The first part of this Thesis deals with the analysis of piecewise-smooth mechanical systems and the definition of special stability criteria in presence of non-conservative follower forces. To illustrate the peculiar stability properties of this kind of dynamical system, a reference 2 d.o.f. structure has been considered, composed of a rigid bar, with one and constrained to slide, without friction, along a curved profile, whereas the other and is subject to a follower force. In particular, the curved constraint is assumed to be composed of two circular profiles, with different and opposite curvatures, defining two separated subsystems. Due to this jump in the curvature, located at the junction point between the curved profiles, the entire mechanical structure can be modelled by discontinuous equations of motion, the differential equations valid in each subsystem can be combined, leading to the definition of a piecewise-smooth dynamical system. When a follower force acts on the structure, an unexpected and counterintuitive behaviour may occur: although the two subsystems are stable when analysed separately, the composed structure is unstable and exhibits flutter-like exponentially-growing oscillations. This special form of instability, previously known only from a mathematical point of view, has been analysed in depth from an engineering perspective, thus finding a mechanical interpretation based on the concept of non-conservative follower load. Moreover, the goal of this work is also the definition of some stability criteria that may help the design of these mechanical piecewise-smooth systems, since classical theorems cannot be used for the investigation of equilibrium configurations located at the discontinuity. In the literature, this unusual behaviour has been explained, from a mathematical perspective, through the existence of a discontinuous invariant cone in the phase space. For this reason, starting from the mechanical system described above, the existence of invariant cones in 2 d.o.f. mechanical systems is investigated through Poincaré maps. A complete theoretical analysis on piecewise-smooth dynamical systems is presented and special mathematical properties have been discovered, valid for generic 2~d.o.f. piecewise-smooth mechanical systems, which are useful for the characterisation of the stability of the equilibrium configurations. Numerical tools are implemented for the analysis of a 2~d.o.f. piecewise-smooth mechanical system, valid for piecewise-linear cases and extendible to the nonlinear ones. A numerical code has been developed, with the aim of predicting the stability of a piecewise-linear dynamical system a priori, varying the mechanical parameters. Moreover, “design maps” are produced for a given subset of the parameters space, so that a system with a desired stable or unstable behaviour can easily be designed. The aforementioned results can find applications in soft actuation or energy harvesting. In particular, in systems devoted to exploiting the flutter-like instability, the range of design parameters can be extended by using piecewise-smooth instead of smooth structures, since unstable flutter-like behaviour is possible also when each subsystem is actually stable. The second part of this Thesis deals with the numerical analysis of an elastic cloak for transient flexural waves in Kirchhoff-Love plates and the design of special metamaterials for this goal. In the literature, relevant applications of transformation elastodynamics have revealed that flexural waves in thin elastic plates can be diverted and channelled, with the aim of shielding a given region of the ambient space. However, the theoretical transformations which define the elastic properties of this “invisibility cloak” lead to the presence of a strong compressive prestress, which may be unfeasible for real applications. Moreover, this theoretical cloak must present, at the same time, high bending stiffness and a null twisting rigidity. In this Thesis, an orthotropic meta-structural plate is proposed as an approximated elastic cloak and the presence of the prestress has been neglected in order to be closer to a realistic design. With the aim of estimating the performance of this approximated cloak, a Finite Element code is implemented, based on a sub-parametric technique. The tool allows the investigation of the sensitivity of specific stiffness parameters that may be difficult to match in a real cloak design. Moreover, the Finite Element code is extended to investigate a meta-plate interacting with a Winkler foundation, to analyse how the substrate modulus transforms in the cloak region. This second topic of the Thesis may find applications in the realization of approximated invisibility cloaks, which can be employed to reduce the destructive effects of earthquakes on civil structures or to shield mechanical components from unwanted vibrations.

