scholarly journals Pulsatile flow in ventricular catheters for hydrocephalus

2017 ◽  
Vol 375 (2096) ◽  
pp. 20160294 ◽  
Author(s):  
Á. Giménez ◽  
M. Galarza ◽  
U. Thomale ◽  
M. U. Schuhmann ◽  
J. Valero ◽  
...  
Keyword(s):  
Boundary Conditions ◽  
Computational Study ◽  
Three Dimensional ◽  
Mathematical Methods ◽  
Basic Principles ◽  
Heart Beating ◽  
Ventricular Catheters ◽  
Flow Through ◽  
Three Dimensional Models ◽  
Previous Computational Study

The obstruction of ventricular catheters (VCs) is a major problem in the standard treatment of hydrocephalus, the flow pattern of the cerebrospinal fluid (CSF) being one important factor thereof. As a first approach to this problem, some of the authors studied previously the CSF flow through VCs under time-independent boundary conditions by means of computational fluid dynamics in three-dimensional models. This allowed us to derive a few basic principles which led to designs with improved flow patterns regarding the obstruction problem. However, the flow of the CSF has actually a pulsatile nature because of the heart beating and blood flow. To address this fact, here we extend our previous computational study to models with oscillatory boundary conditions. The new results will be compared with the results for constant flows and discussed. It turns out that the corrections due to the pulsatility of the CSF are quantitatively small, which reinforces our previous findings and conclusions. This article is part of the themed issue ‘Mathematical methods in medicine: neuroscience, cardiology and pathology’.

STUDY OF OPTICS FOR LED LIGHT DEVICES AND METHODS OF ITS COMPUTER MODELING

2020 ◽  
pp. 27-31
Author(s):  
I. I. Bayneva ◽  
N. S. Komarov
Keyword(s):  
Computer Modeling ◽  
Three Dimensional ◽  
Simulation Method ◽  
Optical Systems ◽  
Mathematical Methods ◽  
Optical Elements ◽  
Led Light ◽  
Secondary Use ◽  
Three Dimensional Models ◽  
The Cost

The article discusses optical systems for LED lighting devices, the principles of the propagation of rays in lenses of various designs. Analyzed the features of the secondary use of the optical elements in the form of lenses and prisms for different LED emission patterns in space. Considered the features and problems of calculation of the secondary optical systems. Problems and prospects of application are considered, research and computer modeling of optics, which is used to form the required light distribution in LED light devices. Computer modeling technologies and the mathematical methods that underlie them determine the possibility of developing such optical systems in lighting installations. The article considers the numerical Monte Carlo simulation method, which allows one to organize ray tracing modeling in optical systems. The TracePro software package for modeling and research of lighting devices and their optical elements allows you to automate the stage of their calculation and design, this significantly reduces the cost of developing new products. The prototyping of three-dimensional models of lens systems opens up great opportunities for manufacturers of optics for LEDs, allows research on prototypes planned for production of serial products.

Study of the Effect of Boundary Conditions on Residual Stresses in Welding Using Element Birth and Element Movement Techniques

2003 ◽  
Vol 125 (4) ◽  
pp. 432-439 ◽  
Author(s):  
Ihab F. Z. Fanous ◽  
Maher Y. A. Younan ◽  
Abdalla S. Wifi
Keyword(s):  
Residual Stresses ◽  
Boundary Conditions ◽  
Three Dimensional ◽  
Welding Process ◽  
Computation Time ◽  
The Other ◽  
Two Dimensional ◽  
The Media ◽  
Three Dimensional Models ◽  
Element Movement

The structure in which the welding process is performed highly affects the residual stresses generated in the welding. This effect is simulated by choosing the appropriate boundary conditions in modeling the welding process. The major parameters of the boundary conditions are the method by which the base metal is being fixed and the amount of heat being applied through the torch. Other parameters may include the coefficients of thermal heat loss from the plate which may simulate the media in which the welding is taking place. In modeling the welding process, two-dimensional forms of approximation were developed in analyzing most of the models of such problem. Three-dimensional models analyzing the welding process were developed in limited applications due to its high computation time and cost. With the development of new finite element tools, namely the element movement technique developed by the authors, full three-dimensional analysis of the welding process is becoming in hand. In the present work, three different boundary conditions shall be modeled comparing their effect on the welding. These boundary conditions shall be applied to two models of the welding process: one using the element birth technique and the other using the element movement technique showing the similarity in their responses verifying the effectiveness of the latter being accomplished in a shorter time.

