Numerical Studies on Cavitation and Surface Roughness

2019 ◽  
Vol 793 ◽  
pp. 79-84 ◽  
Author(s):  
Jithin Ambarayil Joy ◽  
Vijayakumar Mathaiyan ◽  
Muhammad Sajjad ◽  
Dong Won Jung
Keyword(s):  
Biological Sciences ◽  
Surface Roughness ◽  
Parametric Analysis ◽  
Smooth Surface ◽  
Material Surface ◽  
Cavitation Damage ◽  
Numerical Studies ◽  
Flow Features ◽  
The One ◽  
Topical Interest

The study of cavitation is of topical interest in both physical and biological sciences. The surface roughness changes the effect of cavitation on a material surface. Due to cavitation, the material with low surface roughness value has relatively more damage, when compared to the one with higher value. In this paper, preliminary numerical studies are carried on cavitation and surface roughness. As a part of the code validation and calibration, the numerically predicted boundary-layer blockage at the Sanal flow choking condition for the channel flow is verified using the closed-form analytical model of V.R. Sanal Kumar et al. (AIP Advances, 8, 025315, 2018) at various surface roughness and found excellent agreement with the exact solution. Parametric analytical studies are carried out for examining the flow features at two different surface roughness and turbulence levels. We noticed that the wavy surface with small waves increases the Nussle number, therefore it is also considered for parametric analysis. Considering the defect-free smooth surface material, we presumed that the cavitation damage in the smooth surface is more than the rough surface because the smooth surface can generate more micro bubbles. These micro bubbles grow into macro bubbles which in turn results in cavitation. This study is a pointer towards for formulating various industrial topics with fluid-structural interaction problems for getting plausible solutions for meeting the needs of various industries.

Modular Turbulence Modeling Applied to an Engine Intake

2013 ◽  
Vol 136 (5) ◽  
Author(s):  
Ugochukwu R. Oriji ◽  
Paul G. Tucker
Keyword(s):  
Surface Roughness ◽  
Turbulence Modeling ◽  
Fluid Dynamic ◽  
Navier Stokes ◽  
Test Cases ◽  
Laminar Separation ◽  
Streamline Curvature ◽  
Favorable Pressure Gradient ◽  
Flow Features ◽  
The One

The one equation Spalart–Allmaras (SA) turbulence model in an extended modular form is presented. It is employed for the prediction of crosswind flow around the lip of a 90 deg sector of an intake with and without surface roughness. The flow features around the lip are complex. There exists a region of high streamline curvature. For this, the Richardson number would suggest complete degeneration to laminar flow. Also, there are regions of high favorable pressure gradient (FPG) sufficient to laminarize a turbulent boundary layer (BL). This is all terminated by a shock and followed by a laminar separation. Under these severe conditions, the SA model is insensitive to capturing the effects of laminarization and the reenergization of eddy viscosity. The latter promotes the momentum transfer and correct reattachment prior to the fan face. Through distinct modules, the SA model has been modified to account for the effect of laminarization and separation induced transition. The modules have been implemented in the Rolls-Royce HYDRA computational fluid dynamic (CFD) solver. They have been validated over a number of experimental test cases involving laminarization and also surface roughness. The validated modules are finally applied in unsteady Reynolds-averaged Navier–Stokes (URANS) mode to flow around an engine intake and comparisons made with measurements. Encouraging agreement is found and hence advances made towards a more reliable intake design framework.

scholarly journals Functional design of sonotrodes for deep-drawing of cardboard

BioResources ◽  
2020 ◽  
Vol 15 (2) ◽  
pp. 2763-2773
Author(s):  
Albrecht Löwe ◽  
Anke Nikowski ◽  
Marek Hauptmann
Keyword(s):  
Surface Roughness ◽  
Deep Drawing ◽  
Vibration Mode ◽  
Influencing Factor ◽  
Vertical Vibration ◽  
Material Surface ◽  
Drawing Process ◽  
Functional Design ◽  
Shape Deviation ◽  
The One

The functional design of ultrasonic sonotrodes for deep-drawing is considered. The achievable stability, shape deviation, and surface roughness of deep-drawn cups were determined as a function of the vibration mode, the vibration amplitude, and the contact pressure as it occurs in the gap between the tools. Because the development of sonotrodes is complex and expensive, substitute experiments were conducted that allowed the cup parameters to be determined even without the manufacture of numerous sonotrodes, thus minimizing the effort involved. The results showed that the vibration mode, which determines the angle at which the vibration hits the material surface, is the most important influencing factor. The best way to increase stability and reduce shape deviation and surface roughness is to use an oscillation that hits the material surface perpendicularly during the entire deep-drawing process. With perpendicular vibration, the strength of the cup wall increased up to 200% compared to the one produced without ultrasound. The surface roughness could be reduced to 50% with the vertical vibration compared to without ultrasonic support.

