• Title, Summary, Keyword: Natural frequency dynamics

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Natural Mode Analysis for Chatter Lobe Estimation (채터로브 계산을 위한 고유모우드 분석법)

  • Yoon, Moon-Chul;Cho, Hyun-Deog;Lee, Eung-Soog
    • Journal of the Korean Society of Manufacturing Process Engineers
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    • v.2 no.2
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    • pp.60-66
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    • 2003
  • For the estimation of chatter lobe boundary it is very important to calculate the natural mode of cutting process. There are many time series algorithms for getting the natural mode of structural endmilling dynamics considering the cutting process. In this study, we have compared several time series methods such as AR algorithm, ARX, ARMAX, ARMA, Box Jenkins, Output Error, Recursive ARX, Recursive ARMAX considering the sampling frequency. As a results, the ARX, ARMAX and IV 4 are more desirable algorithms for the calculation of modal parameters such as natural frequency and damping ratio In endmilling operation. Also these algorithms may be adopted for the natural mode estimation of endmilling operation for chatter lobe prediction.

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An Efficient Model to Calculate Axial Natural Vibration Frequency of Power Transformer Winding

  • Li, Kaiqi;Guo, Jian;Liu, Jun;Zhang, Anhong;Yu, Shaojia
    • Journal of Magnetics
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    • v.21 no.3
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    • pp.431-436
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    • 2016
  • In the design of transformer winding, natural vibration frequency is an important parameter. This paper presents a 2D model to calculate axial vibration natural frequency of power transformer winding based on the elastic dynamics theory, and according to the elastic support equivalent principle of radial pressboards. The 3D model to calculate natural vibration frequency can be simplified as a 2D one as the support of pressboards on the winding is same. It is verified that results of the 2D model are consistent with those of 3D one, but the former can achieve much higher calculation efficiency. It shows that increasing the width and number of pressboards can improve axial natural frequency through formula analysis and simulation, and also the relations between the changes of axial pre-compression and axial natural vibration frequency on the windings are investigated. Finally, the proposed 2D model's effectiveness is proved when compared with tested ones.

Vibration analysis of defected and pristine triangular single-layer graphene nanosheets

  • Mirakhory, M.;Khatibi, M.M.;Sadeghzadeh, S.
    • Current Applied Physics
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    • v.18 no.11
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    • pp.1327-1337
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    • 2018
  • This paper investigates the vibration behavior of pristine and defected triangular graphene sheets; which has recently attracted the attention of researchers and compare these two types in natural frequencies and sensitivity. Here, the molecular dynamics method has been employed to establish a virtual laboratory for this purpose. After measuring the different parameters obtained by the molecular dynamics approach, these data have been analyzed by using the frequency domain decomposition (FDD) method, and the dominant frequencies and mode shapes of the system have been extracted. By analyzing the vibration behaviors of pristine triangular graphene sheets in four cases (right angle of 45-90-45 configuration, right angle of 60-90-30 configuration, equilateral triangle and isosceles triangle), it has been demonstrated that the natural frequencies of these sheets are higher than the natural frequency of a square sheet, with the same number of atoms, by a minimum of 7.6% and maximum of 26.6%. Therefore, for increasing the resonance range of sensors based on 2D materials, nonrectangular structures, and especially the triangular structure, can be considered as viable candidates. Although the pristine and defective equilateral triangular sheets have the highest values of resonance, the sensitivity of defective (45,90,45) triangular sheet is more than other configurations and then, defective (45,90,45) sheet is the worst choice for sensor applications.

