009

Numerical design optimization of a fan-shaped hole for film-cooling has been carried out to improve film-cooling effectiveness by combining a three-dimensional Reynolds-averaged Navier-Stokes analysis with the radial basis neural network method, a well known surrogate modeling technique for optimization. The injection angle of hole, lateral expansion angle of hole and ratio of length-to-diameter of the hole are chosen as design variables and spatially averaged film-cooling effectiveness is considered as an objective function which is to be maximized. Twenty training points are obtained by Latin Hypercube sampling for three design variables. Sequential quadratic programming is used to search for the optimal point from the constructed surrogate. The film-cooling effectiveness has been successfully improved by the optimization with increased value of all design variables as compared to the reference geometry.

• Journal of Mechanical Science and Technology
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• v.16 no.12
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• pp.1693-1701
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• 2002

The intermittent spray characteristics of a multi-hole and a single-hole diesel nozzle were experimentally investigated. The hole number of the multi-hole nozzle was 5, and the hole diameter of the 5-hole and the single-hole nozzle was the same as d$\_$n/=0.32 ㎜ with the constant hole length to diameter ratio(l$\_$n//d$\_$n/=2.81). The droplet diameters of the spray, including the time-resolved droplet diameter, SMD (Sauter mean diameter) and AMD (arithmetic mean diameter) , injected intermittently from the two nozzles into the still ambient were measured by using a 2-D PDPA (phase Doppler particle analyzer). Through the time-resolved evolutions of the droplet diameter, it was found that the structure of the multi-hole and the single-hole nozzle spray consisted of the three main parts : (a) the leading edge affected by surrounding air. and composed of small droplets; (b) the central part surrounded by the leading edge and mixing flow region and scarcely affected by the resistance of air, (c) the trailing edge formed by the passage of the central part. The SMD decreases gradually with the increase in the radial distance, and the constant value is obtained at the outer region of the radial distance (normalized by hole diameter) of 7-8 and 6 for the 5-hole and single-hole nozzle, respectively. The SMD along the centerline of the spray decrease shapely with the increase in the axial distance after showing the maximum value near the nozzle tip. The SMD remains the constant value near the axial distance(normalized by hole diameter) of 150 and 180 for the 5-hole and the single-hole nozzle, respectively.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.28 no.12
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• pp.2004-2011
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• 2004

The applicability of the ultrasonic C-scan inspection is restricted due to the deterioration of mechanical properties of specimen during the test. Therefore, the aim of this research is applied to Eddy Current (EC) test substitute for the C-scan inspection in CFRP tube containing defects. This research is to evaluate the EC signals for the inspection of CFRP tube containing various circular hole defects (20% to 100% depth to the specimen thickness) using the unloading specimen and radial loading specimen. This study was considered the following points; 1) Analysis of EC signals for the inspection of saw-cut defect and circular hole defect, 2) The evaluation of defect depths and EC signals relationship. 3) Variation of EC signal owing to the radial load. In conclusions, the high frequency such as 300∼500 kHz made it possible to the inspection of 40% to 100% defects. Particularly, in case of 20% defect, the EC signal was not detected due to the noise of micro-crack and delamination. While the depth of the hole defects were decreasing, the difference of the phase angle between unloading specimen and radial loading specimen was gradually increasing.

• Proceedings of the KSME Conference
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• 2003.11a
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• pp.1121-1126
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• 2003

Strength evaluation was carried out for the fillet and oil hole of crankshaft of medium speed diesel HiMSEN engine to verify initial concept design. Alternating torque obtained from torsional vibration analysis and radial force due to firing pressure were applied. It was assumed that the maximum alternating torque and radial force occur simultaneously. Weak points in view of fatigue are proceeding fillet and crank pin fillet area and the minimum normalized fatigue safety factor is 1.17 at crank pin fillet. The fatigue strength of the oil hole was evaluated to verify the effect of the surface roughness of the oil hole. As results, the specific level of the inner surface roughness and the polishing depth of the oil hole for sufficient fatigue strength was suggested. The maximum stress value and stress distribution at the inner surface of the oil hole can be easily estimated at initial design stage by the newly developed method.

• International Journal of Fluid Machinery and Systems
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• v.6 no.1
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• pp.18-24
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• 2013

In order to apply the design method of diagonal flow fan based on axial flow design to the design of radial-outflow type diagonal flow fan which has lower specific speed of 600-700 [$min^{-1}$, $m^3/min$, m], radial-outflow type diagonal flow fan which specific speed was 670 [$min^{-1}$, $m^3/min$, m] was designed by a quasi three-dimensional design method. Experimental investigations were conducted by fan characteristics test, flow surveys by a five-hole probe and a hot wire probe. Fan characteristics test agreed well with the design values. In the flow survey at rotor outlet, the characteristic region was observed. Two flow phenomena are considered as the cause of the characteristic region, one is tip leakage vortex near rotor tip and another is pressure surface separation on the rotor blade.

• Journal of the Korean Society for Precision Engineering
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• v.21 no.6
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• pp.131-138
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• 2004

The objective of this paper is to decide optimal location of a pin-hole to minimize stress concentration around the hole in a rotating disc. The focus of this investigation is to evaluate the effect of pin-hole on stress distribution around the hole using optimum design technique and finite element analysis. Design variables are the radial and the angular location of pin-hole from center of the hole and objective function is the maximum stress around hole in a rotating disc. Using first order method of optimization technique, we found that the maximum equivalent stress around the hole with optimized pin-hole could be reduced by 15.1% compared to that without pin-hole.

• Journal of the Korean Society of Propulsion Engineers
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• v.16 no.3
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• pp.69-76
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• 2012

An achieving method of highly progressive pressure gradient is presented to enhance the missile ejection system's performance by using a gas generator in the condition of preventing erosive burning. To obtain and confirm a stable burning, a ground burning test was performed to evaluate the new methods of a radial-hole and a multi-row propellant grain. The test results show that a radial-hole grain takes good effect on erosive burning and not on ejection performance. On the other hand, a multi-row grain which reduces the length-to-diameter ratio(L/D) of grain is very effective to prevent the erosive burning and to enhance the ejection performance simultaneously.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2011.11a
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• pp.432-439
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• 2011

An achieving method of highly progressive pressure gradient is presented to enhance the missile ejection system's performance by using a gas generator in the condition of preventing erosive burning. To obtain and confirm a stable burning, a ground burning test was performed to evaluate the new methods of a radial-hole and a multi-row propellant grain. The test results show that a radial-hole grain takes good effect on erosive burning and not on ejection performance. On the other hand, a multi-row grain which reduces the legnth-to-diameter ratio(L/D) of grain is very effective to prevent the erosive burning and to enhance the ejection performance simultaneously.