• Title/Summary/Keyword: loading frequency

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Wave propagation in a concrete filled steel tubular column due to transient impact load

  • Ding, Xuanming;Fan, Yuming;Kong, Gangqiang;Zheng, Changjie
    • Steel and Composite Structures
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    • v.17 no.6
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    • pp.891-906
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    • 2014
  • This study aims to present a three dimensional finite element model to investigate the wave propagation in a concrete filled steel tubular column (CFSC) due to transient impact load. Both the concrete and steel are regarded as linear elastic material. The impact load is simulated by a semi sinusoidal impulse. Besides the CFSC models, a concrete column (CC) model is established for comparing under the same loading condition. The propagation characteristics of the transient waves in CFSC are analyzed in detail. The results show that at the intial stage of the wave propagation, the velocity waves in CFSC are almost the same as those in CC before they arrive at the steel tube. When the waves reach the column side, the velocity responses of CFSC are different from those of CC and the difference is more and more obvious as the waves travel down along the column shaft. The travel distance of the wave front in CFSC is farther than that in CC at the same time. For different wave speeds in steel and concrete material, the wave front in CFSC presents an arch shape, the apex of which locates at the center of the column. Differently, the wave front in CC presents a plane surface. Three dimensional effects on top of CFSC are obvious, therefore, the peak value and arrival time of incident wave crests have great difference at different locations in the radial direction. High-frequency waves on the waveforms are observed. The time difference between incident and reflected wave peaks decreases significantly with r/R when r/R < 0.6, however, it almost keeps constant when $r/R{\geq}0.6$. The time duration between incident and reflected waves calculated by 3D FEM is approximately equal to that calculated by 1D wave theory when r/R is about 2/3.

Comparative Study of Approximate Optimization Techniques in CAE-Based Structural Design (구조 최적설계를 위한 다양한 근사 최적화기법의 적용 및 비교에 관한 연구)

  • Song, Chang-Yong;Lee, Jong-Soo
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.34 no.11
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    • pp.1603-1611
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    • 2010
  • The comparative study of regression-model-based approximate optimization techniques used in the strength design of an automotive knuckle component that will be under bump and brake loading conditions is carried out. The design problem is formulated such that the cross-sectional sizing variables are determined by minimizing the weight of the knuckle component that is subjected to stresses, deformations, and vibration frequency constraints. The techniques used in the comparative study are sequential approximate optimization (SAO), sequential two-point diagonal quadratic approximate optimization (STDQAO), and approximate optimization based on enhanced moving least squares method (MLSM), such as CF (constraint feasible)-MLSM and Post-MLSM. Commercial process integration and design optimization (PIDO) tools are utilized for the application of SAO and STDQAO. The enhanced MLSM-based approximate optimization techniques are newly developed to ensure constraint feasibility. The results of the approximate optimization techniques are compared with those of actual non-approximate optimization to evaluate their numerical performances.

A Study on the Quality and Image of School Meal Service and Student Satisfaction with the Service: Focused on Moderating Effect of Distribution Types (학교급식에 대한 급식품질, 급식이미지, 만족도에 관한 연구: 배식형태의 조절효과를 중심으로)

  • Yim, Hui-Rang;Kim, Hak-Seon
    • Culinary science and hospitality research
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    • v.19 no.5
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    • pp.11-22
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    • 2013
  • This study aimed to identify the relationships between the quality and image of school meal service and satisfaction perceived from high school students and to access the moderating effect of its distribution types. For the empirical analysis, this study used SPSS 18.0 and AMOS 18.0 and conducted frequency analysis, reliability analysis, exploratory and confirmatory factor analysis, path analysis and chi-square difference test. As a result of the analyses, the validity and reliability were identified showing over 0.4 factor loading value, ${\chi}^2$=258.831, d.f.=98, RMR=0.059, GFI=.822, AGFI=.776, NFI=0.908, IFI=0.941, CFI=0.940. The results of the structural equation modeling analysis are as follows: first, the quality of school meal service had a significant influence on its image; next, the image of school meal service had a significant influence on satisfaction with the service; last, there is a significant moderating effect of distribution types in the relationship between the image of school meal service and satisfaction with the service.