Industrial steel storage racks are pre-engineered lightweight structures commonly used to store goods from supermarkets to big warehouses. These systems are framed structures, usually made of cold-formed steel profiles and characterised by non-standard details. Their performance is quite complex and the prediction of their global response is more difficult than for the traditional steel frames. This difficulty is due to the racks’ main features: the use of cold-formed thin-walled steel sections which are sensitive to different buckling modes, the presence of regular perforation patterns on the uprights, the highly non-linear behaviour of joints, the influence of the structural imperfections and the significant frame sensitivity to second order effects. The behaviour of racks becomes even more complex when seismic or accidental events induce significant horizontal forces acting on the structures. The complexity and variability that characterise racks make it difficult to identify general design solutions. Hence, racks design is traditionally carried out by using the “design by testing” approach, which requires the experimental characterisation of the main structural components, of the joints and the sub-assemblies. The complexity of the racks also affects their numerical modelling, which results in complex analyses that must take into account all the aforementioned features. The work presented in this thesis focuses on the study of a typical steel pallet rack, identified as case study. The research aims to contribute to building up a comprehensive knowledge of the response of both the main rack components and of the whole structure. The main rack components were first individually studied. The behaviour of the uprights, of the base-plate joints and of the beam-to-column joints was experimentally investigated. The experimental data were then taken as reference for the calibration of FE models that enabled exploring each component’s performance. These models were then incorporated into the whole rack model. The response of the uprights was first investigated through stub column tests. The non-negligible interaction between axial force and bending moment of the upright response was then experimentally and numerically analysed to define the M-N domains. In addition, the rules provided by different European standards for the design of isolated members subjected to combined axial load and bending moment were considered and critically compared, identifying the main critical issues of the different design approaches. Although the contribution of joints on the rack global response is of paramount importance, to date, the knowledge is quite limited. In particular, the experimental studies of the behaviour of base-plate joints are still rather modest, especially for the cyclic range. Therefore, an experimental campaign on the rack base-plate joints was carried out: three levels of axial load were considered and the response in both the down-aisle and the cross-aisle direction was investigated under monotonic and cyclic loadings. Similarly, the beam-to-column joint was tested both monotonically and cyclically, taking into account its non-symmetric behaviour. Numerical models for both joint types were developed and validated enabling the characterisation of joints in the monotonic and cyclic range. This in-depth knowledge of the response of individual components facilitated the evaluation of the global rack behaviour. As a final stage of the research, full-scale tests of four-level two-bay racks were performed taking advantage of an innovative full-scale testing set-up and, on the basis of the experimental outcomes, the racks’ global behaviour was numerically investigated. Critical standards issues and needs for future research were further identified.

Many environmental crises are threatening to collapse human societies, but also life on the Earth as we may know. Climate change due to anthropogenic global emissions is one of the main issues, but also soil degradation, and the management of the enormous amount of organic wastes that are harmfully released into the environment by human activities. On the one hand, direct spreading of biowastes onto the land is often limited due to eutrophication or pollution by toxic compounds. On the other hands, these biomasses may contain nutrients, such as phosphorus (listed as a critical raw material) and nitrogen, which could be recovered to sustain the high demand in expensive soil amendments and fertilizers. Thus, finding new solution to close the loop towards circular economy and sustainable processes is crucial, nowadays, to convert the global trends and restore the delicate equilibrium in the water-food-energy nexus, with soil ‘under special surveillance’. In this framework, many researchers are focusing their attention on hydrothermal carbonization (HTC) as a possible candidate, in particular to treat moist biowastes and obtain useful solid (hydrochar) and liquid (HTC liquor) products. Nutrients contained in biowastes are sensitive to HTC process parameters and initial feedstock properties, thus it is crucial to analyze their distribution and (im)mobilization among the HTC products for their reuse in soil. On the other hand, since some organic compounds are generated during the thermochemical process, which may be responsible for toxicity to plants and other organisms, analysis of their possible toxicity towards the biosphere becomes crucial before implementation at a large scale. This thesis collects our efforts to explore new processes and deepen the knowledge about the possibility to produce amendments suitable for soil application from hydrochar. The core is from a process engineering perspective, focusing on the production phase and the characterization of the products, never forgetting any possible limits or the implications on ecotoxicological issues. In the first part of the thesis, ‘How to make hydrochar a soil amendment?’ is the main question. Based on few pioneer studies about composting of hydrochar, we assessed a complete analysis of hydrochar co-compost, produced from the 25-day aerobic stabilization of digestate of organic fraction of municipal solid waste, together with a fraction of its hydrochar, and green waste. Under the umbrella of C2Land project (funded by The European Institute of Innovation & Technology -EIT), we produced this new amendment in specifically designed bioreactors, then we characterized the products from the point of view of physico-chemical properties, nutrients distribution, toxicity to plants and mammalian cells. We are confident that the crucial result of toxicity removal from hydrochar through composting will attract the interest of many stakeholders, since implementing HTC in anaerobic/aerobic plants is almost ready to be applied at a large scale. Moreover, an experimental campaign performed at the University of Leeds further explored the effect of some other post-treatments on hydrochar composition and phytotoxicity, depending on the initial feedstocks (manure, sewage digestate, water hyacinth, and grass). The second part of the thesis was dedicated to nutrients recovery, necessary when some harmful matrixes - such as the municipal sewage sludge digestate - are not allowed to be reused for agricultural purposes, due to law limitations or pollution issues. In this case, nutrients recovery (N, P) could be achieved chemically, via HTC and struvite precipitation, being struvite recognized as a good fertilizer. Firstly, we performed a techno-economic assessment of the implementation at a district level of HTC-centered sewage sludge management. The mass reduction of waste streams may have some important effects on transportation costs, while the recirculation of HTC liquor back to the anaerobic digestors can imply more biomethane production with increased revenues. A mass balance for the potential of N and P recovery through struvite precipitation in the centralized facility was also assessed. Secondly, a near-zero waste treatment process for municipal sewage sludge via HTC was designed according to the available literature and preliminarily analyzed at lab level. The fractionation of the different types of phosphorus was analyzed through the STM-P protocol before and after HTC, confirming the mineralization of organic phosphorus during the process. Citric acid was validated as a good green solvent for phosphorus extraction and high-quality struvite precipitation, even if the process was not still optimized in terms of yields. Future works may identify the best process parameters for final metal recovery from liquid byproducts in order to internally recirculate them back to water line, and to characterize the leached hydrochar as purified renewable fuel or soil amendment. Thus, the proof-of-concept chain would be confirmed and could be applied to the sustainable HTC-centered biorefineries of the future.

