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Article
Publication date: 28 April 2014

Seth Dillard, James Buchholz, Sarah Vigmostad, Hyunggun Kim and H.S. Udaykumar

The performance of three frequently used level set-based segmentation methods is examined for the purpose of defining features and boundary conditions for image-based…

Abstract

Purpose

The performance of three frequently used level set-based segmentation methods is examined for the purpose of defining features and boundary conditions for image-based Eulerian fluid and solid mechanics models. The focus of the evaluation is to identify an approach that produces the best geometric representation from a computational fluid/solid modeling point of view. In particular, extraction of geometries from a wide variety of imaging modalities and noise intensities, to supply to an immersed boundary approach, is targeted.

Design/methodology/approach

Two- and three-dimensional images, acquired from optical, X-ray CT, and ultrasound imaging modalities, are segmented with active contours, k-means, and adaptive clustering methods. Segmentation contours are converted to level sets and smoothed as necessary for use in fluid/solid simulations. Results produced by the three approaches are compared visually and with contrast ratio, signal-to-noise ratio, and contrast-to-noise ratio measures.

Findings

While the active contours method possesses built-in smoothing and regularization and produces continuous contours, the clustering methods (k-means and adaptive clustering) produce discrete (pixelated) contours that require smoothing using speckle-reducing anisotropic diffusion (SRAD). Thus, for images with high contrast and low to moderate noise, active contours are generally preferable. However, adaptive clustering is found to be far superior to the other two methods for images possessing high levels of noise and global intensity variations, due to its more sophisticated use of local pixel/voxel intensity statistics.

Originality/value

It is often difficult to know a priori which segmentation will perform best for a given image type, particularly when geometric modeling is the ultimate goal. This work offers insight to the algorithm selection process, as well as outlining a practical framework for generating useful geometric surfaces in an Eulerian setting.

Details

Engineering Computations, vol. 31 no. 3
Type: Research Article
ISSN: 0264-4401

Keywords

Article
Publication date: 24 March 2021

Reza Fallahtafti and Mohammadjavad Mahdavinejad

Natural ventilation is an environmentally friendly effective way of improving thermal comfort and the quality of indoor conditions if applied properly. This study aims to…

268

Abstract

Purpose

Natural ventilation is an environmentally friendly effective way of improving thermal comfort and the quality of indoor conditions if applied properly. This study aims to investigate the physical mechanism of the air movement and also the influence of building geometry in a cross-ventilated room through a parametric study of window geometrical characteristics using computational fluid dynamics.

Design/methodology/approach

Momentum and continuity equations are solved by the control volume method using a commercially available software. Standard kɛ turbulence model is employed to simulate the incompressible airflow and SIMPLE algorithm to solve the conservation equations. Mean air velocity magnitude is measured at three different surfaces of different heights, and the effect of incoming wind velocity inside the building is studied.

Findings

The research concluded that window hood and sill projections reduce indoor wind velocity magnitude, play a major role in incoming wind direction and thus have a crucial impact on wind circulation and indoor air quality.

Social implications

The paper has evaluated redesigning of a both practical and ornamental architectural element named Palekaneh, which is found in many historical buildings in several hot places in the world. Its optimal design could increase indoor natural ventilation quality and decrease a space's cooling load. Therefore, a new passive cooling architectural element could be re-introduced to the regions previously enjoying such ornaments. This is economically efficient because it eventually saves a considerable amount of energy in the long run and is socially important because of the revitalization of architectural identity.

Originality/value

The role of a building envelope's physical features, although being studied for solar absorption and daylight availability, has rarely been investigated for natural ventilation, especially in a small scale, thus making the paper novel in this regard. This provides a guideline for designers to assess the impact of their design on redirecting wind-induced natural ventilation the very early stages of design.

Details

Engineering, Construction and Architectural Management, vol. 28 no. 9
Type: Research Article
ISSN: 0969-9988

Keywords

Article
Publication date: 1 March 2004

Scott Johnson, John R. Williams and Benjamin Cook

The efficiency of a discrete element implementation relies on several factors, including the particle representation, neighbor‐sorting algorithm, contact resolution, and…

Abstract

The efficiency of a discrete element implementation relies on several factors, including the particle representation, neighbor‐sorting algorithm, contact resolution, and force generation. The focus of this paper is on the four‐arc approximation for an ellipsoid – a geometrical representation useful in simulations of large numbers of smoothly shaped particles. A new contact resolution algorithm based on the four‐arc approximation is presented, which takes advantage of the properties of the geometry to provide favorable empirical convergence properties compared with the method proposed earlier. Special attention is given to the software implementation of the algorithm, and a discussion of the computational efficiency of the algorithm is provided.

Details

Engineering Computations, vol. 21 no. 2/3/4
Type: Research Article
ISSN: 0264-4401

Keywords

Article
Publication date: 1 March 2004

Y.T. Feng and D.R.J. Owen

This paper proposes an energy‐based general polygon to polygon normal contact model in which the normal and tangential directions, magnitude and reference contact position…

Abstract

This paper proposes an energy‐based general polygon to polygon normal contact model in which the normal and tangential directions, magnitude and reference contact position of the normal contact force are uniquely defined. The model in its final form is simple and elegant with a clear geometric perspective, and also possesses some advanced features. Furthermore, it can be extended to a more complex situations and in particular, it may also provide a sound theoretical foundation to possibly unifying existing contact models for all types of (convex) objects.

