• Proceedings of the Korean Society For Composite Materials Conference
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• 2001.05a
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• pp.69-73
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• 2001

Damage induced by low-velocity impact on the curved composite laminates was experimentally evaluated for CFRP cylindrical shells with the radius of curvatures of 50, 150, 300, and 500 mm. The result was then compared with that of flat laminates. The radius of curvatures and the effective shell stiffness appeared to considerably affect the dynamic impact response of curved shells. Under the same impact energy level, the maximum contact force increased with the decreasing radius of curvatures, with reaching 1.5 times that for plates at the radius of curvature of 50 mm. Since the maximum contact force is directly related to the impact damage, curved laminates can be more susceptible to delamination and less resistant to the low-velocity impact damage. The distribution of delamination along the thickness direction of curved laminates are also different from that of flat plates. Delamination was distributed rather even]y at each interface along the thickness direction of curved laminates. This implies that the effect of curvatures has to be considered for the design of a curved composite laminate.

• Journal of computational fluids engineering
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• v.19 no.1
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• pp.57-63
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• 2014

This study performed numerical analysis for the characteristics of flow-induced forces and the flow instability depending on the cross-sectional shape of the cylinder in laminar flow. To implement the cylinder cross-section, we adopted an Immersed Boundary Method with marker particles. We analyzed flow characteristics based on the radius of corner curvature. Main parameters are corner radius and Reynolds number (Re). With Re = 40, 50, 150 we calculated the flow field, drag coefficient, RMS of lift coefficient, pressure coefficient and Strouhal number in conjunction with the corner radius variation. Also, we calculated critical Reynolds number ($Re_c$) depending on the corner radius variation.

• Proceedings of the Korean Society For Composite Materials Conference
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• 2005.11a
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• pp.35-38
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• 2005

The Objective of this work was to design Composite Antenna Structures (CAS) and investigate impact behavior of CAS which was various curvature. This term, CAS, indicates that structural surface becomes antenna. Constituent materials were selected considering electrical properties, dielectric constants and tangent loss as well as mechanical properties. For the antenna performance, microstrip antenna layers inserted into structural layers were designed for satellite communication at the resonant frequency of 12.5 GHz and final demonstration article was. After making five kinds of curved CAS, which radii of curvature are flat, 200, 150, 100, 50 mm. The antenna performance changed in accordance with variation of curvature. The Reflection coefficient was independent of curvature but the gain decreased with the radius of curvature. The impact test equipment was Dyna-8250 drop weight tester. The impact characteristic in accordance with curvature is maximum absorb energy is same each other. The impact energy was 8.5 J. For various Impact energy test, five energy levels 3 J, 5 J, 7 J, 10 J, 20 J were used. The performance of impact damaged antenna was estimated by measuring the return loss and the radiation pattern. It was revealed that the performance of antenna was not related to the impact damage. Because the impactor did not damage the patch directly. CAS have good impact stability for the antenna performance.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2006.05a
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• pp.377-378
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• 2006

The knuckle crane mainly consists of six parts such as swing, main boom, outer boom, extension boom, hydraulic rotor and knuckle. And the hydraulic rotor is connected at the end of extension boom has rotor block, rotor body, rotor vane. In this study, we carried out kinematics analysis of the hydraulic rotor block curvature for a knuckle crane. Then, we showed the formula to establish the radius of a circumscribed circle to form the rotor block curvature. Third, we analyzed the stress at each point of the rotor block curvature according to the contact angle. From the result of this study, we designed the rotor block curvature with a proper contact angle for a knuckle crane to guarantee the stability of hydraulic rotor.

• Bulletin of the Korean Mathematical Society
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• v.61 no.2
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• pp.401-419
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• 2024

Let K, H, K_II and H_II be the Gaussian curvature, the mean curvature, the second Gaussian curvature and the second mean curvature of a timelike tubular surface T_γ(α) with the radius γ along a timelike curve α(s) in Minkowski 3-space E³₁. We prove that T_γ(α) must be a (K, H)-Weingarten surface and a (K, H)-linear Weingarten surface. We also show that T_γ(α) is (X, Y)-Weingarten type if and only if its central curve is a circle or a helix, where (X, Y) ∈ {(K, K_II), (K, H_II), (H, K_II), (H, H_II), (K_II , H_II)}. Furthermore, we prove that there exist no timelike tubular surfaces of (X, Y)-linear Weingarten type, (X, Y, Z)-linear Weingarten type and (K, H, K_II, H_II)-linear Weingarten type along a timelike curve in E³₁, where (X, Y, Z) ∈ {(K, H, K_II), (K, H, H_II), (K, K_II, H_II), (H, K_II, H_II)}.

