[diss] Insinööritieteiden korkeakoulu / ENG

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  • Modelling, design, and control of hybrid ground source heat pump system coupled with district heating in an educational building complex
    (2025) Xue, Tianchen
     School of Engineering | Doctoral dissertation (article-based)
    Ground source heat pumps (GSHPs) are an efficient solution for the decarbonization of building heating and cooling systems. They utilize borehole fields to extract heat from the ground for heating. The borehole fields can also supply free cooling energy for buildings in cold climates. Since buildings are heating-dominated in cold climates, conventional GSHPs face significant underground thermal imbalances. This often requires larger and more costly borehole fields to sustain high operating performance. An effective way to improve operational viability and financial sustainability is to integrate GSHPs with backup heating sources, such as district heating (DH), creating a hybrid GSHP system. This thesis investigated the modeling, design, and control of a hybrid GSHP system coupled with DH in an educational building complex based on simulation studies. The simplified modeling of an asymmetric-layout borehole field was validated using onsite brine temperature measurements. High-performing design methods for the hybrid GSHP system were explored by adjusting key design parameters, such as air handling unit (AHU) cooling water temperature level, indoor air temperature heating and cooling setpoints, GSHP design heating power, borehole number, and borehole depth. Regarding control, a cost-effective control strategy was developed to reduce system energy costs. The effects of power limitations, the input coefficient of performance (COP) value, and the control time horizon within the control algorithm were analyzed. Furthermore, a demand response control strategy was implemented to utilize the thermal storage of building thermal mass, investigating various DR control algorithms and parameters. Results indicate the simplified-geometry borehole field models can predict average inlet and outlet brine temperatures within a deviation of 1 °C from measured data and can also reduce computational time by up to 72% compared to the detailed models. Compared to the reference hybrid GSHP system design, increasing AHU cooling water temperature level and using lower indoor air temperature heating and cooling setpoints can raise the minimum outlet brine temperature from –6 °C to –3 °C over a 25-year lifetime, while also slightly improving the average heat pump COP in the last heating season. To ensure non-freezing boreholes, it is still necessary to increase the overall borehole length or reduce the GSHP design heating power. Compared to a GSHP-prioritized control strategy, the cost-effective control strategy, which incorporates power limitations and optimizes input COP values for control, achieves a 6.4% reduction in annual energy costs with hourly electricity and DH pricing. Implementing the DR control strategy to space heating enhances energy flexibilities for both electricity and DH networks without compromising indoor thermal comfort. Among studied DR control algorithms, the dual-price DR algorithm yields the highest cost savings. When it is combined with the cost-effective control, the hybrid GSHP system can achieve by up to a 10.8% reduction in annual energy costs with hourly electricity and DH pricing.
  • Put emissions on the map - geospatial approach to air pollution emission analysis
    (2025) Paunu, Ville-Veikko
     School of Engineering | Doctoral dissertation (article-based)
    Air pollution poses one of the most harmful environmental human health risks. To assess the health impacts of air pollution, georeferenced emission inventories are needed. The spatial interpolation, i.e. spatial distribution of the emissions in these inventories is essential for any impact assessment, but assessing the quality and uncertainty of the distribution is difficult, and there is a lack of scientific literature on the topic. There is no clear real-world quantity with which to validate the spatial distribution of emissions, as, for example, air quality measurements consider concentrations of the pollutants, not the emissions. The aim of this research is to utilize geospatial approach to improve methods of spatial distribution of air pollution emissions. To study this problem, this work considers and answers the following research questions: 1. How to assess the uncertainty of the spatial distribution of air pollution emissions? 2. What are the best data to use for proxies for spatial distribution of air pollution emissions in the most relevant source sectors? 3. What role does spatial resolution have in health impact assessment? For the first question, the lack of reference data for the spatial distributions meant that no one-forall method to assess the uncertainty was found. Comparison of the distributions of the emissions in different inventories was deemed as the best available method to assess the quality of the spatial proxies. To quantify the similarity of the distributions, an index of agreement was utilized. The index proved to be a good tool to support the comparison of spatial distributions, alongside visual analysis of maps and assessment of the data used for the proxies. For the second question, three source sectors were focused on: residential wood combustion, road transport, and machinery and off-road. Developed Nordic emission inventory was compared to both local and European level inventories. While European level inventories were able to produce similar spatial distributions as the Nordic inventory based on national methods, this was on resolution that was coarser than what the Nordic inventory offers, meaning modifiable areal unit problem (MAUP) needs to be considered for the emission data. In general, for the spatial distribution the difference between urban and rural areas in the spatial proxies was found to be crucial. Furthermore, local characteristics were important to take into consideration. Regarding the third question, health impact estimates from local emissions were concluded to be sensitive to the assessment resolution, and the effect was strongest in urban areas. The results highlight the importance of spatial distribution of the emissions on high resolution especially in urban areas. This work bridges the gap between geospatial theory and air pollution emission inventory framework. The spatial proxies used to describe the spatial distribution of the emissions have been assessed with practical geospatial methods to help analyse the ways the proxies can be developed. The work also describes the state-of-the-art data recommendations for spatial proxies for the three emissions sources sectors.
