首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   20篇
  免费   0篇
航空   7篇
航天技术   2篇
航天   11篇
  2019年   2篇
  2017年   1篇
  2016年   1篇
  2014年   1篇
  2013年   1篇
  2012年   2篇
  2011年   3篇
  2009年   1篇
  2008年   1篇
  2007年   3篇
  2006年   1篇
  2003年   1篇
  2000年   1篇
  1993年   1篇
排序方式: 共有20条查询结果,搜索用时 250 毫秒
1.
The low-speed flowfield for a generic unmanned combat air vehicle (UCAV) is investigated both experimentally and numerically. A wind tunnel experiment was conducted with the Boeing 1301 UCAV at a variety of angles of attack up to 70 degrees, both statically and with various frequencies of pitch oscillation (0.5, 1.0, and 2.0 Hz). In addition, pitching was performed about three longitudinal locations on the configuration (the nose, 35% MAC, and the tail). Solutions to the unsteady, laminar, compressible Navier–Stokes equations were obtained on an unstructured mesh to match results from the static and dynamic experiments. The computational results are compared with experimental results for both static and pitching cases. Details about the flowfield, including vortex formation and interaction, are shown and discussed, including the non-linear aerodynamic characteristics of the vehicle.  相似文献   
2.
Abstract

Participants (N = 78) studied a visualization of a route through a complex building and walked that route in the real building without further assistance. Erroneous turns on the route as well as indicators of uncertainty such as hesitations were assessed. Three types of route visualizations were compared: (1) an allocentric, map-based visualization with the route indicated in floor maps, (2) an ordered sequence of pictures of decision points shown from the egocentric perspective, and (3) an animation showing a virtual walk of the route from the egocentric perspective. In addition to the experimental variation, gender differences, differences in visual-spatial abilities and differences in self-reported wayfinding strategies were considered as predictor variables. Wayfinding performance did not differ between allocentric (map) and egocentric (decision point pictures and animation) visualizations. However, wayfinding performance was better with animated than with static egocentric visualizations. Individual differences in the ability to encode visual-spatial information from the visualization played a critical role for route learning. Self-reported sense of direction related to egocentric wayfinding strategies also predicted wayfinding performance. Gender differences were attributable to differences in visual-spatial abilities and egocentric wayfinding strategies. Interactions between visualizations and individual differences were not found. It is concluded that animations of virtual walks are suitable to convey route information in complex buildings. Successful acquisition of route knowledge from maps is possible but might depend on the comprehensibility of the structure of the building.  相似文献   
3.
This paper presents the results of a mission concept study for an autonomous micro-scale surface lander also referred to as PANIC – the Pico Autonomous Near-Earth Asteroid In Situ Characterizer. The lander is based on the shape of a regular tetrahedron with an edge length of 35 cm, has a total mass of approximately 12 kg and utilizes hopping as a locomotion mechanism in microgravity. PANIC houses four scientific instruments in its proposed baseline configuration which enable the in situ characterization of an asteroid. It is carried by an interplanetary probe to its target and released to the surface after rendezvous. Detailed estimates of all critical subsystem parameters were derived to demonstrate the feasibility of this concept. The study illustrates that a small, simple landing element is a viable alternative to complex traditional lander concepts, adding a significant science return to any near-Earth asteroid (NEA) mission while meeting tight mass budget constraints.  相似文献   
4.
5.
We present a hybrid algorithm to analyse complex interferograms with significant fringe deformations without an a-priori given zero-phase image containing the optical aberration of the instrument. Situations of this type frequently appear in fluid physics experiments using lateral shearing interferometers. The algorithm proposed employs a wavelet transformation in parallel with an approximation of the phase field directly after the experimental container is filled applying Zernike polynomials. As a result the aberrations of the interferometer can be described by a few coefficients. The subtraction of these phase aberrations can be traced back to a complex multiplication in the wavelet space which strongly reduces the effort of the phase unwrapping using the Goldstein algorithm. We explain the performance of the algorithm, which is not restricted to a particular interferometer type, by applying it to interferograms captured during a recent microgravity experiment.  相似文献   
6.
The alpha-particle X-ray spectrometer (APXS) for the Mars Science Laboratory (MSL) mission was calibrated for routine analysis of: Na, Mg, Al, Si, P, S, Cl, K, Ca, Ti, Cr, Mn, Fe, Ni, Zn, Br, Rb, Sr, and Y. The following elements were also calibrated, but may be too low to be measured (10s–100s ppm) for their usual abundance on Mars: V, Cu, Ga, As, Se and W. An extensive suite of geological reference materials, supplemented by pure chemical elements and compounds was used. Special attention was paid to include phyllosilicates, sulfates and a broad selection of basalts as these are predicted minerals and rocks at the Gale Crater landing site. The calibration approach is from first principles, using fundamental physics parameters and an assumed homogeneous sample matrix to calculate expected elemental signals for a given instrument setup and sample composition. Resulting concentrations for most elements accord with expected values. Deviations in elements of lower atomic number (Na, Mg, Al) indicate significant influences of mineral phases, especially in basalts, ultramafic rocks and trachytes. The systematics of these deviations help us to derive empirical, iterative corrections for different rock groups, based on a preliminary APXS analysis which assumes a homogeneous sample. These corrections have the potential to significantly improve the accuracy of APXS analyses, especially when other MSL instrument results, such as the X-ray diffraction data from CheMin, are included in the overall analysis process.  相似文献   
7.
We report on our recent progress in modeling non-LTE atmospheres of O-stars including blanketing by lines from the iron group elements. The numerical method to account for the huge number of atomic levels and line transitions is presented. Results of exploratory model calculations examining the effects on the temperature structure, the hydrogen and helium line profiles and UV/EUV fluxes are discussed.  相似文献   
8.
In the upcoming generation of satellite sensors, hyperspectral instruments will play a significant role. This payload type is considered world-wide within different future planning.Our team has now successfully finalized the Phase B study for the advanced hyperspectral mission EnMAP (Environmental Mapping and Analysis Programme), Germans next optical satellite being scheduled for launch in 2012. GFZ in Potsdam has the scientific lead on EnMAP, Kayser-Threde in Munich is the industrial prime.The EnMAP instrument provides over 240 continuous spectral bands in the wavelength range between 420 and 2450 nm with a ground resolution of 30 m×30 m. Thus, the broad science and application community can draw from an extensive and highly resolved pool of information supporting the modeling and optimization process on their results. The performance of the hyperspectral instrument allows for a detailed monitoring, characterization and parameter extraction of rock/soil targets, vegetation, and inland and coastal waters on a global scale supporting a wide variety of applications in agriculture, forestry, water management and geology. The operation of an airborne system (ARES) as an element in the HGF hyperspectral network and the ongoing evolution concerning data handling and extraction procedures, will support the later inclusion process of EnMAP into the growing scientist and user communities.  相似文献   
9.
Keeping astronauts healthy during long duration spaceflight remains a challenge. Artificial gravity (AG) generated by a short arm human centrifuges (SAHC) is proposed as the next generation of integrated countermeasure devices that will allow human beings to safely spend extended durations in space, although comparatively little is known about any psychological side effects of AG on brain function.  相似文献   
10.
Liquid rocket engines for launch vehicles and space crafts as well as their subsystems need to be verified and qualified during hot-runs. A high test cadence combined with a flexible test team helps to reduce the cost for test verification during development/qualification as well as during acceptance testing for production. Test facility intelligence allows to test subsystems in the same manner as during complete engine system tests and will therefore reduce development time and cost.This paper gives an overview of the maturing of test engineering know how for rocket engine test stands as well as high altitude test stands for small propulsion thrusters at EADS-ST in Ottobrunn and Lampoldshausen and is split into two parts:
• Part 1 gives a historical overview of the EADS-ST test stands at Ottobrunn and Lampoldshausen since the beginning of Rocket propulsion activities in the 1960s.
• Part 2 gives an overview of the actual test capabilities and the test engineering know-how for test stand construction/adaptation and their use during running programs.
Examples of actual realised facility concepts are given to demonstrate cost saving potential for test programs in both cases for development/qualification issues as well as for production purposes.

