1,724,154 research outputs found
Correcting inertia sensors of a navigation systems in spite to perform a successfull neural network approach
No full textA challenging open question regards the combined use of low cost GPS systems together with low cost
Inertia navigation systems in vehicle navigation tools. Apart from the principle of working, The two systems
are characterized by di erent features. The rst provides (when suitably operating) optimal precision for
long distance and observation time, the second one is very e cient only within a short observation time as
being a ected by the so called random walking e ect. In many recent papers the NN have been used to
increase the accuracy of the Inertia Measurement Systems together with GPS signals. However, the direct
use of the cinematic variables in the network provided results whose reliability are restricted to limited
classes of events (or trip). A more interesting approach is the possibility to use Neural Network system to
try to increase the reliability of the inertia measurements while being able to foresee the origin of sensor
mistakes. In this paper attention is focused on the capability to get a successful training of a neural network.
As a matter of fact, the optimal choice of the input parameters of a NN is fundamental to achieve a general
training, that is to say not focused on a particular set of observations. The more these parameters are
directly connected to the physical source of errors, the more the network will be capable of a general (not
specialised) use
New experimental set-up to approach pipeline fracture behaviour by Three Point Bending Specimens
Full text linkThe work deals with the effective shape of the fracture during a Drop Weight Tear Test
(DWT). An inexpensive technique, able to determine the geometrical shape of the fracture,
is discussed and presented. The technique is capable to perform reliable measurements and
offers a mathematical description of the fracture profile. In few words, the fracture tunneling
measurement and its correlated effects are the objectives of this work. The technique is
based on a copy of the fracture by a silicone mold, followed by a digital analysis of the
tomographic images. The attention is finally focused on two different steels used in inshore
gas piping. The tunneling measurement is exploited in a finite element simulation of the
fracture propagation, thus opening the opportunity to update the kinematic models
applied for Crack Tip Opening Angle assessment
Correlation between Preload and Geometric Characterisation of metal meshes for space antenna reflectors
No full textContact management in knitted metal mesh through an adaptive node placing
No full textThe structural analysis of metal knitted meshes needs important computational resources due to non-linear behavior. The structures made of several filiform elements interlaced together often show large displacements and several contacts among yarns, so that they require advanced methods to predict their response. In this work, a contact-search algorithm between thin curved beams is presented. The contact recognition is based on the intersections between single elements to evaluate possible contact and its location. The method allows simplifying the 3D problem of contacts among wires into a 2D structure, easy to manage and model with a reduced computational cost. The filiform elements are modeled through a Wire Element, whose characteristic is to decouple its structural behavior – based on ending nodes – to its geometrical internal shape that is used for contact management. The Wire Element considers thin wires with circular sections. Its shape is entrusted to intrinsic geometry using a cubic polynomial function whose independent variable is the angle of the tangent to the curve. This approach is useful when analyzing complex structures such as meshes in which several loops are intertwined and subjected to contact activation during loading. Some examples to explain the method and its potential are shown
Updated Lagrangian Curvilinear Beam Element for 2D Large Displacement Analysis
No full textThis paper presents a 2D curvilinear beam finite element model focusing the interest on its use for non-linear analysis caused by very large displacements, addressed with the Update Lagrangian strategy. The method allows using very long curvilinear beams even when high geometric nonlinearities occur. This is due inasmuch the proposed formulation does not require any pre-set shape function that would inevitably force to use a huge number of elements to achieve reliability. The lack of shape-functions is overcome using the integration of the compatibility equations, that provide the whole internal displacement field from the only knowledge of the element nodal degree of freedom. Section-slices subdivision allows to sum, not to assemble, the flexibility contribute of each slice and consequently to build up the end-to-end tangent stiffness matrix of a generic curvilinear beam element. Moreover, the flexibility feature of every slice can be deduced analytically once and for all. To validate the proposed element some comparisons are carried out with analytical and numerical solutions obtained with Runge–Kutta integration method or cubic isoparametric finite elements
Bending Ovalization of Thin-Walled Circular Tube
No full textThis paper presents a new analytical model to predict the mechanical behaviour of an elastic straight thin-walled circular tube (pipe) subjected to bending. A thin-walled pipe cannot be modelled as a simple beam, inasmuch it presents a shell-like behaviour due to the ovalization (inplane warping) of the cross-section when loaded. The section modification implies a non-linear trend between the applied moment and the axial curvature, i.e. a non-invariance of the section moment of inertia. Two analytical ways are proposed in the reference literature: a rigorous one due to Reissner use a stress-function approach, and an approximated one, first due to Brazier, that follows Ritz approach. The Reissner model is analytically unsolvable and difficult to face numerically due to some integral conditions to fulfill. On the contrary, the Ritz approach is easy to implement, but being Heuristic is limited to circular sections. To overcome the previous mentioned difficulties a new geometrically exact Pipe model in terms of displacements is proposed, which turns out to be a mix between a shell and a beam model. The present approach leads to a system of ODEs accompanied by Boundary Value Problems (not requiring any integral conditions) that can be solved using a direct collocation method. After solving it, we build-up the dimensionless (non-linear) moment-curvature diagram, valid for any straight pipe, i.e. for every diameter, thickness, and whatever linear elastic material. The results are compared with other literature solutions performed using the Ritz’s approach and with Finite Element Analysis
An explicit procedure to evaluate the configuration and stress of Pipelinesduring Lifting and Laying operations by multi-hooking points
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