• Energy Research
• 2016-2025close

In this thesis, I focus on the system design and performance analysis of wireless communication networks with radio frequency (RF) energy harvesting. Battery re-placement/recharging has always been a challenging issue in wireless communication networks, especially in large-scale networks like wireless sensor networks (WSNs). Recently, RF energy harvesting (EH) technology has been developed as a new viable solution to extend the lifetime of wireless networks via enabling wireless devices to harvest energy from RF signals. Inspired by this technique, wireless-powered communication networks (WPCNs) have attracted an upsurge of research interest. According to the protocols proposed in current literature, an EH user will exhaust all the energy it harvests straightway during this transmission block. This may be a sub-optimal solution, since this little amount of energy may not be able to contribute to an effective transmission. Therefore, in this thesis, I consider energy accumulation at each EH node by providing an energy storage (e.g. a rechargeable battery), so that it can an accumulate sufficient amount of harvested energy before transmission and wait to transmit in an appropriate time slot. To begin with, I first investigate wireless energy harvesting (WEH) technique in cooperative communication networks where the source and relay can both communicate with the destination. I refer to this kind of network as wireless-powered cooperative communication networks (WPCCNs). This WEH technique offers a new cooperation manner for wireless devices since the relay node is now able to harvest energy from the source’s information. In this thesis, I consider the relay as a wireless-powered node that has no external power supply; but it is equipped with an EH unit and a rechargeable battery so that it can harvest and accumulate energy from RF signals broadcast by the source. By fully incorporating the EH feature of the relay, an opportunistic relaying protocol was developed, termed accumulate-then-forward (ATF), for the ...

Akumulace energie, a to jak elektrické tak energie jiného druhu je tématem kterému je v dnešní době věnována větší a větší pozornost. Důvodem jsou převážně obnovitelné zdroje energie (OZE), ale také zlepšení účinnosti dodávek elektrické energie a elektromobilita. Právě účelem této práce je nastínit některé způsoby akumulace energie,popsat některá média ,která se v daných akumulátorech mohou vyskytovat a popsat jejich praktickou realizaci. Nadále pak určit porovnávací kritéria ,která budou sloužit k porovnání dříve popsaných způsobů akumulace energie a jejich médií. Na závěr bude uvedeno jaké způsoby a média jsou nejvhodnější pro zvolené aplikace. ; Obhájeno ; The accumulation of energy, both electrical and other form, is a topic that is still receiving more and more attention nowadays. The reason is mainly renewable energy sources (RES), but also improving efficiency of electricity supply and electromobility. The purpose of this thesis is to outline some ways of energy accumulation, describe some media used in this systems, and describe their practical implementation. Criteria for comparison will then be determined, which will be used to compare the previously described methods of energy storage and their media. Finally, methods and media that are most suitable for the selected applications will be stated.

To address the climate change, the development of electrification is being rapidly conducted worldwide, especially in automobile industry. Regarding mobile machinery, many companies also have been forced to develop electrification technologies with a focus on electric mini excavators. Nevertheless, concerning middle class or larger sizes of excavators, it is not regarded that electrification technologies are the best solution, demanding huge battery capacity. Hence, it is expected that machines powered by internal combustion engines (ICE) will continue to be indispensable. To make hydraulic excavator more efficient, numerous studies to reduce throttling losses being major losses in hydraulic systems have been conducted. However, less throttling losses are likely to lead to inefficient operation considering the ICE efficiency map.In order to solve this issue, a hydraulic system called STEAM being one of the constant pressure systems has been proposed to improve overall system efficiency. Important features of this system are that the ICE can be operated at the most efficient point, and recoverable energy is allowed to be recuperated by accumulators. However, it might be difficult to be accepted by the industry due to using a multitude of valves. Alternatively, a three pump open center system allows engineers to design simple layout of the machines and enables machines to provide fluid efficiently by three pumps with less throttling losses. It seems that there is a new possibility by merging both architectures. Therefore, the purpose of this study is set to design a new hybrid architecture which combines an open center system with STEAM.In this thesis, basic principles and a design guideline to develop a hydraulic circuit of the new hydraulic architecture are discussed. To confirm the improvement of the system efficiency, simulations and experiments with the test rig are carried out and achievements are discussed. Dissertation, RWTH Aachen University, 2023; Düren : Shaker Verlag, Reihe Fluidtechnik. D 115, 1 Online-Ressource : Illustrationen (2024). doi:10.18154/RWTH-2024-04089 = Dissertation, RWTH Aachen University, 2023 Published by Shaker Verlag, Düren

This article discusses application of nanomodified heat accumulators on the basis of paraffin modified by carbon nanostructures for various technological processes aiming at increase in their energy efficiency. Thermal and physical properties of nanomodified paraffins have been studied. Procedure of adaptation of heat accumulating materials for various operation modes of industrial processes is presented. Copyright © EM International.

For countries with limited access to conventional hydrocarbon gases, methane hydrates appear as a possible source of energy or as a strategic concern for the creation of alternative natural gas reserves. Currently, natural gas hydrates are beginning to be included in the considerations of gas supply for the next decades. From a perspective point of view, the accumulation of natural gas in the form of hydrate structures and subsequent release, if necessary, proves to be very advantageous. Storing gas in such a form creates an energy-efficient interest in developing and innovating technology in this area.

