US 3314391 A Abstract available in Claims available in Description (OCR text may contain errors) J. DUPORT 3,314,391 METHODS AND MEANS FOR EFFECTING OPTIMUM PROPULSION OPERATING April 18. 1967 CONDITIONS IN A JET PROPELLED SHIP 5 Sheets-Sheet 1 Filed March 12, 1965 INVENTOR JACQUES DUPORT ATTORNEY April 18, 1967 J. DUPORT 3,314,391 METHODS AND MEANS FOR EFFECTING OPTIMUM PROPULSION OPERATING CONDITIONS IN A JET PROPELLED SHIP Filed March 12, 1965 5 Sheets-Sheet z INVENTOR JACQUES DUPO/ZT BY V M ATTORNEY April 18, 1967 J. DUPORT 3,314,391 METHODS AND MEANS FOR EFFECTING OPTIMUM PROPULSION OPERATING CONDITIONS IN A JET PROPELLED SHIP March 5 Sheets-Sheet 5 N MOTOR PROPULSION V T SYSTEM PUMP CON ROL UNIT N -roa --s. v 24 21? N VALUE N N MEASURE INDICATOR UNIT 25 501 v) OPERATOR rs SHIPS W CHART J MOTION v VALUE V r O I NDI CATOR. M u rfir r26 727 s CONTROL 5 MEASURE UNIT UNIT F i E N, M T R %*;:*+%3- CONTROL UNIT ,N M'oToR-PuMP u MEASURE 4 UNIT ,28 5 s (N V) Y SHIP'S OPERATOR. CALCULATOR MOTION ;v v VALUE v V A V MEASURE V INDICATOR UNIT .S '29 Si s s CONTROL 5 MEASURE 'T UNIT INVENTOR F i 537 JA CQUES DUPORT B-Y iTTORNEY A ril 18, 1967 J. DUPORT METHODS AND MEANS FOR EFFECTING OPTIMUM PROPULSION OPERATING CONDITIONS IN A JET PROPELLBD SHIP Filed March 12, 1965 5 Sheets-Sheet 4 35 23 Mom CONTROL UNIT 5 Mm'QRoPUMP N MEASURE UNIT 0" SHIP'S OPERATOR v CALCULATOR MOT'ON 3 v v -v I MEASURE M a r v UNIT ACCELERATION CONTROL UNIT 5 \I s s CONTROL MEASURE 55 UNIT UNIT F 1 E r51 39 23 MOTOR. pmgsg arq CONTROL UNIT -MOTOR PUMP 40 4/ t a f G scam Q SHIP'S CALCULATOR. iffg MOTION ACCELERATION .-v 1 CONTROL UNIT UNIT N s s cow-mom. OPERATOR MEASURE UNIT ,5 ?, a INVENTOR JA C QUES DUPORT April 18. 1967 METHODS AND MEANS FOR EFFECTING OPTIMUM PROPULSION OPERATING CONDITIONS IN A JET PROPELLED SHIP Filed March 12, 1965 5'Sheets-Sheet 5 MOTOR PROPULSION co QL U M06$MP con-ram. UNIT 5 DISCHARGE OF 5 MEASURE DISCHARGE um-r CALCULATOR Q. MEASURE 1 5 (0. v) UNIT ffl O 'T l N DISCHARGE r V F 37 V I As T a ACCELERATION CALCULATOR v MEASURE CONTROL scQvJ UNIT UNIT INLET CONTROL UNIT 5 NLET OPERATOR. OF S INLET MESEILIErRE 'INVENTOR JACQUES DUPORT VMV X/WATTORNEY United States Patent C METHODS AND MEANS FOR EFFECTING OPTI- MUM PROPULSION OPERATING CONDITIONS IN A JET PROPELLED SHIP Jacques Duport, Montbonnot, lsere, France, assignor to Societe Grenobloise dEtudes et dApplications Hydrauliques, Grenoble, France, a corporation of France Filed Mar. 12, 1965, Ser. No. 439,283 Claims priority, application France, Mar. 17, 1964, 4,660 11 Claims. (Cl. 115-16) This invention relates to that method of propelling ships which makes use of the reaction of jets of water discharging in a direction opposite to that of the required thrust. These propulsion jets are usually produced by pumps forcing water through one or more orifices discharging astern. In certain known layouts the discharge orifices are made adjustable to control their direction of discharge and are utilized for both propulsion and steering purposes. It is one of the principal objects of the present invention, to provide an improved propulsion system in which the discharge nozzles, which may or may not be adjustable for direction, and if necessary also the inlet orifices, are provided with mobile elements whose positions can be modified to change the discharge orifice cross-section and hence also the jet cross-section. Thus, in accordance with the invention, the ships speed will be controlled (that is to say held in a constant value, accelerated, or decelerated) by simultaneous action on the pump rotational speed (and where necessary on its blade settings, if adjustable) and on the geometry of the discharge orifices (and also, if necessary, on the geometry of the inlet orifices) by means of the aforesaid mobile elements. The values which define the control element positions, the pump rotational speed and the pump blade position are determined by a combined relationship allowing for instantaneous ships speed, and also for depth of submersion if variable. This unique combined relationship for a given ship and propulsion system is determined from the following factors: (a) The observance of the limitations which aifect the propulsion system pump at any moment and condition (critical cavitation, power limit, etc.). (b) The consistently minimum propulsion system input consumption which is required for a given ships acceleration and instantaneous speed, for both steady and unsteady ships motion. (c) For any ships speed V, the maximum thrust which is compatible with the characteristics of both the ship and its propulsion system. The maximum thrust thus achieved is substantially greater than that obtainable by action on only part of the aforesaid controlling elements, or by combining them according to a different relationship. The manner of calculating the aforesaid combine-d relationship will be hereinafter described. Such relationship may be determined by a calculating unit provided on board the ship, and some possible designs of which are subsequently described. Where control is to be effected manually, the calculator may work out the control element positions and pump rotational speed, and transmit this information to indicators for use by the helmsman or person controlling the ship. In the case of automatic control, the orders issuing from the calculator are transmitted directly by a feedback control system to the items to be controlled (e.g. pump motor input, and