• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2011.04a
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• pp.443-444
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• 2011

This paper discusses a model order reduction for large order rotor dynamics systems results from the finite element discretization. Typical rotor systems consist of a rotor, built-on parts, and a support system, and require prudent consideration in their dynamic analysis models because they include unsymmetric stiffness, localized nonproportional damping and frequency dependent gyroscopic effects. When the finite element model has a very large number of degrees of freedom because of complex geometry, repeated dynamic analyses to investigate the critical speeds, stability, and unbalanced response are computationally very expensive to finish within a practical design cycle. In this paper, the Krylov-based model order reduction via moment matching significantly speeds up the dynamic analyses necessary to check eigenvalues and critical speeds of a Nelson-Vaugh rotor system. With this approach the dynamic simulation is efficiently repeated via a reduced system by changing a running rotational speed because it can be preserved as a parameter in the process of model reduction. The Campbell diagram by the reduced system shows very good agreement with that of the original system. A 3-D finite element model of the Nelson-Vaugh rotor system is taken as a numerical example to demonstrate the advantages of this model reduction for rotor dynamic simulation.

• Wind and Structures
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• v.31 no.3
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• pp.217-227
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• 2020

Based on translation models, both Gaussian and non-Gaussian wind fields are generated using spectral representation method for investigating the influence of non-Gaussian characteristics and directivity effect of wind load on fatigue damage of wind turbine. Using the blade aerodynamic model and multi-body dynamics, dynamic responses are calculated. Using linear damage accumulation theory and linear crack propagation theory, crack initiation life and crack propagation life are discussed with consideration of the joint probability density distribution of the wind direction and mean wind speed in detail. The result shows that non-Gaussian characteristics of wind load have less influence on fatigue life of wind turbine in the area with smaller annual mean wind speeds. Whereas, the influence becomes significant with the increase of the annual mean wind speed. When the annual mean wind speeds are 7 m/s and 9 m/s at hub height of 90 m, the crack initiation lives under softening non-Gaussian wind decrease by 10% compared with Gaussian wind fields or at higher hub height. The study indicates that the consideration of the influence of softening non-Gaussian characteristics of wind inflows can significantly decrease the fatigue life, and, if neglected, it can result in non-conservative fatigue life estimates for the areas with higher annual mean wind speeds.

• The Korean Journal of Food And Nutrition
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• v.28 no.6
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• pp.1011-1018
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• 2015

The effects of mixing speed (3, 6 and 10 speed) and time (2, 5 and 10 min) on the dynamic viscoelasticity of dough and the baking properties of gluten-free rice bread were investigated. The specific gravity of the dough was not affected by the mixing speed and time before and after fermentation. The elasticity (G') and viscosity (G") of the dough increased and the tan ${\delta}$ (G"/G') decreased with higher mixing speeds and longer mixing times. The specific volume of the gluten-free rice bread was affected by the mixing time in response surface methodology (RSM). The hardness of the gluten-free rice bread showed a decreasing trend as the specific volume for the gluten-free rice bread increased. The appearance of the gluten-free rice bread was symmetrical at high mixing speeds and long mixing times. Overall results indicated that the quality of gluten-free rice bread could be improved by controlling the mixing speeds and mixing times for the dough.

• Structural Engineering and Mechanics
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• v.50 no.1
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• pp.19-36
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• 2014

This paper focuses on a model order reduction (MOR) for large-scale rotordynamic systems by using finite element discretization. Typical rotor-bearing systems consist of a rotor, built-on parts, and a support system. These systems require careful consideration in their dynamic analysis modeling because they include unsymmetrical stiffness, localized nonproportional damping, and frequency-dependent gyroscopic effects. Because of this complex geometry, the finite element model under consideration may have a very large number of degrees of freedom. Thus, the repeated dynamic analyses used to investigate the critical speeds, stability, and unbalanced response are computationally very expensive to complete within a practical design cycle. In this study, we demonstrate that a Krylov subspace-based MOR via moment matching significantly speeds up the rotordynamic analyses needed to check the whirling frequencies and critical speeds of large rotor systems. This approach is very efficient, because it is possible to repeat the dynamic simulation with the help of a reduced system by changing the operating rotational speed, which can be preserved as a parameter in the process of model reduction. Two examples of rotordynamic systems show that the suggested MOR provides a significant reduction in computational cost for a Campbell diagram analysis, while maintaining accuracy comparable to that of the original systems.

• Korean Journal of Materials Research
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• v.30 no.3
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• pp.111-116
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• 2020

Two different casting speeds of 60 and 80mm/min are adopted to determine the effect of casting speed on the microstructure and mechanical properties of Al-Mg-Si/Al hybrid material prepared by duo-casting. The obtained hybrid material has a uniform and straight macro-interface between the pure Al side and the Al-Mg-Si alloy side at both casting speeds. When the casting speed is increased to 80mm/min, the size of primary α phases in Al-Mg-Si alloy decreases, without change of shape. Although the Al-Mg-Si alloy produced at higher casting speed of 80mm/min shows much higher ultimate tensile strength (UTS) and 0.2 % proof stress and lower elongation, along with higher bending strength compared to the case of the 60mm/min in casting speed, the tensile properties and bending strength of the hybrid material, which are similar to those of pure Al, are the same regardless of the increase of casting speed. Despite the different casting speeds, deformation and fracturing in hybrid materials are observed only on the pure Al side. This indicates that the macro-interface is well-bonded, allowing it to endure tensile and bending deformation in all hybrid materials.

