Massimo Milani

In this paper, the suction capabilities of an innovative high speed external gear pump have been measured and analysed for verifying its potential use as a reliable and efficient power unit for electro-hydraulic actuated automotive transmissions. In particular, with the aim to face extremely challenging operating conditions, mainly in terms of rotational speed, this specific type of volumetric machine is designed with both two suction and delivery ports. All the experimental measurements have been performed by using a specifically tailored test bench, equipped with a double Cardan joint and an overdrive, designed for running the pump over a wide range of rotational speeds, spanning between 400 and 7000 rpm, and applying a delivery pressure of about 45 bar, very close to a typical actuation value of a high-performance automotive hydraulic transmission. Furthermore, with the aim to confirm the consistency of the experimental measurements, two identical prototypes of the high speed external gear pump have been tested and compared for two different values of the operating temperature, respectively equal to 40 and 60oC. First of all, the higher efficiency of the pump primary suction port has been clearly highlighted and evaluated. Moreover, for rotational speed values higher than 4000 rpm, a significant increase of the volumetric flow rate delivered by the pump can be achieved using both the suction ports together and, thus, this particular hydraulic configuration can be considered as a very promising design solution for the entire actuation system.

This paper proposes a CFD methodology for the simulation of the slipper’s dynamics of a swash-plate axial piston unit under actual operating conditions. The study considers a typical slipper design, including a vented groove at the swash-plate interface. The dynamic fluid–body interaction (DFBI) model is exploited to find the instantaneous position of the slipper, while the morphing approach is adopted to cope with the corresponding mesh distortion. A modular approach is adopted to ensure high-quality mesh on the entire slipper surface and sliding interfaces provide the fluid dynamic connection between neighboring regions. The external forces acting on the slipper are included by means of user-defined lookup tables with the simulation estimating the lift force induced by fluid compression. Moreover, the force produced by the metal-to-metal contact between the slipper and the swash plate is modeled through a specific tool of the software. The pressure signal over an entire revolution of the pump is taken as an input of the simulation and a variable time step is used to manage the high-pressure gradients occurring in the regions of inner and outer dead points of the piston. The weakly compressible characteristic of the fluid is considered by a specific pressure-dependent density approach, and the two-equation eddy-viscosity k-ω SST (shear stress transport) model is used to assess the turbulent behavior of the flow. Furthermore, the transitional model predicts the onset of transition, thus solving different equations depending on whether the flow enters a laminar or turbulent regime. In conclusion, the proposed methodology investigates the motion of the slipper in response to several external forces acting on the component. The numerical results are discussed in terms of variable clearance height, pressure distribution within the gap, and lift forces acting on the slipper under specific pump operations.

The geometric complexity and high-pressure gradients that characterize the design of the flow field of gear pumps make it very difficult to obtain an accurate CFD simulation of the component. Usually, assumptions are made both in terms of geometrical features and physics being included in the analysis. The contact between the teeth, which is a key factor for the correct functioning of these pumps, represents a critical challenge in 3D CFD simulations, mainly due to the intrinsic limits of the dynamic meshing techniques that can hardly effectively manage a zero or close to zero gap point forming during gear rotation. The geometric complexity and high-pressure gradients that characterize the gear pump flow field make a CFD analysis quite difficult, and the contact between the gear teeth is usually avoided, thus being an extremely important feature. In this paper, a gear pump composed of inlet and outlet pipes was considered, and the contact between the gear’s teeth was modeled in two different ways, one where it is effectively implemented and one where it is avoided using distancing and a proper casing modification. Herein, a new methodology is proposed for the application of the dynamic mesh method in the Simcenter STAR-CCM+ environment using an adaptive remeshing technique. The proposed methodology is compared with the alternative overset meshing method available in the software. The new meshing method is implemented using a user-routing that reproduces the real geometry of the gears while rotating during the pump operation, with teeth contact included. The routine is optimized in order to limit the additional computation and time needed for the remeshing process. The results that can be obtained using the two meshing approaches for the gear pump are compared in terms of computational effort and the accuracy of the results. The two methods showed opposite results in almost all the reported results, with the overset being more precise in the radial pressure evaluation and the dynamic being more reliable in the cavitation/aeration extension cloud.

