EP3458827A1

EP3458827A1 - Estimation of a physical quantity on exit from a hydraulic circuit

Info

Publication number: EP3458827A1
Application number: EP17731611.4A
Authority: EP
Inventors: Nicolas LEMOINE
Original assignee: ArianeGroup SAS
Current assignee: ArianeGroup SAS
Priority date: 2016-05-20
Filing date: 2017-05-19
Publication date: 2019-03-27
Also published as: FR3051554B1; WO2017198963A1; FR3051554A1

Abstract

A method for estimating at least one physical quantity on exit from a hydraulic circuit comprising an entry node (A), an exit node (D), at least one internal node (B, C) and hydraulic components disposed between the entry node and the exit node, the method comprises: - a step of obtaining a numerical model of the hydraulic circuit, said model comprising a global transfer function of predetermined form whose coefficients are determined on the basis of intermediate transfer functions of each segment of the hydraulic circuit delimited by two successive nodes, each intermediate transfer function giving the relation between physical quantities on entry and physical quantities on exit from the segment that it represents; - a step of estimating the physical quantity on exit from the hydraulic circuit on the basis of the numerical model and of an entry value of at least one physical quantity and/or of operating parameters of the hydraulic circuit.

Description

Estimation of a physical quantity at the output of a hydraulic circuit

FIELD OF THE INVENTION

The present disclosure relates to the field of hydraulic circuits, and more particularly to a method for estimating at least one physical quantity at the output of a hydraulic circuit. Such a method finds its application especially for hydraulic circuits of rocket engines.

TECHNOLOGICAL BACKGROUND

In the field of liquid propellant rockets, the effect name POGO has been given to the resonance input of a liquid propellant in the power supply circuit of the rocket engine with mechanical oscillations of the rocket. Since the thrust of the rocket engine varies with the propellant flow supplied by the supply circuit, such a resonance input can cause rapidly diverging oscillations, and thus give rise to guiding difficulties, and even to damage that may occur. go to the total loss of its payload, or even the vehicle. The name POGO effect does not come from an acronym, but "pogo sticks" or jumping stilts, toys formed by a spring rod whose leaps have reminded technicians violent longitudinal oscillations of rockets caused by this effect. Since the beginning of the development of liquid propellant rockets, it has therefore proved very important to characterize this POGO effect in order to better control it.

Since it is extremely expensive to reproduce the POGO phenomenon on the ground, the stability of a launcher compared to the POGO effect is generally studied by numerical simulation, thanks to a mechanical model coupled to a hydraulic model. The hydraulic model includes among others the equations expressing the fluctuations of flow and pressure in propellant tanks as a function of the fluctuations of injected flow rates and pressure in the combustion chamber. The way to establish these equations differs depending on the type of rocket engine studied. In gas-generating cycle rocket engines, turbopump turbines are driven by a gas generator that produces gases from a small portion of the propellants taken from the fuel line of the combustion chamber. For these rocket motors, except the samples to the gas generator, the hydraulic components (line, pump, turbine, restriction, etc.) are assembled in series from the tanks to the combustion chamber. In addition, knowing that the flow rates to the gas generator are low, it is possible to neglect these flow rates and consider the hydraulic circuit as a simple linear circuit comprising components assembled in series. The modeling of such a circuit is relatively easy, since it is sufficient to represent each component by a system of equations giving the quantities at the output of the component as a function of the quantities at the input of the component (we also speak of transfer function), and successively solving the equations (or multiplying or composing the transfer functions, in the mathematical sense of the composition of functions).

On the other hand, in Expander engines, the turbines are driven directly by a heated propellant, usually hydrogen, which is then reinjected into the combustion chamber. The engine may further comprise bypass lines corresponding to the bypass turbines driving the different pumps. The hydraulic circuit of an expander cycle therefore comprises at least one node formed by the intersection of at least three hydraulic branches. Moreover, unlike the gas-generating cycle, it is not possible to make an assumption on the distribution of flows in the various branches of the circuit and no branch can be neglected. Therefore, the modeling method used for gas generator cycles is not suitable for modeling an expander hydraulic circuit. There is therefore a need for a new type of method for estimating at least one physical quantity at the output of a hydraulic circuit, in particular a physical quantity reflecting the state of the system, for example fluctuations in flow rate and / or pressure.

