• Journal of Welding and Joining
• /
• v.35 no.2
• /
• pp.13-22
• /
• 2017

In laser full penetration welding process, full penetration hole(FPH) is formed as a result of force balance between the vapor pressure and the surface tension of the surrounding molten metal. In this work, a three-dimensional numerical model based on a conserved-mass level-set method is developed to simulate the transport phenomena during laser full penetration welding process, including full penetration keyhole dynamics. Ray trancing model is applied to simulate multi-reflection phenomena in the keyhole wall. The ghost fluid method and continuum method are used to deal with liquid/vapor interface and solid/liquid interface. The effects of processing parameters including laser power and scanning speed on the resultant full penetration hole diameter, laser energy distribution and energy absorption efficiency are studied. The model is validated against experimental results. The diameter of full penetration hole calculated by the simulation model agrees well with the coaxial images captured during laser welding of thin stainless steel plates. Numerical simulation results show that increase of laser power and decrease of welding speed can enlarge the full penetration hole, which decreases laser energy efficiency.

• Journal of Drive and Control
• /
• v.11 no.4
• /
• pp.25-31
• /
• 2014

This paper details application of a DLC(Diamond Like Carbon)-coating to the swash plate and the ball joint of pistons that make sliding contact with the piston shoes of an axial piston pump. This process, aimed to reduce the frictional and leakage power losses of the hydrostatic piston shoe bearings at the low speed range. At lower speeds than 100rpm, the positive effects of the DLC-coating on the power loss reduction of the hydrostatic piston shoe bearings could be confirmed. These effects resulted in little improvement in volumetric efficiency of the test pump, but the mechanical efficiency could be raised by up to 5% at 100rpm; here, the DLC-coated swash plate played a more dominant role than the DLC-coated ball joint.

• ETRI Journal
• /
• v.37 no.3
• /
• pp.471-479
• /
• 2015

Traditional designs of cognitive radio (CR) focus on maximizing system throughput. In this paper, we study the joint overlay and underlay power allocation problem for orthogonal frequency-division multiple access-based CR. Instead of maximizing system throughput, we aim to maximize system energy efficiency (EE), measured by a "bit per Joule" metric, while maintaining the minimal rate requirement of a given CR system, under the total power constraint of a secondary user and interference constraints of primary users. The formulated energy-efficient power allocation (EEPA) problem is nonconvex; to make it solvable, we first transform the original problem into a convex optimization problem via fractional programming, and then the Lagrange dual decomposition method is used to solve the equivalent convex optimization problem. Finally, an optimal EEPA allocation scheme is proposed. Numerical results show that the proposed method can achieve better EE performance.

• KSII Transactions on Internet and Information Systems (TIIS)
• /
• v.11 no.11
• /
• pp.5301-5323
• /
• 2017

Small cell deployment offers a low-cost solution for the boosted traffic demand in heterogeneous cellular networks (HCNs). Besides improved spatial spectrum efficiency and energy efficiency, future HCNs are also featured with the trend of network architecture convergence and feasibility for flexible mobile applications. To achieve these goals, dual connectivity (DC) is playing a more and more important role to support control/user-plane splitting, which enables maintaining fixed control channel connections for reliability. In this paper, we develop a tractable framework for the downlink SINR analysis of DC assisted HCN. Based on stochastic geometry model, the data-control joint coverage probabilities under multi-frequency and single-frequency tiering are derived, which involve quick integrals and admit simple closed-forms in special cases. Monte Carlo simulations confirm the accuracy of the expressions. It is observed that the increase in mobility robustness of DC is at the price of control channel SINR degradation. This degradation severely worsens the joint coverage performance under single-frequency tiering, proving multi-frequency tiering a more feasible networking scheme to utilize the advantage of DC effectively. Moreover, the joint coverage probability can be maximized by adjusting the density ratio of small cell and macro cell eNBs under multi-frequency tiering, though changing cell association bias has little impact on the level of the maximal coverage performance.

• Journal of Digital Convergence
• /
• v.14 no.4
• /
• pp.221-230
• /
• 2016

This is an experimental study which is designed to identify the joint relationship between communication density and centrality as independent factors to team performance, discovering how they would jointly affect work team performance. Specially different from existing studies, separating team performance into team efficiency and team effectiveness, we identified differential influences to the two independent factors. Findings suggest a competing relationship between communication density and centrality. A framework was proposed to help managers understand the joint effect of density and centrality on performance. Work team has high communication density and low centrality is "Innovating", which is likely to have a great extent of ideas, knowledge and information sharing, and reach high effectiveness. Team with high centrality and low density is characterized as "centralized". Such communication structure may reduce diversity of perspectives and accelerate team decision making. When both density and centrality are low, the team is "Autonomous". To increase external validity, other factors such as leadership, organizational climate influencing on team performance should be reflected in the future research.

