• Steel and Composite Structures
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• v.42 no.6
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• pp.791-804
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• 2022

As a type of semi-rigid connection, the top and seat angle connections are popular in current structures owing to their good cyclic performance and simple erection. However, their stiffness and load bearing capacity are relatively insufficient. This study proposes two strengthening methods to further increase the stiffness and strength of bolted-angle joints while maintaining satisfactory energy dissipation capacity (EDC) and ductility. Cyclic loading tests were conducted on six joint specimens with different strengthened angle components. Based on the test results, the influence of the following important factors on the cyclic behavior of steel joint specimens was investigated: the position of the rib stiffeners (edge rib stiffeners and middle rib stiffener), steel strength grade of rib stiffeners (Q345 and Q690), and additional stiffeners or not. In addition, the finite element models of these specimens were built and validated through a comparison of experimental and numerical results. The stiffness and bearing capacity of the bolted-angle joints could be improved significantly by utilizing the novel strengthened joints proposed in this study. Moreover, this can be achieved with almost no increase in the amount of steel required, and the EDC of this joint could also satisfy the requirements of seismic codes from various countries.

• Steel and Composite Structures
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• v.24 no.2
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• pp.227-237
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• 2017

This paper presents optimization of a long-span portal steel frame under dynamic wind loads using a surrogate-assisted evolutionary algorithm. Long-span portal steel frames are often used in low-rise industrial and commercial buildings. The structure needs be able to resist the wind loads, and at the same time it should be as light as possible in order to be cost-effective. In this work, numerical model of a portal steel frame is constructed using structural analysis program (SAP2000), with the web-heights at five locations of I-sections of the columns and rafters as the decision variables. In order to evaluate the performance of a given design under dynamic wind loading, the equivalent static wind load (ESWL) is obtained from a database of wind pressures measured in wind tunnel tests. A modified formulation of the problem compared to the one available in the literature is also presented, considering additional design constraints for practicality. Evolutionary algorithms (EA) are often used to solve such non-linear, black-box problems, but when each design evaluation is computationally expensive (e.g., in this case a SAP2000 simulation), the time taken for optimization using EAs becomes untenable. To overcome this challenge, we employ a surrogate-assisted evolutionary algorithm (SAEA) to expedite the convergence towards the optimum design. The presented SAEA uses multiple spatially distributed surrogate models to approximate the simulations more accurately in lieu of commonly used single global surrogate models. Through rigorous numerical experiments, improvements in results and time savings obtained using SAEA over EA are demonstrated.

• Journal of Broadcast Engineering
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• v.23 no.4
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• pp.495-502
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• 2018

JVET (Joint Video Exploration Team) which explored evolving technologies of video coding with capabilities beyond HEVC (High Efficiency Video Coding), released a references software codec named the Joint Exploration Model (JEM) for performance verification of coding technologies. JEM has 67 intra prediction modes that extend the 35 modes of HEVC for intra prediction. Therefore, the enhancement of the coding performance is limited due to the overhead of prediction mode coding. In this paper, we analyze the probabilities of prediction modes selections, and then we propose a more efficient intra prediction mode coding based on the results of analyzed mode occurrence. In addition, we propose a context modeling for CABAC (Context-Adaptive Binary Arithmetic Coding) of the proposed mode coding. Experimental results show that the BD-rate gain is 0.02% on the AI (All Intra) coding structure compared to JEM 7.0. We need to optimize context modeling for additional coding performance enhancement.

• Journal of Korean Foot and Ankle Society
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• v.8 no.1
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• pp.31-38
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• 2004

Purpose: The purpose of the study was to identify the subtypes of idiopathic osteoarthritis of the tarsometatarsal joints based on accompanying hindfoot, midfoot, or foot deformities and their corresponding surgical options and also to evaluate the overall clinical results. Materials and Methods: The study included 59 patients (67 feet) with idiopathic tarsometatarsal joint osteoarthritis. Tarsometatarsal fusion was performed for tarsometatarsal joint and accompanied secondary change was divided into subtypes and various bony reconstruction was carried out. The patients were evaluated with the AOFAS midfoot score and FFI. The average patient age was 60.2 years with 40.6 months follow-up. Fifty-four feet (80.6%) had been treated with realignment fusion. Twenty-six feet had first and second tarsometatarsal joint fusion, and 20 feet had first tarsometatarsal fusion only. Six subtypes were identified based on associated foot deformities: 1) in-situ without deformities (18%), 2) pes planovalgus (45%), 3) rockerbottom (15%), 4) cavus foot (1%), 5) hallux valgus (12%), and 6) hallux valgus with pes planovalgus or rockerbottom (9%). Plantar-medial closing-wedge resection was used in 10 feet to correct rockerbottom. For pes planovalgus, a medial sliding calcaneal osteotomy was done. Lateral column lengthening with medial sliding calcaneal osteotomy was done for severe pes planovalgus, and triple arthrodesis was done for rigid pes planovalgus. Hallux valgus was corrected with the Lapidus procedure (85.7%). Results: AOFAS midfoot scores improved from preoperative 34.1 points to postoperative 83.9 points (p<0.05). The Foot Function Index postoperatively also showed significant improvement (p<0.05), with a high satisfaction rate (86.6%). There were 29 complications, most commonly sesamoid pain. Conclusion: Idiopathic tarsometatarsal OA feet can be classified into six categories. Pes planovalgus feet should be treated with medial sliding calcaneal osteotomy, lateral column lengthening, or triple arthrodesis in addition to tarsometatarsal joint realignment fusion. Rockerbottom and hallux valgus deformities should also be addressed.

