Tallinn University of Technology
  • Tallinn, Harjumaa, Estonia
Recent publications
Deriving benefits from a variety of flexible sources to lower or even eliminate renewable energy resources challenges is an imperative issue in the management of power systems. Constructing a well compatible flexibility evaluation method that encompasses cost minimization and flexibility improvement is crucial to tackle this. In this paper, a stochastic economical flexibility evaluation method is proposed based upon the envelope of the feasible operation region to the uncertain space. The probability distribution function of the network's flexibility is provided for each hour. Furthermore, the flexibility that storage systems as a flexible source provide for the distribution networks is quantified. The flexibility sensitivity to the storage facility capacity is scrutinized. The simulation results show the impact of PV generation and energy storage systems on the flexibility improvement. Moreover, the sensitivity outcomes reveal that which storage capacity should be adopted for the secure distribution grid operation.
The campus of Tallinn University of Technology consists of 26 buildings with a total annual heat demand of approximately 20 GWh. A local natural gas-fired boiler provides annually approximately 13 GWh of heating to 12 buildings in the campus and 14 buildings are connected to district heating system. This paper analyses the possibilities of replacing the natural gas boiler with district heating. Two systems were modelled using EnergyPRO software and compared to the reference system of the local boiler and heating network: connection to an existing high-temperature district heating network and a low-temperature energy cascade. All the three systems were modelled with two different energy price scenarios. The results were analysed from the perspective of the university campus and the entire city’s system. The low-temperature energy cascade connection to the city’s network will reduce carbon dioxide emissions by 955 tonnes CO2. The conventional high-temperature connection would reduce the emission by 765 tons CO2. District heating connection will also lead to primary energy savings supporting the university’s efforts towards achieving its sustainable development goals. The low-temperature energy cascade utilising the return water of the city’s district heating network reduces the heat losses and increases the efficiency of heat and electricity production when compared to the systems with separate campus heating or the conventional high-temperature district heating.
Equivalent Single Layer (ESL) approach is extended to model ultimate strength of stiffened panels under a combination of in-plane compression and shear. Ultimate strength under this combined loading depends on the loading path and could be lower than for only uni-axial compression since shear load can produce axial forces. Thus, to account for this effect, the recent ESL model is extended to include A13 stiffness component as non-zero value. Procedure to accurately obtain A13 is presented. In ESL approach, a stiffened panel is transformed into a two-dimensional (2D) single layer with the same stiffness obtained from unit cell simulations. To obtain non-linear stiffness matrix of ESL, elastic–plastic material properties and initial imperfection were applied to the unit cell. ESL responses were validated by comparing numerical and experimental results from the literature. Several stiffened panel configurations were analyzed to obtain different collapse modes. Combined loads were applied for shear to compression ratio of 0, 1, and 2. Lateral pressure loading was also considered in the simulations. Analyses were carried out based on the load sequences consisting of: 1) compression and shear loaded simultaneously and 2) shear applied first, followed by compression. The results show that the modified ESL can well capture the effect of shear load on ultimate strength in comparison to a detailed 3D FEM model of stiffened panels. The accuracy of the ESL varies depending on the collapse mode of stiffened panels.
The 5th Generation District Heating and Cooling (5GDHC) network has great advantages in terms of integration of low-temperature resources, bi-directional operation, decentralised energy flows, and possible energy sharing. One way to develop the idea and concept of 5GDHC is to identify potential agents, including residential buildings, office buildings, shopping malls, data centres, electrical transformers, and so on, in 5GDHC in each target context. The prospects for 5GDHC have been assessed in light of the conditions in the Baltics. The multi-criteria analysis method was used to quantify the main identified barriers and drivers behind the implementation of 5GDHC systems. It should be noted that new urban areas in the Baltic states are being actively developed with low-energy buildings, so 5GDHS can be integrated to supply heat to these areas. The highest score in the multi-criteria assessment was achieved by Lithuania due to support availability and open heating market conditions. When all applied criteria are weighted equally, Estonia has the most favourable conditions for 5GDHC systems due to widespread use of heat pumps and greater excess heat potential.
The incompatibility of 3D concrete printing (3DCP) with conventional reinforcement methods is well known. Recently, solutions have suggested the insertion of helical reinforcement rods through a screwing motion into the freshly printed material. The current study focuses on the bond properties of such reinforcement and its relation to placement time relative to the 3D printed concrete age, of which until now hardly any data exists. Confined pull-out tests and micro-computed tomography (μCT) scans were performed to characterize the time-dependent bond properties for automatically placed screw-type reinforcement in 3D printed concrete in the range of 0-200 min after material deposition. An experimental program was carried out using a gantry type 3D concrete printer and a robotic hand with the Automated Screwing Device to automate the reinforcement placement process. In total 200 specimens were produced and tested in pull-out. μCT scans were done on the specimens to quantify air content in the vicinity of the reinforcement, for every other time stamp. Two different screw geometries were used. A high mechanical interlock was achieved resulting in a high bond strength in confined pull-out tests. It was concluded from the confined pull-out tests that the pull-out performance is not influenced significantly by the time of application after mortar deposition in a time frame of up to 200 min. This firmly positions automatically applied helical reinforcement as a viable method to reinforce 3DCP structures.
