무선 센서 네트워크에서 에너지 효율적인 멀티홉 스킴 기반의 라우팅 알고리즘

박순례 성균관대학교 일반대학원 2009 국내석사

센서네트워크에서 어떤 센서노드가 다른 노드 혹은 베이스스테이션으로 패킷을 보내려고 할 때, 아이디얼한 통신환경을 가정한다면, 그 때의 센서노드가 소모하는 에너지는 거리에 의존적이며 일반적으로 1/dα 로 표현할 수 있다. 여기에서 d는 transmitter와 receiver 사이의distance를 의미하며 α는 path-loss( indoor environment : 2~4)를 의미한다. 이와 같이 에너지 소모와 거리의 상관관계로 인하여 기존의 많은 연구에서는 통신반경 내에 센서노드들이 조밀하게 위치하고 있더라도 Single-Hop 보다는 Multi-Hop 기반의 라우팅 알고리즘을 설계해 왔다. 그러나 short range의 멀티홉 라우팅은 에너지 소모에 있어 문제점 역시 가지고 있다. 그것은 일반적으로 센서노드의 에너지 소모가 데이터를 송,수신할 때 가장 크기 때문이며 Switching 모드 즉, TX 모드에서 RX모드로의 전환 혹은 RX모드에서 TX모드로의 전환 시에 발생되는 에너지 소모와 CSMA/CA가 동작할 때의 에너지 소모 역시 결코 간과할 수 없는 수준을 보이고 있기 때문이다. short range의 통신거리를 기반으로 한 Rahul C. Shah 의 Energy Aware Routing 은 네트워크의 규모가 커질수록 빈번한 Switching과 hop count가 많아짐으로 인해 TX, RX, 모드 전환, CSMA/CA 등에서 발생되는 에너지 소모가 극심해져서 전체적인Network Lifetime을 단축시킬 수 있다. 이러한 이유로, 본 논문에서는 energy efficient한 multi-path 중 상대적으로hop count가 최소인 경로를 선택하게 하고 hop count가 같을 때는 데이터 송,수신 경로로 사용되었던 path에 weight를 주어 weight 값이 작은 노드를 먼저 선택되게 함으로써 Energy Aware Routing의 short range에서 발생되는 overhead 를 개선하고자 하였다. 우리는 시뮬레이션 결과를 통해 EAR보다 향상된 Network survivability를 확인할 수 있었다. Energy conservation is critical in wireless sensor networks. Conventionally, energy consumption is represented by, when d is the distance between a TX and a RX, and is the path-loss (generally between 2 and 4 for indoor environments). Such a correlation between the energy consumption of sensor node and the distance between a transmitter and a receiver allows a researcher to develop multi-hop routing algorithms rather than single-hop routing algorithms even in the networks with densely placed sensor nodes. Short-ranged multi-hop routing algorithms, however, induce noticeable energy consumption particularly under the two situations 1) when the TX mode is changed to the RX mode and when the RX mode is changed to the TX mode and 2) when CSMA/CA is used. A large-scale network would require more frequent switching and hop counts. To reduce these overhead, we propose a energy-efficient multi-hop scheme based on routing algorithm (EEMS), which use relatively minimum hop count and node weight. Simulation result presents that our proposed scheme shows better performance for network survivability.