PRESENTATION OF THE INVENTION

For this purpose, the present disclosure relates to a method of estimating at least one physical quantity at the output of a hydraulic circuit comprising an input node, an output node, at least one internal node and hydraulic components arranged between the input node and the output node, the method comprising:

a step of obtaining a numerical model of the hydraulic circuit, said model comprising a global transfer function of predetermined shape whose coefficients are determined from intermediate transfer functions of each section of the hydraulic circuit delimited by two successive nodes, each intermediate transfer function giving the relationship between input physical quantities and physical quantities at the output of the section that it represents;

a step of estimating the physical quantity at the output of the hydraulic circuit from the numerical model and an input value of at least one physical quantity and / or operating parameters of the hydraulic circuit.

In this presentation, a node is the intersection of at least three branches. By way of exception, the input node and the output node may be only the intersection of two branches; however, it is possible to treat said two branches as a single branch and to bring the input or the output of the circuit to the intersection of three branches nearest. In any case, an "internal" node is the intersection of at least three branches. As mentioned previously, the at least one internal node is distinct from the input node and the output node. Two nodes are called successive if there is a section that connects these two nodes and does not pass through another node. Thus, a section delimited by two successive nodes is a section on which all the components are in series. In the context of the present application, it is considered that a section is limited by two successive nodes, while a branch is limited by two non-successive nodes and therefore comprises several sections, or is limited on one side by a node in succession. being unlimited on the other side; in other words, a branch may have one of its ends outside the considered system.

The hydraulic circuit comprises hydraulic components, that is to say at least one hydraulic component. However, if the hydraulic system comprises a single hydraulic component, it is likely that it does not have an internal node.

A hydraulic circuit goes from a fluid inlet (inlet node) to a fluid outlet (exit node), without necessarily including a loop. A transfer function is a function that expresses the relationship between a quantity at a point in the hydraulic circuit and this same quantity and / or at least a different quantity at another point in the hydraulic circuit. More particularly, the global transfer function is the transfer function of the entire hydraulic circuit. Thus, the global transfer function provides a quantity at the output of the hydraulic circuit as a function of the same quantity or at least one other quantity at the input of the hydraulic circuit.

The intermediate transfer function of a section is the transfer function translating the transformation between quantities on this entire section, that is to say between the two nodes delimiting the section. Finally, the elementary transfer function of a component is the transfer function of this component alone.

A physical quantity, or simply "quantity", is a variable representing the state of the system, measurable or can be deduced from from measurable variables. It can be for example the pressure, the flow rate, the amplitude of modal deformation, the speed of rotation of a rotating machine such as a turbine or a pump, the resonant frequency of the system, the mechanical damping etc. Other examples will be given later.

An operating parameter is a variable that affects the state of the system but is not fully controlled by the system. For example, operating parameters may be the surrounding temperature, the nature of the fluid, etc.

The obtaining step may include both the generation of the digital model at the same time of the obtaining step as the recovery of a digital model previously generated and / or generated by another system.

The method according to the invention makes it possible to simply estimate magnitudes at the output of a hydraulic circuit comprising an internal node, sometimes called a non-series circuit. Contrary to an experimental characterization of the hydraulic circuit, in which tests would be carried out on the basis of which a transfer function would be interpolated, the present method easily adapts to changes of components in the hydraulic circuit. The obtaining step provides a model once and for all, so that the estimation step can then be repeated with several parameters or input values.

In addition, the way in which the global transfer function is obtained can ensure that no information is lost and that the global transfer function contains all the information contained in the intermediate transfer functions. Thus, knowing the global transfer function, in particular its shape and the value of its coefficients, and the shape of the hydraulic circuit, it is possible to estimate the physical quantity studied at any point of the hydraulic circuit, and not only at its output. Unlike gas-generator cycles in which the global transfer function derives directly from the elementary transfer functions, the fact of imposing (predetermining) the form of the global transfer function makes it possible to take into account the presence of internal nodes without hypothesis of fluid distribution between the different branches.

