Balkan Journal of Mechanical Transmissions (BJMT)
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Balkan Journal of Mechanical Transmissions RO manian Association of (BJMT) Balkan Association of ME chanical Power Transmissions Volume 2 (2012), Issue 1, pp. 61-72 Transmissions (BAPT) ISSN 2069–5497 (ROAMET) AN EXTENSION OF THE ELECTROMECHANICAL ANALOGY IN THE DOMAIN OF HYDROSTATIC TRANSMISSIONS Part I. THE ELECTROMAGNETIC AND ELECTROMECHANICAL ANALOGIES Mircea RADULESCU ABSTRACT. The paper aims to expand the electromechanical analogy in other domains of technology: hydraulic, pneumatic, acoustic, sonic, and even in thermodynamics. In addition to the similarity of the equations and mathematical models, in the domain of fluidic systems we have highlighted the analogy of the circuit elements and some basic structures, for which the equivalent schemes are given. Analogy tables are presented, including the important sizes, units, symbols and generalized mathematical models applicable in all domains above and the advantages of the analogy and its limits of application are highlighted . KEYWORDS. Electromechanic / hydraulic analogy, generalized parameters, electric / mechanical / hydraulic resistance / inductance / capacity / impedance, analogy of sizes / equations, limits of the analogy. 3 NOMENCLATURE V, ∆V [ m ] volume; finite fluid volume variation Symbol Description ω; ω rad / s angular/natural frequency r r r 0 A ; B= ∇ × A electrodynamic vector potential z= x + jy complex number (j = − 1) −1 Be [Ω ] electric susceptance (R ;θ ; λ ) spatial polar coordinates 2 τ apparent power mass density BL [ N / m ] bulk modulus of elasticity of liquid C= S−1 [ F ] electric capacity / elastance ABBREVIATIONS e e P.C. particular case f Hz circular frequency B.C.; I.C. boundary conditions/initial conditions S.C.P.; S.D.P. lumped/distributed parameters system IH = ∆ H/ L [ − ] hydraulic slope E.S.F.; M.S.F. electric/magnetic quasi-stationary field diffusion coefficient in KD L.F.; I.F. local (differential)form / integral form electrochemistry O.D.E.; P.D.E. ordinary/partial differential equations 3 KH [ m ] flow module in hydrodynamics E.Q.S.;M.Q.S. electric/magnetic quasistationary Le [ H ] electric inductance 1. INTRODUCTION 2− 5 MH [ s m ] hydraulic module in hydrodynamics The analogy is one of the basic methods used to nondimensional exponent of RH - research various areas of physics-specific n − hydraulic resistance to motion phenomena, being based on the formal identity of 3 mathematical models that describe the original Q;∆ Qm [ /] s volumetric flow/leakage flow phenomenon and the similar phenomenon. Therefore, pp;∆ = pi − p e pressure; drop/jump pressure the analogy method allows solving problems in a particular domain, using the results from another field, R= G −1 [ Ω ] electric resistance / conductance e e where the phenomena of the two domains have the Re =vd ν −1[ − ] Reynolds number in hydraulic pipes same mathematical model (are analogue). linear/linearised hydraulic resistance R;'[ R Ns / m 5 ] The scale of analogy is the constant ratio between the L to fluid motion values of the two similar sizes, which belong to the n two domains and must verify the (formally identical) Ns non-linear hydraulic resistance to R mathematical models which express the conduct of N 3n+ 2 motion of fluid m the two phenomena. The analogy is partial, if only s [ m] curvilinear coordinate; string deviation some of the quantities involved in the description of T [ K] thermodynamic temperature phenomena are analogue. During the dynamic U [Nm] scalar potential of the force modeling of complex systems, difficulties arise, Basic geometrical volume of rotary regarding their direct analysis, so that sometimes the V[ m3 / rot ] g hydraulic volumic machines application of methods of study and indirect analysis 61 are required, allowing the complete knowledge of the 6. Any analogy must respect the principle of studied phenomenon, based on observations and conservation of energy, so that the condition of experimental research performed on similar models. compatibility from an analogy to the other derived from it, is to be a biunique correspondence of The biunivocal correspondence between the original powers for the two domains of the similar phenomenon and its model allows that, on the basis phenomena; for this reason, the equations from of rules and assumptions established a priori, the the mathematical model of the analog electrical variables that can not be assessed on the primary circuit must be isomorphic with the mathematical (original) system can be determined on the analog model equations of the studied (original) system, model; based on information obtained from the model, as defined in the biunique correspondence. some conclusions can be drawn on the original behavior. Frequently, the