• Journal of Korean Society of Disaster and Security
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• v.8 no.1
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• pp.5-13
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• 2015

In this study, the lateral overflow discharge coefficients for the curvatures of side weir on meandering channel were analyzed. The side weir installed in accordance with the variation of the radius of curvature of the central angle bends with $180^{\circ}$. FLOW-3D model is applied to calculate the discharge coefficients of the side-weir on meandering and straight channels and the characteristics of the discharge coefficients are analysed. In order to verify the numerical model, the results from the hydraulic experiment conducted by the former research are compared with the results simulated by FLOW-3D in the same conditions. The discharge coefficients are calculated for the ratio between curvature ($R_c$) and channel width (b), and the ratio between over flow discharge of the straight channel ($Q_{wc}$) and the meandering channel ($Q_{wc}$) are compared. As the result, the discharge coefficients depend on the weir depth on upstream, and the radius of curvature, so that the discharge coefficients of side weir on the meandering channel can be estimated by them on the straight channel.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2005.10a
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• pp.322-325
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• 2005

In order to make a doubly-cowed sheet metal effectively, the sheet metal forming process has been developed by adopting the flexibility of the incremental forming process and the principle of bending deformation which causes slight deformation in thickness. The developed process is an unconstrained forming process without holder. The experimental equipment has been set up with the roll set which consists of two pairs of support rolls and one center roll. In order to analyze process parameters in the incremental roll forming process for the application to doubly curved ship hull plate, the orthogonal array is adopted. From the FEM results, among the process parameters, the distance between supporting rolls in pairs along the direction of one principal radius of curvature as well as the forming depth is shown to influence the generation of curvature in the same direction significantly. That is, the other distance between supporting rolls in pairs which are not located in the same direction of one principal radius of curvature, does not have an significant effect on the generation of the curvature in that direction. Also, the forming load and torque from the FEM simulation are acceptable to the system development of the incremental roll forming process for the forming of ship hull plate.

• Journal of the Korean Society of Clothing and Textiles
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• v.29 no.8 s.145
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• pp.1168-1175
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• 2005

Clothing pressure has close relation with clothing comfort and depends on the pattern and properties of textile fabrics. Choosing a suitable clothing pressure is an essential factor for designing functional clothing such as the foundation for reshaping of a body contour or medical items for bum patient, and etc. However, it is hard to measure pressure values at the curved surface of a human body correctly. Recently, an air pack type pressure sensor, which has relatively excellent performance has been used to measure clothing pressure, however, it is still inconvenient to apply because it is a contact- type sensor. Therefore, in this paper, we suggest an indirect method that can measure clothing pressure without touching the subject by improving the equation of Kirk and Ibrahim (1966). However, confusions have been occurred when someone use the equation since the definition of parameters are somewhat vague. Furthermore, the estimated clothing pressure obtained by the previous method are quite different from the real values because this method does not consider the 3D effect of a human body and property changes of a transformed fabric. In this paper, the direction of principal stress and the radius of curvature in the principal direction were searched in the 3D image of the deformed girdle to get more accurate clothing pressure. The estimated clothing pressure was verified by comparing the result of the air pack type pressure sensor. It was found that the accuracy of the pressure estimation was improved by considering the 3D curvature of human body and the directional characteristics of textile fabrics.

• Transactions of the Korean Society of Automotive Engineers
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• v.14 no.1
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• pp.79-85
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• 2006

CFRP(Carbon Fiber Reinforced Plastics) of the advanced composite materials as structural materials for vehicle, has a wide application in light-weigh structural materials of airplanes, ships and automobiles because of high strength and stiffness, However, there is a design variable to be considered in practical application of the laminate composite materials, these materials are vulnerable to transverse impact. This paper is to study the effects of stacking sequence and curvature on the penetration characteristics of composite laminate shell. They are stacked to $[0_3/90_3]S,\;[90_3/0_3]s\;and\;[0_2/90_3/0]s,\;[90_2/0_3/90]s$ and their interlaminar number two and four. They are manufactured to various curvature radius (R=100, 150, 200mm and $\infty$), When the specimen is subjected to transverse impact by a steel ball, the velocity of the steel ball was measured both before and after impact by determing the time for it to pass two ballistics-screen sensors located a known distance apart. The critical penetration energy of specimen A and B with less interfaces were a little higher than those of C and D. As the curvature increases, the critical penetration energy increases linearly because the resistance to the in-plane deformation as well as bending deformation increases, which need higher critical penetration energy. The specimen A and C have higher critical penetration energy than B and D because of different stacking sequences. We examined crack length through a penetration test. For the specimen A with 2interfaces, the longest circumferential direction crack length were observed on the first interface from the impact point. For the specimen B 4-interface, the longest circumferential direction crack length were observed on the second interface from the impact point.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.14 no.2
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• pp.121-136
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• 1989

In this paper, an attempt has been made to analyze the theoretically and verify experimentally the effect of curvature on the radiation characteristics of microstrip array antennas mounted conformally on the concave surface and the convex surface of the cylindrical body. The analysis of single element microstrip antenna is made by using the analysis method of Transmission Line Model. The theory of array antennas is established by application of the method of transformed coordinates, in which the translation and the ratation about each single element arrayed two-demensionally on the nonplanar surface are under consideration, and it is investigated by computation of the synthetic electric field strength in the far zone. In addition, various radiation characteristics, such as return loss, resonant frequency, radiation pattern, half-power, beamwidth, gain, are measrued and compared with the theroetical values according to the variation of curvature, by designing and building 4-element array microstrip antenna operating at 10 GHz, and microstrip feed lines. As predicted in theroy, it is verified that radiation pattern of antennas mounted on the concave and the convex surfaces alike broadens as the radius of curvature decreases. And for the curved surfaces, aggrement between computed values of the total synthetic radiation power pattern by the method of transformed coordinates and measured valuse is good. Besides, it is found that resonant frequency, input impedance and gain are hardly affected by the radius of curvature.