the orifice and pump blading controls). The discussion now following and the drawings attached hereto are intended to more clearly illustrate the special features of the invention by demonstrating the methods, which also form part of the subject matter of this invention, whereby optimum discharge orifice dimensions (and if necessary also optimum inlet orifice dimensions if of the variable geometry type) can be determined for various ships speeds (and where applicable, for various degrees of immersion) and pump rotational speeds (and where applicable, for various adjustable blade settings). In the drawings: FIG. 1 is a graph showing characteristic pump curves; FIG. 2 is a graph showing the operating boundaries for the pump of FIG. 1 and curves of constant thrust therefor; FIG. 3 is a graph similar to FIG. 2 and includes a parabola indicating the locus of possible operating points for the ships speed; FIG. 4 is a graph showing efiiciency curves; FIG. 5 is a graph showing parabolas related to the ships speed; FIG. 6 is a diagram showing the manner in which a propulsion system in accordance with the invention may be manually operated; FIG 7 is a diagram showing how the system of FIG. 6 may be made more automatic; FIG. 8 is a diagram showing a further modification of the system of FIG. 6; FIG. 9 is a diagram showing a still further modification of the system of FIG. 6; FIG. 10 is a diagram showing a modification of the sys tem of FIG. 9; and FIG. 11 is a diagrammatic view of a form of inlet and jet control mechanism embodying the invention. The graph of FIG. 1 of the drawings shows characteristic pump curves with the discharge Q delivered by the pump plotted along the abscissa (0Q), and the head H produced by the pump plotted along the ordinate (OH). The representative operating points for a pump running at constant rotational speed lie on a curve referred to as the constant-speed characteristic. By selecting appropriate rotational pump speed and discharge circuit characteristics, any operating point can theoretically be obtained within the area bounded by the coordinates and the constant-speed characteristic corresponding to the maximum rotational speed (curve 1 in FIG. 1). The possible operating range of a pump and its motor is, however, usually also subject to other limitations, viz. the following: (i) A limit characteristic of the type shown by curve 2 in FIG. 1, due to a minimum rotational speed condition. (ii) The maximum driving motor output, which generally varies with rotational speed, which nearly always results in the type of limit shown by curve 3 in FIG, 1. (iii) A limit arising from the need to avoid cavitation or at least to reduce it to acceptable proportions and indicated by the curve 4 in FIG. 1. Any limitation of the operating region due to mechanical or hydraulic factors affecting both the hydraulic circuit and the pump unit can generally be expressed in the QH plane by a curve or a family of curves which, in addition to depending on Q and H, may also depend on the ships speed V, or intake orifice position, or on discharge orifice cross section adjustment. Whereas limitations associated with output and rota tional speeds (curves 1, 2 and 3 in FIG. 1) only depend on the pump and its motor, that associated with cavitation depends both on the properties of the pump and the particular features of the hydrauiic circuit in 'which it operates. More precisely, the limits set by cavitation are defined in terms of net positive suction head (NPSH), which is the absolute head at the pump inlet less the vapor pressure-with the pump center line as the datum for absolute head. These quantities are expressed as a height of water. NPSH is defined by the following formula: Pa. P1) where NPSH=Net positive suction head. Pa=The absolute pressure at the pump center line at a point just upstream from the pump inlet. Pv=Vapor pressure of water. v: Mean velocity in the same cross-section as Pa. za=Specific gravity of water. g a-cceleration of gravity. For a given pump and a given operating point in terms of Q and H, there is a minimum NPSH below which caviration would produce unacceptable effects. This minimum NPSH is referred to as the minimum required NPSH ('NPSH and, for a given pump, depends on the Q and H coordinates of the operating point. Furthermore, the characteristics of the hydraulic circuit in which the pump is operating usually require that there be a definite relationship between available NPSH (NPSH at the pump inlet and discharge Q. The limiting operating condition due to cavitation for a pump operating in a given circuit is expressed by the following relation: and the equation of the representative curve for the corresponding limit is: NPSH (Q,H)=NPSH, (Q) Curve 4 in FIG. 1 is one of this type. The available NPSH rat the inlet of 'a ships propulsion pump is given by the foil-owing expression: where NPSH =Available net positive suction. head at the pump inlet. h =barometric pressure in head of water. h =vapor pressure in head of water. z=height of pump center line above the free surface (negative where, as frequently occurs, the pump center line is below the free surface). ' V=ships speed. In the case of an adjustable blade pump (e.g. variablepitch propeller pump), such parameters as rotational speed, absorbed in power, minimum required net positive suction head (NPSHQ are not fully defined by given operating point coordinates Q and H, as the same (Q, H) point can be obtained for a whole combination of different rotational speeds and blade settings. In seeking to achieve a given operating point characterized by discharge Q, head H and net positive suction head NPSH, however, one would naturally choose the rotational speed and blade setting combination requiring the smallest possible pump motor input for that particular point, with due allowance for cavitation limitations. Once this optimum combination is established, therefore, the properties of the' pump are in fact fully defined by the (Q, H) coordinates of the considered operating point. 