  • Articles on the impact of diversification on real estate firms
    (2025) Ibrahim, Islam
     School of Engineering | Doctoral dissertation (article-based)
    Real estate portfolio diversification is a common investment strategy among real estate firms worldwide. When implemented across markets with imperfectly correlated performance, diversification can reduce a firm's cash-flow volatility, positively impacting its capital costs and overall value. However, diversification can also increase agency and information costs, exacerbating issues such as overinvestment and inefficient capital allocation. Therefore, the net effect of diversification on a real estate firm reflects a balance between these potential benefits and costs. Accordingly, this dissertation quantitatively investigates the net effect of different dimensions of diversification on a real estate firm's capital cost and value. The dissertation empirically highlights, with robust evidence, that different dimensions of diversification can affect a firm's debt costs differently. Specifically, it finds that property-type diversification is associated with a decrease in public debt costs. In contrast, domestic diversification is associated with an increase in public debt costs. In the same context, this dissertation reveals that credit rating agencies and public lenders may assess the impact of diversification on credit risk differently. The present research also examines the impact of two levels of geographical diversification—domestic and international—on real estate firm value. International diversification may be more effective in delivering the benefits of geographical diversification due to the lower correlation between international markets compared to domestic markets, hence presenting a different effect on firm value. However, the findings illustrate that the potential benefits of geographical diversification, whether domestic or international, are often outweighed by negative implications stemming from agency and information problems, resulting in a reduction in firm value. Additionally, this dissertation identifies operating efficiency and risk premiums as channels through which geographical diversification can negatively impact firm value. Finally, the findings of this dissertation reveal time variation in the net effects of diversification, showing that the balance between the benefits and costs of diversification varies with market conditions. During periods of high market volatility, the benefits of diversification appreciate, counterbalancing the associated costs. At the same time, it is demonstrated that market volatility has adverse effects on real estate firms; however, diversified real estate firms experience a mitigated effect of market volatility. Consequently, the findings suggest that diversification can moderate the adverse effects of market volatility.
  • Process Modelling of the cruise passenger travel experience
    (2024) Akter, Sabina
     School of Engineering | Doctoral dissertation (article-based)
    Decision making in the service industry, particularly in the experience business such as cruise services, is a multi-criteria and -stakeholder problem. It emphasizes the significance of decision-making models for navigating the unpredictable cruise industry, in which time spans and stakeholders associated with ship design, building and operations vary substantially. It also highlights the necessity for long- and short-term, as well as stable and adaptable, decisions. This thesis proposes viewing decision making as a multi-stage and multi-stakeholder process that involves learning from customer data, understanding data interrelationships and biases, and engaging users strategically. It integrates views from both passenger experiences (lower level, short time spans) and organizational perspectives (upper level, longer time spans). This thesis presents a framework to improve onboard environmental decision making on cruise ships in relation to the passenger experience. A comprehensive model is developed, integrating onboard environmental factors such as ambience, ship layout and design, social interactions, product and service quality, and overall enjoyment in the resulting customer satisfaction. Customer satisfaction is considered from the perspective of internal responses, including cognitive, affective, physiological and behavioural, and their influence on decision making is discussed. The cruise experience process spans from initial experiences during the purchasing phase of the journey and resulting expectations to the final, post-cruise satisfaction and resulting customer behaviour (e.g., loyalty, including word-of-mouth, recommendation, intention to repurchase, repeat purchase and regret regulation). A holistic understanding and interpretation of behavioural models is vital for making informed decisions in both the design and operation phases of the cruise ship within the experience-based tourism industry. The results derived from the developed model with actual customer data highlight the importance of fully understanding onboard environmental factors and their relation to customer reactions in enhancing the customer experience and satisfaction within the cruise tourism industry. This thesis offers a robust framework for future research and practical applications by synthesizing existing research and developing a comprehensive model for multi-criteria and -stakeholder decision making. The developed theoretical model offers insights for both scholarly research and practical applications in the cruise industry. It aims to assist cruise ship designers, builders and operators in designing and managing their ships, optimizing customer satisfaction and enhancing loyalty.
  • Influence of Anisotropy on Edge Fracture of Advanced High-strength Steels
    (2024) Li, Zinan
     School of Engineering | Doctoral dissertation (article-based)
    Advanced high-strength steels (AHSS) have been developed with superior properties for wide applications in the automotive industry. Among them, dual-phase (DP) steels and Quenching and Partitioning (QP) steels, as representatives from the first and third generations of development, are attracting great interest. Despite the benefits of the enhanced high strength, the formability of these materials becomes unpredictable in the forming processes, especially in the largely deformed local area. AHSS is more susceptible to edge fracture compared to traditional mild steels, due not only to reduced ductility but also to distinct local fracture behavior. To deepen the knowledge of the edge fracture behavior of AHSS, it is necessary to find a characterization method that accurately describes fracture failure. The study aims to accurately predict edge fracture by addressing often-overlooked factors such as anisotropy evolution, localization, and stress-state-dependent fracture behavior. To achieve this goal, a combination of experimental and numerical approaches is employed. First, a category of tensile tests with various geometries and loading directions was conducted to characterize the anisotropic fracture properties of DP and QP steels. Next, hole expansion tests (HET) were carried out to assess edge formability under both smooth and blanked edge conditions. In addition to the classic fracture dependency on stress states, the spotlight is on the anisotropic behavior in terms of both plasticity and fracture. The evolving non-associated Hill48 (enHill48) model is applied to describe anisotropic plasticity, while the anisotropic fracture models are formulated to represent fracture behavior. The novelty of this study lies in uncovering that the edge fractures of examined DP steel are primarily driven by anisotropy-induced strain localization, while the edge fractures of the investigated QP steel, though less sensitive to anisotropic plasticity, are strongly dependent on anisotropic fracture and stress triaxiality, governed by fracture limits. A partially anisotropic fracture model is found effective for DP steel in capturing anisotropic plasticity and localization but remains limited in accurately describing fracture-dominated local formability for QP steel. Consequently, a fully anisotropic model is proposed for QP steel, based on the linear transformation of plastic strain within the damage initiation criterion. This model is validated for both anisotropic fracture behavior and edge formability with improved prediction accuracy. The findings emphasize the crucial role of anisotropy in edge fracture assessment, which not only enhances modeling precision but also introduces a design concept to elevate material edge formability.