AMIP II 기간에 모사된 모형 대기 에너지 수지의 분석

오현택 연세대학교 대학원 2001 국내석사

기후 변화의 이해와 예측을 위해서 필수적인 고품위 기후 시스템 모형의 평가에서 에너지와 수증기의 광역 수지는 매우 중요한 사항이다. 이 연구는 연세대학교 대기 대순환 모형 대류권 7층 판 YONU AGCM Tr7로 AMIP Ⅱ 기간 곧 1979.1 - 1996.2의 17년 2개월 기간에 대해서 모사된 모형 대기의 에너지 수지를 분석하고, 해양 대기로부터 육지 대기에로의 에너지 수송 및 수증기 수송사이의 관계를 파악하고자 하는 것이다. 이 연구에 사용된 모형 자료는 AMIP II에 출품된 YONU AGCM Tr7의 표준 모형 출력 자료이고, 검증 자료는 NCEP/DOE 재분석 자료이다. AMIP Ⅰ과 AMIP Ⅱ에 대하여 각각 모사된 에너지 수지 성분들의 상호 비교와 이들의 검증으로부터 YONU AGCM T r7의 오류 교정을 통한 괄목할 만한 모형 품위의 개선이 확인되었다. 특히, AMIP Ⅱ 기간에 모형의 에너지 속은 대기 상단에서 하향으로 9.4 W/㎡, 그리고 지표에서 하향으로 1.4 W/㎡ 이고, 대기의 에너지 불균형은 8.0 W/㎡이다. 이 8.0 W/㎡ 불균형은 AMIP Ⅰ의 25 W/㎡ 에 비해 대폭적으로 감소된 것이다. 이 불균형을 해양과 육지의 구별없이 대기안에서 소실된 것이라고 보면 육지 대기는 17.7 W/㎡의 에너지 부족을, 그리고 해양 대기는 6.7 W/㎡의 에너지 여분을 각각 보인 것으로 해석된다. 이 해석에 따라 해양에서 육지로 일어날 에너지 수송은 4.8 × 1015 W 이다. 이 값은 해양 또는 대기를 통하여 저위도에서 고위도로 일어나는 에너지 수송과 대략적으로 같은 수준이다. 해양에서 육지로 일어나는 이 에너지 수송에 대한 잠열 수송의 기여가 얼마인가를 알기 위해서 모형에서 일어난 유수를 통하여 추정한 결과, 해양에서 육지에로의 잠열 수송은 5.5 × 1015 W 이었다. 이 값은 전체 에너지 수송 4.8 × 1015 W 보다 더 크다. 이는 엔탈피와 지위 에너지의 형식으로 에너지가 육지에서 해양으로 0.7 × 1015 W의 율로 흘러 나간다는 것을 의미한다. 이 결과에 비추어 해양과 육지 사이에 일어나는 에너지와 수증기의 흐름은 매우 밀접하게 연관된 것임이 확인된다. As a valuation of quality, global energy budget and water vapor budget are very important component. This research is an analysis of the model atmosphere energy budget and transportation from ocean atmosphere to land atmosphere by means of between the energy and water vapor relation for the AMIP II period, 1979.1 - 1996.2, simulated with Yonsei University Atmospheric General Circulation Model with 7 vortical levels. To understand and predict the climate system, we must have a high-quality climate system model. Most principal climate models had been participating the AMIP do intercompare the models, and do asses their quality. The data used in this research is the YONU AGCM Tr7 AMIP II standard output that is submitted to the AMIP II For verification of the output is NCEP/DOE(National Centers for Environmental Prediction/United States Department of energy) reanalysis data. When we study the simulated normal mean fields of energy flux components and patterns of the global distribution, we can find remarkable improvement on the model quality achieved by some development and error correction of YONU AGCM Tr7. Especially analysed atmospheric energy imbalance during AMIP II period is downward 9.4 W/㎡ at the top of the atmosphere, downward 1.4 W/㎡ at the surface, thus 8.0 W/㎡ at the atmosphere. Comparing with energy imbalance during AMIP. I period which was 25 W/㎡ energy surplus, we could get a sharp decrease of the atmospheric imbalance, and confirm the approachment to the energy balance. When we consider the global atmospheric energy imbalance, we can infer that the land atmosphere have 17.7 W/㎡ energy deficit, the ocean atmosphere have 6.7 W/㎡ energy surplus. According to energy deficit and surplus, the energy of the transportation from ocean atmosphere to land atmosphere is 4.8 × 10^(15) W. This value is the same level energy from low latitude to high latitude occording to ocean and land. To investigate how the latent heat do contribute the energy flux from ocean to land, we calculated runoff by YONU AGCM Tr7. So we could get that the estimated latent heat flux is 5.5 × 10^(15) W. This is apparently larger than total energy flux, means that the energy follow from land to ocean by means of the form of entalphy and geopotential energy. This result confirm that the stream of the energy and water vapor between ocean and land does have closely relation.