Utbredningen av en brand inuti en byggnad kan leda till global eller lokal strukturell kollaps, särskilt i stålramkonstruktioner. Faktum är att stålkonstruktioner är särskilt utsatta för termiska angrepp på grund av ett högt värde av stålkonduktivitet och tvärsnitten med små tjockleken. Som en viktig aspekt av konstruktionen bör brandsäkerhetskrav uppnås antingen enligt föreskrivande regler eller enligt antagande av prestationsbaserad brandteknik. Trots möjligheten att använda enkla metoder som involverar membersanalys kombinerat med nominella brandkurvor, är en mer exakt analys av det termomekaniska beteendet hos en stålkonstruktion ett tilltalande alternativ eftersom det kan leda till mer ekonomiska och effektiva lösningar genom att ta hänsyn till möjliga gynnsamma mekanismer. Denna analys kräver vanligtvis utredning av delar av strukturen eller till och med av hela strukturen. För detta ändamål och för att få en djupare kunskap om strukturelementens beteende vid förhöjd temperatur bör numerisk simulering användas. I denna avhandling utvecklades och användes termomekaniska finita element som är lämpliga för analys av stålkonstruktioner utsätta för brand. Relevanta fallstudier utfördes. Utvecklingen av både ett termomekaniskt skal- och 3D balkelement baserade på en korotationsformulering presenteras. De flesta relevanta strukturfall kan undersökas på ett adekvat sätt genom att antingen använda något av dessa element eller kombinera dem. Korotationsformuleringen är väl lämpad för analyser av strukturer där stora förskjutningar, men små töjningar förekommer, som i fallet med stålkonstruktioner i brand. Elementens huvuddrag beskrivs, liksom deras karakterisering i termomekaniskt sammanhang. I detta avseende övervägdes materialnedbrytningen på grund av temperaturökningen och den termiska expansionen av stål vid härledningen av elementen. Dessutom presenteras en grenväxlingsprocedur för att utföra preliminära instabilitetsanalyser och få viktig inblick i efterknäckningsbeteendet hos stålkonstruktioner som utsätts för brand. Tillämpningen av de utvecklade numeriska verktygen ges i den del av avhandlingen som ägnas åt det publicerade forskningsarbetet. Flera aspekter av knäckningen av stålkonstruktionselement vid förhöjd temperatur diskuteras. I Artikel I tillhandahålls överväganden om påverkan av geometriska imperfektioner på beteendet hos komprimerade stålplattor och kolonner vid förhöjda temperaturer, liksom implikationer och resultat av användningen av grenväxlingsprocedur. I Artikel II valideras det föreslagna 3D-balkelementet genom meningsfulla fallstudier där torsionsdeformationer är signifikanta. De utvecklade balk- och skalelementen används i en undersökning av knäckningsmotstånd hos komprimerade vinkel-, Tee- och korsformade stålprofiler vid förhöjd temperatur som presenteras i Artikel III. En förbättrad knäckningskurva för design presenteras i detta arbete. Som ett exempel på tillämpningen av principerna för brandsäkerhetsteknik presenteras en omfattande analys i Artikel IV. Två relevanta brandscenarier identifieras för den undersökta byggnaden, som modelleras och analyseras i programmet SAFIR. / The ignition and the propagation of a fire inside a building may lead to global or local structural collapse, especially in steel framed structures. Indeed, steel structures are particularly vulnerable to thermal attack because of a high value of steel conductivity and of the small thickness that characterise the cross-sections. As a crucial aspect of design, fire safety requirements should be achieved either following prescriptive rules or adopting performance-based fire engineering. Despite the possibility to employ simple methods that involve member analysis under nominal fire curves, a more accurate analysis of the thermomechanical behaviour of a steel structural system is an appealing alternative, as it may lead to more economical and efficient solutions by taking into account possible favourable mechanisms. This analysis typically requires the investigation of parts of the structure or even of the whole structure. For this purpose, and in order to gain a deeper knowledge about the behaviour of structural members at elevated temperature, numerical simulation should be employed. In this thesis, thermomechanical finite elements, suited for the analyses of steel structures in fire, were developed and exploited in numerical simulation of relevant case studies. The development of a shell and of a 3D beam thermomechanical finite element based on a corotational formulation is presented. Most of the relevant structural cases can be adequately investigated by either using one of these elements or combining them. The corotational formulation is well suited for the analyses of structures in which large displacements, but small strains occur, as in the case of steel structures in fire. The main features of the elements are described, as well as their characterization in the thermomechanical context. In this regard, the material degradation due to the temperature increase and the thermal expansion of steel were considered in the derivation of the elements. In addition, a branch-switching procedure to perform preliminary instability analyses and get important insight into the post-buckling behaviour of steel structures subjected to fire is presented. The application of the developed numerical tools is