Modular Turbulence Modelling Applied to an Engine Intake

2013 ◽  
Author(s):  
Ugochukwu R. Oriji ◽  
Paul G. Tucker
Keyword(s):  
Surface Roughness ◽  
Richardson Number ◽  
Eddy Viscosity ◽  
Fluid Dynamic ◽  
Test Cases ◽  
Laminar Separation ◽  
Streamline Curvature ◽  
Flow Features ◽  
Unsteady Rans ◽  
The One

The one equation Spalart Allamaras (SA) turbulence model in an extended modular form is employed for the prediction of cross wind flow around the lip of a 90 degree sector of an intake with and without surface roughness. The flow features around the lip are complex. There exists a region of high streamline curvature. For this the Richardson number would suggest complete degeneration to laminar flow. Also there are regions of high favourable pressure gradient (FPG) sufficient to laminarize a turbulent boundary layer (BL). This is all terminated by a shock and followed by a laminar separation. Under these severe conditions, the SA model is insensitive to capturing the effects of laminarization and the reenergization of eddy viscosity which promotes the momentum transfer and correct reattachment prior to the fan face. Through distinct modules, the SA model has been modified to account for the effect of laminarization and separation induced transition. The SA modules have been implemented in Rolls-Royce HYDRA Computational Fluid Dynamic (CFD) solver. They have been validated over a number of experimental test cases involving laminarization and also surface roughness. The validated modules are finally applied in unsteady RANS mode to flow around an engine intake and comparisons made with measurements. Encouraging agreement is found and hence advances made towards a more reliable intake design framework.

scholarly journals Deep Learning Approach for Vibration Signals Applications

Sensors ◽  
2021 ◽  
Vol 21 (11) ◽  
pp. 3929
Author(s):  
Han-Yun Chen ◽  
Ching-Hung Lee
Keyword(s):  
Surface Roughness ◽  
Tool Wear ◽  
Parameters Optimization ◽  
Frequency Spectra ◽  
Vibration Signals ◽  
Bearing Faults ◽  
Time Frequency ◽  
And Performance ◽  
The One ◽  
Short Time

This study discusses convolutional neural networks (CNNs) for vibration signals analysis, including applications in machining surface roughness estimation, bearing faults diagnosis, and tool wear detection. The one-dimensional CNNs (1DCNN) and two-dimensional CNNs (2DCNN) are applied for regression and classification applications using different types of inputs, e.g., raw signals, and time-frequency spectra images by short time Fourier transform. In the application of regression and the estimation of machining surface roughness, the 1DCNN is utilized and the corresponding CNN structure (hyper parameters) optimization is proposed by using uniform experimental design (UED), neural network, multiple regression, and particle swarm optimization. It demonstrates the effectiveness of the proposed approach to obtain a structure with better performance. In applications of classification, bearing faults and tool wear classification are carried out by vibration signals analysis and CNN. Finally, the experimental results are shown to demonstrate the effectiveness and performance of our approach.

scholarly journals On the Two-phase Fractional Stefan Problem

2020 ◽  
Vol 20 (2) ◽  
pp. 437-458 ◽  
Author(s):  
Félix del Teso ◽  
Jørgen Endal ◽  
Juan Luis Vázquez
Keyword(s):  
Free Boundary ◽  
Stefan Problem ◽  
Free Boundary Problems ◽  
Classical Problem ◽  
Nonlocal Diffusion ◽  
Two Phase ◽  
Boundary Problems ◽  
Numerical Studies ◽  
The One ◽  
Evolution Type

AbstractThe classical Stefan problem is one of the most studied free boundary problems of evolution type. Recently, there has been interest in treating the corresponding free boundary problem with nonlocal diffusion. We start the paper by reviewing the main properties of the classical problem that are of interest to us. Then we introduce the fractional Stefan problem and develop the basic theory. After that we center our attention on selfsimilar solutions, their properties and consequences. We first discuss the results of the one-phase fractional Stefan problem, which have recently been studied by the authors. Finally, we address the theory of the two-phase fractional Stefan problem, which contains the main original contributions of this paper. Rigorous numerical studies support our results and claims.

scholarly journals Deformation-Induced Roughening by Contact Compression in the Presence of Oils with Different Viscosity: Experiment and Numerical Simulation

2020 ◽  
Vol 68 (4) ◽  
Author(s):  
Grzegorz Starzynski ◽  
Ryszard Buczkowski ◽  
Bartlomiej Zylinski
Keyword(s):  
Numerical Simulation ◽  
Surface Roughness ◽  
Smooth Surface ◽  
Steel Sample ◽  
Normal Contact ◽  
Contact Loading ◽  
Uniaxial Stretching ◽  
Structure Interaction ◽  
Finite Element Calculations ◽  
Similarities And Differences