서울시 주거용 소형 건축물 에너지효율 2등급 달성을 위한 설계요소 최적화 방안

정영대 연세대학교 공학대학원 2020 국내석사

This study is to suggest optimal design factors that could have energy efficiency class 2 in a case of multi-level building depending on Seoul Green-Building design criteria, corresponding to residence which has from 30 or more to less than 300. The energy efficiency rating certification criteria are used as indicators in the other certification system. When evaluating energy sector of Green-Building certification for apartment housing, residential complex, and office building, advantageous scores apply to the energy sector assessment either &energy performance index& or &Building Energy Efficiency& certification level. The higher level a building has, the higher score Green-Building certification energy sector could get, so that it is advantageous for getting a score. It is the reason to set the energy efficiency class 2 as a criterion that, although Seoul Green-Building design criteria are all obligations, there are realistic difficulties to get the class 2 in design, construction, and construction cost. If a residential building get an energy efficiency class 1, construction cost becomes more expensive upto about 5% to 7%, compared to energy efficiency class 3. This study considered that it is not helpful for both building industry clients and actual consumers. In the case of multi-level building that Seoul designates, there is no case study yet that selected and researched efficiency of construction, machine, and electrical design element in order to aim at the energy efficiency class 2. Even though there has been a lot of studies about improving general energy efficiency or focusing on each design factor of them, there is no research, considering both the economic efficiency and the efficiency of national energy policy, which could satisfy all of producers and consumers. Therefore, this study selected a small residential building, constructed actually in Seoul as the case of energy reduction design factors, and it researched changes in primary energy requirements, depending on the changes of energy demands and requirements from window specifications, energy demands and requirements from heat exchangers, and energy demands and requirements from boiler efficiency, by utilizing ECO2 simulation. Then, it applied the design factors into Gwangju-si and Busan-si where it shows different weather data, and it compared and analyzed them with each other. This study expects this research could be utilized as basic data for a design with the optimal level when planning to acquire the energy efficiency level. As a result, the optimal conditions to have the energy efficiency class 2 in the multi-level building are as follows. In Seoul with external insulation structure, if a building is planned to have a boiler, a small capacity boiler should be used in the case of equal efficiency. In the case of windows, solar heat gain coefficient could influence heating energy requirement. The less solar heat gain coefficient becomes, the smaller heating energy requirement becomes, and then primary energy requirement is becoming reduced also. Although, if the window specifications are Roy Duplex Double window, Argon filling, and the use of heat exchanger, it will influence heating energy to be reduced, the use of heat exchanger does not affect primary energy saving a lot due to use of ventilation energy. Air flow of the applied heat exchanger is 50CMH. 본 연구에서는 서울시 녹색건축 설계기준에 의한 적용대상인 30세대 이상부터 300세대 미만의 주거지에 해당하는 서울시 녹색건축 설계기준 다 등급 건축물에 있어 에너지 효율 2등급을 획득할 수 있는 최적의 설계요소를 제시하는데 그 목표가 있다. 건축물 에너지효율등급 인증기준은 타 인증제도에서 에너지부문 지표로 활용된다. 녹색건축물 인증제도의 공동주택, 주거복합, 업무용 건축물의 에너지부문 평가 시 건축물 에너지절약 설계기준의 ‘에너지성능지표’나 ‘건축물 에너지효율’ 인증 등급 중 유리한 점수로 에너지부분의 평가에 적용된다. 등급이 높을수록 녹색건축물 인증 에너지부문 항목에 높은 점수를 획득하여 점수 확보에 유리하게 적용된다. 건축물 에너지효율등급 2등급을 그 기준으로 선택한 이유는 건축물의 설계, 시공, 공사비 등 문제로 30세대 이상부터 300세대 미만 기준에 해당하는 주거용 건축물은 에너지효율 2등급 획득 의무사항 임에도 불구하고 등급획득에 많은 현실적인 어려움이 따른다. 소형 주거용 건축물의 에너지효율등급을 1등급까지 높일 경우 3등급 대비 건축공사비가 5~7% 이상 상승 건축주와 실소비자 모두에게 유인이 없다고 판단했기 때문이다. 서울시에서 지정하고 있는 다 등급 건축물의 경우 에너지효율 2등급을 목표로 건축, 기계, 전기 설계요소의 효율성을 선별 연구한 사례는 아직 없다. 에너지 효율 전반을 개선시키는 내용이나 그 각각의 설계요소의 효율성에 주목한 경우는 많았으나 생산자와 소비자 모두의 필요를 만족시킬 경제적 효율성과 국가에너지 정책의 효율성을 함께 고려한 연구는 거의 전무한 실정이다. 이에 본 연구는 실제 서울시에 시공된 소형 주거용 건축물의 사례로 에너지절약 설계요소 사례를 선정하여 창호 사양에 따른 에너지 요구량 및 소요량, 전열교환기 적용에 따른 에너지 요구량 및 소요량, 보일러 효율에 따른 에너지 요구량 및 소요량 설계요소 사례 변화에 따른 1차 에너지 소요량의 변화 추이를 ECO2 시뮬레이션을 통해 살펴보고 그에 따른 설계요소를 기상데이터가 다른 광주, 부산 지역에 도 적용하여 비교분석 해보았다. 본 연구는 등급 획득 계획 시 적정수준 설계를 위한 기초 자료로 활용하고자 한다. 연구결과 다 등급 주거용 건축물에서 에너지효율 2등급을 획득하기 위한 최적의 조건은 다음과 같다. 서울지역의 경우, 외단열 구조에 보일러의 효율이 같다면, 용량이 작은 보일러를 사용하고, 태양열 취득률 계수가 낮은 창호를 사용하는 것이 난방에너지 소요량이 적은 것으로 확인된다. 예를 들어, 창호사양은 로이복층이중창에 아르곤 충진, 전열교환기 사용은 난방에너지 절감에 영향을 미치지만 환기에너지의 사용으로 전열교환기 사용이 1차 에너지절감에 크게 작용하지 않은 것을 볼 수 있었다. 전열교환기의 사양은 풍량 50CMH 일 때 1차 에너지소요량이 감소하여, 용량이 작을수록 등급획득에 유리한 것을 확인 할 수 있었다.

