131 research outputs found
A complete data-driven framework for the efficient solution of parametric shape design and optimisation in naval engineering problems
In the reduced order modeling (ROM) framework, the solution of a parametric partial differential equation is approximated by combining the high-fidelity solutions of the problem at hand for several properly chosen configurations. Examples of the ROM application, in the naval field, can be found in [31, 24]. Mandatory ingredient for the ROM methods is the relation between the high-fidelity solutions and the parameters. Dealing with geometrical parameters, especially in the industrial context, this relation may be unknown and not trivial (simulations over hand morphed geometries) or very complex (high number of parameters or many nested morphing techniques). To overcome these scenarios, we propose in this contribution an efficient and complete data-driven framework involving ROM techniques for shape design and optimization, extending the pipeline presented in [7]. By applying the singular value decomposition (SVD) to the points coordinates defining the hull geometry --- assuming the topology is inaltered by the deformation ---, we are able to compute the optimal space which the deformed geometries belong to, hence using the modal coefficients as the new parameters we can reconstruct the parametric formulation of the domain. Finally the output of interest is approximated using the proper orthogonal decomposition with interpolation technique. To conclude, we apply this framework to a naval shape design problem where the bulbous bow is morphed to reduce the total resistance of the ship advancing in calm water
A unified steady and unsteady formulation for hydrodynamic potential flow simulations with fully nonlinear free surface boundary conditions
This work discusses the correct modeling of the fully nonlinear free surface
boundary conditions to be prescribed in water waves flow simulations based on
potential flow theory. The main goal of such a discussion is that of
identifying a mathematical formulation and a numerical treatment that can be
used both to carry out transient simulations, and to compute steady solutions
-- for any flow admitting them. In the literature on numerical towing tank in
fact, steady and unsteady fully nonlinear potential flow solvers are
characterized by different mathematical formulations. The kinematic and dynamic
fully nonlinear free surface boundary conditions are discussed, and in
particular it is proven that the kinematic free surface boundary condition,
written in semi-Lagrangian form, can be manipulated to derive an alternative
non penetration boundary condition by all means identical to the one used on
the surface of floating bodies or on the basin bottom. The simplified
mathematical problem obtained is discretized over space and time via Boundary
Element Method (BEM) and Implicit Backward Difference Formula (BDF) scheme,
respectively. The results confirm that the solver implemented is able to solve
steady potential flow problems just by eliminating null time derivatives in the
unsteady formulation. Numerical results obtained confirm that the solver
implemented is able to accurately reproduce results of classical steady flow
solvers available in the literature.Comment: The final version of the present paper has been accepted for
publication on Applied Mathematical Modellin
Hull Shape Design Optimization with Parameter Space and Model Reductions, and Self-Learning Mesh Morphing
In the field of parametric partial differential equations, shape optimization represents a challenging problem due to the required computational resources. In this contribution, a data-driven framework involving multiple reduction techniques is proposed to reduce such computational burden. Proper orthogonal decomposition (POD) and active subspace genetic algorithm (ASGA) are applied for a dimensional reduction of the original (high fidelity) model and for an efficient genetic optimization based on active subspace property. The parameterization of the shape is applied directly to the computational mesh, propagating the generic deformation map applied to the surface (of the object to optimize) to the mesh nodes using a radial basis function (RBF) interpolation. Thus, topology and quality of the original mesh are preserved, enabling application of POD-based reduced order modeling techniques, and avoiding the necessity of additional meshing steps. Model order reduction is performed coupling POD and Gaussian process regression (GPR) in a data-driven fashion. The framework is validated on a benchmark ship
PyGeM: Python Geometrical Morphing
PyGeM is an open source Python package which allows to easily parametrize and deform 3D object described by CAD files or 3D meshes. It implements several morphing techniques such as free form deformation, radial basis function interpolation, and inverse distance weighting. Due to its versatility in dealing with different file formats it is particularly suited for researchers and practitioners both in academia and in industry interested in computational engineering simulations and optimization studies
IT Driven Modernization in Agriculture
The information systems (IS) literature has largely neglected the study of implementations of large scale strategic initiatives to modernize the agricultural business. This paper reports on an ongoing empirical study that follows the efforts of a multibillion-dollar organization to modernize its operations through the modernization of its supplier base. Modernization, as an external force effecting organizations, is a new and different phenomenon respect to organizational change normally considered as an internal effort. Modernization is an ongoing, evolutionary, process performed by organizations in order to survive and prosper. Yet, the rationality of the decision to modernize is likely to face the forces of entrenched traditions and practices, the feelings and the social significance of established ways of those with the power to derail the modernization project. Using institutional theory as theoretical lens to study the role of information and communication technologies (ICT) in modernization strategy, the paper suggests that managers should care beyond the reasons for change, considering the physical, social and cultural needs of the stakeholders involved. Our study extends the extant literature on agribusiness management highlighting the tensions between the initiator of the modernization effort and the suppliers with their need to adapt and respond
Immunolocalisation of vasoactive intestinal peptide and substance P in the developing gut of Dicentrarchus labrax (L.)