  • Porous Aerostatic Seals and Bearings for Large Rotors
    (2024) Miettinen, Mikael
     School of Engineering | Doctoral dissertation (article-based)
    Aerostatic lubrication can be used in precision and high-speed applications. Aerostatic porous bearings and seals form a lubricating gas film between two surfaces by supplying pressurized gas to the gap through a permeable surface. Externally pressurized porous bearings can be used for simultaneous sealing and bearing functions. The aim of this research is to theoretically and experimentally investigate the performance of aerostatic bearings and seals and to improve modeling of flow in porous externally pressurized bearings and seals. Developed bearing and seal models use the modified Reynolds equation that includes a porous feeding term. The proposed analytical and numerical solutions are verified with multiple experiments under static conditions. Experimental setup and measurement methods of bearing and seal performance parameters are developed. Outer diameter of the experimentally investigated bearings and seals are in the range of 40 mm to 62 mm. It is shown that the analytic solution is equivalent to numerical solutions of the Reynolds equation on the most significant performance metrics under static conditions. Investigated performance characterizing metrics of aerostatic bearings and seals include load capacity, air gap height, stiffness, air consumption, and leakage. Further, effect of design and operational parameters on the performance are investigated. The investigated design parameters include the permeability of the porous restrictor and the seal width, while investigated operational parameters include the supply and chamber pressures and preload of the seal. Some of the results are presented in nondimensional form for better applicability to general problems. Finally, a robust aerostatic bearing concept tolerant of large movements of the guide surface is developed and its performance is investigated under realistic dynamic conditions for paper machine applications. The developed bearing concept achieved a load capacity of 18.5 kN. These results give corroborative evidence on feasibility of the proposed bearing for use in paper machinery. The results of this research are relevant for design of aerostatic bearings and seals and applications where good motion accuracy or low friction motion are required.
  • Evaluating Hydrodynamic Influences on Ice Load from Ship-Ice Glancing Impact: The Roles of Sea Waves and Hydrodynamic Interactions
    (2024) Jiang, Zongyu
     School of Engineering | Doctoral dissertation (article-based)
    With climate change increasing accessibility to polar maritime routes, understanding ice loads on ship hull has become crucial for safe navigation. Traditional methods for evaluating ice loads, such as the Popov method, often simplify the geometry of ships and ice floes, and neglect the complex hydrodynamic interactions and waves that significantly influence ice loads. These simplifications can lead to inaccurate predictions of ice loads, especially in the Marginal Ice Zone (MIZ), where ships and small to medium-sized ice floes are dynamically affected by sea waves. This research aims to fill this gap by developing a comprehensive model that incorporates these factors to enhance the precision of energy-based ice load evaluations. To address these shortcomings, this research proposes a novel approach using the Boundary Element Method (BEM) to assess the hydrodynamic interaction between an advancing ship and an ice floe. This approach incorporates the linear superposition principle to combine the radiation potentials of both bodies and the encounter frequency method to account for the ship's speed. This results in a detailed calculation of added mass and damping coefficients, which are critical for understanding the hydrodynamic interactions between the ship and ice. Further, a Computational Fluid Dynamics (CFD) model is developed to investigate the hydrodynamic coefficients under the interaction between side-by-side structures, focusing on how the surrounding fluid flows affect the hydrodynamic coefficients. The CFD model helps understand the physical significance of specific subsections of the hydrodynamic coefficient matrix, essential for accurate ice load evaluations. The research integrates these findings into an extended energy-based model for ice load evaluation, considering effects of waves and hydrodynamic interactions. This model is illustrated through a case study involving an ice-class ship and ice floes of varying sizes. Key findings of this thesis include the realization that traditional ice load evaluation methods may underestimate ice loads by not accounting for sea waves and hydrodynamic interactions. The novel BEM approach developed in this research provides a more accurate representation of these interactions, leading to better predictions of ice loads. The study also reveals that the impact of wave-induced motions is more pronounced than that of added mass. This research makes significant contributions to maritime engineering by uncovering the influence of hydrodynamics on ice load evaluations. It provides valuable insights for the design and operation of ice-going ships, ensuring safer navigationin ice-infested waters.