provided in the part of the thesis devoted to the published research work. Several aspects of the buckling of steel structural elements at elevated temperature are discussed. In paper I, considerations about the influence of geometrical imperfections on the behaviour of compressed steel plates and columns at elevated temperatures are provided, as well as implications and results of the employment of the branch-switching procedure. In Paper II, the proposed 3D beam element is validated for meaningful case studies, in which torsional deformations are significant. The developed beam and shell elements are employed in an investigation of buckling resistance of compressed angular, Tee and cruciform steel profiles at elevated temperature presented in Paper III. An improved buckling curve for design is presented in this work. Furthermore, as an example of the application of Fire Safety Engineering principles, a comprehensive analysis is proposed in Paper IV. Two relevant fire scenarios are identified for the investigated building, which is modelled and analysed in the software SAFIR.

Metamaterials are typically described as materials with ’unusual’ wave propagation properties. Originally developed for electromagnetic waves, these materials have also spread into the field of acoustic wave guiding and cloaking, with the most relevant of these ’unusual’ properties, being the so called band-gap phenomenon. A band-gap signifies a frequency region where elastic waves cannot propagate through the material, which in principle, could be used to protect buildings from earthquakes. Based on this, two relevant concepts have been proposed in the field of seismic engineering, namely: metabarriers, and metamaterial-based foundations. This thesis deals with the development of the Metafoundation, a metamaterial-based foundation system for the seismic protection of fuel storage tanks against excessive base shear and pipeline rupture. Note that storage tanks have proven to be highly sensitive to earthquakes, can trigger sever economic and environmental consequences in case of failure and were therefore chosen as a superstructure for this study. Furthermore, when tanks are protected with traditional base isolation systems, the resulting horizontal displacements, during seismic action, may become excessively large and subsequently damage connected pipelines. A novel system to protect both, tank and pipeline, could significantly augment the overall safety of industrial plants. With the tank as the primary structure of interest in mind, the Metafoundation was conceived as a locally resonant metamaterial with a band gap encompassing the tanks critical eigenfrequency. The initial design comprised a continuous concrete matrix with embedded resonators and rubber inclusions, which was later reinvented to be a column based structure with steel springs for resonator suspension. After investigating the band-gap phenomenon, a parametric study of the system specifications showed that the horizontal stiffness of the overall foundation is crucial to its functionality, while the superstructure turned out to be non-negligible when tuning the resonators. Furthermore, storage tanks are commonly connected to pipeline system, which can be damaged by the interaction between tank and pipeline during seismic events. Due to the complex and nonlinear response of pipeline systems, the coupled tank-pipeline behaviour becomes increasingly difficult to represent through numerical models, which lead to the experimental study of a foundation-tank-pipeline setup. Under the aid of a hybrid simulation, only the pipeline needed to be represented via a physical substructure, while both tank and Metafoundation were modelled as numerical substrucutres and coupled to the pipeline. The results showed that the foundation can effectively reduce the stresses in the tank and, at the same time, limit the displacements imposed on the pipeline. Leading up on this, an optimization algorithm was developed in the frequency domain, under the consideration of superstructure and ground motion spectrum. The advantages of optimizing in the frequency domain were on the one hand the reduction of computational effort, and on the other hand the consideration of the stochastic nature of the earthquake. Based on this, two different performance indices, investigating interstory drifts and energy dissipation, revealed that neither superstructure nor ground motion can be disregarded when designing a metamaterial-based foundation. Moreover, a 4 m tall optimized foundation, designed to remain elastic when verified with a response spectrum analysis at a return period of 2475 years (according to NTC 2018), reduced the tanks base shear on average by 30%. These results indicated that the foundation was feasible and functional in terms of construction practices and dynamic response, yet unpractical from an economic point of view. In order to tackle the issue of reducing the uneconomic system size, a negative stiffness mechanism was invented and implemented into the foundation as a periodic structure. This mechanism, based on a local instability, amplified the metamaterial like properties and thereby enhanced the overall system performance. Note that due to the considered instability, the device exerted a nonlinear force-displacement relationship, which had the interesting effect of reducing