A refined trigonometric shear deformation theory for thermoelastic bending of functionally graded sandwich plates

A refined trigonometric shear deformation theory (RTSDT) taking into account transverse shear deformation effects is presented for the thermoelastic bending analysis of functionally graded sandwich plates. Unlike any other theory, the number of unknown functions involved is only four, as against five in case of other shear deformation theories. The theory presented is variationally consistent, does not require shear correction factor, the displacement components are expressed by trigonometric series representation through the plate thickness to develop a two-dimensional theory and gives rise to transverse shear stress variation such that the transverse shear stresses vary parabolically across the thickness satisfying shear stress free surface conditions. The sandwich with homogeneous facesheet and FGM core is considered. Material properties of the present FGM core are assumed to vary according to a power law distribution in terms of the volume fractions of the constituents. The influences played by the transverse shear deformation, thermal load, plate aspect ratio, and volume fraction distribution are studied. Numerical results for deflections and stresses of functionally graded metal–ceramic plates are investigated. It can be concluded that the proposed theory is accurate and simple in solving the thermoelastic bending behavior of functionally graded plates.     

环形刀等残留高度多轴加工步距计算

针对不同曲面的环形刀多轴加工,提出了最大步距计算的数学模型,建立了残留高度为常数时步距与刀轴倾角之间的函数关系,通过函数关系推导出最佳步距的值。实验表明,该算法在保证加工精度的前提下,能有效缩短加工刀轨路径,提高加工效率。     

New frontiers in design synthesis

The Intelligent Synthesis Environment (ISE), which is one of the major strategic technologies under development at NASA centers and the University of Virginia, is described. One of the major objectives of ISE is to significantly enhance the rapid creation of innovative affordable products and missions. ISE uses a synergistic combination of leading-edge technologies, including high performance computing, high capacity communications and networking, human-centered computing, knowledge-based engineering, computational intelligence, virtual product development, and product information management. The environment will link scientists, design teams, manufacturers, suppliers, and consultants who participate in the mission synthesis as well as in the creation and operation of the aerospace system. It will radically advance the process by which complex science missions are synthesized, and high-tech engineering systems are designed, manufactured and operated. The five major components critical to ISE are human-centered computing, infrastructure for distributed collaboration, rapid synthesis and simulation tools, life cycle integration and validation, and cultural change in both the engineering and science creative process. The five components and their subelements are described. Related U.S. government programs are outlined and the future impact of ISE on engineering research and education is discussed.     

Comparison of Two Adaptive Methods for Time Delay Estimation

Two adaptive algorithms for estimating the time delay between two-sensor outputs are compared. These methods are similar in that they employ the least mean square (LMS) gradient approach to estimate the time difference of arrival to two sensors. However, they involve the LMS gradient method in different ways, and thus have different properties. Some theoretical aspects are addressed. Also, they are compared via computer simulations for a variety of cases, including time-varying delay functions corresponding to moving source or receivers.     

Relationships of mineral deposits and lineament analysis of the Red Sea region,northeastern Sudan

The Red Sea region of northeastern Sudan is the most favorable target for mineral prospection. It is the place where almost all types of mineral deposits, so far recorded in Sudan, were represented. Lineament analysis of a 1:1,000,000-scale Landsat image mosaic indicate, among others, two prominent N-S and ENE structural trends to control magmatic activities and the related mineralization in the Red Sea region. Mineralization, tectonic, and magmatic activities in the Proterozoic appear to be closely correlative with the recent events connected with the formation of the Red Sea.     

A Note on Satellite Dynamics

It is demonstrated here that inertial differentiation of angular momentum-is independent of the choice of the moving reference coordinate system. The results agree with Greensite [1] and contradict Sen's results [2] by indicating a basic error in his derivation. However, Sen's step [2] is correct.     

Landsat model for groundwater exploration in Nuba Mountains,Sudan

The region of Nuba Mountains is largely dominated by Precambrian crystalline basement rocks, and often experiences acute shortage of water for domestic and irrigation purposes especially during the dry season (February – May). A Landsat model essentially based on lineament and drainage analysis is proposed to delineate potential target zones for groundwater prospecting. Target zones are indicated by the overlap of the high-intensity lineament contours and the low-intensity drainage contours, and by intersection of a stream channel and lineament structure. Most wells lying within the defined targets are successful.     

Control of Synchronous Orbit Using Lyapunov Stability Theory

A state-dependent control law is proposed using the Lyapunov stability theorem and its usefulness for closed-loop control of a synchronous orbit is investigated. It is shown that a sequential scheme using a modified control law provides a more practical means of orbit control.     

European R&D in the satellite communication user Earth segment

This paper refers to a study (specificaly to its chapter 7)¹ carried out by Euroconsult for ESA on the key characteristics of European R&D in the satellite communications user Earth segment. The study was initiated by the Working Group on Satellite Communications Policy² of the Joint Board on Communications Satellite Programmes (JCB), which was established by the Director General of ESA in July 1990 to contribute to the European agency's response to the EC Green Paper. The working group specifically expresses the European space communications industry's point of view.     

Real-time sensor fault detection and isolation for LEO satellite attitude estimation through magnetometer data

Attitude estimation is a critical component of the Attitude Determination and Control System (ADCS) of any satellite. It is used to convert the sensor observation data to an estimated attitude using filtering algorithms. However, in the presence of sensor faults, the ADCS fails to achieve the desired attitude accuracy. In this paper, the Fault Tolerant Extended Kalman Filter (FTEKF) is proposed to handle this imperfection. In accordance, various filtering steps are included in the FTEKF design to enhance both attitude estimation and sensor fault detection. The developed algorithm can detect and isolate any unexpected sensor faults in real time, which provides a reliable attitude estimation. A comparative study with the classical and robust Kalman filters is performed through numerical simulations in order to validate the effectiveness of the adopted filter in case of magnetometer fault data.