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951.
随着石油储备建设的高速发展,油罐规模正向大型化以及能适应极限工况的方向发展.为了避免油温过低而造成凝罐等安全事故,需要准确掌握罐内油品温度场的变化规律.本文根据能量守恒定律,采用分步式算法求解储罐传热系数,将其代入到由Taylor级数展开法所建立的节点非稳态传热离散方程中,并进行数值求解.对大庆某10×104m3浮顶储罐的应用分析表明:随着环境温度的降低,罐内油品温度降速率逐渐增大,储罐液位越高,容积越大,罐内原油温度就越高,温降速率就越小.研究结果对于优化大型浮顶罐的储存工艺设计,保障油库安全经济运行提供了重要的技术支持. 相似文献
952.
Wei Zhou Xiaoming Huang Linbing Wang 《International Journal of Pavement Engineering》2017,18(4):285-291
The objective of this study was to analyse the void reduction behaviour of porous asphalt mixture under load. A three-dimensional discrete element model of porous asphalt mixture based on aggregate gradation and void gradation was built in PFC3D software. The parameter of the model was obtained from creep test. The rutting test was simulated using this discrete element model. And a new method was developed to obtain and analyse the void structure in discrete element model. The simulation results were compared with one of the laboratory test. The comparative analysis indicates that, the discrete element method can be used to simulate the creep response and void reduction behaviour of porous asphalt mixture. Further research shows that porosity, effective porosity, number of connected components and section pores have a good correlation with strain of porous asphalt mixture. With the increase in strain, the proportion of section pores with diameter less than 2 mm increases. In the initial stage of loading, the void reduction is the main reason for rut increment of porous asphalt mixture. In the later stage, the void structure is almost incompressible; the lateral deformation of mixture becomes the domination factor. 相似文献
953.
Energy shortages and environmental problems associated with nonrenewable energy generation techniques have become increasingly prominent worldwide. Solar photovoltaic power generation is able to supply clean, environmentally friendly, and inexhaustible energy. Together with issues related to the expansion of scale, strong stochastic volatility and unpredictability have posed huge challenges to the stability and reliability of this power generation system. The present study proposed a reliable method to evaluate the stationary distribution probability based on the Markov chain method. First, the solar generation system was modeled based on the solar battery. Second, the stochastic property of the solar energy output power was derived and the simulation experiment adopted to verify the feasibility of results. Third, the energy storage device discharge process was modeled based on the Markov chain method and the evaluation method for the reliability of the solar power generation system obtained. Finally, validity of the method was simulated and verified. 相似文献
954.
With its simplicity and feasibility, password‐based remote user authentication becomes a popular way to control remote access to network. These years, numerous password‐based authentication schemes have been proposed. Recently, Maitra et al proposed a smart card–based scheme which claims to be resistant to various attacks. Unfortunately, we found some important flaws in this scheme. Therefore, in this paper, we will demonstrate that the scheme of Maitra et al is not secure enough as claimed: neither resisting against off‐line password guessing attack and insider attack nor preserve forward secrecy. To overcome those flaws, we put forward an improved new scheme which not only is resistant to all known attacks but also provides many attractive attributes, such as user revocation and re‐register. Also, we compared the scheme with other related schemes, the result proved the superiority of our scheme. Particularly, we show a new way (beyond the conventional Deffie‐Hellman approach) to achieve forward secrecy. Furthermore, we put some efforts into exploring the design principle of authentication schemes. 相似文献
955.
In previous works, we have devoted to using the reproducing kernel methods solving integer order differential equations, based on the review of previous works, in this paper, we mainly present a method for solving a class of higher order fractional differential equations with general boundary value problems by using Taylor formula into reproducing kernel space. Its analytical solution is represented in the form of series. The analytical solution and approximate solution obtained by this method is given and it is uniformly converge to the exact solution and its corresponding derivatives. The numerical examples are studied to demonstrate the accuracy of the present method. 相似文献
956.
The discrete coupled algebraic Riccati equation (DCARE) has wide applications in control theory and linear system. In general, for the DCARE, one discusses every term of the coupled term, respectively. In this paper, we consider the coupled term as a whole, which is different from the recent results. When applying eigenvalue inequalities to discuss the coupled term, our method has less error. In terms of the properties of special matrices and eigenvalue inequalities, we propose several upper and lower matrix bounds for the solution of DCARE. Further, we discuss the iterative algorithms for the solution of the DCARE. In the fixed point iterative algorithms, the scope of Lipschitz factor is wider than the recent results. Finally, we offer corresponding numerical examples to illustrate the effectiveness of the derived results. 相似文献
957.
It is well known that the existence of unstable sampled zero dynamics is recognised as a major barrier in many control problems. When the usual digital control with zero-order hold (ZOH) or fractional-order hold (FROH) input is used, unstable sampled zero dynamics inevitably appear in the discrete-time model even though the continuous-time system with relative degree more than or equal to three is of minimum phase. In this paper, we show how an approximate sampled-data model can be obtained for nonlinear systems by the use of multirate input and hold such as a generalised sample hold function (GSHF) in order that discrete zero dynamics of the resulting model can be arbitrarily placed. Furthermore, the properties of sampled zero dynamics are studied and the conditions for ensuring the stability of sampling zero dynamics of the desired model are derived. The results presented here generalise well-known notion of sampling zero dynamics from the linear case to nonlinear systems, and GSHF can provide some advantages over ZOH or FROH in terms of stability of discrete system zero dynamics. 相似文献
958.
Autoregressive conditional heteroskedasticity (ARCH)() models nest a wide range of ARCH and generalized ARCH models including models with long memory in volatility. Existing work assumes the existence of second moments. However, the fractionally integrated generalized ARCH model, one version of a long memory in volatility model, does not have finite second moments and rarely satisfies the moment conditions of the existing literature. This article weakens the moment assumptions of a general ARCH( ) class of models and develops the theory for consistency and asymptotic normality of the quasi‐maximum likelihood estimator. 相似文献
959.
This paper provides a survey of the main advanced control techniques currently adopted in factory automation. In particular, it focuses on five classes of control approaches, namely: model-based control, control based on computational intelligence, adaptive control, discrete event systems-based control and finally event-triggered and self-triggered control. A particular focus is put on the most significant and recent contributions in these areas with attention to their application in the factory automation domain. Finally, open issues, challenges and the requirements of further research efforts for each class are pointed out. 相似文献
960.
The process of redesigning production systems is usually complex, for which virtual design tools are available. These tools are used to analyse and evaluate planned changes prior to implementation, making it possible to identify and prevent costly design mistakes. Despite this, design mistakes arise during and after the implementation. A source for design mistakes is incorrect or insufficient spatial data of the production systems used in the virtual design tools. The aim of this paper is to show how to reduce the time required for planning and implementing the redesign by supporting the process with realistic visualisation, created from accurate spatial data of the real production systems. Three industrial studies were carried out to evaluate how address realistic visualisation in order to support the redesign process. The result shows terrestrial 3D laser scanning to be suitable for capturing spatial data for realistic visualisation of production systems. The realistic visualisation can be used to virtually analyse design alternatives of the production systems, by, for example, combining the 3D laser scan data with 3D CAD models. The realistic visualisation enabling effective and accurate planning, which gives the opportunity to reduce the time required for planning and implementing redesigned production systems. 相似文献