• Proceedings of the Korea Concrete Institute Conference
• /
• 2004.11a
• /
• pp.789-792
• /
• 2004

This study aims to detect only voids and estimate the cross-sectional size and thickness of voids using radar. A new method based on radar image processing is carried out with various void sizes and depths. The regression relationship between void size which has different depth and the amplitude characteristics of the radar return is considered in a new method of this research. For the purpose of examining; this regression relationship, experiments with change of void depth, surface area and thickness were carried out. Finally, the threshold value for image processing which aims to represent only voids to be fitted size (width) can be obtained. As the results, a proposed method in this study has a possibility of detecting only voids and estimating void size and thickness with good accuracy.

• Advances in aircraft and spacecraft science
• /
• v.10 no.5
• /
• pp.457-471
• /
• 2023

The paper evaluates the aerodynamic coefficients on a blunt-nose re-entry capsule with a conical cross-section followed by a cone-flare body. A computer code is developed to solve three-dimensional compressible inviscid equationsfor flow over a Space Recovery Experiment (SRE) configuration at different flare-cone half-angle at Mach 6 and angle of attack up to 5°, at 1° interval. The surface pressure variation is numerically integrated to obtain the aerodynamic forces and pitching moment. The numerical analysis reveals the influence of flare-cone geometry on the flow characteristics and aerodynamic coefficients. The numerical results agree with wind tunnel results. Increase of cone-flare angle from 25° to 35° results in increase of normal force slope, axial forebody drag, base drag and location of centre of pressure by 62.5%, 56.2% and 33.13%, respectively, from the basic configuration ofthe SRE of 25°.

• Journal of Korean Tunnelling and Underground Space Association
• /
• v.21 no.6
• /
• pp.779-793
• /
• 2019

The ventilation rate (Qreq) requirement in road tunnels is not just a basic information for determining the tunnel cross-sectional area, but also a major factor for the ventilation system selection. The Qreq is predominantly dependent on the vehicle traffic volume, while among others, the vehicle exhaust emissions and permissible standards are critical. This paper analyzes the changes in the Qreq designing criteria and/or recommendations suggested by World Road Association and local authorities over the last 20 years, since the first local designing criteria was established in 1997 by Korea Expressway Corporation. Additionally, based on the updated vehicle emission standards of Ministry of Environment and recent recommendations of the World Road Association (WRA), changes in the Qreq and its effects are studied in terms of the length and grade of the tunnel.

• Wind and Structures
• /
• v.30 no.6
• /
• pp.633-648
• /
• 2020

The objective of this work was to investigate the interference effects of two-parallel bridge decks on aerodynamic coefficients, vortex-induced vibration, flutter instability and flutter derivatives. The two bridges have significant difference in cross-sections, dynamic properties, and flutter speeds of each isolate bridge. The aerodynamic static tests and aeroelastic tests were performed in TU-AIT boundary layer wind tunnel in Thammasat University (Thailand) with sectional models in a 1:90 scale. Three configuration cases, including the new bridge stand-alone (case 1), the upstream new bridge and downstream existing bridge (case 2), and the downstream new bridge and the upstream existing bridge (case 3), were selected in this study. The covariance-driven stochastic subspace identification technique (SSI-COV) was applied to identify aerodynamic parameters (i.e., natural frequency, structural damping and state space matrix) of the decks. The results showed that, interference effects of two bridges decks on aerodynamic coefficients result in the slightly reduction of the drag coefficient of case 2 and 3 when compared with case 1. The two parallel configurations of the bridge result in vortex-induced vibrations (VIV) and significantly lower the flutter speed compared with the new bridge alone. The huge torsional motion from upstream new bridge (case 2) generated turbulent wakes flow and resulted in vertical aerodynamic damping H1^* of existing bridge becomes zero at wind speed of 72.01 m/s. In this case, the downstream existing bridge was subjected to galloping oscillation induced by the turbulent wake of upstream new bridge. The new bridge also results in significant reduction of the flutter speed of existing bridge from the 128.29 m/s flutter speed of the isolated existing bridge to the 75.35 m/s flutter speed of downstream existing bridge.

• The Journal of Korean Orthopaedic Ultrasound Society
• /
• v.1 no.1
• /
• pp.64-72
• /
• 2008

Compression neuropathy around elbow and wrist are one of the common disturbing problems in the upper extremity. The understanding of normal nerve architectures and pathophysiologic changes in compression neuropathy is important to interpret the ultrasonographic images correctly. Compression neuropathies have characteristic ultrasonographic imaging features of flattened nerve at compression and hypoechoic swollen nerve with loss of fascicular patterns at proximal segments. Dynamic ultrasonographic imagings on motion can show dymanic subluxation of ulnar nerve and medial head of triceps muscle over the medial epicondyle in snapping triceps syndrome. Dynamic compression of median nerve also can be visualized in pronator teres syndrome by dynamic imaging studies. A quantitative measures of cross sectional area or compression ratio can be helpful to diagnose compression neuropathies, such as carpal tunnel syndrome or cubital tunnel syndrome. With the clinical features and electeophysiologic studies, the untrasonographic imagings are useful tool for evaluation of the compression neuropathies in the upper extremities.

