• Journal of Electrical Engineering and Technology
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• v.7 no.5
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• pp.705-713
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• 2012

In this paper, a novel 12/14 hybrid pole type bearingless switched reluctance motor (BLSRM) with short flux path and no flux-reversal in the stator is proposed. The proposed BLSRM has separated rotating torque and suspending force poles. Because of independent characteristics between torque and suspending force poles, the torque control can be decoupled from the suspending force control. Due to the short flux path without any reversal flux, compared to the 8/10 hybrid stator pole BLSRM, the output torque is significantly improved and the air-gap is easier to control. Meanwhile, basic design principle for the proposed structure is described. To verify the proposed structure, finite element method (FEM) is employed to get characteristics of the proposed structure and 8/10 hybrid stator pole BLSRM. Based on the analysis, a prototype of the proposed BLSRM is designed and manufactured. Finally, validity of the proposed structure is verified by the experimental results.

• Proceedings of the Korean Society of Marine Engineers Conference
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• 2006.06a
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• pp.53-54
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• 2006

Experimental analyses on the Hydroelastic Flow-Structure Interactions on pulsed impinged jet is measured with the FSIMS(Flow-Structure Interaction Measurement System. The nozzle diameter is D=15mm and two major experiments have been carried out for the cases of the distance between the nozzle tip to the elastic wall is 6.0. The pulsed jets were controlled by a solenoid valve and were impinged onto an elastic plate (material: silicon, diameter: 350mm, thickness: 0.5mm, hardness: 15). The Reynolds numbers were 20,000 and 24,000 when the jets were impinged with the volume velocities. The results showed that the elastic plate moved slightly to the opposite direction of the jet direction at the time of valve opening. It has been shown that the vortices travelling over the surface of the wall made the elastic wall distorted locally due to a vector forces between rotating forces of the vortex and a newly-incoming flow.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.5 no.4
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• pp.72-78
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• 2006

Inherent in machine tool structures are the vibrations which are generated by rotating parts such as motors, spindles and chucks. The vibrations not only hurt the precision machining but also damage the structures, and become more serious with time. Many of the old machine tools show severe vibrations for the desired accuracy of the modern industries. It is too much of a waste, however, to get rid of them as scraps. There have been many researches in order to suppress the vibrations of old machine tool structures using the tool post which utilizes actuators to compensate the existing vibrations and using the dampers or absorbers attached to some critical parts. In this paper, the dynamic properties are analyzed to obtain the natural frequencies and mode shapes of a machine tool structure which reflect the main reasons of the biggest vibrations under the given operating conditions. And the feasibility of improving the stability of the structure has been investigated with minor design changes and expenses. The result of the study shows that simple changes based on proper system identification can considerably improve the stability of the machine tool structure.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.28 no.7
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• pp.834-841
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• 2004

Experimental study on the three-dimensional topology of hairpin packet structures in turbulent boundary layers were carried out. Two different Reynolds number based on momentum thickness, Re$\sub$$\theta$/=514 and 934 were generated in a blowing type wind tunnel under the condition of zero pressure gradient. Simultaneous measurements of velocity fields at a wall-normal plane and wall-parallel plane by a plane PIV and a Stereo-PIV systems. The two Nd:Yag laser systems and three CCD cameras were synchronized to obtain instantaneous velocity fields at the same time. To avoid optical noise at the crossing line by the two laser light sheets, a new optical arrangement using polarization was applied. The obtained velocity fields show the existence of hairpin packet structure vividly and the idealized hairpin vortex signature is confirmed by experiment. Two counter-rotating vortex pair which reflects the cutting plane of hairpin legs are found both side of a strong streaky structure when the wall-normal plane cuts the hairpin head.

• Advances in aircraft and spacecraft science
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• v.6 no.1
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• pp.31-49
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• 2019

Flutter is a dangerous phenomenon encountered in flexible structures subjected to aerodynamic forces. This includes aircraft, helicopter blades, engine rotors, buildings and bridges. Flutter occurs as a result of interactions between aerodynamic, stiffness and inertia forces on a structure. The conventional method for designing a rotor blade to be free from flutter instability throughout the helicopter's flight regime is to design the blade so that the aerodynamic center (AC), elastic axis (EA) and center of gravity (CG) are coincident and located at the quarter-chord. While this assures freedom from flutter, it adds constraints on rotor blade design which are not usually followed in fixed wing design. Periodic Structures have been in the focus of research for their useful characteristics and ability to attenuate vibration in frequency bands called "stop-bands". A periodic structure consists of cells which differ in material or geometry. As vibration waves travel along the structure and face the cell boundaries, some waves pass and some are reflected back, which may cause destructive interference with the succeeding waves. In this work, we analyze the flutter characteristics of a helicopter blades with a periodic change in their sandwich material using a finite element structural model. Results shows great improvements in the flutter forward speed of the rotating blade obtained by using periodic design and increasing the number of periodic cells.

