• Journal of Mechanical Science and Technology
• /
• 제18권2호
• /
• pp.313-324
• /
• 2004

A rich phenomenon in the dynamics of azimuthal vortices in a circular cylinder caused by the inertial oscillation is investigated numerically at high Reynolds numbers and moderate Rossby numbers. In the actual spin-up flow where both the Ekman circulation and the bottom friction effects are included, the first appearance of a seed vortex is generated by the Ekman boundary-layer on the bottom wall and the subsequent roll-up near the corner bounded by the side wall. The existence of the small vortex then rapidly propagates toward the inviscid region and induces a complicated pattern in the distribution of azimuthal vorticity, i.e. inertial oscillation. The inertial oscillation however does not deteriorate the classical Ekman-pumping model in the time scale larger than that of the oscillatory motion. Motions of single vortex and a pair of vortices are further investigated under a slip boundary-condition on the solid walls. For the case of single vortex, repeated change of the vorticity sign is observed together with typical propagation of inertial waves. For the case of a pair of vortices with a two-step profile in the initial azimuthal velocity, the vortices' movement toward the outer region is resisted by the crescent-shape vortices surrounding the pair. After touching the border between the core and outer regions, the pair vortices weaken very fast.

• 대한기계학회논문집A
• /
• 제33권1호
• /
• pp.27-33
• /
• 2009

Human postural responses appeared to have stereotyped modality, such as ankle mode, knee mode and hip mode in response to various perturbations. We examined whether human postural control gain of full-state feedback could be decoupled along with the eigenvector. To verify the model, postural responses subjected to fast backward perturbation were used. Upright posture was modeled as 3-segment inverted pendulum incorporated with feedback control, and joint torques were calculated using inverse dynamics. Postural modalities such as ankle, knee and hip mode were obtained from eigenvectors of biomechanical model. As oppose to the full-state feedback control, independent eigenvector control assumes that modal control input is determined by the linear combination of corresponding modality. We used optimization method to obtain and compare the feedback gains for both independent eigenvector control and full-state feedback control. As a result, we found that simulation result of eigenvector feedback was not competitive in comparison with that of full-state feedback control. This implies that the CNS would make use of full-state body information to generate compensative joint torques.

• 한국산업융합학회 논문집
• /
• 제18권3호
• /
• pp.139-149
• /
• 2015

In this paper, we describe a new approach to perform real-time implementation of an robust controller for robotic manipulator based on digital signal processors in this paper. The Texas Instruments DSPs chips are used in implementing real-time adaptive control algorithms to provide enhanced motion control performance for dual-arm robotic manipulators. In the proposed scheme, adaptation laws are derived from model reference adaptive control principle based on the improved direct Lyapunov method. The proposed adaptive controller consists of an adaptive feed-forward and feedback controller and time-varying auxiliary controller elements. The proposed control scheme is simple in structure, fast in computation, and suitable for real-time control. Moreover, this scheme does not require any accurate dynamic modeling, nor values of manipulator parameters and payload. Performance of the proposed adaptive controller is illustrated by simulation and experimental results for robot manipulator consisting of dual arm with eight degrees of freedom at the joint space and cartesian space.

• 전자공학회논문지B
• /
• 제33B권1호
• /
• pp.6-14
• /
• 1996

이 논문에서는 수중 표적추적을 방해하는 교란근원으로부터 추적표적을 판별해 내기 위한 알고리듬을 제안하였다. 이 표적 판별 알고리듬은 순차적 가설 검증을 이용한다. 교란근원은 추적표적으로부터 분리되어, 정지된 위치에서 거짓의 시선 거리와 도플러 측정을 발생시켜 표적으로 혼동되도록 한 것이다. 제안된 알고리듬은 표적운동과 교란근원의 위치를 추정하기 위한 확장 Kalman필터의 이노베이션으로부터 계산된 로그 공산비를 이용하여 판별을 위한 검증을 수행한다. 다양한 시나리오에 대한 수치실험을 통해 제안된 알고리듬이 빠른 시간내에 높은 성공률로 표적과 교란근원을 판별할 수 있음을 확인하였다.

• 한국유체기계학회 논문집
• /
• 제14권6호
• /
• pp.35-44
• /
• 2011

Membrane filtration has become firmly established as a primary process for ensuring the purity, safety and efficiency of treatment of water or effluents. Several researches have been performed to develop and design membrane systems in order to increase the accuracy and performance of the processes. In this study, a lattice Boltzmann method for the cake layer has been developed using particle dynamics based on an immersed boundary method and the cake layer formation process on membrane has been numerically simulated. Case studies including various particle sizes were also performed for a microfiltration process. The growth rate of the cake layer thickness and the permeation flow rate along the membranes were predicted. The results of this study agreed well with that of previous experiments. Effects of various particle diameters on the membrane performance were studied. The cake layer of a large particle tended to be growing fast and the permeation flow going down rapidly at the beginning. The layer thickness of a small particle increased constantly and the flow rate was smaller than that of the large particle at the end of simulation time.