Geostructures experience repetitive load cycles, which gradually affect their long-term performance. This thesis explores the long-term response of soils subjected to mechanical load-unload, heat-cool, freeze-thaw, and atmospheric pressure oscillations. The research methodology involves new instrumented cells (oedometer, temperature-controlled triaxial chamber, and pressure-controlled drying chamber), various geophysical monitoring methods (X-ray micro-CT, NMR, S-wave, and EM-waves), and simulations using discrete element modeling. Results show that soils subjected to repetitive mechanical or environmental loading experience shear and volumetric strain accumulation and changes in saturation (during barometric pressure cycles). In all cases, soils evolve towards an asymptotic terminal void ratio; the change in void ratio is pronounced when the soil exhibits grain-displacive ice formation during freeze-thaw cycles. The initial stress obliquity defines the shear strain response, which may be either shakedown -at low stress obliquity-, or ceaseless shear strain accumulation in ratcheting mode when the maximum stress obliquity approaches failure conditions. Finally, we provide simple engineering guidelines to estimate the long-term behavior of soils subjected to repetitive mechanical or environmental loading.

Виконаний аналіз основних систем накопичення електричної енергії, які можуть використовуватися трейдерами для підвищення ефективності роботи на ринку електричної енергії в Україні. Розглянуто основні технічні характеристики та особливості функціонування різних видів систем накопичення енергії в умовах ринку електричної енергії України. Розроблено критерій економічної ефективності використання систем накопичення енергії для роботи трейдерів, який враховує поточну ситуацію на ринку електричної енергії, технічні характеристики систем накопичення та особливості функціонування конкретного трейдера. З використанням запропонованого критерію визначено найбільш ефективні системи накопичення енергії для роботи трейдерів в умовах нового лібералізованого ринку електричної енергії в Україні. ; The analysis of the energy storage systems role in the electric power systems operation in modern conditions of energy storage technologies development and the introduction of the electricity market in Ukraine performed. The energy storage systems classification by energy storage type, which is based on the World Energy Council general approach, has been reviewed. The analysis of the main technical characteristics and functioning features of energy storage systems various types that can be used by traders to improve the work efficiency in the conditions of the Ukraine electric energy market has been performed. The traders work features in the conditions of reforming the Ukraine electric energy market identified. Based on these features, the possibility of increasing the traders' work efficiency when using energy storage systems is revealed. The economic efficiency criterion in the energy storage systems using for the traders work, which takes into account the current situation on the electric energy market, the energy storage systems technical characteristics and the particular trader operating characteristics, has been developed. The using traders possibility comparison of various energy storage systems when working on the Ukraine electric energy market has been carried out. The most effective energy storage systems for the traders work in the new liberalized Ukraine electric energy market are determined using the proposed technical and economic criterion.

A minimal energy demand should be required in buildings both to optimize the performance of the building façade and to control solar gains. According to the existing studies and national standards, the climate zone classification is usually based on both the degree-days methodology and outdated climate data, thus managing HVAC systems inappropriately or leading to users’ thermal discomfort in indoor spaces. To evaluate the current limitations and to characterize solar gains in the Spanish building stock, an innovative approach is presented. For this purpose, seven clustering algorithms were implemented by distinguishing between winter and summer seasons during the calculation procedures. Solar irradiation from 8,948 locations in Spain were used. Likewise, the control of solar gains was analysed with the regulatory approach of Spain and with those developed through the study. The results of this research revealed that climate zones set by the Spanish Technical Building Code could imply to use values of monthly accumulated solar irradiation with discrepancies between 43.17 and 84.41 kWh/m2, compared to the real values. Hence, an accurate method focused on k-means clustering should be adopted. Furthermore, the results can be used for a more accurate analysis of solar control and improve the energy efficiency of buildings. Spanish Ministry of Science and Innovation Project PID2021-122437OA-I00 “Positive Energy Buildings Potential for Climate Change Adaptation and Energy Poverty Mitigation (+ENERPOT)” Thematic Network 723RT0151 “Red Iberoamericana de Eficiencia y Salubridad en Edificios” (IBERESE) financed by the call for Thematic Networks of the CYTED Program for 2022

Progressive multiple sclerosis (MS) is characterized clinically by the accumulation of neurological disability without unequivocal recovery. Understanding the mechanisms that determine entering in this stage of the disease is a great challenge in order to identify potential therapeutic targets. Recent advances in defining more accurately the progressive phenotype of MS, have concluded that differences between primary and secondary progressive forms of disease are relatively quantitative rather than qualitative. In both cases, a large number of molecular and cellular events that might lead to neurodegeneration have been suggested. These include microglia activation, chronic oxidative injury, accumulation of mitochondrial damage in axons, age-related disturbances and dysfunctional axonal transport among others. Commonly, these pathological mechanisms have been considered as a result of inflammatory demyelination but a primary degenerative condition has also been argued. It is now clear that both events contribute to the progression of the disease, however their temporal sequence is still a matter of debate. A detailed knowledge of progressive MS pathogenesis will allow to develop effective treatments for both progression and symptom management that should be based on a combination of anti-inflammatory, regenerative and neuroprotective strategies. In this review, we summarize current data and recent hypothesis about pathological forces that drive progression of damage in MS, i.e. cumulative cortical demyelination and neurodegeneration as well as diffuse alterations (microglia activation, axonal injury and atrophy) throughout white and grey matter in the brain and spinal cord. Finally, we discuss the potential of the aforementioned proposed disease mechanisms with regard to developing suitable therapies to halt the progression in MS pathology. Work in our laboratory is funded by CIBERNED, Gobierno Vasco (EJ/GV) and MINECO (SAF2013-45084-R).