• Journal of Korean Port Research
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• v.12 no.1
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• pp.75-86
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• 1998

To design a coastal structure in the nearshore region, engineers must have means to estimate wave climate. Waves, approaching the surf zone from offshore, experience changes caused by combined effects of bathymetric variations, interference of man-made structure, and nonlinear interactions among wave trains. This paper has attempted to find out the effects of two of the more subtle phenomena involving nonlinear shallow water waves, amplitude dispersion and secondary wave generation. Boussinesq-type equations can be used to model the nonlinear transformation of surface waves in shallow water due to effect of shoaling, refraction, diffraction, and reflection. In this paper, generalized Boussinesq equations under the complex bottom condition is derived using the depth averaged velocity with the series expansion of the velocity potential as a product of powers of the depth of flow. A time stepping finite difference method is used to solve the derived equation. Numerical results are compared to hydraulic model results. The result with the non-linear dispersive wave equation can describe an interesting transformation a sinusoidal wave to one with a cnoidal aspect of a rapid degradation into modulated high frequency waves and transient secondary waves in an intermediate region. The amplitude dispersion of the primary wave crest results in a convex wave front after passing through the shoal and the secondary waves generated by the shoal diffracted in a radial manner into surrounding waters.

• Journal of Power Electronics
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• v.18 no.3
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• pp.714-722
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• 2018

This paper presents a wide-range speed control scheme of brushless DC (BLDC) motors based on a hall sensor with separated low- and normal-speed controllers. However, the use of the hall sensor signal is insufficient to detect motor speed in the low-speed region because of low sensor resolution and time delay. In the proposed method, a micro-stepping current control method according to the torque angle variation is presented. In this mode, the motor current frequency and rotating angle are determined by the reference speed without the actual speed fed by the hall sensor. The detected torque angle is used to adjust the current value in a limited band to control the current value in accordance with the load. The torque angle is detected exactly at the changing point of the hall sensor signal. The rotor can follow the rotating flux with the variable torque angle. In a normal speed range, the conventional vector control scheme is used to control the motor current with a PI speed controller using the hall sensor. The torque characteristics are analyzed on the basis of the back EMF and current shape. To adopt the vector control scheme, the continuous rotor position is estimated by the measured speed and hall sensor position. At the mode changing point between low and normal speed range, the proper initial current command and reference rotor position are calculated. The calculated current command can reduce the torque ripple during transient mode. The proposed method is simple but effective in extending the speed control range of a conventional BLDC motor with hall sensor without the need for a high-resolution encoder. The effectiveness of the proposed method is verified by various experiments on a practical BLDC motor.

• Journal of the Society of Naval Architects of Korea
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• v.28 no.1
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• pp.60-68
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• 1991

The updated Lagrangian Finite Element Method is introduced to analyse rigid body-fluid impact problem which is characterized by incompressible Navier-Stokes equations and impact-contact conditions between free surface and rigid body. For the convenience of numerical computation, velocity fields are splinted into vicous and pressure parts, and then the governing equations and boundary conditions are decomposed in accordance with the decomposition. However, Viscous stresses acting an the solid boundaries are neglected on the assumption that very small velocity gradients may occur during extremely small time interval of the impact. Four coded quadrilateral elements are used to discretize the space domain and the fully explicit time-marching algorithm is employed with a reasonably small time step. At the beginning of each time step, contact velocity of the rigid body is computed from the momentum balance between the body and the fluid. The velocity field is then computed to satisfy the discretized equations of motions and incompressibility and contact constraints as well as an exact free surface boundary condition. At the end of each time step, the fluid domain is updated from the velocity field. In the present time stepping numerical analysis, behaviour of the free surface near the body can be observed without any difficulty which is very important in the water impact problem. The applicability of the algorithm is illustrated by a wedge type falling body problem. The numerical solutions for time-varying pressure distributions and impact loadings acting ion the surface are obtained.

• Journal of the Society of Naval Architects of Korea
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• v.28 no.1
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• pp.38-52
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• 1991

In this paper, a semi-Lagrangian method is used to solve the nonlinear hydrodynamics of a three-dimensional body beneath the free surface in the time domain. The boundary value problem is solved by using the boundary integral method. The geometries of the body and the free surface are represented by the curved panels. The surfaces are discretized into the small surface elements using a bi-cubic B-spline algorithm. The boundary values of $\phi$ and $\frac{\partial{\phi}}{\partial{n}}$ are assumed to be bilinear on the subdivided surface. The singular part proportional to $\frac{1}{R}$ are subtracted off and are integrated analytically in the calculation of the induced potential by singularities. The far field flow away from the body is represented by a dipole at the origin of the coordinate system. The Runge-Kutta 4-th order algorithm is employed in the time stepping scheme. The three-dimensional form of the integral equation and the boundary conditions for the time derivative of the potential Is derived. By using these formulas, the free surface shape and the equations of motion are calculated simultaneously. The free surface shape and fille forces acting on a body oscillating sinusoidally with large amplitude are calculated and compared with published results. Nonlinear effects on a body near the free surface are investigated.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.20 no.8
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• pp.80-87
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• 2006

This paper analyzed the characteristics of the claw pole PM stewing motor by using 3D FEM. As the magnetization occurs along the z-axis of the motor, it is necessary to apply 3D FEM for analysis of the claw pole PM stewing motor. Considering the computation time, reducing the number of the analysis model is effective method of the methods of the reducing analysis time. By using the "Design Of Experiments(DOE)", efficient analysis was able to be done. To see the effects of the design factors, the 3D FEM is applied only to the selected models. As the design factors, the teeth selected models, the number of turns and the permanent magnet overhang was selected.

