• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2007.11a
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• pp.210-215
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• 2007

In this paper, excitation systems using an active tuned mass damper (ATMD) are presented in order to simulate the wind induced responses of a building structure. The actuator force for the excitation systems is calculated by using the inverse transfer function of a target structural response to the actuator. The analyses results from a 76-story benchmark building problem in which wind load obtained by wind tunnel test is given, indicate that the excitation system installed at a specific floor can approximately embody the structural responses induced by the wind load applied to each floor of the structure. The excitation system designed by the proposed method can be effectively used for evaluating the wind response characteristics of a practical building structure and for obtaining an accurate analytical model of the building under wind load.

• Wind and Structures
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• v.21 no.2
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• pp.183-202
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• 2015

Experiments on two-dimensional rectangular prisms with various side ratios (B/D=2, 3, and 4, where B is the along-wind dimension, and D is the across-wind dimension) and rounded corners (R/D=0%, 5%, 10%, and 15%, where R is the corner radius) are reported in this study. The tests were conducted in low-turbulence uniform flow to measure the wind pressures on the surfaces of 12 models for Reynolds numbers ranging from $1.1{\times}10^5$ to $6.8{\times}10^5$. The aerodynamic force coefficients were obtained by integrating the wind pressure coefficients around the model surface. Experimental results of wind pressure distributions, aerodynamic force coefficients, and Strouhal numbers are presented for the 12 models. The mechanisms of the Reynolds number effects are revealed by analyzing the variations of wind pressure distributions. The sensitivity of aerodynamic behavior to the Reynolds number increases with increasing side ratio or rounded corner ratio for rectangular prisms. In addition, the variations of the mean pressure distributions and the pressure correlations on the side surfaces of rectangular prisms with the rounded corner ratio are analyzed at $Re=3.4{\times}10^5$.

• Wind and Structures
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• v.37 no.4
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• pp.303-314
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• 2023

In this study, two steady RANS turbulence models (SST k-ω and Realizable k-ε) and four unsteady turbulence models (URANS SST k-ω and Realizable k-ε, SST-SAS, and SST-IDDES) are evaluated with respect to their capacity to predict crosswind characteristics on high-speed trains (HSTs). All of the numerical simulations are compared with the wind tunnel values and LES results to ensure the accuracy of each turbulence model. Specifically, the surface pressure distributions, time-averaged aerodynamic coefficients, flow fields, and computational cost are studied to determine the suitability of different models. Results suggest that the predictions of the pressure distributions and aerodynamic forces obtained from the steady and transient RANS models are almost the same. In particular, both SAS and IDDES exhibits similar predictions with wind tunnel test and LES, therefore, the SAS model is considered an attractive alternative for IDDES or LES in the crosswind study of trains. In addition, if the computational cost needs to be significantly reduced, the RANS SST k-ω model is shown to provide relatively reasonable results for the surface pressures and aerodynamic forces. As a result, the RANS SST k-ω model might be the most appropriate option for the expensive aerodynamic optimizations of trains using machine learning (ML) techniques because it balances solution accuracy and resource consumption.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.15 no.8
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• pp.630-640
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• 2003

As tunnel ventilation has recently been playing a major role in the tunnel construction and maintenance, longitudinal ventilation systems with jet fans have been utilized a great deal because they are economical and effective. However, due to the length of tunnels and heavy traffic, it is hard to take the field measurements. In this study, therefore, the computer simulation and the model experiment of producing a wind tunnel were carried out simultaneously and the results were compared. The ultimate objective of this research was to interpret the air flow pattern inside the tunnel with a jet-fan was set up, and to offer the useful data for jet-fan installation and operation. The experiment was carried out with varying the jet-fan diameters, location of installation, the discharge velocity. Result showed that as the initial static pressure came up with the negative pressure, the tunnel air flowed into the inside of tunnel from outside due to the entrainment-effect and the backflow-phenomenon by separation-effect was observed in the lower half part of the tunnel. As the jet-fan was getting closer to the tunnel wall, the entrainment-effect caused by the interaction with the wall was increased; however, the mixing distance and irregular flow section became longer, and also the air pressure loss generated by wall friction was large.

• Wind and Structures
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• v.35 no.4
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• pp.269-285
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• 2022

The pressure-mitigating effects of a high-speed train passing through a tunnel with a partially reduced cross-section are investigated via the numerical approach. A compressible, three-dimensional RNG k-ε turbulence model and a hybrid mesh strategy are adopted to reproduce that event, which is validated by the moving model test. Three step-like tunnel forms and two additional transitions at the tunnel junction are proposed and their aerodynamic performance is compared and scrutinized with a constant cross-sectional tunnel as the benchmark. The results show that the tunnel step is unrelated to the pressure mitigation effects since the case of a double-step tunnel has no advantage in comparison to a single-step tunnel, but the excavated volume is an essential matter. The pressure peaks are reduced at different levels along with the increase of the excavated earth volume and the peaks are either fitted with power or logarithmic function relationships. In addition, the Arc and Oblique-transitions have very limited gaps, and their pressure curves are identical to each other, whereas the Rec-transition leads to relatively lower pressure peaks in C_Pmax, C_Pmin, and ΔC_P, with 5.2%, 4.0%, and 4.1% relieved compared with Oblique-transition. This study could provide guidance for the design of the novel railway tunnel.

