• Journal of the Korean Society for Aviation and Aeronautics
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• v.32 no.2
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• pp.135-141
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• 2024

Despite the innovative technological advances in the aviation industry, hard landing events that occur during aircraft landing account for 13% of all accidents. Hard landing when landing an aircraft affects normal operation by generating a large load on the landing gear and the fuselage. In order to identify these risk factors, the airline monitors the high vertical acceleration event, a precursor to hard landing, through QAR (Quick Access Recorder) flight data analysis, and prepares and implements mitigation measures. In this study, it is intended to contribute to safety management based on flight data analysis that identifies the characteristics of high vertical acceleration G event data that can cause such hard landing and detailed parameters of precursor signs, and to identify the causal relationship of the occurrence of the event by applying statistical analysis methods such as variance analysis, correlation analysis, and regression analysis models to identify the characteristics of the event occurrence and eliminate the cause in advance.

• Journal of the Korean GEO-environmental Society
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• v.12 no.1
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• pp.81-87
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• 2011

The characteristics of vertical to horizontal ratio of response spectrum from 20 recent earthquakes were analysed. Response spectrum of 260 horizontal and 130 vertical ground motions were normalized by peak ground acceleration at each resonance frequency from 0.1 to 50Hz. It has been identified that the ratio of vertical to horizontal response spectrum has strong dependancy on epicentral distance and resonance frequency. The ratio of vertical to horizontal response spectrum for the 0-50km epicentral distance group are larger than 2/3 values, which is a standard engineering rule-of-thumb V/H=2/3, at resonance frequency above 7-8Hz. All the 3 groups such as 50-100, 100-150- and 150-200km epicentral distance have shown larger values of vertical to horizontal ratio than 2/3 at resonance frequency above 15Hz and also are larger than 2/3 at resonance frequency below 8-10Hz. Even though there are differences in specific resonance frequency values which depend on the epicentral distance group, we should be careful of seismic design of vertical component of the structures winch are located within the range of about 200km distance. form the potentially seismic causative faults.

• 한국방재학회:학술대회논문집
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• 2011.02a
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• pp.74-74
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• 2011