Moreover, the fact of giving the global transfer function a predetermined form makes it possible to impose this form according to external criteria, for example the requirement that the global transfer function must be of a form that is compatible with tools or modules of calculations previously used or used in other contexts.

The estimation method can be implemented by numerical simulation.

The step of estimating the physical quantity at the output of the hydraulic circuit can also be performed from mechanical and vibratory equations of the system.

In certain embodiments, the global transfer function is obtained by solving a system of equations verified by the coefficients of the global transfer function as a function of coefficients of the intermediate transfer functions. Indeed, the shape of the global transfer function is predetermined and can be given in the form of an expression whose coefficients are unknown. By writing the physical relations between the components of the hydraulic circuit and the different sections, it is possible to express the coefficients of the global transfer function as a function of the coefficients of the intermediate transfer functions, which gives a system of equations. It is then enough to solve this system to obtain the coefficients of the global transfer function. In the present application, a system of equations may include one or more equations. Conversely, the general term of equation used in the singular can also, depending on the context, refer to a system of equations comprising several equations.

Alternatively, it would be possible to obtain the global transfer function by numerical simulation, by providing a simulation program with intermediate transfer functions. The program can then estimate, in a numerical and non-analytical way, the global transfer function from responses of the hydraulic circuit for different discrete solicitations. However, compared to this alternative method, the resolution of a system of equations as mentioned above is more precise, because of the lack of discretization, and less cumbersome to implement.

In certain embodiments, before or during the obtaining step, the intermediate transfer functions are calculated from the elementary transfer functions of each hydraulic component. By definition of a section, all the hydraulic components of the same section are associated with each other in series. In these embodiments, it is possible for example to compose (multiply) the elementary transfer functions of the successive components of a section to obtain the intermediate transfer function of this section. According to one example, this calculation step can be performed iteratively: on a given section, two successive hydraulic components are considered in series and replaced by an equivalent intermediate hydraulic component, that is to say a fictitious component filling the same function as the combination of the two hydraulic components considered. We continue then until there is only one component on the section. At the scale of the entire hydraulic circuit, this step can be repeated until it is no longer possible to find two components in series in the hydraulic circuit.

In some embodiments, the hydraulic circuit includes two loops having at least one common node. A loop is a circuit portion that can be cyclically traversed, that is to say by returning to its starting point, regardless of the actual flow direction of the fluid. Two different loops are said to be nested if they have at least one node in common. A simple example of two nested loops is a circuit consisting of three parallel hydraulic components.

The proposed method is particularly advantageous in the case where the hydraulic circuit comprises two loops having at least one common node, because it makes it possible to formally replace the two loops by a single global component without making any assumption on the distribution of the fluid between the two loops. If the entire hydraulic circuit is reduced to said two loops, the transfer function of the global component may be the global transfer function.

In some embodiments, the form of the global transfer function may be predetermined depending on the form of the intermediate transfer functions. More particularly, in some embodiments, the global transfer function and the intermediate transfer functions are of the same form. This identity or form analogy simplifies the calculations and ensures that the global transfer function is as general as possible and compatible with all the formalisms implemented for the sections.

In some embodiments, the global transfer function is a linear combination of its variables. Linear is here to be understood in a broad sense, encompassing affine combinations having a constant. The linear combination can be scalar or matrix, depending on the number of input and / or output variables to be estimated. The variables can in particular comprise the physical quantity at the input, the physical quantity at the output, at least one other physical quantity representing the state of the system and the operating parameters of the device. system. However, not all operating parameters are necessarily linearly combined.