• 드라이브 ㆍ 컨트롤
• /
• 제11권1호
• /
• pp.8-13
• /
• 2014

Hydraulic servo valves are widely used in various fluid power systems because of their fast response and precision control. In this paper, we studied the effect of metering notch shapes and amount of their openings on the flow characteristics within the spool valve using a computational fluid dynamic (CFD) code, FLUENT. To obtain the results for more realistic operating conditions, viscous heating due to the jet flow and viscosity variation of the hydraulic fluid with temperature were considered. For two types of notch shape, streamlines, oil temperature and viscosity distributions, and variations of flow and friction forces acting on spool were showed. The flow and friction forces affected by the metering notch shapes and their openings, and oil temperature rise near metering notch was significant enough to results in the jamming phenomenon. A thermohydrodynamic (THD) flow analysis adopted in this paper can be used in optimum design of hydraulic servo valves.

• 한국소음진동공학회:학술대회논문집
• /
• 한국소음진동공학회 2011년도 추계학술대회 논문집
• /
• pp.711-716
• /
• 2011

Today, high-speed trains enjoy wide acceptance as fast, convenient and environment-friendly means of transportation. However, increase in the speed of the train entails a concomitant increase in the aerodynamic noise, adversely affecting the passenger comfort. At the train speed exceeding 300 km/h, the effects of turbulent flows and vortex sheddding are greatly amplified, contributing to a significant increase in the aerodynamic noise. Drawing a biomimetic analogy from low-noise flight of owl, a method to reduce aerodynamic noise at inter-coach space of high-speed trains is investigated. The proposed method attempts to achieve the noise reduction by modifying the turbulent flow and vortex shedding characteristics at the inter-coach space. To determine the aerodynamic noise at various train speeds, wind tunnel testing and numerical CFD (Computational Fluid Dynamics) simulation for the basic inter-coach spacing model are carried out, and their results compared. The simulation and experimental results reveal that there are discrete frequency components associated with turbulent air flow at constant intervals in the frequency domain

• 한국소음진동공학회:학술대회논문집
• /
• 한국소음진동공학회 2013년도 춘계학술대회 논문집
• /
• pp.141-146
• /
• 2013

This research investigates the stability analysis for the rotating and the stationary grooved journal bearing. The dynamic coefficients of the journal bearing are calculated by using FEM and the perturbation method. When journal bearing is in whirling motion, the dynamic coefficients have time-varying components as a sine wave due to the reaction force of oil film toward the center of journal even in the steady state. The solutions for the equations of motion can be assumed as the Fourier series expansion. The equations of motion can be rewritten as the linear algebraic equations with respect to the Fourier coefficients. Then, stability of the grooved journal bearing can be calculated by Hill's infinite determinant. The periodic function of dynamic coefficients is derived using Fourier Fast Transform(FFT).The stability of journal bearing is determined as rotating speed increases and the stability of rotating grooved journal bearing is compared and discussed with the stability of stationary grooved journal bearing.

• 한국정밀공학회:학술대회논문집
• /
• 한국정밀공학회 1996년도 추계학술대회 논문집
• /
• pp.759-763
• /
• 1996

This paper presents a new approach to the design of neural control system using digital signal processors in order to improve the precision and robustness. Robotic manipulators have become increasingly important in the field of flexible automation. High speed and high-precision trajectory tracking are indispensable capabilities for their versatile application. The need to meet demanding control requirement in increasingly complex dynamical control systems under significant uncertainties, leads toward design of intelligent manipulation robots. The TMS320C31 is used in implementing real time neural control to provide an enhanced motion control for robotic manipulators. In this control scheme, the networks introduced are neural nets with dynamic neurons, whose dynamics are distributed over all the network nodes. The nets are trained by the distributed dynamic back propagation algorithm. The proposed neural network control scheme is simple in structure, fast in computation, and suitable for implementation of real-time control. Performance of the neural controller is illustrated by simulation and experimental results for a SCARA robot.

• 한국생산제조학회지
• /
• 제21권6호
• /
• pp.878-884
• /
• 2012

In this paper, we consider the sway suppression control problem for container cranes with the frictions between the trolley and the rail. If the friction effects in the system can be modelled, there is an improved potential to design controllers that can cancel the effects. The proposed control improves the trolley positioning and sway suppressing against various frictions. The proposed synthesis combines a variable structure control and the adaptive control to cope with various frictions including the unknown constants. First, the variable structure control with the simple switching action is designed, which is based on a class of feedback lineariztion methods for the fast stabilization of the under-actuated sway dynamics of container. Second, the adaptive control with a parameter estimation is designed, which is based on Lyapunov stability methods for suppressing the oscillation of the trolley travelling, especially due to Coulomb friction in the vicinity of the target position. The asymptotic stability of the overall closed-loop system is assured irrespective of variations of rope length. Simulation are shown under initial sway, external wind disturbances, and various frictions.