• Title/Summary/Keyword: Single beam simulation

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An improved modal strain energy method for structural damage detection, 2D simulation

  • Moradipour, Parviz;Chan, Tommy H.T.;Gallag, Chaminda
    • Structural Engineering and Mechanics
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    • v.54 no.1
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    • pp.105-119
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    • 2015
  • Structural damage detection using modal strain energy (MSE) is one of the most efficient and reliable structural health monitoring techniques. However, some of the existing MSE methods have been validated for special types of structures such as beams or steel truss bridges which demands improving the available methods. The purpose of this study is to improve an efficient modal strain energy method to detect and quantify the damage in complex structures at early stage of formation. In this paper, a modal strain energy method was mathematically developed and then numerically applied to a fixed-end beam and a three-story frame including single and multiple damage scenarios in absence and presence of up to five per cent noise. For each damage scenario, all mode shapes and natural frequencies of intact structures and the first five mode shapes of assumed damaged structures were obtained using STRAND7. The derived mode shapes of each intact and damaged structure at any damage scenario were then separately used in the improved formulation using MATLAB to detect the location and quantify the severity of damage as compared to those obtained from previous method. It was found that the improved method is more accurate, efficient and convergent than its predecessors. The outcomes of this study can be safely and inexpensively used for structural health monitoring to minimize the loss of lives and property by identifying the unforeseen structural damages.

Vibration behaviors of a damaged bridge under moving vehicular loads

  • Yin, Xinfeng;Liu, Yang;Kong, Bo
    • Structural Engineering and Mechanics
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    • v.58 no.2
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    • pp.199-216
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    • 2016
  • A large number of bridges were built several decades ago, and most of which have gradually suffered serious deteriorations or damage due to the increasing traffic loads, environmental effects, and inadequate maintenance. However, very few studies were conducted to investigate the vibration behaviors of a damaged bridge under moving vehicles. In this paper, the vibration behaviors of such vehicle-bridge system are investigated in details, in which the effects of the concrete cracks and bridge surface roughness are particularly considered. Specifically, two vehicle models are introduced, i.e., a simplified four degree-of-freedoms (DOFs) vehicle model and a more complex seven DOFs vehicle model, respectively. The bridges are modeled in two types, including a single-span uniform beam and a full scale reinforced concrete high-pier bridge, respectively. The crack zone in the reinforced concrete bridge is considered by a damage function. The bridge and vehicle coupled equations are established by combining the equations of motion of both the bridge and vehicles using the displacement relationship and interaction force relationship at the contact points between the tires and bridge. The numerical simulations and verifications show that the proposed modeling method can rationally simulate the vibration behaviors of the damaged bridge under moving vehicles; the effect of cracks on the impact factors is very small and can be neglected for the bridge with none roughness, however, the effect of cracks on the impact factors is very significant and cannot be neglected for the bridge with roughness.

Three-dimensional surgical accuracy between virtually planned and actual surgical movements of the maxilla in two-jaw orthognathic surgery

  • Hong, Mihee;Kim, Myung-Jin;Shin, Hye Jung;Cho, Heon Jae;Baek, Seung-Hak
    • The korean journal of orthodontics
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    • v.50 no.5
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    • pp.293-303
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    • 2020
  • Objective: To investigate the three-dimensional (3D) surgical accuracy between virtually planned and actual surgical movements (SM) of the maxilla in two-jaw orthognathic surgery. Methods: The sample consisted of 15 skeletal Class III patients who underwent two-jaw orthognathic surgery performed by a single surgeon using a virtual surgical simulation (VSS) software. The 3D cone-beam computed tomography (CBCT) images were obtained before (T0) and after surgery (T1). After merging the dental cast image onto the T0 CBCT image, VSS was performed. SM were classified into midline correction (anterior and posterior), advancement, setback, anterior elongation, and impaction (total and posterior). The landmarks were the midpoint between the central incisors, the mesiobuccal cusp tip (MBCT) of both first molars, and the midpoint of the two MBCTs. The amount and direction of SM by VSS and actual surgery were measured using 3D coordinates of the landmarks. Discrepancies less than 1 mm between VSS and T1 landmarks indicated a precise outcome. The surgical achievement percentage (SAP, [amount of movement in actual surgery/amount of movement in VSS] × 100) (%) and precision percentage (PP, [number of patients with precise outcome/number of total patients] × 100) (%) were compared among SM types using Fisher's exact and Kruskal-Wallis tests. Results: Overall mean discrepancy between VSS and actual surgery, SAP, and PP were 0.13 mm, 89.9%, and 68.3%, respectively. There was no significant difference in the SAP and PP values among the seven SM types (all p > 0.05). Conclusions: VSS could be considered as an effective tool for increasing surgical accuracy.