• Journal of the Korean Society for Nondestructive Testing
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• v.21 no.5
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• pp.493-500
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• 2001

The detection of axial cracks using conventional MFL pig is a significant challenge in the gas pipeline inspection. In this study, a technique using interaction of circumferentially induced torrents with axial stress corrosion crack is presented. The feasibility of this technique is investigated using finite element modeling. Finite element analysis of such interaction is a difficult problem in terms of both computation time and memory requirements. The challenges arise due to the nonlinearity of material properties, the small sire of tight cracks relative to that of the magnetizer, and also time stepping involved in modeling velocity effects. This paper presents an approach based on perturbation methods. The overall analysis procedure is divided into 4 simple steps that can be performed sequentially. Modeling results show that this technique can effectively detect colonies of SCC as well as single SCC.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.36 no.8
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• pp.728-733
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• 2008

Unsteady aerodynamic analysis of an air-pressure-levitated high-speed ground vehicle moving over the nonplanar ground surface are performed using the boundary-element method. The potential flow solution is included in a time-stepping loop and the wake is captured as part of the solution. When the vehicle moving inside the channel, the lift coefficient and the pitching moment coefficient of the vehicle are increased further because the air trapped by the channel increases the ground effect. In other words, the nonplanar ground surface such as the channel decreases further the longitudinal stability of the vehicle. On the other hand, there is little difference between the ground and the channel in the lateral stability of the vehicle because the lift increment due to the nonplanar ground surface such as the channel takes place on both sides of the wing with the same rate of increase.

• Proceedings of the Korean Institute Of Construction Engineering and Management
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• autumn
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• pp.78-84
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• 2002

In VE(Value Engineering) process, function analysis technique is utilized as a stepping stone to induce creative idea. However, function analysis is regarded as the most difficult job for VE team to undertake. For this reason, the function analysis is not properly applied or even omitted in construction VE studies. The current problems of function analysis in construction VE are following: 1) lack of basic understanding of the function analysis as problem solving technique, 2) the sequential step-by-step analysis process, 3) lack of interrelationship between function analysis and other phase in th VE process, 4) lack of time, experience, training, and quantitative data etc. The existing function analysis is faultiness theoretically. However, it is not enough for efficient use in practice, Thus The study aims to suggest an function analysis application method and to develop a computerized FAST(function Analysis System Technique) diagramming model, called Easy-FAST, for the efficient and effective function analysis on construction VE projects.

• Journal of Korean Physical Therapy Science
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• v.10 no.1
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• pp.30-37
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• 2003

Purpose : The purpose of this study is giving the healthy promotion and it's related data base for out-patients who had stroke via evaluating the general characters of their active daily living and physical therapy Method : This study researched 81 patients who had received physical therapy service in 6 general hospitals located Pusan city responded to the self-assessment questionnaires from July 2002 to August 2002. Conclusion : In this study, patients were composed of 61.7% of male, 65.4% of 50's-60's in the age, 56.8% of cerebral infarction, and 60.5% of right hemiplegia. 74.1% of patients received physical therapy after 6 months from an attack, only 62.9% used orthosis & gait aids, and 59.2% received medical care 2 or 3 times per week. 40.7% of patients had over 9 hours sleeping time and 22% had reduced $1{\sim}2hours$ before hospitalization. 90% did not have drinking and smoking. 91.4% had 3 times eating per day, and 67.7% did not have good nutrition. The reasons of that were their eating habit, 542% of eating-giver, 3.7% of economic problem. 46.9% of patients used healthy food. In active daily living, patients can't do drinking by cup, voiding & defication by themselves, however patients can't do wearing/take off, etiquette for dressing, bathing, stepping by themselves. 40.7% of patients don't wear orthosis, 55.6% of patients don't use W/C. Part of physical therapy that patients concerned importantly exercise for prevention of joint distortion, management of affected side, and 80% of patients was also concerned other's part, significantly. 71.8% of patients & care-givers want to receive physical therapy at home, and 74% of patients do physical therapy by themselves at home along teached hospitalization.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2014.05a
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• pp.465-468
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• 2014

In this paper, we describe a method capable of measuring biological signals including respiration, heart rate, blood pressure, and blood sugar, using UWB (Ultra Wide Band) pulses, while does not contact the human body. Physiological signal is a basic data for checking the health. Because life is longer and active area of human becomes very broad, the medical system and the physical human resources which are focused on existing hospital must be located close patient, In that way, they hope be to engage in healthy life by stepping a quick step and treatment. Thus, it must be fitted closely to the patient. It is necessary to monitor the health without inconvenience on an ongoing basis. How to utilize radio waves in this way have been studied for a long time. However, the characteristics of radio waves on the human body has not been accurately grasped and developed as such. Accordingly, it is a level that can not be applied clinically. So, it is not widely put to practical use. In this paper, We analyzed and described the impact and characteristics of UWB pulses to the human body is a problem existing.