• Korean Journal of Geomatics
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• 제5권1호
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• pp.43-49
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• 2005

It is well known that GPS technique can be used for high accuracy leveling positioning if a precise geoid model is available to use at a surveying point. In this study, KOGD2003 geoid model was developed in and around Korean peninsula and this geoid model could be achieved by combining GPS/leveling data with the formerly developed KOGD2002. To this end, the software for orthometric height obtaining and geodetic datum transformation has been implemented with the visual C++ language, what we called GPS-GeoL v.1.0. In order to evaluate the performance and the accuracy of the software, GPS field tests were carried out in the Korean second-order leveling network over Chollabukdo area. Results of the tests have shown that the mean value of the differences between outputs of the software developed in this research and officially announced orthometric heights by NGII (National Geographic Information Institute) was 0.0221 m and also those of RMS was 0.0332 m. Therefore, it was possible to conclude that the KOGD2003 and GPS-GeoL v.1.0 software could be used to determine orthometric heights for civil construction field applications with cm-level accuracy.

• Steel and Composite Structures
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• 제24권3호
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• pp.339-349
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• 2017

In this paper, a conventional refined plastic hinge analysis is improved to account for the effects of local buckling and lateral-torsional buckling. The degradation of flexural strength caused by these effects is implicitly considered using practical LRFD equation. The second-order effect is captured using stability functions to minimize modeling and solution time. An incremental-iterative scheme based on the generalized displacement control method is employed to solve the nonlinear equilibrium equations. A computer program is developed to predict the second-order inelastic behavior of space steel frames. To verify the accuracy and efficiency of the proposed program, the obtained results are compared with the existing results and those generated using the commercial finite element package ABAQUS. It can be concluded that the proposed program proves to be a reliable and effective tool for daily use in engineering design.

• Structural Engineering and Mechanics
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• 제52권4호
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• pp.687-699
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• 2014

Based on the energy method considering the second order effects, the natural frequencies of externally prestressed simply supported beam and the compression softening effect of external prestress force were analyzed. It is concluded that the compression softening effect depends on the loss of external tendon eccentricity. As the number of deviators increases from zero to a large number, the compression softening effect of external prestress force decreases from the effect of axial compression to almost zero, which is consistent with the conclusion mathematically rigorously proven. The frequencies calculated by the energy method conform well to the frequencies by FEM which can simulate the frictionless slide between the external tendon and deviator, the accuracy of the energy method is validated. The calculation results show that the compression softening effect of external prestress force is negligible for the beam with 2 or more deviators due to slight loss of external tendon eccentricity. As the eccentricity and area of tendon increase, the first natural frequency of the simply supported beams noticeably increases, however the effect of the external tendon on other frequencies is negligible.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2008년도 춘계학술대회논문집
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• pp.634-637
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• 2008

A large eddy simulation with an explicit filter on unstructured mesh is presented. The flow filed is semi-implicitly marched by a fractional step method. Spatial discretization of the solver is designed to guarantee the second order accuracy. An isotropic explicit filter is adopted for measuring the level of subgrid scale velocity fluctuation. The filter is linearity-preserving and has second order commutation error. The developed subgrid scale model is basically eddy viscosity model which depends on the explicitly filtered fields and needs no additional ad hoc wall treatment, such as van Driest damping function. For the validation, the flows in a channel and a pipe are calculated and compared to experimental data and numerical results in the literature.

• Water Engineering Research
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• 제3권1호
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• pp.23-30
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• 2002

A numerical model for the solution of two-dimensional dam break problems using fractional step method is developed on unstructured grid. The model is based on second-order Weighted Averaged Flux(WAF) scheme with HLLC approximate Riemann solver. To control the nonphysical oscillations associated with second-order accuracy, TVD scheme with SUPERBEE limiter is used. The developed model is verified by comparing the computational solutions with analytic solutions in idealized test cases. Very good agreements have been achieved in the verifications.

