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Electrification is an increasing trend in developing the next generation of large-scale off-road vehicles. Benefits of electrification are high operating efficiency, low emissions, the possibility of using energy coming from renewable sources, and improved controllability. Despite the growth of these technologies there is no clear direction for how the system should be electrified. This research focuses on defining a standardized methodology to design different electro-hydraulic units that can function as a prime mover for a wide variety of applications. The electro-hydraulic units are designed using a genetic algorithm-based optimization that couples one model dedicated to the hydraulic machine and one model dedicated to the electric machine and determines the optimal parameters of the electro-hydraulic unit given a specific application. After having designed an external gear-type, internal gear-type, and an axial piston-type hydraulic machine, several prototypes are produced, and tested on a reference machine.

Gerotor pumps are a common pump choice used in the automotive, agricultural, and construction fields for their low cost and durability. Recently, demanding applications have called for significant design improvements in gear geometry. To address these design challenges, multi-objective optimization has been applied to gear geometry. The goal of this work is to introduce minimizing of lateral-gap leakage to the multi-objective optimization. An objective function for evaluating lateral-gap leakage based on 1D, pressure driven flow is proposed. This simplified approach is compared to CFD simulation solving of Reynolds equation with two pressure boundaries. Comparison of the simplified relation and the CFD simulation are used to validate the objective function for use in optimization.

Selecting the proper material and surface treatment methods for elements is one of the essential problems when designing water hydraulic components due to the corrosiveness and poor lubricity of water. Experimental investigation was performed to study the tribological properties of ion-nitrided 2Cr13, a kind of martensitic stainless steel, sliding on carbon fiber–reinforced polyetheretherketone (CFRPEEK). The influence of factors such as sliding velocity, load, and lubrication condition were studied through experiments mainly under tap water lubrication. It was found that the friction coefficients are influenced by both the pressure and the sliding velocity. In contrast, the friction coefficients between quenched 2Cr13 and CFRPEEK are much higher. Compared to water lubrication, both the wear rate and friction coefficients increase in the case of dry friction. Wear mainly occurred on the CFRPEEK. By examining the worn surfaces of the specimens, it was found that adhesion was the main form of wear of the PE...

Gerotor pumps are a kind of fluid power machines widely used in the automotive field, especially for fuel injection as well as lubrication. To improve the performance of these units, virtual prototyping is necessary to decrease time and cost related to trial and error. Within this research a simulation model for Gerotor units has been developed with the aim of predicting accurately the performance of a generic unit. The model can accurately predict the system behavior regarding mechanical and volumetric losses by considering real machining tolerances and their interactions. Ultimately, this model should help to design new generations of Gerotor units and to improve existing ones by improving their efficiency. To justify and refine the model, a test-rig which can enable measurements of rotor micro-motions of the gears of Gerotors is needed. This paper proposes an innovative approach for measuring micro-motions together with the design of a test-rig specifically conceived to allow such measurements. Reference Gerotor units will be put in a specially designed pump housing. The measurements will be performed using capacitive sensors capable of measuring the lubricant film thickness in the lubricated gaps. In this way, the micro-motions of the reference Gerotor unit can be detected. A data acquisition system will be created to collect the experimental data. Results will be analyzed to understand the correctness of the prediction given by the model. With these results, the lumped parameter model is expected to be validated or refined allowing more precise predictions in the future.

External gear pump is an important category of positive displacement fluid machines used to perform the mechanical–hydraulic energy conversions in many fluid power applications. An efficient numerical simulation program is needed to simulate the system in order to provide a direction for design purpose. The model consists of a lumped parameter fluid dynamic model and a model that simulates the radial micro-motions of the gear’s axes of rotation. The system consists of a set of ordinary differential equations related to the conservation on mass of the internal control volumes of the pump, which are given by the tooth space volumes of the gears. Flow connections between the control volumes are introduced, as laminar or turbulent orifices to model the displacing action and the internal leakages of the unit. In order to optimize the numerical solution, the whole system is described in C++ and the ODEs are solved using linear multistep methods. The results of the simulation successfully match the experimental results as well as the predictions of a previously developed simulation tool. The results detail several features of the model, such as its capability of predicting the instantaneous tooth space volume pressure, the micro-motion of the gears and the outlet flow oscillations. The simulation model can be utilized in future research on external gear pump, as well as for design purposes. In particular, with its simulation swiftness the model is particularly suitable for virtual prototyping within numerical optimization procedures.

