1,721,016 research outputs found
Citochine radiomarcate e loro usi come traccianti scintigrafici per la visualizzazione delle infiammazioni croniche linfocito-mediate
No full textNumerical simulations of air inclusions using ROBOOST simulation tool
No full textThis work describes the application of original Computer Graphics methods to examine the effect of air inclusions within solid rocket motor thrust chamber. The adoptance of a dynamic 3D triangular mesh with a self-intersections removal algorithm, as the core of the burning surface regression module, allows to reach the above-mentioned target. Many phenomena not measurable in an analytical closed form, like different-shaped voids within the grain, can be investigated. Indeed, both local heterogeneities and surface imperfections could generate unexpected variations in combustion chamber pressure pattern and early thermal protections exposure. The above-mentioned techniques are developed and tested on ROBOOST (Rocket BOOst Simulation Tool) which is a ballistic simulator developed at the Laboratory of Propulsion and Mechanics of the University of Bologna in collaboration with AVIO S.p.a. Computer Graphics methods to improve mesh handling are explained in detail. Simulations results are carried out and discussed
A simplified approach to predict friedman curl effect in a solid rocket motor using ROBOOST simulation tool
No full textIn the design and development of solid propellant rocket motors (SRMs), the use of numerical tools able to simulate, predict and reconstruct the behavior of a given motor, in all its operative conditions is fundamental: more accurate performance predictions would reduce the need of expensive testing, thus lowering the cost of development for each SRM. This paper is intended to provide a simplified physical model to predict the pressure peak close to tail-off phase, namely Friedman Curl effect. This phenomenon depends on many factors, which are analyzed and discussed. The equations numerical treatment is explained in detail. Comparing between simulations and experimental results is carried out. Simulations are obtained with ROBOOST (Rocket BOOst Simulation Tool), a ballistic simulator developed at the Laboratory of Propulsion and Mechanics of the University of Bologna in collaboration with AVIO S.p.a
0d unsteady-1d quasi-steady internal ballistic coupling for ROBOOST simulation tool
No full textThe work presented here deals with the non-negligible problem of simulating the internal ballistic and thus the performance prediction of a Solid Rocket Motor (SRM). The internal ballistic consists in the thermodynamic and fluid dynamic description of the combustion inside the rocket and the behavior of the propellant grain’s regression vs time. Many numerical and simplified analytical models have been used since the beginning of solid rocket’s industrialization; depending on the motor’s length-to-diameter ratio, zero dimensional or mono dimensional models are exploited in the preliminary design phase of a SRM, and steady or non-steady models are also used to predict the performances of the working phase under examination. The coupled zero-dimensional non-steady (0D-NS) and mono dimensional quasi-steady (1D-QS) ballistic model is the main state of the art for designing in a time and cost-effective fashion. An analytical model for the 0D NS – 1D QS internal ballistic is here developed and numerically implemented in a SRM simulator developed at the Propulsion Laboratory of the University of Bologna (Department of Industrial Engineering), named ROBOOST (Rocket BOOst Simulation Tool). An investigation of several commercial motors performances is then performed for validation’s purpose
A novel procedure to determine the effects of debonding on case exposure of solid rocket motors
Full text linkSolid rocket motors are complex systems which need to withstand extreme physical conditions in terms of temperature, pressure, and high-density energy release. Therefore, specific attention should be brought to the flaws that may occur during motor manufacturinghandling phases prior to launch. An example of such flaws is debonding, usually arising at the interface between case insulation and solid grain. When debonding is significant in size, it may result in the premature case exposure to combustion chamber hot gases, and, in worst cases, it may even cause a complete motor failure. This work is intended to evaluate the impact of propellant debonding on solid rocket motor case-insulating layer, making predictions about the most unfavorable regions where the debonding could occur. Numerical simulations are performed with an in-house simulation software applied to an actual solid rocket motor stage
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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