• Title, Summary, Keyword: Free vibration

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Investigation on hygro-thermal vibration of P-FG and symmetric S-FG nanobeam using integral Timoshenko beam theory

  • Matouk, Hakima;Bousahla, Abdelmoumen Anis;Heireche, Houari;Bourada, Fouad;Bedia, E.A. Adda;Tounsi, Abdelouahed;Mahmoud, S.R.;Tounsi, Abdeldjebbar;Benrahou, K.H.
    • Advances in nano research
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    • v.8 no.4
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    • pp.293-305
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    • 2020
  • In the current research, the free vibrational behavior of the FG nano-beams integrated in the hygro-thermal environment and reposed on the elastic foundation is investigated using a novel integral Timoshenko beam theory (ITBT). The current model has only three variables unknown and requires the introduction of the shear correction factor because her uniformed variation of the shear stress through the thickness. The effective properties of the nano-beam vary according to power-law and symmetric sigmoid distributions. Three models of the hygro-thermal loading are employed. The effect of the small scale effect is considered by using the nonlocal theory of Eringen. The equations of motion of the present model are determined and resolved via Hamilton principle and Navier method, respectively. Several numerical results are presented thereafter to illustrate the accuracy and efficiency of the actual integral Timoshenko beam theory. The effects of the various parameters influencing the vibrational responses of the P-FG and SS-FG nano-beam are also examined and discussed in detail.

Study on Strain Measurement of Agricultural Machine Elements Using Microcomputer (Microcomputer를 이용(利用)한 농업기계요소(農業機械要素)의 Strain 측정(測定)에 관(關)한 연구(硏究))

  • Kim, Kee Dae;Kim, Tae Kyun;Kim, Soung Rai
    • Korean Journal of Agricultural Science
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    • v.8 no.1
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    • pp.90-96
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    • 1981
  • To design more efficient agricultural machinery, the accurately measuring system among many other factors is essential. A light-beam oscillographic recorder is generally used in measuring dynamic strain but it is not compatible with the extremely high speed measuring system such as 1,000 m/s, also is susceptable to damage due to vibration while using the system in field. The recorder used light sensitive paper for strip chart recording. The reading and analysis of data from the strip charts is very cumbersome, errorneous and time consuming. A microcomputer was interfaced with A/D converter, microcomputer program was developed for measuring, system calibration was done and the strain generated from a cantilever beam vibrator was measured. The results are summarized as follows. 1. Microcomputer program was developed to perform strain measuring of agricultural machine elements and could be controled freely the measuring intervals, no. of channels and no. of data. The maximum measuring speed was $62{\mu}s$. 2. Calibration the system was performed with triangle wave generated from a function generator and checked by an oscilloscope. The sampled data were processed using HP 3000 minicomputer of Chungnam National University computer center the graphical results were triangle same as input wave and so the system have been out of phase distorsion and amplitude distorsion. 3. The strain generated from a cantilever beam vibrator which has free vibration period of 0.019 second were measured by the system controlled to have l.0 ms of time interval and its computer output showing vibration curve which is well filted to theoretical value. 4. Using microcomputer on measuring the strain of agricultural machine elements could not only save analyzing time and recording papers but also get excellent adaptation to field experiment, especially in measurement requiring high speed and good precision.

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Investigation of Axially Loaded Jacked Pile Behavior by Pile Load Test (말뚝재하시험을 통한 압입강관말뚝의 연직지지거동 분석)

  • Baek, Sung-Ha;Do, Eun-Su;Kim, Seok-Jung
    • Journal of the Korean Geotechnical Society
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    • v.34 no.7
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    • pp.39-49
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    • 2018
  • Jacked pile that involves the use of hydraulic jacks to press the piles into the ground is free from noise and vibration, and is possibly installed within a limited construction area. Thus, as an alternative to conventional pile driving methods, pile jacking could become widely accepted for the construction projects in urban area (e.g., reconstruction or remodeling construction projects). Great concern has arisen over the prediction of axially loaded jacked pile behavior. Against this background, a series of pile load tests were hence conducted on a jacked steel pipe pile installed in weathered zone (i.e., weathered soil and weathered rock). From the test results, base resistance and shaft resistance for each test condition were evaluated and compared with the values predicted by the previous driven pile resistance assessment method. Test results showed that the previous driven pile resistance assessment method highly underestimated both the base and shaft resistances of a jacked pile; differences were more obviously observed with the shaft resistance. The reason for this discrepancy is that a driven pile normally experiences a larger number of loading/unloading cycles during installation, and therefore shows significantly degraded stiffness of surrounding soil. Based on the results of the pile load tests, particular attention was given to the modification of the previous driven pile resistance assessment method for investigating the axially loaded jacked pile behavior.