In applications such as in agriculture, construction, and aerospace applications, high pressure hydraulics is the preferred technology to transmit mechanical power. As a consequence, the energy efficiency of the hydraulic system used to perform the mechanical actuations is of primary concern to reduce the energy consumptions in the abovementioned applications. In an hydraulic system, the primary component determining the energy efficiency is the hydraulic pump. This work focuses on the study of a particular pump design, also referred as external gear pump, particularly used in applications in which the cost of the hydraulic system has to be minimized. The large use of this type of pump calls for research towards more efficient designs solutions. In particular, new designs for external gear pumps have been developed by Dr. Andrea Vacca’s research group at Purdue using a detailed pump model. This study is intended to gain detailed understanding about the fluid dynamic part of this model by performing detailed comparisons between the simulation results obtained by a different simulation tool, based on a computational fluid dynamics (CFD) approach to simulate the entire pump operation (including the primary displacing action and the internal leakages). After the comparison is made for a commercial geometry, the study will focus on a innovative prototype design, developed to reduce the noise generation while increasing energy efficiency. The results from the CFD approach were validated against the experimentally-backed lumped parameter approach result. The differences between the modeling methods produced differences in the results which were analyzed for both the unit efficiency and flow ripple production.

External spur gear pumps are exceedingly useful components in common hydraulic systems. The main issue with external gear pumps is that all current models are limited to only fixed-displacement. This means that for every revolution of the gears inside the pump, a set amount of fluid will always be displaced. Consequently, external gear pumps are limited in their use because they can only operate at full throttle causing inefficiencies when reduced displacement is needed. The successful procurement of a variable displacement gear pump will allow a more efficient use of hydraulic systems, such as in the displacement controlled systems used in some heavy construction equipment. In this research approach, the displacement is varied by changing the timing of the gears inside the pump. More specifically, changing the timing of the gears’ connections with the inlet and outlet grooves alters the available volume in the gears’ spaces, subsequently varying the displacement. With this in mind, additional research was conducted to develop an actuation system for the aforementioned process. This includes the design of new gears, bearing blocks, and additional hydraulics for use in a modified existing commercial pump. Simulations have shown the implementation of the design allowed for a 67% reduction in displacement, and thus successful introduction of variable displacement into an external gear pump. Additional research is needed to determine the optimal designs for the actuation system and variable displacement concept used in the gear pump.

Most of the control methodology of Mobile hydraulic crane is not as energy efficient as people think or want, and the desire to innovate novel, energy-efficient control strategy is the target of most hydraulic experts. To develop or test the control method under real road and off-road conditions, a platform that could simulate the movement and vibration of the crane truck is desired. To design and build the multi-operation platform, a design process includes brain storming, design selection, FEA (Fundamental Element Analysis), mechanical sizing, hydraulic sizing and Bill of Material is required and preferred. After going through all the steps mentioned above, the design that use simple cylinders in the vertical position has been selected, and the proper dimension has been settled down. Most of the part are directly sponsored by Parker, CO, the sponsor of MAHA lab. The design method and process is duplicable and could be used to design other similar or relative products.

The study of the interaction of mud-flows with obstacles is important to define inundation zones in urban areas and to design the possible structural countermeasures. The paper numerically investigates the impact of a mud-flow on rigid obstacles to evaluate the force acting on them using two different depth-integrated theoretical models, Single-Phase Model (SPM) and Two-Phase Model (TPM), to compare their performance and limits. In the first one the water-sediment mixture is represented as a homogeneous continuum described by a shear-thinning power-law rheology. Alternatively, the two-phase model proposed by Di Cristo et al in 2016 is used, which separately accounts for the liquid and solid phases. The considered test cases are represented by a 1D landslide flowing on a steep slope impacting on a rigid wall and a 2D mud dam-break flowing on a horizontal bottom in presence of single and multiple rigid obstacles. In the 1D test case, characterized by a very steep slope, the Two-Phase Model predicts the separation between the two phases with a significant longitudinal variation of the solid concentration. In this case the results indicate appreciable differences between the two models in the estimation of both the wave celerity and the magnitude of the impact, with an overestimation of the peak force when using the Single-Phase Model. In the 2D test-cases, where the liquid and solid phases remain mixed, even if the flow fields predicted by the two models present some differences, the essential features of the interaction with the obstacles, along with the maximum impact force, are comparable.