Three Dimensional Thermoacoustic Oscillation in a Premix Combustor

2001 ◽  
Author(s):  
S. Akamatsu ◽  
A. P. Dowling
Keyword(s):  
Boundary Conditions ◽  
Acoustic Waves ◽  
Linear Equations ◽  
Three Dimensional ◽  
Total System ◽  
Mean Flow ◽  
Modal Coupling ◽  
Rate Of Heat Release ◽  
Flow Through ◽  
Combustion Processes

A theory is developed to describe high frequency three-dimensional thermoacoustic waves in a simplified geometry representing a typical premix combustor. The theory considers linear modes of frequency ω and circumferential mode number m i.e. proportional to eiωt+imθ. The radial and axial dependence is determined for a cylindrical combustor. Simple geometries are investigated systematically to analyze the effect of different inlet boundary conditions to the combustion chamber on the frequency of oscillation and on the susceptibility to instability, both near and away from the cut-off frequencies. The model includes a one-dimensional mean flow, radial mode coupling and idealized combustion processes, which are added in stages to build up an understanding of the complicated acoustics of the premix combustor geometry. It is demonstrated that the flow through the premix ducts provides a frequency-dependent boundary condition at combustor inlet and causes modal coupling. Generalized linear equations of conservation of mass, momentum and energy, together with boundary conditions, are solved to identify the eigenfrequencies, ω, of the total system. Then Real ω determines the frequency of the oscillation, while Imaginary ω indicates the growth rate of the disturbance. It is found that strong resonant peaks in the pressure waves exist close to the cut-off condition for acoustic waves and that the relationship between the unsteady rate of heat release and the flow significantly influences the instability of oscillation.

Modeling Thermal Microspreading Resistance in Via Arrays

2016 ◽  
Vol 138 (1) ◽  
Author(s):  
Michael Fish ◽  
Patrick McCluskey ◽  
Avram Bar-Cohen
Keyword(s):  
Boundary Conditions ◽  
Effective Properties ◽  
Three Dimensional ◽  
Thermal Characteristics ◽  
Simulation Software ◽  
Electronic Packages ◽  
Isothermal Boundary ◽  
Unit Cells ◽  
Flow Through ◽  
Management Techniques

As thermal management techniques for three-dimensional (3D) chip stacks and other high-power density electronic packages continue to evolve, interest in the thermal pathways across substrates containing a multitude of conductive vias has increased. To reduce the computational costs and time in the thermal analysis of through-layer via (TXV) structures, much research to date has focused on defining effective anisotropic thermal properties for a pseudohomogeneous medium using isothermal boundary conditions. While such an approach eliminates the need to model heat flow through individual vias, the resulting properties are found to depend on the specific boundary conditions applied to a unit TXV cell. More specifically, effective properties based on isothermal boundary conditions fail to capture the local “microspreading” resistance associated with more realistic heat flux distributions and local hot spots on the surface of these substrates. This work assesses how the thermal microspreading resistance present in arrays of vias in interposers, substrates, and other package components can be properly incorporated into the modeling of these arrays. We present the conditions under which spreading resistance plays a major role in determining the thermal characteristics of a via array and propose methods by which designers can both account for the effects of microspreading resistance and mitigate its contribution to the overall thermal behavior of such substrate–via systems. Finite element modeling (FEM) of TXV unit cells is performed using commercial simulation software (ansys).

Effect of Pitch Chord Ratio and Side Wall Expansion Angle on Flow Through Vane Swirlers

2006 ◽  
Author(s):  
R. Thundil Karuppa Raj ◽  
V. Ganesan
Keyword(s):  
Computational Study ◽  
Three Dimensional ◽  
Flow Characteristics ◽  
Side Wall ◽  
Reynolds Stress Model ◽  
Swirl Flow ◽  
Expansion Angle ◽  
Turbulence Effects ◽  
Flow Field Characteristics ◽  
Flow Through

This paper is concerned with the computational study of steady flow through the vane swirlers. Swirl flow field characteristics for various pitch chord ratio (s/c) at swirler mean radius are studied for a 45° vane swirler under both sudden and gradual expansions with side-wall expansion angles of 90° and 45° respectively. In the computational study the geometry and meshing is done using pre-processor GAMBIT. Three-dimensional flow within the geometry and through the swirler has been simulated by solving the appropriate governing equations viz. conservation of mass and momentum using FLUENT code. Turbulence effects are taken care of by the Reynolds stress model and shear stress transport k-ω model for high swirls and standard k-ε model for low and medium swirls. The effect of pitch to chord ratio (s/c) on flow characteristics have been studied. The predicted results are validated with the experimental data available in the literature for s/c ratio of 1. The numerical results of axial velocity profiles downstream of the swirler at various axial planes are found to be in close agreement with the experimental results. It is found that the s/c ratio of 1 provides good turning efficiency.

