861 research outputs found
Livestock vulnerability to flooding
No full textThis paper investigates the vulnerability of livestock to flooding. A conceptual model is developed to evaluate the toppling and sliding instability of farm animals exposed to floodwaters. Numerical simulations are also employed to assess the drag, lift and contraction coefficients for some animals among the most commonly farmed. Using the results of the above model together with the few information available in literature, the vulnerability functions for these farm animals exposed to floodwaters are proposed. This is expected to improve flood damage assessment in the agricultural sector, while also enhancing flood risk evaluation and communication to farmers
On the non singular higher order terms in bi-dimensional and three-dimensional engineering applications
No full textIn stress analysis of cracked plates, alongside the stress intensity factor which quantifies the singular stress component perpendicular to the crack plane, the role played in crack growth by the constant term parallel to the crack plane, called the T-stress, has been widely investigated by many researchers. There are, however, cases of practical interest where the influence on the stress field of the higher order terms in the series expansion for the crack tip stress field, is not negligible. The main aim of the present investigation is to present and apply a set of equations able to describe more accurately the stress components for those cases where the mode I and mode II stress intensity factors used in combination with the T-stress are unable to characterise with sufficient precision the complete stress field ahead the crack tip. The starting point is represented by the Williams' solution (Williams, 1957) where stresses as expressed in terms of a power series. An example is investigated of a thin-thickness welded lap joint characterized by various joint width to thickness ratios, in the range of d/t ranging from 0.5 to 5. The present paper indicates that the local stresses as well as the strain energy averaged over a control volume which embraces the slip tip, can be evaluated with satisfactory precision only by taking into account a further four terms besides KI, KII and T-stress. Dealing with three-dimensional models the influence of higher order terms tied to mode II loading on the out-ofplane singular mode is investigated here dealing with cracked plates. An accurate analysis of mode II higher order terms and their effects on mode O is carried out by means of a large bulk of 3D numerical models.Filippo Berto, Paolo Lazzarin and Andrei Kotouso
A notch stress intensity approach applied to fatigue life predictions of welded joints with different local toe geometry
No full textIn the Notch Stress Intensity Factor (N-SIF) approach the weld toe region is modelled as a sharp V-shaped corner and local stress distributions in planar problems can be expressed in closed form on the basis of the relevant mode I and mode II N-SIFs. Initially thought of as parameters suitable for quantifying only the crack initiation life, N-SIFs were shown able to predict also the total fatigue life, at least when a large part of the life is spent as in the propagation of small cracks in the highly stressed region close to the notch tip. While the assumption of a welded toe radius equal to zero seems to be reasonable in many cases of practical interest, it is well known that some welding procedures are able to assure the presence of a mean value of the weld toe radius substantially different from zero. Under such conditions any N-SIF-based prediction is expected to underestimate the fatigue life. In order to investigate the degree of conservatism, a total of 128 fillet welded specimens are re-analysed in the present work by using an energy-based N-SIF approach. The local weld toe geometry, characterised by its angle and radius, has been measured with accuracy for the actual test series. The aim of the work is to determine if the N-SIF-based model is capable of taking into account the large variability of the toe angle, and to quantify the inaccuracy in the predictions due to the simplification of setting the toe radius equal to zero
Solar cooling plants: some characteristic system arrangements
No full textSome schemes of operating plants are reported analysing the role of the storage and the sizing of solar section and absorption chiller together with recorded results. After considering some schemes described in the literature, a hot and cold storage tank system design by the author is presented. First of all lay out and control logic are detailed, then experimental data recorded on
the plant are illustrated concerning the seasonal performance both of the solar section and of the
absorption chiller
Singolarita fuori-piano indotte da effetti tridimensionali in prevalente modo 2
No full textIn the application of the Strain Energy Density (SED) approach for fatigue strength assessments of welded joints a well-defined control volume is considered. This volume surrounds the weld root or weld toe, both modelled like sharp (zero radius) V-notches with different opening angles. The volume becomes a circular sector under plane strain conditions, with the radius being about 0.3 mm for welded joints made of structural steel. The mean value of the SED mainly depends on the singular stress fields when the main plate thickness is large enough, whereas the influence of the T-stress component cannot be neglected in the case of thin-walled welded joints. Both contributions are directly accounted for by using finite element models, also when the relevant meshes are quite coarse. This fact makes the application of the SED approach easier than any stress-based approach in the case of complex structures. Due to three-dimensional effects, a non conventional out-of-plane singular mode can be present, in addition to mode I and mode II stress singularities according to Williams’ solution. This out-of-plane mode, which has recently been presented by Kotousov, is discussed here with reference to welded (seam) lap joints under tensileshear loads.P. Lazzarin, F. Berto, A. Kotousov and S. Hardin
Hybrid photovoltaic-thermal heat pump systems: energy and economic performance evaluations in different climates