'For a given pump set, degree of immersion and ships speed, therefore, there is always a definite region of the (Q, H) plane within which the pump can operate, which region is hereinafter referred to as the workable region. This workable region is bounded by the curves 1, 2, 3 and 4 in FIG. 1 to provide a closed curvilinear contour, all the points of which are at a finite distance, and which generally features some corner points. It should be noted for subsequent reference that the pump rotational speed, shaift power and motor input are known for any (Q, H) point within this region. Following is a description of the method in accordance with the present invention, whereby the optimum combination of pump rotational speed and discharge orifice cross-section (and where applicable also inlet orifice cross-section) can be determined: Consider a ship travelling at speed V, and let the required thrust be P (for constant V, P will be equal to the overall resistance to the ships forward motion at the said speed V). P ,Q V) P: propulsive thrust. =density of water. S:cross-sectional area of the jet at the vena contracta. Q, V=predetermined pump discharge and ships speed. where: where H, Q, V, g, S are given quantities, and A is the duct loss coefficient (total circuit head loss divided by the square of the discharge). Owing to the influence of the inlet orifices, this coefficient may also depend on the ships speed V and discharge Q. Where the inlet orifices are adjustable, the function 7\ depends on a parameter allowing for the position of the mobile element controlling the inlet orifice cross-section. For a jet discharging above the free surface, a term I1 allowing for the height of the jet center line above the free surface has to be added into the expression for H. This term does not affect the reasoning and conclusions presented in the following discussion in which the case of a drowned jet (i.e. one discharging below the free sunface) will be considered; the advantages claimed for the system according to the invention over conventional systems apply equally to jets discharging into free air and to jet discharging under water. By eliminating S from Equations 5 and 6, the following thrust relationship is obtained: Consequently, the locus of the points-in the (Q, H) plane for which a thrust P can be obtained for a velocity V is a curve of the following equation: also cause additional drag in certain cases, the amount of which depends on both jet cross-section and discharge Q. In thrust Equation 8, P is the net thrust, that is to 5 say the difference between gross jet thrust and the forms of additional induced drag defined above. It can be shown that the curve for Equation 8 in the (Q, H) plane is concave upwards; the axis is asymptotic with respect both to this curve and to the one representing the head losses in the circuit, the equation of which is: Curves of the type given by (8) will be referred to herein as constant-thrust curves. It can be shown that the entire curve of this type referring to a thrust P lies above the one for P if P P and that two constantthrust curves referring to different thrusts do not have any points in common at a finite distance. FIG. 2 is a further operating diagram for the pump in FIG. 1, showing the boundaries of the operating or workable region defined by the aforesaid curves 1, 2, 3 and 4 for a given ships speed V. It also shows the constantthrust curve 5 given by Equation 8, which curve by reference to P for the same ships speed V, will intersect the boundaries of the workable region at the two points, A and B. The points of arc AB of curve 5 represent all the operating points at which thrust P is obtainable for the ships forward speed V. As previously explained, the motor input is known for each of these points, and there is at least one of them for which this input is a minimum, so that thrust P and ships speed V being constant-the overall efliciency is a maximum. This is the point which is chosen according to the invention to obtain thrust P for a ships forward speed V. Let this optimum point of arc AB of curve 5 be called C. As only one constant-speed pump characteristic passes through this point C, the corresponding rotational speed n can therefore be defined. The jet cross-section S for which operating point C can be obtained, can be calculated from Equation 6. If Q H; are the coordinates of point C, S is then given by the following relationship: As already stated, S is the value in this equation to select for the jet cross-section. H and Q; are the coordinates of the optimum point, and g, x and V are given quantities. The above discussion shows how the optimum jet crosssection S and optimum pump rotational speed n can be determined in terms of the required ships forward speed and thrust from the pump and the hydraulic circuit characteristics. It should be noted that whether