Towards low carbon development : an analysis of Botswana's energy sector transformation

Mareledi Gina Maswabi Green School Graduate School of Energy and Environ 2020 국내박사

The UNFCCC and global governments are working towards stabilization of GHG concentrations in the atmosphere to levels that will not harm the environment. In 2015, the governments collectively adopted the Paris Agreement with a goal to suppress global warming to temperatures well below 2°C. In line with this, the government of Botswana made a voluntary commitment to reduce emissions by 15% by the year 2030, against a 2010 base year. However, as a developing country, Botswana has to increase energy production to meet the increasing demand and for now, her current energy expansion plans are biased towards coal as it presents the least cost option. This will proliferate CO2 emissions and dissuade the country’s aspirations to reduce atmospheric emissions. In order to strike a balance, transitioning from reliance on coal towards increase in use of cleaner options such as solar and improved efficiency is vital. There seems to be a strong political will from the Botswana government in this regard, considering the ratification of various international environment and climate change treaties that promote low carbon development. On this note, the government can take a stance to power the currently non-electrified remote villages with solar and improve efficiency of the current system hence eliminate the need for additional electricity production from coal. A research framework was developed for this study and used to analyse Botswana’s existing policy and institutional frameworks to examine their likelihood to steer transformation of the energy system towards low carbon development. The framework analyses the impacts of external pressure (top-down) on the existing electricity regime as well as regime changes that come as a result of learnings from previous niche experiments (bottom-up). The review of documents has shown that global pressure exerted on governments has led to changes in the focus of Botswana’s energy policy instruments, which now support energy transition. Interviews with experts, on the other hand, revealed a number of barriers that can impede transformation of the energy sector. Currently, the use of solar in Botswana is very insignificant, constrained mainly by absence of clear policy instruments and/or clear roadmaps for scaling up of this resource. There is also a technology lock-in driven by the government’s subsidy on conventional power, which makes solar expensive and exorbitant. This study makes some recommendations for changes that can be effected in the current regime in order for Botswana to facilitate solar energy development. The recommendations are confined to energy transition in the electricity subsector and not transformation of the holistic energy system because electricity generation contributes the most to Botswana’s total emissions and electricity is an enabler for other sectors of the economy. Energy transition will not only assist the government to meet its global obligation of reducing GHG emissions, but can also attribute; (i) increasing energy access, (ii) facilitating local market for renewable energies, (iii) promotion of local renewable energy-related industries, (iv) job creation, and (v) provision of affordable energy from on-site production through decentralised systems.

Energy-Efficient Scheduling Algorithms for Real-Time Tasks on Single and Multiprocessors

선주형 고려대학교 대학원 2020 국내박사

With the advancement of technologies such as the Internet of Things, high-performance computing, and cloud computing technologies, embedded systems have become an integral part of our lives enabling a large number of users to run their diverse applications. Since the behavior of embedded systems is typically restricted by time, though they may not necessarily have any real-time constraints, the optimality of real-time tasks has to be considered for supporting time-sensitive systems. In addition, modern systems have various processor types, such as single-processor, multi-processors, and many-processors, which consume a relatively large fraction of the total energy compared with other components such as I/O, network, and memory. In addition, system power supplies such as batteries are limited and the static energy consumption (i.e., leakage power dissipation) has become a significant contributor to the total dissipation of chip power. Therefore, this dissertation presents methodologies for scheduling real-time tasks under time constraints (i.e., deadlines) and managing the energy consumptions of single-, multi-, and many-processors. The objective is to guarantee the optimality of scheduling real-time tasks and simultaneously reduce the energy consumption of various systems. To achieve this objective, real-time scheduling is formulated as an optimization problem to find an optimal solution to guarantee meeting all the real-time task deadlines. To reduce both dynamic and static energy consumption, dynamic voltage/frequency scaling and dynamic power management are introduced to the real-time scheduling algorithms. These methodologies are summarized as follows. (1) For multimedia services on a single-processor, an energy-efficient scheduling algorithm is proposed to reduce the dynamic power consumption using dynamic voltage/frequency scaling while deterministically guaranteeing a feasible schedule for weakly hard real-time tasks. This work was conducted on a laptop computer and the actual power consumption was measured using a digital power-meter to evaluate energy savings using the proposed algorithm. (2) For scheduling hard real-time tasks on symmetric homogeneous multi-processors, an energy-efficient scheduling algorithm is proposed to achieve static energy savings using dynamic power management. The scheduling problem in this work is formulated as an optimization problem to guarantee the optimality of real-time tasks. It is then transformed into a flow network model to utilize idle time for dynamic power management. (3) The methodology for expanding the previous algorithm in (2) onto a large-scale system consisting of many processing elements, such as high-performance computing, cloud computing, and data center, is proposed. This work achieves static energy savings by shutting down the inactive processing elements and guarantees the optimality of real-time tasks from the modified formulated optimization problem. In addition, it discusses several practical issues that arise when the previous algorithm (2) is applied in a cloud computing.

