• Title/Summary/Keyword: Natural Frequency

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Effect of prestressing on the first flexural natural frequency of beams

  • Jaiswal, O.R.
    • Structural Engineering and Mechanics
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    • 제28권5호
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    • pp.515-524
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    • 2008
  • In this paper the effect of prestressing force on the first flexural natural frequency of beams is studied. Finite element technique is used to model the beam-tendon system, and the prestressing force is applied in the form of initial tension in the tendon. It is shown that the effect of prestressing force on the first natural frequency depends on bonded and unbonded nature of the tendon, and also on the eccentricity of tendon. For the beams with bonded tendon, the prestressing force does not have any appreciable effect on the first flexural natural frequency. However, for the beams with unbonded tendon, the first natural frequency significantly changes with the prestressing force and eccentricity of the tendon. If the eccentricity of tendon is small, then the first natural frequency decreases with the prestressing force and if the eccentricity is large, then the first flexural natural frequency increases with the prestressing force. Results of the present study clearly indicate that the first natural frequency can not be used as an easy indicator for detecting the loss of prestressing force, as has been attempted in some of the past studies.

상하동요하는 2차원 원주의 고유진동수 (Natural Frequency of 2-dimensional Heaving Circular Cylinder)

  • 이승준
    • 대한조선학회논문집
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    • 제45권4호
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    • pp.389-395
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    • 2008
  • It is very well known that the natural frequency of an oscillating body on the free surface is determinable only after the added mass is given. However, it is hard to find analytical investigations in which actually the natural frequency is obtained. Difficulties arise from the fact that in order to determine the natural frequency we need to compute the added mass at least for a range of frequencies, and to solve an equation where the frequency is a variable. In this study, first, a formula is obtained for the added mass, and then an equation for finding the natural frequency is defined and solved by Newton's iteration. It is confirmed that the formula shows a good agreement with the results given by Ursell(1949), and the value of natural frequency is reduced by 21.5% compared to the pre-natural frequency, which is obtained without considering the effect of added mass.

하부 구조의 고유 진동수비에 따른 돔 구조의 고유 진동 특성에 관한 연구 (A Study on Natural Vibration Characteristics of Dome Structure According to Natural Frequency Ratio of Substructure)

  • 박광섭;김윤태
    • 한국공간구조학회논문집
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    • 제18권3호
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    • pp.75-82
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    • 2018
  • Large space structures exhibit different natural vibration characteristics depending on the aspect ratio of structures such as half-open angle. In addition, since the actual large space structure is mostly supported by the lower structure, it is expected that the natural vibration characteristics of the upper structure and the entire structure will vary depending on the lower structure. Therefore, in this study, the natural vibration characteristics of the dome structure are analyzed according to the natural frequency ratio by controlling the stiffness of the substructure. As the natural frequency of the substructure increases, the natural frequency of the whole structure increases similarly to the natural frequency of the upper structure. Vertical vibration modes dominate at $30^{\circ}$ and $45^{\circ}$, and horizontal vibration modes dominate at $60^{\circ}$ and $90^{\circ}$.

시뮬레이션에 의한 유체 유동 파이프 계의 곡관부의 각도 변화에 따른 고유진동수 고찰 (A Simulation for the Natural Frequencies of Curved Pipes Containing Fluid Flow with Various Elbow Angles)

  • 최명진;장승호
    • 한국시뮬레이션학회논문지
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    • 제10권1호
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    • pp.63-65
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    • 2001
  • To investigate the natural frequencies of curved piping systems with various elbow angles conveying flow fluid, a simulation is performed considering Initial tension due to the inside fluid. The system is analyzed by finite element method utilizing straight beam element. Elbow part is meshed using 4 elements, and the initial tension is considered by inserting equivalent terms into the stiffness matrix. Without considering the initial tension, the system becomes unstable, that is, the fundamental natural frequency approaches to zero value fast, as the flow velocity reaches critical value. With the initial tension terms, the system becomes stable where there is no abrupt decrease of the fundamental natural frequency. The change rate of the natural frequency with respect to the flow velocity reduces. As elbow angle increases, the system becomes stiffer, then around 150 degrees of the elbow angle the natural frequency has the largest value, the value decreases after the angle of the largest natural frequency. When angle is between 170 degrees and 179 degrees, the natural frequency is very sensitive. This means that small change of angle results in great change of natural frequency, which is expected to be utilized in the control of the natural frequency of the piping system conveying flow fluid.

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유한요소해석법을 이용한 평형형 진동이송기의 고유진동수 특성분석에 관한 연구 (A Study on the Vibrational Characteristics of Natural Frequency with Balancing type Vibratory Conveyor Using Finite Element Methods)

  • 이승용;이성일;김철호;최영재;최우천
    • 대한기계학회:학술대회논문집
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    • 대한기계학회 2001년도 추계학술대회논문집A
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    • pp.568-572
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    • 2001
  • An industrial vibratory conveyor system is devised for large-scale feeding by the low-power, using natural frequency of the system. The important thing in this system is to determine the natural frequency and to drive by it. The purpose of this study is to build up reliance on the system with changing of element parameters for vibration characteristics of balancing type vibratory conveyor by using F.E.M. modeling. For investigating the natural frequency, modal testing is performed by using impact hammer, accelerometer and LMS/Vibration Analysis System. Experimental results are compared with F.E.M results. The results of the comparisons within the errors of less than 2 percent can verify the reliability of the F.E.M. analysis of the system. Also we can verify that the characteristics of natural frequency have linearly decreased(-6%) as adding the mass($50{\sim}600kg$). We can find that controlling driving frequency is necessary for triggering the natural frequency, but natural frequency is less affected by adding the mass on the balancing weight.

