• The KSFM Journal of Fluid Machinery
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• v.19 no.5
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• pp.20-27
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• 2016

The Francis-99 is a workshop initiated by the Norwegian University of Science and Technology (NTNU), Norway, and Lulea University of Technology (LTU), Sweden, in order to further validate the capabilities of the CFD technologies. The goal of the first workshop is to determine the state of the art of numerical predictions for steady operating conditions. When performing the CFD analysis, some geometry details are often neglected. In case of Francis Turbine, labyrinth seals are usually not include in the simulation domain, this may lead to inaccurate prediction of turbine efficiency. In this study, the CFD analysis for Francis-99 Workshop model has been performed for full domain of machine including top and bottom labyrinth seals. The efficiency value and distribution of velocity and pressure have been investigated and compared to the experimental data obtained from NTNU. By comparing the results, it was found that: With the top and bottom labyrinth seals in the domain, the CFD result was significantly improved in prediction of efficiency at all the operating point, especially at part load.

• Geomechanics and Engineering
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• v.19 no.5
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• pp.447-462
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• 2019

The vacuum preloading method has been used in many countries for ground improvement and land reclamation works. A sand cushion is required as a horizontal drainage channel for conventional vacuum preloading. In terms of the dredged-fill foundation soil, the treatment effect of the conventional vacuum preloading method is poor, particularly in Tianjin, China, where a shortage of sand exists. To solve this problem, straight-line vacuum preloading without sand is widely adopted in engineering practice to improve the foundation soil. Based on the engineering properties of dredged fill in Lingang City, Tianjin, this paper presents field instrumentation in five sections and analyzes the effect of a prefabricated vertical drain (PVD) layout and a vacuum pumping method on the soft soil ground treatment. Through the arrangement of pore water pressure gauges, settlement marks and vane shear tests, the settlement, pore water pressure and subsoil bearing capacity are analyzed to evaluate the effect of the ground treatment. This study demonstrates that straight-line vacuum preloading without sand can be suitable for areas with a high water content. Furthermore, the consolidation settlement and consolidation degree system is developed based on the grey model to predict the consolidation settlement and consolidation degree under vacuum preloading; the validity of the system is also verified.

• 한국연소학회:학술대회논문집
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• 2001.06a
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• pp.106-118
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• 2001

A rigorous study of single droplet vaporization under quiescent high pressure atmosphere is attempted adopting method of flash evaporation calculation for vapor-liquid equilibrium. Results due to flash method shows excellent agreement with measurement. Also shown is the present model fairly capable of depicting transients of droplet vaporization under high pressure environment, such as ambient gas solubility, property variation, and multicomponent transports. Systematic treatment of these effects with emphasis on vapor-liquid phase equilibrium revealed; conventional treatment for subcritical droplet vaporization, such as $d^2$-law, leads to erroneous prediction of droplet history, augmented gas solubility is significant under supercritical pressure, and vaporization rate proportionally increase with pressure.

• Proceedings of the Korean Geotechical Society Conference
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• 2010.03a
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• pp.1212-1221
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• 2010

A theoretical equation was proposed to consider the effect of fill and ponding for the excess pore water pressure in agricultural reservoir on soft clay ground. For the purpose of verification of the proposed equation, laboratory model tests and field tests were performed and excess pore water pressure was compared to those predicted with the Terzaghi's method. The degree of consolidation according to ponding predicted by applying the proposed equation was close to the observed degree of consolidation on the double drainage condition(at DP-3) but it was less than the observed degree of consolidation on the single drainage condition(at DP-5). The predicted excess pore water pressure according to fill and ponding was very applicable to practice because it was close to the observed data.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.24 no.8
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• pp.606-612
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• 2014

Vehicle simulation models for noise and vibration prediction have been developed so far generally in two schemes. One is FE models generally used for problems below 200 Hz such as booming noise, and the other is SEA models for high frequencies of more than 1 kHz, representatively related to sound packages. There have been many researches to develop a simulation model for 200~1000 Hz, so-called mid-frequency region, and this paper shows one practical result that covers the trimmed body of a sedan vehicle. The simulation model is developed based on an FE model, and then FE elements at some areas are substituted with SEA elements to reduce DOFs. SEA panels are described by modal density, radiation efficiency, stiffness and damping characteristics that are found from some numerical assessments. Sound packages are modeled similarly as a conventional SEA model. The results obtained from the hybrid model were compared to experimental results. Predicted pressure and vibrational velocity generally show a good agreement. The developed simulation model and related technology are successfully being used in vehicle development process.

• Journal of the Korean Society of Safety
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• v.29 no.5
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• pp.22-28
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• 2014

This study is compare to model-based analysis and experimental data of the response characteristic of interior impulse noise. Interior impulse noise and the pressure response characteristics of the building structure on its analysis are presented the impulse pressure acting on the rear wall 90 N-sec. The force acting on the wall $CFD^{{+}{+}}$ which are compared measurement and simulation analysis. Results of simulation and measurement data were shown. In this study, a high dimension of the degree of virtual space in the numerical space of the lesser degree in order to calculate folding method was applied. The results of this study contribute safety evaluation and model development for the interior impulse noise that affects the basic data for the interior impulse noise model validate for the physical quantity prediction.

