• Geomechanics and Engineering
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• 제29권5호
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• pp.567-582
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• 2022

In the present study, a series of physical experiments and numerical simulations were conducted to investigate the effects of mode I and mixed-mode I/II cracks on the fracture modes and stability of roadway tunnel models. The experiments and simulations incorporated different inclination angle flaws under both static and dynamic loads. The quasi-static and dynamic testing were conducted by using an electro-hydraulic servo control device and drop weight impact system (DWIS), and the failure process was simulated by using rock failure process analysis (RFPA) and AUTODYN software. The stress intensity factor was also calculated to evaluate the stability of the flawed roadway tunnel models by using ABAQUS software. According to comparisons between the test and numerical results, it is observed that for flawed roadways with a single radical crack and inclination angle of 45°, the static and dynamic stability are the lowest relative to other angles of fractured rock masses. For mixed-mode I/II cracks in flawed roadway tunnel models under dynamic loading, a wing crack is produced and the pre-existing cracks increase the stress concentration factor in the right part of the specimen, but this factor will not be larger than the maximum principal stress region in the roadway tunnel models. Additionally, damage to the sidewalls will be involved in the flawed roadway tunnel models under static loads.

• 한국전산유체공학회지
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• 제15권1호
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• pp.71-80
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• 2010

The violent free-surface motions and the corresponding impact loads are numerically simulated by using the Moving Particle Semi-implicit (MPS) method, which was originally proposed by Koshizuka and Oka (1996) for incompressible flows. In the original MPS method, there were several shortcoming including non-optimal source term, gradient and collision models, and search of free-surface particles, which led to less-accurate fluid motions and non-physical pressure fluctuations. In the present study, how those defects can be remedied is illustrated by step-by-step improvements in respective processes of the revised MPS method. The improvement of each step is explained and numerically demonstrated. The numerical results are also compared with the experimental results of Martin and Moyce (1952) for dam-breaking problem. The current numerical results for violent free-surface motions and impact pressures are in good agreement with their experimental data.

• International Journal of Ocean System Engineering
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• 제2권3호
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• pp.151-159
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• 2012

The characteristics of an impact load and pressure were experimentally investigated. Drop tests were carried out using a modified Wigley with CB = 0.56. The vertical force, pressures, and vertical accelerations were measured. A 6-component load cell was used to measure the forces, piezo-electric sensors were used to capture the impact pressure, and strain-gauge type accelerometers were used to measure the vertical accelerations. A 50-kHz sampling rate was applied to capture the peak values. The repeatability of the measured data was confirmed and the basic characteristics of the impact load and pressure such as the linearity to the falling height were observed for all of the measurements. A simple formula was derived to extract the physical impact load from the measured force based on a simple mass-sensor-mass diagram, which was validated by comparing impact forces with existing data using the mathematical model of Faltinsen and Chezhian (2005). The effects of the elasticity of the model and change in acceleration during the water entry were investigated. It is interesting to observe that the impact loads occurred and reached peak values at the same time duration after water entry for all drop heights.

• Structural Engineering and Mechanics
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• 제64권2호
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• pp.183-194
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• 2017

This paper presents the experimental investigation into a new type of steel-concrete hybrid outrigger system developed for the high-rise building structure. The steel truss is embedded into the reinforced concrete outrigger wall, and both the steel truss and concrete outrigger wall work compositely to enhance the overall structural performance of the tower structures under extreme loads. Meanwhile, metal dampers of low-yield steel material were also adopted as a 'fuse' device between the hybrid outrigger and the column. The damper is engineered to be 'scarified' and yielded first under moderate to severe earthquakes in order to protect the structural integrity of important structural components of the hybrid outrigger system. As such, not brittle failure is likely to happen due to the severe cracking in the concrete outrigger wall. A comprehensive experimental research program was conducted into the structural performance of this new type of hybrid outrigger system. Studies on both the key component and overall system tests were conducted, which reveal the detailed structural response under various levels of applied static and cyclic loads. It was demonstrated that both the steel bracing and concrete outrigger wall are able to work compositely with the low-yield steel damper and exhibits both good load carrying capacities and energy dispersing performance through the test program. It has the potential to be applied and enhance the overall structural performance of the high-rise structures over 300 m under extreme levels of loads.

• Geomechanics and Engineering
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• 제14권1호
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• pp.19-27
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• 2018

It follows from the basic principles of mechanics of deformable solids relating to the strength, stability and propagation of elastic waves that the Earth's inner core cannot exist in the form of a spherical structure in the assumed thermobaric conditions and calculation values of physico-mechanical parameters. Pressure level reaches a value that is significantly greater than the theoretical limit of medium strength in the model approximations at the surface of the sphere of the inner core. On the other hand, equilibrium state of the sphere is unstable on the geometric forming at much lower loads under the influence of the "dead" surface loads. In case of the action of "follower" loads, the assumed pressure value on the surface of the sphere is comparable with the value of the critical load of "internal" instability. In these cases, due to the instability of the equilibrium state, propagation of homogeneous deformations becomes uneven in the sphere. Moreover, the elastic waves with actual velocity cannot propagate in such conditions in solid medium. Violation of these fundamental conditions of mechanics required in determining the physical and mechanical properties of the medium should be taken into account in the integrated interpretations of seismic and laboratory (experimental) data. In this case, application of the linear theory of elasticity and elastic waves does not ensure the reliability of results on the structure and composition of the Earth's core despite compliance with the required integral conditions on the mass, moment of inertia and natural oscillations of the Earth.

