• 한국항공우주학회지
• /
• 제36권2호
• /
• pp.131-136
• /
• 2008

본 연구는 다양한 배열 상태에 놓인 2원주 주위의 유동장 특성을 PIV를 이용하여 파악한 것이다. 직렬배열에서 하류측 원주의 후방에서 측정한 Strouhal 수는 수평 간격비가 클수록 작게 나타났다. 직렬배열에서 2원주 사이의 흐름은 거의 정체되어 있으며, 상류측 원주에 가까울수록 정체 범위가 크게 나타났다. 직렬배열에서 자유류와 2원주의 중심선이 이루는 받음각()의 미소 변화(${\alpha}$=${\pm}1.0^{\circ}$)에 따라 2원주 사이에는 서로 반대 방향의 와류가 생성되었다. 병렬배열에서 수직 간격비가 클수록 2원주 사이의 유속이 크게 나타났다.

• Wind and Structures
• /
• 제30권5호
• /
• pp.475-483
• /
• 2020

This work investigates Reynolds number Re (= 50 - 200) effects on the flows around a single cylinder and the two tandem (center-to-center spacing L^⁎= L/D = 4) cylinders, each of a diameter D. Vorticity structures, Strouhal numbers, and time-mean and fluctuating forces are presented and discussed. For the single cylinder, with increasing Re in the range examined, the vorticity magnitude, Strouhal number and fluctuating lift all monotonically rise but time-mean drag, vortex formation length, and lateral distance between the two rows of vortices all shrink. For the two tandem cylinders, the increase in Re leads to the formation of three distinct flows, namely reattachment flow (50 ≤ Re ≤ 75), transition flow (75 < Re < 100), and coshedding flow (100 ≤ Re ≤ 200). The reattachment flow at Re = 50 is steady. When Re is increased from 75 to 200, the Strouhal number of the two cylinders, jumping from 0.113 to 0.15 in the transition flow regime, swells to 0.188. The two-cylinder flow is more sensitive to Re than the single cylinder flow. Fluctuating lift is greater for the downstream cylinder than the upstream cylinder while time-mean drag is higher for the upstream cylinder than for the other. The time-mean drags of the upstream cylinder and single cylinder behaves similar to each other, both declining with increasing Re.

• 제어로봇시스템학회논문지
• /
• 제10권10호
• /
• pp.915-921
• /
• 2004

In this paper, a variable structure controller(VSC) is used to control the position of the hydraulic servo system subjected to unknown disturbances. The system consists of two cylinders, which connected in series. One cylinder executes position control, the other executes force control to generate disturbances. In order to control each cylinder, interaction must be considered between two cylinders because two cylinders are connected in series. Therefore, the controller is designed regarding interaction between two cylinders as disturbances. Performance of the proposed controller was verified through experiments and compared to PID controller. The experiments showed that the proposed controller had a good performance and robustness.

• 대한기계학회:학술대회논문집
• /
• 대한기계학회 2003년도 추계학술대회
• /
• pp.1614-1619
• /
• 2003

In this study, position and force simultaneous trajectory tracking control system with pneumatic cylinder driving apparatus is proposed. The pneumatic cylinder driving apparatus that consists of two pneumatic cylinders constrained in series and two proportional flow control valves offers a considerable advantage as to non-interaction of the actuators because of the low stiffness of the pneumatic cylinders. The controller applied to the driving system is composed of a non-interaction controller to compensate for interaction of two cylinders and a disturbance observer to reduce the effect of model discrepancy of the driving system in the low frequency range that cannot be suppressed by the non-interaction controller. The experimental results with the proposed control system show that the interacting effects of two cylinders are eliminated remarkably and the proposed control system tracks the given position and force trajectories accurately.

• 한국전산유체공학회지
• /
• 제21권2호
• /
• pp.81-89
• /
• 2016

Numerical simulations are carried out for the fluid flow and particle transport around two nearby circular cylinders in a side-by-side arrangement. The present study aims to understand the effects of the particle Stokes number and the spacing between two cylinders on particle dispersion and deposition characteristics. Simulations are based on an Eulerian-Lagrangian approach where the motion of particles is calculated by a Lagrangian approach based on one-way coupling. Results show that the flow structure is very different depending on the cylinder spacing, eventually affecting the overall pattern of particle dispersion significantly. It is also found that particles with smaller Stokes number tend to be distributed more uniformly in the wake of two cylinders, being located even inside the vortex cores. Meanwhile, particle deposition is analyzed in terms of the deposition efficiency and deposition location. The deposition efficiency of particles strongly depends on the Stokes number, whereas it is slightly affected by the cylinder spacing. The deposition location gets wider as the Stokes number increases, and it becomes asymmetric about the center of each cylinder as the cylinders get close.