Design Improvement via Structural Dynamics Modification - Application to Noise Reduction in Outdoor Unit of Air Conditioner (구조물 동특성 변경을 통한 설계 개선 -공조기 실외기 소음 저감 적용)

  • Choi, Sang-Hyeon;Park, Nam-Gyu;Park, Youn-Sik
    • Transactions of the Korean Society for Noise and Vibration Engineering
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    • v.12 no.5
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    • pp.355-364
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    • 2002
  • The goal of this research is to reduce noise level of an outdoor unit of air conditioner by changing its dynamic characteristics using SDM (structural dynamics modification) technique. At first, the emitting noise was measured and analyzed. The measurement records show the most critical frequency components which influences on the noise level. Then it was tried to move the natural frequencies outside the critical frequency region by SDM. Since it is very difficult to get a reliable FE model of air conditioner, experimentally measured frequency response functions were used to derive sensitivities that are very important to obtain design changes. The positions of modification and the thickness of modifying structures were determined to improve the dynamic characteristics of air conditioner. The recommended design guideline to move its natural frequencies outside the targeting frequency range was obtained. Then in order to prove its effectiveness, the changed design was experimentally tested and found that the SDM result is very effective to reduce not only its vibration but also its emitting noise.

What are measures to reduce interior noise for KTX in tunnel with concrete track? (콘크리트 궤도 터널 주행 시 KTX차량의 실내소음 저감방안은 무엇인가?)

  • Kim J.C.;Koh H.I.;Lee C.W.
    • Proceedings of the Korean Society of Precision Engineering Conference
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    • pp.29-30
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    • 2006
  • The interior noise of KTX in tunnel has become an issue since the commercial operating in April 2004. The analysis of the interior noise of KTX in tunnel with concrete track shows sharply increased noise level in the range of 80Hz that is the natural frequency of the KTX carbody. We know that the booming noise inside KTX in tunnel with concrete track is generated by noise outside gangway and rolling noise at the carbody natural frequency. In this Study noise reduction methods are discussed on the basis of the comparison of the KTX and KHST noise characteristics. Alternatively, the effect of the modified mud-flap on the interior noise is introduced.

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Natural Frequency Analysis of an Extensible Curved Pipe Conveying Fluid (유체가 흐르는 인장 가능한 곡선관의 고유진동수 해석)

  • Jung, Du-Han;Chung, Jin-Tai
    • Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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    • pp.792-795
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    • 2005
  • The vibration of a curved pipe conveying fluid is studied when the pipe is clamped at both ends. To consider the nonlinearity, this study adopts the Lagrange strain theory for large deformation and the extensible dynamics based on the Euler-Bemoulli beam theory for slenderness assumption. By using the Hamilton principle, the non-linear partial differential equations are derived. To investigate the dynamic characteristics of the system the discretized equations of motion are derived from the Galerkin method. The natural frequencies varying with the flow velocity are computed. From these results, we should consider the nonlinearity to analyze dynamics of a curved pipe conveying fluid more precisely.

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A Simulation for the Natural Frequencies of Curved Pipes Containing Fluid Flow with Various Support Locations (시뮬레이션에 의한 유체 유동 굴곡파이프의 지지점 변화에 따른 고유 진동수 고찰)

  • 최명진
    • Journal of the Korea Society for Simulation
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    • v.7 no.2
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    • pp.115-123
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    • 1998
  • A simulation is performed to investigate the effect of the pipe supports on the change of the natural frequencies of curved pipe systems containing fluid flow, for different elbow angles and geometry of the pipe systems. Based upon the Hamilton's principle, the equations of motions are derived, and the finite element equation is constructed to solve the corresponding eigenvalue problem. The angles of elbows do not affect the change of the fundamental natural frequency, but affect the change of the third or higher natural frequencies. Without any support, the change of the fundamental natural frequency due to the geometric change is smaller than the change of the second or higher natural frequencies. The more curve parts exist in the pipe system, the less change of lower frequency range, compared with the change of higher frequency range, is observed. Spring supports can be used to reduce the fundamental natural frequency, without change of the second or higher natural frequencies. To avoid resonance, which is critically dangerous from the view point of structural dynamics, the mechanical properties such as stiffness or the location of pipe supports are need to be changed to isolate the natural frequencies from the frequency range of dominant vibration modes.