• Journal of the Society of Naval Architects of Korea
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• v.59 no.1
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• pp.39-45
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• 2022

Normal strategy of structure optimization procedure has been minimum cost or weight design. Minimum weight design satisfying an allowable stress has been used for the ship and offshore structure, but minimum cost design could be used for the case of high human cost. Natural frequency analysis and forced vibration one have been used for the strength estimation of marine structures. For the case of high precision experiment facilities in marine field, the structure has normally enough margin in allowable stress aspect and sometimes needs high natural frequency of structure to obtain very high precise experiment results. It is not easy to obtain a structure design with high natural frequency, since the natural frequency depend on the stiffness to mass ratio of the structure and increase of structural stiffness ordinary accompanies the increase of mass. It is further difficult at the grillage structure design using the profiles, because the properties of profiles are not continuous but discrete, and resource of profiles are limited at the design of grillage structure. In this paper, the grillage structure design system under the constraint of high natural frequency is introduced. The design system adopted genetic algorithm to realize optimization procedure and can be used at the design of the experimental facilities of marine field such as a towing carriage, PMM, test frame, measuring frame and rotating arm.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 1991.10a
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• pp.23-28
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• 1991

A simple, yet effective, material model of concrete is presented in this paper. Based on the orthotropic model in which the assumption of orthogonal principal strain axes is used, the incremental stress-strain relation of concrete is defined in the biaxial stress condition and the rotating crack model is adopted to represent realistically the change of the crack direction according to the different loading pad after cracking. Numerical results obtained from the finite element analysis are compared favourably with the available experimental data. By the parametric study, moreover, it was found that He most important factor in the structural behavior when the reinforced concrete structure is subjected to the dominent shear forces is the tension stiffening effect. The influences of the tension stiffening effect remarkably appears as the steel ratio decreases.

• Ocean Systems Engineering
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• v.2 no.1
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• pp.1-16
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• 2012

Offshore wind turbines are complex structural and mechanical systems located in a highly demanding environment. This paper proposes a multi-level system approach for studying the structural behavior of the support structure of an offshore wind turbine. In accordance with this approach, a proper numerical modeling requires the adoption of a suitable technique in order to organize the qualitative and quantitative assessment in various sub-problems, which can be solved by means of sub-models at different levels of detail, both for the structural behavior and for the simulation of loads. Consequently, in a first place, the effects on the structural response induced by the uncertainty of the parameters used to describe the environmental actions and the finite element model of the structure are inquired. After that, a meso-level FEM model of the blade is adopted in order to obtain the detailed load stress on the blade/hub connection.

• Journal of Institute of Convergence Technology
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• v.2 no.2
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• pp.49-54
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• 2012

These conventional reciprocating compressor(reciprocating type compressor) or household refrigerators and car air conditioning rotary compressor, rotary compressor, has been used by a reciprocating piston torque variability and the deepening of the vibration problem, the suction valve and discharge valvein this study, as a result of the losses in the current use of the scroll compressor, scroll compressor with the features of low noise, high efficiency, small size, light weight, has increased. fixed Scroll(fixed scroll) scroll compressor with orbiting scroll (rotating scroll) vibration experiments were performed in order to identify the vibration characteristics of the structure of the Analysis was performed using the commercial finite element program(ANSYS) for the sake of comparison, the experimental results using a finite element model of research about the natural vibration characteristics due to a material change.

• Proceedings of the Korean Vacuum Society Conference
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• 2014.02a
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• pp.288.2-288.2
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• 2014

InP quantum dots were grown by using the molecular beam epitaxy technique. Quantum dots are connected and composed string-like one-dimensional structure due to the strain field along [110] crystal direction. Two prominent photoluminescence transitions from normal quantum dots and string-like one-dimensional structure were observed which show strong optical anisotropy along [1-10] and [110] crystal directions. Both peaks also showed blue-shift while rotating emission polarization from [1-10] to [110] direction. Such optical transition behaviors are the consequence of the valence band mixing caused by strain field along the [110] crystal direction.