본 연구에서는 중앙경간 54m, 교폭 4m의 사장교형식의 보도교로 측경간은 계단으로 이루어진 1경간 케이블교량을 대상으로 보행하중에 의한 수직진동을 제어하기 위해 제진장치(TMD)를 적용하기로 하고 실물 TMD의 설계 및 제작 그리고 설치 및 제어성능실험을 수행하였다. 우선 사장교형식의 교량. 그리고 1경간 교량이라는 점에서 상대적으로 감쇠율이 낮을 것으로 예측되었고 또한 54m의 경간장이 보행자가 가진 주파수에 근접한 고유진동수를 나타낼 것으로 사료되어 Eurocode 2 part 2(EC5-2)의 규준에 따라 1인 및 다수 보행하중에 의한 보도교의 발생가속도를 산출하였다. 이 경우 최대가속도는 다수의 보행자가 연속적으로 진행할 때 발생하였으며, 수직방향의 가속도가 사용성기준을 초과하는 것으로 나타났다. 또한 구조해석프로그램에 의한 고유치 해석결과, 보행하중의 주파수대역내에 진동모드가 존재하는 것으로 나타났다. 따라서 본 교량의 설계단계에 있어서 보행진동을 제어하기 위하여 유지관리가 용이한 수동형의 동조질량감쇠장치(Tuned Mass Damper)를 적용하기로 하였으며 TMD의 설계에서는 TMD의 제어목표를 만족시킬 수 있는 TMD의 가동질량(moving mass)을 우선적으로 결정하였고, 이로부터 Den Hartog의 제안식에 따라 TMD의 고유진동수비, 유효감쇠비를 산정하였다. 산정된 변수들을 이용하여 설계된 TMD는 현장설치 및 튜닝의 편의성을 고려하여 수평 외팔보형식으로 설계, 제작되었으며 제작된 TMD의 경우 회전축에 대해 질량, 스프링, 댐퍼의 중심거리를 조정함으로써 TMD의 진동수, 강성, 감쇠력을 상대적으로 매우 용이하게 조절할 수 있으며, 조정범위 또한 광범위하여 일반 TMD에 비해 현장설치시 대상구조물에 동조시키기가 용이하며, 작동시 마찰감쇠가 거의 없다는 장점이 있다. 현장설치전에 제작된 TMD를 대상으로 자유진동 시험을 통하여 질량의 중심거리, 스프링 크기 그리고 댐퍼의 설치유무를 각각 변화시키며 TMD의 자유진동 데이터를 취득하였다. 각각의 시험에서 얻어진 데이터로부터 스펙트럼해석을 통하여 고유진동수를 구하였고, 자유진동 파형으로 부터 감쇠비를 구하였다. TMD는 일반적으로 제어모드의 변형형상이 가장 큰 곳에 설치되었을 때 최대의 제진효과를 발휘할 수 있다. 그러나 현장여건상 설치가 불가능하거나 미관을 해치는 경우에는 가능한 범위 내에서 TMD 제어효율이 가장 크게 발휘할 수 있는 곳을 선택하여야 한다. 본 보도교의 경우, 중앙경간 중심부에서 가장 큰 모드변형형상을 나타내지만, 보도교의 상판 연결부 등에 따른 TMD 시공문제로 인하여 TMD 설치위치는 교량 중앙에서 양 방향으로 1.25m 떨어진 곳에 대칭으로 총 2기를 설치하기로 하였다. 일반적으로 TMD의 모든 설계변수는 구조물의 설계단계에서 수행된 구조해석결과에 근거하여 설정하므로 완공된 구조물, 즉 실제보도교의 동적특성을 계측하여 정확하게 진동수를 튜닝하여야 한다. 구조해석에 의한 보도교의 수직방향(TMD 작동방향) 고유진동수는 1.5225 Hz이며, 감쇠비는 규준에 의하여 0.6 %로 가정하였다. 그러나 이 값들은 구조해석모델 및 재료적 특성과 시공상의 오차에 의하여 실제와 다를 수 있으므로 현장계측에 의한 확인이 요구된다. 또한 TMD의 제진효율이 설계시의 목표대로 확보되었는지도 확인해야 하므로 현장튜닝 및 성능시험을 실시하였다. 보도교의 가진은 사전에 실시한 상시 미진동계측결과를 토대로 2Hz를 목표로 하여 인력가진실험을 수행하였고, 탁월진동 주파수는 1.9896Hz로 나타나 구조해석결과와 오차가 있음을 알 수 있다. 가진실험결과를 토대로 TMD의 진동수를 최적진동수비로 튜닝하고 인력가진 실험을 다시 실시하여 TMD의 진동제어성능을 검토하였다. TMD 튜닝 전, 후의 보도교 감쇠비를 비교한 결과, TMD를 설치함으로써 약 4.218%의 감쇠비 증가가 있음을 알 수 있다.

• Journal of Aerospace System Engineering
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• v.15 no.5
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• pp.33-42
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• 2021

Modern aircraft fighters improve the maneuverability and performance with the RSS (Relaxed Static Stability) concept and therefore these aircrafts are susceptible to abrupt pitch-up in the transonic and moderate Angle-of-Attack (AoA) flight region where the shock wave is formed and the mean aerodynamic center is moved forward during deceleration. Also, the modeling of the aircraft flying in this flight region is very difficult due to complex flow filed and unpredictable dynamic characteristics and the model-based control design technique does not fully cover this problem. In this paper, we analyzed the performance of the TPMC (Transonic Pitching Moment Compensation) control based on the model-based IDI (Incremental Dynamic Inversion) and the Hybrid IDI based on the model and sensor based IDI during the SDT (Slow Down Turn) in transonic region. As the result, the Hybrid IDI had quicker response and the same maximum g suppression performance and provided the predictable flying qualities compared to the TPMC control. The Hybrid IDI improved the performance of the Over-G protection controller in the transonic and moderate AoA region

• Tunnel and Underground Space
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• v.19 no.6
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• pp.490-497
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• 2009