the band-gap instead of increasing it. Furthermore, time history analyses demonstrated that with 50% of the maximum admissible negative stiffness, the foundation could be reduced to 1/3 of its original size, while maintaining its performance. Last but not least, a study on wire ropes as resonator suspension was conducted. Their nonlinear behaviour was approximated with the Bouc Wen model, subsequently linearized by means of stochastic techniques and finally optimized with the algorithm developed earlier. The conclusion was that wire ropes could be used as a more realistic suspension mechanism, while maintaining the high damping values required by the optimized foundation layouts. In sum, a metamaterial-based foundation system is developed and studied herein, with the main findings being: (i) a structure of this type is feasible under common construction practices; (ii) the shear stiffness of the system has a fundamental impact on its functionality; (iii) the superstructure cannot be neglected when studying metamaterial-based foundations; (iv) the complete coupled system can be tuned with an optimization algorithm based on calculations in the frequency domain; (v) an experimental study suggests that the system could be advantageous to connected pipelines; (vi) wire ropes may serve as resonator suspension; and (vii) a novel negative stiffness mechanism can effectively improve the system performance.

Over the past decades, public concern about global environmental change has grown, following the progressive increase in both frequency and intensity of extreme events. Even though the problem is global, it has proved to have very different societal and environmental impacts at local level, further widening the gap between disadvantaged and advantaged communities, according to the degree of vulnerability of their social, economic and environmental systems. Among the various anthropogenic activities, the agricultural sector is particularly linked to global environmental change by a two-way relationship: on the one hand, intensive mono-cultures, together with intensive livestock production, compromise the environment and produce huge CO$_2$ emissions (one of the most important factors behind global warming); on the other hand, smallholder farming is one of the most endangered sectors by global environmental change, precisely because it depends heavily on the natural resources of the territory, including favourable weather and climate. Scientific research, supported by international institutions, has been working on this subject for several decades, analysing phenomena at global and local scale and providing medium and long-term forecasts capable of directing economic and political strategies. Such complex investigations become even more complex in contexts lacking reliable environmental data, where their low-quality and low representativeness weaken their reliability, compromising the reliability of the outcomes as well. This thesis seeks to respond to the increasing need of realistically addressing environmental phenomena that threaten rural communities and the environment on which they depend in low-income countries, by investigating two of the main environmental factors affecting tropical farming practices: river-floodplain dynamics and climate change. Despite data-related constraints, the environment of tropical rural areas still provides a unique opportunity to study several near-natural processes, such as the morphodynamics of mostly free-flowing rivers. Especially in foothill regions, unconfined or partially confined conditions of tropical rivers allow evaluating the natural dynamics of erodible river corridors, with erosion and accretion shaping their interactions with the adjacent floodplain and related human activities. At the same time, the complex terrain characterizing the river valleys at the foothills of high mountain chains also offers the opportunity to study interesting local meteorological processes, especially considering the interaction between synoptic-scale dynamics and local convective phenomena. In this context, local bottom-up initiatives and new and tailored-to-context strategies for adaptation to the ongoing environmental change are deepened following a multidisciplinary approach. This PhD research has been framed within an international cooperation project entitled “Sustainable Development and Fight against Climate Change in the Upper Huallaga basin (Peru)”, promoted by Mandacarù ONLUS, and funded by the Autonomous Province of Trento. The project aimed to enhance the resilience of the local farmers of the Upper Huallaga valley (Peru), facing the consequences of climate change and implementing new agricultural initiatives with a special attention to plantain and banana fields. Thanks to the support of the involved partners (Redesign by PROMER s.a.c., the Universidad Agraria Nacional de la Selva de Tingo Maria, in Peru, and the Edmund Mach Foundation of San Michele all’Adige, in Italy), the project provided the opportunity to carry out a consistent set of fieldwork activities over an 8-months period collecting hydro-morphological data, interviewing the local population, and installing two weather stations. The PhD thesis has been structured along two main parts, related to to the assessment of climate change effects on local agricultural practices, and the interplay between