Numerical Method to Provide Cavitation Index for Control Valves

2013 ◽  
Author(s):  
Stefano Malavasi ◽  
Marco M. A. Rossi ◽  
Gianandrea V. Messa ◽  
Giacomo Ferrarese
Keyword(s):  
Computational Cost ◽  
Technical Standards ◽  
Perforated Plates ◽  
Control Valves ◽  
Cavitation Inception ◽  
Mechanical Parts ◽  
Control Devices ◽  
Multi Phase ◽  
Low Computational Cost ◽  
Good Agreement

Cavitation is a harmful phenomenon for control valves. Starting from noise and vibration, cavitation can bring erosion and pitting of mechanical parts. Experimental costs for cavitation tests are high, not even considering the difficulties to test large-sized valves. For those reasons a CFD analysis could be an attractive solution to predict cavitation. However, a reliable numerical prediction of cavitation inception is hard to achieve and the computational cost of complex multi-phase models, necessary for a correct description of this phenomenon, is often very high. The purpose of this research is to overcome those difficulties by using a single-phase model to predict the onset of cavitation, in terms of the incipient cavitation index introduced in several technical standards. A method, based on the generalized pressure criterion reported in previous works, is applied to particularly complex control devices, namely the Cage Ball control valves, in which perforated plates are inserted to increase the energy dissipation with respect to a traditional Ball valve. Numerical results are compared with our own experimental data of acceleration induced by cavitation vibrations, showing good agreement. The final result is a simple and reliable method, with low computational cost, to evaluate the incipient cavitation index for control valves.

scholarly journals CONTRIBUTIONS TO THE MARINE PROPELLERS HYDRODYNAMIC DESIGN

2014 ◽  
Vol 13 (2) ◽  
pp. 41
Author(s):  
B. I. Favacho ◽  
J. R. P. Vaz ◽  
A. L. A. Mesquita
Keyword(s):  
Control Volume ◽  
Computational Cost ◽  
Momentum Balance ◽  
Marine Propellers ◽  
Energy And Momentum ◽  
Thrust And Torque ◽  
The Mathematical Model ◽  
Low Computational Cost ◽  
Bem Theory ◽  
Good Agreement

The navigation in Amazon region is very important due to the length of navigable rivers and the lack of alternative road network, as well as being a form of transportation costless for the flow of agricultural and manufacturing production. This kind of transportation present social, economic and technological importance for this region. Thus, this work objective to develop a mathematical approach for the marine propellers design, using a formulation for chord and pitch angle optimization, taken into account the equations of mass, energy and momentum balance for the theoretical calculation of thrust and torque relationships on an annular control volume, ie, the mathematical model is based in the Blade Element Momentum (BEM) theory. The proposed hydrodynamic model present low computational cost and it is easy to implement. The results are compared with classical Glauert's theory and the experimental data of the Wageningen B3-50 propeller, presenting good agreement.

scholarly journals The revised FLORIDyn model: Implementation of heterogeneous flow and the Gaussian wake

2022 ◽  
Author(s):  
Marcus Becker ◽  
Bastian Ritter ◽  
Bart Doekemeijer ◽  
Daan van der Hoek ◽  
Ulrich Konigorski ◽  
...  
Keyword(s):  
Wind Farm ◽  
Computational Cost ◽  
Parametric Model ◽  
Computational Time ◽  
Flow Conditions ◽  
Heterogeneous Flow ◽  
The Mean ◽  
Wake Model ◽  
Low Computational Cost ◽  
Good Agreement

Abstract. In this paper a new version of the FLOw Redirection and Induction Dynamics (FLORIDyn) model is presented. The new model uses the three-dimensional parametric Gaussian FLORIS model and can provide dynamic wind farm simulations at low computational cost under heterogeneous and changing wind conditions. Both FLORIS and FLORIDyn are parametric models which can be used to simulate wind farms, evaluate controller performance and can serve as a control-oriented model. One central element in which they differ is in their representation of flow dynamics: FLORIS neglects these and provides a computationally very cheap approximation of the mean wind farm flow. FLORIDyn defines a framework which utilizes this low computational cost of FLORIS to simulate basic wake dynamics: this is achieved by creating so called Observation Points (OPs) at each time step at the rotor plane which inherit the turbine state. In this work, we develop the initial FLORIDyn framework further considering multiple aspects. The underlying FLORIS wake model is replaced by a Gaussian wake model. The distribution and characteristics of the OPs are adapted to account for the new parametric model, but also to take complex flow conditions into account. To achieve this, a mathematical approach is developed to combine the parametric model and the changing, heterogeneous world conditions and link them with each OP. We also present a computational lightweight wind field model to allow for a simulation environment in which heterogeneous flow conditions are possible. FLORIDyn is compared to SOWFA simulations in three- and nine-turbine cases under static and changing environmental conditions.The results show a good agreement with the timing of the impact of upstream state changes on downstream turbines. They also show a good agreement in terms of how wakes are displaced by wind direction changes and when the resulting velocity deficit is experienced by downstream turbines. A good fit of the mean generated power is ensured by the underlying FLORIS model. In the three turbine case, FLORIDyn simulates 4 s simulation time in 24.49 ms computational time. The resulting new FLORIDyn model proves to be a computationally attractive and capable tool for model based dynamic wind farm control.