In some embodiments, the magnitude is selected from a flow rate, a pressure, a hydraulic force, a torque, a displacement, a speed, an acceleration, an angle, an angular velocity, an angular acceleration, a frequency, a damping, and any size calculated from the previous ones. The flow rate and the fluid pressure in the hydraulic circuit are particularly interesting quantities for the simulation of the POGO effect. Hydraulic force is the force exerted by the fluid on the mechanical structures of the hydraulic circuit. The torque may be the rotational torque of a turbomachine, for example a turbopump. The displacement can be the displacement amplitude of the structure of the hydraulic circuit under the effect of hydraulic forces, and the speed can be the speed associated with this displacement. The angle can be the rotation angle of a turbomachine, having an associated angular velocity. The frequency may be the POGO resonance frequency and the damping may be a positive term (damping stricto sensu) or negative (amplification) created by the POGO loop at a given frequency.

In some embodiments, the hydraulic circuit is a rocket engine propellant circuit, in particular an expander cycle rocket engine. In particular, the hydraulic circuit may be a propellant circuit located between the output of the regenerative propellant heating circuit and the inlet for reinjecting the propellant into the combustion chamber. In other embodiments, the hydraulic circuit is a fuel circuit of an aircraft.

In some embodiments, the overall transfer function takes as an input variable the rotational speed of at least one turbine or pump. The turbine and / or the pump preferably belong to the hydraulic circuit. The present disclosure is also directed to a program comprising instructions for executing the steps of the method described above when said program is executed by a computer or a microprocessor.

In a particular embodiment, the various steps of the estimation method are determined by instructions of computer programs.

Consequently, the present disclosure also relates to a program on an information medium, this program being capable of being implemented in an estimation device or more generally in a computer, this program comprising instructions adapted to the implementation of steps of an estimation method as described above.

This program can use any programming language, and be in the form of source code, object code, or intermediate code between source code and object code, such as in a partially compiled form, or in any other form desirable shape.

The formal processing of the step of obtaining the numerical model makes it possible to automate the proposed method as much as possible, thus reducing the risk of introducing errors.

The invention also relates to a computer-readable or microprocessor-readable information medium, and comprising instructions of a program as mentioned above.

The information carrier may be any entity or device capable of storing the program. For example, the medium may comprise storage means, such as a ROM, for example a CD ROM or a microelectronic circuit ROM, or a magnetic recording medium, for example a floppy disk or a disk. hard. On the other hand, the information medium may be a transmissible medium such as an electrical or optical signal, which may be conveyed via an electrical or optical cable, by radio or by other means. The program according to the invention can be downloaded in particular on an Internet type network.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention and its advantages will be better understood on reading the following detailed description of embodiments of the invention given as non-limiting examples. This description refers to the accompanying drawings, in which:

- Figure 1 shows schematically a propellant supply circuit of a rocket engine expander cycle;

- Figure 2 formally represents the hydraulic circuit of Figure 1 before the application of the estimation method according to one embodiment of the invention;

- Figure 3 shows the hydraulic circuit of Figure 2 at a subsequent step of the estimation method according to the embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION Referring to FIG. 1, a propellant supply circuit 80 of an expander cycle rocket engine will now be described.

FIG. 1 represents a rocket engine whose combustion chamber 10 is fed with propellants, for example hydrogen (first propellant) and oxygen (second propellant), by a hydraulic circuit 100 between the components 20 and 46, described later. of the supply circuit 80.

More specifically, the second propellant, for example liquid oxygen, is supplied from a reservoir (not shown) by a supply line 12, passes through a second pump 34a, a second valve 14, and is injected into the combustion chamber 10. The first propellant, for example liquid hydrogen, is supplied from a reservoir (not shown) by a feed line 16, passes through a first pump 24a and circulates in a heat exchanger 18. heat 18 is provided to cool the combustion chamber 10 and thereby heat said propellant. The first propellant leaves the heat exchanger 18 via a pipe 20, 22 connected to a first turbine 24b driving the first pump 24a. The output of the first turbine 24b is connected by a line 26, 32 to a second turbine 34b. The second turbine 34b drives the second pump 34a. The outlet of the second turbine 34b is connected to the combustion chamber 10 by lines 44, 46, the pipe 46 being provided with a first valve 48.

In addition, the hydraulic circuit 100 comprises a first bypass line connecting the upstream of the first turbine 24b (turbine of the hydrogen turbopump) downstream of the second turbine 34b. The first bypass line, also called "hydrogen bypass line", extends between an input node A and an internal node C and successively comprises a pipe 38, a valve 40 (hydrogen bypass valve) and a pipe 42.