river-floodplain dynamics and floodplain agriculture. The part on the assessment of climate change includes two main research elements. First, a novel approach is used to evaluate climate change in data-scarce contexts: non-conventional data sources (population survey) are compared with conventional data sources (few local historical weather stations and global reanalysis data series – ERA5), to better account for the sub-daily time scale (local conventional sources only provide daily data), correlating weather changes perceived by farmers (more thunderstorms and longer drought periods) with climate variations deduced from quantitative data. Second, after having determined the most impacting meteorological variables on crops through the survey, a weather early-warning system has been developed to provide agro-meteorological forecasts to the \textit{bananeros} (banana farmers) of the Upper Huallaga valley. The system, based on the Weather Research and Forecasting (WRF) model, and enhanced with the assimilation of real-time observations from local meteorological stations installed during the project fieldwork, issues an alert when the predicted wind speed exceeds thresholds related to potential damage to the harvest, and spreads the warning via text messages. Such alerting system contains several novel features in relation to the socio-environmental context, allowing to discuss its potential for replication in analogous, vulnerable situations. The part on river-floodplain dynamics also includes two main research elements. First, a remote-sensing analysis is conducted at reach scale in two different reaches of the Huallaga River, quantifying geomorphological river trajectories and land use changes in the adjacent floodplain. The outcomes show that river morphology reacts differently depending on the agricultural systems (extensive or intensive) in the nearby floodplain, revealing a high geomorphological sensitivity of such a near-natural, highly dynamic river reach. Second, riverine agriculture within the erodible river corridor is analysed in association with riverine islands dynamics, at the geomorphic unit scale, evaluating the morphological evolution and agricultural suitability of two cultivated fluvial islands. The three main drivers of agricultural suitability within river erodible corridors, i.e. river disturbance, cultivation windows of opportunity, and soil suitability are quantified, allowing to generalize a process-based conceptual model of riverine islands as complex-adaptive-systems.

The static and dynamic response of lattice materials is investigated to disclose and control the connection between microstructure and effective behavior. The analytical methods developed in the thesis aim at providing a new understanding of material instabilities and strain localizations as well as effective tools for controlling wave propagation in lattice structures. The time-harmonic dynamics of arbitrary beam lattices, deforming flexurally and axially in a plane, is formulated analytically to analyze the influence of the mechanical parameters on the dispersion properties of the spectrum of Floquet-Bloch waves. Several forms of dynamic localizations are shown to occur for in-plane wave propagation of grid-like elastic lattices. It is demonstrated that lattices of rods, despite being `simple' structures, can exhibit a completely different channeled response depending on the characteristics of the forcing source (i.e. frequency and direction) as well as on the slenderness of the elastic links. It is also shown how the lattice parameters can be tuned to attain specific dispersion properties, such as flat bands and sharp Dirac cones. In the research field of material instabilities, a key result proposed in this thesis is the development of both static and dynamic homogenization methods capable of accounting for second-order effects in the macroscopic response of prestressed lattices. These methods, the former based on an incremental strain-energy equivalence and the latter based on the asymptotic analysis of lattice waves, allow the identification of the incremental constitutive operator capturing the macroscopic incremental response of arbitrary lattice configurations. The homogenization framework has allowed the systematic analysis of prestress-induced phenomena on the incremental response of both the lattice structure and its `effective' elastic solid, which in turn has enabled the identification of the complex interplay between microstructure, prestress, loss of ellipticity (shear band formation) and short-wavelength bifurcations. Potential new applications for the control of wave propagation are also shown to be possible by leveraging the inclusion of second-order terms in the incremental dynamics. In particular, the tunability of the prestress state in a square lattice structure has been exploited to obtain dynamic interfaces with designable transmission properties. The interface can be introduced in a material domain by selectively prestressing the desired set of ligaments and the prestress level can be tuned to achieve total reflection, negative refraction, and wave channeling. The obtained results open new possibilities for the realization of engineered materials endowed with a desired constitutive response, as well as to enable the identification of novel dynamic material instabilities.

