共查询到20条相似文献，搜索用时 428 毫秒
1.
Dean Karnopp 《Journal of The Franklin Institute》1979,308(3):219-234
Bond graph modeling techniques yield state equations intimately related to energy storage in physical systems. The easy physical interpretation of the state variables from a bond graph model aids in the realization of modern automatic control schemes involving state variable feedback. When it is inconvenient or impossible or measure certain state variables, the useful device of an observer may be used to estimate the missing state variables. It is shown that the same bond graph used to model the system can be used to derive a complete or reduced order observer. The partial observers use derivative causality in a new way and in some cases, the effects of completely unknown disturbances may be accounted for. 相似文献
2.
The transport of thermal energy in thermodynamics is described as the product of entropy flow and of the absolute temperature, in analogy to the volume flow and pressure in oil hydraulics and to electric charge flow (= current) and voltage in electronics. Bond graphs are shown to be especially suitable to describe the splitting of applied thermal energy into internal energy and external mechanical work. Transformers and the 0- and 1-junctions of Paynter can illustrate various entropy flow processes, including Carnot engines and heat exchangers. Entropy flow in heat conduction is distinguished from entropy convection, or transport by moving mass, where the entropy/temperature characteristic or equation of state is important. Irreversibilities are represented by impedance transformers reducing temperature and increasing entropy flow but conserving power. 相似文献
3.
Bond graph formulation of an optimal control problem for linear time invariant systems 总被引：1，自引：0，他引：1
A recent communication has proposed a conjectural procedure for representing a category of optimal control problems in bond graph language [W. Marquis-Favre, B. Chereji, D. Thomasset, S. Scavarda, Bond graph representation of an optimal control problem: the dc motor example, in: ICBGM’05 International Conference of Bond Graph Modelling and Simulation, New Orleans, USA, January 23-27, 2005, pp. 239-244]. This paper aims at providing a fundamental theory for proving the effectiveness of this procedure. The class of problem that the procedure can deal with has been extended. Its application was formerly restricted to linear time invariant siso system. The systems considered now are linear time invariant mimo systems. The optimization objective is the minimization of dissipation and input. The developments concerning the optimal control problem are based on the Pontryagin maximum principle and the proof of the effectiveness of the procedure makes a broad use of the port-Hamiltonian concept. As a result, the bond graph representation of the given optimization problem enables the analytical system, which provides the optimal solution, to be derived. The work presented in this paper is the first step in research with perspectives towards formulating dynamic optimization problems in bond graph and, towards coupling this formulation with a sizing methodology using bond graph language and a state-space inverse model approach. This sizing methodology, however, is not the topic of this paper and thus is not presented here. 相似文献
4.
Bond graphs have proven to be useful in modeling a wide variety of physical systems where multiports are needed to represent coupling phenomena. Here we show the relationship between bond graphs and more conventional notations utilizing connection N-ports and system graphs. This provides a rigorous foundation for bond graph manipulations and highlights certain difficulties with sign conventions and casual assignments that arise when junction structure loops are present. 相似文献
5.
Donald L. Margolis 《Journal of The Franklin Institute》1980,310(2):107-117
Bond graphs are used to construct finite mode representations of inherently distributed systems. These systems are, perhaps, only part of an overall dynamic system. The “causal” information provided by the bond graph permits the derivation of an automatable algorithm which produces the state equations as well as all output variables associated with the finite modes. The procedure requires only the a priori knowledge of modal masses, frequencies, and associated mode shapes for general boundary conditions of the distributed parts of the system. Thus, the algorithm is applicable to any multidimensional distributed system which is representable by normal modes. 相似文献
6.
Previous works have shown the usefulness of bond graphs for modeling and simulation of interacting lumped and distributed systems. Frequently, when damping is included in the model, the overall system is “stiff”, possessing widely disparate characteristic times. This makes simulation difficult and time consuming.Bond graphs are used here to represent the interacting lumped and modal dynamics of a system while treating the damping as an external forcing onto the system. By performing a second modal decomposition, a second bond graph model can be formulated where the damping can now be physically represented. The result is a total system model in which the characteristic times can be controlled through elimination of high frequency modes. 相似文献
7.