scholarly journals WearGP: A UQ/ML Wear Prediction Framework for Slurry Pump Impellers and Casings

2020 ◽  
Author(s):  
Anh Tran ◽  
Yan Wang ◽  
John Furlan ◽  
Krishnan V. Pagalthivarthi ◽  
Mohamed Garman ◽  
...  
Keyword(s):  
High Performance ◽  
Computational Cost ◽  
Operating Conditions ◽  
Wear Prediction ◽  
Wear Rates ◽  
Computing Platform ◽  
Multi Phase ◽  
Performance Computing ◽  
Low Computational Cost ◽  
High Computational Cost

Abstract Dedicated to the memory of John Furlan. Wear prediction is important in designing reliable machinery for slurry industry. It usually relies on multi-phase computational fluid dynamics, which is accurate but computationally expensive. Each run of the simulations can take hours or days even on a high-performance computing platform. The high computational cost prohibits a large number of simulations in the process of design optimization. In contrast to physics-based simulations, data-driven approaches such as machine learning are capable of providing accurate wear predictions at a small fraction of computational costs, if the models are trained properly. In this paper, a recently developed WearGP framework [1] is extended to predict the global wear quantities of interest by constructing Gaussian process surrogates. The effects of different operating conditions are investigated. The advantages of the WearGP framework are demonstrated by its high accuracy and low computational cost in predicting wear rates.

THD Analysis of Journal Bearings: A Finite Element Algorithm for Groove Mixing Conditions

2005 ◽  
Author(s):  
Fabrizio A. Stefani
Keyword(s):  
Finite Element ◽  
Solution Method ◽  
Energy Equation ◽  
Computational Cost ◽  
Three Dimensional ◽  
Mixing Conditions ◽  
Energy Conserving ◽  
Element Algorithm ◽  
Low Computational Cost ◽  
Good Agreement

A finite element method of solving the mass and energy-conserving lubrication problem, including the energy balance in the feed grooves, is proposed. As mass continuity in the whole film is considered, cavitation is taken into account properly. Both a two-dimensional (2D) and a quasi-three-dimensional (3D) solution of the energy equation in the lubricant film have been adopted. Some results are presented for a two-axial groove journal bearing. The quasi-3D solution method (cross-film conduction included in the model) showed good agreement with experimental results and incurred low computational cost.

A simple scheme for calculating the energy harvesting figures of merit of porous ceramics

2021 ◽  
Vol 0 (0) ◽  
Author(s):  
Rogelio O. Caballero-Pérez ◽  
Julián Bravo-Castillero ◽  
Leslie D. Pérez-Fernández
Keyword(s):  
Energy Harvesting ◽  
Effective Properties ◽  
Computational Cost ◽  
Good Alternative ◽  
Porous Ceramics ◽  
Figures Of Merit ◽  
Effective Coefficients ◽  
Analytical Formulae ◽  
Low Computational Cost ◽  
Good Agreement

Abstract We propose a scheme based on recursively applying analytical formulae for effective properties to a class of porous ceramics for calculating their energy harvesting figures of merit. We approximate the structure of freeze-cast PZT parallel laminae joined by links (or bridges) by a model that can be broken down into two directions along which the structure resembles a laminate. The effective coefficients obtained in the first step of the recursion are then used as input on the second step which gives the final effective moduli. The comparison of those with calculations via Finite Element Method (FEM) on a non-recursive model shows good agreement. Finally, we calculate the piezoelectric and pyroelectric figures of merit and compare them with experimental results. The proposed scheme is a good alternative since it relies only on known simple analytical formulae and has a very low computational cost with respect to other methods that may be applied to such a geometry.

scholarly journals Cavitation Bubble Cloud Break-Off Mechanisms at Micro-Channels