• 전산구조공학
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• 제10권4호
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• pp.195-203
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• 1997

본 논문에서는 충격이나 폭발하중에 의해 발생되는 응력파와 균열의 상호작용을 수치적으로 계산하였다. 수치해법으로는 응력파의 물리적 특징을 잘 재현시켜주는 Bicharacteristic Method가 사용되었다. 충격하중에 대한 동적응력확대계수 K/sub I/(t)가 수치해석적으로 시뮬레이션된 코오스틱곡선에 의해 계산되었으며, Kalthoff의 실험에 의해 얻어진 결과와 잘 일치함을 보여주었다. 또한 균열 주변에 구멍이 존재하는 경우에 응력파가 구멍의 효과에 의해 균열의 응력확대계수에 미치는 영향을 조사하였으며 실험과 비교하여 만족할만한 결과를 얻었다.

• 한국운동역학회지
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• 제23권3호
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• pp.245-252
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• 2013

The purpose of this study was to analyze the effect that various loads have on the lower limb biomechanics. The following variables were measured and analyzed; performance time for each phase, lower limb moments and joint angles, and ground reaction forces. The kinematic and kinetic data was recorded by 2 force platforms and a motion capture system while 12 healthy adults in their twenties stepped down three steps under loads of 0%, 10%, 20% BW. Results are as follows. First, the different loading conditions did not seem to significantly affect the performance times and the joint angles. Second, the largest ground reaction forces were observed at the 1 step at the 10% BW condition. Finally, at the 0% BW loading condition the right hip extension moment was the smallest and the left hip flexion moment was the largest. The results show that there are not any significant changes in the biomechanics of the lower limbs under loading conditions up to 20% BW. Further investigations including more loading conditions with more weights and more additional steps analyzed are needed.

• Wind and Structures
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• 제38권3호
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• pp.203-214
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• 2024

Large-span cantilevered roof represents a unique type of structure that is vulnerable to wind loads. Inspired by the need to maximumly reducing the rooftop wind loads, this study examined the feasibility of positioning vented slots on the leading edge, and the effectiveness of such aerodynamic mitigation measures are assessed via both physical and numerical simulations. The reliability of numerical simulation was evaluated via comparisons with the wind tunnel tests. The results indicated that, the variation of venting hole arrangement can cause significant change in the rooftop wind load characteristics. For the cases involved in this study, the maximum reduction of mean and peak wind suction coefficients are found to be 9% and 8% as compared to the original circular slot without venting holes. In addition, the effect of slot shape is also evident. It was shown that the triangular shaped slot tends to increase the wind suction near the leading edge, whereas the hexagonal and octagonal shaped slots are found to decrease the wind suction. In particular, with the installation of octagonal shaped slot, the maximum reduction of wind suction coefficients near the leading edge reaches up to 31% as compared to the circular shaped slot, while the maximum reduction of mean wind suction coefficients is about 30%.

• 산업경영시스템학회지
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• 제25권1호
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• pp.9-13
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• 2002

The objective of this study was to analyze and make comparison between the physical responses such as oxygen consumption rate, heart rate, and EMG-measurement for lifting tasks. Lifting activities with three different working frequencies(5, 8, 11 lifts/min) and two different weights(10, 20kg) for a lifting range(from floor to 76cm height) were studied. It was found that theme are positive correlations between the oxygen consumption rate and the EMG-measurements on the region of law back. Even though these physical responses were influenced by work weights and work frequency, it was found that the work frequency plays more important role in making muscle fatigue than the work weight. From these finding it is suggested that the work frequency should be considered as a more influencing factor than the work weight as long as the weight belongs to the permissible range based on the viewpoint of the biomechanical criterion for designing a job of manual materials handling tasks.

• Structural Engineering and Mechanics
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• 제81권3호
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• pp.259-266
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• 2022

Based upon differential quadrature method (DQM) and nonlocal strain gradient theory (NSGT), an investigation on the free vibrations of 2D plate systems with nano-dimensions has been provided taking into account the effects of different mechanical loadings. In order to capture different mechanical loadings, a general form of variable compressive load applied in the axial direction of the plate system has been introduced. The studied plate has been constructed from two types of particles which results in graded material properties and nanoscale pores. The established formulation for the plate is in the context of a novel shear deformable model and the equations have been solved via a semi-numerical trend. Presented results indicate the prominence of material composition, nonlocal coefficient, strain gradient coefficient and boundary conditions on vibrational frequencies of nano-size plate.