• Journal of information and communication convergence engineering
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• v.11 no.2
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• pp.82-94
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• 2013

In this paper, we propose a novel tunnel-free scheme in a proxy mobile IPv6 (PMIPv6)-based nested network mobility environment; several mobile nodes (MNs) and mobile routers (MRs) compose a hierarchical wireless network topology. Because tunnels created by several MRs overlap and data packets travel along several local mobility anchors (LMAs), the utilization of the wireless section is reduced and the packet forwarding path of the wire-line section is not optimal. In our tunnel-free scheme, the mobile access gateway (MAG) plays an important role in both the wireless and wire-line sections. Using a local binding update, this tunnel-free scheme forwards data packets with a host-based routing table without any tunnel. Establishing a direct tunnel between the MAG and the last LMA, this scheme removes nested tunnels between intermediate LMAs and MRs, and optimizes the forwarding path to the MN in the wire-line section.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2005.05a
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• pp.772-775
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• 2005

Most engineers, related to soil and civil dynamic field, have been interested in the direct dynamic design of building transmitted from soil and rock to structure due to blasting. However it is not easy to estimate the dynamic response of structures due to blasting by using analytical method because of difficulties of soil modeling, prediction of excitation force and so on. In this paper, dynamic analysis have been performed to predict vibration level and evaluate dynamic safety of structure adjacent to tunnel blast and the semi empirical method, which is based on vibration measurement data, has been employed to consider blast vibration characteristics.

• Wind and Structures
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• v.35 no.5
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• pp.323-336
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• 2022

This study investigates the applicability of the direct identification of flutter derivatives in the time domain using Rational Function Approximation (RFA), where the extraction procedure requires either a combination of at least two wind speeds or one wind speed. In the frequency domain, flutter derivatives are identified at every wind speed. The ease of identifying flutter derivatives in the time domain creates a paradox because flutter derivative patterns sometimes change in higher-order polynomials. The first step involves a numerical study of RFA extractions for different deck shapes from existing bridges to verify the accurate wind speed combination for the extraction. The second step involves validating numerical simulation results through a wind tunnel experiment using the forced vibration method in one degree of freedom. The findings of the RFA extraction are compared to those obtained using the analytical solution. The numerical study and the wind tunnel experiment results are in good agreement. The results show that the evolution pattern of flutter derivatives determines the accuracy of the direct identification of RFA.

• Wind and Structures
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• v.15 no.6
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• pp.495-508
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• 2012

The present paper is focused on the prediction of the acrosswind aeroelastic response of square tall buildings. In particular, a semi-analytical procedure is proposed based on the assumption that square tall buildings, for reduced velocities corresponding to operational conditions, do not experience vortex shedding resonance or galloping and fall in the range of positive aerodynamic damping. Under these conditions, aeroelastic wind tunnel tests can be unnecessary and the response can be correctly evaluated using wind tunnel tests on rigid models and analytical modeling of the aerodynamic damping. The proposed procedure consists of two phases. First, simultaneous measurements of the pressure time histories are carried out in the wind tunnel on rigid models, in order to obtain the aerodynamic forces. Then, aeroelastic forces are analytically evaluated and the structural response is computed through direct integration of the equations of motion considering the contribution of both the aerodynamic and aeroelastic forces. The procedure, which gives a conservative estimate of the aeroelastic response, has the advantage that aeroelastic tests are avoided, at least in the preliminary design phase.

• Journal of Mechanical Science and Technology
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• v.18 no.6
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• pp.1002-1009
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• 2004

Direct contact air conditioning systems, in which heat and mass are transferred directly between air and water droplets, have many advantages over conventional indirect contact systems. The purpose of this research is to investigate the cooling and heating performances of direct contact air conditioning system for various inlet parameters such as air velocity, air temperature, water flow rate and water temperature. The experimental apparatus comprises a wind tunnel, water spray system, scrubber, demister, heater, refrigerator, flow and temperature controller, and data acquisition system. The inlet and outlet conditions of air and water are measured when the air contacts directly with water droplets as a counter flow in the spray section of the wind tunnel, and the heat and mass transfer rates between air and water are calculated. The droplet size of the water sprays is also measured using a Malvern Particle Analyzer. In the cooling conditions, the outlet air temperature and humidity ratio decrease as the water flow rate increases and as the water temperature, air velocity and temperature decrease. On the contrary, the outlet air temperature and humidity ratio increase in the heating conditions as the water flow rate and temperature increase and as the air velocity decreases.