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Structural Dynamics Modification Using Surface Grooving Technique: Application to HDD Cover Model (그루브를 이용한 표면형상변형 동특성 변경법 : HDD 커버에 대한 적용)

  • Park, Mi-You;Park, Youngjin;Park, Youn-sik
    • Transactions of the Korean Society for Noise and Vibration Engineering
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    • v.15 no.3
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    • pp.341-345
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    • 2005
  • Structural Dynamics Modification (SDM) is a very effective technique to improve structure's dynamic characteristics by adding or removing auxiliary structures, changing material properties and shape of structure. Among those of SDM technique, the method to change shape of structure has been mostly relied on engineer's experience and trial-and-error process which are very time consuming. In order to develop a systematic method to change structure shape, surface grooving technique is studied. In this work, the shape of base structure was modified to improve its dynamic characteristics such as natural frequencies via surface grooving technique. Grooving shape was formed by mergingthe neighboring small embossing elements after analyzing frequency increment sensitivities of all the neighboring emboss elements. For this process, Criterion Factor was introduced and the initial grooving was started from the element having highest strain energy and the grooving is expanded into neighboring element. The range of targeting grooving area to check its frequency variations restricted to their neighboring area to reduce the computation effort. This surface grooving technique was successfully applied to a hard disk drives (HDD) cover model to raise its natural frequency by giving some groove on its surface.

Electromechanical coupled nonlinear dynamics of euler beam rails for electromagnetic railgun

  • Xu, Lizhong;Wu, Dewen
    • Smart Structures and Systems
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    • v.19 no.2
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    • pp.213-224
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    • 2017
  • The electromagnetic field can cause an essential change of the dynamic behavior of the railgun. The evaluation of the dynamics performance of railgun is a mandatory task. Here, a nonlinear electromagnetic force equation of the railgun is given in which the clearance, the thickness and the width of the rail are considered. Based on it, the nonlinear electromechanical coupled dynamics equations of Euler beam rails for the railgun are proposed. Using the equations, the nonlinear free vibration frequency of the railgun is investigated and the effects of the system parameters on the frequency are analyzed. The nonlinear forced responses of the rail to the electromagnetic excitation are investigated as well. The results show that as the nonlinearity of the railgun system is considered, the vibration frequencies of the railgun system increase; as the current in the rail increases, the difference between the natural frequencies and the nonlinear vibration frequencies increases significantly; the nonlinearity of the railgun system is more obvious for smaller distance between the two rails, smaller rail thickness, and smaller stiffness of the elastic foundation; the unstable dynamics state of the rail system occurs when the armature runs to the exit of the railgun. The results are useful for design and application of the railgun system.

Optimal Structural Dynamics Modification Using Eigen Reanalysis Technique of Technique of Topological Modifications (위상 변경 고유치 재해석 기법을 이용한 최적 구조물 동특성 변경)

  • 이준호;박영진;박윤식
    • Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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    • pp.77-81
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    • 2003
  • SDM (Structural Dynamics Modification) is a tool to improve dynamic characteristics of a structure, more specifically of a base structure, by adding or deleting auxiliary (modifying) structures. In this paper, the goal of the optimal SDM is set to maximize the natural frequency of a base plate structure by attaching serially-connected beam stiffeners. The design variables are chosen as positions of the attaching beam stiffeners, where the number of stiffeners is considered as a design space. The problem of non-matching interface nodes between the base plate and beam stiffeners is solved by using localized Lagrange multipliers, which act to glue the two structures with non-matching interface nodes. As fer the cases of non-matching interface nodes problem, the governing equation of motion of a structure can be considered from the viewpoint of a topological modification, which involves the change of the number of structural members and DOFs. Consequently, the eigenpairs of the beam-stiffened plate structure are obtained by using an eigen reanalysis technique of topological modifications. Evolution Strategies (ES), which is a probabilistic population-based optimization technique that mimics the principles from biological evolution in nature, is utilized as a mean for the optimization.

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