scholarly journals NUMERICAL ANALYSIS OF WAVE AND NEARSHORE CURRENT FIELDS AROUND LOW-CRESTED PERMEABLE DETACHED BREAKWATERS

2012 ◽  
Vol 1 (33) ◽  
pp. 80
Author(s):  
Takeshi Nishihata ◽  
Yoshimitsu Tajima ◽  
Shinji Sato
Keyword(s):  
Anisotropic Diffusion ◽  
Good Accuracy ◽  
Friction Model ◽  
Diffusion Type ◽  
Reflection And Transmission ◽  
Turbulent Friction ◽  
Wave Fields ◽  
Friction Term ◽  
Wave Breaking Model ◽  
Transmission Capability

A Boussinesq type numerical model was developed which can simulate both wave fields and current fields around permeable detached breakwaters. The validity of the model was verified through measurements of waves and nearshore currents in hydraulic experiments investigating reflection and transmission capability. The porosity of the structure was accounted by a friction term incorporating turbulent resistance. The combination of turbulent friction model and anisotropic diffusion type wave breaking model was found to reproduce wave fields around the detached breakwaters and nearshore current fields behind the structures with a good accuracy.

Reflection and transmission responses in a layered transversely isotropic medium with horizontal symmetry axis

Geophysics ◽  
2019 ◽  
Vol 84 (3) ◽  
pp. C143-C157 ◽  
Author(s):  
Song Jin ◽  
Alexey Stovas
Keyword(s):  
Good Accuracy ◽  
Symmetry Axis ◽  
Local Property ◽  
Transversely Isotropic ◽  
Weak Anisotropy ◽  
Reflection And Transmission ◽  
Numerical Tests ◽  
Transversely Isotropic Media ◽  
Horizontal Symmetry ◽  
Isotropic Media

Seismic wave reflection and transmission (R/T) responses characterize the subsurface local property, and the widely spread anisotropy has considerable influences even at small incident angles. We have considered layered transversely isotropic media with horizontal symmetry axes (HTI), and the symmetry axes were not restricted to be aligned. With the assumption of weak contrast across the interface, linear approximations for R/T coefficients normalized by vertical energy flux are derived based on a simple layered HTI model. We also obtain the approximation with the isotropic background medium under an additional weak anisotropy assumption. Numerical tests illustrate the good accuracy of the approximations compared with the exact results.

scholarly journals Approximate approach for improving pressure attenuation accuracy during hydraulic transients

2021 ◽  
Author(s):  
Chao Yu ◽  
Xiaodong Yu ◽  
Lei Zhang ◽  
Bhusan Neupane ◽  
Jian Zhang
Keyword(s):  
Reynolds Number ◽  
Water Hammer ◽  
Friction Model ◽  
Pipe Network ◽  
Network Systems ◽  
Initial Flow ◽  
Friction Term ◽  
Smooth Pipe ◽  
The Relationship ◽  
Good Agreement

Abstract The quasi-steady friction model is generally adopted in water hammer simulation in pipe network systems, which cannot accurately reflect the attenuation of pressure, while the existing unsteady friction model is challenging to use in complex pipe network systems. In this study, a convenient method for treating the friction term is proposed based on the Moody diagram. The attenuation process of water hammer pressure can be accurately reflected by reading the relationship curve between Reynolds number and the Darcy friction factor in the pipeline transient process. Combined with the classical water hammer experiment and the long pipe valve closing experiment in our laboratory, the accuracy of this model is verified, and the influence of absolute roughness (e) and Reynolds number (Re) on the model was analyzed as well. The results show that the pressure attenuation using the Method of Characteristics (MOC) and the proposed friction model has a good agreement with the experimental data. The absolute roughness has little influence on the results in hydraulically smooth pipe, while the minimum Reynolds number has a significant influence. When selecting the minimum Reynolds number, 2% ∼ 5% of the initial flow rate is recommended for calculation.

scholarly journals Role of friction terms in two-dimensional modelling of dense snow avalanches

2020 ◽  
Author(s):  
Marcos Sanz-Ramos ◽  
Ernest Bladé ◽  
Pere Oller ◽  
Carlos A. Andrade ◽  
Glòria Furdada
Keyword(s):  
Friction Model ◽  
Snow Avalanches ◽  
Turbulent Friction ◽  
Newtonian Flows ◽  
Wide Range ◽  
Avalanche Dynamics ◽  
Long Tails ◽  
Solid Friction ◽  
Upwind Discretization ◽  
The Moment