• Journal of Korean Association for Spatial Structures
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• v.15 no.1
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• pp.65-73
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• 2015

This paper presents the structural model verification process of whole wind turbine blade including blade model which proposed in Part1 paper. The National Renewable Energy Laboratory (NREL) Phase VI wind turbine which the wind tunnel and structural test data has publicly available is used for the study. In the Part1 of this paper, the processes of structural model development and verification process of blade only are introduced. The whole wind turbine composed by blade, rotor, nacelle and tower. Even though NREL has reported the measured values, the material properties of blade and machinery parts are not clear but should be tested. Compared with the other parts, the tower which made by steel pipe is rather simple. Since it does not need any considerations. By the help of simple eigen-value analysis, the accuracy of structural stiffness and mass value of whole wind turbine system was verified by comparing with NREL's reported value. NREL has reported the natural frequency of blade, whole turbine, turbine without blade and tower only models. According to the comparative studies, the proposed material and mass properties are within acceptable range, but need to be discussing in future studies, because our material properties of blade does not match with NREL's measured values.

• Journal of the Society of Naval Architects of Korea
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• v.59 no.1
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• pp.9-17
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• 2022

In this paper, wind load on a semi-submersible rig was investigated using Computational Fluid Dynamics (CFD). A maritime atmospheric boundary layer model for wind profile was implemented such that the wind profile shapes were retained throughout the computational domain. Wind load on the semi-submersible rig was calculated under the maritime atmospheric boundary layer and matched well with the results from wind tunnel test within a ±20% error. Overturning moments with variation of draft were investigated by decomposing into drag and lift components. It was observed that the contribution from lift to the overturning moments increased as the draft got higher. The majority of the lift components originated from deckbox which served as a lifting body due to the accelerated streamlines between waterline and the bottom of the deckbox.

• Wind and Structures
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• v.6 no.2
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• pp.127-140
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• 2003

An investigation into the effect of corner cuts on the Strouhal number of rectangular cylinders with various dimensional ratios and various angles of attack is described. The Strouhal number given as a function of corner cut size is obtained directly from the aerodynamic behavior of the body in a uniform flow through a series of wind-induced vibration tests. For a quick verification of the validity of the Strouhal numbers obtained in this way, they are compared with the approximated the Strouhal numbers based on Shiraishi's early research. The test results show that the Strouhal number of the model with various corner cuts has a fluctuating trend as the angle of attack changes. For each cutting ratio as the angle of attack increases at each cutting ratio above $15^{\circ}$, the Strouhal number decreases gradually, and these trends are more evident for larger corner cut sizes. However, a certain corner cut size which is effective in reducing the wind-induced vibration can be identified by larger Strouhal numbers than those of other corner cut sizes. Three distinct characteristics of Strouhal number variation can be identified in three regions which are termed as Region I, II, and III based on the general trend of the test results. It is also found that the corner cut is effective in one region (Region-II) and less effective in another one (Region-III) when only the vortex-induced vibration occurs.

• Wind and Structures
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• v.7 no.1
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• pp.41-54
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• 2004

An analysis refinement of the Messina Strait suspension bridge project has been recently required, concerning mainly the yaw angle effects on the multi-box deck section aerodynamics and the vortex shedding at low reduced velocities $V^*$. In particular the possible interaction of the axial flow with the large cross beams has been investigated. An original test rig has been designed at this purpose allowing for both forced motion and free motion aero elastic tests, varying the average angle of attack ${\alpha}$ and the deck yaw angle ${\beta}$. The hydraulic driven test rig allowed for both dynamic and stationary tests so that both the stationary coefficients and the flutter derivatives have been evaluated for each yaw angle. Specific free motion tests, taking advantage from the aeroelastic features of the section model, allowed also the study of the vortex shedding induced phenomena.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.40 no.2
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• pp.146-156
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• 2012

In-flight icing remains as one of the most persistent hazards for aircraft operations. The effect of icing on aircraft performance and safety has to be evaluated during the development and airworthiness certification process. The scaling method is a procedure to determine the scaled test conditions in icing wind tunnels in order to produce the same result as when the reference model is exposed to the desired cloud conditions. In this study, a scaling program is developed to provide an easy-to-use tool to the aero-icing community. The Olsen and Ruff 4th methods are employed for this purpose and the velocity is calculated by matching the dimensionless Weber number. To validate the program, the results are compared with the NASA scaling results. The scaling examples based on FAR (Federal Aviation Regulation) Part 25 Appendix C are also presented. Finally, a validation study using a state-of-the-art icing simulation code FENSAP-ICE is presented.