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공진회피를 위한 철도차량의 고유진동수 해석 및 측정에 관한 연구 (Investigating Natural Frequency Analysis and Measurement of Railway Vehicle to Avoid Resonance)

  • 홍도관;정재부;정승욱;김경배;안찬우
    • 한국소음진동공학회논문집
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    • 제22권8호
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    • pp.713-719
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    • 2012
  • This paper deals with the natural frequency analysis and two experiments to evaluate first twisting and bending natural frequency of railway vehicle. The KS R 9228 testing method is generally performed as pseudo FRF(frequency response function) which is widely used by two accelerometers. The exciting method is utilized using the load weight(1 ton release). The modal testing is used to verify KS R 9228 testing result and the natural frequency analysis result. The first twisting and bending natural frequency should be above 10 Hz by resonance which is mostly generated between bogie and vehicle frame exciting low frequency. The first twisting and bending natural frequency of railway vehicle are successfully verified between analysis and test.

해상 풍력 발전 JACKET의 고유 진동수에 관한 연구 (A Study of Natural Frequency of Offshore Wind Turbine JACKET)

  • 이정탁;손충렬;이강수;원종범;김상호;김태용
    • 한국소음진동공학회:학술대회논문집
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    • 한국소음진동공학회 2006년도 추계학술대회논문집
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    • pp.434-438
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    • 2006
  • The purpose of this paper is that investigates the Natural Frequency behavior characteristic of Wind Turbine Jacket Type Tower model, and calculated that the stress values of Thrust Load, Wave Load, Wind Load, Current Loda, Gravity Load, etc., environment evaluation analysis during static Operating Wind Turbine Jacket Type Tower model, carried out of Natural Frequency analysis of total load case to stress matrix, Frequency calculated that calculated Add Natural Frequency to stiffness matrix for determinant to stress results. The finite element analysis is performed with commercial F.E.M program (ANSYS) on the basis of the natural frequency and mode shape.

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해상 풍력 발전 JACKET의 고유진동수에 관한 연구 (A Study of Natural Frequency of Offshore Wind Turbine JACKET)

  • 이강수;이정탁;손충렬
    • 한국소음진동공학회논문집
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    • 제17권2호
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    • pp.130-135
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    • 2007
  • The purpose of this paper is that investigates the Natural Frequency behavior characteristic of wind turbine jacket type tower model, and calculated that the stress values of thrust load, wave load, wind load, current loda, gravity load, etc., environment evaluation analysis during static operating wind turbine jacket type tower model, carried out of natural frequency analysis of total load case to stress matrix, frequency calculated that calculated add natural frequency to stiffness matrix for determinant to stress results. The finite element analysis is performed with commercial F.E.M program (ANSYS) on the basis of the natural frequency and mode shape.

스마트 기기용 강화유리&사파이어 유리 전용 가공기의 진동해석을 통한 설계 개선에 관한 연구 (A Study on Design Improvement by Vibration Analysis of Hardened Glass & Sapphire Machining Equipment for Smart IT Parts Industry)

  • 조준현;박상현;안범상;이종찬
    • 한국기계가공학회지
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    • 제15권2호
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    • pp.51-56
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    • 2016
  • High brittleness is a characteristic of glass, and in many cases it is broken during the process of machining due to processing problems, such as scratches, chipping, and notches. Machining defects occur due to the vibration of the equipment. Therefore, design techniques are needed that can control the vibration generated in the equipment to increase the strength of tempered glass. The natural frequency of the machine tool via vibration analysis (computer simulation) must be accurately understood to improve the design to ensure the stability of the machine. To accurately understand the natural frequency, 3D modeling, which is the same as actual apparatus, was used and a constraint condition was also applied that was the same as that of the actual apparatus. The maximum speeds of ultrasonic and high frequency, which are 15,000 rpm and 60,000 rpm, respectively, are considerably faster than those of typical machine tools. Therefore, an improved design is needed so that the natural frequency is formed at a lower region and the natural frequency does not increase through general design reinforcement. By restructuring the top frame of the glass processing, the natural frequency was not formed in the operating speed area with the improved design. The lower-order natural frequency is dominant for the effects that the natural frequency has on the vibration. Therefore, the design improvement in which the lower-order natural frequency is not formed in the operating speed area is an optimum design improvement. It is possible to effectively control the vibrations by avoiding resonance with simple design improvements.

Natural frequency analysis of tractor tire with different ground contacts and inflation pressures

  • Cuong, Do Minh;Sihong, Zhu
    • Coupled systems mechanics
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    • 제9권5호
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    • pp.455-471
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    • 2020
  • This paper presents the results of the study of vertically natural frequency of tractor tires are effected by changing different ground contacts and inflation pressures using the Free Decay Method. The results show that the natural frequencies of the tire are not affected while the vertical acceleration increased strongly due to the increase of inflation pressure when the tire performs free decay vibration on rigid ground. In addition, the number of natural frequency peaks of the tire also increases with increasing tire inflation pressure. On the other hand, the natural frequencies of the tractor tire increases strongly while the vertical acceleration decreases slightly with the increase of tire inflation pressure as the tire performs free decay vibration on soft soil. Further, the natural frequencies of tire-soil system are always higher than that of tire only, and it changed with changing the soil depth. Results also show the natural frequency of tire and tire-soil system is in the range of 3.0 to 10.0 Hz that lie within the most critical natural frequency range of the human body. These findings have to be mentioned and used as design parameters of the tractor suspension system.