Energy Mapping and Energy-Aware Path Planning for Field Robots

Wei, Minghan ProQuest Dissertations & Theses University of Minn 2021 해외박사(DDOD)

Autonomous mobile robots are finding increasing use in areas such as agriculture, environmental monitoring, and search. Most field robots are currently powered by batteries and therefore have limited energy budgets. As a result, these robots have to finish tasks or visit recharging stations before the batteries run out of power. Addressing these limitations by designing energy-aware robot navigation algorithms is gaining importance in order to improve the operation time, save the robot energy, and ensure task success. The research in this dissertation focuses on energy mapping and energy-aware path planning for field robots.Specifically, we identify and address two new challenges associated with energy-constrained robot planning: (1) With the energy constraint, robots may not be able to finish the mission with onboard power. The need to visit a recharging station to get recharged and then continue the mission adds to the complexity of designing planning algorithms. New algorithms with optimality or near-optimality guarantees are needed. (2) Path planning algorithms often require environment maps. However, there is a disconnect between theoretical results and real applications because of the difficulty of obtaining energy-cost maps for planning energy-optimal paths. Modeling ground robot energy consumption on rough terrains can be rather complex. Obtaining energy-cost maps in a practical setting has not been sufficiently addressed in the prior literature. Based on these challenges, we study two research problems: energy-aware coverage path planning, and energy mapping for navigation path planning to goal locations.In the energy-aware coverage planning problem, the goal is to plan paths for robots to visit every location of given environments. Prior work tends to plan a single path for the robot, assuming an unlimited energy budget. However, the energy constraint inhibits the robots to complete coverage in one iteration especially for large environments, whichcalls for designing new planning algorithms to incorporate this restriction. We focus on a geometric version where the environment is represented as a polygonal grid with a single charging station in it. Energy consumption throughout the environment is assumed to be uniform and proportional to the moving distance. The robot needs to visit the charging station before it runs out of battery. Thus multiple paths need to be planned for coverage. The optimization goal is to minimize the total number of paths and their length. We present a constant-factor (4) approximation algorithm for contour-connected environments (defined in Chapter. 2, Sec. 2.5), and the approximation rate for general environments is proportional to the number of reflex vertices. To obtain better performance in complex environments that have many reflex vertices, we also present a log(D)-approximation algorithm, where D is the environment diameter.The second part of this dissertation focuses on the energy-mapping problem for navigation. The goal of this part is to obtain a practical energy-consumption model for ground robots, as opposed to the uniform model assumed in the energy-aware coverage planning problem. With such an energy-cost map, we can plan a path between any two locations in a given environment that consumes the least amount of energy. While there is a large amount of research on offline and online path planning algorithms given an environment map (a partial map in the online case), how to build the energy-cost map efficiently for energy-optimal path planning is less addressed. We take advantage of both aerial vehicles and ground vehicles for data collection to build energy-cost maps. The aerial robots can easily cover a large field to collect terrain appearance information. The ground robots can collect the actual energy consumption data on the field. A deep neural network is then applied to learn from both measurements and to predict the energy-cost map for the entire area. We validate our methods through simulated and real experiments and demonstrate that accurate energy-cost maps are built and paths planned by our map consume less energy compared to baseline methods. Chapter. 3 and Chapter. 4 focus on environments with and without slopes, respectively.This dissertation makes progress towards tackling robot planning challenges arising from practical constraints. The focus in our work is on the energy constraint, which can help alleviate the pressure on energy resources in world development. Other constraints robots can face in the real world can come from time and motion constraints, and sensing constraints such as the field of view of the sensors. We believe our results will bring robots to execute tasks in diverse environments under these constraints.