optimum point C is distinct from the extreme points A and B or coincides with either of them depends on the case considered. Where C is distinct from A and B, the maximum efiiciency point is generally stationary. In other words, at this point the derivative of the efficiency along curve with respect to any one of the parameters Q, S or n is zero. Where the inlet orifices are adjustable as well, the 7\ function again depends on a parameter representative of the position of the element controlling the inlet crosssection. In this case, Equation 8 plots, for a given ships speed V, a set of curves depending on a parameter, on each of which the optimum point C can be selected by the method previously defined herein. Among all these optimum points C for a given thrust P and ships speed V, some represent a minimum input, and one of these will be chosen as the operating point for the considered thrust P and ships speed V. The choice of this optimum point also involves that of the constant-thrust curve on which it lies, and thus defines the inlet orifice setting. As explained in the case of the constant orifice, the position of this point fully defines the position of the adjustment parameters, i.e., the pump rotational speed, and the discharge orifice cross-section, and where applicable also, the pump blade setting. It will be noted that while in the case 0 fan adjustable inlet orifice, certain bound- 6 aries of the operating region may vary with the parameter defining the inlet adjustment, the above method still applies in the same way to such case. It follows from the above that, by optimisation of the inlet orifice, a single constant-thrust curve can be made to correspond to each pair of thrust and ships speed quantities. The same calculation can be repeated for the same ships speed V with other required values of the thrust P. Thus, if P is made to increase successively to P P curves 6 and 7 of FIG. are obtained, which satisfy equations obtained by replacing P by P then by P then by P and so on, in Equation 8. These curves do not have any points in common and lie increasingly farther away from the origin as the corresponding thrust increases. At increasing values of P, therefore, a stage is reached at which limits such as points A and B come increasingly closer together, until they finally coincide at a point M on the boundary when P reaches a certain limit value P This point P is the point of maximum thrust obtainable at a ships forward speed V, allowing for the various limitations expressed by curves 1 to 4. Curve 8 of FIG. 2 is the constant-thrust curve for the thrust limit P and the aforesaid point M is shown thereon. If M is an aligned point on one of the curves forming the boundary, it will also be the point of tangency between the constant-thrust curve P and the boundary. If, as may happen, point M is a boundary corner point, the boundary and the constant-thrust curve P will touch at a single point (M), but will not generally be tangent to each other. In both cases (i.e. M on aligned or corner point), the entire boundary except M will lie below the constant-thrust curve P It also follows that point M is one of the set of points C giving the minimum input for a given thrust and ships speed. There is, therefore, no discontinuity between the combinations giving minimum input for a given thrust (i.e. the relationships described above giving values for n and S and the combination whereby maximum thrust is obtained for a given ships speed within the operating limitations affecting the pump. The advantages of the process of the invention will now be demonstrated, first by comparing the performance obtainable for the same pump with a system embodying the invention and with a constant-section discharge orifice system, respectively. Where the cross-section S is constant, and where, as is usually the case, the function x can be considered to be practically independent of Q and V, Relationship 6 can be represented in the plane (Q, H) by a family of parabolae whose axis is OH and all having the same parameter: 1 gSH-k and all peaking at ordinate point One of the parabolae in this family corresponds to a given ships speed V. The OQ, OH coordinate system of FIG. 2 is shown again in FIG. 3, together with the boundary of the operating region for ships speed V, and the constant-thrust curve 5 referring to thrust P Parabola 9 shown on the graph of FIG. 2 is determined from Equation 6 and refers to the same value of V as the one on which the other curves illustrated are based. Parabola 9 is the locus of the possible operating points for ships speed V and a constant jet cross-section S. It intersects curve 5 at a point D which is usually dis tinct from the point C defined above. Point D is the one whereby thrust P can be obtained for ships speed V and a constant jet cross-section S. The fact that this point is distinct from C implies, by the very. definition of point C, that the input at D will be greater than at C. The overall efficiency for a constant orifice is generally lower than the optimum efliciency obtainable by application of the method according to the inventidn. The operating point giving maximum thrust for the above ships speed V and cross-sectional area S is the point on parabola 9 farthest along the abscissa which, in particular, results from Formula 5. This operating point will therefore be point B, at which the parabola 9 intersects the boundary of the operating region, and which will