Details

Engineering Computations, vol. 21 no. 2/3/4
Type: Research Article
ISSN: 0264-4401

Keywords

Article
Publication date: 8 May 2018

Kazuo Matsuura, Kotaro Matsui and Naoki Tani

This paper aims to investigate global pressure fluctuations in compressible transitional flows in a low-pressure turbine cascade because of variations in the free-stream…

Abstract

Purpose

This paper aims to investigate global pressure fluctuations in compressible transitional flows in a low-pressure turbine cascade because of variations in the free-stream turbulence and its interaction with the boundary layers.

Design/methodology/approach

Transition process resolving numerical simulations are performed with different types of inflow turbulence. The unsteady three-dimensional fully compressible Navier–Stokes equations are solved using a sixth-order compact difference and a tenth-order filtering method. First, simulations of both K-regime and bypass transitions are conducted for a flat plate boundary layer to validate the use of the filter in computing different transition routes. Second, computations of the cascade flows are conducted. Cases of no free-stream turbulence, isotropic free-stream turbulence of 5 per cent and wakes from an upstream cylinder are compared. For wakes, variations in wake trajectory depending on the cylinder blade relative position are also taken into account.

Findings

The different transition routes are successfully reproduced by the present method even with strong filtering. When feedback phenomena occur near the trailing edge, high-frequency oscillations dominate in the flow field. Low-frequency oscillations become dominant when the blade boundary layer becomes turbulent. Thus, the effects of the free-stream turbulence and its interaction with the boundary layer appear as changes in the global pressure fluctuation.

Originality/value

The free-stream turbulence qualitatively affects global pressure fluctuations, which become a medium to convey boundary-layer information away from the cascade.

Details

International Journal of Numerical Methods for Heat & Fluid Flow, vol. 28 no. 5
Type: Research Article
ISSN: 0961-5539

Keywords

Article
Publication date: 15 August 2019

Etienne Muller, Dominique Pelletier and André Garon

This paper aims to focus on characterization of interactions between hp-adaptive time-integrators based on backward differentiation formulas (BDF) and adaptive meshing…

Abstract

Purpose

This paper aims to focus on characterization of interactions between hp-adaptive time-integrators based on backward differentiation formulas (BDF) and adaptive meshing based on Zhu and Zienkiewicz error estimation approach. If mesh adaptation only occurs at user-supplied times and results in a completely new mesh, it is necessary to stop the time-integration at these same times. In these conditions, one challenge is to find an efficient and reliable way to restart the time-integration. The authors investigate what impact grid-to-grid interpolation errors have on the relaunch of the computation.

Design/methodology/approach

Two restart strategies of the time-integrator were used: one based on resetting the time-step size h and time-integrator order p to default values (used in the initial startup phase), and another designed to restart with the time-step size h and order p used by the solver prior to remeshing. The authors also investigate the benefits of quadratically interpolate the solution on the new mesh. Both restart strategies were used to solve laminar incompressible Navier–Stokes and the Unsteady Reynolds Averaged Naviers-Stokes (URANS) equations.

Findings

The adaptive features of our time-integrators are excellent tools to quantify errors arising from the data transfer between two grids. The second restart strategy proved to be advantageous only if a quadratic grid-to-grid interpolation is used. Results for turbulent flows also proved that some precautions must be taken to ensure grid convergence at any time of the simulation. Mesh adaptation, if poorly performed, can indeed lead to losing grid convergence in critical regions of the flow.

Originality/value

This study exhibits the benefits and difficulty of assessing both spatial error estimates and local error estimates to enhance the efficiency of unsteady computations.

Details

International Journal of Numerical Methods for Heat & Fluid Flow, vol. 29 no. 7
Type: Research Article
ISSN: 0961-5539

Keywords

Article
Publication date: 17 June 2019

Muhammad Raees Ul Haq, Hang Xu and Liang Zhao

The purpose of this study is to obtain the numerical as well as regularity results for the nonlinear elliptic set of equations arising in the study of fluid flow in…

Abstract

Purpose

The purpose of this study is to obtain the numerical as well as regularity results for the nonlinear elliptic set of equations arising in the study of fluid flow in microchannel induced by the pressure in the presence of interfacial electrokinetic effects.

Design/methodology/approach

For the numerical study, the authors implemented traditional FDM approach, and for the regularity results they used the classical energy estimates. The interfacial electrokinetic effects result in an additional source term in classical momentum equation, hence affecting the characteristics of the flow and heat transfer. The sinusoidal temperature variation is assumed on side walls.