Fluids ◽  
2021 ◽  
Vol 6 (6) ◽  
pp. 215
Author(s):  
Paul McGinn ◽  
Daniel Pearce ◽  
Yannis Hardalupas ◽  
Alex Taylor ◽  
Konstantina Vogiatzaki
Keyword(s):  
Cavitation Bubble ◽  
Cavitation Inception ◽  
Wave Dynamics ◽  
Bubble Cloud ◽  
Cloud Dynamics ◽  
Micro Channels ◽  
Physical Insight ◽  
Cloud Process ◽  
Good Agreement

This paper provides new physical insight into the coupling between flow dynamics and cavitation bubble cloud behaviour at conditions relevant to both cavitation inception and the more complex phenomenon of flow “choking” using a multiphase compressible framework. Understanding the cavitation bubble cloud process and the parameters that determine its break-off frequency is important for control of phenomena such as structure vibration and erosion. Initially, the role of the pressure waves in the flow development is investigated. We highlight the differences between “physical” and “artificial” numerical waves by comparing cases with different boundary and differencing schemes. We analyse in detail the prediction of the coupling of flow and cavitation dynamics in a micro-channel 20 m high containing Diesel at pressure differences 7 MPa and 8.5 MPa, corresponding to cavitation inception and "choking" conditions respectively. The results have a very good agreement with experimental data and demonstrate that pressure wave dynamics, rather than the “re-entrant jet dynamics” suggested by previous studies, determine the characteristics of the bubble cloud dynamics under “choking” conditions.

scholarly journals Computing Expectiles Using k-Nearest Neighbours Approach

Symmetry ◽  
2021 ◽  
Vol 13 (4) ◽  
pp. 645
Author(s):  
Muhammad Farooq ◽  
Sehrish Sarfraz ◽  
Christophe Chesneau ◽  
Mahmood Ul Hassan ◽  
Muhammad Ali Raza ◽  
...  
Keyword(s):  
Computational Cost ◽  
Real Life ◽  
Distance Measures ◽  
Computational Time ◽  
High Dimensional ◽  
Test Error ◽  
Nearest Neighbours ◽  
Comparable Performance ◽  
Asymmetric Least Squares ◽  
Low Computational Cost

Expectiles have gained considerable attention in recent years due to wide applications in many areas. In this study, the k-nearest neighbours approach, together with the asymmetric least squares loss function, called ex-kNN, is proposed for computing expectiles. Firstly, the effect of various distance measures on ex-kNN in terms of test error and computational time is evaluated. It is found that Canberra, Lorentzian, and Soergel distance measures lead to minimum test error, whereas Euclidean, Canberra, and Average of (L1,L∞) lead to a low computational cost. Secondly, the performance of ex-kNN is compared with existing packages er-boost and ex-svm for computing expectiles that are based on nine real life examples. Depending on the nature of data, the ex-kNN showed two to 10 times better performance than er-boost and comparable performance with ex-svm regarding test error. Computationally, the ex-kNN is found two to five times faster than ex-svm and much faster than er-boost, particularly, in the case of high dimensional data.

scholarly journals Directional TGV-Based Image Restoration under Poisson Noise

2021 ◽  
Vol 7 (6) ◽  
pp. 99
Author(s):  
Daniela di Serafino ◽  
Germana Landi ◽  
Marco Viola
Keyword(s):  
Computed Tomography ◽  
Image Restoration ◽  
Gaussian Noise ◽  
Computational Cost ◽  
Data Fitting ◽  
Poisson Noise ◽  
Glass Fibres ◽  
Leibler Divergence ◽  
Generalized Variation ◽  
Low Computational Cost

We are interested in the restoration of noisy and blurry images where the texture mainly follows a single direction (i.e., directional images). Problems of this type arise, for example, in microscopy or computed tomography for carbon or glass fibres. In order to deal with these problems, the Directional Total Generalized Variation (DTGV) was developed by Kongskov et al. in 2017 and 2019, in the case of impulse and Gaussian noise. In this article we focus on images corrupted by Poisson noise, extending the DTGV regularization to image restoration models where the data fitting term is the generalized Kullback–Leibler divergence. We also propose a technique for the identification of the main texture direction, which improves upon the techniques used in the aforementioned work about DTGV. We solve the problem by an ADMM algorithm with proven convergence and subproblems that can be solved exactly at a low computational cost. Numerical results on both phantom and real images demonstrate the effectiveness of our approach.

scholarly journals An optimal and low computational cost fractional Newton-type method for solving nonlinear equations

2021 ◽  
pp. 107650
Author(s):  
Giro Candelario ◽  
Alicia Cordero ◽  
Juan R. Torregrosa ◽  
María P. Vassileva
Keyword(s):  
Nonlinear Equations ◽  
Computational Cost ◽  
Type Method ◽  
Low Computational Cost
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