generally be distinct from the point Mdefined above. A constant-thrust curve P passing through this point E, is shown by curve 10 in FIG. 3. As previously indicated, by the definition of P and of the constant-thrust curve 8, no point of the operating region boundary will lie above the latter. Point E, which is part of the boundary and distinct from M, therefore lies below curve 8, so that, due to the constant-thrust properties explained above, the value of P is smaller than that of P In other words, all other things being equal, the maximum thrust obtainable with a constant jet cross-sectional area is generally less than that obtainable with a variable jet cross-section and an adjustment procedure in accordance with the invention. FIG. 4 shows by way of example overall efliciency curves plotted against thrust for a ships speed V. These curves are all assumed to refer to the same given pump set. Thrust P is plotted along the abscissa, and overall etficiency N along the ordinate. Curve 11 shows the variation of this efficiency with thrust for a system with a constant orifice cross-section, and curve 12 shows the same function for the case of a variable orifice according to the invention. It will be seen that the whole of curve 12 lies above curve 11, and that its extreme point lies at an abscissa P greater than P at the end of curve 11. On the strength of the aforesaid various considerations, the performance of the conventional method can be compared with that of the method according to the invention for a given ships speed V. The advantages of the method according to the invention are even more clearly illustrated by the relationship between propulsion system performance and ships speed. Equation 3 for NPSH includes a term V /2g, which can assume considerable proportions in the case of a fast ship travelling at full speed. For example, in the case of a ship travelling at 30 knots (15 m./sec.) with its propulsion pump set at a depth of 2 m. below the water surface, the NPSH will amount to about 24 m., about half of this being accounted for by the term V /2g. As a result of this, the net head falls off considerably at low ships speeds. Thus in the case of the above discussed ship, the net head will be down to about 15 m. at half-speed, and to 12. m. at very low speed. The consequence of this is a substantial reduction in the maximum thrust obtainable at low speeds. It will be shown that this difficulty can to a very large extent be overcome by the use of an adjustable orifice in accordance with the invention, and that such an orifice can produce much greater thrust at low speed than a conventional one of constant crosssecti-on. This demonstration will be made with the aid of the critical cavitation parameter, or Thoma number, which is NPSH divided by the head produced by the pump, i.e.: Thoma number 6 Z where NPSI-I and H are previously defined quantities. Available 6 is defined-as follows: NPSH,,, BV H from which it follows that the non-cavitation condition will be given by: As it happens, the constant 6, curves in the (Q, H) plane can as a first approximation be considered to be parabolae peaking at the origin and whose axis is the H-axis (l). 6, will be a minimum for one of these parabolae. For operating points to either side of the parabola concerned, however, 6, increases rapidly (i.e. for a given pump, 6, is a function of 11/0 showing a very pronounced minimum at a definite value of H 0 The graph of FIG. 5 shows the (Q, H) coordinate system, and the parabola 9 previously defined for ships speed V and discharge orifice cross-section S. Parabola 13 is the locus of the points for which 6, is a minimum. Let F be the point of intersection of these two curves and assume this point to be the nominal operating point of the propulsion unit for ships speed V. We will now consider the case of a ship travelling at a speed v much lower than V. (a) If the orifice cross-section S remains constant, the locus of the possible operating points at ships speed v is the parabola obtained from parabola 9 by upward translation of K E 9 a Let G be the point at which parabolas 14 and 13 intersect. P is the thrust at speed V (with point F), and P is the thrust at speed v (with point G). It can be shown that where suction head losses are sion system, the following relationship applies: ' increase in NPSH a limit point fairly close to point G cannot be exceeded, which is shown as G in FIG. 5 and is the point of intersection of curve 14 and the limit cavitation curve for speed v. (b) By the method according to the invention, an operating point G" can be taken whose abscissa Q and ordinate H are both greater than those of point G, without running into cavitation. As G" is on (13), its 6., is smaller than that for G, i.e. T( T( Since the head H is given by NPSH We have and since G" is on the limb of (13) to the right of (I4): Q( Q( It then follows from Formula 5 that the thrust at G" is distinctly greater than at G, which clearly shows up the advantage of the method according to the invention in the case of a ship travelling at reduced speed. The above discussion regarding the limitation of thrust by cavitation can also be applied to efficiency. The regio of maximum efliciency of a pump can be assumed to lie near a parabola (usually near the minimum 6" parabola), so that, in the case of a system featuring an orifice with a constant cross-section, high thrust is only obtainable at low ships speeds in a region