1,721,006 research outputs found
Numerical solution for the one-phase Stefan problem by piecewise constant approximation of the interface
No full textThe classical one-phase one-dimensional Stefan problem is numerically solved on rectangles, Rj, of increasing size controlled by the Stefan condition. This approach is based on a scheme introduced by E. Di Benedetto and R. Spigler in 1983. The practical implementation rests on the representation via thermal potentials of the solution uj(x, t) to the heat equation in Rj. The quantity uxj(xj, jΔt) which determines the (j+1)-th rectangle is evaluated analytically by solving explicitly an integral equation. The solution in Rj+1 is then obtained by numerically evaluating a further integral expression. The algorithm is tested by solving two problems whose solution is explicitly known. Convergence, stability and convergence rate as Δx→0, Δt→0 have been tested and plots are shown. © 1990 Springer-Verlag
Un metodo per la risoluzione numerica del problema di Stefan ad una fase in una dimensione
No full textRisoluzione Numerica dell' Equazione Non Lineare Integro-Differenziale di Fokker-Planck che Descrive il Modello di Kuramoto-Sakaguchi
No full textRisoluzione numerica del problema di Stefan ad una fase mediante approssimazione costante a tratti dell' interfaccia
No full textThe "phase function" method to solve second-order asymptotically polynomial differential equations
No full textMethodologies for virtual sensing applied to aeronautical and ship structures
Full text linkIn this thesis the problem of achieving a full, experimentally based, representation of the load and elastic deflection response of aeronautical and ship structures is concerned by the development of numerical procedures and their assessment via related experimental activities. The objective is to provide reliable estimations of elastic deflections and external forces throughout the structure using noisy pointwise measurements. This issue is critical for some important structural engineering applications such as Structural Health Monitoring and Condition-Based Maintenance.
The most important tools generally used for this purpose (e.g., Kalman filter) have been first reviewed, pointing strengths and critical issues out. Then, an approach based on an optimal second-order natural observer has been proposed also integrating this with signal processing approaches like discrete wavelet transform and finite-element component analysis approaches like dynamics condensation. The developed and integrated numerical framework was finally applied to the state estimation of two specific structures, namely, an aircraft and surface vessel operating under unsteady environmental conditions featured by wind gust or sea waves, respectively.
More in detail, a scaled physical model of a fast catamaran, tested in the towing-tank, and a numerical model of a flexible aircraft were studied as significant test cases for assessing the introduced methodologies. Both the structures involved are interesting in their respective research fields.
The accurate and complete estimation of the structural dynamics behavior of the fast catamaran is particularly interesting since in real world it might be exposed to critical slamming phenomena on the wetdeck region. The experimental set-up and in particular the choice of the structural measurements were crucial to have a minimum but reliable database for the reconstruction of the structural deflection field. By applying the above methodologies, it was also possible to provide a deeper insight relative to violent fluid-structure interaction phenomena and to evaluate possible fatigue-life reduction for components where direct monitoring was not possible.
The other case study consists of an aircraft research model that experiences a particular kind of instability involving both aeroelasticity and flight dynamics. In such aeronautical application, the structural measurements are virtually obtained by means of simulations based on a flight dynamics and aeroelasticity toolbox developed for the present purpose and featured by an accurate description of the coupling caused by aerodynamic and inertial forces. This case has been performed to investigate numerically the technique proposed in this thesis by integrating the methodology with multi-resolution analysis
Importance and Unpredictability of Self-organization Processes in Fusion Burning Plasmas
No full textSelf-organization processes are considered to have an important role in well confined plasmas produced by present day experiments where the heating source is externally applied. The observation of ``Profile Consistency'' [1] is viewed as a manifestation of the presence of these processes. In the case of fusion burning plasmas close to self-sustainment (ignition) most of the heating due to fusion products is strongly dependent on the evolution of both the plasma temperature and density profiles. Therefore, self-organization is expected to be of considerably greater importance than in the case of non-reacting plasmas. This fact involves a significant degree of unpredictability on the outcome of envisioned experiments on burning plasmas that has to be added to the complexity of the collective modes that are expected to emerge. Thus, one of the motivations for the Ignitor program is to shed light on these issues and minimize the uncertainties for the design of more ambitious undertakings such as a Compact Pilot Plant. *Sponsored in part by CNR of Italy. [1] B. Coppi, Comm. Plasma Phys. Cont. Fusion extbf{5}, 261 (1980)
Nonconforming finite elements for Reissner--Mindlin plates
No full textWe report on recent results about some nonconforming finite elements for plates. All the elements are locking-free and exhibit optimal convergence rates
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