original system (a The analogy of non-electrical elements and circuits mechanical, acoustic, hydraulic, pneumatic or thermal (mechanic, acoustic, thermic, hydraulic, pneumatic, system) is studied on an analog electric model, this sonic etc.) with the electrical ones allows the modeling providing the research of the phenomenon on an of the original system, based on some active circuit equivalent electric or electronic circuit, which allows elements (sources) connected to passive elements the processing of results and the implementation of (resistances, inductances, capacities, perditances) solving methods from the electric field in the area of through specific junction elements. Since the analogy interest. Similar models in the electric field are of sizes and mathematical models also aims an preferred, as their structure and operation have been analogy of the physical laws specific to analogue improved based on results obtained in the theory of circuits (systems), some theorems and laws of the electrical circuits. In these circumstances, the analogy electric disciplines can be properly translated into laws can be a process of synthesis of complex non-electric and theorems expressing the phenomena of the circuits, based on synthesis algorithms specific to domain of interest (the original domain); example: electric or electronic circuits. Kirchhoff’s theorems, Ohm’s law, the law of electromagnetic induction, the transfiguration A detailed approach of the studies regarding the theorem, superposition theorem, Y↔∆ transfiguration analogy is shown by Olson (1958), Kinsler (1962), etc. (as shown by Mocanu, 1979, Şora, 1982, Levi (1966), Hackenschmidt (1972), Stanomir (1989), Stanomir, 1989). and Fransua (1999). 3. GENERALIZED PARAMETERS 2. REQUIREMENTS OF THE ELECTROMECHANICAL ANALOGY The need to extend the electromechanical analogy to other non-electric domains, which derive from The electromechanic analogy has the advantage that mechanics, becomes obvious with the approach of it can easily adapt to the following requirements interdisciplinary researches with applicability in specific to the study of physical phenomena by science vanguard fields like space flight engineering, modeling (as shown by Stanomir, 1982). mecatronics etc. There is also a need to establish a 1. The model should ensure a broad representation common language based on the essential role of the of the original, that is to allow highlighting its extended analogy between the domains unknown properties; they must be better known corresponding to physical systems that aim the than the ones of the original, or must be easily interdisciplinary science objectives. experimentally modeled; The degree of generality of the analogy can be 2. The bonds of the non-electric system must be significantly increased if the quantities involved in the holonome, scleronome and linear and the system description of the phenomena are brought to must have a linear equivalent graph and only dimensionless forms and if a common language, with elementary one-port structures. general validity is adopted. In order to highlight the domain of application for some extended analogies, 3. The specific dynamic process of the original generalized power variables are introduced: f (flow) system to be studied on the analog model will and e (effort), and on this basis we can define the strictly collapse (limit) to the domain of interest; generalized energy variables (as shown by Buculei, 4. Based on the scheme of the original model, we 1993, Rădulescu, 2005). can establish the equivalent electrical scheme; for We can generalize some non-electric sizes, similar to example, the series / parallel connection of those associated with passive circuit elements elements that goes into the original, must be (resistances, inductances, capacities, perditances replaced with similar elements of circuit, connected etc.); these quantities are introduced taking into properly, in series / parallel; account the analogy of some basic laws from the 5. The physical character of a quantity of the original disciplines with non-electric profile, with laws and system must be maintained to the study on the equations of circuit and electrical machines theory. analogue system; for example, the hydraulic Table 1 gives a generalization of the basic parameters potential must have as analogous the electric that characterize some systems/devices and the potential, etc. elements of machines and circuits. 62 Table 1 . Generalized parameters Parameters t Displacement: qt()()()=∫ fτ d τ , q 0 = 0 0 t Pulse: ℑ=()()()t∫ eτ d τ , ℑ= 0 0 e t General General Generalized power: P= ef = Π W ; Generalized energy: Et()()()=∫ PdEτ τ , 0 = 0 J 0 −1 Action: At( ) = qt( ) ℑ ( t) J ; Impedance: ZefRjXY=/ =+= Ω ; j =− 1 Admittance: Y= G − jB S =Ω −1 x m , strokelength−