• 제목/요약/키워드: Natural Frequency

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복합재 철도차량 차체 고유진동수에 대한 해석 및 시험적 연구 (Analytical and Experimental Studies on the Natural Frequency of a Composite Train Carbody)

  • 정종철;조세현;서승일;김정석
    • 대한기계학회논문집A
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    • 제30권4호
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    • pp.473-480
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    • 2006
  • This paper explains analytical and experimental studies to evaluate the natural frequency of a composite carbody of Korean tilting train. The composite carbody with length of 23m was manufactured as a sandwich structure composed of 40mm-thick aluminium honeycomb core and 5mm-thick woven fabric carbon/epoxy face. From the finite element analysis, the 1st bending and 1st twisting natural frequency of the composite carbody were 11.67Hz and 14.4Hz, respectively. In order to verify the analytical results, the natural frequency measuring tests were performed. The measured 1st bending and twisting natural frequencies of the composite carbody were 10.25Hz and 11.0Hz, respectively. Both of these results satisfied the design requirement.

Connection stiffness and natural frequency of DuraGal lightweight floor systems

  • Zhao, X.L.;Taplin, G.;Alikhail, M.
    • Structural Engineering and Mechanics
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    • 제15권3호
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    • pp.269-284
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    • 2003
  • This paper reports a series of component tests on a lightweight floor system and a method to predict the natural frequency of the floor using a frame analysis program. Full-scale floor tests are also briefly described. DuraGal steel Rectangular Hollow Sections (in-line galvanised RHS) are used as joists, bearers and piers in DuraGal lightweight floor systems. A structural grade particleboard is used as decking. Connection stiffness between different components (bearer, joist, pier and floor decking) was determined. A 40% composite action was achieved between the RHS joist and the particleboard. Both 2D and 3D models were developed to study the effect of connection stiffness on predicting the natural frequency of DuraGal lightweight floor systems. It has been found that the degree of shear connection between the bearer and the joist has a significant influence on the floor natural frequency. The predicted natural frequencies are compared with measured values from full scale floor testing.

유체 연성이 작용하는 동축 원통형 쉘의 고유진동 (The Natural Frequency of a Coaxial Cylindrical Shell with Fluid Coupling)

  • 안병준;정경훈;이성철
    • 한국정밀공학회:학술대회논문집
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    • 한국정밀공학회 1994년도 추계학술대회 논문집
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    • pp.975-979
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    • 1994
  • The experimental and finite element studies of a coaxial cylindrical shell filled with liquid in the annular gap were performed to understand its vibration characteristics. Finite element analysis was achieved by using ANSYS code. Form the investigation of the changing trend of natural frequencies for the change of annular gap we know that the natural frequency of the coaxial cylindrical shell varies according to the mode shape. that is, in case of in-phase mode the natural frequency decrease as annular gap increase, but in case of out-of-phase mode the natural frequency increase. Finite element analysis results show the excellent agreement with the experimental results both in air and in water case, so that analysis on other cases with be possible without experiment.

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상하동요하는 2차원 주상체의 고유진동수; 주파수 영역 해석 (Natural Frequency of 2-Dimensional Cylinders in Heaving; Frequency-Domain Analysis)

  • 송제하;이승준
    • 대한조선학회논문집
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    • 제52권1호
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    • pp.25-33
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    • 2015
  • Following the previous works on the natural frequency of heaving circular cylinder, i.e. Lee and Lee (2013) and Kim and Lee (2013), an investigation of the same spirit on the 2-dimensional cylinder of Lewis form has been conducted. As before, the natural frequency is defined as that corresponding to the local maximum of the MCFR (Modulus of Complex Frequency Response), which is given by the equation of motion in the frequency domain analysis. Hydrodynamic coefficients were found by using the Ursell-Tasai method, and numerical results for them were obtained up to much higher frequencies than before, for which the method was known as numerically unstable in the past. For a wide range of H, the beam-draft ratio, and ${\sigma}$, the sectional area coefficient, including their practical ranges for a ship, results for the natural frequency were computed and presented in this work. Two approximate values for the natural frequency, one proposed by Lee (2008) and another one by the damped harmonic oscillator, were also compared with the current results, and for most cases it was observed that the current result is between the two values. Our numerical results showed that the values of the local maximum of MCFR as well as the natural frequencye increase as ${\sigma}$ increases while H decreases. At present, extension of the present finding to the 3-dimensional ship via the approximate theory like the strip method looks promising.

유용방향법 최적화 알고리즘을 사용한 고유진동수에 대한 구조 최적설계 FEA 모듈 개발 (Structure Optimization FEA Code Development Under Frequency Constraints by Using Feasible Direction Optimization Method)

  • 조희근
    • 한국생산제조학회지
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    • 제22권1호
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    • pp.63-69
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    • 2013
  • In order to find the optimum design of structures that have characteristic natural frequency range, a numerical optimization method to solving eigenvalue problems is a widely used approach. However in the most cases, it is difficult to decide the accurate thickness and shape of structures that have allowable natural frequency in design constraints. Parallel analysis algorithm involving the feasible direction optimization method and Rayleigh-Ritz eigenvalue solving method is developed. The method is implemented by using finite element method. It calculates the optimal thickness and the thickness ratio of individual elements of the 2-D plane element through a parallel algorithm method which satisfy the design constraint of natural frequency. As a result this method of optimization for natural frequency by using finite element method can determine the optimal size or its ratio of geometrically complicated shape and large scale structure.