• Journal of Advanced Marine Engineering and Technology
• /
• 제32권1호
• /
• pp.82-93
• /
• 2008

The flowfield behind two cylinders and flow-induced noise generated from the cylinders in various arrangement are numerically investigated based on the finite difference lattice Boltzmann model with 21 velocity bits. which is introduced a flexible specific heat ${\gamma}$ to simulate diatomic gases like air. In an isolated cylinder with two type of mesh. some flow parameters such as Strouhal number $S_t$ and acoustic pressure ${\Delta}p$ simulated from the solution are given and quantitatively compared with those provided the previous works. The effects of the center-to-center pitch ratio $L_{cc}/d=2.0$ in staggered circular cylinders as shown in Fig. 1 and angles of incidence ${\alpha}=30^{\circ}(T_{cc}/d=0.5)$, $45^{\circ}(T_{cc}/d =0.707)$ and $60^{\circ}\;(T_{cc}/d=0.866)$, respectively, are studied. Our analysis focuses on the small-scale instabilities of vortex shedding, which occurs in staggered arrangement. With the results of drag $C_d$ and lift $C_l$ coefficients and vorticity contours. the mechanisms of the interference phenomenon and its interaction with the two-dimensional vortical structures are present in the flowfields under $Re\;{\le}\;200$. The results show that we successively capture very small pressure fluctuations, with the same frequency of vortex shedding, much smaller than the whole pressure fluctuation around pairs of circular cylinders. The upstream cylinder behaves like an isolated single cylinder, while the downstream one experiences wake-induced flutter. It is expected that, therefore, the relative position of the downstream cylinder has significant effects on the flow-induce noise, hydrodynamic force and vortex shedding characteristics of the cylinders.

• 한국지능시스템학회논문지
• /
• 제20권1호
• /
• pp.109-115
• /
• 2010

수문 제어의 주요기술은 두 개의 실린더가 하나의 수문을 동시에 10[m] 이상 들어 올리는 행정 동안 정밀하게 제어되도록 하여 동기 작동 시키는 것이다. 실린더에 공급되는 유량 및 압력이 일정하지 않으며, 실린더 피스톤의 비선형적인 마찰력에 의해 두 개의 실린더 위치 오차가 발생하게 되면 수문의 개폐 시 비틀림 현상을 야기 시켜서 수문의 마모를 발생시키고, 수문의 개폐작동 불능 현상을 만들기도 한다. 배수갑문용 유압실린더의 위치 및 동기 제어기를 설계하기 위하여 fuzzy PI 제어기를 이용하여 두 개의 실린더의 위치 및 동기제어기를 설계하고, 시뮬레이션을 통해 효용성을 제시한다.

• International Journal of Railway
• /
• 제1권2호
• /
• pp.72-81
• /
• 2008

This paper introduces a new steel jacketing method for reinforced concrete columns with lap splice and evaluates its performance by a series of axial tests of concrete cylinders. At first, 45 concrete cylinders were fabricated with varying the design compressive strengths of 21, 27 and 35 MPa and, then, the part of them was jacketed with two-split-steel jackets under lateral confining pressure. The parameters in the first test were the steel jacket's thickness and the existence of adhesive between steel and concrete surface. In the second test, whole steel jackets were used to wrap cylinders with lateral pressure. Also, a double-layer jacket consisted of two steel plates was introduced; a cylinder was jacketed by two steel plates one after another. The effect of the new method was verified through comparing the results of the compressive tests for plain and jacketed cylinders. The steel jacket built following the new method showed good results of increasing the compressive strength and ductility of the jacketed cylinders with respect to the plain cylinders. The thicker steel jackets showed the more increased compressive strength, and the ductility at failure depended on the welding quality on steel jackets. The adhesive between steel and concrete surface reduced the confining effect of the steel jackets. The whole jacket showed more ductile behavior than the two-split jackets. The double-layered jackets were estimated to possess an equal performance to that of a single steel jacket having the same thickness of the double-layered jacket. Finally, the experimental results were compared with the constitutive model of steel-jacketed concrete; which showed a good agreement between the experimental results and the models.

• 대한조선학회논문집
• /
• 제57권4호
• /
• pp.213-220
• /
• 2020

In the present paper, implosion responses of two adjacent cylindrical tubes under external hydrostatic pressure were experimentally investigated. The cylinder models were fabricated of aluminium alloy 6061-T6 commercial tubes. In the experiment, a pair of two-cylinders were placed inside of a support frame in a medium-size pressure chamber, whose design pressure was 6.0MPa. The distance between the two-cylinders was 30 millimeter measured from outer shell at the mid-length. The implosion tests were performed with water and compressed nitrogen gas as the pressurizing media. The ambient static pressure of the chamber and local dynamic pressure near the two-imploded models were measured simultaneously. It was found that the energy released during an implosion from the first, weaker cylinder triggered the instability of the second, stronger cylinders. In other words, the resulting shock wave of the first implosive impact from the weaker cylinder could cause the premature failure of the neighboring stronger cylinders. The non-contact implosion phenomena from the two-cylindrical tube were clearly observed.

• 한국가시화정보학회지
• /
• 제18권2호
• /
• pp.39-45
• /
• 2020

Problems related with flows around structures are typical in various engineering fields. The characteristics of these flow structures depend strongly on the shape of the body. The flow regime around square cylinders which are also employed in various applications has also been investigated. In addition to a single body, flows past closely spaced structures arranged in tandem are observed in numerous practical applications. In this study, the flow characteristics around the circular and the square cylinder were investigated according to S/D. The velocity fields and Reynolds stress of the single cylinders were acquired to explain the flow behaviors between tandem cylinders. The differences observed in the flow behaviors of square and circular cylinders were studied. The flow patterns around two tandem cylinders can be classified into three types of wake interference behaviors according to S/D. This is related with the flows between cylinders.