The hydraulic circuit 100 also comprises a second bypass line connecting the upstream of the second turbine 34b (turbine of the oxygen turbopump) downstream of the second turbine 34b. The second bypass line, also called "oxygen bypass line" extends between an internal node B and an output node D and comprises a pipe 28 provided with a valve 30 (oxygen bypass valve).

The hydraulic circuit 100 is shown diagrammatically in FIG. 2, on which the various hydraulic components have been represented indifferently by blocks. In the example of the present embodiment, the pipe 20 is the output of the regenerative circuit, the pipe 22 is the inlet line of the first turbine 24b (turbine inlet line hydrogen), the pipe 26 is the exit line of the first turbine 24b (hydrogen turbine outlet), the pipe 32 is the inlet line of the second turbine 34b (oxygen turbine inlet line), the pipe 36 is the output line of the second turbine 34b (oxygen turbine output line), the pipe 44 is a first supply pipe of the combustion chamber 10 first propellant (first hydrogen chamber line), the pipe 46 is a second feed pipe of the combustion chamber 10 first ergol (second line hydrogen chamber). Arrows indicate the normal flow direction of the first propellant between the components. The first and second bypass lines AC and BD are respectively referenced 37 and 27 in FIG.

As indicated above, the hydraulic circuit comprises an input node A, an output node D and two internal nodes B and C. As can be seen from FIG. 2, the hydraulic circuit 100 has two nested loops having the nodes B and C in common. Furthermore, as can be seen from FIGS. 1 and 2 and from the foregoing description, the hydraulic circuit 100 comprises a single input node A and a single output node D. Thus, the hydraulic circuit 100 is such that the first propellant entering the hydraulic circuit 100 by the input node A can not exit elsewhere than by the output node D, and conversely, the first propellant leaving the hydraulic circuit 100 by the output node D is necessarily entered by the node A. The hydraulic circuit 100 is so-called "closed" between the input node A and the output node D.

The elementary transfer functions of each of the components of FIG. 2 are assumed to be known. These elementary transfer functions provide, for each component, a quantity at the output of the component as a function of at least one quantity (of the same quantity and / or of a different quantity) at the input of the component, possibly based on hydraulic system parameters. In the As a further example of this, the flow and pressure of ergol will be taken as examples of quantities; however, the method according to the invention can be used to calculate other quantities.

According to a first step of the method according to the present embodiment of the invention, a first step comprises calculating the intermediate transfer functions of each section from the elementary transfer functions of each hydraulic component. Here, the hydraulic circuit comprises 5 sections: AB, BC, CD, AC and BD. As explained previously and as illustrated in FIG. 2, each section comprises a series of components connected in series. The intermediate transfer function of each section can thus be obtained by successively composing (multiplying) the elementary transfer functions of each of the components of this section.

According to one example, the elementary transfer function of each component is a linear combination of the type:

where Qi is the flow at the input of the component, Pi is the pressure at the input of the component, Qo is the flow at the output of the component, Po is the pressure at the output of the component, ΩΟ is the rotational speed of the component the second turbopump 34a, 34b (oxygen turbopump), ΩΗ is the rotational speed of the first turbopump 24a, 24b (hydrogen turbopump), q is the modal coordinate (that is to say the amplitude factor on the distortion) , in displacement, associated with a mode of vibration of the structure) and the other terms are coefficients of the elementary transfer function, supposed known.

When the elementary transfer functions are not linear, it is possible to linearize them locally, under the assumption of small fluctuations, even if it means losing the generality of the analysis and having to reiterate it in several points. Alternatively and / or in addition, the The following resolution principle can be adapted to non-linear mathematical solutions.

Because the elementary transfer function gives two quantities (flow Q and pressure P) at the output as a function of these input quantities or vice versa (which is equivalent since the function is invertible), the component is said to be represented. by a quadrupole.