well outside the maximum pump efiiciency region. By the method according to the invention, on the other hand, a much higher efficiency is obtainable at low speeds because the pump can be run within the peak efficiency region, and moreover, the same thrust can also be obtained at lower jet discharge velocities than with an orifice of constant cross-section. By applying the method according to the invention, therefore, the performance of a jet propulsion system based on a given pump can be improved and the pump and motor dimensions reduced. Thanks to the possibility of varying the jet orifice, the pump adopted for a given system design can have a higher specific speed 1 and hence also smaller dimensions than if the orifice size were constant. The higher NPSI-I associtated with the higher specific speed is compensated for by the possibility, at any ships favorable region as regards cavitation. Advantage can be taken of these smaller dimensions by installing a given ship a propulsion systems with a hi her efficiency than obtainable from conventional systems, for the efficiency of propulsion is known to increase with decreasing recoil, recoil r being defined as the difference between jet velocity W and ships speed V, divided by jet velocity, W, i.e. However, the dimensions of the pump and motor will also increase as recoil decreases for the smaller the recoil, the greater the discharge required from the pump and the smaller the head produced. As the pump and motor dimensions can be reduced by application of the method according to the invention, propulsion systems with a lower recoil can therefore be installed in the same amount of space, and will therefore provide a higher efficiency than a conventional system. In the following description some examples are given of propulsion systems designed according to the invention and in all of which are included the following items: (i) At least one pump with its motor. (ii) Controls as are necessary to start and stop the pump, adjust its rotational speed, and where applicable, to adjust its blade settings (e.g. variable pitch propeller pumps). (iii) One or more suction orifices, possibly adjustable. (iv) One or more discharge orifices, of which at least some are provided with adjustable shutters whereby the orifice cross-section or convergence angle can be adjusted. (v) Remote controls as are necessary for the adjustment of the shutters in (iv) above. (vi) Arrangements whereby the optimum control settings defined by the methods as aforesaid can be achieved. The inventioncan also be practiced in those arrangements which are designed not necessarily to give a strict optimum relationship obtained by the aforesaid methods, but which instead provide an approximate relationship allowing for any special properties of the mechanical components in the propulsion system (e.g., stepped control). The invention also provides for the possibility of maintaining constant (e.g., maximum or minimum) jet and where applicable inletcross-sections at certain ships operating conditions, in which case, the curves repre- 'lhe specific speed of a pump is given by the following relationship Ql/Z 10 senting the constant cross-sections become the boundaries of the pump operating region. The optimum combination enabling the jet crosssection to be adjusted in terms of pump rotational speed n and ships speed V (for instance) is obtainable either by manual or automatic control, as follows: (a) Manual c0ntr0l.In this case, the combination system comprises the following items: (i) Instrumentation comprising pick-ups, remote meas urement sequences, indicating instruments measuring system input quantities (e.g., pump rotational speed, ships forward speed, or other quantities referred to later on herein). These pick-ups measurement sequences and indicators can all be of a conventional type. (ii) A chart of a calculator for the determination of the optimum value of the quantity to be adjusted (e.g., the orifice cross-section or some other appropriate quantity). This calculator may be a device combining the equip ment indicating input quantities (e.g., a crossed-pointer dial featuring constant-value curves for the quantities to be adjusted), or it may be one directly working out the quantity to be adjusted from the combined input quantities supplied by the above-mentioned measurement sequences. For the determination of a function of two variables, the calculator may be electrical, electronic, mechanical, hydraulic, pneumatic or of any other conventional type, and will generally feature a cam or an equivalent electronic device. Where an automatic calculator of this type is used, it directly transmits the value of the quantity to be adjusted to an indicator, thus dispensing with the need for special input quantity indicators. The operator controls the ships speed by adjusting either the pump speed or the orifice cross-sectional area by means of one or the other of the above-mentioned control arrangements, which, depending on requirements, may or may not feature automatic feedback. The amount by which the operator adjusts the orifice cross-section, or the pump speed as the case may be, will depend on the chart of calculator indications. (12) Automatic c0ntr0l.