  • Production, process and properties of 3d printed multi-metal parts
    (2024) Mousapour, Mehrdad
     School of Engineering | Doctoral dissertation (article-based)
    Additive manufacturing (AM), also known as 3D printing, is an advanced technology that enables the fabrication of multi-material parts with intricate internal structures and lightweight lattice designs. Compared to conventional manufacturing methods, AM offers opportunities for engineering optimization and performance enhancements. Its material efficiency minimizes waste and usage, aligning with sustainability goals and economic considerations. Particularly, multi-metal parts additive manufacturing (MMAM) represents a transformative approach that integrates multiple metals within a single component, leading to superior material properties, structural complexity, and functional optimization. Despite its promising potential, multi-metal AM faces several limitations and challenges. Key issues include maintaining metallurgical compatibility between dissimilar metals, controlling thermal stresses and distortions during the process, achieving high-quality interfaces between different materials, and high production costs associated with some specific AM technologies. Additionally, the development of reliable process parameters, effective post-processing techniques, and robust quality control methods remains critical for the widespread adoption of multi-metal AM. Addressing these challenges is essential to unlock the full potential of multi-metal additive manufacturing and expand its applications across various industries, including aerospace, automotive, and biomedical engineering. This dissertation explores the feasibility of utilizing cost-effective additive manufacturing (AM) technologies to produce multi-metal parts. The study evaluates the properties, challenges, and limitations associated with this manufacturing approach, providing valuable insights into its potential applications and advancements in the field of multi-metal AM. Additionally, the interface between the two metals is specifically characterized in terms of their microstructural features, including porosity, intermetallic compound formation, and hardness mismatch. The dissertation employs material extrusion (MEX) and vat photopolymerization (VPP) additive manufacturing methods, known for their high availability and cost-effectiveness. These desktop printers are widely utilized in engineering, product design, dentistry, and other fields requiring high-resolution, intricate 3D printed parts. However, multi-metal parts produced using MEX and VPP technologies often exhibit poor mechanical properties inherent to sintered parts, primarily due to high levels of porosity. The de-binding process results in the formation of voids among the metal particles, making it challenging to diminish these voids during the sintering process, even with elevated temperatures and prolonged durations.
  • Cities as carbon sinks - biogenic carbon sequestration and storage
    (2024) Kinnunen, Antti
     School of Engineering | Doctoral dissertation (article-based)
    In an era marked by escalating environmental and social crises, transforming urban systems is necessary. Currently, urban environments epitomise the degenerative impacts of anthropogenic activities—net-consumers of natural resources and ecosystem functions, contributing little to their production. However, this need not be the case. By harnessing the internal transformative capacity of the built environment, urban systems can contribute to environmental benefits. This dissertation explores biogenic carbon sequestration and storage (CSS) in redefining the built environment's role in climate regulation, embodying restorative and regenerative urban planning principles. Integrating natural and built structures, the research explores enhancing carbon sink capacity within urban landscapes, offering mitigation and adaptation benefits in the face of rapid urbanisation and accelerating climate change. The research presents a case study of biogenic CSS capacity in the built environment. It employs theoretical and empirical approaches, broad literature reviews, and precise case studies to build the key findings and main argument. The research uses quantitative and qualitative perspectives, mixing them to increase the robustness and credibility of the presented causal argumentation. The ensuing results are reflected upon the identified theoretical and conceptual frameworks and used to draw connections across all the studied scopes, accounting for inherent limitations, uncertainties, and potential weak points in the adopted research approach. Through this comprehensive analysis, the dissertation concludes that significant capacity exists for biogenic CSS improvement in the built environment. Integrating natural and built components into the urban carbon pool by increasing green space and canopy cover, using biogenic materials, and mimicking natural ecosystems' structure and functions presents potential to match or exceed pre-development CSS rates. This requires considering intertwined causal drivers, suggesting that increasing the carbon sink capacity of the built environment is best achieved in tandem with broader urban sustainability transformation. However, contemporary planning and development strategies characterised by simple heuristics often fail to harness this potential. The findings propose that these strategies inadvertently compromise the ecological quality of the built environment by neglecting urban complexity and its functionalities. Thus, the dissertation argues for a fundamental shift in urban planning and development strategies—from singular, performance-targeted approaches to holistic, multicriteria perspectives that embrace urban systems' complexity. The thesis significantly contributes to advancing urban carbon accounting discourse, conceptualising cities as active producers of carbon sink capacity.
  • Lapset kaupunkisuunnittelukysymyksenä 1950–1970-lukujen Helsingissä
    (2024) Moll, Veera
     School of Engineering | Doctoral dissertation (article-based)
    This dissertation examines the shaping of childhood as an urban planning issue in Helsinki. It focuses on the most intense decades of urbanization, the 1950s to the 1970s, when urban planning discussions about children, along with legislation on and standardization of children's environments, increased. These discussions have had far-reaching consequences, contributing to the foundation of the contemporary understanding of children's needs and their role in urban environments. The research material consists of a large collection of reports and planning instructions dealing with urban childhood, as well as written memoirs from the capital region. Theoretical tools used in the work include concepts such as independent mobility, affordances, and the spatial politics of children's geographies. The concept of modern childhood is also a key focus of the work. This multidisciplinary research is primarily anchored within two fields. Firstly, the work contributes to the field of urban planning history by focusing on children's perspectives. It examines children's urban spaces, including yards, streets, urban nature, and particularly built playgrounds. Additionally, the study of child-specific norms represents a novel approach within the context of Finnish planning history research and contributes to the wider historical and societal discussions on standardization in urban planning. In the field of the history of childhood, the main contribution of this work is to show that the modern childhood of the 20th century was also constructed through urban planning. Building instructions related to children in the city, as well as the discussions that preceded and followed them, influenced where children spent their time. They also shaped perceptions of suitable and unsuitable environments for children. The study presents five key findings. First of all, in the 20th century, known as the century of the child, 1) children shifted from being a relatively overlooked group to an important focus in urban planning. In addition, 2) the issue of children as an urban planning concern took shape as a result of multi-professional negotiations. Helsinki's childhood as a planning issue is also 3) a history of redirection. This means that children were typically not considered to be in suitable places where they already were, such as courtyards, streets, or other areas in which they found themselves. Childhood as an urban planning issue also developed 4) as a part of suburban development. Additionally, 5) children as an urban planning issue took shape subordinated to the development of a car-centric transport system.