운전자용 의자의 부강성 진동 절연 시스템 (Vibration Isolation System for Driver's Seats with Negative Stiffness)

  • 박성태;이상주
    • 한국자동차공학회논문집
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    • 제18권2호
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    • pp.114-121
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    • 2010
  • As a vehicle speed increases, more vibration energy is transmitted from chassis to a driver. Current isolation system for the driver's seat by damping control can reduce the transmitted vibration energy near resonance area. But in higher frequency region than natural frequency multiplied by $\sqrt{2}$, the vibration energy transmitted to the driver has a tendency to be increased. Therefore, the method by natural frequency reduction of the system is preferred to increase the effectiveness of the anti-vibration. However, the natural frequency could not be freely reduced due to the nature of the isolation system structure. A new passive suspension system to reduce the natural frequency is proposed. The theoretical analysis and experimental results show better vibration attenuation compared with the current isolation system.

Free Vibration Analysis of Axisymmetric Conical Shell

  • Choi, Myung-Soo;Yeo, Dong-Jun;Kondou, Takahiro
    • 동력기계공학회지
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    • 제20권2호
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    • pp.5-16
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    • 2016
  • Generally, methods using transfer techniques, like the transfer matrix method and the transfer stiffness coefficient method, find natural frequencies using the sign change of frequency determinants in searching frequency region. However, these methods may omit some natural frequencies when the initial frequency interval is large. The Sylvester-transfer stiffness coefficient method ("S-TSCM") can always obtain all natural frequencies in the searching frequency region even though the initial frequency interval is large. Because the S-TSCM obtain natural frequencies using the number of natural frequencies existing under a searching frequency. In this paper, the algorithm for the free vibration analysis of axisymmetric conical shells was formulated with S-TSCM. The effectiveness of S-TSCM was verified by comparing numerical results of S-TSCM with those of other methods when analyzing free vibration in two computational models: a truncated conical shell and a complete (not truncated) conical shell.

구조물-가진기 상호작용에 의한 공진주파수 변동에 대한 해석 (Analysis on the Measured Natural Frequencies Due to the Structure-Exciter Interaction)

  • 한상보
    • 대한기계학회논문집A
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    • 제20권7호
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    • pp.2108-2117
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    • 1996
  • The purpose of this paper is to investigate the influence of the exciter attached for the measurement of natural frequencies when extracting the frequency response functions of the test structure in experimental modal analysis. The procedure is first to model the attached exciter as an additional degree of freedom system and next to verify the suggested model by experimentally extracting the natural frequencies of the test structure with various values of exciter mass, stinger stiffness and attachment position of the exciter on the test structure. It is concluded that as additional degree of freedom system which includes the natural frequency of the exciter itself and axial stiffness of stinger should be considered to quantatively define the coupling effects of structure-exciter interaction on the measured natural frequencies. It is not the mass of the exciter itself but the coupling effect of the additional degree of freedom mass-spring system consisting of exciter body and armature coil that characterizes the natural frequency deviation. Therefore, when the natural frequency of this additional mass-spring system is outside of the test frequency range, the coupling effect of structure-exciter interaction can be minimized.

고유진동수 접근현상을 고려한 쉘 구조물의 설계최적화기법 (Shell Design Optimization Technique considering the Appearance of Close Frequencies in Optimization Process)

  • 배정은;이상진
    • 한국소음진동공학회:학술대회논문집
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    • 한국소음진동공학회 2006년도 추계학술대회논문집
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    • pp.248-251
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    • 2006
  • This paper provides the basic theory and numerical results of shell design optimization considering the appearance of close natural frequencies in optimization process. In this study the fundamental natural frequency to be maximized is considered as the objective function and the initial volume of structures is used as the constraint function. In addition, the constraints related to natural frequency is also adopted to avoid the natural frequency closeness phenomenon during the optimization iteration. The Coon's patch is used to represent the shape and thickness distribution of shells. A degenerated shell finite element is adopted to calculate the fundamental natural frequency of the shells. The SQP available in the optimizer DoT is used to search optimum solution. From numerical results, the introduction of the frequency constraint into shell design optimization can deeply affect on the final optimum shape of shells although it is likely to be used to avoid the frequency closeness phenomenon.

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고속 운영을 위한 능동거니플랩 설계 변경 및 고유진동수 예측 (Active Gurney Flap Design Modification for High Speed Operation and Natural Frequency Estimate)

  • 김태주;김도형;백승길
    • 한국소음진동공학회논문집
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    • 제25권10호
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    • pp.667-676
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    • 2015
  • Working displacement variation by elastic deformation of active Gurney flap which was operated on high frequency was observed. Flap-wise natural frequency was lower than mode analysis result and hinge boundary condition was identified to be the cause through the simple modal test. Design modification for increasing natural frequency was conducted for minimizing the elastic deformation at maximum 35 Hz operating condition which was design requirement condition. Brass bushing was applied instead of rotating bearing for gap minimization and Gurney flap design modification was conducted to increase of the flap-wise natural frequency. Design modification effect was validated by natural frequency comparison with mode analysis result and modal test result of design modification model.