• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.20 no.9
• /
• pp.2854-2865
• /
• 1996

The concept of variable-geometry truss structure(VGTS) is introduced as a class of actively controlled adaptive structure. VGTS can purposefully vary its geometric configurations by changing the lengths of some members of the structure. General kinematics and inverse kinematics of a statically determinate VGTS(variable geometry truss structure) are studied. The solution technique is based on the Jacobian matrix obtained via joint equilibrium equations. Pseudoinverse control method is applied to resolve the redundancy of a large VGTS. two types of actuator layout of octahedral type VGTS, VG truss and Stewart platform, are compared. Introducing the concept of performance index, Stewart platform based layout was found to has less consumption energy and manipulation time. A functional VGTS model with 3 octahedral modules is designed and manufactured for the labaratory demonstration. Six vertically located length-variable members are used to create general 6 d.o.f. motions.

• Journal of the Korean Society of Propulsion Engineers
• /
• v.23 no.2
• /
• pp.1-12
• /
• 2019

A fundamental study on a gas injection variable thrust method for thrust throttling in a liquid rocket engine was conducted. The gas injection variable thrust has the advantage of not only being able to control the thrust with a simple structure but it also increases the atomization performance through the injection pressure drop that increases in direct proportion to the density reduction. In this study, spray characteristics such as spray instability, spray pattern, spray angle, and breakup length based on changes in the liquid mass flow rate and amount of injected gas were investigated using effervescent swirl injectors.

• The KIPS Transactions:PartC
• /
• v.12C no.1 s.97
• /
• pp.97-104
• /
• 2005

One of the problems of the currently used IPv4 addressing-structure is the fact that there is a shortage of IP addresses and many addresses are being wasted, especially on sub-netting design. The variable subnet masking is a resolution to reduce IP address wasting. We propose an effective subnet W address calculation and management method on VLSM. Also, with the proposed subnet IP address management method, a web based subnet allocation and management system is introduced.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.32 no.3C
• /
• pp.249-255
• /
• 2007

In general, a large amount of the memory accesses are required for the CAVLC decoding in H.264/AVC. It is a serious problem for the applications such as a DMB and videophone services because the considerable power is consumed for accessing the memory. In order to solve this problem, we propose an efficient decoding method for the coeff-token which is one of the syntax elements of CAVLC. In this paper, the variable length code table is re-designed with the new codewords which are defined by investigating the architecture of the conventional codeword for the coeff_token element. A new coeff_token decoding method is developed based on the suggested table. The simulation results show that the proposed algorithm achieves an approximately 85% memory access saving without video-quality degradation, compared to the conventional CAVLC decoding.

• Journal of the Korean Institute of Telematics and Electronics S
• /
• v.35S no.6
• /
• pp.72-80
• /
• 1998

A method is proposed for directional vector quantization using the wavelet packets. After partitioning the wavelet packet coefficients into 9 edges according to the corresponding directions, it encodes and transmits locally dominant edges. The directions of the edges are encoded with a variable length coding and conditional switching of codebooks, while the contents of them with the vector quantization followed by the variable length index coding. The proposed algorithm is superior to various conventional image coding algorithms in the sense of PSNR, which is relatively more significant at very low bit rate such as 0.1~0.3 bpp. As the proposed algorithm preserves the edges which is the most important for the human visual system, it also provides the reconstructed images of good subjective quality even at very low bit rate.

• Journal of the Korean Society for Precision Engineering
• /
• v.27 no.3
• /
• pp.73-79
• /
• 2010

A preliminary study on a length-variable rotor blade for a small unmanned helicopter has been conducted. After surveys on previous researches, and examining requirements for application to a small unmanned helicopter, a length-variable rotor blade was designed and manufactured to be driven by centrifugal force from rotor revolution with no mechanical actuator. The rotor blade was divided into a fixed inboard section and an outboard section sliding in span-wise direction. In order to determine the operating conditions of the length-variable rotor during revolution, and to derive the design variables of extension spring and rotor weight, a series of analyses from multi-body dynamics solution were conducted. The manufactured prototype was verified of its length-varying mechanism from a rotor stand, the results and required future improvements are discussed.

• Journal of the Institute of Electronics Engineers of Korea TC
• /
• v.37 no.9
• /
• pp.24-29
• /
• 2000

As a result of the continuing increase in the high capacity and high speed requirement, ATM will be important technology. But previous AAL type cant support service that is variable length, low speed. So AAL2 is the most recently standardized AAL type, which is aimed at providing for the bandwidth efficient transmission of low-rate, short, and variable length packets in delay-sensitive applications. In this paper, we propose the architecture and the behavior of scalable AAL2 switch that are far different from ATM switch. Also, the performance of the designed switch is analyzed by computer simulation.

• The Journal of the Institute of Internet, Broadcasting and Communication
• /
• v.13 no.5
• /
• pp.235-238
• /
• 2013

In this paper, ㄷ-type MSA for the QMSA structure is proposed. Transformed ㄷ-type MSA is stacked three dielectrics. ㄷ-type MSA structure was load upper & lower surface of the dielectric radiating patch and the ground turn-up left right capacity between parallel plates and radiating patch. Between the dielectric permittivity of the dielectric insert by 2.55 by varing the frequency was shifted. Designed ㄷ-type MSA sturcture of L1 was varied up to 1mm~22mm and frequency was shifted from 3.65GHz~3.84GHz. Also Designed ㄷ-type MSA was measured 1.95dBi maximum gain and bandwidth of 1.61 to 3.64%.

• Journal of the Korean Society of Propulsion Engineers
• /
• v.15 no.3
• /
• pp.22-30
• /
• 2011

There is a many way of LPRE throttling methods, high-pressure-drop systems, dual-manifold injector, gas injection, multiple chambers, pulse modulation and movable injector components. Especially dual-manifold injector is essentially combines two fixed-area injectors into a common structure, with independent feed systems controlling flow to each injector manifold. In this paper, using indirect photography and liquid film thickness measurement with various injection pressure and tangential entry diameter to decide stability of spray over a wide thrust range in dual manifold injector.

• The Journal of the Institute of Internet, Broadcasting and Communication
• /
• v.23 no.1
• /
• pp.37-43
• /
• 2023

Compressed still image or video bitstreams require protection from channel errors in a wireless channel. Embedded Zerotree Coding(EZW), SPIHT could have provided unprecedented high performance in image compression with low complexity. If bit error is generated by dint of wireless channel transmission problem, the loss of synchronization on between encoder and decoder causes serious performance degradation. But wavelet zerotree coding algorithms are producing variable-length codewords, extremely sensitive to bit errors. The idea is to partition the lifting coefficients. A many partition of lifting transform coefficients distributes channel error from wireless channel to each partition. Therefore synchronization problem that caused quality deterioration in still image and video stream was improved.