• International Journal of Aeronautical and Space Sciences
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• v.14 no.1
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• pp.75-84
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• 2013

In this paper, the guidance law for formation flight and collision avoidance of multiple Unmanned Aerial Vehicle (UAV)s is proposed. To construct the physically comprehensible guidance law for formation flight, the virtual structure approach is used. To develop a guidance law for collision avoidance considering both other UAVs and unknown static obstacles, a geometric approach using information such as a relative position vector is utilized. Through the Lyapunov theorem, the stability of the proposed guidance law is proved. To combine guidance commands, the concept of the elastic weighting factor inspired by the elastic behavior of shape memory polymer, which tends to regain its original shape after deformation, is introduced. By using the concept of elastic weighting factor, multiple UAVs are able to cope actively with the situation of a collision between both UAVs and static obstacles during the formation flight. To verify the performance of the proposed method, numerical simulations are performed.

• Earthquakes and Structures
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• v.5 no.6
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• pp.679-702
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• 2013

During an earthquake, soils filter and send out the shaking to the building and simultaneously it has the role of bearing the building vibrations and transmitting them back to the ground. In other words, the ground and the building interact with each other. Hence, soil-structure interaction (SSI) is a key parameter that affects the performance of buildings during the earthquakes and is worth to be taken into consideration. Columns are one of the most crucial elements in RC buildings that play an important role in stability of the building and must be able to dissipate energy under seismic loads. Recent earthquakes showed that formation of plastic hinges in columns is still possible as a result of strong ground motion, despite the application of strong column-weak beam concept, as recommended by various design codes. Energy is dissipated through the plastic deformation of specific zones at the end of a member without affecting the rest of the structure. The formation of a plastic hinge in an RC column in regions that experience inelastic actions depends on the column details as well as soil-structure interaction (SSI). In this paper, 854 different scenarios have been analyzed by inelastic time-history analyses to predict the nonlinear behavior of RC columns considering soil-structure interaction (SSI). The effects of axial load, height over depth ratio, main period of soil and structure as well as different characteristics of earthquakes, are evaluated analytically by finite element methods and the results are compared with corresponding experimental data. Findings from this study provide a simple expression to estimate plastic hinge length of RC columns including soil-structure interaction.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2007.11a
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• pp.178-188
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• 2007

In this paper, a half-scaled substructure test was performed to evaluate the buckling and structural safety of an existing transmission tower subjected to wind load. A loading scheme was devised to reproduce the dead and wind loads of a prototype transmission tower, which uses a triangular jig that is mounted on the reduced model to which the similarity law of a half length was applied. As a result of the preliminary numerical analysis carried out to evaluate the stability of a specimen for the design load, it was confirmed that the calculated axial forces of tower leg members were distributed to $80{\sim}90%$ of an admissible buckling load. When the substructured transmission tower was loaded by 270% of its maximum admissible buckling load, it was failed due to the local buckling that is occurred in joints with weak constraints for out-of-plane behavior of leg members. By inspection of load-displacement curves, displacements and strains of members, it is considered that this local buckling was due to additional eccentric force by unbalanced deformation because the time that is reached to yielding stress due to the bending moment is different at each point of a same section.

• Journal of computational fluids engineering
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• v.16 no.1
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• pp.7-13
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• 2011

The fluid-structure interaction of a towed body is simulated using a developed code, which is based on the flux-difference splitting scheme on the hybrid Cartesian/immersed boundary method. To improve the stability in the coupling between the fluid and structure domains, a scheme is used, in which the effects of structure deformation are treated implicitly. The developed code is validated for the fluid-structure interaction problem through comparisons with other results on the vortex-induced vibration of elastically mounted cylinders. To simulate behavior of a towed body, an asymmetric tension modelling for a towing cable is suggested. In the suggested model, the tension is proportional to the elongation of the cable, but the cable has no effect on the body motion whenever the distance between the endpoints of the cable is smaller than the original length of the cable. The fluid-structure interactions of a towed body are simulated on the basis of different parameters of the towing cables. It is observed that the suggested tension model predicts the snapping for a shorter towing cable, which is in accordance with the reported results.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.11a
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• pp.205-208
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• 2008

Steel-embedded composite piers can enhance the resistance of core concrete by confinement of the steel elements and also can strengthen the stability of the embedded steel elements by concrete parts, so that the resistance of the composite members and seismic requirements can be provided without increasing section dimensions and self-weight. While modular composite piers with single segment do not need prestressing, precast segment composite piers with multiple segments need to have prestressing to prevent excessive cracking at the joints. Initial stresses and deformation by the introduced prestress are changed by long-term properties of concrete and need to be considered in the design. This paper deals with the prestress losses by the measurement of load cells, strains of reinforcements, concrete and embedded steel tubes.