• 한국전산유체공학회:학술대회논문집
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• 2008.03b
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• pp.341-344
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• 2008

The complicated helical flow formed in the regenerative turbomachines is usually decomposed into a peripheral component and a circulatory component. On the basis of the momentum exchange theory, the circulatory flow plays a critical role of imparting angular momentum to the peripheral flow. Therefore, the accuracy of performance prediction is dominated by the circulatory flow modeling. Until now the circulatory flow has been accounted of a standstill flow normal to the peripheral flow. However, the circulatory path from the impeller exit to the re-entrance inlet is exposed to the adverse pressure gradient, so it would be more realistic to describe that the circulatory flow is formed on the skewed plane not perpendicular to the peripheral flow. Present study suggests new circulatory flow loss model including the effect of adverse pressure gradient and modifies the effective circulatory flow rate and circulatory pivot which were previously published.

• International Journal of Fluid Machinery and Systems
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• v.10 no.3
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• pp.197-208
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• 2017

When Francis turbines operate at partial load, residual swirl in the draft tube causes low-frequency pulsation of pressure and power output. Scale effects and system response may bias the prediction of prototype behavior based on laboratory tests, but could be overcome by means of a 1D analytical model. This paper deals with the two most important features of such a model, the compliance and the source of excitation. In a distributed-parameter version, compliance should be represented as an exponential function of local pressure. Lack of similarity due to different Froude number can thus be compensated. The normally unknown gas content in the vortex cavity has significant influence on the pulsation, and should therefore be measured and considered as a test parameter.

• Journal of the Korean earth science society
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• v.45 no.1
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• pp.37-47
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• 2024

In the summer of 2018, the Korea-Japan (KJ) region experienced an extremely severe and prolonged heatwave. This study examines the GloSea6 model's prediction performance for the 2018 KJ heatwave event and investigates how its prediction skill is related to large-scale circulation patterns identified by the k-means clustering method. Cluster 1 pattern is characterized by a KJ high-pressure anomaly, Cluster 2 pattern is distinguished by an Eastern European high-pressure anomaly, and Cluster 3 pattern is associated with a Pacific-Japan pattern-like anomaly. By analyzing the spatial correlation coefficients between these three identified circulation patterns and GloSea6 predictions, we assessed the contribution of each circulation pattern to the heatwave lifecycle. Our results show that the Eastern European high-pressure pattern, in particular, plays a significant role in predicting the evolution of the development and peak phases of the 2018 KJ heatwave approximately two weeks in advance. Furthermore, this study suggests that an accurate representation of large-scale atmospheric circulations in upstream regions is a key factor in seasonal forecast models for improving the predictability of extreme weather events, such as the 2018 KJ heatwave.

• Wind and Structures
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• v.36 no.4
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• pp.237-247
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• 2023

The emergence of high-rise buildings has necessitated frequent structural health monitoring and maintenance for safety reasons. Wind causes damage and structural changes on tall structures; thus, safe structures should be designed. The pressure developed on tall buildings has been utilized in previous research studies to assess the impacts of wind on structures. The wind tunnel test is a primary research method commonly used to quantify the aerodynamic characteristics of high-rise buildings. Wind pressure is measured by placing pressure sensor taps at different locations on tall buildings, and the collected data are used for analysis. However, sensors may malfunction and produce erroneous data; these data losses make it difficult to analyze aerodynamic properties. Therefore, it is essential to generate missing data relative to the original data obtained from neighboring pressure sensor taps at various intervals. This study proposes a deep learning-based, deep convolutional generative adversarial network (DCGAN) to restore missing data associated with faulty pressure sensors installed on high-rise buildings. The performance of the proposed DCGAN is validated by using a standard imputation model known as the generative adversarial imputation network (GAIN). The average mean-square error (AMSE) and average R-squared (ARSE) are used as performance metrics. The calculated ARSE values by DCGAN on the building model's front, backside, left, and right sides are 0.970, 0.972, 0.984 and 0.978, respectively. The AMSE produced by DCGAN on four sides of the building model is 0.008, 0.010, 0.015 and 0.014. The average standard deviation of the actual measures of the pressure sensors on four sides of the model were 0.1738, 0.1758, 0.2234 and 0.2278. The average standard deviation of the pressure values generated by the proposed DCGAN imputation model was closer to that of the measured actual with values of 0.1736,0.1746,0.2191, and 0.2239 on four sides, respectively. In comparison, the standard deviation of the values predicted by GAIN are 0.1726,0.1735,0.2161, and 0.2209, which is far from actual values. The results demonstrate that DCGAN model fits better for data imputation than the GAIN model with improved accuracy and fewer error rates. Additionally, the DCGAN is utilized to estimate the wind pressure in regions of buildings where no pressure sensor taps are available; the model yielded greater prediction accuracy than GAIN.