Abstract. Voellmy–Salm friction model is one of the most extensively used theories for assessing the frictional terms of the equations that describe the motion of non-Newtonian flows such as snow avalanches. Based on the Coulomb- and turbulent-type friction, this model has been implemented in numerical tools for computation of snow avalanche dynamics based on the Shallow Water Equations (SWE). The range of the Voellmy parameters has been discussed widely, focusing mainly on the required values for achieving good results for the description of the moment and position of the avalanche when it stops. However, effects of parameters on the SWE terms, and their physical interpretation have not been investigated sufficiently. This work focuses on analysing the effects of the Voellmy–Salm parameters and cohesion on the avalanche characteristics and evolution of the new SWE-based numerical model Iber. In the numerical scheme, an upwind discretization was used for the solid friction and cohesion terms, while a centred one was used for the turbulent friction. Results show that the Voellmy–Salm model dominates the avalanche dynamics and the cohesion model allows the representation of long tails, whereas the friction and cohesion parameters may vary within a wide range.

Modeling and Identification of Friction Behaviors of Hydraulic Forging Press Machine

2013 ◽  
Vol 328 ◽  
pp. 77-83
Author(s):  
Qing Pan ◽  
Ming Hui Huang ◽  
Yi Bo Li
Keyword(s):  
Good Accuracy ◽  
Friction Model ◽  
Lugre Model ◽  
Modified Model ◽  
Identification Method ◽  
Lugre Friction Model ◽  
Lugre Friction ◽  
Forging Press

A novel modified LuGre friction model is proposed by taking pressure of the cylinders into consideration. And a practical identification method to estimate the parameters associated with the modified friction model is presented. The validity of the modified model is investigated experimentally. It is shown that the modified LuGre model can demonstrate the comprehensive friction behaviors of the forging machine with a fairly good accuracy.

Wave Interaction with an Emerged Porous Media

2014 ◽  
Vol 6 (5) ◽  
pp. 680-692 ◽  
Author(s):  
I. Magdalena ◽  
S. R. Pudjaprasetya ◽  
L. H. Wiryanto
Keyword(s):  
Porous Media ◽  
Wave Reflection ◽  
Wave Interaction ◽  
Staggered Grid ◽  
Transmission Curve ◽  
Reflection And Transmission ◽  
Reflection And Transmission Coefficient ◽  
Friction Term ◽  
Horizontal Flux ◽  
Volume Method

AbstractIn this paper, we study wave interaction with an emerged porous media. The governing equation is shallow water equations with a friction term of the linearized Dupuit-Forcheimer’s formula. From the continuity of surface and horizontal flux, we derived the wave reflection and transmission coefficient formulas. They are similar with the corresponding formulas of the submerged solid bar breakwater. We solve the equations numerically using finite volume method on a staggered grid. The numerical wave reduction in the porous media confirms the analytical wave transmission curve.

Parabolas from Reconstructed Surfaces Observed in Convergent-Beam RHEED Patterns

1990 ◽  
Vol 48 (2) ◽  
pp. 398-399
Author(s):  
M. Gajdardziska-Josifovska
Keyword(s):  
Electron Microscopy ◽  
High Energy ◽  
Two Dimensional ◽  
High Energy Electron ◽  
Reflection And Transmission ◽  
Experimental Diffraction Pattern ◽  
Surface Resonance ◽  
Reconstructed Surfaces ◽  
Reflection Electron Microscopy ◽  
Convergent Beam

Parabolas have been observed in the reflection high-energy electron diffraction (RHEED) patterns from surfaces of single crystals since the early thirties. In the last decade there has been a revival of attempts to elucidate the origin of these surface parabolas. The renewed interest stems from the need to understand the connection between the parabolas and the surface resonance (channeling) condition, the latter being routinely used to obtain higher intensity in reflection electron microscopy (REM) images of surfaces. Several rather diverging descriptions have been proposed to explain the parabolas in the reflection and transmission Kikuchi patterns. Recently we have developed an unifying general treatment in which the parabolas are shown to be K-lines of two-dimensional lattices. Here we want to review the main features of this description and present an experimental diffraction pattern from a 30° MgO (111) surface which displays parabolas that can be attributed to the surface reconstruction.