Fault Detection Method for Beam Structure Using Modified Laplacian and Natural Frequencies (수정 라플라시안 및 고유주파수를 이용한 보 구조물의 결함탐지기법)

  • Lee, Jong-Won
    • Journal of the Korea Academia-Industrial cooperation Society
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    • v.19 no.5
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    • pp.611-617
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    • 2018
  • The application of health monitoring, including a fault detection technique, is needed to secure the structural safety of large structures. A 2-step crack identification method for detecting the crack location and size of the beam structure is presented. First, a crack occurrence region was estimated using the modified Laplacian operator for the strain mode shape obtained from the distributed local strain data. The crack location and size were then identified based on the natural frequencies obtained from the acceleration data and the neural network technique for the pre-estimated crack occurrence region. The natural frequencies of a cracked beam were calculated based on an equivalent bending stiffness induced by the energy method, and used to generate the training patterns of the neural network. An experimental study was carried out on an aluminum cantilever beam to verify the present method for crack identification. Cracks were produced on the beam, and free vibration tests were performed. A crack occurrence region was estimated using the modified Laplacian operator for the strain mode shape, and the crack location and size were assessed using the natural frequencies and neural network technique. The identified crack occurrence region agrees well with the exact one, and the accuracy of the estimation results for the crack location and size could be enhanced considerably for 3 damage cases. The presented method could be applied effectively to the structural health monitoring of large structures.

Variability of Mid-plane Symmetric Functionally Graded Material Beams in Free Vibration (중립면 대칭 기능경사재료 보의 자유진동 변화도)

  • Nguyen, Van Thuan;Noh, Hyuk-Chun
    • Journal of the Computational Structural Engineering Institute of Korea
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    • v.31 no.3
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    • pp.127-132
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    • 2018
  • In this paper, a scheme for the evaluation of variability in the eigen-modes of functionally graded material(FGM) beams is proposed within the framework of perturbation-based stochastic analysis. As a random parameter, the spatially varying elastic modulus of FGM along the axial direction at the mid-surface of the beam is chosen, and the thru-thickness variation of the elastic modulus is assumed to follow the original form of exponential variation. In deriving the formulation, the first order Taylor expansion on the eigen-modes is employed. As an example, a simply supported FGM beam having symmetric elastic modulus with respect to the mid-surface is chosen. Monte Carlo analysis is also performed to check if the proposed scheme gives reasonable outcomes. From the analyses it is found that the two schemes give almost identical results of the mean and standard deviation of eigen-modes. With the propose scheme, the standard deviation shape of respective eigen-modes can be evaluated easily. The deviated mode shape is found to have one more zero-slope points than the mother modes shapes, irrespective of order of modes. The amount of deviation from the mean is found to have larger values for the higher modes than the lower modes.

Comparison of Vision-based Displacement Measurement Results for Various Target Shooting Angles (표적 촬영 각도에 따른 영상기반 변위계측 결과 비교)

  • Shin, Seung Hoon;Park, Won Bin;Seol, Dong Hyeon;Kim, Hong Jin
    • Journal of the wind engineering institute of Korea
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    • v.22 no.3
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    • pp.103-109
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    • 2018
  • In this paper, we deal with a method to compensate distorted displacement according to the distortion image in any axial direction by updating the MPC (mm / pixel coefficient) every frame of the acquired image. For the compulsory distortion of images, we set various shooting angles. We collected and analyzed the images by adjusting 12 shooting angles in $5^{\circ}$ increments from $0^{\circ}$ to $55^{\circ}$ through the installation position of the camcorder. Prior to this experiment, preliminary experiments were conducted to evaluate the validity of the vision-based displacement measurement, and it is judged that the vision-based displacement measurement system has sufficient validity by comparing GPS and accelerometer measurement results. The maximum amplitude and the estimated frequency of the structure were found by analyzing the collected images for various target shooting angles. Additional comparisons were conducted by estimating the damping ratio from the measured free vibration. As a result of the analysis, the error in the maximum amplitude was 0.325 mm and in the error rate was 5.72%. In the frequency estimation, except for the shooting angle of $50^{\circ}$, the overall error rate is less than 1% and very similar estimation results are obtained. The damping ratio according to the varying target shooting angle is estimated from 1.025% to 1.189%. The overall damping ratio was similar.

A Study on Dynamic Behaviour of Cable-Stayed Bridge by Vehicle Load (차량하중에 의한 사장교의 동적거동에 관한 연구)

  • Park, Cheun Hyek;Han, Jai Ik
    • Journal of The Korean Society of Civil Engineers
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    • v.14 no.6
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    • pp.1299-1308
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    • 1994
  • This paper is considered on the dynamic behavior and the dynamic impact coefficient on the cable-stayed bridge under the vehicle load. The method of static analysis, that is, the transfer matrix method is used to get influence values about displacements, section forces of girder and cable forces. Gotten influence values were used as basic data to analyse dynamic behavior. This paper used the transfer matrix method because it is relatively simpler than the finite element method, and calculating speed of computer is very fast and the precision of computation is high. In the process of dynamic analysis, the uncoupled equation of motion is derived from simultaneous equation of the motion of cable-stayed bridge and vehicle travelling by using mode shape, which was borne from system of undamped free vibration. The solution of the uncoupled equation of motion, that is, time history of response of deflections, velocity and acceleration on reference coordinate system, is found by Newmark-${\beta}$ method, a kind of direct integral method. After the time history of dynamic response was gotten, and it was transfered to the time history of dynamic response of cable-stayed bridge by linear transformation of coordinates. As a result of this numerical analysis, effect of dynamic behavior for cable-stayed bridge under the vehicle load has varied depending on parameter of design, that is, the ratio of span, the ratio of main span length, tower height, the flexural rigidity of longitudinal girder, the flexural rigidity of tower, and the cable stiffness, investigated. Very good agreements with the existing solution in the literature are shown for the uncracked plate as well as the cracked plate.