• Journal of the Korea institute for structural maintenance and inspection
• /
• v.18 no.4
• /
• pp.77-83
• /
• 2014

Prestressed concrete girder bridge has been one of the most widely used bridges in the world because of its excellent construction feasibility, economic efficiency, serviceability, and safety. In certain situations, the prestressing tendon is supposed to be bent by the construction error and the radius of curvature at the continuous joint of PSC girders, and this leads to the loss of prestressing force. However, this kind of prestress loss is not considered in the design and construction processes. This study proves that the prestress loss occurs at the continuous joint due to the local bending of tendon by the construction error or the radius of curvature. Also, a method that can reduce this type of prestress loss is proposed, and proved by the experiment. The result shows that maximum 10% of prestress loss occurs at the continuous joint and the proposed block-out method can reduce the prestress loss ratio by maximum 5%, approximately. This means that the block-out method can enhance the prestressing efficiency of continuous PSC girder bridges.

• Proceedings of the Korean Institute of Building Construction Conference
• /
• 2006.05a
• /
• pp.189-194
• /
• 2006

The internal construction industry is not situation of cost reduction based on low wages anymore by the increase in wages as insufficient supply of stilled workers. Recently remodeling constructions that only need to change facilities as to stay the existing structures are on the increase. Now the method of piping facility used to remodeling construction needs stilled workers, large work space and a variety of tools. These complex construction process have a difficulty of high-quality and economical construction. In addition it have the hish incidence of warranty and a problem of cost increase as a commitment of manpower by warranty repair. In order to solve these problems it is necessary for appropriate new technology to the internal construction environment. Piping fittings by Insert & Coupling Joint is a method that unskilled workers can be easily constructed though one touch set up and it is convenient to maintain for repair work of piping facility. This technology show the effect of 3 percentages labor cost reduction as compared with piping fittings by press joint on apartment 500 households. Therefore this technology is supposed that attain a cost reduction though the technical and economical construction and a client satisfaction though the high-quality construction on the present construction market.

• Journal of Welding and Joining
• /
• v.29 no.2
• /
• pp.72-79
• /
• 2011

The scope of this investigation is to evaluate the effect of joining parameters on the microstructural features and mechanical properties of dissimilar aluminum alloys, 1mm-thickness fixing AA6K31 at the top position and fixing AA5J32 at the bottom position. The friction stir lap welds were studied under various welding conditions, rotation speed of 1000, 1250, 1500rpm and welding speed of 100, 300, 500, 700mm/min, respectively. Mechanical test has been investigated in terms of tensile shear test and hardness test. The results showed that three type nugget shapes such as onion ring, zigzag type, hooking with the void, have been observed with revolutionary pitch. All welding conditions fractured at the HAZ of top plate, A6K31 and also the strength compare with base metal of lap joints were low efficiency, 52~63%. The thickness of fractured position was decreased with the lower heat input conditions. The relationships were excellent due to linear between the effective thickness of fractured position and peak load. The fractured position was the interface between joint area and not joint area. Also the strength efficiency compared with base metal was lower than decreasing rate of thickness because the hardness was decreased at fractured position due to softened material.

• Journal of the Korea Convergence Society
• /
• v.11 no.5
• /
• pp.175-182
• /
• 2020

The calculation of the optimal trajectory of the stepped top-down robot was made using a genetic algorithm and a computational torque controller. First, the total energy efficiency was minimized using the Red-Cold Generic Algorithm (RCGA) consisting of reproductive, cross, and mutation. The reproducibility condition related to the position assembly of the start and end of the stride and the joints, angles, and angular velocities are linear constraints. Next, the unequal constraint accompanies the condition for preventing the collision of the swing leg at the corner with the outer surface of the stairs, the condition of the knee joint for preventing kinematic peculiarity, and the condition of no moment in safety in the traveling direction. Finally, the angular trajectory of each joint is defined by fourth-order polynomial whose coefficient is to approximate chromosomes. This is to approximate walking. In this study, the energy efficiency of the optimal trajectory was analyzed by computer simulation through a biped robot with seven degrees of freedom composed of seven links.

• The KIPS Transactions:PartC
• /
• v.12C no.2 s.98
• /
• pp.235-242
• /
• 2005

As the demands in a wireless network are recently increasing, it is necessary to promote the power efficiency of a wireless terminal, and to reduce the overhead of a network. To resolve such problems, we propose the paging technology and the structure of paging area with the joint access point in HPi (High-speed Portable Internet) network, which is being studied as the domestic next-generation IP packet data network. The application of the paging technology to the HPi network possesses the advantage of reducing the registration cost while a terminal in dormant state moves around, and the reporting cost of the terminal's location by the joint access point. The technology suggested in this paper causes the advantages that it promotes the power efficiency in user's point of view while it reduces the network overhead and makes the easy rearrangement of joint APs according to the changes of users' moving pattern in the network manager's point of view.