• Title, Summary, Keyword: 고유 진동

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Dynamic Model Prediction and Validation for Free-Piston Stirling Engines Considering Nonlinear Load Damping (자유피스톤 스털링 엔진의 비선형 부하 감쇠를 고려한 동역학 모델 예측 및 검증)

  • Sim, Kyuho;Kim, Dong-Jun
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.39 no.10
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    • pp.985-993
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    • 2015
  • Free-piston Stirling engines (FPSEs) have attracted much attention in the renewable energy field as a key device in the conversion from thermal to mechanical energy, and in the recycling of waste energy. Traditional Stirling engines consist of two pistons that are connected by a mechanical link, while FPSEs are formed as a vibration system by connecting each piston to a spring without a physical link. To ensure the correct design and control of operations, this requires elaborate dynamic-performance predictions. In this paper, we present the performance-prediction methodology using a linear and nonlinear dynamic analytical model considering the external load of FPSEs. We perform linear analyses to predict the operating point of the engine using the root locus technique. Using nonlinear analysis, we also predict the amplitude of pistons by performing numerical integration considering both the linear and nonlinear damping terms of the external load. We utilize the predicted dynamic behavior to predict the engine performance. In addition, we compare the experiment results and existing model predictions for RE-1000 to verify the reliability of the analytical model.

Finite Element Model Updating Based on Data Fusion of Acceleration and Angular Velocity (가속도 및 각속도 데이터 융합 기반 유한요소모델 개선)

  • Kim, Hyun-Jun;Cho, Soo-Jin;Sim, Sung-Han
    • Journal of the Korea institute for structural maintenance and inspection
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    • v.19 no.2
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    • pp.60-67
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    • 2015
  • The finite element (FE) model updating is a commonly used approach in civil engineering, enabling damage detection, design verification, and load capacity identification. In the FE model updating, acceleration responses are generally employed to determine modal properties of a structure, which are subsequently used to update the initial FE model. While the acceleration-based model updating has been successful in finding better approximations of the physical systems including material and sectional properties, the boundary conditions have been considered yet to be difficult to accurately estimate as the acceleration responses only correspond to translational degree-of-freedoms (DOF). Recent advancement in the sensor technology has enabled low-cost, high-precision gyroscopes that can be adopted in the FE model updating to provide angular information of a structure. This study proposes a FE model updating strategy based on data fusion of acceleration and angular velocity. The usage of both acceleration and angular velocity gives richer information than the sole use of acceleration, allowing the enhanced performance particularly in determining the boundary conditions. A numerical simulation on a simply supported beam is presented to demonstrate the proposed FE model updating approach.

Study on the Dynamic Load Monitoring Using the Instrumented Vehicle (계측장치 실장 차량을 이용한 동적 하중 모니터링 연구)

  • Kim, Jong-Woo;Jung, Young-Woo;Kwon, Soon-Min
    • The Journal of The Korea Institute of Intelligent Transport Systems
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    • v.15 no.5
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    • pp.95-107
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    • 2016
  • The axle weight of a vehicle in motion can be measured with a low-speed or high-speed weigh-in-motion (WIM). However, the axial load dynamically change depending on the vehicle's characteristics-such as the chassis or axle structure-or the characteristics of the driving environment such as road flatness. The changes in dynamic load lead to differences between the vehicle's weight measured at rest and the vehicle's weight measured in motion. For this Study, an experiment was conducted with an instrumented vehicle to analyze the range of errors caused by uncontrollable environmental factors by identifying the characteristics of the dynamic load changes of a vehicle in motion, and determine the appropriate scale for the accuracy evaluation of a high-speed WIM, as a preparatory research for the introduction of unmanned overweight enforcement systems in the future. The key findings from the experiment are summarized as follows. First, The gross weight of the tested vehicle changed by approximately 1% at low velocities and approximately by 4% at high velocities, and the vehicle's axle weight changed by approximately 1-3%, at low velocities and by 2-9% at high velocities. A single axle showed larger weight changes than individual axles in a group. Secondly, The vehicle's gross weight and the axle weight on the impact section were up to eight times and three-to-twelve times higher, respectively, than its gross weight and the axle weight on the flat section. The vibration frequency of the vehicle's dynamic load was measured at between 2.4 and 5.8Hz, and found to return to the normal amplitude after moving approximately 30 meters.