• Proceedings of the Korean Geotechical Society Conference
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• 2008.03a
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• pp.494-504
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• 2008

Successful design, construction and maintenance of NATM tunnel demands prediction, control, stability estimation and monitoring of surface settlement, gradient and ground displacement with high accuracy. Back analysis using measured data and forward analysis have been and are indispensable tools to achieve this goal. Sakurai provided the hazard warning levels for assessing the stability of tunnels using the relation of critical strain and apparent Young's modulus. This paper performed the estimation of tunnel stability on construction. Firstly, the apparent Young's modulus concept and back analysis method is introduced for the assessment of tunnel safety during excavation a brief framework. Secondly, this paper deals with case study using "Apparent Young's modulus" and "Back analysis" for the purpose of estimating the stability of NATM tunnel in Korea. Finally, a general method that can be estimated the tunnel stability discussed by a flow chart.

• Geomechanics and Engineering
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• v.24 no.4
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• pp.323-335
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• 2021

This paper aims to estimate the range of the excavation damaged zone (EDZ) formation caused by the tunnel boring machine (TBM) advancement through dynamic three-dimensional large deformation finite element analysis. Large deformation analysis based on Coupled Eulerian-Lagrangian (CEL) analysis is used to accurately simulate the behavior during TBM excavation. The analysis model is verified based on numerous test results reported in the literature. The range of the formed EDZ will be suggested as a boundary under various conditions - different tunnel diameter, tunnel depth, and rock type. Moreover, evaluation of the integrity of the tunnel structure during excavation has been carried out. Based on the numerical results, the apparent boundary of the EDZ is shown to within the range of 0.7D (D: tunnel diameter) around the excavation surface. Through series of numerical computation, it is clear that for the rock of with higher rock mass rating (RMR) grade (close to 1st grade), the EDZ around the tunnel tends to increase. The size of the EDZ is found to be direct proportional to the tunnel diameter, whereas the depth of the tunnel is inversely proportional to the magnitude of the EDZ. However, the relationship between the formation of the EDZ and the stability of the tunnel was not found to be consistent. In case where the TBM excavation is carried out in hard rock or rock under high confinement (excavation under greater depth), large range of the EDZ may be formed, but less strain occurs along the excavation surface during excavation and is found to be more stable.

• Proceedings of the Korean Geotechical Society Conference
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• 2008.03a
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• pp.848-857
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• 2008

In September 2007, the collapses of slopes and landslides are happened at Jeonlanamdo due to heavy rains accompanied with Typoon "Nari". The study area is the tunnel portal slope in new road construction site. This slope consists of pyroclastic rocks and has lots of faults. Particularly, the residual soils of the slope is deteriorated with yellowish mudstone layer as a results of chemical and physical weathering. This has a variety of swelling clay minerals and might be moved easily down at the gentle terrain. The inner factor of $\bigcirc\bigcirc$tunnel portal slope's collapse is the geological weak zone, the convergent topography, the inferiority of drainage and the heavy rain act on the failure as direct trigger.

• Proceedings of the Korean Geotechical Society Conference
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• 2006.03a
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• pp.916-924
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• 2006

This research concentrates on presenting a more reasonable and engineering tunnel interpretation method with the numerical value observation data using the Hoek-Brown Model that uses mining observation data gained during construction, and the experience material constant of m and s for Seoul Underground tunnel field, which was evaluated as RMR III and RMR IV for its bedrock ratings, and by modifying and complementing the properties of ground materials with the direct method, one method in back analysis, and by using the field measurement value.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.17 no.4
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• pp.294-306
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• 2005

Most immersed tunnels investigated have been investigated based on the engineer's experience with design and construction. From engineering point of view, it is very important to understand the wave interaction with the seabed and immersed tunnel, since the stability of an immersed tunnel depends largely on the behavior of the seabed foundation. In this study, for the first stage research to find out the mechanism of the wave interaction with the seabed and immersed tunnel, the benchmarking method called as direct numerical simulation (DNS) was employed to analyze comprehensively the wave-induced pore water pressures, vorticity and flows in seabed or inside rubble stone around the immersed tunnel. The immersed tunnel is modeled based on Busan-Geoje fixed link project in Korea, which is now on the stage of planning. Moreover, the nonlinear water wave interaction with an immersed tunnel/its seabed foundation was thoroughly examined with regard to the stabilities of the immersed tunnel subjected to various water wave conditions, median grain size and so forth.