Current Issue : January - March Volume : 2013 Issue Number : 1 Articles : 5 Articles
This paper describes a detached-eddy simulation (DES) for the flow over a wall-mounted hump. The Reynolds number based\r\non the hump chord is Rec = 9.36 Ã?â?? 105 with an in-let Mach number of 0.1. Solutions of the three-dimensional Reynoldsaveraged\r\nNavier-Stokes (RANS) procedure are obtained using the Wilcox k - ? equations. The DES results are obtained using\r\nthe model presented by Bush and Mani and are compared with RANS solutions and experimental data from NASAââ?¬â?¢s 2004\r\nComputational Fluid Dynamics Validation on Synthetic Jets and Turbulent Separation Control Workshop. The DES procedure\r\nexhibited a three-dimensional flow structure in the wake, with a 13.65% shorter mean separation region compared to RANS and a\r\nmean reattachment length that is in good agreement with experimental measurements. DES predictions of the pressure coefficient\r\nin the separation region also exhibit good agreement with experiment and are more accurate than RANS predictions....
Hybrid rocket engines are promising propulsion systems which present appealing features such as safety, low cost, and\r\nenvironmental friendliness. On the other hand, certain issues hamper the development hoped for. The present paper discusses\r\napproaches addressing improvements to one of the most important among these issues: low fuel regression rate. To highlight the\r\nconsequence of such an issue and to better understand the concepts proposed, fundamentals are summarized. Two approaches\r\nare presented (multiport grain and high mixture ratio) which aim at reducing negative effects without enhancing regression rate.\r\nFurthermore, fuel material changes and nonconventional geometries of grain and/or injector are presented as methods to increase\r\nfuel regression rate. Although most of these approaches are still at the laboratory or concept scale, many of them are promising....
This paper is focused on the development and the flight performance analysis of an image-processing technique aimed at detecting\r\nflying obstacles in airborne panchromatic images. It was developed within the framework of a research project which aims at\r\nrealizing a prototypical obstacle detection and identification System, characterized by a hierarchical multisensor configuration.\r\nThis configuration comprises a radar, that is, the main sensor, and four electro-optical cameras. Cameras are used as auxiliary\r\nsensors to the radar, in order to increase intruder aircraft position measurement, in terms of accuracy and data rate. The paper\r\nthoroughly describes the selection and customization of the developed image-processing techniques in order to guarantee the best\r\nresults in terms of detection range, missed detection rate, and false-alarm rate. Performance is evaluated on the basis of a large\r\namount of images gathered during flight tests with an intruder aircraft. The improvement in terms of accuracy and data rate,\r\ncompared with radar-only tracking, is quantitatively demonstrated....
In the last years the small satellites have played an important role in the technological development. The attractive short period of\r\ndesign and low cost of them and the capacity to solve problems that are usually considered as problems to big and expensive spacecrafts\r\nlead us to study the control problem of these satellites. Active three-axis magnetic attitude stabilization of a low Earth orbit\r\nsatellite is considered in this work. The control is created by interaction between the magnetic moment generated by magnetorquers\r\nmounted on the satellite body and the geomagnetic field. This problem is quite complex and difficult to solve. To overcome this difficulty\r\nguidance control is considered, where we use e-strategies introduced by Pontryagin in the frame of differential games theory.\r\nQualitative analysis and results of numerical simulation are presented....
The work traces a general procedure for the design of a flight simulation tool still representative of the major flight physics of\r\na parachute-payload system along decelerated trajectories. An example of limited complexity simulation models for a payload\r\ndecelerated by one or more parachutes is given, including details and implementation features usually omitted as the focus of\r\nthe research in this field is typically on the investigation of mission design issues, rather than addressing general implementation\r\nguidelines for the development of a reconfigurable simulation tool. The dynamics of the system are modeled through a simple\r\nmultibody model that represents the expected behavior of an entry vehicle during the terminal deceleration phase. The simulators\r\nare designed according to a comprehensive vision that enforces the simplification of the coupling mechanism between the payload\r\nand the parachute, with an adequate level of physical insight still available. The results presented for a realistic case study define the\r\nsensitivity of the simulation outputs to the functional complexity of the mathematical model. Far from being an absolute address\r\nfor the software designer, this paper tries to contribute to the area of interest with some technical considerations and clarifications....
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