Design Characteristics of Tapered Directional Couplers in Optical Communication (광통신용 테이퍼 방향성 결합기의 설계 특성)

  • Son, Seock-Yong;Ho, Kwang-Chun;Kim, Yung-Kwon
    • Journal of the Korean Institute of Telematics and Electronics D
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    • v.36D no.11
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    • pp.18-26
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    • 1999
  • Recently, various simplified simulation techniques such as firite-difference beam propagation method and non-orthogonal coupled-mode theory have proposed to analyze the optical characteristics of tapered directional couplers supported by the coupling of two propagating modes. Although these approaches are often in sufficiently accurate, they do not provide the detailed solutions encountered in the analysis of tapered guiding structures. For this purpose, we introduce and utilize a newly developed modal transmission-line theory to analyze rigorously power transfer of the directional coupler. The numerical result reveals that the propagation constants of even and odd modes converge to a single value as increasing the spacer thickness between two symmetric tapered guides. Furthermore, 97% of the power incident into a guiding channel is transmitted to the other channel at the tapered angle ${\theta}=0.1^{\circ}$, and the efficiency of power transfer decreases dramatically as increasing the angle.

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A Study on the Rejection of Dynamic Disturbance Forces in a Magnetically Suspended System Using Flux Feedback (자기력 부상 시스템에서 자속궤한을 이용한 동적 외란력의 제거에 관한 연구)

  • Kim, Jong-Ki;Lee, Key-Seo;Lee, Jun-Ho
    • Transactions of the Korean Society for Noise and Vibration Engineering
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    • v.16 no.3 s.108
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    • pp.283-290
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    • 2006
  • This study is concerned with static and sinusoidal disturbance rejection for a single periodic input disturbance with known period. In the area of active elimination of a disturbance force, the control input should have two different kinds of gains: one is to deliver a stable control and the other is a force component to cancel the external disturbance force. In this paper we employ a simple state feedback control law to make the balance beam stable and employ a linear observer to estimate the states which represent the external disturbance force components. Simulation results verify our proposed control method to reject a static and sinusoidal disturbance force.

A Study on Fatigue Crack at Coped Stringers of the Plate Girder Subway-Bridge (플레이트거더 지하철교량 세로보의 피로 균열에 관한 연구)

  • Jo, Jae Byung
    • Journal of Korean Society of Steel Construction
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    • v.16 no.5 s.72
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    • pp.713-724
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    • 2004
  • A fatigue crack found at the coped stringer of the old dismantled Dangsan Subway Bridge was numerically simulated. A model of a single span of the plate girder bridge with its beam elements was created and analyzed in order to obtain the nominal stress history caused by trains. A detailed FEM analysis of the coped stringer was conducted using a shell element model. A fracture mechanical model was used to estimate crack propagation. The stress intensity factors were calculated using the J-Integral method. The simulation with some reasonable assumptions showed that the calculated crack lengths were comparable to those found on the site.

Human Safety Assessment for a 4 × 8 Array Antenna Used for Wireless Power Transfer at 2.4 GHz (2.4 GHz의 무선전력전송에 사용되는 4 × 8 배열 안테나에 대한 인체안전성평가)

  • Ju, Young Jun;Kim, Jun Hee;Lee, Yu-ri;Gimm, Yoon-Myoung;Lim, Yong Seok
    • Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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    • 2018.10a
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    • pp.338-341
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    • 2018
  • Wireless Power Transfer(WPT) of array antenna applied to beam-forming techniques enables highly efficient WPT when transmitters and receivers are not contacting and even when they are separated. However, this WPT method is possible to use only when human safety restriction by distance between the transmitters and the receivers is satisfied. In the paper, a $4{\times}8$ array antenna for 2.4 GHz is modeled by simulation, then electric field intensity and 10 gram average head SAR(Specific Absorption Rate) by distance away from the array antenna inputted 1 W of 2.4 GHz sinusoidal wave at each single antenna of the array antenna for 2.4 GHz were obtained. And they were compared with human safety restriction of draft of 2018 ICNIRP(International Commission on Non-Ionizing Radiation Protection) guidelines. As the result, power density of far field derived from the electric field intensity was $33.257W/m^2$, which satisfied with occupational human safety restriction but exceeded public's. In addition, the 10 gram average head SAR exceeded the human safety restriction.

