• Title/Summary/Keyword: optimization problem

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Simulation on CO2 capture process using an Aqueous MEA solution (MEA 흡수제를 이용한 이산화탄소 포집 공정 모사)

  • Woo, Dae-Sik;Nam, Sung-Chan;Jeong, Soon-Kwan;Yoon, Yeo-Il
    • Journal of the Korea Academia-Industrial cooperation Society
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    • v.13 no.1
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    • pp.431-438
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    • 2012
  • The $CO_2$ capture technology using an aqueous amine solution is studied widely now. The entire process consists of an absorber to remove carbon dioxide selectively and a regenerator to regenerate absorbent and acquire pure carbon dioxide. Because there are the complicated design variables that affect performance of the process, it needs optimization and analysis through modeling to make a commercially reliable process. In this study, the decomposition method was proposed to consider convergence problem and sensitivity analysis was executed for the carbon dioxide capture process variables. Non-equilibrium model was used in the simulation to get more realistic results and we designed optimized process with more than 95% purity and 90% recovery.

Mobility Management of M2M Devices with Grouping in the LTE System (LTE 시스템에서 그룹 기반 M2M 단말 이동성 관리)

  • Roh, Hee-Tae;Lee, Jang-Won
    • The Journal of Korean Institute of Communications and Information Sciences
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    • v.37B no.12
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    • pp.1119-1127
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    • 2012
  • The one of features of M2M communications, which are recently attracted attention as a future business of mobile communications, is that there is a large number of devices compared with traditional communication services. Hence, the control signal that are generated by the M2M devices may cause a significant congestion in the network and in order to solve this problem, a standardization is progressing for reducing the redundant signaling by managing M2M devices as a group in 3GPP standardization. In this paper, we propose a method of group based mobility management by managing M2M devices that have the same mobility as a group. In the proposed method, M2M devices that have the same mobility are grouped by the Mobility Management Entity (MME) and the MME elects a group header among the M2M devices in the group. Then, the group header performs the Tracking Area Update (TAU) on behalf of the group members to reduce the signaling overhead of mobility management. With the proposed method, we can achieve 80% decrease of the signaling overhead of mobility management compared with the case where each M2M device individually performs its TAU procedure.

SPMLD: Sub-Packet based Multipath Load Distribution for Real-Time Multimedia Traffic

  • Wu, Jiyan;Yang, Jingqi;Shang, Yanlei;Cheng, Bo;Chen, Junliang
    • Journal of Communications and Networks
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    • v.16 no.5
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    • pp.548-558
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    • 2014
  • Load distribution is vital to the performance of multipath transport. The task becomes more challenging in real-time multimedia applications (RTMA), which impose stringent delay requirements. Two key issues to be addressed are: 1) How to minimize end-to-end delay and 2) how to alleviate packet reordering that incurs additional recovery time at the receiver. In this paper, we propose sub-packet based multipath load distribution (SPMLD), a new model that splits traffic at the granularity of sub-packet. Our SPMLD model aims to minimize total packet delay by effectively aggregating multiple parallel paths as a single virtual path. First, we formulate the packet splitting over multiple paths as a constrained optimization problem and derive its solution based on progressive approximation method. Second, in the solution, we analyze queuing delay by introducing D/M/1 model and obtain the expression of dynamic packet splitting ratio for each path. Third, in order to describe SPMLD's scheduling policy, we propose two distributed algorithms respectively implemented in the source and destination nodes. We evaluate the performance of SPMLD through extensive simulations in QualNet using real-time H.264 video streaming. Experimental results demonstrate that: SPMLD outperforms previous flow and packet based load distribution models in terms of video peak signal-to-noise ratio, total packet delay, end-to-end delay, and risk of packet reordering. Besides, SPMLD's extra overhead is tiny compared to the input video streaming.