The need to consider groundwater and surface water as a single resource has fostered the interest of the scientific community on the interactions between surface water and groundwater. The region below and alongside rivers where surface hydrology and subsurface hydrology concur is the hyporheic zone. This is the region where water exchange determines many biogeochemical and ecological processes of great impact on the functioning of rivers. However, the complex processes taking place in the hyporheic zone require a multidisciplinary approach. The combination of innovative point and distributed techniques originally developed in separated disciplines is of great advantage for the indirect identification of water exchange in the hyporheic zone. Distributed techniques using temperature as a tracer such as fiber-optic distributed temperature sensing can identify the different components of groundwater-surface water interactions based on their spatial and temporal thermal patterns at the sediment-water interface. In particular, groundwater, interflow discharge and local hyporheic exchange flows can be differentiated based on the distinct size, duration and sign of the temperature anomalies. The scale range and resolution of fiber-optic distributed temperature sensing are well complemented by geophysics providing subsurface structures with a similar resolution and scale. Thus, the use of fiber-optic distributed temperature sensing to trace flux patterns supported by the exploration of subsurface structures with geophysics enables spatial and temporal investigation of groundwater-surface water interactions with an unprecedented level of accuracy and resolution. In contrast to the aforementioned methods that can be used for pattern identification at the interface, other methods such as point techniques are required to quantify hyporheic exchange fluxes. In the present PhD thesis, point methods based on hydraulic gradients and thermal profiles are used to quantify hyporheic exchange flows. However, both methods are one-dimensional methods and assume that only vertical flow occurs while the reality is much more complex. The study evaluates the accuracy of the available methods and the factors that impact their reliability. The applied methods allow not only to quantify hyporheic exchange flows but they are also the basis for an interpretation of the sediment layering in the hyporheic zone. For upscaling of the previous results three-dimensional modelling of flow and heat transport in the hyporheic zone combines pattern identification and quantification of fluxes into a single framework. Modelling can evaluate the influence of factors governing groundwater-surface water interactions as well as assess the impact of multiple aspects of model design and calibration of high impact on the reliability of the simulations. But more importantly, this modelling approach enables accurate estimation of water exchange at any location of the domain with unparalleled resolution. Despite the challenges in 3D modelling of the hyporheic zone and in the integration of point and distributed data in models, the benefits should encourage the hyporheic community to adopt an integrative approach comprising from the measurement to the upscaling of hyporheic processes.

The present work regards the development of a methodology for the study of atmospheric particulate matter (PM) which is alternative to instrumental measurements. The methodology developed exploits the surfaces already present in the field as samplers of PM. In particular, conifer needles and building facades are employed to investigate different temporal ranges: conifer needles potentially retain particles circulating in the atmosphere from the recent past up to now, while building facades could retain particles from an older period up to know. The field of application of the approach developed are the situations in which a wide territory must be monitored, eventually including remote locations, or information on past pollution scenario must be reconstructed in the absence of monitoring stations. For instance, the evaluation of the improved efficiency of off-gas abatement systems of industrial plants is a typical case of application. These pollution sources affect large areas and might have been active before regulation on air quality required constant monitoring of their emissions. Typically in such a case the methodology could assist in evaluating how large was in the past and it is nowadays the area of impact of the plant. In general, such an approach could be valuable whenever relying on instrumental measurements is cost and time consuming in terms of installing a large network of monitoring stations to study the dispersion of pollutants from a single or few sources. To have a detailed description of the spatial distribution of pollutant particles, they are studied individually with subsequent higher magnification. Where no traces of a source are detected by scanning electron microscopy coupled with energy dispersive x-ray spectroscopy (SEM-EDXS), the samples are analyzed with the higher resolution of transmission electron microscopy coupled with energy dispersive x-ray spectroscopy (TEM-EDXS) and selected area electron diffraction (SAED) in order to make sure that no smaller particles, able to travel farther from their source, are present at a certain site. All data provided by electron microscopy analysis of particles collected by conifer needles are placed in the context of elemental concentrations measured by inductively coupled plasma atomic emission spectroscopy (ICP-AES), which is a bulk analytical technique. The same is not possible for the data on single particles present on building facades given the inorganic matrix of the substrate, especially in the case of metal oxide paints, which does not allow the bulk measurement. Both the preparation of the samples for bulk analytical techniques and single particle analysis by electron microscopy were optimized. For method development and evaluation, the analytical protocol was applied to estimate spatial and temporal trends of accumulation of inorganic pollutants that can be related with changes in the emissions of atmospheric pollutants by an electric arc furnace (EAF) steelmaking plant located in a test site. The benefits of combining the single particle and bulk analytical techniques emerged especially for the discrimination of the emissions from different sources.

