• Structural Engineering and Mechanics
• /
• v.65 no.6
• /
• pp.761-769
• /
• 2018

In this work, an optimization method of Friction Tuned Mass Damper (FTMD) parameters is presented. Friction tuned mass dampers (FTMD) are attached to mechanical structures to reduce their vibrations with dissipating the vibratory energy through friction between both bodies. In order to exploit the performances of FTMD, the determination of the optimum parameters is recommended. However, the presence of Coulomb's friction force requires the resolution of a non-linear stick-slip problem. First, this work aims at determining the responses of the vibratory system. The responses of the main mass and of the FTMD are determined analytically in the sticking and sliding phase using the equivalent damping method. Second, this work aims to optimize the FTMD parameters; the friction coefficient and the tuned frequency. The optimization formulation based on the Ricciardelli and Vickery method at the resonance frequencies, this method is reformulated for a system with a viscous damping. The inverse problem of finding the FTMD parameters given the magnitude of the force and the maximum acceptable displacement of the primary system is also considered; the optimization of parameters leads to conclude on the favorable FTMD giving significant vibration decrease, and to advance design recommendations.

• International journal of advanced smart convergence
• /
• v.9 no.3
• /
• pp.207-214
• /
• 2020

Currently, the operation of unmanned aerial vehicle (UAV) is regulated to be able to fly only within the visible range, but in recent years, the needs for operation in the invisible area, in the urban area and at night have increased. In order to operate UAVs in the invisible area, at night, and in the urban area, a flight path for UAVs must be prepared like those operated by manned aircraft, and for this, it is necessary to establish an unmanned aircraft system traffic management (UTM). In order to establish the UTM, information on the minimum separation distance to prevent collisions with UAVs and buildings is required, and accordingly, information on the navigation performance of UAVs is required. In order to analyze the navigation performance of an UAV, total system error (TSE), which is the difference between the planned flight path and the actual location of the UAV, is required. If the collected data are insufficient and classification according to integrity, independence, and direction is not performed, accurate navigation performance is not derived. In this paper, propose a navigation performance analysis method of UAV that is derived TSE using flight data and modeled with normal distribution, analyze performance.

• The Journal of the Institute of Internet, Broadcasting and Communication
• /
• v.18 no.5
• /
• pp.1-8
• /
• 2018

The latest cyber attack utilizing advanced technologies is more rapidly advancing than developing speed of defense technology, thereby escalates the security risk. In responding to this recent threat, academia and industries are developing some sophisticated security technologies applying various methods. Based on these technologies, security systems are used in many fields. This article aims to select noticeable network security related technologies for the security systems. In particular, we compared and analyzed the trend, performance, and functions of both foreign and domestic technologies in regard to UTM having the largest portions among network security systems so far. We will also discuss the prospect for the change in network infrastructure due to the emergence of the next-generation network technology.

• KSII Transactions on Internet and Information Systems (TIIS)
• /
• v.7 no.12
• /
• pp.3118-3134
• /
• 2013

This paper deliberates for a multimedia transmission scheme combining multiple description coding (MDC) and network coding (NC). Our goal is to take advantage from the property of MDC to provide quantized and compressed independent and identically distributed (iid) descriptions and also from the benefit of network coding, which uses network resources efficiently to recover lost data in the network. Recently, p-cycle NC has been introduced to recover and protect any lost or distorted descriptions at the receiver part exactly without need of retransmission. So far, MDC have not been explored using this type of NC. Compressed and coded descriptions are transmitted through the network where p-cycle NC is applied. P-cycle based algorithm is proposed for single and multiple descriptions lost. Results show that in the fixed bit rate, the PSNR (Peak Signal to Noise Ratio) of our reconstructed image and also subjective evaluation is improved significantly compared to previous work which is averaging method joint with MDC in order to conceal lost descriptions.

• Journal of Power Electronics
• /
• v.16 no.3
• /
• pp.982-993
• /
• 2016

A method for the fault-tolerant vector control of star-connected 3-phase Induction Motor (IM) drive systems based on Field-Oriented Control (FOC) is proposed in this paper. This method enables the control of a 3-phase IM in the presence of an open-phase failure in one of its phases without the need for control structure changes to the conventional FOC algorithm. The proposed drive system significantly reduces the speed and torque pulsations caused by an open-phase fault in the stator windings. The performance of the proposed method was verified using MATLAB (M-File) simulation as well experimental tests on a 1.5kW 3-phase IM drive system. This paper experimentally compares the operation of the proposed fault-tolerant vector controller and a conventional vector controller during open-phase fault.