가공 시간과 임펠러 황삭을 위한 에너지 소비사이의 균형 무역 오프 : Balancing Tradeoffs between Machinning Time and Energy Consumption for Impeller Rough Machinning

벨라스케 아리아자 오스카 전북대학교 일반대학원 2014 국내석사

Energy efficiency has increasingly become a relevant issue within the past years due to economic and environmental factors involved. The use of electrical energy is directly linked to society prosperity across the globe; much of this due to the diverse machining and manufacturing processes. Performing machining processes with higher energy efficiency will, therefore, significantly reduce the total industrial consumption of energy. The energy consumed during machining processes is a matter of investigation, not only for its environmental impact, is also crucial to consider it for productivity and competitiveness factors. In this thesis a multiple response optimization for machining time and energy consumption is presented by applying a response surface methodology together with a desirability function in order to obtain an adequate balance of the independent factors involved in 5-axis rough machining of an impeller. Four independent factors were selected to analyze the energy consumption and machining time relationship. These four factors are the spindle speed, feed rate, depth and width of cut. A series of experiments were performed to obtain meaningful data of the process behavior. The balance of parameters given by the regression model is a width of cut of 2.7mm, depth of cut of 1.8mm, spindle speed of 8,000 rpm and a feed rate of 740mm/min. This balance of parameters results on the lowest theoretical time and energy consumption to machine an impeller region, obtaining a machining time of 48 minutes and 30 seconds, and energy consumption of 4.45 Kwh. The regression model was verified by machining a set of extra experimental runs using the proposed setup. The output values obtained from this final runs are, machining time of 53.5 minutes and 4.67 Kwh of consumed energy. The percent error between the regression model and the actual machining is 9.35% for the machining time and 4.75% for the energy consumption response. The corroborated results showed that is possible to find balance between outputs, and that for this study case it is possible to achieve an optimization for both responses with a relative small error. The results showed that selecting an appropriate feed rate is crucial to balance the tradeoffs between energy and time. Spindle speed is the major factor that consumes more energy, while width of cut is the most influential factor on machining time.

Numerical and experimental evaluation on thermal performance of hybrid Geo-structures