Oil shale is a calcium-rich fossil fuel, and its combustion in power plants generates high CO2 emissions, which must be reduced drastically. Thus, this study conducts a comparative techno-economic analysis of adding CO2 capture technologies, namely, post- and oxy-fuel combustion technologies, to existing oil shale power plants in Estonia. Estonia's energy sector is unique due to its heavy reliance on oil shale. The study's technical analysis indicates that oxy-fuel combustion capture would outperform post-combustion capture in oil shale power generation. However, integration of CO2 capture technology would result in reductions in power units' heat rate performances by more than 10% points due its energy requirements. From a financial perspective, the feasibility of Estonian oil shale power plant CO2 capture depends upon the long-term trends in the electricity market and CO2 emissions trading system. Full-capacity operation over an assumed 24-year lifetime would cost at least 89 euros per ton of CO2 captured and stored in 2021 values. The actual cost might exceed paying CO2 emission allowance fees and environmental charges or result in a competitive disadvantage. Thus, only in the event that the negative externalities resulting from CO2 emissions and national energy security concerns cannot be feasibly mitigated with alternative, stable, and controllable energy sources should state aid be used for CO2 capture technologies for oil shale power plants. The need to impose higher taxes, ceteris paribus, to cover the state aid or transfer the CO2 capture costs to the private sector might reduce the Estonian economy's overall competitiveness.
Developing energy-efficient and scalable microstructural solutions that enable both an intrinsically high strength and high ductility has always been a pursuit in materials science. We have used a spark plasma sintering synthesis strategy to efficiently fabricate a duplex high-entropy nanocomposite composed of the high-entropy nano-intermetallic precipitates and high-entropy nanoscale solid-solution domains. The high-entropy nanocomposite with spontaneous phase separation accompanied by the reorganization of high-entropy components achieves the minimal lattice misfit (∼0.07%) integration of the high-entropy nano-intermetallic precipitates with the high-entropy nanoscale solid-solution domains. The resulting high-entropy nanocomposite exhibited a high tensile strength (i.e., a fracture strength close to 1.7 GPa) and large plasticity (i.e., a uniform elongation close to 20%). The duplex nanostructure in our high-entropy nanocomposite described herein had multi-type dislocation substructure evolution during deformation, including dislocation planar slip, coplanar dislocation arrays, dislocation walls, microbands, and stacking faults in solid-solution domains. Because of the dominance of multiple hardening modes, our high-entropy nanocomposite could ensure that the plasticity was large enough to maintain a high strength. Our findings break through the challenge of the tradeoff between efficiency and superb performance in preparing nanostructured materials, thereby significantly facilitating the development of high-performance nanocomposites and advanced nanostructured materials.
The current state of power-to-heat integration into the heat supply in the Baltics is examined. In the socio-economic analysis, three scenarios for prospective district heating electrification development in the Baltic countries until 2050 were investigated and compared: Baseline scenario, Grid Tariff scenario, and Investment Support scenario. Large-scale HPs were analysed as key future technologies. Furthermore, the results are focused on excess heat and renewable thermal energy sources used for heat supply, as well as expanding the representation of DH areas. In 2050, large-scale HPs will generate more than half of the heat for the Baltic states in the Baseline scenario, while biomass plants will generate one-third. One of the dominating fossil fuels in heat supply (natural gas) consumption should gradually decrease from 7.9 TWh in 2020 to 1.4 TWh in the same period. Large HPs generated the lowest quantity of heat in the Grid Tariff scenario. The current network tariffs in each of the Baltic countries, it may be inferred, are an impediment to the introduction of HPs. In 2050, only up to 1/4 of thermal energy will be produced by large-scale HPs. Investments in large-scale HPs are half-subsidised in the Investment Support scenario, which greatly affects the introduction of HPs, and, according to this scenario, in 2050, up to 68% of heat will be produced via HPs in the Baltic states. Detailed results are presented for Estonia, Latvia, and Lithuania.