Mud flows represent one of the major causes of natural hazards in mountain regions. Similarly to debris flows, they consist of a hyper-concentrated mixture of water and sediments flowing down a slope and may cause serious damages to people and structures. The present paper investigates the force produced by a dam-break wave of mud impacting against a rigid wall. A power-law shear-thinning model is used to describe the rheology of the hyper-concentrated mixture. A one-dimensional shallow water model is adopted and a second-order Finite Volume scheme is employed to numerically solve the governing equations. The results indicate that depending on the fluid rheological parameters and on the bottom slope, there exists a minimum value of the wall distance above which the peak force does not exceed the asymptotic value of the hydrostatic final condition. For two different values of the channel slope, the dimensionless value of this lower bound is individuated for several values of the power-law exponent and of a dimensionless Basal Drag coefficient. An estimation of the maximum peak force for wall distance smaller than the minimum value is also provided.

A two–sided model is proposed to investigate the stability problem of the steady uniform flow of a power–law fluid layer down an inclined porous layer. The governing equations for the clear fluid flow are coupled with the ones for the seepage in the porous layer, for which the generalized Darcy’s law is employed. A linear stability analysis of both two–dimensional and depth–integrated formulations is carried out in order to individuate the neutral stability conditions. The influence of the dimensionless governing parameters on the stability properties is deeply discussed. The nonlinear effects on the stability of the flow are finally investigated through the numerical solution of the depth–integrated model.

This paper investigates the role of a different composition of board of directors on firm’s performance. The study is based on the analysis of 149 Italian listed firms over the 2011-2017 period. Our regression results show that size board, gender diversity, independent directors and CEO gender have a significant effect on firm’s performance. This analysis uses as measure of firm’s performance two accounting-based measures ROE and ROA and one market-based measure TobinQ. The study shows that gender diversity, independent directors and CEO gender are associated positively respectively with ROE, ROA and TobinQ, while size board is negatively associated with ROE and TobinQ.

The flow between two parallel plates driven by a pulsatile pressure gradient was studied analytically with a second-order velocity expansion. The resulting velocity distribution was compared with a numerical solution of the momentum equation to validate the analytical solution, with excellent agreement between the two approaches. From the velocity distribution, the analytical computation of the discharge, wall shear stress, discharge, and dispersion enhancements were also computed. The influence on the solution of the dimensionless governing parameters and of the value of the rheological index was discussed.

Bank failure is an important phenomenon in geomorphic processes. In the presence of river banks or steep bedforms, collapse mechanisms induced by the water-level rise deeply affect the bed evolution along with the sediment-transport processes. In this paper an algorithm capable of simulating such mechanisms in a two-dimensional two-phase morphodynamic model is presented. A mixed Cell-Centered and Node-Centered Finite-Volume discretization, which makes use of an unstructured triangular mesh and allows the slope in each cell to be univocally defined, is proposed. The geo-failure operator guarantees that when in the cell the bed slope exceeds a critical angle, the corresponding bed material and pore water will become part of the bed transport and will then follow the dynamic equations of the two-phase flow. The algorithm effectiveness is shown by the numerical reproduction of some experimental tests from the literature.

The adoption of the Diffusive Wave (DW) instead of the Full Dynamic (FD) model in the analysis of mud flood routing within the shallow-water framework may provide a significant reduction of the computational effort, and the knowledge of the conditions in which this approximation may be employed is therefore important. In this paper, the applicability of the DW approximation of a depth-integrated Herschel–Bulkley model is investigated through linear analysis. Assuming as the initial condition a steady hypocritical decelerated flow, induced by downstream backwater, the propagation characteristics of a small perturbation predicted by the DW and FD models are compared. The results show that the spatial variation on the initial profile may preclude the application of DW model with a prescribed accuracy. Whenever the method is applicable, the rising time of the mud flood must satisfy additional constraints, whose dependence on the flow depth, along with the Froude number and the rheological parameters, is deeply analyzed and discussed.