By writing that, on a given section, the flow rate and the pressure at the outlet of a component are respectively equal to the flow rate and the input pressure of the next component, it is possible to inject (compose) the transfer function. a component in that of the adjacent component and thereby obtain, step by step, the intermediate transfer function of the section as a whole. Since the elementary transfer functions are all of the same shape and where this form is linear, the intermediate transfer function of the section will also be of the form:

where Qi, Pi are the flow and pressure at the inlet of the section and Qo, Po the flow and pressure at the outlet of the section. The coefficients z, ο ', h', b '(i and j varying from 1 to 2) are determined, by conventional calculations, as a function of the coefficients of the elementary transfer functions.

By thus calculating the intermediate transfer functions of each section, the hydraulic circuit is formally simplified by bringing it back to the configuration illustrated in FIG. 3. On the hydraulic circuit of FIG. 3, each section comprises a single fictitious component (called intermediate component ) whose transfer function is the intermediate transfer function of said section. The simplified hydraulic circuit no longer contains serial components.

Schematically, the intermediate component 25 corresponds to the section 23 (hydrogen turbine section), the intermediate component 29 corresponds to the section 27 (oxygen bypass section), the intermediate component 35 corresponds to the section 33 (oxygen turbine section), the intermediate component 39 corresponds to the section 37 (hydrogen bypass section), and the intermediate component 45 corresponds to the section 43 (chamber section). hydrogen).

In the equation above, some coefficients may be zero. For example, if we consider the intermediate component 25 which comprises the hydrogen turbine 24b, the coefficients o'I and o'2 relating to the speed of rotation of the oxygen turbopump are zero. Conversely, if we consider the intermediate component 35 which comprises the oxygen turbine 34b, the coefficients h'1 and h'2 relating to the rotational speed of the hydrogen turbopump are zero. Moreover, if we consider the intermediate component 29 which represents the oxygen bypass line, the coefficients o'I and o'2 relating to the speed of rotation of the oxygen turbopump, and h'1 and h'2 relating to the rotational speed of the hydrogen turbopump are all zero.

To obtain a numerical model of the hydraulic circuit, it is necessary to search for the global transfer function corresponding to the transformation of the quantities studied between the input node A and the output node D. In accordance with the invention, the global transfer function has a predetermined form whose coefficients are determined from intermediate transfer functions of each section. It is therefore first of all to choose a form of the global transfer function.

The form of the global transfer function may depend on the form of the intermediate transfer functions if it is desired not to lose information. In fact, in order to keep all the information contained in the intermediate transfer functions, the global transfer function will have to depend linearly on these intermediate transfer functions and depend on all the variables on which the intermediate transfer functions. The absence of loss of information is then guaranteed by the reversibility (bijectivity) of the calculations and in particular by the absence of projection.

The form of the global transfer function may also depend on the use that is made of it elsewhere. For example, if the global transfer function is used in a computation module that requires a certain form, this form must be respected.

In this case, the transfer function is imposed in a form identical to that of the intermediate transfer functions. This choice makes it possible to cumulate the aforementioned advantages: not only does the global transfer function linearly depend on the intermediate transfer functions so that no information is lost, but in addition the global transfer function thus has a shape similar to the form representing a section or component. In this way, this choice of shape amounts to modeling the hydraulic circuit 100 by a global component whose transfer function is the global transfer function.

Therefore, in the described embodiment, the shape of the global transfer function is a quadrupole. More specifically, the function

In this embodiment, the global transfer function is therefore a linear combination of its variables.

Then, according to the invention, the coefficients of the global transfer function are determined from the coefficients of the intermediate transfer functions. This can be done through the physical equations governing the hydraulic circuit.

For example, in the embodiment shown, the intermediate transfer function of each intermediate component is written. The transfer function of an intermediate component provides an equation the type of equation (2) above. By separating the equation (2) component by component, each intermediate component thus provides an equation per magnitude, here an equation for the flow and an equation for the pressure. As shown in FIG. 3, there are five intermediate components 25, 35, 29, 39, 45. This therefore gives five equations for the flow rate and five equations for the pressure, ie ten equations.

