• Title/Summary/Keyword: 강제가진

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Flow Control and Heat Transfer Enhancement from a Heated Block by an Inflow Pulsation (II) Thermal Field Computation (입구 유동 가진에 의한 사각 발열체 주위의 유동제어 및 열전달촉진 (II) 온도장 수치해석)

  • 리광훈;김서영;성형진
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.14 no.7
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    • pp.599-606
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    • 2002
  • uniform temperature. The surfaces of the block are taken at a constant higher temperature. The channel walls are assumed to be adiabatic. Results on the time-dependent temperature field are obtained and averaged over a cycle of pulsation. The effect of the important governing parameters, such as the Strouhal number on the flow and the heat transfer is investigated in detail. The results indicate that the recirculating flow behind the block are substantially affected by the pulsation frequency. These, in turn, have a strong influence on the thermal transport from the heated element to the pulsating flow. The frequency at which the enhancement is maximum is determined.

Nonlinear Analysis of a Forced Beam with Internal Resonances (내부공진을 가진 보의 비선형 강제진동해석)

  • 이원경;소강영
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.15 no.6
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    • pp.1897-1907
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    • 1991
  • An analysis is presented for the primary resonance of a clamped-hinged beam, which occurs when the frequency of excitation is near one of the natural frequencies, .omega.$_{n}$. Three mode interactions, .omega.$_{2}$=3.omega.$_{1}$, and .omega.$_{3}$=.omega.$_{1}$+2.omega.$_{2}$, are considered and their influence on the response is studied. The case of two mode interaction, .omega.$_{2}$=3.omega.$_{1}$, is also considered in order to compare it with the case of three mode interactions. The straight beam experiencing mid-plane stretching is governed by a nonlinear partial differential equation. By using Galerkin's method the governing equation is reduced to a system of nonautonomous nonlinear ordinary differential equations. The method of multiple scales is applied to obtain steady-state responses of the system. Results of numerical investions show that there exists no significant difference between both modal interactions.

Forced Vibration Analysis of Lattice Type Structure by Transfer Stiffness Coefficient Method (전달강성계수법에 의한 격자형 구조물의 강제진동 해석)

  • 문덕홍;최명수
    • Journal of KSNVE
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    • v.8 no.5
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    • pp.949-956
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    • 1998
  • Complex and large lattice type structures are frequently used in design of bridge, tower, crane and aerospace structures. In general, in order to analyze these structures we have used the finite element method(FEM). This method is the most widely used and powerful method for structural analysis lately. However, it is necessary to use a large amount of computer memory and computational time because the FEM requires many degrees of freedom for solving dynamic problems exactly for these complex and large structures. For analyzing these structures on a personal computer, the authors developed the transfer stiffness coefficient method(TSCM). This method is based on the concept of the transfer of the nodal dynamic stiffness coefficient matrix which is related to force and displacement vector at each node. And we suggested TSCM for free vibration analysis of complex and large lattice type structures in the previous report. In this paper, we formulate forced vibration analysis algorithm for complex and large lattice type structures using extened TSCM. And we confirmed the validity of TSCM through computational results by the FEM and TSCM, and experimental results for lattice type structures with harmonic excitation.

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Viscoelastic properties of electrorheological fluids (전기유변유체의 점탄성 특성에 관한연구)

  • Choe, Yun-Dae;Kim, Sang-Guk
    • Korean Journal of Materials Research
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    • v.2 no.3
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    • pp.220-227
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    • 1992
  • Electrorheological(ER) fluid's storage shear modulus(G') and loss factor(${\eta}$) have been directly measured using small amplitude forced oscillating rheometer as a function of oscillating frequency, strain amplitude and applied electric field. Two types of experiment were performed , (a) frequency sweep and (b) amplitude sweep. Two kinds of sample were employed for this experiment ; cornstarch particles in corn oil and zeolite particles in silicone oil. The storage shear modulus was a strong function of driving frequency. Generally, the modulus increased with driving frequency. On the other hand, the loss factor was not well behaved as storage modulus, but as the driving frequency increases the loss factor slightly decreases was the trend of the material's characteristics. Also the modulus was a strong function of strain amplitude. Generally, modulus decreased with increasing strain, but loss factor increases slightly with increasing strain amplitude. For G', cornstarch in corn oil ER fluid has higher values than zeolite based fluid as we increased applied electric field. On the other hand, zeolite based fluid has higher values for ${\eta}$. There is a reasonable agreement between theoretical calculation and experiment.

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Comparison of Measured Natural Frequencies of a Railway Bridge Specimen Between Different Excitation Methods (철도교량 시험체의 가진방법에 따른 고유진동수 측정치 변동에 대한 비교 분석)

  • Kim, Sung-Il;Lee, Jungwhee;Lee, Pil-Goo;Kim, Choong-Eon
    • KSCE Journal of Civil and Environmental Engineering Research
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    • v.30 no.6A
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    • pp.535-542
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    • 2010
  • Precise estimation of a structure's dynamic characteristics is indispensable for ensuring stable dynamic responses during lifetime especially for the structures which can experience resonance such as railway bridges. In this paper, the results of forced vibration tests of different excitation methods (vibration exciter and impact hammer) are compared to examine the differences and the cause of differences of extracted natural frequencies. Consequently a natural frequency modification method is suggested to eliminate effects of non-structural disturbance factors. Also, sequential forced vibration tests are performed before and after track construction according to the construction stage of a railway bridge, and the variation of natural frequencies are examined. Effect of added mass of vibration exciter and variation of support condition due to the level of excitation force are concluded as the major cause of natural frequency differences. Thus eliminating these effects can enhance the reliability of the extracted natural frequencies. Construction of track affects not only the mass of structure but also the stiffness of the structure. Also, the amount of increase in stiffness varies according to the level of structural deflection. Therefore, reasonable estimation of the level of structural response during operation is important for precise natural frequency calculation at design phase.