• ETRI Journal
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• 제35권2호
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• pp.218-225
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• 2013

The pull-out frequency of a second-order phase lock loop (PLL) is an important parameter that quantifies the loop's ability to stay frequency locked under abrupt changes in the reference input frequency. In most cases, this must be determined numerically or approximated using asymptotic techniques, both of which require special knowledge, skills, and tools. An approximating formula is derived analytically for computing the pull-out frequency for a second-order Type II PLL that employs a sinusoidal characteristic phase detector. The pull-out frequency of such PLLs can be easily approximated to satisfactory accuracy with this formula using a modern scientific calculator.

• 천문학회지
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• 제28권2호
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• pp.223-243
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• 1995

We describe the implementation of a multi-dimensional numerical code to solve the equations for idea! magnetohydrodynamics (MHD) in cylindrical geometry. It is based on an explicit finite difference scheme on an Eulerian grid, called the Total Variation Diminishing (TVD) scheme, which is a second-order-accurate extension of the Roe-type upwind scheme. Multiple spatial dimensions are treated through a Strang-type operator splitting. Curvature and source terms are included in a way to insure the formal accuracy of the code to be second order. The constraint of a divergence-free magnetic field is enforced exactly by adding a correction, which involves solving a Poisson equation. The Fourier Analysis and Cyclic Reduction (FACR) method is employed to solve it. Results from a set of tests show that the code handles flows in cylindrical geometry successfully and resolves strong shocks within two to four computational cells. The advantages and limitations of the code are discussed.

• Communications for Statistical Applications and Methods
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• 제28권5호
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• pp.563-582
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• 2021

This paper deals with developing a general class of accelerated sequential procedures and obtaining the associated second-order approximations for the expected sample size and 'regret' (difference between the risks of the proposed accelerated sequential procedure and the optimum fixed sample size procedure) function. We establish that the estimation problems based on various lifetime distributions can be tackled with the help of the proposed class of accelerated sequential procedures. Extensive simulation analysis is presented in support of the accuracy of our proposed methodology using the Pareto distribution and a real data set on carbon fibers is also analyzed to demonstrate the practical utility. We also provide the brief details of some other inferential problems which can be seen as the applications of the proposed class of accelerated sequential procedures.

• International Journal of Precision Engineering and Manufacturing
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• 제4권5호
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• pp.15-21
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• 2003

In order to improve the quality of a spindle unit it is important to increase its rotational accuracy. The rotational accuracy of a spindle unit can be defined as the stability or immobility of its spindle axis while rotating. Spindle rotation in the rolling bearings causes the disturbing influence, which leads to the oscillation of a rotation axis. The purpose of this study is to investigate the oscillation sources and find a way to decrease the runout without additional expenses. The main source of oscillation is the interaction between rolling bodies and ring races. The first oscillation source was the out-of-shape imperfection of inner bearing ring. The mutual compensation of oscillation by proper rings orientation was proposed, which sometimes allow to decrease the radial runout of spindle rotation axis by approximate 40％ down. Also the outer ring harmonics were explored as the second oscillation source. The analysis shows the dependency between the number of rolling bodies and the outer ring race harmonics. The conclusion on the orientation of bearing cages and the bearing rings was made, which makes possible to obtain the optimal variant of their mounting in the spindle unit when the rotational accuracy of the spindle is maximal, and the spindle runout considerably less.

• 대한기계학회논문집B
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• 제28권6호
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• pp.619-627
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• 2004

In most industrial applications, the geometrical complexity is combined with the moving boundaries. These problems considerably increase the computational difficulties since they require, respectively, regeneration and deformation of the grid. As a result, engineering flow simulation is restricted. In order to solve this kind of problems the immersed boundary method was developed. In this study, the immersed boundary method is applied to the numerical simulation of stationary, rotating and oscillating cylinders in the 2-dimensional square cavity. No-slip velocity boundary conditions are given by imposing feedback forcing term to the momentum equation. Besides, this technique is used with a second-order accurate interpolation scheme in order to improve the accuracy of flow near the immersed boundaries. The governing equations for the mass and momentum using the immersed boundary method are discretized on the non-staggered grid by using the finite volume method. The results agree well with previous numerical and experimental results. This study presents the possibility of the immersed boundary method to apply to the complex flow experienced in the industrial applications. The usefulness of this method will be confirmed when we solve the complex geometries and moving bodies.