Resonance Frequency Analysis of A Baseball Bat by Impact Angle (가진 각도에 따른 야구배트의 공진주파수 분석)

  • Park, Sun-Hyang;Chung, Woo-Yang;Jung, Hwan-Hee;Lee, Sang-Joon
    • Journal of the Korean Wood Science and Technology
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    • v.43 no.6
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    • pp.777-783
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    • 2015
  • Wood is an anisotropic material that shows the changes in hardness, quality and dimensions depending on the types of cells on three cross sections, size, array and so on. It can also be used in different ways according to its use, which requires a meticulous research, in order to maximize the utilization by understanding the nature and use; and by clarifying the theory and technologies. The research on relationship among wood's physical properties, density, and elasticity of modulus have been studied in Korea and abroad, but those studies were based on correlation gained through standardized specimen. Rather, the study on complete product is rare. Moreover, the previous reports are mostly concentrating on vibration mode and batting, though the wood's physical properties as a material have not been in the main focus. Therefore, this study will carried out for analyzing MOE through figuring material property out and comparing frequency adapting to the Canadian HardMaple bat. For comparison of material properties, we studied the annual ring and density of the bat; calculated the MOE with resonance frequency and formula (ASTM C1259); and verified the repulsive force of this material. As a result, the relevance of the resonance frequency and annual ring is weak, and in comparison in the grain direction in wood, the MOE value is higher when the grain direction in wood is excited horizontally than when is excited vertically, because the material is repulsive when grain direction is horizontal.

Manufacturing and Structural Analysis of Thick Composite Spar Using AFP Machine (AFP로 제작된 두꺼운 복합재료 스파의 제작 및 구조 해석)

  • Kim, Ji-Hyeon;Han, Jun-Su;Bae, Byung-Hwan;Choi, Jin-Ho;Kweon, Jin-Hwe
    • Composites Research
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    • v.28 no.4
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    • pp.212-218
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    • 2015
  • A large composite spar was manufactured using an automatic fiber placement (AFP) machine. To verify its structural performance, the weakest part of the structure, which is called 'corner radius', was tested under bending and examined by finite element analysis. Since the application of AFP machine to composite structure fabrication is still in early stage in Korea, this paper presents the summary of whole process for manufacturing composite spar using AFP machine from mandrel design and analysis to verification test. The deflection and stress by mandrel weight and AFP machine force, thermal deformation and natural frequency were all examined for mandrel design. The target structure was composite C-spar and cured in an autoclave. Test results were compared with nonlinear finite element analysis results to show that the structure has the strength close to the theoretical value. It was confirmed that the corner radius of the spar manufactured by AFP process showed deviation less than 20% compared with first ply failure strength. The results indicate that the AFP technology could be used for large scale composite structure production in the near future.

Development of Rotordynamics Program Based on the 2D Finite Element Method for Flywheel Energy Storage System (2차원 유한요소법을 적용한 플라이휠 에너지 저장 장치 동특성 해석 프로그램 개발)

  • Gu, Dong-Sik;Bae, Yong-Cae;Lee, Wook-Ryun;Kim, Jae-Gu;Kim, Hyo-Jung;Choi, Byeong-Keun
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.34 no.11
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    • pp.1757-1763
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    • 2010
  • Flywheel energy storage system (FESS) is defined as a high speed rotating flywheel system that can save surplus electric power. The FESS is proposed as an efficient energy storage system because it can accumulate a large amount of energy when it is operated at a high rotating speed and no mechanical problems are encountered. The FESS consists of a shaft, flywheel, motor/generator, bearings, and case. It is difficult to simulate rotor dynamics using common structure simulation programs because these programs are based on the 3D model and complex input rotating conditions. Therefore, in this paper, a program for the FESS based on the 2D FEM was developed. The 2D FEM can model easier than 3D, and it can present the multi-layer rotor with different material each other. Stiffness changing of the shaft caused by shrink fitting of the hub can be inputted to get clear solving results. The results obtained using the program were compared with those obtained using the common programs to determine any errors.

Laboratory Validation of Bridge Finite Model Updating Approach By Static Load Input/Deflection Output Measurements (정적하중입력/변위출력관계를 이용한 단경간 교량의 유한요소모델개선기법: 실내실험검증)

  • Kim, Sehoon;Koo, Ki Young;Lee, Jong-Jae
    • Journal of the Korea institute for structural maintenance and inspection
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    • v.20 no.3
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    • pp.10-17
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    • 2016
  • This paper presents a laboratory validation of a new approach for Finite Element Model Updating(FEMU) on short-span bridges by combining ambient vibration measurements with static load input-deflection output measurements. The conventional FEMU approach based on modal parameters requires the assumption on the system mass matrix for the eigen-value analysis. The proposed approach doesn't require the assumption and even provides a way to update the mass matrix. The proposed approach consists of two steps: 1) updating the stiffness matrix using the static input-deflection output measurements, and 2) updating the mass matrix using a few lower natural frequencies. For a validation of the proposed approach, Young's modulus of the laboratory model was updated by the proposed approach and compared with the value obtained from strain-stress tests in a Universal Testing Machine. Result of the conventional FEMU was also compared with the result of the proposed approach. It was found that proposed approach successfully estimated the Young's modulus and the mass density reasonably while the conventional FEMU showed a large error when used with higher-modes. In addition, the FE modeling error was discussed.

