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排序方式: 共有389条查询结果,搜索用时 15 毫秒
1.
Bengt Sundén Tor Sköldheden 《International Communications in Heat and Mass Transfer》1985,12(5):559-566
An experimental investigation of heat transfer and pressure drop from a new type of corrugated channels is presented. The investigation has been carried out for Reynolds numbers in the range of for one corrugated and one smooth channel. It is found that the heat transfer from the corrugated channel is up to 3.5 times higher than for the smooth one. The pressure drop is however large (5 – 6 times the value of a smooth channel) and it is suggested that the corrugation height and length should be altered in order to balance the increases in heat transfer and pressure drop. 相似文献
2.
Lise T. Sagdahl Mari-Ann Einarsrud Tor Grande 《Journal of the European Ceramic Society》2006,26(16):3665-3673
The sintering properties of La1−xSrxFeO3−δ (x = 0.1, 0.25) mixed conductors have been investigated with particular emphasis on the effect of secondary phases due to cation non-stoichiometry (±5 mol% La excess and deficiency). Secondary phases, located at grain boundaries in cation non-stoichiometric materials, increased the sintering temperature compared to single-phase materials. Extensive swelling in final stage of sintering was observed in all materials, which resulted in micro-porous materials. The swelling was most pronounced in the phase pure and two-phase materials due to La-deficiency, while refractory secondary phases in La-excess materials inhibited both sintering, grain growth and swelling. In La-deficient materials, formation of molten secondary phases resulted in rapid swelling due to viscous flow. The present findings demonstrated the importance of controlling sintering temperature and time, as well as careful control of the cation stoichiometry of La1−xSrxFeO3−δ in order to achieve fully dense and homogenous La1−xSrxFeO3−δ ceramics. 相似文献
3.
Object-oriented design is an approach to systems development that proposes the use of system objects to build new systems and rebuild old ones. An important goal of object-oriented development is to change the nature of traditional software development from designing and writing models from scratch to building systems through the assembly of reusable software objects. This article discusses the productivity potential as well as the limitations of object-oriented systems development and makes recommendations for its use. 相似文献
4.
This study investigated the effect of moving from small offices to a landscape environment for 19 Visual Display Unit (VDU) operators at Alcatel Denmark AS. The operators reported significantly improved lighting condition and glare situation. Further, visual discomfort was also significantly reduced on a Visual Analogue Scale (VAS). There was no significant correlation between lighting condition and visual discomfort neither in the small offices nor in the office landscape. However, visual discomfort correlated significantly with glare in small offices i.e. more glare is related to more visual discomfort. This correlation disappeared after the lighting system in the office landscape had been improved. There was also a significant correlation between glare and itching of the eyes as well as blurred vision in the small offices, i.e. more glare more visual symptoms. Experience of pain was found to reduce the subjective assessment of work capacity during VDU tasks. There was a significant correlation between visual discomfort and reduced work capacity in small offices and in the office landscape. When moving from the small offices to the office landscape, there was a significant reduction in headache as well as back pain. No significant changes in pain intensity in the neck, shoulder, forearm, and wrist/hand were observed.The pain levels in different body areas were significantly correlated with subjective assessment of reduced work capacity in small offices and in the office landscape.By careful design and construction of an office landscape with regard to lighting and visual conditions, transfer from small offices may be acceptable from a visual-ergonomic point of view. 相似文献
5.
The online computational burden of linear model predictive control (MPC) can be moved offline by using multi-parametric programming, so-called explicit MPC. The solution to the explicit MPC problem is a piecewise affine (PWA) state feedback function defined over a polyhedral subdivision of the set of feasible states. The online evaluation of such a control law needs to determine the polyhedral region in which the current state lies. This procedure is called point location; its computational complexity is challenging, and determines the minimum possible sampling time of the system. A new flexible algorithm is proposed which enables the designer to trade off between time and storage complexities. Utilizing the concept of hash tables and the associated hash functions, the proposed method solves an aggregated point location problem that overcomes prohibitive complexity growth with the number of polyhedral regions, while the storage–processing trade-off can be optimized via scaling parameters. The flexibility and power of this approach is supported by several numerical examples. 相似文献
6.
Esten Ingar Gr?tli Tor Arne Johansen 《Journal of Intelligent and Robotic Systems》2012,65(1-4):265-282
We will in this paper address the problem of offline path planning for Unmanned Aerial Vehicles (UAVs). Our goal is to find paths that meet mission objectives, are safe with respect to collision and grounding, fuel efficient and satisfy criteria for communication. Due to the many nonconvex constraints of the problem, Mixed Integer Linear Programming (MILP) will be used in finding the path. Approximate communication constraints and terrain avoidance constraints are used in the MILP formulation. To achieve more accurate prediction of the ability to communicate, the path is then analyzed in the radio propagation toolbox SPLAT!, and if the UAVs are not able to communicate according to design criteria for bandwidth, constraints are modified in the optimization problem in an iterative manner. The approach is exemplified with the following setup: The path of two UAVs are planned so they can serve as relay nodes between a target without line of sight to the base station. 相似文献
7.
8.
SeyedMehrdad Hosseini Alireza Fatehi Tor Arne Johansen Ali Khaki Sedigh 《Journal of Process Control》2012,22(9):1732-1742
This paper provides a systematic method for model bank selection in multi-linear model analysis for nonlinear systems by presenting a new algorithm which incorporates a nonlinearity measure and a modified gap based metric. This algorithm is developed for off-line use, but can be implemented for on-line usage. Initially, the nonlinearity measure analysis based on the higher order statistic (HOS) and the linear cross correlation methods are used for decomposing the total operating space into several regions with linear models. The resulting linear models are then used to construct the primary model bank. In order to avoid unnecessary linear local models in the primary model bank, a gap based metric is introduced and applied in order to merge similar linear local models. In order to illustrate the usefulness of the proposed algorithm, two simulation examples are presented: a pH neutralization plant and a continuous stirred tank reactor (CSTR). 相似文献
9.
Jan Gulliksen Bengt G ransson Inger Boivie Stefan Blomkvist Jenny Persson sa Cajander 《Behaviour & Information Technology》2003,22(6):397-409
The concept of user-centred systems design (UCSD) has no agreed upon definition. Consequently, there is a great variety in the ways it is applied, which may lead to poor quality and poor usability in the resulting systems, as well as misconceptions about the effectiveness of UCSD. The purpose of this paper is to propose a definition of UCSD. We have identified 12 key principles for the adoption of a user-centred development process, principles that are based on existing theory, as well as research in and experiences from a large number of software development projects. The initial set of principles were applied and evaluated in a case study and modified accordingly. These principles can be used to communicate the nature of UCSD, evaluate a development process or develop systems development processes that support a user-centred approach. We also suggest activity lists and some tools for applying UCSD. 相似文献
10.
A design perspective of mechanical function and its object-oriented representation scheme 总被引:5,自引:0,他引:5
The purpose of this paper is to present a functional schema which can be used to develop computer tools to assist designers during the early stages of the mechanical product design process. The schema is based on an analysis of the meaning of function. five main types of mechanical function are described: performance, assembly, manufacturing, marketing and maintenance. The paper focuses on the specification and representation of performance functions. These are defined using a natural language, which is an extension of the verb-noun pair technique. Three levels of performance functions are identified: overall, embodiment and geometric. The relationship between these levels of functions and the physical structures required to implement them is discussed in detail. An architecture to implement the schema using object-oriented technology is described. A research prototype based on this architecture has been developed in the programming language Incr Tcl/Tk. 相似文献