• Wind and Structures
• /
• v.24 no.3
• /
• pp.223-247
• /
• 2017

By using numerical simulation, vast and detailed information and observation of the physics of flow over a train model can be obtained. However, the accuracy of the numerical results is questionable as it is affected by grid convergence error. This paper describes a systematic method of computational grid refinement for the Unsteady Reynolds Navier-Stokes (URANS) of flow around a generic model of trains using the OpenFOAM software. The sensitivity of the computed flow field on different mesh resolutions is investigated in this paper. This involves solutions on three different grid refinements, namely fine, medium, and coarse grids to investigate the effect of grid dependency. The level of grid independence is evaluated using a form of Richardson extrapolation and Grid Convergence Index (GCI). This is done by comparing the GCI results of various parameters between different levels of mesh resolutions. In this study, monotonic convergence criteria were achieved, indicating that the grid convergence error was progressively reduced. The fine grid resolution's GCI value was less than 1%. The results from a simulation of the finest grid resolution, which includes pressure coefficient, drag coefficient and flow visualization, are presented and compared to previous available data.

• Transactions on Electrical and Electronic Materials
• /
• v.15 no.1
• /
• pp.7-11
• /
• 2014

The Polarization and Depolarization Current (PDC) measurement is an efficient and effective diagnostic technique based on time domain measurement, for evaluating the high voltage insulation condition. This paper presents a review and comparison results from several published papers on the application of the PDC method to finding the conductivity and moisture content of various types of insulators. For solid insulation, the study was focused on cable insulation, electric machine stator insulation, and paper insulator in transformer insulation with different conditions. For liquid insulation, the review and comparison was done on biodegradable and mineral transformer oils, with fresh oil condition, and aged condition. The results from previous researchers tests were complied, analyzed and discussed, to evaluate the application of the PDC method to monitor the conductivity and moisture of HV equipment insulation systems. From the review results, the PDC technique successfully gives an indication of the conductivity and moisture level of high voltage insulation.

• Journal of the Korean Society for Aviation and Aeronautics
• /
• v.29 no.2
• /
• pp.94-99
• /
• 2021

UTM is an air traffic management ecosystem under development for autonomously controlled operations of UAS by the FAA, NASA, other federal partner agencies, and industry. They are collaboratively exploring concepts of operation, data exchange requirements, and a supporting framework to enable multiple UAS operations beyond visual line-of-sight at altitudes under AGL 500ft in airspace where air traffic services are not provided. Minimum Safe Altitude is a generic expression, used in various cases to denote an altitude below which it is unsafe to fly owing to presence of terrain or obstacles. The European drone regulation mentions that the UAS is maintained within 120 metres from the closest point of the surface of the earth during flight, except when overflying an obstacle. This study attempted to develop a minimum flight altitude database system. Based on domestic and international rules and regulations on setting the minimum flight altitude it is expected that it can be applied to the operation of aircraft and unmanned aerial system in UTM environments for specific area in Korea.

• Journal of International Academy of Physical Therapy Research
• /
• v.12 no.2
• /
• pp.2345-2353
• /
• 2021

Background: This study evaluated the effectiveness of upper thoracic manipulation (UTM) and proprioceptive training versus proprioceptive training alone on forward head posture (FHP) and cervicocephalic joint position sense (CJPS) in asymptomatic university students during a short interval of time. Objectives: To evaluate whether the suggested combination would provide greater benefit, and be superior to proprioceptive training alone in improving proprioceptive acuity and head posture. Design: A single-blind randomized controlled trial. Methods: Thirty-three university student volunteers with asymptomatic FHP were recruited. Subjects were randomly assigned to a manipulation group (n=16) receiving UTM combined with proprioceptive training or a proprioception group (n=17) receiving proprioceptive training only. The intervention period lasted 5 weeks in total, and consisted of one 15 to 20-minute session per week. FHP and CJPS were assessed before and after the intervention. Results: A significant pre- to post-intervention decrease in FHP and joint position error was identified in both groups (P<.05). Subjects in the manipulation group demonstrated greater improvements in CJPS and head posture compared to the proprioception group (P<.05). Conclusion: These findings support employing either intervention for treating asymptomatic students with FHP. However, the addition of UTM to proprioceptive training was more effective than proprioceptive training alone in reducing joint position errors and improving head posture.

• 기계와재료
• /
• v.9 no.2 s.32
• /
• pp.70-88
• /
• 1997