A Markov Approximation-Based Approach for Network Service Chain Embedding (Markov Approximation 프레임워크 기반 네트워크 서비스 체인 임베딩 기법 연구)

  • Chuan, Pham;Nguyen, Minh N.H.;Hong, Choong Seon
    • Journal of KIISE
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    • v.44 no.7
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    • pp.719-725
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    • 2017
  • To reduce management costs and improve performance, the European Telecommunication Standards Institute (ETSI) introduced the concept of network function virtualization (NFV), which can implement network functions (NFs) on cloud/datacenters. Within the NFV architecture, NFs can share physical resources by hosting NFs on physical nodes (commodity servers). For network service providers who support NFV architectures, an efficient resource allocation method finds utility in being able to reduce operating expenses (OPEX) and capital expenses (CAPEX). Thus, in this paper, we analyzed the network service chain embedding problem via an optimization formulation and found a close-optimal solution based on the Markov approximation framework. Our simulation results show that our approach could increases on average CPU utilization by up to 73% and link utilization up to 53%.

Intelligent Digital Redesign for Uncertain Nonlinear Systems Using Power Series (Powrer Series를 이용한 불확실성을 갖는 비선형 시스템의 지능형 디지털 재설계)

  • Sung Hwa Chang;Park Jin Bae;Go Sung Hyun;Joo Young Hoon
    • Journal of the Korean Institute of Intelligent Systems
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    • v.15 no.7
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    • pp.881-886
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    • 2005
  • This paper presents intelligent digital redesign method of global approach for hybrid state space fuzzy-model-based controllers. For effectiveness and stabilization of continuous-time uncertain nonlinear systems under discrete-time controller, Takagi-Sugeno(TS) fuzzy model is used to represent tile complex system. And global approach design problems viewed as a convex optimization problem that we minimize the error of the norm bounds between nonlinearly interpolated linear operators to be matched. Also, by using the power series, we analyzed nonlinear system's uncertain parts more precisely. When a sampling period is sufficiently small, the conversion of a continuous-time structured uncertain nonlinear system to an equivalent discrete-time system have proper reason. Sufficiently conditions for the global state-matching of tile digitally controlled system are formulated in terms of linear matrix inequalities (LMIs). Finally, a TS fuzzy model for the chaotic Lorentz system is used as an example to guarantee the stability and effectiveness of the proposed method.

A Study of Carbon NCF Prepreg Manufacturing and Stacking Pattern Optimal Design Using Structure Analysis (CFRP 적용을 위한 Carbon NCF Prepreg 제작 및 구조해석을 활용한 적층패턴 최적설계 연구)

  • Kim, S.;Shin, H.C.;Ha, Sung Kyu
    • Composites Research
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    • v.33 no.1
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    • pp.13-18
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    • 2020
  • Recently, the fire rescue truck in problem proceed research it for the fast works action and for pass the small road. So we were research for weight reduction. In this study, the (NO. 5) fifth boom of the fire rescue truck have 288 mm(W) × 299 mm(D) × 3,691 mm(L) with a maximum load of 876 kg and the thickness of 3 mm of the Steel Boom. This changing of Steel (STRENX960) to CFRP was weave Carbon Fiber NCF (±45°, 2axis) and then it make the NCF Prepreg. This process was designed based on structural analysis, the effects of NCF Prepreg (±45°) on torsion were identified, and the optimal design was made with Stacking Pattern (b). Stack patterns were optimized for levels equal or higher than existing Steel Boom and CFRP Boom stacked in the UD direction, and finally, the lightening effect on weight of approximately 49.6% of the steel was identified.

