A seismic study combined with well data of a circular oil field in Cass County, Michigan, indicates that the structure's origin may be related to an impact event. The structural closures in the time structure maps and drilling results both show a central uplift. The fault system in the Trempealeau Formation shows a structure similar to other proven astroblemes. Undisturbed layers just beneath the central uplift also provide an evidence of an impact structure. The impact event occurred on the Utica shale of the Late Ordovician age. The subsequent uplifting and erosion formed the missing of some Late Ordovician rocks in the center of the oil field. A delayed isostatic adjustment may resulted in the structural closures of the Silurian and Devonian sedimentary formations which played the role of structural trap as a hydrocarbon reservoir. The diameter of the original crater was at least 2 kilometers. The meteorite seems likely to be as heavy as about 9×10⁴ tons and as large as 36-50 meters in its diameter depending on itscomposition.

본 논문에서 얻은 결과를 요약하면 다음과 같다. 1) slamming 충격력에 의한 선각의 굽힘 모우멘트와 전단력의 계산은 본 논문의 이론 전개방법에 의해 구하는 것이 Antonides의 적용 방법보다 더 타당하다고 생각된다. 2) 수치계산 예에서 보면 선체 중앙단면에서 가장 큰 sagging moment가 발생하며 Antonides의 결과치 보다 3~5%정도 더 크게 나타났다. 3) 기준진동형의 중첩항 수는 주어진 문제의 특성 및 요구되는 정도에 따라 결정되어야 하므로 고차 진동형에 대한 실측치와 이론치의 비교 분석이 선행되어야 한다고 생각된다.

정면규칙파중에서 Bow-flare부 충격은 선저충격에 비해서 작용 시간이 길고, 선체 수직운동진폭이 큰 상태이거나, 파고가 큰 입사파가 적용되는 경우에 선체에 작용하는 충격력은 상당히 크며, 파고가 높아지면, 발생하는 모우멘트도 증가한다. 2. Bow-flare부가 큰 선형의 경우에는 선저노출이 일어나지 않더라도 부가질량의 급격한 증가에 따라 상당히 큰 충격력이 작용한다. 3. Deckwetness, 불규칙파중에서의 응답해석, 상대변위를 구할 때 Dynamic Swell-up의 양을 고려한 계산 등의 검토가 요망된다.

With continuous industrial development, the types, and amount of particulate matter (PM) have been increasing. Since 2018, environmental standards regarding PM have become more stringent. Pulse air jet bag filters are suitable for PM under the 20㎛ and, can function regardless of size, concentration and type. Filtration velocity and shape are important factors in the operation and design of the pulse air jet bag filters however, few established studies support this theory. In this research, numerical simulations were conducted based on experimental values and, several methods were employed for minimizing the pressure drop. In the pilot system, as the inlet duct velocity was faster than 19 m/sec, flow was not distributed equally and, re-entrainment occurred due to the hopper directional vortex. The multi-inlet system decelerated the hopper directional vortex by 25 ~ 30% , thereby decreasing total pressure drop by 6.6 ~ 14.7%. The guide vane system blocked the hopper directional vortex, which resulted optimal vane angle of 53°. The total pressure of the guide vane system increased by 0.5 ~ 3% at 1.5 m/min conditions. However, the filtration pressure drop decreased by 4.8 ~ 12.3% in all conditions, thereby reducing the operating cost of filter bags.

The numerical model was developed to estimate the transient behavior of pressure waves in pipe systems. The computational algorithm was proposed to model the water hammer phenomenon in a pipe system with pump shutdown at midstream and sudden valve closure at downstream. To predict the pressure head and the flow velocity as a function of time as a result of rapidly closing a valve and pump shutdown, two boundary conditions at the ends considering pump operation and valve control can be implemented as specified equations of the pressure head and flow velocity based on the characteristics method. It was shown that the effects of transient flow make it determine the needs for protection devices, such as surge tanks, surge relief valves, or air valves, at various points in the system against overpressure and low pressure. It produced reasonably good performance with the results of the proposed transient model for pipeline systems. The proposed numerical model can be used as an efficient tool for the safety assessment of hydropower plants due to water hammer.

Foot mechanisms play the role of interface between the main body of robotic systems and the ground. Biomimetic design of the foot mechanism is proposed in the paper. Specifically, multi-chained and multiple contact characteristics of general foot mechanisms are analyzed and their advantages are highlighted in terms of impulse. Using Newton-Euler based closed-form external and internal impulse models, characteristics of multiple contact cases are investigated through landing simulation of an articulated leg model with three kinds of foot. It is shown that in comparison to single chain and less articulated linkage system, multi-chain and articulated linkage system has superior characteristic in terms of impulse absorption as well as stability after collision. The effectiveness of the simulation result is verified through comparison to the simulation result of a commercialized software.

In this study, an analytical study on the effect of the support structure deflection on the impact test result was carried out to set up the accurate impact test method. Various impact analyses of the CEDM(control element drive mechanisms) impact test were performed using LS-DYNA commercial FE program. Finally, the effect of the boundary condition of the support structure and impact loading duration were investigated.