A Numerical Analysis of Bidirectional Ducted Tidal Turbines in Yawed Flow

2013 ◽  
Vol 47 (4) ◽  
pp. 23-35 ◽  
Author(s):  
Clarissa S.K. Belloni ◽  
Richard H.J. Willden ◽  
Guy T. Houlsby
Keyword(s):  
Computational Study ◽  
Three Dimensional ◽  
Turbine Rotor ◽  
Navier Stokes ◽  
External Diameter ◽  
Tidal Turbines ◽  
Turbine Performance ◽  
Ducted Turbine ◽  
Flow Through ◽  
Porous Disc

AbstractThe paper presents a computational study of ducted bidirectional tidal turbines using three-dimensional Reynolds-averaged Navier-Stokes simulations. We model the outer duct as a solid body and use a porous disc to represent the turbine rotor, a simplification that captures changes in linear momentum and thus the primary interaction of the turbine with the flow through and around the duct while greatly reducing computational complexity. The duct is modeled using linearly converging and diverging sections and a short straight pipe at the duct throat.We investigate the performance of bare and ducted turbines and relate these to the flows through the devices. For the ducted turbine under investigation, we show a substantial decrease in power generated relative to a bare turbine of diameter equal to the external diameter of the duct. In the case of ducted turbines with concave duct exteriors, we observe two external flow regimes with increasing turbine thrust: nozzle-contoured and separation dominated regimes. Maximum power occurs within the separation dominated flow regime due to the additional channel blockage created by the external separation.The ducts of ducted tidal turbines have been argued to provide a flow straightening effect, allowing modest yaw angles to be readily accommodated. We present a comparison of bare and ducted turbine performance in yawed flow. We show that while bare turbine performance decreases in yawed flow, ducted turbine performance increases. This is due to both a flow straightening effect and also an increase in effective blockage as ducts present greater projected frontal area when approached nonaxially.

The Calculation of Three Dimensional Viscous Flow Through Multistage Turbomachines

1990 ◽  
Author(s):  
J. D. Denton
Keyword(s):  
Boundary Conditions ◽  
Unsteady Flow ◽  
Viscous Flow ◽  
Calculation Method ◽  
Three Dimensional ◽  
Mixing Process ◽  
Three Dimensional Flow ◽  
Flow Calculation ◽  
Dimensional Flow ◽  
Flow Through

The extension of a well established three dimensional flow calculation method to calculate the flow through multiple turbomachinery blade rows is described in this paper. To avoid calculating the unsteady flow, which is inherent in any machine containing both rotating and stationary blade rows, a mixing process is modelled at a calculating station between adjacent blade rows. The effects of this mixing on the flow within the blade rows may be minimised by using extrapolated boundary conditions at the mixing plane.

Streamwise Computation of Three-Dimensional Flows Using Two Stream Functions

1993 ◽  
Vol 115 (2) ◽  
pp. 233-238 ◽  
Author(s):  
M. S. Greywall
Keyword(s):  
Boundary Conditions ◽  
Stream Function ◽  
Potential Flow ◽  
Three Dimensional ◽  
Streamwise Velocity ◽  
Spatial Coordinate ◽  
Independent Variables ◽  
Dependent Variables ◽  
Stream Functions ◽  
Flow Through

An approach to compute three-dimensional flows using two stream functions is presented. The independent variables used are χ, a spatial coordinate, and ξ and η, values of stream functions along two sets of suitably chosen intersecting stream surfaces. The dependent variables used are the streamwise velocity, and two functions that describe the stream surfaces. Since the value of a stream function is constant along the solid boundaries, this choice of variables makes it easy to satisfy the boundary conditions. To illustrate the approach, computations of incompressible potential flow through a circular-to-rectangular transition duct are also presented.

scholarly journals Virtual Reality Technologies and Universal 3D Reconstruction Interface Development

2020 ◽  
pp. 192-205
Author(s):  
Maxim Mironenko ◽  
Viktor Chertopolokhov ◽  
Margarita Belousova
Keyword(s):  
Virtual Reality ◽  
Motion Tracking ◽  
Tracking System ◽  
Three Dimensional ◽  
Urban Landscapes ◽  
Mathematical Methods ◽  
Historical Sources ◽  
Reconstruction Process ◽  
Software And Hardware ◽  
Three Dimensional Models

The article summarizes the results of a two-year study of the issues related to the virtual reality and augmented reality technologies use to virtually reconstruct Moscow Bely Gorod in the 16th-18th centuries. The authors describe mathematical methods, software and hardware which grant access to the historical reconstruction of historical urban landscapes. An important feature of the reconstruction is the source verification module which was used to construct three-dimensional models of the landscape, buildings and the general scenery. The article names the basic principles which the verification module and its interface are based on and considers some optimum problems solved when constructing the interface. The project uses a hybrid motion tracking system as a combination of optical and inertial data. The archival sources used in the reconstruction process are presented in the virtual environment by means of a 3D graphical user interface for the virtual reality. The information displayed is generated from the database of historical sources which includes information about the urban development and individual buildings of Bely Gorod, their parts, location, purpose, owners and construction date. The database contains both text and graphic historical sources. The results obtained also include new algorithms, software and hardware systems as well as the experiment results. 

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