The lung is the human organ mainly affected by the severe coronavirus disease (COVID-19) caused by the novel coronavirus SARS-CoV-2. In this pathology, the dynamic lung function and the respiratory mechanics are compromised, leading to the development of the ARDS (acute respiratory distress syndrome). The resulting damage is the progressive reduction of gas exchange and death in the most critical patients. For these reasons, it is important to study and analyze how this virus adversely affects lung dynamics. The main objective of the present paper proposes a modeling method of SARS-CoV-2 virus particles spread in the 23rd generation of lung tree and the mechanical estimation of how a severe stage of COVID-19 characterized by pulmonary fibrosis affects the alveolar sac expansion and hence the breathing capability of the sick person. In this context, the dynamic analysis of the influence of SARS-CoV-2 spread on human lung under real conditions has been shown by means of a numerical approach. Therefore, a multiphase three-dimensional computational fluid dynamics (CFD) study is performed to estimate the COVID-19 virus particles dispersion throughout a simplified model of the 23rd generation of the bronchial tree, at the alveolar region. Then, a fully coupled fluid-structure interaction (FSI) with the mesh morphing technique and solid displacement characteristics are used to obtain and evaluate a realistic wall displacement during the expansion of the alveolar sac. A comparison is made between a healthy and a diseased lung. These phases are studied under cyclic steady-state conditions The novelties of this analysis are: first, the innovative CFD method proposed in order to model the particles spread inside the alveolar region, and second the evaluation of how the presence of Sars-Cov-2 can affect the mechanical properties of the alveolar sac and damage the lung function of a sick person at an advanced stage of infection, such as a person affected by pulmonary fibrosis.

In a brake system the contact between the friction grooves of the discs and the steel elements leads to a consistent heat dissipation that is excised by the oil thermal vector in its flowing along the grooves channels. These are very complicated physical system were many variables may be taken in consideration, first of all the extensive integration of the different time scheduling actions that take place and that characterizes the translation of the interacting bodies and the correspondent deceleration, and also the heat dissipation derived from this contact. The simulations of similar physical system may result in too expensive computational efforts leading to very complicated simulations that need to take in account an extensive coupling between many physics, first of all the solid/liquid heat transfer and then the turbulence and the bi-phase models for the oil/air mixture that serves as thermal refrigerator vector in the braking system. Herein a simplified 3D model that focuses only on a discs / piston coupling is presented were the braking action is simulated in a simplified way modelling the velocity of rotation of the elements and the dissipated heat during the braking cycle. Focusing on the grooves channels the oil flows and thermal averaged flows are presented and detail contours are used to characterise a single brake event.

This paper proposes a statistical approach for modeling vertical walking forces induced by single pedestrians. To account for the random nature of human walking, the individual vertical walking force is modeled as a series of steps and the gait parameters are assumed to vary at each step. Walking parameters are statistically calibrated with respect to the results of experimental tests performed with a force plate system. Results showed that the walking parameters change during walking and are correlated with each other. The force model proposed in this paper is a step-by-step model based on the description of the multivariate distribution of the walking features through a Gaussian Mixture model. The performance of the proposed model is compared to that of a simplified load model and of two force models proposed in the literature in a numerical case study. Results demonstrate the importance of an accurate modeling of both the single step force and the variability of the individual walking force.

As a demanding motor act, running activates considerably the musculoskeletal, cardiovascular and pulmonary apparatus both in subjects with a low degree of training, and in semi-professional and professional athletes. It consists in a set of motor patterns that are repeated all the time during the entire covered distance. In particular for an athlete, it is essential to monitor and

The pre-adolescent age is basic in the beginning of the development of body kinematics. During this age the body structure needs to continuously search for stabilization due to the modification in body segment lengths. This behavior can evolve into incorrect postural attitudes that, if not properly treated, can lead to behaviors that are difficult to recover with advancing

The most well known circulating tumor cells (CTCs) enrichment approaches from whole blood samples utilize biological and/or physical CTC features, and mainly encompass size-based, positive and negative immune-affinity-based, and density-based methods or their combinations. Unfortunately, so far CTC technologies have not been fully and clinically made advantageous. Some of the most

The lubrication process is a critical issue in preventing the degradation of the friction material, enhancing the efficiency of the brake system and reduce the wear behavior. The paper proposes a novel concept for axels dry braking system in off-road vehicles by implementing an oil recovery system in the friction plates chamber. The new system is able to remove the oil in the