AbstractThe aim of the work is to show both the similarities and differences in the formation of deformation-induced roughness in contact compression in the presence of oil and the problem of free surface roughing during uniaxial stretching in a plastic area. The relationships between changes in the roughness are caused by the deformation of the sample and the viscosity of oil at the contact area. It has been shown that normal contact loading with the presence of oil initially leads to an increase in surface roughness, then to its smoothening. The results of the experimental research have been compared with numerical simulation made using FSI (Fluid Structure Interaction) and ABAQUS systems. Using finite element calculations, it was possible to explain the phenomenon of roughness formation on the surface of a smooth steel sample. The changes in the structure of the smooth surface resulting from compression in the presence of oil are caused by the rotation and deformation of surface grains. The roughness of this structure is dependent on the viscosity of oil: the more viscous the liquid is, the rougher texture is formed.

Large-Eddy Simulation of Roughened NACA65 Compressor Cascade

2017 ◽  
Author(s):  
Jongwook Joo ◽  
Gorazd Medic ◽  
Om Sharma
Keyword(s):  
Surface Roughness ◽  
Large Eddy Simulations ◽  
Surface Imaging ◽  
Potential Solution ◽  
Discrete Elements ◽  
Compressor Cascade ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Rans Modeling ◽  
The One

Large eddy simulations over a NACA65 compressor cascade with roughness were performed for multiple roughness heights. The experiments show flow separation as airfoil roughness is increased. In LES computations, surface roughness was represented by regularly arranged discrete elements using guidelines from Schlichting. Results from wall-resolved LES indicate that specifying an equivalent sandgrain roughness height larger than the one in experiments is required to reproduce the same effects observed in experiments. This highlights the persisting uncertainty with matching the experimental roughness geometry in LES computations, pointing towards surface imaging and digitization as a potential solution. Some initial analysis of flow physics has been conducted with the aim of guiding the RANS modeling for roughness.

Capillary Forces Described by Effective Contact Angle Distributions via Simulations of the Centrifuge Technique

MRS Advances ◽  
2016 ◽  
Vol 1 (31) ◽  
pp. 2237-2245
Author(s):  
Myles Thomas ◽  
Elizabeth Krenek ◽  
Stephen Beaudoin
Keyword(s):  
Surface Roughness ◽  
Contact Angle ◽  
Smooth Surface ◽  
Adhesion Force ◽  
Capillary Forces ◽  
Angle Distribution ◽  
Particle Adhesion ◽  
Multiple Factors ◽  
Effective Contact ◽  
Condensed Moisture

ABSTRACTUnderstanding particle adhesion is vital to any industry where particulate systems are involved. There are multiple factors that affect the strength of the adhesion force, including the physical properties of the interacting materials and the system conditions. Surface roughness on the particles and the surfaces to which they adhere, including roughness at the nanoscale, is critically important to the adhesion force. The focus of this work is on the capillary force that dominates the adhesion whenever condensed moisture is present. Theoretical capillary forces were calculated for smooth particles adhered to smooth and rough surfaces. Simulations of the classical centrifuge technique used to describe particle adhesion to surfaces were performed based on these forces. A model was developed to describe the adhesion of the particles to the rough surface in terms of the adhesion to a smooth surface and an ‘effective’ contact angle distribution.

scholarly journals and nature, a complex relationship

2020 ◽  
Vol 13 (26) ◽  
pp. 73-78
Author(s):  
Maria Antonietta Maria Antonietta Sbordone ◽  
Barbara Barbara Pizzicato
Keyword(s):  
Biological Sciences ◽  
Technological Innovation ◽  
Design Thinking ◽  
Point Of View ◽  
The Other ◽  
Complex Relationship ◽  
Other Hand ◽  
Evolutionary Line ◽  
Man And Nature ◽  
The One

Over the course of its history, design has never lost sight of nature as a term of comparison, sometimes taking from it, sometimes moving away from it. To investigate the complex relationship between the two terms, design and nature, we cannot ignore the evolution of man and how it has been profoundly influenced by technological innovation, which is the most evident result of science. Tracing an evolutionary line of design thinking, a double trajectory can be registered: on the one hand the tension towards progress and the myth of the machine, on the other hand the idea of a harmonious co-evolution with nature and the need to be reconnected with it. Besides, it is progress that allows mankind to thoroughly investigate natural mechanisms and make them their own. Contemporary design, autonomous but at the same time increasingly interdisciplinary, has got blurred boundaries which intersect with the most advanced fields of biological sciences. This evolution has opened up a whole new field of investigation that multiplies the opportunities of innovation, especially from a sustainability-oriented point of view. Today the dramatic breaking of the balance between man and nature has turned into the concept of permanent emergency, which is now matter of greatest interest for design, a design that attempts to react, mend, adapt to change in an authentically resilient way.

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