  • Digital Situational Awareness Systems for Infrastructure Project Management: Characteristics, Development, and Perceptions
    (2024) Lappalainen, Eelon
     School of Engineering | Doctoral dissertation (article-based)
    Complex infrastructure projects in urban communities, such as public transportation projects, have been challenging to manage. They often receive negative publicity due to cost and schedule overruns and quality problems. Situational awareness (SA) and situational management (SM) have been developed to support decision-making in complex environment by providing robust methodologies and concepts that are now being examined in the field of infrastructure construction. This study explores how public infrastructure projects have addressed these problems by developing digital systems based on SA and SM to support project management's sense of awareness. SA systems aim to continuously monitor and assess events in the environment and to track progress, resource availability, risks, and many other variables that are used for decision-making.The dissertation consists case studies of 5 infrastructure projects, a workshop with 36 participants, 9 expert interviews, 23 system user interviews, and 21 user interviews. 65 professionals from 28 companies participated in the research. The first contribution presents the characteristics of SA systems developed in large-scale projects, including customizability, reliability, social applicability, technical lifespan, ease of implementation, usability, and data security. However, weaknesses were identified, such as limited adoption of SA frameworks developed in other sectors. Only the first level of SA—data collection and the representation of data in visual key metrics—is partially automated. The adoption of SA systems is particularly challenging in design management, as data collection relies heavily on meetings, reporting, and manual processes, although it is possible to automatically collect data from design softwares.The second contribution highlights how SA system development has focused on project management, while the use of SA in design and site production management seems to remain limited. This narrow focus may reduce contractors' motivation to collect data. Participants questioned the accuracy of SA data, citing industry practices of withholding information and manual collection. As a result, subjective expert judgment is often preferred over the information provided by the system. When information is mistrusted, the responsible person's opinion is sought for decision-making. The third contribution identifies how the construction sector applies SA and SM concepts. Instead of automated SA, the sector relies on validation by responsible individuals. During the first years of operation, SA system use is technology-driven, with less emphasis on human factors. However, the study suggests that the use of SA in the management of complex infrastructure projects can enhance the problem-solving skills of system users, facilitate decision-making, and promote open discussions, especially among project managers. Further development should focus on increasing awareness of SA models from other sectors and better integrating design and site management in SA systems.
  • Modeling, Design and Testing Techniques for New Generation Industrial Rotors
    (2024) Giorio, Lorenzo
     School of Engineering | Doctoral dissertation (monograph)
    This dissertation explores relevant topics regarding the application of machine fault diagnosis in the design, monitoring, and diagnosing of industrial rotating machinery. Bearings, fundamental components in rotating systems influencing the dynamics of the entire system, are affected by roundness errors developed during production and assembly and may suffer damage during operation, causing unwanted vibration with a detrimental effect on the efficiency and quality of production. In the context of Industry 4.0, sensor-equipped rolling bearings can be used as a sentry for the whole rotor system, providing both internal bearing damage detection and external rotor system anomalies monitoring. This dissertation focuses upon the installation, sensorization, and experimental activity on a test rig for the monitoring of medium-sized industrial bearings while operating in industrial conditions, available at the Laboratory of Mechanics of Politecnico di Torino. The state-of-the-art of modeling techniques for rolling bearings with localized defects was also examined. An analytical numerical model of the rotor-bearing system was developed, validated through some experimental data acquired on the test rig, able to identify vibrational features from defects and to perform component- and system-level monitoring activities within its vibrational response. A dataset was created for condition monitoring of medium-size spherical roller bearings with various localized defects. Noise reduction in experimental vibration signals, particularly using the Discrete Wavelet Transform (DWT), was also investigated using an experimental literature dataset. A screening of DWT parameters was conducted for the appropriate parameters selection for the identification of localized defects in bearings, enhancing previous literature studies. Furthermore, the effect of the geometry of the bearing installation seat on the roundness error of bearing inner ring was also analysed. Extensive experimental activity, performed in the ARotor Lab at Aalto University, validated the roundness error stacking methodology to evaluate the roundness error of mounted inner ring raceways considering the roundness error of the tapered shaft and the thickness variation of the inner ring. The existence of an optimal orientation between the components that minimizes the roundness error of the raceways in the assembly was highlighted. The study further explored the application of 3D conical grinding to the tapered installation seats of a large rotor to compensate for roundness error. A significant reduction in the roundness errors of installed inner ring raceways and rotor's subcritical vibration was experimentally demonstrated, also compared to previously published methodologies based on cylindrical grinding and the use of adapter sleeves. Results showed that unmounted bearing inner ring roundness is irrelevant to the final raceway roundness, and that bearing manufacturers should focus on minimizing the thickness variation of the bearing inner ring.
  • Engineering strategies for designing lightweight ship windows
    (2024) Heiskari, Janne Matias
     School of Engineering | Doctoral dissertation (article-based)
    Modern cruise ships employ many insulating glass unit (IGU) type windows around the superstructure for increased passenger experience. The IGUs have become weight-critical structures that require weight optimization for better overall vessel efficiency. The optimization is challenged by the lack of details and accurate design methods in the early design phase, where the window's major parameters are decided. Therefore, this dissertation aims to improve the IGU design framework during the ship's early design phase to determine the glass pane thickness for reduced weight. The analysis methods are called engineering strategies, and they consist of (1) numerical optimization and (2) finite element method (FEM), which includes (3) geometric nonlinearity of the glass panes, (4) shear transfer of laminated glass, and (5) load sharing due to the hermetically sealed cavity. Hence, the thickness determination is more accurate than the typical classification rule-based method and has more design flexibility, such as window shape and boundary conditions. The results show that using such strategies is beneficial, as potential weight savings of up to 50% were found with respect to the classification rules. The findings are more evident for large, thin IGUs of monolithic glass panes. The most important factors affecting the weight and bending behavior were the allowable deflection limit, glass pane thickness configuration, IGU shape, and interlayer stiffness in laminated glass. Based on the results and observations in this dissertation, we can conclude that the proposed engineering strategies offer the ship designers better design principles for thickness determination than those currently in use. This helps to reduce glass weight and accomplish the novel ideas dreamed by the ship owners. However, we must further discuss this matter with the corresponding classification societies as they ensure the ship's safe design. This dissertation can work as a foundation for that discussion.