Heavy-weight Impact Sound Characteristics of Floor Structure of a Small-Sized Wall-Slab Apartment Building having Joist Slab (장선슬래브를 갖는 소형평형 벽식구조 아파트 바닥구조의 중량충격음 특성)

  • Chun, Young-Soo
    • Journal of the Korea institute for structural maintenance and inspection
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    • v.24 no.1
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    • pp.8-15
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    • 2020
  • In the present paper, as a way of reducing heavyweight impact sounds, in particular, among floor impact sounds which have come to the forefront as a social issue recently, a floor joist slab is proposed that is expected to bring an effect of reducing heavyweight impact sounds through a shift in the natural frequency by installing a floor joist on a flat-type slab to increase the rigidity of the floor slab, differently from the existing method that increases the thickness of floor slab, and the heavyweight impact sound characteristics depending on the floor joist height and interval are interpretively analyzed. As a result of the analysis, though a trend is shown where the sound pressure level decreases as the slab thickness of floor joist increases, and as no difference is shown when thickness is above a certain value, it is thought that there is a threshold for the effect of an increase in floor thickness on blockage of heavyweight impact sounds. Also, as an increase in floor rigidity resulting from an increase in the floor joist height and a decrease in the interval does not lead to a consistent increase in the performance of blocking heavyweight impact sounds, it is thought that a different floor joist height and interval should be applied to each type of house to expect optimum performance of blocking heavyweight impact sounds, and an increase of 100mm in the floor joist height or a decrease of about 100mm in the interval is expected to bring an effect of reducing heavyweight impact sounds by about 1dB to 2dB.

Rheological Properties of ${\beta}-Glucan$ Isolated from Non-waxy and Waxy Barley (메성 및 찰성보리 ${\beta}-Glucan$의 리올로지 특성)

  • Choi, Hee-Don;Park, Yong-Gon;Jang, Eun-Hee;Seog, Ho-Moon;Lee, Cherl-Ho
    • Korean Journal of Food Science and Technology
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    • v.32 no.3
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    • pp.590-597
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    • 2000
  • The rheological properties of ${\beta}-glucans$ isolated from non-waxy and waxy barley were investigated. ${\beta}-Glucan$ solutions showed pseudoplastic properties and their behaviors were explained by applying Power law model in the range of concentrations$(1{\sim}4%)$ and temperatures$(20{\sim}65^{\circ}C)$. The effects of temperature and concentration on the apparent viscosity at $700\;s^{-1}$ shear rate were examined by applying Arrhenius equation and power law equation, and their effect was more pronounced in waxy ${\beta}-glucan$ solutions. The activation energy for flow of ${\beta}-glucan$ solutions decreased with the increase of concentration, and the concentration-dependent constant A increased with the increase of temperature. The intrinsic viscosity of waxy ${\beta}-glucan$ was higher than that of non-waxy ${\beta}-glucan$. The transition from dilute to concentrate region occurred at a critical coil overlap parameter $C^*[{\eta}]=0.02.$ The slopes of non-waxy and waxy ${\beta}-glucan$ at $C[{\eta}] were similar, but the slope of waxy ${\beta}-glucan$ at $C[{\eta}]>C^*[{\eta}]$ was higher than that of non-waxy ${\beta}-glucan$. Dynamic viscoelasticity measurement showed that cross-over happened, and storage modulus was higher than loss modulus at frequency range above cross-over. ${\beta}-Glucan$ solutions formed weak gels after stored for 24 hr.

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An Experimental Study on Dynamic Behavior Evaluation of Transitional Track (접속부 궤도의 동적거동분석을 위한 실험적 연구)

  • Cho, Sung-Jung;Choi, Jung-Youl;Chun, Dae-Sung;Kim, Man-Cheol;Park, Yong-Gul
    • Proceedings of the KSR Conference
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    • pp.1379-1385
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    • 2007
  • In domestic transitional zone design, there is regulation to prevent generation of irregular substructure behaviors that negatively influence in prevention of plasticity settlement on approach section and contact section as well as relieve overall track rigidity by reducing sectional foundation and track stiffness difference, but design guideline that considers dynamic behavior of transitional track in actual service line is very insignificant. Therefore in this study, characteristics of transitional track dynamic behaviors by substructure stiffness are researched and measured dynamic response of transitional track by substructure stiffness in order to prove correlation between substructure and track and calculate elasticity(stiffness) and track load of transitional track by using measurement and formula to provide basic information for developing design guideline considering dynamic behavior of service line transitional track.

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