• Journal of the Korean Society of Manufacturing Process Engineers
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• v.15 no.4
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• pp.73-82
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• 2016

Recently, automobile industries have been developing many structural automotive parts made of thin, high-strength steel strips to produce safer and more environmentally friendly cars. The roll forming process has been considered one of the most efficient processes in manufacturing high-strength steel parts because it is a high-speed process that forms sheets in increments. However, most automotive parts vary longitudinally in their cross-sections. Therefore, it is difficult to apply the roll forming process to automotive parts made of high-strength steel. A variable section roll forming process has been proposed in recent studies. The rotational axes of the forming rolls are fixed, and the forming rolls have three-dimensional shape. As such, the cross-section of the part varies linearly along its length, and the angle between the bend line and longitudinal axis is less than 1 degree. Thus, the rate of cross-sectional variation along the length is relatively small. In this study, the rate of cross-sectional change along the length of a forming roll has been increased. Moreover, the angle between the bend line and longitudinal axis has been increased up to 15 degrees. The variable sections of the forming rolls have been designed for high strength steel parts with a symmetric u-type cross-section that varies linearly and symmetrically along the longitudinal axis.

• Steel and Composite Structures
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• v.30 no.5
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• pp.471-481
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• 2019

Beam-columns are structural members subjected to a combination of axial and bending forces. Lateral-torsional buckling is one of the main failure modes. Beam-columns that are bent about its strong axis may buckle out of the plane by deflecting laterally and twisting as the values of the applied loads reach a limiting state. Lateral-torsional buckling failure occurs suddenly in beam-column elements with a much greater in-plane bending stiffness than torsional or lateral bending stiffness. This study intends to establish a unique convenient closed-form equation that it can be used for calculating critical elastic lateral-torsional buckling load of beam-column in the presence of a known axial load. The presented equation includes first order bending distribution, the position of the loads acting transversely on the beam-column and mono-symmetry property of the section. Effects of axial loads, slenderness and load positions on lateral torsional buckling behavior of beam-columns are investigated. The proposed solutions are compared to finite element simulations where thin-walled shell elements including warping are used. Good agreement between the analytical and the numerical solutions is demonstrated. It is found out that the lateral-torsional buckling load of beam-columns with mono-symmetric sections can be determined by the presented equation and can be safely used in design procedures.

• The Journal of the Korea institute of electronic communication sciences
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• v.4 no.3
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• pp.236-242
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• 2009

When two-link flexible arm is rotated about an joint axis, transverse vibration may occur. In this paper, vibration dynamics of flexible robot arm is modeled by using Bernoulli-Euler beam theory and Lagrange equation. Using the fact that matrix $\dot{D}$-2C is skew symmetric, new controllers which have a simplified structure with less computational burden is proposed. Lyapunov stability theory is applied to achieve a stable deterministic nonlinear controller for the regulation of joint angle.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.28 no.6
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• pp.652-658
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• 2004

In this paper, we report the numerical and experimental solutions of the axi-symmetric flows in the axial plane driven by an impingement of fluid from the bottom wall of a circular cylinder. We managed to visualize successfully the flow pattern shown on the vertical plane through the container axis. The numerical results are shown to compare well with the experimental results for the case of infinity Rossby number. The satisfactory agreement between the two results was possible when in the numerics the free surface was treated as a solid wall so that a no-slip condition was applied on the surface. The numerical solutions reveal that inertial oscillation plays an important role at small Rossby numbers, or at a larger background rotation.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1993.10a
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• pp.575-581
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• 1993

This paper deals with analysis of articulated robot manipulator used for Arc welding and Material handling. Compared with present robot of which weight holding capacity is 6kg, this robot shows wider and symmetric working range for it's serial type mechanism. The link length is determined to have widest working range by using optimal simulation. To reduce body's weight, small AC servo motor is adopted and driving peak torque exerted at each joint is reduced by using dynamic analysis. So it is possible to reduce body's weight by 40% compared with the same class's robot and get wider working range. And by adopting modular design concept, each axis is designed to be changed easily for user's special need and repair.

• The Journal of Korean Society for Radiation Therapy
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• v.14 no.1
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• pp.109-116
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• 2002

The mordem linear accelerators are equipped with X-ray collimators that can be moved independently to allow asymmetric fields with field centers positioned away from the true central axis of the beam. We have studied the dosimetric of an independent collimator system using measurements performed quarter fields. The field size factors for asymmetric fields are compared to those for symmetric fields. Dosimetric measurements include portent depth don, beam penumbra and shape of isodose curves for symmetric and quarter fields.

• Proceedings of the KSME Conference
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• 2003.04a
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• pp.96-100
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• 2003

In the tensile loading of sheet metals made from polycrystalline aluminum alloys, a single deformation band appears inclined to the elongation axis in the early stage of plastic deformation, and symmetric double bands are observed in the later stage. This character of the localized deformation bands has been analyzed by a perturbation method. Macroscopic slip modes composed of slip planes and slip directions were assumed to describe the tensile and shear strains. Along time integration path, the value of the perturbation growth parameter was checked to find at which angle to the elongation axis the localized deformation bands are generated. It was shown that the mode of the localized deformation is related to asymmetry of material property.

• 한국전산유체공학회:학술대회논문집
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• 1999.05a
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• pp.85-89
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• 1999

Numerical Analysis has been done for the supersonic off-design jet flow due to the pressure difference between the jet and the ambient fluid. The difference of pressure generates an oblique shock or an expansion wave at the nozzle exit, The waves reflect repeatedly at the center axis and on the sonic surface in the shear layer, and the pressure difference is resolved across these waves interacted with the turbulence mixing layer. In this paper, the axi-symmetric Navier-Stokes equation has been used with two equation $k-{\varepsilon}$ turbulence closure model. The second order TVD scheme with flux limiters, based on the flux vector split by the smooth eigenvalue split, has been used to capture internal shocks and other discontinuities. The correction term for the compressible flow and the damping function are used in the turbulence model. Numerical calculations have been done to analyze the off-design jet flow due to the pressure difference. The variation of pressure along the flow axis is compared with an experimental result and other numerical result. The characteristics of the interaction between the shock cell and the turbulence mixing layer have been analyzed.

• Journal of the Chungcheong Mathematical Society
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• v.16 no.1
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• pp.7-14
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• 2003

Let $P_c(z)=z^n+c$ be a complex polynomial with an integer $n{\geq}2$. We derive a criterion that the critical orbit of $P_c$ escapes to infinity and investigate its applications to the degree-n bifurcation set. The intersection of the degree-n bifurcation set with the real line as well as with a typical symmetric axis is explicitly written as a function of n. A well-defined escape-time algorithm is also included for the improved construction of the degree-n bifurcation set.

• Proceedings of the KIEE Conference
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• 2004.10a
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• pp.70-72
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• 2004

The ferromagnetic pole piece of permanent magnet assembly for magnetic resonance imaging(MRI) is optimally designed to get high homogenious magnetic field, taking into account the non-linearity of the magnetic materials. In the design, the pole face is kept smooth and axis-symmetric by using B-spline parameterization, and nonlinear design sensitivity analysis is used for search direction.