Article Outline

1. Introduction
2. Historical overview
2.1. Ottobrunn
2.1.1. Air-breathing propulsion
2.2. Lampoldshausen
2.2.1. Attitude control systems
2.2.2. Launcher Propulsion
3. Today's status of hot firing test facilities at Lampoldshausen
4. Test facility engineering know how
5. Conclusion and outlook
References

1. Introduction

Test facilities are an indispensable element for the development and acceptance of space systems/subsystems and components. Hot-test facilities especially with environment simulation (e.g., altitude simulation) are very unique and are specifically designed to their needs.In Germany rocket propulsion developments were started during the 1950s in Ottobrunn near Munich. Beginning in the 1960s developments of attitude control engines and thruster for space crafts were started in Lampoldshausen. In addition to these two plants with test facilities and test capabilities, a third centre with test facilities operated by ERNO in Trauen was built up for the development of the ELDO Launcher (Europa III).In the frame of the consolidation of the different Space Propulsion activities within Dasa (Daimler-Benz Aerospace) in the 1990s as well as the creation of EADS-Space, all test activities were concentrated to the Lampoldshausen site, concluded in 2000.Main reasons for this concentration to one test site were:
• One EADS-ST test-centre in Germany.
• One EADS-ST Test and Engineering Team at one location.
• Multi-use of the three EADS test fields in Lampoldshausen instead of 10 facilities.
• Experts with test engineering know how for development and production programs at one location.
• Synergy effects for test facility modification/maintenance and field support together with DLR.
In addition, cost aspects, especially for test conductions have to be reduced. Therefore, the facility and test requirements have been changed by:
• Using more intelligence in the design and features of the facility (e.g., several test objectives to be tested during one hot-firing test).
• Use of test data for computer simulations as code calibration and therefore reduction of the total number of needed tests.
• Multi-function of test specialists with the main goal to reduce the test team size.
• Computer aided test set-up, firing sequencing and online documentation.

2. Historical overview

2.1. Ottobrunn

A complete overview of all technologies created since the mid of the 1950s is given by Hopmann in [1]. Within this chapter the focus was set on technologies and know how generated in the frame of the Ariane cyrogenic developments at P 59 and air-breathing propulsion [2] and [3].The start of the ARIANE 1 programme and the contract for the development of the HM7-A thrust chamber called for a new facility complex. The erection of the P 59 Test facility was the first high-pressure thrust chamber facility in Europe with a storage level of 800 bars. This high pressure gas was needed to feed the 400 bar LH2 and LOX vacuum insulated run-tanks. For this facility also a special valve test facility was erected in order to test the facility valves in advance to their integration into the test bench (Fig. 1).  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号