A depth-averaged model with a power-law rheology, usually adopted for debris flow of fine sediment-water mixtures, is analytically studied, considering the complete (Full Dynamic Model) and the simplified momentum equations, known as Kinematic, Diffusion, and Quasi-steady Models. Applying the Laplace transform to the linearized equations, the analytical first-order expressions of the upstream and downstream spatio-temporal channel response functions are derived for the full and the approximate models. Both shear-thinning and shear-thickening fluids have been considered in hypocritical and linearly stable conditions, to investigate the influence of the rheology on the wave propagation. The effect of the upstream and downstream boundary conditions is considered assuming a finite channel length. The analytic description of the various linearized approximations allows a multi-faceted comparison of the wave propagation. About the basic wave characteristics, in the entire investigated range of Froude numbers and for all the considered rheologies, the Kinematic and Diffusive models underestimate the primary wave celerity and the Quasi-steady model underestimates the wave round-trip time. However, the examination of the response function reveals that the approximate models may provide relatively accurate reproduction of the full dynamic response. Moreover, the analytical solutions in the Laplace variables permit a systematic analysis of some relevant shape factors of the response functions. Independently on the models and the rheology, the damping of the downstream response function is several orders of magnitude larger than that of the upstream one. The results of the shape factor analysis of the upstream response function indicate that the diffusive approximation is the most accurate one. The performed comparison among the wave characteristics of the different approximations provides indications on the applicability of the simplified models for predicting debris or mud flows.

Climate change is exposing more and more frequently flood prone areas to potential casualties and damages. The capability of the flow to carry relevant quantities of sediments interacts with the presence of obstacles in flood-inundated areas and contributes to the increase the related hazard, constituting a relevant concern in the framework of risk analysis. Unfortunately, existing literature on this topic is rather scarce, especially for the features of sediment transport and the forces acting on rigid obstacles. In the paper, a recent two-phase shallow-water morphodynamical model, particularly suited to the analysis of fast geomorphic transients, is applied to the numerical simulation of the propagation of a dam-break wave over an erodible floodplain in presence of a rigid obstacle. The geometry of the test-case is inspired to a recent fixed-bed study reported in the literature, for which extensive experimental and numerical data concerning the flow field and the dynamic loading against the obstacle are available. Results of the numerical simulations contribute to highlight the effect of the obstacle on the changes in the bottom topography, along with the subsequent change on the loading condition on it. * Corresponding author Engineering EPiC SeriesinEngineering Volume3,2018,Pages564571 HIC 2018.13thInternational Conference onHydroinformatics G.

The paper explores the possibility of predicting the occurrence of antidunes in gradually-varied flows through non-equilibrium morphological models natively derived, under the long-wave approximation, for fast geomorphic transients. Starting from a recent two-phase gradually-varied flow model, an improved version, which partially accounts for the bottom curvature effects, is proposed and analyzed. The normal mode analysis carried out on the linearized gradually-varied flow model shows the existence of unstable conditions at moderate Froude numbers characterized by bed perturbations migrating in the upstream direction. However, a proper wavelength selection may be obtained only when the bottom curvature is accounted for. Direct numerical simulations in linear regime of the improved model indicate the existence of unstable dominant wavelengths, which comply with experimental evidences. Full non-linear simulations confirm the ability of the improved two-phase model in predicting the antidunes formation.

Simplified wave models - such as kinematic, diffusion and quasi-steady - are widely employed as a convenient replacement of the full dynamic one in the analysis of unsteady open-channel flows, and especially for flood routing. While their use may guarantee a significant reduction of the computational effort, it is mandatory to define the conditions in which they may be confidently applied. The present paper investigates the applicability conditions of the kinematic, diffusion and quasisteady dynamic shallow wave models for mud flows of power-law fluids. The power-law model describes in an adequate and convenient way fluids that at low shear rates fluids do not posses yield stress, such as clay or kaolin suspensions, which are frequently encountered in Chinese rivers. In the framework of a linear analysis, the propagation characteristics of a periodic perturbation of an initial steady uniform flow predicted by the simplified models are compared with those of the full dynamic one. Based on this comparison, applicability criteria for the different wave approximations for mud flood of power-law fluids are derived. The presented results provide guidelines for selecting the appropriate approximation for a given flow problem, and therefore they may represent a useful tool for engineering predictions.

"The occurrence of roll-waves in mud-flows is commonly investi-gated starting from the formulation of the marginal stability threshold of a linearized one-dimensional viscoplastic (shear-thinning) flow model. Since for this non-newtonian rheological model such a threshold may oc-cur in hypocritical flow, the downstream boundary condition may have a non-negligible effect on the spatial growth\/decay of the perturbation. The paper presents the solution of the 1D linearized flow of a Herschel & Bulkley fluid in a channel of finite length, in the neighbourhood of a hypocritical base uniform flow. Both linearly stable and unstable condi-tions are considered. The analytical solution is found applying the Laplace transform method and obtaining the first-order analytical expressions of the upstream and downstream channel response functions in the time domain. The effects of both the yield stress and the rheological law exponent are discussed, recovering as particular cases both power-law and Bingham fluids. The theoretical achievements may be used to extend semi-empirical criteria commonly employed for predicting roll waves occurrence in clear-water even to mud-flows."

