• Korean Journal of Environmental Biology
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• v.38 no.4
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• pp.554-562
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• 2020

Tremex fuscicornis (Siricidae), known as the xylophagous horntail, and Leucospis japonica (Leucospidae), known as the parasitoid wasp, are wood-boring wasps belonging to the order Hymenoptera. These insects are interesting sources of biological inspiration for the development of drilling mechanisms. To study the biomimicry aspects, the morphological characters of the ovipositor of T. fuscicornis and L. japonica were analyzed using a stereoscopic microscope, a field emission scanning electron microscope, and an optical microscope. There were many differences in the ovipositors between the two species, such as shape, length, surface structure, and arrangement of the teeth. Evenly arranged teeth were developed at the tip of both the dorsal valve and the ventral valve of the ovipositor of T. fuscicornis and looked like a rotating drill bit. In contrast, in L. japonica, the teeth, which looked like a saw, were found only on the ventral valve. Moreover, the tip of the ovipositor of T. fuscicornis was symmetrically divided into four parts, while that of L. japonica was divided into three parts having a 2:1:1 ratio. However, in the case of T. fuscicornis, after the 14th tooth, four parts melded into three parts maintaining a 2:1:1 ratio, and a dovetail joint was found on the horizontal cross-section of the ovipositor that allowed vertical movement for making a hole. These morphological differences of the ovipositor may be due to the insects' lifestyles and phylogenetic distance. Finally, zinc was commonly found at the tip of the ovipositors of both species, a probable result of ecological adaptation created by drilling wood.

• Explosives and Blasting
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• v.36 no.1
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• pp.20-33
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• 2018

A locally damaged structure is a structure that cannot be reused due to having parts that have lost their structural function as a result of abnormal load across the interior or exterior of the structure. The causes of the abnormal load occurrences can be classified into natural disaster and artificial disaster. Locally damaged structures caused by this abnormal load have risk factors that may lead to the possibility of additional secondary collapses, so such structures require immediate and complete dismantling. The case presented in this study involves the application of explosive demolition to a steel truss structured bridge in the Philippines that was damaged due to construction failures and the hurricane. Although shaped charges were needed in explosive demolitions, difficulties in locally obtaining such material. So, we made a charge container to charging of emulsion explosive during the explosive demolition. The explosive demolition resulted in the vertical free fall of the mid-section of the bridge and the free fall rotating of the both end section of the bridge. The neighboring posts and bridge piers did not show signs of damages, while post-demolition fragmentation of removed parts was found to be satisfactory.

• Journal of Ocean Engineering and Technology
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• v.25 no.6
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• pp.91-96
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• 2011

In this paper, friction welded joints were constructed to investigate the mechanical properties of welded 15-mm diameter solid bars of Mg alloy (AZ31B). The main friction welding parameters were selected to endure reliable quality welds on the basis of visual examination, tensile tests, impact energy test, Vickers hardness surveys of the bonds in the area and heat affected zone (HAZ), and macrostructure investigations. The study reached the following conclusions. The tensile strength of the friction welded materials (271 MPa) was increased to about 100% of the AZ31B base metal (274 MPa) under the condition of a heating time of 1 s. The metal loss increased lineally with an increase in the heating time. The following optimal friction welding conditions were determined: rotating speed (n) = 2000 rpm, heating pressure (HP) = 35 MPa, upsetting pressure (UP) = 70 MPa, heating time (HT) = 1 s, and upsetting time (UT) = 5 s, for a metal loss (Mo) of 10.2 mm. The hardness distribution of the base metal (BM) showed HV55. All of the BM parts showed levels of hardness that were approximately similar to friction welded materials. The weld interface of the friction welded parts was strongly mixed, which showed a well-combined structure of macro-particles without particle growth or any defects. In addition, an acoustic emission (AE) technique was applied to derive the optimum condition for friction welding the Mg alloy nondestructively. The AE count and energy parameters were useful for evaluating the relationship between the tensile strength and AE parameters based on the friction welding conditions.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.36 no.11
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• pp.1441-1446
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• 2012

An axial-piston-type hydraulic motor involves friction and leakage losses at the sliding parts, contact loss at the mechanism assembly parts, volumetric loss caused by the pressure drop, housing oil churning loss and compressibility from the hydraulic oil pipe resistance, etc. the friction and volumetric loss at the hydrostatic bearing between the piston shoe and the swash plate rotating at high speed and having an oil film gap of 8-15 ${\mu}m$ strongly affects the total efficiency of the hydraulic motor. In this study, a variable swash-plate-type hydraulic piston motor operating under a maximum pressure of 35 MPa, maximum speed of 2,500 rpm, and displacement of 320 cc/rev is tested to verify the optimal ratio of the hydrostatic bearing which is closely related to the hydraulic motor performance.