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Principal Component Analysis on Marine Casualties Occurred at Korean Littoral Sea in Recent 5 Years (최근 5년간 국내 연근해에서 발생한 해양사고에 대한 주성분분석)

  • KIM, Yeong-Sik
    • Journal of Fisheries and Marine Sciences Education
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    • v.28 no.2
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    • pp.465-472
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    • 2016
  • Principal Component Analysis (PCA) is useful statistical technique for finding patterns in data, and expressing the data in such a way as to highlight their similarities and differences. In this paper, 1417 marine casualties occurred in Korean littoral sea in recent 5 years, were examined by the PCA. The main results obtained were as follows : 1. Most of marine casualties resulted from the human factors such as careless operation and insufficient engine maintenance. 2. Collision and standing mainly resulted from steering room-related human factors such as careless guard, inadequate ship-handling, however engine damage and fire explosion mainly resulted from engine room-related human factor such as bad handling of engine system. 3. No. 1 principal component represents accident frequency, No. 2 principal component represents the cause and No. 3 principal component represents the pattern of marine casualties, respectively.

Four-Elements L-Shaped Slot Array Monopole Antenna with Dipole-like Radiation Pattern (다이폴형 방사 패턴을 갖는 4소자 L-슬롯 배열 모노폴 안테나)

  • Nam, Sung-Soo;Lee, Hong-Min
    • The Journal of Korean Institute of Electromagnetic Engineering and Science
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    • v.20 no.3
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    • pp.273-279
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    • 2009
  • In this paper, an antenna which has dipole-like radiation pattern and low profile is proposed. The antenna is composed of four elements slot array based on L-shaped 0.43 $\lambda_g$ slot element. It presents a omni-directional radiation patter in the azimuth plane and has a null toward broad-side direction. In the design, a small mono-pole antenna which acts as a large capacitance element, combined with the partially removed ground plane by four L-shaped slots. As a result, these structure act as a LC resonator for radiation. The measured result shows, the impedance bandwidth(VSWR$\leq$2) of the proposed antenna is 60 MHz(2.35$\sim$2.41 GHz). The measured maximum radiation gain and efficiency of proposed antenna is 0.02 dBi, 56.7 % at center frequency 2.38 GHz, respectively. The proposed antenna can be applied to wireless tan access point system.

A Flexible Multi-body Dynamic Model for Analyzing the Hysteretic Characteristics and the Dynamic Stress of a Taper Leaf Spring

  • Moon Il-Dong;Yoon Ho-Sang;Oh Chae-Youn
    • Journal of Mechanical Science and Technology
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    • v.20 no.10
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    • pp.1638-1645
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    • 2006
  • This paper proposes a modeling technique which is able to not only reliably and easily represent the hysteretic characteristics but also analyze the dynamic stress of a taper leaf spring. The flexible multi-body dynamic model of the taper leaf spring is developed by interfacing the finite element model and computation model of the taper leaf spring. Rigid dummy parts are attached at the places where a finite element leaf model is in contact with an adjacent one in order to apply contact model. Friction is defined in the contact model to represent the hysteretic phenomenon of the taper leaf spring. The test of the taper leaf spring is conducted for the validation of the reliability of the flexible multi-body dynamic model of the taper leaf spring developed in this paper. The test is started at an unloaded state with the excitation amplitude of $1{\sim}2mm/sec$ and frequency of 132 mm. First, the simulation is conducted with the same condition as the test. Then, the simulations are conducted with various amplitudes in a loaded state. The hysteretic diagram from the test is compared with the ones from the simulation for the validation of the reliability of the model. The dynamic stress analysis of the taper leaf spring is also conducted with the developed flexible multi-body dynamic model under a dynamic loading condition.

GPS/RTS data fusion to overcome signal deficiencies in certain bridge dynamic monitoring projects

  • Moschas, Fanis;Psimoulis, Panos A.;Stiros, Stathis C.
    • Smart Structures and Systems
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    • v.12 no.3_4
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    • pp.251-269
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    • 2013
  • Measurement of deflections of certain bridges is usually hampered by corruption of the GPS signal by multipath associated with passing vehicles, resulting to unrealistically large apparent displacements. Field data from the Gorgopotamos train bridge in Greece and systematic experiments revealed that such bias is due to superimposition of two major effects, (i) changes in the geometry of satellites because of partial masking of certain satellites by the passing vehicles (this effect can be faced with solutions excluding satellites that get temporarily blocked by passing vehicles) and (ii) dynamic multipath caused from reflection of satellite signals on the passing trains, a high frequency multipath effect, different from the static multipath. Dynamic multipath seems to have rather irregular amplitude, depending on the geometry of measured satellites, but a typical pattern, mainly consisting of a baseline offset, wide base peaks correlating with the sequence of main reflective surfaces of the vehicles passing next to the antenna. In cases of limited corruption of GPS signal by dynamic multipath, corresponding to scale distortion of the short-period component of the GPS waveforms, we propose an algorithm which permits to reconstruct the waveform of bridge deflections using a weak fusion of GPS and RTS data, based on the complementary characteristics of the two instruments. By application of the proposed algorithm we managed to extract semi-static and dynamic displacements and oscillation frequencies of a historical railway bridge under train loading by using noisy GPS and RTS recordings. The combination of GPS and RTS is possible because these two sensors can be fully collocated and have complementary characteristics, with RTS and GPS focusing on the long- and short-period characteristics of the displacement, respectively.