Findings

The results were obtained for various combinations of physical parameters appearing in the governing equations. This study concludes that in the presence of electric double layer, the average heat transfer rate reduces along with larger values of Reynolds number. It is observed that the heat transfer increases with the increase in amplitude ratio and phase deviation. The flow behavior and heat transfer rate inside the microchannel are also strongly affected by the presence of κ (kappa).

Originality/value

To the best of the authors’ knowledge, the problem of heat transfer through microchannel in combination with sinusoidal temperature variation at boundary with electric double layer effects has not been considered previously. Hence, this paper focuses on the influence of the sinusoidal boundary temperature distributions on both sidewalls of a rectangular microchannel through parallel plates with electrokinetic effects on the pressure-driven laminar flow. In addition, a detailed mathematical analysis is also to be carried out to verify the regularity of this model with the proposed boundary conditions. The study used the classical energy method to get the regularity results.

Details

International Journal of Numerical Methods for Heat & Fluid Flow, vol. 29 no. 10
Type: Research Article
ISSN: 0961-5539

Keywords

Content available
Article
Publication date: 1 August 2001

Jon Rigelsford

31

Abstract

Details

Industrial Robot: An International Journal, vol. 28 no. 4
Type: Research Article
ISSN: 0143-991X

Article
Publication date: 30 August 2019

Wojciech Piotr Adamczyk, Marcin Gorski, Ziemowit Ostrowski, Ryszard Bialecki, Grzegorz Kruczek, Grzegorz Przybyła, Rafal Krzywon and Rafal Bialozor

Large structural objects, primarily concrete bridges, can be reinforced by gluing to their stretched surface tapes of fiber-reinforced polymer (FRP). The condition for this…

129

Abstract

Purpose

Large structural objects, primarily concrete bridges, can be reinforced by gluing to their stretched surface tapes of fiber-reinforced polymer (FRP). The condition for this technology to work requires the quality of the bonding of FRP and the concrete to be perfect. Possible defects may arise in the phase of construction but also as a result of long-term fatigue loads. These defects having different forms of voids and discontinuities in the bonding layer are difficult to detect by optical inspection. This paper aims to describe the development of a rapid and nondestructive method for quantitative assessment of the debonding between materials.

Design/methodology/approach

The applied technique belongs to the wide class of active infrared (IR) thermography, the principle of which is to heat (or cool) the investigated object, and determine the properties of interest from the recorded, by an IR camera, temperature field. The methodology implemented in this work is to uniformly heat for a few seconds, using a set of halogen lamps, the FRP surface attached to the concrete. The parameter of interest is the thermal resistance of the layer separating the polymer tape and the concrete. The presence of voids and debonding will result in large values of this resistance. Its value is retrieved by solving an inverse transient heat conduction problem. This is accomplished by minimizing, in the sense of least squares, the difference between the recorded and simulated temperatures. The latter is defined as a solution of a 1D transient heat conduction problem with the already mentioned thermal resistance treated as the only decision variable.

Findings

A general method has been developed, which detects debonding of the FRP tapes from the concrete. The method is rapid and nondestructive. Owing to a special selection of the compared dimensionless measured and simulated temperatures, the method is not sensitive to the surface quality (roughness and emissivity). Measurements and calculation may be executed within seconds. The efficiency of the technique has been shown at a sample, where the defects have been artificially introduced in a controlled manner.

Originality/value

A quantitative assessment procedure which can be used to determine the extent of the debonding has been developed. The procedure uses inverse technique whose result is the unknown thermal resistance between the member and the FRP strip.

Details

International Journal of Numerical Methods for Heat & Fluid Flow, vol. 30 no. 5
Type: Research Article
ISSN: 0961-5539

Keywords

Article
Publication date: 3 May 2016

Carlo Nonino and Stefano Savino

The purpose of this paper is twofold: to describe a relevant improvement to an in-house FEM procedure for the heat transfer analysis of cross-flow micro heat exchangers…

Abstract

Purpose

The purpose of this paper is twofold: to describe a relevant improvement to an in-house FEM procedure for the heat transfer analysis of cross-flow micro heat exchangers and to study the influence of microchannel cross-sectional geometry and solid wall thermal conductivity on the thermal performance of these microdevices.

Design/methodology/approach

The velocity field in each microchannel is calculated separately. Then the energy equation is solved in the whole computational domain. Domain decomposition and grids that do not match at the common interface are employed to make meshing more effective. Some flow maldistribution effects are taken into account.

Findings

The results show that larger thermal conductivities of the solid walls and rectangular cross-sectional geometries with higher aspect ratios allow the maximization of the total heat flow rate in the device. However, on the basis of the heat transfer per unit pumping power, the square cross-section could be the best option.

Research limitations/implications

The value of the average viscosity is assumed to be different in different microchannels, but constant within each of the microchannels.

Practical implications

The procedure can represent a valuable tool for the design of cross-flow micro heat exchangers.

Originality/value

In spite of requiring limited computational resources, the improved procedure can take into account flow maldistribution effects stemming from non-uniform microchannel temperatures.

Details

International Journal of Numerical Methods for Heat & Fluid Flow, vol. 26 no. 3/4
Type: Research Article
ISSN: 0961-5539

Keywords

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