이석재 Graduate School, Korea University 2020 국내박사

Among the renewable energy technologies, the ground heat source pump (GSHP) which utilizes the ground heat exchangers (GHEXs) is evaluate to be an effective system to heating and cooling for the buildings. From the GHEXs, the thermal energy is extracted or released from or to the ground formations. The closed-loop vertical GHEXs are usually equipped in the GSHP system which have a high construction cost because of additional budget for the borehole drilling and construction sites. Therefore, several types of GHEXs, which can save the additional budget by modifying the configurations of GHEXs or fabricating the GHEXs in the geo-structures, had been studied recently. First, the coaxial-type GHEX possesses a concentric tube-in-tube configuration which can enlarge the heat exchange area and induce the turbulent flow more actively than conventional closed-loop GHEXs. With the coaxial-type GHEX, the construction cost can be saved by reducing the boring depth compare to the conventional GHEX. Second, the GHEXs fabricated in the geo-structures, such as energy slabs and energy piles, can dramatically save the construction cost because the additional borehole drilling and construction site are unnecessary. The energy slabs are equipped in the floor or wall slab of the building with a horizontal layout of heat exchange pipes. Because of the energy slab configurations, this GHEX evaluated to have lower thermal performance than the conventional GHEXs. However, if the energy slabs are installed in the underground structures with a sophisticated thermal insulation layer, the thermal performance of the energy slabs can obviously be improved. The energy piles utilize geothermal energy via embedded heat exchange pipes in the pile foundations. These GHEXs also had been reported to have lower thermal performance than conventional GHEXs because the energy piles can utilize only a limited amount of geothermal source due to short installation length. These drawbacks had been overcome by using a large-diameter cast-in-place concrete pile, which has a large borehole surface area to extract or release the thermal energy from or to the ground formations. Most recently, the steel pipe heat exchanger (SPHX) was devised from a STG800 high-strength steel pipe of yield strength 800 MPa to substitute for the deformed rebars in large-diameter cast-in-place concrete piles. Energy piles encasing SPHXs are expected to fulfill multiple functions, i.e., supporting structural loads and serving as heat exchangers without requiring additional heat exchange pipes. In this study, comprehensive studies for the hybrid geo-structures, which were devised for saving the construction cost for the conventional GHEXs, were conducted with experimental and numerical evaluations. First, the factors governing the thermal performance of coaxial-type GHEX were identified through field tests (i.e., thermal response test (TRT), thermal performance test (TPT)). As a result, the thermal performance of coaxial-type GHEXs is directly influenced by the thermal conductivity of the pipe and grouting material. The pipe diameter also influences the thermal performance of coaxial-type GHEX. Especially, it is noted that an optimal flow rate exists, which maximizes the thermal performance of the coaxial-type GHEX. Then, computational fluid dynamic (CFD) model was developed by the field test data to perform the parametric studies considering various influential factors (i.e., pipe length, inner and outer diameters, and flow rate). In the results, as the flow rate and pipe length increased, the heat exchange amount of coaxial-type GHEX increased. In particular, increasing the residence time for circulating fluid by enlarging the hydraulic diameter was the most dominant factor for the heat exchange amount. In addition, the GSPH system was installed in the residential building basement with four coaxial-type GHEXs and a closed-loop vertical GHEX, which was designed with a ground loop heat exchanger design program (GLHE Pro). Then, a series of field tests without the GSHP system (i.e., Thermal Response Tests (TRTs), Thermal Performance Tests (TPTs)) was conducted to compare the thermal performances of constructed GHEXs. Resultingly, the coaxial-type GHEX showed 20 % and 6.7 % better thermal performance in TRT and TPT, respectively, than the closed-loop vertical GHEX. Finally, short-term heating operations of the GSHP system were simulated to investigate the Coefficient of Performance (COP) and the energy-saving ratio according to the type of GHEXs. When the coaxial-type GHEX is adopted to the GSHP system, the more stable and efficient operation was carried out than when using the closed-loop vertical GHEX. Similarly, two different field-scale energy slabs (i.e., floor-type and wall-type energy slabs) were constructed in a test bed, and two types of heat exchange pipes (i.e., STS pipe and HDPE pipes) were installed in each energy slab to evaluate the thermal performance through a series of TRT and TPT. Use of the STS heat exchange pipe enhanced the thermal performance of energy slabs. Additionally, the wall-type energy slab had a similar thermal performance to the floor-type energy slab, which infers the applicability of the additional use of the wall-type energy slab. Note that if an energy slab is not thermally cut off from the building’s interior space with the aid of thermal insulation layers, heat exchange within the energy slabs should be significantly influenced by fluctuations in ambient temperature. Then, a CFD model was developed by calibrating with TPT results, and conducted to comprehensively assess the effect of influential factors (i.e., thermal conductivity of ground formations and concrete and flow rate of working fluid) on the thermal performance of energy slabs. In particular, considering the performance of thermal insulation and economic feasibility, a PF (phenol foam) board is found to be the suitable material for the energy slab considered in this paper. Furthermore, a design method for energy slabs using the artificial neural network (ANN) was proposed. A set of databases constructed through the numerical analysis in ideal condition was implemented by the ANN. From this approach, the thermal performance of energy slabs for a typical condition can be quickly predicted without time-consuming numerical simulations. Finally, the applicability of cast-in-place energy piles equipped with novel SPHXs is investigated herein as substitutes for deformed rebars. Two cast-in-place energy piles encasing SPHXs of different diameters were constructed in a test bed. Then, pile load tests (i.e., dynamic load test and lateral load test) were conducted to estimate the bearing capacities of these energy piles. Consequently, both energy piles secured safety factors greater than 2.0, and the allowable lateral loads were sufficient, indicating acceptable structural capacities as pile foundations. In addition, a series of TPT was performed with constructed energy pile, and the results was compared with that of a conventional cast-in-place energy pile to assess the heat exchange capacity of the energy pile with SPHXs. The thermal performance of the cast-in-place energy pile considered herein was 30% greater than that of the conventional energy pile of similar scale, which shows the applicability of the proposed energy piles. With the TPT results, a CFD model for the energy piles with SPHXs was developed to investigate the effect of influential factors (i.e., the thermal conductivity of ground formation, thermal conductivity of concrete, the flow rate of working fluid, and configuration of SPHX). As a result, the thermal conductivities of concrete and ground formations have a significant effect on the thermal performance of the energy piles with SPHXs for short and long-term, respectively. In addition, the flow rate of working fluid was recommended to maintain below 11.35 lpm for the efficient GSHP system operation. Especially, when more than 10 pairs of U-tube heat exchange pipes were installed, the thermal performance increase of the energy piles with SPHX was decreased dramatically