Hydrothermal carbonization (in acronym, HTC) is a thermochemical conversion process through which it is possible to directly transform wet organic substrates into a carbonaceous material, referred as hydrochar. Hydrochar has chemical and physical characteristics that make it similar to fossil peats and lignite. Depending on the process conditions, mostly temperature and residence time, this material can be enriched in its carbon content, modifying its structure and providing it interesting characteristics that make it possible to be used for several applications, such as for energy production, as a soil conditioner and improver, for carbon dioxide sorption and sequestration, and some others reported in literature. HTC is a different process, if compared to other common thermochemical processes, such as pyrolysis, torrefaction, gasification, etc., because it works in wet conditions (humidity content higher than 60%). As a matter of fact, biomass is transformed into hydrochar because of the properties of hot pressurized water, that acts both as a reactant and as a catalyst. The HTC process has been studied from many years, although at present not all the chemical reactions that occur during the process are completely known. Moreover, the application of this quite new process to different substrates can bring to different results. Even though HTC can be applied to any kind of organic material (of both animal and vegetable derivation), the possible uses of hydrochar can strongly be influenced by the characteristics of the feedstock. This, for example, can be due to legislative constraints. In Chapter 1, an overview of the existing literature is presented. To get insights on this process, a small bench scale batch reactor has been designed and built at the Department of Civil, Environmental and Mechanical engineering of the University of Trento, Italy. This reactor has been tested, prior to be used with real substrates. In Chapter 2 the reactor and the preliminary tests done are described. In this work, the HTC process applied to three different substrates have been studied: grape marc, the EWC 19.05.03 residue and the EWC 19.12.12 residue. In Chapter 3 the three raw substrates are described. Grape marc is produced by the winery industries or by distilleries. This feedstock is composed by woody seeds and holocellulosic skins and it presents an average humidity content of about 60%. At present, it is used for the production of animal food or it is landfilled. In this case, the application of HTC can be an interesting alternative to these end uses because, through this process, grape marc can be recovered, for example, for energy production. The hydrochar produced from this feedstock could be even used as a soil conditioner. In Chapter 4 several analyses on the hydrochar, on the process water and on the gaseous phase obtained during the carbonization tests are presented. The EWC 19.05.03 residue is a by-product of the composting treatment applied to the organic fraction of municipal solid waste (MSW). In collaboration with Contarina S.p.A., a company that collects and treats MSW in the province of Treviso, in the North-East of Italy, this by-product was carbonized and tested both as a soil conditioner and for energy production. Results of the analyses on the solid, liquid and gaseous phases produced by the HTC process are reported in Chapter 5. The EWC 19.12.12 residue is a by-product of the refuse derived fuel (RDF) production, from the residual fraction of the MSW. This substrate was provided by Contarina S.p.A. and preliminary tests on the exploitability of the hydrochar for energy production are reported in Chapter 6, together with analyses on both the liquid and gaseous phases. A rigorous energy balance has been proposed in Chapter 8, based on the experimental data obtained for grape seeds. In this chapter, all the hypotheses and the assumptions taken to evaluate the enthalpy of the HTC reaction at different process conditions (namely, three different temperatures and three residence times) are described. In Chapter 8 a kinetic model is proposed, based on a two-step reaction mechanism. The activation energy and pre-exponential factor of the various degradation reactions were determined by means of least square optimization versus the experimental data of grape marc. A thermo fluid model is even proposed in this chapter. The model integrates mass, momentum and heat equations within the reactor domain by means of the finite volumes method (f.v.m.) approach. Convective and radiative exchange between the reactor and the fluid within the reactor have been implemented in the f.v.m. model. Under two strong assumptions (mono-component and mono-phase fluid, which fulfils the reactor), it was possible to estimate the behaviour of an equivalent fluid (eq_fluid), in terms of thermal properties of the fluid (thermal capacity, thermal conductivity and thermal diffusivity). Moreover, a simplified dynamic analytic model is also presented – based on lumped capacitance method – in order to simulate the thermal behaviour of the system, using the actual temperature profile imposed by the reactor external heater. A resistance-capacitance network was used to describe the system. Finally, the Henry’s law has been applied to assess the amount of gas really produced during the HTC process. In Chapter 9, the main conclusions of this work are reported.