The morphological and structural changes of dual-phase tungsten specimens with high entropy alloy (HEA) as a second phase (95% W, 5% of FeNiCuCrMn) are investigated after deuterium plasma irradiation. The heat flux factor of deuterium plasma pulses is comparable to transient events (ELM-s and VDE-s) in ITER. The study shows that the use of HEA as a second phase reduces significantly the extent of crack generation in comparison with pure tungsten, and even with a dual-phase alloy of W and FeNi as a second phase. The hardness of W-HEA depends on the manufacturing method (spark plasma sintering, or pressure-less sintering) and is comparable with spark plasma sintered pure tungsten. The layer with decreased hardness is present after irradiation and has a thickness of about 50–80 µm which is less than in the case of pure tungsten.
Coastal wetlands are considered important stores of blue carbon, containing some of the largest stores of pedologic and biotic carbon per unit area on the planet. These ecosystems are however highly sensitive to Climate Change and changes in the management practices. It is of utmost importance to address relevant ecosystem scales in order to fully understand carbon dynamics in coastal wetlands. In this regard, Unoccupied Aerial Vehicles (UAVs) can provide spatial scales detailed enough to address the fine scale patters of topsoil organic carbon accumulation in coastal wetlands. This study demonstrates the use of multispectral and photogrammetric data derived from UAVs to accurately map plant communities and topsoil organic carbon concentration in coastal wetlands. The overall accuracies from the classification of plant communities ranged from 88% to 97% whereas RMSE for topsoil organic carbon concentration ranged from 2.44% to 0.74%. By combining both models, site-specific variations in topsoil carbon concentrations among plant communities were unveiled. Open pioneer communities consistently showed the lowest topsoil organic carbon concentration, while the concentrations vary considerably across plant communities characterized by denser vegetation coverage. Furthermore, Sentinel-1 radar data was used to assess the spatial patterns of flood frequency. GAMs were used to combine flood frequency with the plant communities and topsoil organic carbon models, as well as an aboveground biomass (AGB) model from a previous study. GAMs revealed a stronger effect than flood frequency on topsoil organic carbon. Regarding flooding, increased flood frequency generally led decreased topsoil organic concentrations across communities and sites. However, the relative contribution of flood frequency to topsoil organic carbon concentration in Baltic coastal wetlands depends strongly on the location of the wetland and the nature of the floods. Higher flood frequencies could lead to increased topsoil organic carbon in wetlands subject to the input of estuarine sediments. Lastly, the integration of remote sensing platforms constitutes an effective tool for revealing spatial heterogeneity of carbon storage in coastal wetlands.
While the design of goods and services is undeniably important in cultivating customer engagement (CE) with industrial innovations, the theoretical interface of industrial design, innovation, and CE remains nebulous, exposing an important literature-based gap. Relatedly, while the literature has focused on the firm as the focal designing stakeholder, further knowledge building is needed regarding the engagement of other stakeholders (e.g., employees or fellow customers), who may co-design an industrial firm's offering (e.g., by contributing to its product development activity), and its effect on CE. That is, as co-designing stakeholders can help design industrial offerings through their respective engagement, we advance an omni-stakeholder perspective of industrial design in this paper. We address these issues by composing a conceptual model and an associated set of propositions that explore the effect of different stakeholders' engagement in co-designing industrial innovations, and their respective effect on CE with the innovation. Next, we introduce the papers contained in this Issue and their links to the framework. We conclude by outlining further research avenues that arise from our analyses.
Symmetric monoidal theories (SMTs) generalise algebraic theories in a way that make them suitable to express resource-sensitive systems, in which variables cannot be copied or discarded at will. In SMTs, traditional tree-like terms are replaced by string diagrams , topological entities that can be intuitively thought of as diagrams of wires and boxes. Recently, string diagrams have become increasingly popular as a graphical syntax to reason about computational models across diverse fields, including programming language semantics, circuit theory, quantum mechanics, linguistics, and control theory. In applications, it is often convenient to implement the equations appearing in SMTs as rewriting rules . This poses the challenge of extending the traditional theory of term rewriting, which has been developed for algebraic theories, to string diagrams. In this paper, we develop a mathematical theory of string diagram rewriting for SMTs. Our approach exploits the correspondence between string diagram rewriting and double pushout (DPO) rewriting of certain graphs, introduced in the first paper of this series. Such a correspondence is only sound when the SMT includes a Frobenius algebra structure. In the present work, we show how an analogous correspondence may be established for arbitrary SMTs, once an appropriate notion of DPO rewriting (which we call convex ) is identified. As proof of concept, we use our approach to show termination of two SMTs of interest: Frobenius semi-algebras and bialgebras.
In recent years, several mining companies worldwide have made efforts towards establishing sustainable value-adding rare earth element (REE) supply chains to compete with China. Lynas and Iluka are two Australian mining companies that recently announced their plans to construct REE refinery plants to process and separate REE oxides in Western Australia and Texas, US. Though promising, such investments entail high risks. This work discusses the status of the Australian REE industry and uses SWOT and risk analyses to identify and evaluate the challenges and opportunities with respect to building an integrated rare earth supply chain outside of China.
