• Wind and Structures
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• v.1 no.3
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• pp.255-269
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• 1998

Second-order moments of considerable magnitude arise in tall and slender RC chimneys and towers subject to along-wind loading, on account of eccentricities in the distributed self-weight of the tower in the deflected profile. An accurate solution to this problem of geometric nonlinearity is rendered difficult by the uncertainties in estimating the flexural rigidity of the tower, due to variable cracking of concrete and the 'tension stiffening' effect. This paper presents a rigorous procedure for estimating deflections and second-order moments in wind-loaded RC tubular towers. The procedure is essentially based on a generalised formulation of moment-curvature relationships for RC tubular towers, derived from the experimental and theoretical studies reported by Schlaich et al. 1979 and Menon 1994 respectively. The paper also demonstrates the application of the proposed procedure, and highlights those conditions wherein second-order moments become too significant to be overlooked in design.

• The KSFM Journal of Fluid Machinery
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• v.12 no.6
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• pp.7-12
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• 2009

This paper presents a numerical study on the design of side-suction inlet geometry which is used for multi stage centrifugal pumps or inline centrifugal pumps. In order to achieve an optimum inlet geometry and to explain the interactions between the different geometric configurations, the three dimensional computational fluid dynamics and the design of experiment methods have been applied. Geometric design variables describing the cross sectional area distribution through the inlet were selected. The objective functions are defined as the non-uniformity of the velocity distribution at the passage exit which is just in front of the impeller eyes. From the 2k factorial design results, the most important design variable was found and the performance of the side suction inlet was improved compared to the base line shape.

• Journal of the Korean Mathematical Society
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• v.43 no.3
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• pp.507-528
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• 2006

In this paper we show that the Koecher's Jordan automorphic generators of one variable on an irreducible symmetric cone are enough to determine the elements of scalar multiple of the Jordan identity on the attached simple Euclidean Jordan algebra. Its various geometric, Jordan and Lie theoretic interpretations associated to the Cartan-Hadamard metric and Cartan decomposition of the linear automorphisms group of a symmetric cone are given with validity on infinite-dimensional spin factors

• Structural Engineering and Mechanics
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• v.13 no.2
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• pp.231-239
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• 2002

The problem of dynamic analysis of truss structures based on probability is studied in this paper. Considering the randomness of both physical parameters (elastic module and mass density) of structural materials and geometric dimension of bars respectively or simultaneously, the stiffness and mass matrixes of the elements and structure have been built. The structure dynamic characteristic based on probability is analyzed, and the expressions of numeral characteristics of inherence frequency random variable are derived from the Rayleigh's quotient. The method of structural dynamic analysis based on probability is developed. Finally, two examples are given.

• Steel and Composite Structures
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• v.33 no.6
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• pp.767-776
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• 2019

In this article, a simple and robust multi-objective assessment method to control design angles and node positions connected among steel outrigger truss members is proposed to approve both structural safety and economical cost. For given outrigger member layouts, the present method utilizes general-purpose prototypes of outrigger members, having resistance to withstand lateral load effects directly applied to tall buildings, which conform to variable connecting node and design space deposition. Outrigger layouts are set into several initial design conditions of height to width of an arbitrary given design space, i.e., variable design space. And then they are assessed in terms of a proposed multi-objective function optimizing both minimal total displacement and material quantity subjected to design impact factor indicating the importance of objectives. To evaluate the proposed multi-objective function, an analysis model uses a modified Maxwell-Mohr method, and an optimization model is defined by a ground structure assuming arbitrary discrete straight members. It provides a new robust assessment model from a local design point of view, as it may produce specific optimal prototypes of outrigger layouts corresponding to arbitrary height and width ratio of design space. Numerical examples verify the validity and robustness of the present assessment method for controlling prototypes of outrigger truss members considering a multi-objective optimization achieving structural safety and material cost.

• Journal of the Society of Naval Architects of Korea
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• v.57 no.2
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• pp.96-103
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• 2020

The new geometric disturbance is proposed to control the flow around the bluff body. The new geometry is characterized by the variable pitch which is applied on the Helically Elliptic Twisted (HET) cylinder. The performance of the HTE geometry as a biomimetic passive flow control was confirmed by Jung and Yoon (2014). The Large Eddy Simulation (LES) is used for the evaluation of the flow control performance of the Variable Pitch HTE (VPHTE) cylinder at Reynolds number (Re) of 3000 corresponding to the subcritical regime. The circular and HTE cylinders are also considered to compare the performance of the VPHTE cylinder at the same Re. The VPHTE cylinder gives the smallest values of the force coefficients than the circular and HTE cylinders. The drag and lift coefficients of the VPHTE cylinder are about 15.2% and 94.0% lower than those of the circular cylinder, respectively. Especially, the VPHTE cylinder achieves about 2.3% and 30.0% reduction of the drag coefficient and the root mean square of the lift coefficient than the HTE cylinder, respectively. Furthermore, The VPHTE cylinder forms more elongated and stabilized separated shear layer than the circular cylinder, which supports the reduction of the force coefficients.