No full textDue to European Directives (2010/31/UE on buildings energy performance, 2009/28/CE on the use of renewable energy, 2012/27/UE on the energy efficiency) the electric and thermal energy needs of new and retrofitted buildings are faced by increasing percentages of renewable energy. Solar energy and heat pumps are the most promising technologies mainly in residential buildings as they have reached great maturity. Anyway, in most cases solar energy utilizations systems are thermal (which convert solar energy to thermal energy) and photovoltaic (which convert solar energy to electricity) used as separated collectors. Commercial photovoltaic modules have nowadays an efficiency around 15 % - 18 %. It means that the most relevant part of solar radiation is lost. PhotoVoltaic / Thermal cogeneration (PV/T) aims to utilize the same area both for producing electricity and heat. As solar cells are sensitive to temperature (their efficiency lowers when temperature increases), heat is beneficially collected even if it cannot be available at too high temperatures. For civil applications the electrical and thermal energy can be suitably used respectively to partially cover the needs for electricity and domestic hot water/space heating. An electric compression heat pump can be coupled to the PV/T panels to contribute to the space heating demand partially using the self-produced electricity. So, some Italian climates and economic incentives scenarios are taken into account with Trnsys simulations to evaluate the energy and economic viability of the proposed PV/T-heat pump hybrid technology
Photovoltaic/Thermal (PV/T)/ground dual source heat pump: Optimum energy and economic sizing based on performance analysis
No full textDual or multisource heat pumps were conceived to obviate to the defects of a single source, such as outside air, ground, water or solar radiation. Concerning the latter, the use of Photovoltaic/Thermal (PV/T or PVT) modules allows not only to partially recover the otherwise lost heat, but also to cool the PV and increase its electrical efficiency. Many studies simulated the possible behavior of combination of PVT with other sources, but generally unglazed PVT collectors were used. Only few results based on coupling glazed PVT to ground source heat pumps are available in literature. The use of glazed PVT increases thermal efficiency of the collector, and the coupling of ground allows to keep the electrical efficiency at high values without the risk of cells damage due to overheating. A refurbished building located in Northern Italy will be equipped by a PVT dual source heat pump, operating with the ground as source/sink, whereas the PVT drives the heat pump compressor and acts as a dual source. When the heat pump does not need heat or operates for summer air conditioning, the ground is the heat sink both for the heat pump and for the PVT cooling. A dynamic simulation allowed to size the plant and set up a suitable control logic of the main equipment. Very high efficiency and low primary energy consumption are demonstrated for the whole plant, thanks also to the high energy independency from the grid
Fatigue-relevant stress field parameters of welded lap joints: pointed slit tip compared with keyhole notch
No full textThe notch stress intensity factor (NSIF) based analytical frame is applied to the slit tips (or weld roots) of welded joints with inclusion of the T-stress component. This T-stress can be determined from FE models evaluating the ligament stresses close to the pointed slit tip. An alternative analytical frame is presented for the corresponding keyhole notches based on analytical solutions from the literature, which are applied to the ligament stresses.
In the slit tip models, the mean local strain energy density (SED) with inclusion of the T-stress effect is determined analytically and numerically in comparison, using two different fatigue-relevant control radii, R(0) = 0.28 mm and R(0) = 0.15 mm, the former value well proven for thick-sheet welded joints made of structural steel. The latter smaller value is tentatively proposed for thin-sheet welded joints, in the direction suggested in the recent literature where a reduction of the microstructural support length for laser beam welds and resistance spot welds is recommended. The FEM-based and analytical stress concentration factors (SCF) for the lap joint keyhole model and also the SED values for the corresponding pointed slit tips are found to be in good agreement. The J-integral consisting of the first and second component (the latter containing the T-stress) is compared with the corresponding SED values
An efficient physics-based modeling strategy for pluvial floods in urban areas with a subgrid scheme for the stormwater drainage network
No full textThis study presents an efficient physics-based modeling strategy for simulating urban pluvial floods, which uses a subgrid approach to account for the contribution of (part of) underground drainage pipes. Coupled with a two-dimensional (2D) hydrodynamic model solving the porous version of the shallow water equations for the free-surface flow, the subgrid formulation allows running rain-on-grid (RoG) simulations while avoiding the time-consuming inclusion of the many small-scale components forming the stormwater network, such as one-dimensional (1D) pipes and storm drains. The proposed model accounts for the anisotropic additional conveyance provided by the stormwater drainage networks, assuming that the water level represents both the local free-surface elevation and the piezometric head for flow in pipes. Model parameters such as pipe direction, diameter, roughness, and spacing, can be derived from aerial images and limited surveys, thus reducing the data requirement and allowing for an easier model implementation than with classical dual-drainage models. Different applicative tests demonstrate that the use of the subgrid model ensures reasonable accuracy with low modelling effort and computational cost. The proposed approach offers an efficient and practical solution for pluvial flood assessment, particularly in data-limited and/or large-scale urban areas, providing support for flood management and mitigation strategies
Photovoltaic/Thermal (PV/T) to drive a dual source heat pump (ground and PV cooling): Performance analysis in a real application
No full textA large fraction (more than 80%) of the solar radiation impinging a PV panel is lost. A Photovoltaic/Thermal (PV/T or PVT) module allows not only to partially recover the otherwise lost heat, but also to cool the PV and increase its electrical efficiency. A retrofitted building located in Northern Italy will be equipped by a PVT dual source heat pump, operating with the ground as source/sink, whereas the PVT drives the heat pump compressor and acts as a dual source. When the heat pump does not need heat or operates for summer air conditioning the ground is the heat sink both for the heat pump and for the PVT cooling. A dynamic simulation allowed to size the plant, revealing high values of heat pump coefficient of performance for the favorable thermal levels of the heat source, and better thermal levels of the ground source that receives heat from the PVT panels when it is not required by the heat pump.Very high efficiency and low primary energy consumption are demonstrated for the whole plant, thanks the high energy independency from the grid
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