This paper numerically investigates the effects of a harmonic volume forcing of prescribed frequency on the turbulent pipe flow at a Reynolds number, based on bulk velocity and pipe diameter, of 5900. The thickness of the Stokes layer, resulting from the oscillatory flow component, is a small fraction of the pipe radius and therefore the associated vorticity is confined within a few wall units. The harmonic forcing term is prescribed so that the ratio of the oscillating to the mean bulk velocity ($\ensuremath{\beta} $) ranges between 1 and 10.6. In all cases the oscillatory flow obeys the Stokes analytical velocity distribution while remarkable changes in the current component are observed. At intermediate values $\ensuremath{\beta} = 5$, a relaminarization process occurs, while for $\ensuremath{\beta} = 10. 6$, turbulence is affected so much by the harmonic forcing that the near-wall coherent structures, although not fully suppressed, are substantially weakened. The present study focuses on the analysis of the time- and space-averaged statistics of the first- and second-order moments, vorticity fluctuations and Reynolds stress budgets. Since the flow is unsteady not only locally but also in its space-averaged dynamics, it can be analysed using phase-averaged and time-averaged statistics. While the former gives information about the statistics of the fluctuations about the mean, the latter, postponed to a subsequent paper, shows how the mean is affected by the fluctuations. Clearly, the two phenomena are connected and both of them deserve investigation.

Summary This paper analyses conditions for roll-waves formation in homogeneous granular flows with the aim of predicting their occurrence in finite length channels. With reference to a wide class of constitutive equations of the flowing medium, the response of the linearized one-dimensional flow model to a pointwise instantaneous disturbance is studied and a closed form of the Green’s function, in both stable and unstable conditions, is provided. The exponential growth of the disturbance peak is used to predict the spatial evolution of roll-waves in dry flows of dense granular materials and a criterion for the minimum channel length necessary to appreciate roll-wave development is proposed. The comparison among theoretical and experimental data available in the literature appears promising.

The present work investigates the effect of the flow profile induced by an inlet condition on the roll-wave evolution in turbulent clear-water flows. The study employs theoretical and numerical analyses. Firstly, the influence of the inlet condition on the spatial evolution of a single perturbation in a hypercritical flow is examined through the expansion near a wavefront analysis. The results show that an accelerated unperturbed profile reduces the disturbance spatial growth. A decelerated profile causes an increase. The effect of the flow profile on the spatial evolution of roll-wave trains is then numerically investigated solving the Saint Venant equations with a second-order Runge-Kutta Total Variation Diminishing (TVD) Finite Volume scheme. The numerical simulations comply with the analytical results for the initial and transition phases of the roll-wave development. The unperturbed profile influences even the roll-waves statistical characteristics in the final stage, with a more evident effect in case of accelerated profiles. The influence of the flow profile should be therefore accounted for in the formulation of predictive criteria for roll-waves appearance based on the estimation of the disturbance spatial growth rate.

The fully developed turbulent flow in an annular pipe with radius ratio of 1/2 is investigated for Reynolds numbers based on hydraulic diameter and bulk velocity ranging from 12000 to 46000. The study is carried out processing data obtained from wall resolved large eddy simulations employing the dynamic subgrid scale eddy viscosity model of Germano et al. (1991) as modified by Lilly (1992). Scaling in wall variables shows that the turbulence intensities in the inner radius region are systematically less than the corresponding plane channel data, while the differences in the outer radius region reduce considerably. Because of the transverse curvature the total shear stress deviates from the linear distribution by as much as 12% in the inner wall region at y^+ =100. The curvature effects decrease as the Reynolds number is increased. Thus in the low Reynolds number range similarity arguments have to be considered with augmented caution with respect to the plane channel case.

Direct numerical simulation of an equilibrium turbulent pipe flow at a Reynolds number of 2500, based on bulk velocity and pipe diameter, has been carried out with a grid of about 7.4 x 10(5) points and a fully resolved wall layer. The simulation fills the existing gap in the availability of accurate turbulence data in the low Reynolds number range, so that the sensitivity of the main statistical quantities to the Reynolds number effects could be completed. The systematic dependence of the turbulent stress tenser components upon Re in the near wall region, when the normalization is based upon the wall shear stress and kinematic viscosity, is confirmed. Normalization based on the Kolmogorov velocity and length scales as suggested by Antonia and Kim [1] in the context of plane channel flow, proves effective also for pipe flow at lower Re. The high values attained by the fourth-order moments of the radial and azimuthal velocities are shown to be of truly physical nature and to be related with rare and energetic events characterizing the whole wall layer. Vorticity dynamics analysis suggests that the origin of the high flatness factors is associated with the interaction of counter-rotating streamwise vortices with the wall. Analysis of the transport equations of the turbulent kinetic energy shows that the production, turbulent dissipation and viscous diffusion rates, the leading terms of the budget, increase considerably with Re for gamma (+) < 20. (C) 2001 Elsevier Science Ltd. All rights reserved.