Enhanced Brady-Tachy Heart Automotive (BT-Heartomotive) Device for Heart Rate Monitoring during Driving

2020 ◽  
Vol 17 (1) ◽  
pp. 7599-7606
Author(s):  
M. A. H. Mohd Adib ◽  
N. H. M. Hasni
Keyword(s):  
Heart Rate ◽  
Mobile Applications ◽  
Good Accuracy ◽  
Rate Measurement ◽  
Road Accidents ◽  
Heart Rate Monitoring ◽  
Physical Conditions ◽  
Car Accidents ◽  
Heart Rate Level ◽  
Main Components

Driving with brady-tachy syndrome is one of the main causes of car accidents. In order to prevent drivers from brady-tachy driving, there is a strong demand for driver monitoring systems. Other than problems in driving attitudes and skills, road accidents are also caused by uncontrollable factors such as medical conditions and drowsiness. These factors can be avoided by having early detection. Therefore, the brady-tachy heart automotive so-called BT-Heartomotive device is developed. This BT-Heartomotive device can detect early signs of drowsiness and health problems by measuring the heart rate of the drivers during driving. The device also could use the data to send an alert to the passengers that they’re in precaution. The device shows a good accuracy in the detection of the heart rate level. The device comprised three main components; wristband, monitor and integrated mobile applications. Heart rate measurement can reveal a lot about the physical conditions of an individual. The BT-Heartomotive device is simple, easy to use and automated.

Techniques for assessing the performance of circuit materials at microwave and millimetre-wave frequencies

2003 ◽  
Vol 783 ◽  
Author(s):  
Charles E Free
Keyword(s):  
Loss Tangent ◽  
Good Accuracy ◽  
Low Cost ◽  
Resonant Cavity ◽  
New Technique ◽  
Millimetre Wave ◽  
A New Technique

This paper discusses the techniques that are available for characterising circuit materials at microwave and millimetre wave frequencies. In particular, the paper focuses on a new technique for measuring the loss tangent of substrates at mm-wave frequencies using a circular resonant cavity. The benefits of the new technique are that it is simple, low cost, capable of good accuracy and has the potential to work at high mm-wave frequencies.

Rubber–Road Contact: Comparison of Physics-Based Theory and Indoor Experiments

2016 ◽  
Vol 44 (3) ◽  
pp. 150-173 ◽  
Author(s):  
Mehran Motamedi ◽  
Saied Taheri ◽  
Corina Sandu
Keyword(s):  
Rough Surface ◽  
Practical Importance ◽  
Surface Profile ◽  
Surface Characteristics ◽  
Mechanical Analysis ◽  
Friction Model ◽  
Rubber Friction ◽  
Optical Profilometer ◽  
Viscoelastic Modulus ◽  
Longitudinal Slip

ABSTRACT For tire designers, rubber friction is a topic of pronounced practical importance. Thus, development of a rubber–road contact model is of great interest. In this research, to predict the effectiveness of the tread compound in a tire as it interacts with the pavement, the physics-based multiscale rubber-friction theories developed by B. Persson and M. Klüppel were studied. The strengths of each method were identified and incorporated into a consolidated model that is more comprehensive and proficient than any single, existing, physics-based approach. In the present work, the friction coefficient was estimated for a summer tire tread compound sliding on sandpaper. The inputs to the model were the fractal properties of the rough surface and the dynamic viscoelastic modulus of rubber. The sandpaper-surface profile was measured accurately using an optical profilometer. Two-dimensional parameterization was performed using one-dimensional profile measurements. The tire tread compound was characterized via dynamic mechanical analysis. To validate the friction model, a laboratory-based, rubber-friction test that could measure the friction between a rubber sample and any arbitrary rough surface was designed and built. The apparatus consisted of a turntable, which can have the surface characteristics of choice, and a rubber wheel in contact with the turntable. The wheel speed, as well as the turntable speed, could be controlled precisely to generate the arbitrary values of longitudinal slip at which the dynamic coefficient of friction was measured. The correlation between the simulation and the experimental results was investigated.

Sign in / Sign up

Export Citation Format

Share Document