• Nuclear Engineering and Technology
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• v.30 no.3
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• pp.245-261
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• 1998

In order to validate the variable aperture channel model that can deal with the non-uniform How rate in flow domain, migration experiments of conservative tracer were performed in two artificial fractures, a parallel and a wedge-shaped fracture. These different fracture shapes were designed to give different flow pattern. The fractures were made from a transparent acrylic plastic plate and a granite slab with dimensions of 10 $\times$ 61 $\times$ 61 cm. Uranine (Fluorescein sodium salt) was used as a conservative tracer. The volumetric flow rates of uranine feed solution were 30 mL/ hr, giving a mean residence time in the fracture of approximately 24 hours for the parallel fracture and 34 hours for the wedge-shaped fracture. The migration plumes of uranine were photographed to obtain profiles in space and time for movement of a tracer in fractures. The photographed migration plume was greatly affected by the geometric shape of fractures. The variable aperture channel model could have predicted the experimental results for the parallel fracture with a large accuracy. It is expected that the variable aperture channel model would be effective to predict the transport of the contaminant, especially, with the flow rate variation in a fracture.

• Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
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• v.16 no.1
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• pp.1-7
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• 1998

SAR data can be achieved independently of weather conditions or sun illumination which is main limitation of electro-optical sensor to get image. The information from imagery can be more enlarged using Shh data be-cause SAR data offers different information from electro-optical sensor. SAR data contains various distortions caused by the radar specification and geometric properties of data acquisition. These distortions should be removed to get the information with acceptable accuracy. In this study, we aimed to correct the radiometric distortion in Shh image caused by the geometric property of the object. For this purpose, we simulated the SAR image by modelling of the power of return beam which is variable according to the geometric configuration between SAR antenna and ground object. Dividing the SAR image by the simulation image, then, we can get the radiometrically corrected image. As a result of this study, we could minimize the effect of radiometric distortion in achieving some qualitative information from SAR image for the related field, such as Geospatial Information System.

• The Bulletin of The Korean Astronomical Society
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• v.43 no.2
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• pp.44.4-45
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• 2018

(4179) Toutatis (Toutatis hereafter) is one of the Near-Earth Asteroids which has been studied most rigorously not only via ground-based photometric, spectroscopic, polarimetric, and radar observations, but also via the in-situ observation by the Chinese Chang'e-2 spacecraft. However, one of the most fundamental physical properties, the geometric albedo, is less determined. In order to derive the reliable geometric albedo and further study the physical condition on the surface, we made photometric observations of Toutatis near the opposition (i.e., the opposite direction from the Sun). We thus observed it for four days on 2018 April 7-13 using three 1.6-m telescopes, which consist of the Korean Microlensing Telescope Network (KMTNet). Since the asteroid has a long rotational period (5.38 and 7.40 days from Chang'e-2, Zhao et al., 2015), the continuous observations with KMTNet matches the purpose of our photometric study of the asteroid. The observed data cover the phase angle (Sun-asteroid-observer's angle) of 0.65-2.79 degree. As a result, we found that the observed data exhibited the magnitude changes with an amplitude of ~0.8 mag. We calculated the time-variable geometrical cross-section using the radar shape model (Hudson & Ostro 1995), and corrected the effect from the observed data to derive the geometric albedo. In this presentation, we will present our photometric results. In addition, we will discuss about the regolith particles size together with the polarimetric properties based on the laboratory measurements of albedo-polarization maximum.

• Journal of Aerospace System Engineering
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• v.17 no.2
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• pp.62-70
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• 2023

We proposed a technique for predicting Stress-Life (S-N) curve or fatigue life using geometric features of a ply-overlap joint structure in which plies of two composite materials are partially or wholly laminated and bonded. Geometric features that could affect fatigue properties of a structure were selected as variables. By analyzing relationships between geometric variables and material constants of the Epaarachchi-Clausen model, a fatigue model for composites, relational expressions of these two factors were proposed. To verify the prediction accuracy of the proposed method, fatigue life of a CFRP/GFRP ply-overlap joint was predicted. Predicted life and life obtained by test data-based model were compared to actual life. High prediction accuracy was confirmed by calculating the coefficient of determination of the predicted S-N curve.