In addition, the conservation equations are written to each node. To illustrate this step, we will take the example of node B. For the flow, the equation consists in writing that the sum of the algebraic flows (positive or negative according to the direction of circulation of the fluid) is null at the node. This equality provides an equation per node, for example:

QolS + QH9 + Qi3S = 0 (4) for node B, where Qo25 is the incoming flow of component 25 (positive given the direction of fluid flow shown in Figure 3), Qi29 is the incoming flow of component 29 (negative considering the direction of fluid circulation indicated in FIG. 3) and Qi35 is the incoming flow of the component 35 (negative considering the direction of fluid circulation indicated in FIG. 3).

For pressure, the equation consists in writing that at the node, the pressures of branches extending from the node are equal. Since there are three branches per node, this provides two equations per node. For example, for node B, we have the equations:

where Po25 is the outlet pressure of component 25, Pi35 is the inlet pressure of component 35 and Pi39 is the inlet pressure of component 39.

The conservation equations thus provide three equations per node, but the simplified hydraulic circuit 100 has four nodes. This gives twelve equations, which are added to the ten equations resulting from the transfer functions, ie a total of twenty-two equations. For these twenty-two equations, the unknowns are the pressure and the flow rate at the inlet and at the outlet of each section (that is to say of each intermediate component), the pressure and the output flow of the whole circuit. hydraulics, as well as rotational speeds ΩΟ and ΩΗ. The system has twenty-six unknowns.

This system of twenty-two equations with twenty-six unknowns can be formally solved by means of formal calculation tools, using conventional resolution algorithms known per se. The objective is to simplify the system to obtain equations giving the flow rate and the pressure at the output of the hydraulic circuit as a function of the flow rate and the inlet pressure of the hydraulic circuit, that is to say two equations with six unknowns ( flow and pressure at the inlet and the outlet of the hydraulic circuit, as well as the speeds of rotation ΩΟ and ΩΗ). The identification of the coefficients of these two equations and the coefficients of the predetermined form of the global transfer function (equation (3) above) then makes it possible to express the coefficients of the global transfer function as a function of the coefficients of the functions intermediary transfers.

It is important to note that no hypothesis has been formulated on the distribution of the fluid between the different branches of the hydraulic circuit. On the contrary, the method employed makes it possible to leave this distribution free, which is therefore determined intrinsically by the hydraulic circuit itself. In addition, the proposed method can numerically model a hydraulic circuit in a form to which said hydraulic circuit is naturally not suitable, here the quadrupole.

The estimation step can be done by combining the global transfer function obtained for the hydraulic circuit 100 with the transfer functions of the other branches of the hydrogen line, upstream of the node A and downstream of the node D. The function thus obtained, called first ergol (hydrogen) global line transfer function, can then be combined with the global second line transfer function. ergol (oxygen), corresponding to the components 12, 34a and 14, then with a hydraulic equation governing the pressure in the combustion chamber as a function of the propellant flow rates at the outlet of the hydraulic circuit, with two mechanical equations governing the driving of the turbopumps ( a turbopump equation) and finally with one or more vibratory equations of the system. Thus, with the two hydraulic equations (global transfer function), at least six equations are available. Assuming data on the pressures (specific to each propellant tank) at the inlet of the hydraulic circuit, at least six unknowns remain (the flow rates of each propellant and the pressure at the outlet of the hydraulic circuit, as well as the rotation speeds ΩΟ and ΩΗ and the modal coordinate (s) q of the mechanical mode or modes considered). It suffices to solve this system of at least six equations with at least six unknowns, for example by means of digital means, to estimate the physical quantities sought at the output of the hydraulic circuit.

In this embodiment, the natural case has been presented in which all the components have transfer functions of the same form. However, the elementary, intermediate and global components could have transfer functions respectively elementary, intermediate and global of different forms. The application of the method presented above is not modified.

In addition, if there is no loss of information when passing from the elementary components to the intermediate components and then to the supercomponent, the proposed method makes it possible to provide the expressions of hydraulic fluctuations (flow and pressure, in the example) at any point in the hydraulic circuit, depending on the variables already mentioned. In mathematical terms, the absence of information loss is guaranteed here by the linearity of the equations and the absence of projections.

