• Steel and Composite Structures
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• 제17권6호
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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.

• 한국터널지하공간학회 논문집
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• 제6권3호
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• pp.247-258
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• 2004

본 연구에서는 터널내 탄성파 탐사로부티 터널막장 전방 파쇄대를 예측하기 위한 두 가지의 3차원 구조보정 기법을 제안하였다. 첫 번째 해석기법은 타원체의 원리에 기초한 것으로 터널 양쪽 벽면에서 각각 독립적으로 탄성파 탐사를 수행하여 얻은 2차원 해석 결과를 이용하여 3차원 구조보정을 수행할 수 있다. 두 번째 해석기법은 파전파 평면의 개념을 도입한 것으로 터널내 탄성파탐사를 터널 한쪽 벽면에서만 송신을 수행한 반면, 수진기는 양쪽 벽면에 설치한 경우에 적용할 수 있는 기법이다. 새로운 구조보정 기법을 현장 터널내 탄성파 탐사 자료에 적용해 보았다. TSP 시험자료를 이용하여 3차원 구조보정을 수행한 후, 그 결과를 터널 굴착과정 중 조사된 지질정보와 비교해 보았다. 그 결과 제안된 구조보정 기법을 통하여 불연속면의 형상을 비교적 정확히 예측할 수 있음을 확인하였다.

• 천문학회지
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• 제36권spc1호
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• pp.101-107
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• 2003

The magnetosphere is often perturbed by impulsive input such as interplanetary shocks and solar wind discontinuities. We study how these initial perturbations are propagating within the magnetosphere over various latitude regions by adopting a three-dimensional numerical dipole model. We examine the wave propagation on a meridional plane in a time-dependent manner and compare the numerical results with multi-satellite and ground observations. The dipole model is used to represent the plasmasphere and magnetosphere with a realistic Alfven speed profile. It is found that the effects of refraction, which result from magnetic field curvature and inhomogeneous Alfven speed, are' found to become important near the plasmapause. Our results show that, when the disturbances are assumed at the subsolar point of the dayside magnetosphere, the travel time becomes smaller to the polar ionosphere compared to the equatorial ionosphere.

• Clinics in Shoulder and Elbow
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• 제26권4호
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• pp.416-422
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• 2023

Background: Advancements in airport screening measures in response to 9/11 have resulted in increased false alarm rates for patients with orthopedic and metal implants. With the implementation of millimeter-wave scanning technology, it is important to assess the changes in airport screening experiences of patients who underwent total shoulder arthroplasty (TSA). Methods: Here, 197 patients with prior anatomic and reverse TSA completed between 2013 and 2020 responded to a questionnaire regarding their experiences with airport travel screening after their operation. Of these patients, 86 (44%) stated that they had traveled by plane, while 111 (56%) had not. The questionnaire addressed several measures including the number of domestic and international flights following the operation, number of false alarm screenings by the millimeter-wave scanner, patient body habitus, and presence of additional metal implants. Results: A total of 53 patients (62%) responded "yes" to false screening alarms due to shoulder arthroplasty. The odds of a false screening alarm for patients with other metal implants was 5.87 times that of a false screening alarm for patients with no other metal implants (P<0.1). Of a reported 662 flights, 303 (45.8%) resulted in false screening alarms. Greater body mass index was not significantly lower in patients who experienced false screening alarms (P=0.30). Conclusions: Patients with anatomic and reverse TSA trigger false alarms with millimeter-wave scanners during airport screening at rates consistent with prior reports following 9/11. Patient education on the possibility of false alarms during airport screening is important until improvements in implant identification are made. Level of evidence: IV.

• Journal of Mechanical Science and Technology
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• 제17권9호
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• pp.1268-1275
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• 2003

In this paper, a compact 3-DOF mobile microrobot with sub-micron resolution is presented. It has many outstanding features : it is as small as a coin ; its precision is of sub-micrometer resolution on the plane ; it has an unlimited travel range ; and it has simple and compact mechanisms and structures which can be realized at low cost. With the impact actuating mechanism, this system enable both fast coarse motion and highly precise fine motion with a pulse wave input voltage controlled. The 1 -DOF impact actuating mechanism is modeled by taking into consideration the friction between the piezoelectric actuator and base. This modeling technique is extended to simulate the motion of the 3-DOF mobile robot. In addition, experiments are conducted to verify that the simulations accurately represent the real system. The modeling and simulation results will be used to design the model-based controller for the target system. The developed system can be used as a robotic positioning device in the micromanipulation system that determines the position of micro-sized components or particles in a small space, or assemble them in the meso-scale structure.