Study on Forced Vibration Behavior of WIG Vehicle Main Wing Structure Excited by Propulsion System (프로펠러 엔진에 의해 가진되는 소형 위그선 주날개의 진동 거동 해석에 관한 연구)

  • Kong, Chang-Duk;Yoon, Jae-Huy;Park, Hyun-Bum
    • Proceedings of the Korean Society of Propulsion Engineers Conference
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    • 2007.11a
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    • pp.7-12
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    • 2007
  • Previously study on structural design of the main wing of the twenty-seat class WIG (Wing in Ground Effect) craft. In the final design, three spars construction was selected for safety in the critical flight load, and the Carbon-Epoxy material was selected for lightness and structural stability. In this study, the forced vibration analysis was performed on the composite main wing structure of the twenty-seat class WIG craft with two-stroke pusher type reciprocating engine. The vibration analysis based on the finite element method was performed using a commercial FEM code, MSC/NASTRAN. Excitations for the frequency response analysis were assumed as the Y-mode (lateral mode), the Z-mode (vertical mode) and the $M_{xyz}$-mode (twisted mode) which are typical main vibration modes of engine. And excitations for the transient response analysis were assumed as the X-mode (longitudinal mode) with the oscillating propeller thrust which occurs in operation.

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Domains of Attraction of a Forced Beam with Internal Resonance (내부공진을 가진 보의 흡인영역)

  • 이원경;강명란
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.16 no.9
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    • pp.1711-1721
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    • 1992
  • A nonlinear dissipative dynamical system can often have multiple attractors. In this case, it is important to study the global behavior of the system by determining the global domain of attraction of each attractor. In this paper we study the global behavior of a forced beam with two mode interaction. The governing equation of motion is reduced to two second-order nonlinear nonautonomous ordinary differential equations. When .omega. /=3.omega.$_{1}$ and .ohm.=.omega $_{1}$, the system can have two asymptotically stable steady-state periodic solutions, where .omega./ sub 1/, .omega.$_{2}$ and .ohm. denote natural frequencies of the first and second modes and the excitation frequency, respectively. Both solutions have the same period as the excitation period. Therefore each of them shows up as a period-1 solution in Poincare map. We show how interpolated mapping method can be used to determine the two four-dimensional domains of attraction of the two solutions in a very effective way. The results are compared with the ones obtained by direct numerical integration.

An Application of Fuzzy Control Models to Inland Drainage Pumping Stations with Different Characteristics for Protection of Inland Flooding (상이한 제원특성을 가진 빗물펌프장에서의 퍼지제어모형 적용)

  • Shim, Jae Hyun;Lee, Won Hwan;Cho, Won Cheol
    • KSCE Journal of Civil and Environmental Engineering Research
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    • v.13 no.3
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    • pp.107-118
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    • 1993
  • Continuous increasing of impervious area due to urbanization and rainfall quantity due to environmental changes aggravate flooding risk in low land area. Therefore. Seoul municipal authorities go on securing an ample budget for reinforcement and establishment of inner water and inland drainage pumping facilities. But. there is no investment for developing optimal operation rules for appropriate application of existing facilities. In this study. fuzzy control techniques are developed. and applied to 57 stations of inner water and inland drainage pump for model assessment. In these results. fuzzy models have more efficiency in the inland flooding protection than the existing pump operation rule by water level in the same conditions.

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The Analysis of NVH Characteristics of 4-Cylinerder Diesel Engine Block by Adapting Balancing Shaft (밸런스 샤프트 적용에 따른 4기통 디젤 엔진 블록의 방사소음 특성 개선 해석)

  • Choi, Cheon;Suh, Myung-Won;Kim, Young-Gin
    • Transactions of the Korean Society of Automotive Engineers
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    • v.8 no.5
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    • pp.129-137
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    • 2000
  • The powertrain is an important factor for the interior and exterior noise behavior of the vehicle Thus, the noise vibration and harshness(NVH) behavior of an engine is becoming a major target of the powertrain development. This paper describes the analyses with the aim to reduce the vibration and noise of an advanced inline 4-cylinder diesel engine block by use of CAE methods. The characteristics of an engine block as a main excitation source of car interior noise is studied. Particularly, The effect of balance shaft to reduce the 2nd order engine excitation force is calculated by forced vibration and radiated noise analysis. The engine exitation forces are obtained under real operating conditions. It is shown that the reduction of vibration and noise level by adapting blancing shaft is well predicted and rediated noise is directly related to the surface velocity of engine block.

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Natural Convection Heat Transfer from a Horizontal Heat Exchanger Tube with a Fin (單一핀을 가진 水平管에서의 自然對流 熱傳達)

  • 정한식;권순석
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.11 no.2
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    • pp.279-286
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    • 1987
  • An numerical and experimental study has been performed on natural convection heat transfer from a horizontal heat exchanger tube with a fin. At s bare tube, by increasing $C_{T}$ (tube conduction parameter), mean Nusselt number and outer wall temperature are apparently increased at $C_{T}$.leq.300, slightly increased at $C_{T}$>300 and they can be represented in an exponential function of $C_{T}$. Natural convection heat transfer characteristics for the tube with a fin at given Rayleigh number are well agreed by those for an isothermal cylinder at a modified Rayleigh number. The local fin Nusselt number of the tube with a downward fin is much higher than that of the tube with an upward fin. The comparisons between numerical and experimental results showed good agreement.reement.