In this paper, the peak impact factor response spectrum is verified through finite element (FE) analysis using a simply supported bridge. The FE model is a slab bridge designed with 4 m width and 8 m length. The FE analysis is applied on the bridge modeled with 2D frame and 3D solid. By considering 5% damping ratio, the peak impact factors of the FE models and the response spectrum are compared. From the results, a very small difference of about 1.5% is found between the FE models and the response spectrum.

Current design standards (Korea Highway Bridge Design, AASHTO), the dynamic behavior under the impact loading has not been considered, only considered static force for designing bridge column against vehicle collisions. In this study, vehicle collisions to concrete bridge column were developed with various boundary conditions, and a comparison study of direct impact analysis of vehicle to bridge-column with in-direct impact analysis was performed.

In this study, impact elastic-wave method was performed at the bottom surface of RC slab cut from an existing highway bridges to survey the horizontal cracks. Before measurements by impact elastic-wave method, impact response analysis was applied to determine optimal steel ball diameter, distance between impact point and receiving point of elastic-wave. Efficiency of analysis-aided impact elastic-wave method was confirmed by drilling and observing the interior of the RC slab by stick scanner. Evaluation results by this method agreed well with results of visual inspection. Thus, validity of the analysis-aided impact elastic-wave method on detection of horizontal cracks in RC slabs of highway bridges was demonstrated.

본 연구에서는 강섬유와 FRP 시트에 의한 충격 저항성능 향상 효과를 평가하기 위하여 고속 충격하중을 받는 2방향 RC 슬래브에 대한 유한요소 해석을 수행하였다. 유한요소 해석 프로그램으로는 충격해석에 탁월하다고 알려진 LS-DYNA를 사용하였으며, 실험결과와의 비교를 위하여 핀란드 VTT 연구소에서 수행한 고속 충격 실험과 동일한 조건으로 해석을 수행하였다. 2100×2100×250 mm의 RC 슬래브에 강 (steel)발사체를 통해 충격하중을 가하였으며 발사체의 무게는 47.5kg, 속도는 134.9m/s였다. 본 연구에서는 별도의 재료부재에 대한 충격실험을 통해 해석에 사용할 재료 모델을 검증하였다. 본 해석에서는 SFRC의 비선형적 연화 현상을 모사하기 위해 elastic-plastic hydro model을 적용하였으며, 보통콘크리트와 FRP의 재료모델을 모사하기 위해서 concrete damage model과 orthotropic elastic model을 각각 사용하였다. 해석 결과, 제안된 해석 기법은 충분한 신뢰성을 가지고 있으며, 보강 재료와 보강 기법의 유효성을 평가하는데 효과적으로 적용할 수 있을 것으로 판단된다. 또한 강섬유와 FRP Sheets 보강방법은 고속충격하중에서 우수한 충격 저항 성능을 보여주는 것을 확인하였다.

Vibration resonance tests offer an efficient NDE method to identify and characterize shallow (near-surface) delamination defects that afflict RC structures. However, efficient implementation of effective modal analysis methods for this purpose is hindered by practical testing limitations. This paper studies vibration resonance data from square, rectangular, and circular near-surface delamination defects in concrete using air-coupled impact resonance test.

In this study, specimens were produced to reach design standard strengths 40, 50 and 60MPa on age 28 days to evaluate the usability of high strength recycled aggregate concrete and the applicability of compressive strength by Impact Echo method and numerical analysis, and after 0, 30, 50 and 100% recycled coarse aggregates were substituted and mixed into each combination, totally 12 combinations were set. And, through compressive strength test, Impact Echo method, shock reverberation technique and numerical analysis on 1, 3, 7 and 28 days of age

충격 하중 재하 실험의 경우 빠른 하중 재하 속도로 인해 실험 데이터를 측정하는 방법에 있어 많은 어려움이 있다. 또한 부재의 국부적 손상을 측정하지 못함으로써 부재의 동적 거동을 왜곡하는 문제점이 존재한다. 따라서, 본 연구에서는 충격 실험에서의 한계를 극복하기 위하여 명시적(explicit) 유한요소 해석 프로그램인 LS-DYNA를 이용하여 FRP Sheet 및 강섬유로 보강된 콘크리트의 저속 충격 하중 하에서의 동적 거동을 분석하였다. 해석 모델은 1방향 및 2방향 부재이며 충격 하중 재하 시 부재의 국부적 파괴를 고려하고 있다. 해석결과 강섬유에 의해 보강된 SFRC와 UHPC 부재의 경우 충격 저항성능이 크게 향상되었다. FRP Sheet로 보강한 경우 GFRP가 CFRP보다 우수한 충격 저항 성능을 보였으며 FRP Sheet의 방향성에 의한 영향은 크게 나타나지 않았다. 본 연구에서 수행된 해석은 충격 실험 결과와의 비교를 통해 그 신뢰성이 검증되었다.