1,480 research outputs found
DNS of gas bubbles behaviour using an improved 3D front tracking model—Model development
In recent years CFD has proven to be a valuable and powerful tool to advance our understanding of complex multiphase flow systems arising in industrial applications. However, the predictive capabilities of this tool are determined by many factors of physical and numerical origin but in particular by the quality of the closures adopted for the description of the interface forces. The objective of this study is to improve the front tracking method in order to compute such forces with sufficient accuracy. This paper describes the further development of a 3D front tracking model to achieve improved volume conservation and circumvent problems related to the representation of surface tension. First, we have included a method to handle the pressure jump at the interface. This causes the spurious currents, observed in conventional front tracking, to decrease with two orders of magnitude. Also the advection scheme has been adapted, using higher order velocity interpolation (using cubic splines), and Runge–Kutta time-stepping, in order to prevent considerable volume changes of the dispersed phase. Test simulations involving a stationary bubble, a standard advection test and an oscillating droplet, demonstrate the effect of these improvements. The implementation of these procedures enlarged the computational window and in particular enabled the simulation of very small bubbles, where large surface forces dominate, without any significant spurious currents or volume loss
A parallel interaction potential approach coupled with the immersed boundary method for fully resolved simulations of deformable interfaces and membranes
In this paper we show and discuss the use of a versatile interaction
potential approach coupled with an immersed boundary method to simulate a
variety of flows involving deformable bodies. In particular, we focus on two
kinds of problems, namely (i) deformation of liquid-liquid interfaces and (ii)
flow in the left ventricle of the heart with either a mechanical or a natural
valve. Both examples have in common the two-way interaction of the flow with a
deformable interface or a membrane. The interaction potential approach (de
Tullio & Pascazio, Jou. Comp. Phys., 2016; Tanaka, Wada and Nakamura,
Computational Biomechanics, 2016) with minor modifications can be used to
capture the deformation dynamics in both classes of problems. We show that the
approach can be used to replicate the deformation dynamics of liquid-liquid
interfaces through the use of ad-hoc elastic constants. The results from our
simulations agree very well with previous studies on the deformation of drops
in standard flow configurations such as deforming drop in a shear flow or a
cross flow. We show that the same potential approach can also be used to study
the flow in the left ventricle of the heart. The flow imposed into the
ventricle interacts dynamically with the mitral valve (mechanical or natural)
and the ventricle which are simulated using the same model. Results from these
simulations are compared with ad- hoc in-house experimental measurements.
Finally, a parallelisation scheme is presented, as parallelisation is
unavoidable when studying large scale problems involving several thousands of
simultaneously deforming bodies on hundreds of distributed memory computing
processors
Optimal Reconstruction of Inviscid Vortices
We address the question of constructing simple inviscid vortex models which
optimally approximate realistic flows as solutions of an inverse problem.
Assuming the model to be incompressible, inviscid and stationary in the frame
of reference moving with the vortex, the "structure" of the vortex is uniquely
characterized by the functional relation between the streamfunction and
vorticity. It is demonstrated how the inverse problem of reconstructing this
functional relation from data can be framed as an optimization problem which
can be efficiently solved using variational techniques. In contrast to earlier
studies, the vorticity function defining the streamfunction-vorticity relation
is reconstructed in the continuous setting subject to a minimum number of
assumptions. To focus attention, we consider flows in 3D axisymmetric geometry
with vortex rings. To validate our approach, a test case involving Hill's
vortex is presented in which a very good reconstruction is obtained. In the
second example we construct an optimal inviscid vortex model for a realistic
flow in which a more accurate vorticity function is obtained than produced
through an empirical fit. When compared to available theoretical vortex-ring
models, our approach has the advantage of offering a good representation of
both the vortex structure and its integral characteristics.Comment: 33 pages, 10 figure
Flexible G1 Interpolation of Quad Meshes
International audienceTransforming an arbitrary mesh into a smooth G1 surface has been the subject of intensive research works. To get a visual pleasing shape without any imperfection even in the presence of extraordinary mesh vertices is still a challenging problem in particular when interpolation of the mesh vertices is required. We present a new local method, which produces visually smooth shapes while solving the interpolation problem. It consists of combining low degree biquartic Bézier patches with minimum number of pieces per mesh face, assembled together with G1-continuity. All surface control points are given explicitly. The construction is local and free of zero-twists. We further show that within this economical class of surfaces it is however possible to derive a sufficient number of meaningful degrees of freedom so that standard optimization techniques result in high quality surfaces
A theoretical reflection on smart shape modeling
