Non-Newtonian cfd modelling of a valve for mud pumps

Mud pumps, like those used in the field of oil well drilling, are typically of the reciprocating type and are designed to circulate drilling fluid under high pressure down the drill string and back up the annulus. automatic valves must be applied to the fluid end in order to grant the desired pumping effect. from the engineering point of view, the design of the valve geometry must ensure that the phenomenon of cavitation does not occur and that, during the pumping action, the stiffness of the reaction coil spring is able to avoid reaching the condition of end stroke of the valve. Cavitation consists in the development of vapour cavities in the liquid phase. Inside the cavities, the pressure is relatively low. When subjected to higher pressure, the voids implode and generate an intense shock waves that promote the wear for the components (i.e. valve, valve seat, etc.). a deep understanding of the fluid behaviour is crucial for an effective design. Transient CfD simulations of the valve opening have been performed using a non-Newtonian fluid model able to describe the drilling muds. after a deep literature review, the Herschel-Bulkley model was selected as the most suitable for emulating the drilling mud. With the abovementioned approach, the reaction spring and design the valve seat to avoid premature wear phenomena were properly designed. The simulations have been also done considering a Newtonian fluid behaviour, in order to better understand the importance of considering the non-Newton behaviour for an effective design

Dynamic modeling of gears: An innovative hybrid FEM-analytical approach

Gearboxes are widely used in several applications ranging from the automotive to the industrial and robotic sectors. A planetary gearbox is a special kinematic gear arrangement that, taking advantage of a planet carrier, ensures high reduction ratios together with a very small design. Therefore, they are widely employed for transmissions which require a high power density. There are several fields of applications including, but not limited to, mechatronic, automation and wind power generation. To improve the design of new solutions, for performing monitoring activities on actual gearboxes and for the definition of maintenance schedules, the availability of physical models able to accurately describe the behavior of the system, both in healthy and damaged conditions, would represent a great support. Experimental and numerical studies of the behavior of gearboxes are already available in the literature. Nevertheless, while the experimental approaches are valid only for the specific configuration tested, the numerical techniques show limitations related to the computational effort required. This paper presents an innovative approach for the characterization of the behavior of two different geared transmissions. It is based on a hybrid approach that combines finite elements (FE) with analytical formulations. In detail, the solver computes separately the macro deformation of the bodies (numerical solution based on a coarse grid) and the contacts (solved analytically avoiding the need of mesh refinements). The computational effort is reduced significantly without affecting the accuracy of the results significantly. This approach was used to investigate and understand the vibro-dynamical behavior of a back-to-back test rig (typically used for the characterization of the surface fatigue strength of gears) and of an industrial planetary gearbox. The results obtained for the healthy - not damaged - gearboxes were compared with experimental measurements for both configurations in order to validate the hybrid approach. Once the models were validated, the same methodology was eventually used to study the effects of typical gear failures and in specifically surface fatigue (pitting), on the vibrational response. The capability to reproduce the effect of damages with the model of a gearbox represents the first indispensable step of a Structural Health Monitoring strategy. State-of-art and challenges are analyzed and discussed in the paper

Impact of the lacks of fusion induced by additive manufacturing on the lubrication of a gear flank

Additive Manufacturing (AM) is becoming a more and more widespread technology. Its capability to produce complex geometries opens new design possibilities. Despite the big efforts made by the scientific community for improving the AM processes, this technology still has some limitations, mainly related to the achievable surface quality. It is known that AM technologies pro-mote the formation of LACKS of fusion inside the material. In some cases, the external surfaces are finished with traditional machining. This is the case of AM‐produced gears. While the grinding operation aims to reduce the surface roughness, the presence of porosities just below the surface of the wrought component, could lead, after grinding, to the exposure of those porosities leading to a pitted surface. This phenomenon is surely not beneficial in terms of structural resistance, but can help the lubrication promoting the clinging of the lubricant to the surface. The aim of this paper is to study this effect. Micro‐Computer‐Tomography (μ‐CT) analyses were performed on a 17‐4 PH Stainless Steel (SS) produced via Selective Laser Melting (SLM). The real geometry of the pores was reproduced virtually and analyzed by means of multiphase CFD analyses in the presence of centrif-ugal effects

Structural modelling of multilayer skis with an open source FEM software

The design process of a ski is characterized by a short time of development due to continuous advancements in the material science and in the manufacturing processes as well as in customer’s requirements. Nowadays, the development process is very often still based on several physical prototypes and trials and Finite Elements Analysis (FEA) is a significant method to reduce times needed. The aim of this work is to develop a reliable numerical simulation of an existing mountaineering ski, able to predict the performance of the real element. For this purpose, an initial mechanical characterization of all the constituents used in the ski manufacturing was performed. Tensile tests in two directions were performed on flat bone-shaped samples laser cut from sheets. Combining the results of the tensile tests with Digital Image Correlation (DIC) data it was possible to approximate the four in-plane (XY) elastic properties, namely, the two elastic modules, the shear module and the Poisson ratio (Ex, Ey, Gxy, νxy). The DIC free software used is GOM Correlate. Results of the combined “tensile tests – DIC” approach were after verified with FEM simulations reproducing the testing configuration. The digital model of the ski was created starting from the nominal geometry. The whole procedure of modelling, meshing and FE analysis was performed in the open source software Code_Aster/Salome-Meca. Using this kind of software, which code is free to use and modify, permits to reduce costs due to its free license. The real component was tested in a three-point bending and torsion test. This kind of experiments were replicated on the FEM model and results were compared. The comparison highlighted discrepancies of 2.5%–10% with respect to the real component