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Stopping Power Ratio Estimation Method Based on Dual-energy Computed Tomography Denoising Images for Proton Radiotherapy Planning (양성자치료계획을 위한 이중에너지 전산화단층촬영 잡음 제거 영상 기반 저지능비 추정 방법)

  • Byungdu Jo
    • Journal of the Korean Society of Radiology
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    • v.17 no.2
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    • pp.207-213
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    • 2023
  • Computed tomography (CT) images are used as the basis for proton Bragg peak position estimation and treatment plan simulation. During the Hounsfield Unit (HU) based proton stopping power ratio (SPR) estimation, small differences in the patient's density and elemental composition lead to uncertainty in the Bragg peak positions along the path of the proton beam. In this study, we investigated the potential of dual-energy computed tomography image-based proton SPRs prediction accuracy to reduce the uncertainty of Bragg peak position prediction. Single- and dual-energy images of an electron density phantom (CIRS Model 062M electron density phantom, CIRS Inc., Norfolk, VA, USA) were acquired using a computed tomography system (Somatom Definition AS, Siemens Health Care, Forchheim, Germany) to estimate the SPRs of the proton beam. To validate the method, it was compared to the SPRs estimated from standard data provided by the National Institute of Standards and Technology (NIST). The results show that the dual-energy image-based method has the potential to improve accuracy in predicting the SPRs of proton beams, and it is expected that further improvements in predicting the position of the proton's Bragg peak will be possible if a wider variety of substitutes with different densities and elemental compositions of the human body are used to predict the SPRs.

Evaluation of Radiation Dose for Dual Energy CBCT Using Multi-Grid Device (에너지 변조 필터를 이용한 이중 에너지 콘빔 CT의 선량 평가)

  • Ju, Eun Bin;Ahn, So Hyun;Cho, Sam Ju;Keum, Ki Chang;Lee, Rena
    • Progress in Medical Physics
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    • v.27 no.1
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    • pp.31-36
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    • 2016
  • The paper discusses radiation dose of dual energy CT on which copper modulation layer, is mounted in order to improve diagnostic performance of the dual energy CT. The radiation dose is estimated using MCNPX and its results are compared with that of the conventional dual energy CT system. CT X-ray spectra of 80 and 120 kVp, which are usually used for thorax, abdominal, head, and neck CT scans, were generated by the SPEC78 code and were used for the source specification 'SDEF' card for MCNPX dose modeling. The copper modulation layer was located 20 cm away from a source covering half of the X-ray window. The radiation dose was measured as changing its thickness from 0.5 to 2.0 mm at intervals of 0.5 mm. Since the MCNPX tally provides only normalized values to a single particle, the dose conversion coefficients of F6 tally for the modulation layer-based dual energy CBCT should be calculated for matching the modeling results into the actual dose. The dose conversion coefficient is $7.2*10^4cGy/output$ that is obtained from dose calibration curve between F6 tally and experimental results in which GAFCHORMIC EBT3 films were exposed by an already known source. Consequently, the dose of the modulation layer-based dual energy cone beam CT is 33~40% less than that of the single energy CT system. On the basis of the results, it is considered that scattered dose produced by the copper modulation layer is very small. It shows that the modulation layer-based dual energy CBCT system can effectively reduce radiation dose, which is the major disadvantage of established dual energy CT.

Dosimetric Influence of Implanted Gold Markers in Proton Therapy for Prostate Cancer (전립선암에 대한 양성자치료에서 금마커에 의한 방사선 선량분포의 영향)

  • Kwak, Jung-Won;Shin, Jung-Wook;Kim, Jin-Sung;Park, Sung-Yong;Shin, Dong-Ho;Yoon, Myong-Geun;Park, So-Ah;Kim, Dong-Wook;Lim, Young-Gyeung;Lee, Se-Byeong
    • Progress in Medical Physics
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    • v.21 no.3
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    • pp.291-297
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    • 2010
  • This study examined the dosimetric influence of implanted gold markers in proton therapy and the effects of their positions in the spread-out Bragg peak (SOBP) proton beam. The implanted cylindrical gold markers were 3 mm long and 1.2 mm in diameter. The dosimetric influence of the gold markers was determined with markers at various locations in a proton-beam field. Spatial dose distributions were measured using a three-dimensional moving water phantom and a stereotactic diode detector with an effective diameter of 0.5 mm. Also, a film dosimetry was performed using Gafchromic External Beam Treatment (EBT) film. The GEANT4 simulation toolkit was used for Monte-Carlo simulations to confirm the measurements and to construct the dose-volume histogram with implanting markers. Motion data were obtained from the portal images of 10 patients to investigate the effect of organ motions on the dosimetric influence of markers in the presence of a rectal balloon. The underdosed volume due to a single gold marker, in which the dose was less than 95% of a prescribed amount, was 0.15 cc. The underdosed volume due to the presence of a gold marker is much smaller than the target volume. However, the underdosed volume is inside the gross tumor volume and is not smeared out due to translational prostate motions. The positions of gold markers and the conditions of the proton-beam field give different impacts on the dose distribution of a target with implanted gold markers, and should be considered in all clinical proton-based therapies.