• Wind and Structures
• /
• v.17 no.2
• /
• pp.163-184
• /
• 2013

An accurate identification of the aerodynamic characteristics of vehicles and the bridge is the premise for the coupled vibration analysis of a wind-vehicle-bridge system. At present, the interaction of aerodynamic forces between the road vehicles and bridge is ignored in most previous studies. In the present study, an experimental setup was developed to measure the aerodynamic characteristics of vehicles and the bridge for different cases in a wind tunnel considering the aerodynamic interference. The influence of the wind turbulence, the wind speed, the vehicle interference, and the vehicle position on the aerodynamic coefficients of vehicles, and the influence of vehicles on the static coefficients of the bridge were investigated, based on the experimental results. The variations in the aerodynamic characteristics of vehicles and the bridge were studied and the measured results were validated according to the results of surface pressure measurements on the vehicle and the bridge. The measured results were further validated by comparing the measured results with values derived numerically. The measured results showed that the wind turbulence, the vehicle interference, and the vehicle position significantly affected the aerodynamic coefficients of vehicles. However, the influence of the wind speed on the aerodynamic coefficients of the studied vehicle is small. The static coefficients of the bridge were also significantly influenced by the presence of vehicles.

• Wind and Structures
• /
• v.20 no.2
• /
• pp.349-361
• /
• 2015

Higher-mode vertical vortex-induced vibrations (VIV) have been observed on several steel box-girder suspension bridges where different vertical modes are selectively excited in turn with wind velocity in accordance with the Strouhal law. Understanding the relationship of VIV amplitudes for different modes of vibration is very important for wind-resistant design of long-span box-girder suspension bridges. In this study, the basic rectangular cross-section with side ratio of B/D=6 is used to investigate the effect of different modes on VIV amplitudes by section model tests. The section model is flexibly mounted in wind tunnel with a variety of spring constants for simulating different modes of vibration and the non-dimensional vertical amplitudes are determined as a function of reduced velocity U/fD. Two 'lock-in' ranges are observed at the same onset reduced velocities of approximately 4.8 and 9.4 for all cases. The second 'lock-in' range, which is induced by the conventional vortex shedding, consistently gives larger responses than the first one and the Sc-normalized maximum non-dimensional responses are almost the same for different spring constants. The first 'lock-in' range where the vibration frequency is approximately two times the vortex shedding frequency is probably a result of super-harmonic resonance or the "frequency demultiplication". The main conclusion drawn from the section model study, central to the higher-mode VIV of suspension bridges, is that the VIV amplitude for different modes is the same provided that the Sc number for these modes is identical.

• Wind and Structures
• /
• v.25 no.4
• /
• pp.343-360
• /
• 2017

The post-flutter state of streamlined steel box girder is studied in this paper. Firstly, the nonlinear aerodynamic self-excited forces of the bridge deck cross section were investigated by CFD dynamic mesh technique and then the nonlinear flutter derivatives were identified on this basis. Secondly, based on the 2-degree-of-freedom (DOF) coupling flutter theory, the torsional amplitude and the nonlinear flutter derivatives were introduced into the traditional direct flutter calculation method, and the original program was improved to the "post-flutter state analysis program" so that it can predict not only the critical flutter velocity but also the movement of the girder in the post-flutter state. Finally, wind tunnel tests were set to verify the method proposed in this paper. The results show that the effect of vertical amplitude on the nonlinear flutter derivatives is negligible, but the torsional amplitude is not; with the increase of wind speed, the post-flutter state of streamlined steel box girder includes four stages, namely, "little amplitude zone", "step amplitude zone", "linearly growing amplitude zone" and "divergence zone"; damping ratio has limited effect on the critical flutter velocity and the steady state response in the post-flutter state; after flutter occurs, the vibration form is a single frequency vibration coupled with torsional and vertical DOF.

• Journal of Korean Tunnelling and Underground Space Association
• /
• v.5 no.2
• /
• pp.209-216
• /
• 2003

The present with in this country, rock bolt installation, shotcrete, and concrete lining in construction order has become accepted as a general tunnelling method in NATM. On the other hand Unlined tunnelling method, which was developed by many countries near Scandinavian Peninsula with hard rocks comparatively, has recently been introduced all over the world, and numerous studies about that have been being devoted to domestic tunnels. Unlined tunnelling method has been developed on the basis of the permanently unsupported openings, and general 7 requirements for them were suggested by Nick Barton. There are no case record about these conditions for Q-system in this country. Therefore, input parameters for Q-system under these conditions were applied to general road tunnel cross-section and numerical analyses for each condition were executed with UDEC-BB, Distinct Element Method.

• Structural Engineering and Mechanics
• /
• v.64 no.4
• /
• pp.449-459
• /
• 2017

High-rise buildings are generally sensitive to strong winds. The evaluation of wind loads for the structural design, structural health monitoring (SHM), and vibration control of high-rise buildings is of primary importance. Nevertheless, it is difficult or even infeasible to measure the wind loads on an existing building directly. In this regard, a new inverse method for evaluating wind loads on high-rise buildings is developed in this study based on a discrete-time Kalman filter. The unknown structural responses are identified in conjunction with the wind loads on the basis of limited structural response measurements. The algorithm is applicable for estimating wind loads using different types of wind-induced response. The performance of the method is comprehensively investigated based on wind tunnel testing results of two high-rise buildings with typical external shapes. The stability of the proposed algorithm is evaluated. Furthermore, the effects of crucial factors such as cross-section shapes of building, the wind-induced response type, errors of structural modal parameters, covariance matrix of noise, noise levels in the response measurements and number of vibration modes on the identification accuracy are examined through a detailed parametric study. The research outputs of the proposed study will provide valuable information to enhance our understanding of the effects of wind on high-rise buildings and improve codes of practice.