This study was carried out on the sea bass (Dicentrarchus labrax) to follow, during development, the appearance and distribution of substance P (SP) and vasoactive intestinal peptide (VIP), which act on gut motility. The results suggest that SP and VIP play an important role as neuromodulators, influencing the motility of the digestive tract starting from the early stages of gut development, even prior to exotrophic feeding. In the peptidergic nervous system, the appearance of immunoreactivity to SP began at the rectum and followed a distal to proximal gradient, whereas for VIP, it began proximally and progressed along a proximal to distal gradient. The two peptides also appeared in gut epithelial cells. In some regions, all the cells were positive. From this distribution of positive cells, we conclude that these peptides may also have other roles, besides being neurotransmitters in the enteric nervous system and hormones of the gastro-entero-pancreatic system. VIP and SP might have paracrine and/or autocrine activity in the physiological maturation of the gut epithelium, as it has already been hypothesised for other peptides
An efficient shape parametrisation by free-form deformation enhanced by active subspace for hull hydrodynamic ship design problems in open source environment
In this contribution, we present the results of the application
of a parameter space reduction methodology based on active subspaces to
the hull hydrodynamic design problem. Several parametric deformations
of an initial hull shape are considered to assess the influence of the
shape parameters considered on the hull total drag. The hull resistance
is typically computed by means of numerical simulations of the
hydrodynamic flow past the ship. Given the high number of parameters
involved - which might result in a high number of time consuming
hydrodynamic simulations - assessing whether the parameters space can
be reduced would lead to considerable computational cost reduction.
Thus, the main idea of this work is to employ the active subspaces to
identify possible lower dimensional structures in the parameter space,
or to verify the parameter distribution in the position of the control
points. To this end, a fully automated procedure has been implemented
to produce several small shape perturbations of an original hull CAD
geometry which are then used to carry out high-fidelity flow
simulations and collect data for the active subspaces analysis. To
achieve full automation of the open source pipeline described, both the
free form deformation methodology employed for the hull perturbations
and the solver based on unsteady potential flow theory, with fully
nonlinear free surface treatment, are directly interfaced with CAD data
structures and operate using IGES vendor-neutral file formats as input
files. The computational cost of the fluid dynamic simulations is
further reduced through the application of dynamic mode decomposition
to reconstruct the steady state total drag value given only few initial
snapshots of the simulation. The active subspaces analysis is here
applied to the geometry of the DTMB-5415 naval combatant hull, which is
which is a common benchmark in ship hydrodynamics simulations
A reduced-order model for segregated fluid-structure interaction solvers based on an ALE approach
This article presents a Galerkin projection model order reduction approach
for fluid-structure interaction (FSI) problems in the Finite Volume context.
The reduced-order model (ROM) is based on proper orthogonal decomposition
(POD), where a reduced basis is formed using energy-dominant POD modes. The
reduced basis also consists of characteristics of the POD time modes derived
from the POD time modes coefficients. In addition, the solution state vector
comprises the mesh deformation, considering the structural motion in FSI. The
results are obtained by applying the proposed method to time-dependent problems
governed by the 2D incompressible Navier-Stokes equations. The main objective
of this work is to introduce a hybrid technique mixing up the classical
Galerkin-projection approach with a data-driven method to obtain a versatile
and accurate algorithm for resolving FSI problems with moving meshes. The
effectiveness of this approach is demonstrated in the case study of
vortex-induced vibrations (VIV) of a cylinder at Reynolds number Re = 200. The
results show the stability and accuracy of the proposed method with respect to
the high-dimensional model by capturing transient flow fields and, more
importantly, the forces acting on the moving objects
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