The article presents a fast pseudo-spectral Navier-Stokes solver for cylindrical geometries, which is shown to possess exponential rate of decay of the error. The formulation overcomes the issues related to the axis singularity, by employing in the radial direction a special set of collocation points together with standard Chebyshev polynomials. A multi-domain technique with patching interfaces yields significant improvements in the conditioning of the algebraic problems arising from the discretization procedure and allows for an enhanced near wall resolution of wall bounded shear flows. The elliptic kernel enjoys the efficiency of an analytic expansion of the harmonic extension, The method is tested by computing the formation of Taylor vortices in a rotating Couette flow for both axisymmetric and non-axisymmetric configurations, A direct numerical simulation of a turbulent pipe flow at moderate Reynolds number demonstrates the effectiveness of the method in as much as the axis singularity is concerned, Results compare well with reference experimental and numerical data, (C) 1999 Academic Press.

The paper describes the effects of a forced harmonic oscillations of fixed frequency and amplitudes in the range Λ = Um /Ub = 1 ÷ 11 on the characteristics of a turbulent pipe flow with a bulk Reynolds number of 5900. The resulting Stokes layer δ is a fraction of the pipe radius (χ = R/δ = 53) so that the vorticity associated to the oscillating motion is generated in a small near wall region. The analysis is carried out processing a set of statistically independent samples obtained from wall resolved Large Eddy Simulations; time and space averaged global quantities, extracted for the sake of comparison with recent experimental data, confirm the presence of a non negligible drag reduction phenomenon. Phase averaged profiles of the Reynolds stress tensor components provide valuable material for the comprehension of the effects of the time varying mean shear upon the near wall turbulent flow structures. The large scale of motion are directly computed through numerical integration of the space filtered three dimensional Navier-Stokes equations with a spectrally accurate code; the subgrid scale terms are parametrized with a dynamic procedure.Copyright © 2003 by ASME

The study of unsteady shallow-layer flows, as those occurring during floods, may be performed through either fully dynamic models or using simplified momentum equations (e.g. kinematic, diffusion and quasi-steady approximations). Among the latter, kinematic approximation may provide a significant reduction of the computational effort, which represents a key advantage in time-critical applications. The proper application of this simplified model is however generally subjected to some limitations, which the modeler has to know and accurately verify to avoid errors. The present paper aims to investigate the applicability range of the kinematic approximation to shallow flows, with special concern to unsteady mud-flows, such as the hyper-concentrated floods. In the present analysis the rheological model proposed by O'Brien et al. (1993), broadly appreciated and widespread in the technical community, is considered. This model relies on a quadratic relationship linking the shear rate to the total shear stress, accounting for turbulent, dispersive and cohesive yield stresses. To provide relatively simple applicability criteria, linear analysis is applied to compare the celerity of a small perturbation of an initial steady uniform flow as predicted by the simplified model with those of the full dynamic model. Based on this comparison, applicability criteria for the kinematic approximation for mud-flows are derived. In particular, the proposed criteria rely on the comparison between the flood rising-time and a threshold time-scale: whenever the former is larger than the latter, the estimation of the propagation celerity of the simplified model is guaranteed with a prescribed accuracy. These criteria are presented considering the effect of all model parameters, based on the particular case of a pyroclastic mud, typically encountered in volcanic areas of southern Italy. The achieved results are discussed, aiming to guide the choice of the appropriate simplified model for mud flood analysis

The direct nonlinear problem of a fluid distribution network in unsteady state of flow is dealt within this paper Referring to a class of nonlinear flow equations several issues related to the mathematical well-posedness are analyzed. A mixed variational formulation in terms of the state variables of the network along with a weak formulation with respect to the time variable is associated to the classical differential algebraic problem formulation. The strict convexity of network functional and the uniform monotonicity of the operator resulting from the temporal discretization allow the proof of the uniqueness of the solution and provide a necessary condition for global stability.