The horizontal and vertical response spectra using the observed ground motion from the recent 5 macro earthquakes were analysed and then were compared to both the seismic design response spectra(Reg Guide 1.60), applied to the domestic nuclear power plants, and the Korean Standard Design Response Spectrum for general structures and buildings(1997). 74 horizontal and 89 vertical observed ground motions, without considering soil types, were used for normalization with respect to the peak acceleration value of each ground motion. The results showed that the horizontal MPOSD(Mean Plus One Sigma Standard Deviation) response spectra revealed much higher values for the whole frequency bands above 1 Hz than Reg. Guide(1.60). For the vertical response spectra, the results showed slightly higher than just between 7 and 8 Hz frequency band. The results were also compared to the Korean Standard Response Spectrum for the 3 different soil types and showed that the horizontal MPOSD response spectra revealed much higher values for the whole periods below 2 second(0.5 Hz) than those of SE soil type. The vertical response spectra showed similar to the values of the Korean Standard Response Spectrum of SD soil type. These spectral values dependent on frequency could be related to characteristics of the domestic crustal attenuation and the effect of each site amplification. However, through the qualitative improvements and quantitative enhancement of the observed ground motions, the conservation of horizontal seismic design response spectrum should be considered more significantly for the whole frequency bands above the 1 Hz.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.20 no.12
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• pp.53-59
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• 2019

To reduce the vibrations and shocks during the cargo transportation of high value-added goods, the vibration history was measured on the truck transportation section (Asan-Uiwang) and the freight train transportation section (Uiwang-Pusan). The internal vibrations of the container were obtained by attaching acceleration sensors in three axis directions (longitudinal, lateral. and vertical directions) on the front and rear bogies. The rail vibration profile (0.29Grms) proposed in ASTM D-4169 was approximately 50% higher than the truck vibration profile (0.54Grms). The overall vibration was 16% and 33 % lower in the longitudinal and transverse directions, respectively, compared to the ASTM truck transport vibration profile. On the other hand, the vertical vibration measurement history partially exceeded the ASTM truck transport vibration profile over the range, 4 - 15Hz, and over 60Hz. The vibration measurement history of the cargo train was similar to that of the road. The longitudinal and lateral vibration history was lower than the ASTM D-4169 rail vibration profile, while the vertical history was over 30Hz.

• Geophysics and Geophysical Exploration
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• v.13 no.3
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• pp.227-234
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• 2010

The vertical response spectra using the observed ground motions from the recent more than 30 macro earthquakes were analysed and then were compared both to the seismic design response spectra (Reg Guide 1.60), applied to the domestic nuclear power plants, and to the Korean Standard Design Response Spectrum for general structures and buildings (1997). 176 vertical ground motions, without considering soil types, were used for normalization with respect to the peak acceleration value of each ground motion. The results showed that response spectrum had strong dependency on epicentral distance. The results also showed that the vertical response spectra revealed much higher values for frequency bands above 5~7 Hz than Reg. Guide (1.60). The results were also compared to the Korean Standard Response Spectrum for the 3 different soil types and showed that the vertical response spectra revealed much higher values for the frequency bands below 0.2 second (5 Hz) than the Korean Standard Response Spectrum (SD soil condition). These frequency-dependent spectral values could be related to the characteristics of the domestic crustal attenuation and the effect of each site amplification. However, through the qualitative improvements and quantitative enhancement of the observed ground motions, the conservation of vertical seismic design response spectrum should be considered more significantly for the frequency bands above 5 Hz.

• Journal of Korean Society of Steel Construction
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• v.22 no.1
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• pp.1-12
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• 2010

According to the capacity design concept which forms the basis of the current steel seismic codes, the braces in concentrically braced frames (CBFs) should dissipate seismic energy through cyclic tension yielding and cyclic compression buckling while the beams and the columns should remain elastic. Brace buckling in inverted V-braced frames induces unbalanced vertical forces which, in turn, impose the additional beam moments and column axial forces. However, due to difficulty in predicting the location of buckling stories, the most conservative approach implied in the design code is to estimate the column axial forces by adding all the unbalanced vertical forces in the upper stories. One alternative approach, less conservative and recommended by the current code, is to estimate the column axial forces based on the amplified seismic load expected at the mechanism-level response. Both are either too conservative or lacking technical foundation. In this paper, three combination rules for a rational estimation of the column axial forces were proposed. The idea central to the three methods is to detect the stories of high buckling potential based on pushover analysis and dynamic behavior. The unbalanced vertical forces in the stories detected as high buckling potential are summed in a linear manner while those in other stories are combined by following the SRSS(square root of sum of squares) rule. The accuracy and design advantage of the three methods were validated by comparing extensive inelastic dynamic analysis results. The mode-shape based method(MSBM), which is both simple and accurate, is recommended as the method of choice for practicing engineers among the three.