• International Journal of Aeronautical and Space Sciences
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• v.16 no.1
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• pp.28-40
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• 2015

This paper aims to address the intelligent active vibration control problem of a flexible rectangular plate vibration involving parameter variation and external disturbance. An adaptive sliding mode (ASM) MIMO control strategy and smart piezoelectric materials are proposed as a solution, where the controller design can deal with problems of an external disturbance and parametric uncertainty in system. Compared with the current 'classical' control design, the proposed ASM MIMO control strategy design has two advantages. First, unlike existing classical control algorithms, where only low intelligence of the vibration control system is achieved, this paper shows that high intelligent of the vibration control system can be realized by the ASM MIMO control strategy and smart piezoelectric materials. Second, the system performance is improved due to two additional terms obtained in the active vibration control system. Detailed design principle and rigorous stability analysis are provided. Finally, experiments and simulations were used to verify the effectiveness of the proposed strategy using a hardware prototype based on NI instruments, a MATLAB/SIMULINK platform, and smart piezoelectric materials.

• Journal of Korean Society for Quality Management
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• v.47 no.3
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• pp.437-451
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• 2019

Purpose: The purpose of this study is to improve the quality of the PGM system by improving the structure and production process of slip-ring rotary joint for radar. Methods: The improvement measures for each cause are established through failure analysis of broken items. Specifically, changing in the housing to improve the heating system. Changing the transportation method to prevent damage to equipment during transport. Changing work process of the attenuator ring to prevent damage. etc. Results: The results of this study are as follows; improving the heating system reduces heat generated by the attenuator by about 7 degrees and obtain additional temperature margins. Reduction of defect rate because of adding X-band rotary joint run-out measurement test, ESS of slip-ring rotary joint and Transportation improvement(reinforced flight boxes, tube protection, etc). Getting stable VSWR values by improving work process of attenuator overheating due to a bad bonding process. Conclusion: Through this study, improvements were made to slip-ring rotary joint that failed repeatedly for various reasons. As a result of the application of the improvements, the same fault does not occur until now, so we can see that the quality of PGM has improved.

• Proceedings of the Korean Geotechical Society Conference
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• 1991.10a
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• pp.179-194
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• 1991

This paper explains outline of a behavior analysis program for underground structures, and its application to a tunnel problem. The program can deal with elasto-plastic behavior of medium and supporting structures, discontinuous behavior due to existing joint, creation and propagation of cracks. in-situ loading condition, and incremental behavior due to stepwise excavation, etc. The program also has additional capabilities such as graphic output of mesh, displacement pattern, stress condition, and safety factor contour, and automatic mesh generation during the excavation steps.

• 제어로봇시스템학회:학술대회논문집
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• 1993.10a
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• pp.895-901
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• 1993

This paper present controller designs based on the configuration control framework for a redundant manipulator to accomplish the basic task of desired, end-effector motion, while utilizing the redundancy to achieve the additional tasks such as joint motion control, obstacle avoidance, singularity avoidance. etc. A task based decentralized adaptive scheme is then applied for the configuration variables to track some reference trajectories as close as possible. Simulation results for a direct-drive three-link arm in the vertical plane demonstrate its capabilities for performing various useful tasks.

• 제어로봇시스템학회:학술대회논문집
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• 1996.10b
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• pp.371-374
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• 1996

This paper presents the kinematic and dynamic analysis of parallel manipulators with redundant joints, obtained by putting additional active joints to an existing parallel manipulator. We develop the kinematic and dynamic models of a parallel manipulator with redundant joints. The redundancy in serial chain, due to the increased number of joints per limb, is considered in the modeling. Based oh the derived models, we define the kinematic and dynamic manipulabilities of a parallel manipulator with redundant joints. The effect of the redundant joints on the performance of parallel manipulators is analyzed in terms of kinematic and dynamic manipulabilities.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2018.05a
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• pp.243-244
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• 2018

This study focused on the fact that there are a lot of alleys in some areas of the Urban Renewal New Deal project. In this study, we proposed a method to construct a spatial module by combining small modules. It is expected that the combination of small modules developed in this way will help revitalize the New Deal of Urban Regeneration. In the future, additional joint details will be developed, structure review will be conducted.