2,727 research outputs found
Recent advances in computational methods for microsystems
No full textAn algorithm, which combines the use of Domain Decomposition and Model Order Reduction methods based on Proper Orthogonal Decomposition, is proposed. The algorithm allows for the efficient handling of electro-mechanical coupled problems in MEMS, with a strong reduction of computing time with respect to standard monolithic or staggered solution strategies. Examples of coupled electro-mechanical problems, concerning a vibrating beam subject to variable electrostatic forces, are presented and discusse
Combined domain decomposition and model order reduction methods for the solution of coupled and non-linear problems
No full textA new strategy for the ecient solution of highly nonlinear structural problems
is proposed in this paper, based on the combined use of Domain Decomposition
(DD) and Proper Orthogonal Decomposition (POD) techniques. The formulation here
presented is tailored for applications in elasto-plastic structural dynamics. In this context
the POD is applied to linear domains and a double strategy to update the reduced basis
is adopted. Examples show that a meaningful computational gain of approximately 50%
with respect to a monolithic solution can be obtained
Domain decomposition and model order reduction methods applied to the simulation of multiphysics problems in MEMS
No full textCoupled electro-mechanical problems are frequently encountered when dealing with micro electro-mechanical systems (MEMS) with capacitive actuation and/or readout systems; their numerical solution can be extremely time consuming, due to the nonlinearity of the coupling terms. Coupled electrostatic – structural dynamic simulations are carried out in this paper through an innovative numerical procedure, based on the use of a domain decomposition technique and of a proper orthogonal decomposition methodology. The approach is assessed through the analysis of the dynamic response of a doubly clamped beam and of a plane resonator subjected to an electrostatic actuation, showing computational gains up to 98%
Combustion of Metal Agglomerates in a Solid Rocket Core Flow
No full textThe need for access to space may require the use of solid propellants. High thrust and density are appealing features for different applications, spanning from boosting phase to other service applications (separation, de-orbiting, orbit insertion). Aluminum is widely used as a fuel in composite solid rocket motors because metal oxidation increases enthalpy release in combustion chamber and grants higher specific impulse. Combustion process of metal particles is complex and involves aggregation, agglomeration and evolution of reacting particulate inside the core flow of the rocket. It is always stated that residence time should be enough in order to grant complete metal oxidation but agglomerate initial size, rocket grain geometry, burning rate, and other factors have to be reconsidered. New space missions may not require large rocket systems and metal combustion efficiency becomes potentially a key issue to understand whether solid propulsion embodies a viable solution or liquid/hybrid systems are better. A simple model for metal combustion is set up in this paper. Metal particles are represented as single drops trailed by the core flow and reacted according to Beckstead's model. The fluid dynamics is inviscid, incompressible, 1D. The paper presents parametric computations on ideal single-size particles as well as on experimental agglomerate populations as a function of operating rocket conditions and geometries
Flame Height Effects on Agglomerate Size in Aluminized Solid Propellants
No full textSolid rocket motors are one of the most used systems for space propulsion. Along with the numbers of advantages like simplicity, low cost, technological maturity and high thrust, this propulsion system exhibits relatively low gravimetric specific impulse among the thermochemical engine family. When metallized, solid propellants release droplets of molten aluminum (agglomerates) causing a further reduction of performance. This phenomenon depends on several parameters (e.g. burning rate, microstructure, propellant formulation, flame position, local temperatures etc.). This work focalizes the attention on the relation between agglomerate size and flame height. A theoretical investigation has been performed to select five representative formulations. An experimental campaign has been performed to characterize the materials in terms of burning rate, agglomerate size, and density. A simple code based on the GDF theory has been used to compute the flame height of interested formulations. Numerical and experimental data have been finally compared revealing a linear dependence of agglomerate size on the flame height, thus confirming the key role played by the flame in agglomerate growing and formation
Enhancing Micrometric Aluminum Reactivity by Mechanical Activation
No full textThe pursuit of solid rocket motor and hybrid rocket engine performance enhancements is pushing toward the research of novel energetic materials replacing the conventional micron-sized aluminum. Nanotechnology opened the way to new concepts, introducing very promising ingredients like nanoaluminum (nAl). Their effectiveness in increasing energetic system performance has been already proven. However, the high cost, the dispersion difficulties and the increased handling risk, hinder a widespread application. On the other hand, activation techniques offer the possibility of micron-sized additives reactivity enhancement while maintaining high safety levels and reduced costs. This work deals with design, production, and characterization of mechanically activated ingredients for solid propellants (SPs) and hybrid rocket fuels (HFs). General guidelines for implementation of powder processing are critically discussed. Additives are characterized in the pre-burning phase, and their effects on the ballistic response of SPs and HFs are investigated. Activated powders improved HF regression rate and reduced the size of the condensed combustion products of SPs, confirming their suitability for micron-sized aluminum replacement
Model order reduction and domain decomposition strategies for the solution of the dynamic elasto-plastic structural problem
No full textA new strategy for the efficient solution of highly nonlinear structural problems is proposed, based on the combined use of Domain Decomposition (DD) and snapshots version of the Proper Orthogonal Decomposition (POD) techniques. The formulation here presented is tailored for applications in elastic-plastic structural dynamics. In this context the POD is applied to domains that remain elastic and a double strategy to update the reduced basis is adopted. First, the Singular Value Decomposition (SVD) proposed allows to update the reduced basis as soon as a new snapshot is stored; secondly, an online adaptation technique of the reduced space is performed, through a plastic check during the reduced analysis. The applications show that the computation time necessary for solving elastic-plastic problems can be reduced of approximately 50%, while keeping accuracy comparable to that obtained for the full model with a classical monolithic method
Who is the author of the 1876 Stefano manuscript?
No full textFor over one hundred years the Stefano manuscript was a private document in the possession of the Baccich family and descendants. It told a story of the 1875 Stefano shipwreck as narrated by the shipwreck survivor and the founding family patriarch Miho Baccich. In these circumstances the question of authorship of the manuscript was immaterial and did not arise as an issue. However, with the publication of the manuscript the author‟s name, or names, need to be formally attributed to it. It turns out that this is not such a clear-cut matter.
As we shall see, all informed sources attributed the authorship, and the ownership, of the manuscript to Miho Baccich. But the manuscript itself was written by Canon Stjepan Skurla – a priest from Miho‟s hometown of Dubrovnik. The question then arises: should Skurla also be considered as an author of the manuscript, or, even as the sole author (as some would have it)
- …