The educational research landscape is still in a very early stage regarding the research in micro-credentials and how they are defined in scientific and policy documents. Whereas the micro-credentials trend is on rapid rise at the international and European level, coherent approaches to the concept, understanding and use of them are yet to be clarified. We addressed the issue through a literature review on the existing terminology and understandings related to micro-credentials in higher education in current scientific papers and policy documents, clustering them based on the granulation level from small units of learning to standalone certifications. Research shows that further research is needed to create a coherent approach for defining what micro-credentials are and how they can be integrated into educational processes, especially in higher education. Even though policy documents and scientific papers converge in numerous cases on creating a common definition for micro-credentials, differences are still present. The vision and practice do not always concur when describing the meaning and use of these innovative certification instruments.
Kesterite-type based thin film solar cell technologies are mainly based on polycrystalline absorber layers. A promising low cost alternative technology uses Cu2ZnSn(SxSe1-x)4 (CZTSSe) monograins (single crystals of 20–100 μm size) which are fixed in a polymer matrix to form a flexible solar cell. The Cu/Zn disorder is discussed as a possible reason for band tailing causing voltage losses limiting the efficiency of CZTSSe-based devices. The experimental determination of the order parameter Q which is a quantitative measure of Cu/Zn disorder, requires a differentiation between the isoelectronic cations Cu+ and Zn2+. An in-depth analysis of neutron diffraction data allows the determination of type and concentration of intrinsic point defects including a distinction between Cu and Zn. Neutron diffraction requires large sample volumes, thus monograins offer the unique possibility to correlate structural disorder in CZTSSe with device performance parameters. In this study we tackle the influence of grinding the monograins on stoichiometry deviations, the Cu/Zn disorder as well as intrinsic point defects and optoelectronic properties of CZTSSe monograins. Moreover, an easy methodology based on Raman scattering spectroscopy is proposed for the assessment of Cu/Zn disorder in the CZTSSe compounds.
Determining the load-bearing capacity of piles using the results of in situ tests is one of the most widely used methods. The objective of this study is to examine suitable cone penetration test (CPT)-based methods for predicting the load-bearing capacity of piles in silty soils. In addition, it is analysed whether standard penetration test (SPT)-based methods can be used with dynamic probing super heavy (DPSH-A) test data to evaluate pile capacity. Five CPTs and one piezocone penetration test (CPTu) based on direct methods were applied to determine the load-bearing capacity of piles. In addition, six SPT direct methods were used based on DPSH-A test data to estimate the load-bearing capacity of the investigated piles. The capacity of the pile obtained by various direct methods was compared with the outcome of the pile load test. Of the direct CPT methods, the LCPC (also known as French method) method and the German method demonstrated decent results when CPT probing reached deeper than the pile. The use of SPT-based direct methods with DPSH-A test data for displacement piles in silty soils seems to be promising. Specifically, the Briaud and Tuckers` method provided excellent results for most of the piles studied.
There is a lack of methods and studies that evaluate the validity of daylight standards such as the EN 17037:2018 in specific local contexts as cold climates. Moreover, the probable adaptation of the EN 17037:2018 by European countries motivated the aim of this investigation: to study the applicability of the EN 17037:2018 in a certain cultural context through the comparison of the subjective perception of Estonian office users with the quantitative assessment defined by the EN 17037:2018, including the four aspects: solar access, view out, daylight provision, and glare protection. In order to study the applicability of the EN 17037:2018 for Estonian office spaces, we used a mixed-method approach based on semi-structured interviews, measurements, and daylight simulations. Poor view out is related with high obstruction levels of urban features, despite the presence of multiple layers in the view. The level of recommendations for good view out in Estonian office rooms might be lower than the thresholds recommended by the EN 17037:2018. Except during winter months, direct sunlight exposure is not appreciated in Estonian office spaces since it is strongly related to glare discomfort caused by sun in the field of view and on computer screens. Working under daylight conditions during the whole year and having an easy-to-use interior shading systems to block the direct sunlight is very valuable for Estonian office users. For daylight and glare protection, there is a good agreement between qualitative evaluations given by office users and quantitative assessments proposed by the EN 17037:2018.
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4,230 members
Eve-Ly Ojangu
  • Department of Chemistry and Biotechnology, Division of Gene Technology
Juri Vain
  • Department of Software Science
Prashanth K G
  • Department of Mechanical and Industrial Engineering
Veiko Karu
  • Department of Geology
Sreekanth Mandati
  • Department of Materials and Environmental Technology
Ehitajate tee 5, 19086, Tallinn, Harjumaa, Estonia
Head of institution
Tiit Land