This paper presents, as far as the authors are aware, a complete and extended new taxonomy of shape specification modeling techniques and a characterization of shape design systems, all based on the relationship of users’ knowledge to the modeling system they use to generate shapes. In-depth knowledge of this relationship is not usually revealed in the regular university training courses such as bachelor’s, master’s and continuing education. For this reason, we believe that it is necessary to modify the learning process, offering a more global vision of all the currently existing techniques and extending training in those related to algorithmic modeling techniques. We consider the latter to be the most powerful current techniques for modeling complex shapes that cannot be modeled with the usual techniques known to date. Therefore, the most complete training should include everything from the usual geometry to textual programming. This would take us a step further along the way to more powerful design environments. The proposed taxonomy could serve as a guideline to help improve the learning process of students and designers in a complex environment with increasingly powerful requirements and tools. The term “smart” is widely used nowadays, e.g. smart phones, smart cars, smart homes, smart cities... and similar terms such as “smart shape modeling”. Nowadays, the term smart is applied from a marketing point of view, whenever an innovation is used to solve a complex problem. This is the case for what is currently called smart shape modeling. However, in the future; this concept should mean a much better design environment than today. The smart future requires better trained and skilled engineers, architects, designers or technical students. This means that they must be prepared to be able to contribute to the creation of new knowledge, to the use of innovations to solve complex problems of form, and to the extraction of the relevant pieces of intelligence from the growing volume of knowledge and technologies accessible today. Our taxonomy is presented from the point of view of methods that are possibly furthest away from what is considered today as “intelligent shape modeling” to the limit of what is achievable today and which the authors call “Generic Shape Algorithm”. Finally, we discuss the characteristics that a shape modeling system must have to be truly “intelligent”: it must be “proactive” in applying innovative ideas to achieve a solution to a complex problem
Subsonic aerodynamic and flutter characteristics of several wings calculated by the SOUSSA P1.1 panel method
The SOUSSA (steady, oscillatory, and unsteady subsonic and supersonic aerodynamics) program is the computational implementation of a general potential flow analysis (by the Green's function method) that can generate pressure distributions on complete aircraft having arbitrary shapes, motions and deformations. Some applications of the initial release version of this program to several wings in steady and oscillatory motion, including flutter are presented. The results are validated by comparisons with other calculations and experiments. Experiences in using the program as well as some recent improvements are described
A locally based construction of analysis-suitable multi-patch spline surfaces
Analysis-suitable (AS-) multi-patch spline surfaces [4] are
particular -smooth multi-patch spline surfaces, which are needed to ensure
the construction of -smooth multi-patch spline spaces with optimal
polynomial reproduction properties [16]. We present a novel local approach for
the design of AS- multi-patch spline surfaces, which is based on the use
of Lagrange multipliers. The presented method is simple and generates an
AS- multi-patch spline surface by approximating a given -smooth but
non-AS- multi-patch surface. Several numerical examples demonstrate the
potential of the proposed technique for the construction of AS-
multi-patch spline surfaces and show that these surfaces are especially suited
for applications in isogeometric analysis by solving the biharmonic problem, a
particular fourth order partial differential equation, over them
Shape optimisation with multiresolution subdivision surfaces and immersed finite elements
We develop a new optimisation technique that combines multiresolution
subdivision surfaces for boundary description with immersed finite elements for
the discretisation of the primal and adjoint problems of optimisation. Similar
to wavelets multiresolution surfaces represent the domain boundary using a
coarse control mesh and a sequence of detail vectors. Based on the
multiresolution decomposition efficient and fast algorithms are available for
reconstructing control meshes of varying fineness. During shape optimisation
the vertex coordinates of control meshes are updated using the computed shape
gradient information. By virtue of the multiresolution editing semantics,
updating the coarse control mesh vertex coordinates leads to large-scale
geometry changes and, conversely, updating the fine control mesh coordinates
leads to small-scale geometry changes. In our computations we start by
optimising the coarsest control mesh and refine it each time the cost function
reaches a minimum. This approach effectively prevents the appearance of
non-physical boundary geometry oscillations and control mesh pathologies, like
inverted elements. Independent of the fineness of the control mesh used for
optimisation, on the immersed finite element grid the domain boundary is always
represented with a relatively fine control mesh of fixed resolution. With the
immersed finite element method there is no need to maintain an analysis
suitable domain mesh. In some of the presented two- and three-dimensional
elasticity examples the topology derivative is used for creating new holes
inside the domain.The partial support of the EPSRC through grant # EP/G008531/1 and EC through Marie Curie Actions (IAPP) program CASOPT project are gratefully acknowledged.This is the final version of the article. It was first available from Elsevier via http://dx.doi.org/10.1016/j.cma.2015.11.01
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