Improvement of existing machine learning methods of digital signal by changing the step-size (학습률(Step-Size)변화에 따른 디지털 신호의 기계학습 방법 개선)

  • Ji, Sangmin;Park, Jieun
    • Journal of Digital Convergence
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    • v.18 no.2
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    • pp.261-268
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    • 2020
  • Machine learning is achieved by making a cost function from a given digital signal data and optimizing the cost function. The cost function here has local minimums in the cost function depending on the amount of digital signal data and the structure of the neural network. These local minimums make a problem that prevents learning. Among the many ways of solving these methods, our proposed method is to change the learning step-size. Unlike existed methods using the learning rate (step-size) as a fixed constant, the use of multivariate function as the cost function prevent unnecessary machine learning and find the best way to the minimum value. Numerical experiments show that the results of the proposed method improve about 3%(88.8%→91.5%) performance using the proposed method rather than the existed methods.

GE 7FA+e DLN-2.6 Gas Turbine Combustor : Part Ⅰ Operating Condition Optimization (GE 7FA+e DLN-2.6 가스터빈 연소기 연구 : Part Ⅰ 운전조건 최적화)

  • Oh, Jeong-Seog;Kim, Min-Ki;Heo, Pil-Won;Lee, Jang-Soo;Yoon, Young-Bin
    • Journal of the Korean Society of Propulsion Engineers
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    • v.12 no.5
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    • pp.43-50
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    • 2008
  • DLN-2.6 combustion tuning was carried out for the maintenance of GE 7FA+e gas turbine at Seo-Incheon combined cycle power plant. DLN-2.6 combustion system has the higher level of yellow plume and combustion vibration problem in the initial operating mode than that of the base mode($100{\sim}160MW$). The objectives of this study are to investigate the causes of yellow plume and combustion vibration problems at the starting mode and to suggest the best operating condition for the reliable working of the real combustors. By the analysis of tuning data, we could conclude that a yellow plume is caused by the rich mixture(${\phi}{\sim}1$) in a PM 1 nozzle at mode 3($20{\sim}30MW$). In addition, the combustion vibration($120{\sim}140Hz$) might be related to the cold flow characteristics of PM 3 nozzles at mode 6B($40{\sim}45MW$).

A Study on the Analysis of Pogo Instability and Its Suppression of Liquid Propellant Rocket (액체추진 로켓의 포고 불안정성 해석과 제어에 관한 연구)

  • Jang, Hong Seok;Yeon, Jeong Heum;Yun, Seong Gi;Jeong, Tae Gyu;Jang, Yeong Sun
    • Journal of the Korean Society for Aeronautical & Space Sciences
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    • v.31 no.3
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    • pp.58-64
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    • 2003
  • Pogo is the instability resulting from the interaction between rocket structure and propulsion system of liquid propellant rocket. The coupling of structure and propulsion system can lead to severe problem in rocket. For the analysis of pogo, a time-invariant linearized mathematical model is developed for a selected flight time. Propulsion system is modeled using element representations for each components. Rocket structure is modeled using FEM. Form the results of modal analysis of structure, the behavior of structure can be represented. System equations for coupling structure and propulsion system are composed. The stability in obtained by the eigen solution of system matrix. The optimization of the design variables such as size, place of accumulator for suppressing pogo instability in carried out. This article of study can be used to determine the degree of stability, and guide the design of pogo suppression system.

A Parametric Study on Optimal Earth-Moon Transfer Trajectory Design Using Mixed Impulsive and Continuous Thrust (혼합 추력 방식의 지구-달 최적 전이궤적 설계인자에 따른 비교연구)

  • Lee, Dae-Ro;No, Tae-Soo;Lee, Ji-Marn;Jeon, Gyeong-Eon
    • Journal of the Korean Society for Aeronautical & Space Sciences
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    • v.39 no.11
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    • pp.1021-1032
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    • 2011
  • This paper presents the results of a parametric study for the design of optimal Earth-Moon transfer trajectory using mixed impulsive and continuous thrust. Various types of the optimal Earth-Moon transfer trajectories were designed by adjusting the relative weight between the impulsive and the continuous thrust, and flight time. Two very different transfer trajectories can be obtained by different combination of design parameters. Furthermore, it was found that all thus designed trajectories permit the ballistic capture by the Moon gravity. Finally, the required thrust profiles are presented and analyzed in detail.