本文介绍了热力学第二定律的教学方法、效果和体会。结合生活中的热现象讲授热力学第二定律,便于学生弄懂热力学第二定律的原理,既能激发学生的学习兴趣,又能提高教学质量。 相似文献
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绿色经济是人类寻求的一种能够促进社会经济与环境和谐发展的新型经济发展模式,其本质是生态经济.绿色经济遵从生态规律,研究热现象中物态转变和能量转换规律的热力学定律对于绿色经济具有重要的意义.文章探究了热力学定律对绿色经济发展的启示,并对绿色经济进行了热力学分析,提出通过构建低熵发展模式、遵循自然生态规律、发展绿色科技、树立低熵观念等途径发展绿色经济. 相似文献
10.
Bond graphs are an extremely useful modeling procedure for representing the actual energy exchange mechanisms of interacting dynamic systems. Governing state equations are straightforwardly obtained from the bond graph; however, for large structures, a restrictively large number of equations can result. A procedure is developed whereby the original equations are reduced to a form suitable for modal decomposition. The resulting modes are reinterpreted in bond graph form with the resulting model being an extremely accurate system representation while requiring only a fraction of the original number of equations. The procedure is demonstrated through example. 相似文献
11.
DNA计算是解决困难问题的一种很重要的方法。应用DNA计算解决图论中的最小支撑树问题。利用DNA的热力学特性,根据边的权长不同,给它们设计不同溶解温度的DNA链。根据温度的不同,电泳时DNA分子的形状不同,电泳的速度也不同,从而根据电泳速度分离出最小支撑树的所有边。在这里给出了5个顶点的赋权图为例来求它的最小支撑树,说明了该方法的简便性。 相似文献
12.
能源效率的七类测度指标及其测度方法 总被引：15，自引：0，他引：15
能源效率已经成为能源政策研究的热点问题之一,但有关能源效率测度指标及其测度方法的系统比较重视不够.本文对传统的和作者提出的能源效率测度指标做全面总结和系统剖析(包括能源宏观效率、能源实物效率、能源物理效率、能源要素利用效率、能源要素配置效率、能源价值效率、能源经济效率等七大类指标).讨论了各类指标的理论基础或假设条件、相互关系、优缺点或适应范围,以及在使用时需要注意的问题,澄清了当前关于能源效率指标的一些认识或应用误区. 相似文献
13.
A complete theory of diffusion of absorbing gases in porous solids is developed. Both ordinary and thermal diffusion are considered. The thermodynamics of irreversible processes is used to derive the general flux equations.A new theoretical model of surface diffusion is presented. Moreover, the proper method of combining surface and gas-phase fluxes is established. The total flux in the pores is represented by a 5 parameter model, which includes the effects of (1) free (gaseous) diffusion, (2) Knudsen diffusion, and (3) surface diffusion.The design of a new diffusion cell is presented along with a stagewise method for analyzing results. The cell is unique in that specimens mounted in copper clad circuit board material permits nonisothermal as well as isothermal operation. Earlier designs were confined to isothermal operation due to mounting specimens in metallic materials such as brass and aluminum. 相似文献
14.
研究了受热阻、热漏和回热损失影响的不可逆斯特林制冷机制冷率和制冷系数的最高和最低界限。为斯特林制冷机工作参数的选择提供了两条有限时间热力学新准则。 相似文献
15.