Optimization of SWCNT-Coated Fabric Sensors for Human Joint Motion Sensing

  • Cho, Hyun-Seung;Park, Seon-Hyung;Yang, Jin-Hee;Park, Su-Youn;Han, Bo-Ram;Kim, Jin-Sun;Lee, Hae-Dong;Lee, Kang-Hwi;Lee, Jeong-Whan;Kang, Bok-Ku;Chon, Chang-Soo;Kim, Han-Sung;Lee, Joo-Hyeon
    • Journal of Electrical Engineering and Technology
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    • v.13 no.5
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    • pp.2059-2066
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    • 2018
  • This study explored the feasibility of utilizing an SWCNT-coated fabric sensor for the development of a wearable motion sensing device. The extent of variation in electric resistance of the sensor material was evaluated by varying the fiber composition of the SWCNT-coated base fabrics, attachment methods, number of layers, and sensor width and length. 32 sensors were fabricated by employing different combinations of these variables. Using a custom-built experimental jig, the amount of voltage change in a fabric sensor as a function of the length was measured as the fabric sensors underwent loading-unloading test with induced strains of 30 %, 40 %, and 50 % at a frequency of 0.5 Hz. First-step analysis revealed the following: characteristics of the strain-voltage curves of the fabric sensors confirmed that 14 out of 32 sensors were evaluated as more suitable for measuring human joint movement, as they yield stable resistance values under tension-release conditions; furthermore, significantly stable resistance values were observed at each level of strain. Secondly, we analyzed the averaged maximum, minimum, and standard deviations at various strain levels. From this analysis, it was determined that the two-layer sensor structure and welding attachment method contributed to the improvement of sensing accuracy.

Design of electromagnetic type transducer to drive round window with high efficiency (고효율 전자기형 정원창 구동 트랜스듀서의 설계)

  • Lee, Jang-Woo;Kim, Dong-Wook;Kim, Myoung-Nam;Cho, Jin-Ho
    • Journal of Sensor Science and Technology
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    • v.19 no.6
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    • pp.449-455
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    • 2010
  • Implantable middle ear hearing devices(IMEHDs) have being actively studied to overcome the problems of conventional hearing aids. Vibration transducer, an output devices of IMEHDs, is attached on the ossicular chain and transmits mechanical vibration to cochlea. This approach allows us to hear more clear sound because mechanical vibration is effective to transfer high frequency acoustics, but occurs some problems such as fatigue accumulation to ossicular chian and reduction of vibration displacement caused by mass loading effect. Recently, many studies for the round window stimulation are announced, because it does not cause such problems. It have been studied by older transducers designed for attaching on ossicular chain. In this paper, we proposed a new electromagnetic transducer which consists of two magnets, three coils and a vibration membrane. The magnet assembly, magnet coupled in opposite direction, were placed in the center of three coils, and the optimum length of each coil generating maximum vibrational force was calculated by finite element analysis(FEA). The transducer was implemented as the calculated length of each coil, and measured vibration displacement. From the results, it is verified the vibration displacement can be improved by optimizing the length of coils.

Pyroshock and Vibration Isolation using SMA Mesh Washer Isolator (형상기억합금 메쉬 와셔 절연계의 파이로 충격 및 진동 절연 시험)

  • Youn, Se-Hyun;Jang, Young-Soon;Han, Jae-Hung
    • Journal of the Korean Society for Aeronautical & Space Sciences
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    • v.37 no.3
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    • pp.307-313
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    • 2009
  • In general, pyroshock is generated from the actuation of separation devices for several stage, fairing, and satellite separation in the flight of a launch vehicle. During these events, transient vibration phenomenon called pyroshock, which shows large acceleration in the high frequency range, occurs and it can result in the malfunction of electronic components which is equipped inside the launch vehicle or satellite. In this paper, mesh washer isolators made out of SMA were introduced for the isolation of pyroshock. One type of isolator primarily used pseudoelastic characteristics of SMA and the other type of isolator used shape memory effect of SMA. For the study of basic load-displacement relationship of each SMA isolator, compressive loading tests were performed and the results showed the capability of the isolator itself. Pyroshock isolation tests were followed and verified the outstanding isolation performance of isolator. In addition, random vibration tests were also performed and checked the dynamic characteristics of each SMA isolator.