• Proceedings of the Korean Geotechical Society Conference
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• 2004.03b
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• pp.730-737
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• 2004

In this paper, in order to examine cyclic hehavior characteristics and safety of underground flexible pipes for electric cables subject to cyclic vehicle load, FEM analysis and cyclic soil box test were carried out. As results of the test, it was revealed that the vertical displacement of the test was larger than that of FEM analysis because thermal effect arising from power cables made reduction of rigidity of the pipe so that large deformation of the pipe induced by the heat occured. Moreover, it was shown that the final vertical displacement under about 0.4 million times of the cyclic load test was not satisfied with elastic allowable displacement of the pipe, and long term stability of the pipe was not stable since behavior characteristics of the pipe exists plastic strain range pasted clastic strain range.

• Earthquakes and Structures
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• v.18 no.5
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• pp.637-648
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• 2020

In this study, a new steel cylindrical shell configuration of the dissipative energy device is proposed to improve lateral ductility and to reduce the damage of the structures against seismic forces. Four nested-eccentric- cylindrical shells are used to constructing this device; therefore, this proposed device is named nested-eccentric-cylindrical shells damper (NECSD). The particular configuration of the nested-eccentric-cylindrical shells is applied to promote the mechanical characteristics, stability, and overall performance of the damper in cyclic loads. Shell-type components are performed as a combination of series and parallel non-linear springs into the in-plan plastic deformation. Numerical analysis with respect to dimensional variables are used to calculate the mechanical characteristics of the NECSD, and full-scale testing is conducted for verifying the numerical results. The parametric study shows the NECSD with thin shells were more flexible, while devices with thick shells were more capacious. The results from numerical and experimental studies indicate that the NECSD has a stable behavior in hysteretic loops with highly ductile performance, and can provide appropriate dissipated energy under cyclic loads.

• Korea-Australia Rheology Journal
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• v.17 no.3
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• pp.99-110
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• 2005

This work presents results of finite element analysis of isothermal incompressible creeping viscoelastic flows with the tensor-logarithmic formulation of the Leonov model especially for the planar geometry with singular comers in the domain. In the case of 4:1 contraction flow, for all 5 meshes we have obtained solutions over the Deborah number of 100, even though there exists slight decrease of convergence limit as the mesh becomes finer. From this analysis, singular behavior of the comer vortex has been clearly seen and proper interpolation of variables in terms of the logarithmic transformation is demonstrated. Solutions of 4:1:4 contraction/expansion flow are also presented, where there exists 2 singular comers. 5 different types spatial resolutions are also employed, in which convergent solutions are obtained over the Deborah number of 10. Although the convergence limit is rather low in comparison with the result of the contraction flow, the results presented herein seem to be the only numerical outcome available for this flow type. As the flow rate increases, the upstream vortex increases, but the downstream vortex decreases in their size. In addition, peculiar deflection of the streamlines near the exit comer has been found. When the spatial resolution is fine enough and the Deborah number is high, small lip vortex just before the exit comer has been observed. It seems to occur due to abrupt expansion of the elastic liquid through the constriction exit that accompanies sudden relaxation of elastic deformation.

• Geotechnical Engineering
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• v.10 no.3
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• pp.97-110
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• 1994

Interaction between an unlined tunnel may cause a serious stability both the tunnel and the overlying and unli Red tunnel interaction meta study on the three dimensional bets a three dimensional elasto plastic the program, a wide range of blur puter analysis such as stress distr menu and tunnel deformation were footing and unlined tunnel. The yes traces the ultimate bearing capacity only on the tunnel size and location revealed is that an unlined tunnel under a square footing is subjected to three dimensional stress pattern along the tunnel axis, and that the magnitudes of stresses in the foundation soil and around tunnel perimeter are considerably smaller when loaded with a square than with a strip footings and the difference varies with the location and the type of stress. It is also revealed that the footing failure mechanism varies with the degree of footing and tunnel interaction.

• Journal of Korean Society of Steel Construction
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• v.17 no.4 s.77
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• pp.439-447
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• 2005

When arch ribs are subjected to vertical loading, they may buckle suddenly towards the in-plane direction. Therefore, the designer should consider their in-plane stability. In this paper, the in-plane elastic and inelastic buckling strength of parabolic, fixed arch ribs subjected to vertical distributed loading were investigated using the finite element method. A finite element model for the snap-through and inelastic behavior of arch ribs was verified using other researchers' test results. The ultimate strength of arch ribs was determined by taking into account their large deformation, material inelasticity, and residual stress. Finally, the finite element analysis results were compared with the EC3 design code.