Aminuddin A. Kayani Khashayar Khoshmanesh Stephanie A. Ward Arnan Mitchell Kourosh Kalantar-zadeh 《Biomicrofluidics》2012,6(3)
The advent of optofluidic systems incorporating suspended particles has resulted in the emergence of novel applications. Such systems operate based on the fact that suspended particles can be manipulated using well-appointed active forces, and their motions, locations and local concentrations can be controlled. These forces can be exerted on both individual and clusters of particles. Having the capability to manipulate suspended particles gives users the ability for tuning the physical and, to some extent, the chemical properties of the suspension media, which addresses the needs of various advanced optofluidic systems. Additionally, the incorporation of particles results in the realization of novel optofluidic solutions used for creating optical components and sensing platforms. In this review, we present different types of active forces that are used for particle manipulations and the resulting optofluidic systems incorporating them. These systems include optical components, optofluidic detection and analysis platforms, plasmonics and Raman systems, thermal and energy related systems, and platforms specifically incorporating biological particles. We conclude the review with a discussion of future perspectives, which are expected to further advance this rapidly growing field. 相似文献
16.
J.L. Finck 《Journal of The Franklin Institute》1948,245(4):301-317
In this paper the concepts “equilibrium” and “reversibility” are examined from the standpoint of the number of independent variables which define a thermodynamic system. The endeavor is made to show that the number of independent variables which are selected is crucial to the basic concepts as well as to the second law of thermodynamics. If this number is less than the minimum required to define the system completely, the equation of state for the internal energy will be incomplete. It is our practice to employ incomplete equations of state, and this results in processes which we consider to be irreversible. The Kelvin-Planck and Clausius principles are shown to be somewhat related to the first law of thermodynamics, and their validity arises from the fact that the equations of state which are used are incomplete. If these equations were complete, that is, if the number of independent variables were not less than the minimum required to describe the systems completely, we should have complete conversion of heat into work, as well as work into heat. The difficulties in realizing complete equations are considered.The entropy concept is considered in detail, and it is shown that there are serious limitations in its application. 相似文献
17.
Unified modeling and analysis of a proportional valve 总被引：4，自引：0，他引：4
Developments in nonlinear control theory have made it possible to design controllers for systems having non-smooth nonlinearities in their dynamics. Hydraulic systems that use inexpensive proportional valves are examples of such systems, where nonlinearities arise due to valve geometry and spool imperfections. Without a proper valve model, however, nonlinear analysis and control of these hydraulic systems is not possible.We have developed nonlinear equations for a generic proportional valve model and have used them to obtain simplified flow rate expressions under generally accepted assumptions. These equations relate a set of geometric spool properties and physical model parameters to the flow rate through the valve ports. The development focuses on obtaining a single set of flow rate equations applicable to critical center, overlapped, and underlapped proportional valves. These unified model equations are useful for simulation and nonlinear controller design. We have also demonstrated that the errors incurred when using the unified valve model are dependent on the damping coefficient alone and are less than 10% in the frequency range within which most valves are used. 相似文献
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钟海琴 《科学技术与辩证法》2009,26(6):49-54
文章以哲学与原子理论二者辗转相辅的发展为背景,论证了玻耳兹曼关于原子、熵和热力学第二定律的概率论基础的统计决定论实质,指出概率论解释成为了科学哲学传统的永恒价值。 相似文献
20.
P.C. Breedveld 《Journal of The Franklin Institute》1984,318(2):77-89
It is shown that a theorem on essential gyrators presented by Rosenberg (1) and used in (2) claims too much and that the internal structure of the multiport elements of the system must be studied in order to be able to decide whether a gyrator is essentially contained in the system or not. Bond graph terminology is used (3)—(6) and a new theorem is formulated, which provides an algorithm to decide on the essentiality of a gyrator by immediate inspection of the bond graph.As a side-result of this approach some new methods for junction structure simplification can be formulated. The significance of junction 3-ports for the concept of the essential gyrator is elaborated by providing equivalence rules for all kinds of junction 3-ports and introducing a unit essential junction 3-port (ES) and a unit non-essential junction 3-port (NES). Finally the hydraulic junction is treated as an example of a physical non-potential junction, i.e. a junction congruent with an ES. 相似文献