  • Evaluating Concrete Compaction: A Multi-modal Approach
    (2024) Ahmed, Hassan
     School of Engineering | Doctoral dissertation (article-based)
    Compaction of concrete plays a crucial role in ensuring the strength and durability of concrete structures. Proper compaction is essential for expelling entrapped air and achieving target density. Under-compaction leaves excessive entrapped air, reducing strength and durability. Conversely, over-compaction leads to uneven density distribution due to segregation, also impacting strength and durability. The quality of compaction is thus dependent on balancing the reduction of entrapped pores with minimal segregation. This thesis investigates methods to assess the quality of concrete compaction by examining both segregation and entrapped pores. The research encompasses four key areas: monitoring segregation during compaction, evaluating segregation in hardened concrete, analyzing theemergence of surface bubbles during compaction, and characterizing entrapped pores in hardened concrete. To monitor segregation during compaction, an AC impedance spectroscopy (ACIS) measurement system was developed. It showed a strong correlation with aggregate distribution, demonstrating its effectiveness in real-time segregation detection. For evaluating segregation in hardened concrete, three indices were proposed based on density measurements and aggregate distribution analysis. These indices provide a comprehensive assessment of segregation levels, offering a practical tool for segregation assessment. The long-standing practice of relying on the rise of bubbles to the surface as an indicator for optimal compaction time was critically examined. Video analysis of surface bubbles during compaction revealed that bubble emergence continues even after segregation occurs, challengingthe reliability of this traditional method. This finding emphasizes the need for more objective compaction quality assessment techniques. X-ray computed tomography (XCT) was employed to analyze entrapped pores in hardened concrete. The study investigated the effects of concrete workability and compaction time on pore characteristics. Results showed that increasing concrete workability reduces entrapped porosity but increases segregation sensitivity during extended vibration. Concentrated regions of entrapped pores were observed within specimens, highlighting the complex relationship between compaction parameters and pore distribution. This thesis concludes that improving compaction quality control requires considering two key factors: segregation extent and entrapped air content. Traditional indicators like surface bubble emergence proved ineffective, showing the importance of advanced monitoring techniques such as ACIS. The proposed segregation indices and XCT analysis methods provide valuable tools for evaluating and improving the quality of compaction. The findings enable future research to develop more effective compaction methods and quality control procedures, potentially leading to improved concrete durability and performance in construction practice.
  • Flexibility and resilience in the transition to a carbon-neutral Finnish energy system
    (2024) Koivunen, Tero
     School of Engineering | Doctoral dissertation (article-based)
    As climate change caused by anthropogenic carbon emissions continues to present a major threat to humanity, the energy sector has a central role in combatting carbon emissions. Inspired by the 2015 Paris Agreement, the European Union has a binding goal of attaining carbon neutrality by 2050. Finland has its own legally binding goal of attaining carbon neutrality already by 2035. In this thesis, the transition towards a carbon neutral energy system in Finland is investigated. This thesis is based on both power and energy system simulations on an hourly resolution. While the power sector in Finland is already mostly decarbonized, heating, industry and transport sectors still require extensive decarbonization measures. This thesis investigates the transition from three different aspects. First, this thesis investigates the technical feasibility of a carbon-free power system. Second, decarbonization methods in industry and transport are investigated. Third, aspects such as economic dispatch, security of supply and demand response are evaluated. This thesis finds that introducing either energy storages, flexible power generation or demand is essential to facilitate the transformation to a carbon neutral energy system. This is due to increasing share of variable renewable electricity generation. Introducing electrification to other sectors such as heating, or industry increases the need for flexibility. Two clear flexibility roles are found: short-term flexibility to counter wind variability and long-term flexibility for seasonal demand variation. Both of these are needed for increasing resilience in the energy system in the transition towards carbon neutrality. Flexibility can be provided either by generation or by varying load. Demand-side management affects especially the short-term flexibility needs. Additionally, to attain carbon neutrality, decarbonization measures must be taken across the energy sector. When industry and transport sectors are decarbonized with electrification, both directly and indirectly via green hydrogen as energy carrier, carbon emissions decrease significantly, and carbon neutrality is possible. However, carbon sinks also need to be considered, therefore increasing biomass usage for electricity and heat production is not a suitable option. Future research should include the whole Nordic electricity system, integrated with heat and hydrogen sectors. This would enable a more comprehensive analysis and help in more accurately quantifying the amount of needed flexibility.