Moreover, the steps described above can be automated and a computerized calculation software can provide, on an intermediate basis, the expressions of the coefficients of the global transfer function as a function of the coefficients of the intermediate transfer functions. The obtaining step may consist simply in recovering such expressions that have been calculated previously.

The embodiment presented comprises a first step of simplification of the hydraulic circuit corresponding to the establishment of intermediate transfer functions. Such a step can be considered as implicitly realized even if the coefficients of the global transfer function are determined directly as a function of the coefficients of the elementary transfer functions. Indeed, the writing of conservation equations for components in series amounts to calculating the corresponding intermediate component. It will be noted that the fact of not explicitly passing through the intermediate transfer functions is less advantageous in computing time.

An estimation device according to one embodiment of the invention is now described. Such an estimation device here has the hardware architecture of a computer. It comprises in particular a processor, a read-only memory, a random access memory, a non-volatile memory and possibly communication means enabling the estimation device to obtain the input quantities of the hydraulic circuit and / or operating parameters of the hydraulic circuit. .

The read-only memory of the estimation device constitutes a recording medium according to the invention, readable by the processor and on which is recorded a computer program according to the invention, comprising instructions for executing the steps of FIG. an estimation method according to the invention, for example the previously described steps.

This computer program defines, in an equivalent manner, functional modules of the estimating device capable of implementing the steps of the estimation method previously described. Thus, in particular, this computer program defines a module for obtaining a digital model of the hydraulic circuit and a module for estimating the physical quantity at the output of the hydraulic circuit from the numerical model. The functions of these modules are described in more detail with reference to the steps of the estimation method.

Although the present invention has been described with reference to specific exemplary embodiments, modifications can be made to these examples without departing from the general scope of the invention as defined by the claims. In particular, individual features of the various embodiments illustrated / mentioned can be combined in additional embodiments. Therefore, the description and drawings should be considered in an illustrative rather than restrictive sense.

Claims

Method for estimating at least one physical quantity at the output of a hydraulic circuit (100) comprising an input node (A), an output node (D), at least one internal node (B, C) and hydraulic components (22, 24b, 26, 28, 30, 32, 34b, 36, 38, 40, 42, 44) disposed between the input node and the output node, the method comprising:

a step of obtaining a numerical model of the hydraulic circuit, said model comprising a global transfer function of predetermined shape whose coefficients are determined from intermediate transfer functions of each section (23, 27, 33, 37, 43) of the hydraulic circuit (100) delimited by two successive nodes, each intermediate transfer function giving the relationship between input physical quantities and physical quantities at the output of the section that it represents;

2. Method according to claim 1, wherein the global transfer function is obtained by solving a system of equations verified by the coefficients of the global transfer function as a function of coefficients of the intermediate transfer functions.

The method according to claim 1 or 2, wherein before or during the obtaining step, the intermediate transfer functions are calculated from the elementary transfer functions of each hydraulic component (22, 24b, 26, 28). , 30, 32, 34b, 36, 38, 40, 42, 44).

4. Method according to any one of claims 1 to 3, wherein the hydraulic circuit (100) comprises two loops having at least one common node (B, C).

The method of any one of claims 1 to 4, wherein the global transfer function and the intermediate transfer functions are of the same form.

The method of any one of claims 1 to 5, wherein the global transfer function is a linear combination of its variables.

7. Method according to any one of claims 1 to 6, wherein the quantity at the inlet or outlet of the hydraulic circuit (100) is selected from a flow rate, a pressure, a hydraulic force, a torque, a displacement, a speed angle, angular velocity, frequency, damping.

The method of any one of claims 1 to 7, wherein the hydraulic circuit is a rocket motor propellant circuit.

9. The method of claim 8, wherein the global transfer function takes as an input variable the rotational speed of at least one turbine or a pump.

10. Program comprising instructions for performing the steps of the method according to any one of claims 1 to 9 when said program is executed by a computer or a microprocessor.

A computer-readable recording medium on which a computer program is recorded including instructions for performing the steps of the method according to any one of claims 1 to 9.