무선 네트워크 환경에서 에너지 효율적인 데이터 전송 방법 연구

최원석 충북대학교 2015 국내박사

본 논문은 무선 네트워크 환경에서 에너지 소비를 절감하기 위한 방안을 제안하였다. 무선 네트워크 환경의 주요 구성요소는 무선 단말과 무선 인프라로 나눌 수 있다. 무선 단말은 IEEE 802.11 WLAN, CDMA, LTE, WiMAX등의 인터페이스를 사용하는 기기로 나눌 수 있으며, 무선 인프라는 IEEE 802.11 WLAN 액세스 포인트, 기지국 등 무선 접속 기술에 따른 인프라로 분류 될 수 있다. 특히, 그 중에서 EEE 802.11 WLAN 기술을 사용하는 무선 단말과 기지국에서의 전력 소모가 크며 에너지 절감을 위한 많은 관심이 고려되고 있다. 따라서, 본 논문은 IEEE 802.11 WLAN을 사용하는 단말에서의 에너지 절감 방안과 기지국에서의 에너지 절감 방안을 제안한다. 먼저, 모바일 단말에서의 에너지 절감을 위해 IEEE 802.11 WLAN 환경에서 비실시간 트래픽 특성을 이용한 에너지 효율적인 2계층 데이터 전송 방안을 제안한다. 전형적으로 액세스 포인트에서의 혼잡 확률과 모바일 단말의 재전송 확률은 같은 액세스 포인트에 접속한 모바일 단말이 증가할수록 높아지는 경향이 있다. 이 혼잡 확률과 재전송 확률이 높아질수록 WLAN에서의 에너지 효율은 감소한다. 따라서 본 논문은 재전송 시도를 줄이기 위해 비실시간 트래픽을 사용하는 모바일 단말에 최대 백오프 카운트를 할당하는 방법을 제안한다. 또한, 모바일 단말에서 재전송에 따른 에너지 소비를 평가하기 위해 새로운 에너지 소비 메트릭을 제안하고 기존 IEEE 802.11 DCF 방법과 포화 네트워크 환경에서 수학적 분석을 통해 비교 분석 하였다. 기지국에서의 에너지 절감을 위해 에너지 효율적인 전송 알고리즘을 제안하였다. 현재 무선 데이터 전송 시스템은 데이터 전송 시 신호대잡음비를 만족시키기 위해 전송 전력을 증가 시키는 방법으로 동작된다. 하지만 이 방법은 전달율과 전송 전력 간의 지수적 관계로 인해 에너지 사용 측면에서 비효율적이다. 따라서 본 논문은 기지국에서 데이터 전송시 에너지 효율을 최대화하기 위해 서비스 타입에 따라 실시간/비실시간 트래픽으로 분류하고 에너지 최적 포인트를 확인한다. 이 정보를 기반으로 기지국에 모바일 단말에 전송하는 데이터양을 제어하여 항상 에너지 효율 최적 지점에서 전송하는 방법을 제안한다. 수학적 분석을 통해 기존 데이터 전송 시스템과 제안하는 에너지 효율적 전송 알고리즘을 비교 분석하였으며 기존 방법에 비해 에너지 효율이 증가함을 확인했다. 다시 말해 본 논문은 무선 네트워크 환경에서 에너지 효율적인 데이터 전송을 위해 모바일 단말의 에너지를 절감하고 기지국의 에너지 효율를 강화하였다. 또한 성능분석을 통해 IEEE 802.11 WLAN에서 모바일 단말의 에너지 절감과 기지국에서의 에너지 절감에 있어 좋은 해결책으로 확인하였다. This dissertation proposes an energy-efficient data transmission method in wireless networks. Wireless network environment can be divided into two elements: mobile terminal and wireless infra. Mobile terminal can be also divided into many types according to wireless interfaces such as WiFi, WiMAX, 3G/CDMA, LTE and etc. Also, wireless infra can be classified by wireless access technologies such as an IEEE 802.11 WLAN access point, a base station and etc. Particularly, many researches have been studied to reduce energy consumption in terms of a mobile terminal and a base station in WLANs. Therefore, this dissertation proposes an energy-efficient data transmission method in terms of a mobile terminal in WLANs. and a base station. Firstly in order to save energy in Terminals, we propose an energy-efficient L2 transmission scheme using the protocol property of non-real-time traffic in IEEE 802.11 WLANs. Typically, the collision probability at the access point and the retransmission probability at the mobile terminals may increase significantly when the number of served mobile terminals constantly increases. As these probabilities are increased, energy efficiency in WLANs is decreased. In order to reduce the retransmission attempts, the proposed scheme allocates the maximum backoff count to an mobile terminal which is using non-real-time traffic. Thus, we propose a new energy consumption metric for retransmission while comparing it to the distributed coordination function by numerical analysis in a saturated network situation. In order to save energy in base stations, we propose an energy-efficient transmission algorithm. Current wireless data transmission system just increases transmit power in order to meet the signal-to-noise ratio of the receiver. However, this method is inefficient in terms of energy usage because the relationship between throughput and transmission power is an exponential function. In order to maximize energy efficiency of base station, we have classified data by the type of service and have verified the presence of the most energy-efficient point, which indicates the optimal amount of data transmitted from base station to users in a wireless cellular network. Based on this classification, the proposed energy-efficient transmission algorithm controls the amount of data transmitted from base station to users. Numerical results are provided for demonstrating the effectiveness of the proposed energy-efficient transmission algorithm. When compared with the existing method, the proposed energy-efficient transmission algorithm gives significantly increased energy efficiency. Consequently, the proposed mechanism can save energy consumption of mobile terminals and enhance energy efficiency of base stations. As a result of performance analysis, it is good solution for mobile terminals in IEEE 802.11 WLAN and base stations.

Energy Estimation of Ultra-High Energy Cosmic Rays (UHECRs) : 초고에너지우주선의 에너지 추정과 시뮬레이션 비교

Jihee Kim 충남대학교 대학원 2011 국내석사