  • The load-bearing capacity of screw piles in silty soils based on mechanical, piezocone and seismic soundings
    (2024) Leetsaar, Lehar
     School of Engineering | Doctoral dissertation (article-based)
    To accurately determine how piles behave in a particular situation, a static pile loading test is considered the most reliable method, although its implementation is restricted to special cases due to its high cost. In Estonia, the estimation of pile capacity is commonly based on dynamic probing data, specifically collected using the DPSH-A method. Furthermore, certain Estonian investigation companies have started to adopt static-dynamic probing tests. Cone penetration testing and piezocone penetration testing have been used in a limited number of site investigations in Estonia. The direct application of sounding outcomes for the determination of pile load-bearing capacity has emerged as a preferred approach. These methods are called direct methods. Such methods may encounter a drawback when relying on cone penetration testing or standard penetration testing data, as they may provide limited support in identifying the connections between load and settlement relation of the pile. When evaluating the load capacity of piles, it is essential to consider the relationship between load and settlement. Researchers have extensively studied analytical soil models based on stress, strain, and strength data obtained from practical experiments to better understand this connection. The small strain shear modulus is a key parameter in these models, and its determination is often done through the seismic cone penetration test. The load-bearing capacity of screw piles in silty soils has been assessed using mechanical, piezocone, and seismic soundings. The findings indicated that there was a significant reduction in the variability of the computed outcomes when the sounding was carried out at a depth greater than several meters below the pile base. In terms of the direct methods relying on the cone penetration test, it was discovered that the LCPC method produced the most satisfactory outcomes for Fundex piles. The Briaud and Tucker (1988) method is distinguished among the different standard penetration test methods for its remarkable ability to accurately predict outcomes for Fundex piles. Comparing values from the cone penetration test and static-dynamic probing test for displacement piles and full displacement piles, it was found that the Eurocode 7 method demonstrated the most favorable performance. These studies provide evidence that the three direct methods (Briaud and Tucker (1988), LCPC, and Eurocode 7) all incorporate the s/B=10% failure criterion and have shown satisfactory outcomes. A comprehensive analysis was conducted to investigate the relationship between normalized operative shear stiffness and normalized pseudo-strain for screw piles in silty soil, leading to a highly significant correlation. The load-bearing capacity of screw piles in silty soils exceeds that of other types of piles, particularly in situations with low strain.
  • Photogrammetry for characterizing rock fracture roughness, physical aperture, and hydromechanical properties
    (2024) Torkan, Masoud
     School of Engineering | Doctoral dissertation (article-based)
    Understanding rock mass behavior is vital for various applications, including nuclear waste disposal and civil projects. Geometrical properties of single rock fractures, like roughness and physical aperture, significantly affect shear strength and fluid flow. This research aimed to characterize single rock fracture properties such as roughness, physical aperture, or hydromechanical attributes using photogrammetry of Kuru granite. Push shear tests were conducted on two sample sizes (200 cm × 100 cm and 50 cm × 25 cm), revealing a reduction of peak shear strength and friction angle for the larger size. Roughness back-calculated from shear tests for the larger sample was lower than the estimates from profilometer or photogrammetry. Scale adjustment was necessary for the correction of roughness estimation for the larger sample. Experimental differences may also stem from matedness. Using low-cost cameras in photogrammetry was investigated for a sample size of 50 cm × 50 cm. While smartphones show promise, caution is advised due to potential accuracy issues. Notably, the sampling intervals of 3D point clouds could affect roughness and physical aperture measurement results. A high-precision photogrammetric method was developed for measuring the physical aperture of three 25 cm × 25 cm samples. Markers at predefined distances used as scale bars were attached to each sample. The Root Mean Square Error (RMSE) between actual and calculated distances ranged from 20 to 30 µm. This method showed high accuracy compared to linear variable displacement transducers (LVDTs) for measuring fracture closure under normal stresses (0, 0.1, 0.3, and 0.5 MPa), with differences ranging from 1 to 8 µm. Achieving this level of accuracy required using at least 200 scale bars. Hydromechanical tests were conducted with fluid pressure gradients from 20 to 200 kPa/m and under the abovementioned normal stresses. The relationship between fluid pressure gradient and flow rate followed the nonlinear Forchheimer equation. Roughness displayed anisotropy, with greater roughness resulting in lower conductivity. Simulations were performed under different conditions and compared with laboratory fluid flow tests for validation. Scale effects study revealed significant variations in roughness and permeability with sample size changes. Three 100 cm × 100 cm surfaces were extracted from the 3D model of the bottom half of the 200 cm × 100 cm sample. Then, square subsample sizes ranging from 5 to 100 cm were extracted to estimate roughness and permeability. The surfaces were duplicated and shifted 350 µm to match the initial physical aperture of the 25 cm × 25 cm samples. Square subsample sizes below 30 cm showed variations in roughness and permeability, while these properties tended to be relatively stable states beyond this sample size. In conclusion, the study showed the feasibility of using photogrammetry to accurately characterize different rough fracture sizes for different applications.
