Begell House Inc.
International Journal for Multiscale Computational Engineering
JMC
1543-1649
17
6
2019
A FICTITIOUS SOURCE METHOD FOR A MULTIFREQUENCY ACOUSTIC SOURCE OVER GROUND WITH VARIABLE IMPEDANCE
563-582
10.1615/IntJMultCompEng.2019030576
Y.
Kamoun
Department of Aerospace Engineering, TechnionāIsrael Institute of Technology Haifa 32000,
Israel
Dan
Givoli
Department of Aerospace Engineering, TechnionāIsrael Institute of Technology, Haifa 32000, Israel; Faculty of Civil Engineering & Geosciences, Technical University of Delft, 2600 GA Delft, The Netherlands
multifrequency
multiscale
SPL
Helmholtz equation
equivalent sources
fictitious sources
acoustic waves
ground impedance
Green's function
aircraft noise
Finding the sound pressure level (SPL) distribution near the ground due to aircraft noise is an important problem in environmental engineering. Since the human hearing range is very wide, ranging from 20 Hz to 20 kHz, the determination of the SPL distribution for a given source spectrum is a difficult multiscale problem, and requires the repeated solution, for many different wave numbers, of the Helmholtz equation in the upper half space, while imposing a given impedance boundary condition on the ground. Previously, a simple computational scheme, based on the use of fictitious sources, was proposed for the efficient solution of such problems, for aflat ground with a given constant impedance. In the present study, this scheme is improved and extended in several ways. First, the ground impedance is allowed to vary with location, representing a varying type of ground (soil, water, asphalt, etc.). Second, a mechanism for verification of the method and for error estimation is developed, whereas previously only the boundary condition residual was evaluated. Third, the use of the appropriate Green's function, associated with a ringlike source, is made precise. Two simplifying assumptions which are maintained are that the ground is flat and that its impedance function is axially symmetric. Numerical experiments are used to demonstrate the performance of the scheme.
SIZE-DEPENDENT GEOMETRICALLY NONLINEAR BENDING AND POSTBUCKLING OF NANOCRYSTALLINE SILICON RECTANGULAR PLATES BASED ON MINDLIN'S STRAIN GRADIENT THEORY
583-606
10.1615/IntJMultCompEng.2020031370
Y.
Gholami
Faculty of Mechanical Engineering, University of Guilan, P.O. Box 3756, Rasht, Iran
Raheb
Gholami
Department of Mechanical Engineering, Lahijan Branch, Islamic Azad University, P.O. Box 1616, Lahijan, Iran
Reza
Ansari
Department of Mechanical Engineering, University of Guilan, P.O. Box 3756, Rasht, Iran
Hessam
Rouhi
Department of Engineering Science, Faculty of Technology and Engineering, East of Guilan, University of Guilan
nanocrystalline silicon rectangular plate
nonlinear bending and postbuckling
strain gradient effect
grain size
surface energy
Using a numerical variational approach, the nonlinear bending and postbuckling problems of rectangular plates made of nanocrystalline materials (NCMs) are addressed in this paper. The most general form of strain gradient theory is utilized in order to consider small-scale influences. Employing a micromechanical model, the effective properties of NCMs are calculated. Moreover, the plates are modeled based on the first-order shear deformation theory (FSDT) and the von Karman hypothesis. The variational differential quadrature (VDQ) technique is applied to obtain and discretize the weak-form governing differential equations. In order to obtain the nonlinear bending and postbuckling responses, the pseudo-arc-length continuation algorithm is employed to solve the resulting discretized nonlinear equations. The effects of thickness-to-length scale ratio, average inclusion radius, the volume fraction of the inclusion phase, length-to-thickness ratio, and density ratio on the nonlinear bending, and postbuckling responses of plates under various boundary conditions are investigated.