• Structural Engineering and Mechanics
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• v.55 no.1
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• pp.111-135
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• 2015

Bridge behavior under passing traffic loads has been studied for the past 50 years. This paper presents how to model congestion on bridges and how the maximum dynamic stress of bridges change during the passing of moving vehicles. Most current research is based on mid-span dynamic effects due to traffic load and most bridge codes define a factor called the dynamic load allowance (DLA), which is applied to the maximum static moment under static loading. This paper presents an algorithm to solve the governing equation of the bridge as well as the equations of motions of two real European trucks with different speeds, simultaneously. It will be shown, considering congestion in eight case studies, the maximum dynamic stress and how far from the mid-span it occurs during the passing of one or two trucks with different speeds. The congestion effect on the maximum dynamic stress of bridges can make a significant difference in the magnitude. By finite difference method, it will be shown that where vehicle speeds are considerably higher, for example in the case of railway bridges which have more than one railway line or in the case of multiple lane highway bridges where congestion is probable, current designing codes may predict dynamic stresses lower than actual stresses; therefore, the consequences of a full length analysis must be used to design safe bridges.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.26 no.10
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• pp.16-26
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• 2012

This study conducted a subjective evaluation of brightness perception and visual discomfort according to dimming speeds and CCTs(Correlated Color Temperatures). Dimming speeds of two different CCT lights(2,700K, 6400K) were set to 1.7%/s, 3.3%/s, 5.0%/s, 6.7%/s, and 10.0%/s respectively. Subjects checked the time when they perceived the change of the brightness and visual discomfort. As a result, when dimming speeds were 1.7%/s, 3.3%/s, 5.0%/s, 6.7%/s, more than half of subjects responded the change of the brightness in 55.0~45.0% dimming ratios, and felt the visual discomfort in 35~25% dimming ratios. When the brightness was changed, dimming level responded to the brightness perception of hight CCT(6,400K) was higher about 8.0% then dimming level responded to the brightness perception of low CCT(2,700K). Dimming level responded to the visual discomfort of low CCT(2,700K) was higher about 5.0% then dimming level responded to the visual discomfort of hight CCT(6,400K).

• Proceeding of EDISON Challenge
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• 2016.03a
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• pp.647-652
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• 2016

To reduce drag force at supersonic speeds, sharp leading edge is hugely efficient. It is, however, incompatible with leading edge shape to have fine aerodynamic characteristics at subsonic and transonic speeds. It is critical to reduce drag force for enhanced cruise performance and higher efficiency. An air superiority fighter, however, required to have high maneuverability for survivability, and sharp leading edge is not proper. Consequently, variable leading edge is demanded to reduce drag force significantly at supersonic speeds for cruise performance. Leading edge altering system is constructed with rigid material to improve possibility of realization, and minimized movement of its components in altering for reduce effects on flight. It is compared with bi-convex airfoil and NACA 65-006 airfoil, which have comparable maximum thickness. At Mach number 1.7 and zero angle of attack, supersonic mode of designed airfoil indicates approximately 17% higher drag coefficient than the bi-convex airfoil indicates, it is, however, 23% lower than the NACA 65-006 indicates. Also, subsonic mode of the designed airfoil shows fine aerodynamic characteristics in comparison with NACA 65-006 airfoil in subsonic and transonic speed range. In this regard, design of the airfoil achieved the object of this study satisfactorily.

• International Journal of Highway Engineering
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• v.15 no.6
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• pp.103-111
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• 2013

PURPOSES : Previous Speed Profile reflects the patterns of speeds in sections of tangents to curves in the roads. However these patterns are uniform of speeds and Acceleration/Deceleration. In oder to supplement these shortcomings. this study made a new profile which can contain factors of Acceleration/Deceleration through theories of Previous Speed Profiles. METHODS : For sakes, this study developed the speed prediction model of Rural Multi-Lane Highways and calculated Acceleration/Deceleration by appling a Polynomial model based on developed speed prediction model. Polynomial model is based on second by second. Acceleration/Deceleration Profile is developed with the various scenarios of road geometric conditions. RESULTS : The longer an ahead tangent length is, The higher an acceleration rate in curve occurs due to wide sight distance. However when there are big speed gaps between two curves, the longer tangent length alleviate acceleration rate. CONCLUSIONS : Acceleration/Deceleration Profile can overview th patterns of speeds and Accelerations/Decelerations in the various road geometric conditions. Also this result will help road designer have a proper guidance to exam a potential geometric conditions where may occur the acceleration/deceleration states.

• Journal of the Korean Society of Clothing and Textiles
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• v.45 no.2
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• pp.335-345
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• 2021

The purpose of this study was to examine the effect of fabric movement on wrinkle recovery in a clothing care system and to propose an algorithm to improve wrinkle removal performance by adjusting fabric movements. With an increase in the reciprocating speed of the movement system, the number and amplitude of curves on the fabric also increased. This allowed the fabric to be applied to a larger tension, resulting in better wrinkle removal performance at higher speeds. However, even at high reciprocating speeds, wrinkles could not be removed effectively because of nodes at a few specific locations. Based on the results of fabric movement and wrinkle recovery, a complex movement algorithm was proposed with a mixture of various reciprocation speeds. It showed a 41%p (24%→65%) improvement of wrinkle recovery when compared with the conventional algorithm that showed simple fabric movement at 180 rpm. This was because the positions of nodes and antinodes changed continuously and the force by the reciprocating motion could be applied evenly to the fabric.