  • Effective integration of renewable energy in Northern European energy systems
    (2024) Hyvönen, Johannes
     School of Engineering | Doctoral dissertation (article-based)
    The European Union (EU) has committed to reaching carbon neutrality by 2050 at the latest, with Finland ambitiously pledging to reach net-zero carbon emissions already by 2035. Reaching these targets will require a rapid expansion in renewable energy generation over the next decade, which will mostly be facilitated by market incentives and private investments in the EU. Yet, it is still somewhat unclear what technologies will effectively enable different sectors to be decarbonized in the future, especially as increased energy market uncertainty and high electricity prices have become common in the last years following the war in Ukraine and the EU energy crisis in 2022. This thesis thus aims to provide new insights into how renewable energy use can be increased effectively in both individual and national energy systems in Northern Europe, with Publications I–III assessing the techno-economic feasibility of solar PV and energy storage systems in end-consumer applications in Finland, and Publications IV–VI focusing on how potential risks, limitations, and challenges may impact the transition to clean energy in Northern Europe.  The results of this thesis indicate that both smaller and larger locally installed solar PV systems can effectively increase the share of renewable energy in residential buildings and data centers in northern countries. Yet, in most cases, this necessitates selling surplus electricity to the grid to be cost-effective, as the use of energy storage to balance solar PV systems is shown to generally increase energy-related costs for end-consumers at higher latitudes. Moreover, the results highlight how resource adequacy and power supply security will be crucial in ensuring the effective transition to clean energy in Northern Europe. Notably, potential limitations in critical mineral and biomass availability pose significant risks to reaching national climate and energy policy targets in Finland and Northern Europe, as the global supply of many critical minerals is currently highly concentrated in a few non-EU countries and will have to be expanded considerably to facilitate the global transition to clean energy, and as Finland and similar countries will need to increase forestry carbon removals substantially to meet EU emission reduction targets for 2030 and to stay on track to attain national carbon neutrality targets. Additionally, the presented analysis suggests that new investments into flexible thermal power generation are necessary to cost-effectively balance the growing share of intermittent wind and solar PV generation in the Finnish power system by 2035. Subsequently, this thesis highlights how further action is needed to facilitate renewable energy integration and attain national climate targets in Northern Europe, as well as to guarantee resource adequacy and energy system reliability in the clean energy transition.
  • Freshwater change in the Earth system - A qualitative-quantitative outlook and implications for planetary boundaries
    (2024) Virkki, Vili
     School of Engineering | Doctoral dissertation (article-based)
    Human actions currently put many life-supporting Earth system processes at risk. The planetary boundaries framework illustrates how this environmental change is pervasive throughout the Earth system and demarcates biophysical boundaries to keep the Earth system stable. Although the framework conceptualisation is sound, especially the definitions of boundaries describing changes in the biosphere and the hydrosphere have been criticised. This thesis provides a comprehensive analysis of global freshwater change and relates this to the planetary boundaries framework. The freshwater cycle supports hydroecological (sustaining ecosystems) and hydroclimatic (regulating climate) functions, which integrally embed freshwater in the Earth system. However, the planetary boundary for freshwater has not captured many of these interconnections, and global-scale approaches have often been limited in analysing and interpreting human-driven freshwater change. Thus, the aim of this thesis is to address the research gap of capturing freshwater change in the Earth system in a way that enables a better representation of freshwater in the planetary boundaries framework. The results of this thesis comprise a thorough qualitative-quantitative assessment of global freshwater change. Using expert knowledge elicitation, blue and green water are shown to strongly interact with other Earth system processes, with variable roles in mediating these interactions. Moreover, associations between common changes in streamflow regimes and their direct and indirect drivers are analysed, using streamflow observations and multivariate global data of the drivers. In-depth analyses of modelled hydrological data further demonstrate the widespread extent and considerable degree of global freshwater change, first through the concept of environmental flow envelopes and then by assessing streamflow and soil moisture deviations beyond pre-industrial reference conditions. This leads to introducing a new planetary boundary for freshwater change, which is defined based on the work conducted for this thesis and parallel studies. Safeguarding freshwater as an integral part of the Earth system requires integrated approaches. The interactions between freshwater and other Earth system processes form a dense and complex network where changes – often anthropogenic in nature – affect more than one component of the freshwater cycle at a time. Thus, setting planetary-scale limits or aggregating freshwater change globally should use the knowledge on the role of freshwater in the Earth system as widely as possible. The findings of this thesis provide a solid background for further advances on understanding the causes and consequences of freshwater change – at local to global scales.
  • Expanding the applicability of large-scale transportation models for the assessment of disruptive mobility technologies
    (2024) Agriesti, Serio Angelo Maria
     School of Engineering | Doctoral dissertation (article-based)
    As the world grows more complex and most aspects of daily life become fluid and more subject to change, transportation is no exception. Urbanization, sprawling, inequalities, and climate change are only a few of the challenges currently facing transportation planners, institutions, and public bodies. Moreover, historical patterns become less reliable as disruptions that once were counted in decades are now happening every few years. To address all these challenges, it is of utmost importance to adapt our approaches to be more flexible and to frame changes in attitudes, utilities, and goals in the urban population.The work presented in this thesis focuses on developing and providing multiple solutions with a specific focus on large-scale urban models. The main objective is to draw a road map of the major issues hindering modeling solutions able to tackle the challenges described above. Once that is accomplished, different methods are designed, developed, and tested on a real case study (Tallinn, the capital city of Estonia).  First, we approach the problem of defining a synthetic population detailed enough to carry out large-scale behavioral studies, without infringing privacy constraints. We then use the resulting dataset to build an activity-based behavioral model for the whole city. We harness machine learning techniques to automate the calibration of the hundreds of behavioral parameters involved, a quantity not yet achieved in the state of the art. We then focus on integrating the behavioral model with state-of-the-art traffic assignment solutions, trying to forge a blueprint for any modeler wanting to expand an existing model (a problem quite common, as many urban traffic assignment models have been developed through the years and are not easily replaceable). An iterative approach is developed and tested, first to frame a baseline situation and then to forecast the impact of disruptive mobility services on both the demand and the supply. Finally, the large-scale urban architecture built by integrating behavioral and traffic assignment models is exploited to test, for the first time with the presented degree of detail, the impacts of both an optimization algorithm and a fairness pricing scheme on an (automated) on-demand system.