3D OBJECTS SEPARATION: UNSUPERVISED SEGMENTATION AND CLASSIFICATION
607-621
10.1615/IntJMultCompEng.2020031969
David
Tal
Department of Civil Engineering and Engineering Mechanics, Columbia University, New York,
NY
Jacob
Fish
Civil Engineering and Engineering Mechanics, Columbia University, New York, New York
10027, USA
unsupervised classification
computer vision
machine vision
objects separation
materials characterization
structural materials
composite materials
Object segmentation for the purpose of object and pattern recognition has been a long-standing subject of interest in the field of machine vision. Despite the significant attention given to the development of segmentation and recognition methods, the critical challenge of separating merged objects did not share the spotlight. In the work presented in this paper, we propose a simple yet novel approach to overcome this hurdle, by developing a methodology for unsupervised classification and separation of objects in 3D. Lower dimensionality classifiers are joined to provide a powerful higher dimensionality classification. The robustness of this approach is illustrated through its implementation on two case studies of merged objects. Applications of this methodology can further extend from structural classification to general problems of clustering and classification in various fields.
PERISTALTIC TRANSPORTATION OF FLUID THROUGH SIMPLE AND COMPLEX WAVY NONUNIFORM CHANNELS: A BIOENGINEERING APPLICATION
623-638
10.1615/IntJMultCompEng.2020032905
Khurram
Javid
Department of Mathematics, Northern University, Nowshera, KPK, Pakistan
Salah Ud-Din
Khan
Sustainable Energy Technologies (SET) Center, College of Engineering, King Saud University,
PO-Box 800, Riyadh 11421, Saudi Arabia
Mohsan
Hassan
Department of Mathematics, COMSATS University Islamabad, Lahore Campus, 54000,
Pakistan
Umer
Saeed
NUST Institute of Civil Engineering, School of Civil and Environmental Engineering, National University of Sciences and Technology
(NUST), Islamabad, Pakistan
Syed Tahir Raza
Rizvi
Department of Mathematics, COMSTAS University Islamabad, Lahore Campus 54000,
Pakistan
Shahab Ud-Din
Khan
National Tokamak Fusion Program, P.O. Nilore, 45650, Islamabad, Pakistan
peristaltic transportation
viscous fluid
simple and complex wave frame channels
In the current research study, a mathematical modeling is developed that is associated with the transportation phenomena due to peristaltic waves in a curve. Because of the complex nature of the regime, curvilinear coordinates are used to govern the system of equations in a fixed frame of reference and then converted into a wave frame by using linear transformations. The analysis is restricted under the creeping hydrodynamic and long wavelength assumptions. The impact of embedded physical parameters, i.e., the dimensionless curvature parameter, phase difference, and nonuniform parameters on the velocity profile, pumping, and trapping phenomena is discussed in detail. Another imperative phenomenon is also discussed that is associated with a comparative study between trains of peristaltic wave and single peristaltic wave propagations on the motion of an incompressible viscous fluid. The results of a straight channel are retrieved from both simple and wavy channels when taking the large value of the radius of the curvature. The pressure gradient in the straight channel is observed to be greater than in the curved channel.
AN OPEN-SOURCE FENICS IMPLEMENTATION OF A PHASE FIELD FRACTURE MODEL FOR MICROPOLAR CONTINUA
639-663
10.1615/IntJMultCompEng.2020033422
Hyoung Suk
Suh
Department of Civil Engineering and Engineering Mechanics, Columbia University, New York,
USA
WaiChing
Sun
Department of Civil Engineering and Engineering Mechanics, Columbia University in the
City of New York, New York, USA
FEniCS
open-source code
micropolar elasticity
phase field fracture
A micropolar phase field fracture model is implemented in an open source library FEniCS. This implementation is based on the theoretical study in Suh, H.S., Sun, W., and O'Connor, D. (under review) in which the resultant phase field model exhibits the consistent micropolar size effect in both elastic and damage regions identifiable via inverse problems for micropolar continua. By leveraging the automatic code generation technique in FEniCS, we provide a documentation of the source code expressed in a language very close to the mathematical expressions without comprising significant efficiency. This combination of generality and interpretability therefore enables us to provide a detailed walk-through that connects the implementation with the regularized damage theory for micropolar materials. By making the source code open source, the paper will provide an efficient development and educational tool for third-party verification and validation, as well as for future development of other higher order continuum damage models.
INDEX, VOLUME 17, 2019
664-669
10.1615/IntJMultCompEng.v17.i6.60