• Wind and Structures
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• v.4 no.4
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• pp.353-366
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• 2001

With respect to serviceability, antenna masts should be designed so that wind-induced motion will not cause unacceptable lack of transmission for broadcasting users and wireless communication. For such antenna masts with directional radio transmission the serviceability limit state is predominantly governed by the tolerable change of the broadcasting angle of the mounted antenna assembly and therefore by the tip distortion of the mast. In this paper it will be shown that refinements of the present state of design of antenna masts are possible by using the statistics of extremes applied to extreme wind situations and by consideration of the statistical and reliability requirements given by the operator such as frequency and return period of passing the serviceability limit.

• 유체기계공업학회:학술대회논문집
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• 1999.12a
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• pp.252-256
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• 1999

In this research, the performance predictions of the submersible mixer were investigated. The variation of the performance characteristics by changing the impeller design parameters were discussed through the flow calculation results by using a commercial program, FLUENT. The performance of the submersible mixers is related to the velocity diffusion profiles downstream of the impeller and also the required input motor power to mix the fluid. In this study, the various design parameters such as the number of blade, the hub and tip diameters, the impeller blade profiles and revolution speed of the blades were taken for the fixed values. The blade sweep direction, the chord length distribution along with the radius of the blade and the inlet blade angle were changed to make different testing models. The flow calculation results show the effect of the changed design parameters on the performance of the submersible mixers and also give some helpful information for designing more efficient submersible mixers.

• International Journal of Fluid Machinery and Systems
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• v.3 no.1
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• pp.39-49
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• 2010

In this paper, a numerical study has been carried out to investigate the influence of jet fan design variables on the performance of a jet fan. In order to achieve an optimum jet fan design and to explain the interactions between the different geometric configurations in the jet fan, three-dimensional computational fluid dynamics and the DOE method have been applied. Several geometric variables, i.e., hub-tip ratio, meridional shape, rotor stagger angle, number of rotor-stator blades and stator geometry, were employed to improve the performance of the jet fan. The objective functions are defined as the exit velocity and total efficiency at the operating condition. Based on the results of computational analyses, the performance of the jet fan was significantly improved. The performance degradations when the jet fan is operated in the reverse direction are also discussed.

• Journal of the Korean Society of Safety
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• v.13 no.3
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• pp.24-31
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• 1998

Variable thickness plates are commonly encountered in the majority of mechanical/structural components of industrial applications. And, as a result of the unsymmetry of the structure or the load and the anisoptropy of the materials, the cracks in engineering structures are generally subjected to combined stresses. In spite of considerable practical interest, however, a few fracture mechanics study on combined mode crack in a variable thickness plate have carried out. In this respect, combined mode I/III stress intensity factors $K_I$ and $K_III$ at the crack tip for a variable thickness plate were obtained by 3-dimensional finite element analysis. Variable thickness plates containing a central slant crack were chosen. The parameters used in this study were dimensionless crack length $\lamda$, crack slant angle $\alpha$, thickness ratio $\beta$ and width ratio $\omega$. Stress intensity factors were calculated by crack opening displacement(COD) and crack tearing displacement(CTD) method.

• The Transactions of the Korean Institute of Electrical Engineers
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• v.40 no.2
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• pp.200-206
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• 1991

In this paper, an output feedback is used to reduce the effect of the vibration in the control of a flexible one-link robot arm. A PD control method with a time varying gain is proposed to improve the performance of the system in tip deflection and settling time for the step reference input. By making the change of feedback gain smoothly, th input torque can be made smooth. When there is a payload with unknown mass, an interpolation method which uses the inrehgrated value of the transient response of the hub angle is proposed for the estimation of teh payload mass. This method can be used when the reference input is known and we can get highly accurate estimate for the unknown payload. It is also demonstrated that flexible one-link arm can be controlled prettry accurately by an output feedback in a noisy environment without knowing the mass of the payload.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2000.11a
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• pp.667-673
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• 2000

A number of issues related with the vibrational behavior of pretwisted rotating beams featuring anisotropic properties and incorporating adaptive capabilities are considered in this paper. The adaptive capabilities are provided by a system of piezoactuators bonded or embedded into the structure. Based on the converse piezoelectric effect and on the out of phase activation, boundary control moments are pizoelectrically induced at the beam tip. A feedback control law relating the induced bending moments with the kinematical response quantities appropriately selected is used, and its beneficial effects, considered in conjunction with that of the beam anisotropy and structural pretwist upon the eigenvibration characteristics are highlighted

• International Journal of Korean Welding Society
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• v.1 no.1
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• pp.71-77
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• 2001

The characteristics of the fume generation in a flux cored arc welding were investigated using the fume collection chamber developed. The Korean Standard concerning the method for the evaluation of the fume generation rate(FGR) was updated by the evaluation method obtained through this study. It was found that the effect of humidity in the test environment should be considered and the automatic welding method had to be employed for the purpose of the exact evaluation of the fume generation rate. The results showed that the fume generation rate was influenced by the welding parameters. The important factors were the welding current arc voltage, travel speed, and contact tip to work distance(CTWD) that affected the heat input as well as the torch angle and the shielding gas flow rate that influenced the shielding effect. The fume generation rate increased as the heat input increased and the shielding effect decreased. It was also observed that the effect of the welding current is much grater than the other welding parameters.

• Journal of the Korean Society for Precision Engineering
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• v.11 no.4
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• pp.38-46
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• 1994

The vibration amplitude of boring bar is generally large at the tool tip, because it has the high length-diameter(L/D) ratio. A new dynamic cutting force model is presented by considering the change of shear angle under dynamic cutting. The boring bar is modelled as a cantilever with dynamic force acting at the tool end point. Based on this realistic continuous system model, the equation of motion of borring bar is solved by numerical computations. A good agreement is found between the proposed model and the experimental results.

• Clinical Endoscopy
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• v.57 no.3
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• pp.293-301
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• 2024

Cap-assisted endoscopy refers to a procedure in which a short tube made of a polymer (mostly transparent) is attached to the distal tip of the endoscope to enhance its diagnostic and therapeutic capabilities. It is reported to be particularly useful in: (1) minimizing blind spots during screening colonoscopy, (2) providing a constant distance from a lesion for clear visualization during magnifying endoscopy, (3) accurately assessing the size of various gastrointestinal lesions, (4) preventing mucosal injury during foreign body removal, (5) securing adequate workspace in the submucosal space during endoscopic submucosal dissection or third space endoscopy, (6) providing an optimal approach angle to a target, and (7) suctioning mucosal and submucosal tissue with negative pressure for resection or approximation. Here, we review various applications of attachable caps in diagnostic and therapeutic endoscopy and their future implications.

• Journal of the Korean Geosynthetics Society
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• v.12 no.4
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• pp.57-66
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• 2013

In this study, pullout tests were carried out to evaluate pullout characteristics of waste fishing net (WFN), which added into bottom ash for recycling both bottom ash and WFN. Three different mesh size of WFN (WFN20:$20mm{\times}20mm$, WFN30:$30mm{\times}30mm$, WFN40:$40mm{\times}40mm$) and geogrid were added as a reinforcement. Pullout characteristics of waste fishing net were compared with those of the geogrid. Pullout test results showed that pullout strength and stiffness of WFN20 are a little less than those of geogrid. However, the pullout friction angle of WFN20 is similar to that of geogrid due to bearing resistance induced from transverse rib because thickness of WFN20 is greater than geogrid. Pullout test results also indicated that distribution of residual strain along reinforcement after test depends on overburden stress. Residual strain at the tip of reinforcement increased with an increase in overburden stress due to concentration of pullout force on the tip of reinforcement.