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Earthquake Simulation Tests of A 1:5 Scale Gravity Load Designed 3-Story Reinforced Concrete Frame (중력하중 설계된 1:5 축소 3층 철근콘크리트 골조의 지진모의실험)

  • 이한선;우성우
    • Magazine of the Korea Concrete Institute
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    • v.10 no.6
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    • pp.241-252
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    • 1998
  • The objective of the research stated herein is to observe the actual responses of a low-rise nonseismic moment-resisting reinforced concrete frame subjected to varied levels of earthquake ground motions. First, the reduction scale for the model was determined as 1 : 5 considering the capacity of the shaking table to be used and the model was manufactured according to the similitude law. This model was, then, subjected to the shaking table motions simulating Taft N21E component earthquake ground motions, whose peak ground accelations (PGAs) were modified to 0.12g, 0.2g, 0.3g, and 0.4g. The lateral accelerations and displacements at each story and local deformations at the critical reginos of the structure were measured. The base shear was measured by using self-made load cells. Before and after each earthquake simulation test, free vibration tests were performed to find the change in the natural period and damping ratio of the model. The test data on the global and local behaviors are interpreted. The model showed the linear elastic behavior under the Taft N21E motion with the PGA if 0.12g, which represents the design earthquake in Korea. The maximum base shear was 1.8tf, approximately 4.7 times the design base shear. The model revealed fairly good resistance to the higher level of earthquake simulation tests. The main components of its resistance to the high level of earthquakes appeared to be 1) the high overstrength, 2) the elongation of the fundamental period, and 3) the minor energy dissipation by inelastic deformations. The drifts of the model under these tests were approximately within the allowable limit.

Dynamic Frictional Behavior of Artificial Rough Rock Joints under Dynamic Loading (진동하중 하에서 거친 암석 절리면의 동력 마찰거동)

  • Jeon Seok-Won;Park Byung-Ki
    • Tunnel and Underground Space
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    • v.16 no.2
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    • pp.166-178
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    • 2006
  • Recently, the frequency of occurring dynamic events such as earthquakes, explosives blasting and other types of vibration has been increasing. Besides, the chances of exposure for rock discontinuities to free faces get higher as the scale of rock mass structures become larger. For that reason, the frictional behavior of rock joints under dynamic conditions needs to be investigated. In this study, artificially fractured rock joint specimens were prepared in order to examine the dynamic frictional behavior of rough rock joint. Roughness of each specimen was characterized by measuring surface topography using a laser profilometer and a series of shaking table tests was carried out. For mated joints, the static friction angle back-calculated ken the yield acceleration was $2.7^{\circ}$ lower than the tilt angle on average. The averaged dynamic friction angle for unmated joints was $1.8^{\circ}$ lower than the tilt angle. Displacement patterns of sliding block were classified into 4 types and proved to be related to the first order asperity of rock joint. The tilt angle and the static friction angle for mated joints seem to be correlated to micro average inclination angle which represents the second order asperity. The tilt angle and the dynamic friction angle for unmated Joints, however, have no correlation with roughness parameters. Friction angles obtained by shaking table test were lower than those by direct shear test.

On the Free Vibration Analysis of Thin-Walled Box Beams having Variable Cross-Sections (단면형상이 변하는 박판보의 진동해석에 관한 연구)

  • Lee, Gi-Jun;Sa, Jin-Yong;Kim, Jun-Sik
    • Journal of the Computational Structural Engineering Institute of Korea
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    • v.30 no.2
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    • pp.111-117
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    • 2017
  • In this paper, a local deformation effect in thin-walled box beams is investigated via a finite element modal analysis. The analysis is carried out for single-cell and multi-cell box beam configurations. The single-cell box beam with and without a neck, which mimics a simple wind-turbine blade, is analyzed first. The results obtained by shell elements are compared to those of one-dimensional(1D) beam elements. It is observed that the wall thickness plays a crucial role in the natural frequencies of the beam. The 1D beam analysis deviates from the shell analysis when the wall thickness is either thin or thick. The shell modes(local deformations) are dominant as it becomes thin, whereas the shear deformation effects are significant as it does thick. The analysis is extended to the single-cell box beam with a neck, in which the shell modes are confined to near the neck. Finally the multi-cell box beam with a taper, which is quite similar to real wind-turbine blade configuration, is considered to investigate the local deformation effect. The results reveal that the 1D beam analysis cannot match with the shell analysis due to the local deformation, especially for the lagwise frequencies. There are approximately 5~7% errors even if the number of segments is increased.