A model-based SHM strategy for gears-development of a hybrid FEM-analytical approach to investigate the effects of surface fatigue on the vibrational spectra of a back-to-back test rig

Transmissions are extensively employed in mechanical gearboxes when power conversion is required. Being able to provide specific maintenance is a crucial factor for both economics and reliability. However, although periodic transmission maintenance increases the systems’ longevity, it cannot prevent or predict sporadic major failures. In this context, structural health monitoring (SHM) represents a possible solution. Identifying variations of a specific measurable signal and correlating them with the type of damage or its location and severity may help assess the component condition and establish the need for maintenance operation. However, the collection of sufficient experimental examples for damage identification may be not convenient for big gearboxes, for which destructive experiments are too expensive, thus paving the way to model-based approaches, based on a numerical estimation of damage-related features. In this work, an SHM approach was developed based on signals from numerical simulations. To validate the approach with experimental measurements, a back-to-back test rig was used as a reference. Several types and severities of damages were simulated with an innovative hybrid analytical-numerical approach that allowed a significant reduction of the computational effort. The vibrational spectra that characterized the different damage conditions were processed through artificial neural networks (ANN) trained with numerical data and used to predict the presence, location, and severity of the damage

Aerodynamic study of moto rcycle racing wheels: A performance evaluation based on numerical CFD simulations

In any racing competitions, the aerodynamic performances of the equipment are determinant. This is true, for example, for cars, where the geometry of the bodywork and of the wings can ensure a lower Cx coefficient and/or a higher down-force and a higher handling. In other competitions, like rowing, the aerodynamics of the hull can reduce the effort done by the athletes. In the cycle and motorcycle racing competitions, other aspects related to aerodynamics become important, such as the manoeuvrability and stability. In the present research, a numerical approach was used in order to compare different front-wheel geometries (of a racing motor-bike) in terms of drag, lift and axial forces. Three different wheel designs have been compared. The first one consists in a traditional seven spokes aluminium design, the second wheel is a 6 spokes magnesium solution and the third a solid-disk wheel. Steady state as well as transient simulations was performed with OpenFOAM®, a free open-source software. This was selected because it allows a higher flexibility with respect to any close-source commercial software. The possibility to customize the solver as well as the boundary conditions allows the analysis of the physical problem of interest. The free license allows a high parallelization of the computations. The steady-state simulations were performed by freezing the wheel position and introducing a rotating reference frame. In this way, the computational time was significantly reduced. For the transient simulations, the computational domain was split into two subdomains. The internal one is cylindrical and contains the wheel. The rotational velocity of the wheel was imposed by applying a rigid rotation to the mesh of the internal subdomain. Mesh interfaces ensures the continuity of the solution across the domains

Bending fatigue behaviour of 17-4 PH gears produced via selective laser melting

The possibility of producing parts via the addition of material, instead of its removing, given by Additive Manufacturing (AM) processes is changing the way in which parts are designed. However, the design of some mechanical components like gears, for instance, requires specific resistance data that, up to now, are not presented in literature. This paper presents a research project aimed at investigating the bending fatigue properties of 17-4 PH steel applied to gears produced via selective laser melting. Single Tooth bending Fatigue (STF) tests were conducted in order to investigate the S-N curve. Results are presented in terms of tooth root stress calculated according to the ISO standard in order to compare them with data of other materials. In addition, Scanning Electron Microscopy (SEM) of the fractured surfaces has been performed on the failed teeth to investigate failure origin and therefore to find causes of tooth breakage

Numerical modeling of the churning power losses of gears: an innovative 3D computational tool suitable for planetary gearbox simulation

Thanks to the recent developments in the computer science, simulations are becoming an increasingly widespread approach that can help the designers in the development of new products. In the specific field of gearboxes, simulations up to now have been used mainly for structural and dynamic analysis. In these fields, the simulation tools have proved to be able to provide reliable information. Moreover, in the field of structural design and strength analysis, with respect to the various failure mechanisms involved, many analytical methods and international standard are available. On the other hand, at present for the prediction of the power losses and the efficiency of gears, neither accurate analytical methods nor automated simulation tools are available, in particular where the interest is focused on load independent power losses. The authors have been working on this topic for several years and have developed new methodologies based on computational fluid dynamics. With respect to general-purpose commercial software, the techniques that have been developed by the authors for the specific application of gears and gearboxes, allow a significant reduction of the computational effort and have the capability to take into account particular physical phenomena that occurs in gears, such as cavitation for instance, and for which no information available in literature, concerning their influence on gears efficiency. The purpose of this paper is to introduce an improved automated strategy, implemented in order to extend the applicability of the previously developed computational method to real complex gearboxes. With this additional improvement, some geometrical limitations adopted in the past can be removed and the tool is now suitable for the application to real complex gearboxes. In order to show the capabilities of this new strategy, a planetary gearbox, which represents one of the most complicated kinematic arrangements of gears has been selected and simulated. At the same time, the planetary gearboxes represents a configuration for which the numerical fluid dynamics simulation can give the major contribution tb the calculation of load independent power losses, due to the peculiar interaction between the lubricant and the planets which are supported by a rotating planet carrier. The simulations have been performed both with planar simplified models and with complete 3D models and compared with experimental data showing the goodness of the approach