• Transactions of the Korean Society of Automotive Engineers
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• v.16 no.4
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• pp.47-55
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• 2008

Turbocharger has a main purpose on recycling of the exhaust gas from the engine cylinder. On the basis of the facility characteristics, the turbocharger supported on floating ring bearings has some problems such as the large volume, oil supplement for lubrication and high power loss due to high operating torque. The air foil bearing has been studied as the bearing element to be able to alternate the floating ring bearing without the problems of the floating ring bearing. In this study, the air foil bearing has 2 parts; journal and thrust bearings, and the test facility consists of the engine, exhaust and intake parts. In addiction, the specification of the turbocharger follows a small turbocharger for SUV engine. The engine speed is varied from 750 (idle rpm) to 2,500 rpm and then, the rotating speed of the turbocharger rotor is accelerated from 0 to 100,000 rpm. From those experiments, the comparison between the performances of the air foil bearing and floating ring bearing is conducted and the results show that the air foil bearing has less power loss, maximum 770 watt, than the floating ring bearing, maximum 5,110 watt. This result verifies that the air foil bearing is more efficient and able to output more power under the same condition of the input power.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.41 no.11
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• pp.1125-1130
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• 2017

The tooth shapes of serration-type and spline-type reactors are optimized using finite element methods to improve the working life of the part and to lower the stress concentration during rotation resulting from contact with the outer race for a reactor operating with $170^{\circ}C$ transmission oil. The results of thermal expansion analyses between an Al reactor and the steel outer race indicate that, before optimization, the gap between the two parts increases further as the serration-type reactor expands by 0.1 mm and the spline-type one strains by 0.08 mm. Because of shape optimization, a trapezoidal shape is obtained from the initial triangular serration and the rectangular spline of the two reactors. The maximum von Mises stress of the serration-type convertor decreased by 24.5 ％, and by 9.3 ％ for the spline-type convertor. In addition, there is a 13 ％ reduction in the axial thickness, as compared to the initially designed model.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.47 no.12
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• pp.881-889
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• 2019

The pre-swirl system is the device that minimizes energy loss of turbine cooling airflow from the stationary parts into rotating parts. In this paper, an off-design analysis was conducted for the ambient air temperature and turbine load conditions. The discharge coefficient was constant for ambient air temperature and turbine load. However, adiabatic effectiveness was increased. This is due to the volume flow rate. The volume flow rate was increased at higher ambient temperature and higher turbine load. It means that the volume of cooling air was increased and the cooling performance of the air was improved. Consequently, adiabatic effectiveness increased by 30.46% at 100% turbine load compared to 20% turbine load. And increased by 18.42% at 55℃ ambient air temperature compared to -20℃ ambient air temperature.

• Magazine of the Korean Society of Agricultural Engineers
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• v.38 no.3
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• pp.82-91
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• 1996

This is a basic study for the static and dynamic analysis on the elasto-plastic and elasto-viscoplastic of an axi-symmetric shell. The objective of this study was to investigate the mechanical characteristics of a nuclear reinforced concrete containment structure, which was selected as a model, by a numerical analysis using a finite element method. The structure was modeled with discrete ring elements of 8-noded isoparametric element rotating against the symmetrical axis, and the interaction between the foundation and the structure was modeled by Winkler's model. Also, the meridional tendon was modeled with 2-node truss elements, and the hoop tendon was done with point elements in two degrees of freedom. The effect of the tendon was considered without the increasement in total degree of freedom as the stiffness matrix of modeled tendon elements was assembled on the stiffness matrix of ring elements linked with the tendon. The results obtained from the analysis of an example were summarized as follows : 1. The stresses in the hoop direction on the interior and exterior surfaces of the structure were shown in changes of similar trend, and high stresses appeared on the structure wall 2. The stresses in the meridional direction on the interior and exterior surfaces were shown in change of different trend. Especially, the stresses at the junctions between the dome and the wall and between the wall and the bottom plate of the structure were very high, compared with those at other parts of the structure. 3. The stress changes in the direction of thickness on the crown of the dome were much linearly distributed. However, as the amount of tendon increased, the stresses in the upper and lower parts of the wall established with the tendon were shown stress concentration. 4. The stress changes in the direction of thickness on the center of the structure wall was linearly distributed in the all cases, and special stress due to the use of the tendon was not shown.

• Journal of the Ergonomics Society of Korea
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• v.24 no.2
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• pp.57-63
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• 2005

Ergonomic intervention techniques were adopted to assess and control potential risk factors of work-related musculoskeletal disorders(WMSDs) in the automated light assembly manufacturing system. Ten different kinds of assembly workstations implemented with a conveyor system and twelve female workers were observed and evaluated with careful video film analysis. Several close examinations using sets of checklists established by qualified safety and health organizations, such as NIOSH, OSHA, and ANSI, were conducted and every workers and staffs in the site participated in the self-report questionnaires and off-line interviews. Typical risk factors and symptoms of the upper extremity musculoskeletal disorders were found and categorized into specific parts of body. To reduce risk factors of WMSDs and improve system productivity new revised workstation standards, physical dimensions, were suggested accordant with anthropometric characteristics of workers and a heuristic decision strategy of rotating shift work schedules according to work contents has proposed to mitigate cumulative physical stress. Finally, ergonomic programs of entire company to prevent WMSDs were structured.

• Journal of Advanced Marine Engineering and Technology
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• v.33 no.2
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• pp.259-266
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• 2009

An experimental study was conducted to investigate the effects of forcing amplitude on the flow structure near the nozzle exit of forced jet diffusion flames. The jet was excited up to the blowout occurrence by a considerable large amplitude with a periodic velocity fluctuation at the tube resonating frequency. In the attached flame regime, we disclosed the very interesting result newly that adding of a moderate forcing amplitude caused the jet flame to become longer in spite of being forced. Particular attention is focused on the turnabout mechanism of vortex roll-up around the elongated flame, which has not been reported previously, and on the inner coherent structure of the forced jet in the attached flame regime. From the velocity and flow visualization results, it was ascertained that the surrounding air due to the occurrence of negative velocity parts was suck into the fuel nozzle. To aid in understanding the rotating phenomenon of coherent structure, we present a schematic diagram of the turnabout mechanism of vortex roll-up. The mechanism of vortex turnabout phenomenon can be easily understood by considering the positive and negative velocity amplitudes about the instantaneous velocity of the forcing flow, as shown in this diagram.