-In this case, the combination system comprises the following items: (i) Instrumentation for the measurement of the input quantity for the combination. This instrumentation may be the same as in a manual control system, except that no indicating equipment is required. Furthermore, the power and characteristics of the output signal must match the characteristics of the automatic regulator described below. (ii) An automatic regulator comprising the following: A calculator for working out the optimum value of the quantity to be adjusted, and a feedback system for automatically controlling the aforesaid quantity in terms of the value determined by the calculator. The calculator may be mechanical, electrical, electronic, hydraulic, pneumatic or of some other suitable type. The feedback system may also be hydraulic, pneumatic, electrical, electronic or of some other suitable type. v In the use of automatic control, the operator controls the ships speed by acting on a single control, which, depending on requirements, may be independent, or feature a feedback system. The automatic controller then sets the quantity to the value required for optimum operation. As a general rule, all the instrumentation, adjustment or control equipment referred to in the above description may be of a type in current use based on me chanical, hydraulic, pneumatic, electrical, electronic or other suitable principles. The three following types of quantities are involved in the operation of a propulsion system according to the invention: (1) A quantity to be adjusted directly so as to increase or reduce the ships speed. This is the quantity the operator controls directly in order to increase or decrease the ships speed, or to maintain a given constant speed. This quantity will be referred to as the acceleration quantity. (2) A quantity to be adjusted automatically or manually, so as to achieve optimum propulsion system operating conditions by the method according to the invention. This quantity will be referred to as the optimisation quantity. (3) Quantities to be measured and from which the value of the optimisation quantity is determined automatically or otherwise. The following are examples of possible acceleration quantities i) Input to the motor (fluids for heat engines and electrical quantities 'for electric motors). (ii) Propulsion orifice cross-section. (iii) Nominal ships speed (in the case of a slave control system). The optimisation quantity may be any of the quantities listed above except the one selected as the acceleration quantity. There are two optimisation quantities" in the case of a pump with adjustable blades (e.g., variable-pitch propeller pumps), one being as defined above, and the other being the angle of blade orientation. In this case, the calculator also gives an optimum value for the latter quantity. There are always at least two optimisation input quantities, which may be, for instance, the ships speed and. associated with it, one of the following: (i) Pump rotational speed. (ii) Pump power. (iii) Motor input. (iv) Propulsion system discharge. (v) Head produced by the pump. Alternatively, the optimisation input quantities may be pump rotational speed combined with pump discharge, or head produced, or power. In the case of a ship designed for varying degrees of immersion (e.g., submarine or hydrofoil vessels) an additional input quantity is necessary, such as the depth of immersion or some quantity directly dependent on immersion depth, such as the total pressure in the suction ducting for instance. This input quantity only intervenes in the calculator at critical cavi tation conditions. In the above description of the optimisation calculation method according to. the invention, pump rotational speed was taken as the acceleration quantity, jet cross-section as the optimisation quantity, and pump rotational and ships speeds as the input quantities. The possibility of using the other groups of quantities defined above results from the characteristic relationships for propulsion system operation and ships motion. Certain functions considered in calculating the optimum combination, such as pump input in terms of discharge and head, critical cavitation, inlet and discharge orifice head losses, etc. are generally defined experimentally by testing the actual pumps or their scale models on a laboratory rig by conventional methods. The relationships governing the combination can also be defined by tests on the propulsion system on board ship, in which case input is measured in terms of pump rotational speed and control element positions (inlet and discharge orifice and pump blade settings) at various degrees of thrust and ships speeds. The variables Q and H previously defined herein can be ignored in interpreting the results of such tests, the variables considered being those playing a direct part in the control adjustment. The optimisation methods are a transposition of those described above. A few examples of the practice of the method of the invention are illustrated in the diagrams of FIGS. 6 to 10, which show the relationships resulting from the operation of the various components of the propulsion system and the equations governing the ships motion. The lines between blocks represent the quantities involved in these relationships; by convention, the arrows on these lines de note an input quantity if pointing towards a block, and an output quantity if heading away from a block. A distinction must be made in these diagrams between the actual and measurement quantities. Measurement and measured quantities are generally of a dilferent nature and may be connected by some relationship, providing it is a bi-univocal one (for example the measured quantity of the propulsion system discharge Q may be a differential pressure which is a quadratic function of Q). The diagram of FIG. 6 shows the operation of a propulsion system according to the invention, in which the acceleration quantity is the pump motor input quantity and the optimisation quantity the jet cross-section. Con trol of the ships speed is efiected in the following manner: The operator sets the required nominal pump rotational speed It. In working this setting out, he can allow for the instantaneous ships speed given by indicator 20. The motor control unit 21 automatically compares the nominal n value with the n-valuc, given by the measurement unit 22 and modifies the input quantity to the motor 23 accordingly. Optimisation is efiected manually; the operator reads the values of V and it off the correspond ing indicators 29- and 24, and ascertains the optimum value of S from chart 25, to which he then sets the discharge orifice cross-section adjustment unit 26. The latter unit, which a feedback system connects to measurement unit 27, automatically brings the jet cross-section S of the propulsion system 23 to the nominal value. In the diagram in FIG. 7, the motor input and jet crosssection are again the acceleration and optimisation quantities respectively. The ships speed is controlled in the same way as in the system illustrated in FIG. 6. Optimisation, on the other hand, is effected automatically. Measured rotational speed it and ships speed V data are fed into the calculator 28, which determines the optimum value of S. The latter is transmitted automatically to the S-control unit 29 featuring feedback arrangements based on exactly the same principle as the one in FIG. 6, which automatically adjusts S for the propulsion system 23 to its optimum value. FIG. 8 is a diagram of a propulsion system according to the invention in which the jet cross-section S is the acceleration value and the pump rotational speed is the optimisation value. Here, the acceleration control is a slave system: the operator selects the required nominal ships speed V, which the acceleration control unit 30 then compares against the value given by V-measurement unit 31 and works out the relationship between the norminal and measured V difference and the variation in jet cross-section S. The result is then transmitted automatically as an order" to the S-control unit 32, which, in this case, is not connected to any direct feedback system but controls the propulsion system 23 jet cross-section S. Optimisation is efiected automatically in the following manner: the data for nominal V given by the operator and S given by measurement unit 34 are fed into the calculator 33, which automatically determines the optimum n value and transmits it to the unit 35 controlling the propulsion system motor 23. Control unit 35 is the same as in the two previous examples, i.e. it compares the optimum value given by the calculator 33 with the value given by measurement unit 3-6 and modifies the input to the propulsion system motor 23 accordingly. FIG. 9 is a diagram of a system according to the invention in which the motor input is the acceleration quantity and the jet cross-section the optimisation quantity. Here again, the acceleration control is a slave system. The operator selects the required nominal value of V, which the acceleration control unit compares with the value given by the V-measurement unit 38 and, via the independent motor control unit 39, adjusts the input to the propulsion system motor 23 accordingly. Optimisation is effected automatically: the measured data for the propulsion system discharge Q {c.g. measured via a differential pressure by unit 41) and ships speed V given by measurement unit 38 being fed into the calculator 40, which automatically works out the optimum value of S and transmits it to the corresponding slave control unit 42. FIG. 10 is a diagram showing a similar system to the 13 one depicted in FIG. 9, except that it includes the inlet orifice cross-section as an additional optimisation quantity. FIG. 11 is a diagrammatic showing by way of example, of a possible form of inlet and jet control mechanism which, for instance, may be employed with the calculators 43 and 4t) and control units 44 and 42 of FIG. 10. In the mechanism of FIG. 11, translatory motion is imparted in the direction of double arrow F to a cam shaft 7 and consequently to the cam 1 attached to such shaft as the ships speed V varies, and rotary motion, as shown by the arrow f, is imparted to such shaft and cam 1 as the propulsion system discharge Q varies. These two measured quantities can, for instance, be given by two conventional instrumentation devices measuring V and Q, respectively. Cam 1 directly controls a flap 3 via a linkage system 2 in order to vary the cross-section of the inlet orifice 8. The movements of this assembly represent the input of the calculator 43 and control unit 44 to the motor of the propulsion system 23. An identical system composed of a cam 4 connected to shaft 7 and therefor movable in unison with cam 1 controls the movements of a shutter 6 via a linkage system in order to vary the cross-section of the jet ejected from the discharge orifice 9 in accordance with the input of the calculator 40 and control equipment 42 to the motor of the propulsion system 23. The acceleration control unit may be of a conventional type, for instance, one comparing a nominal set on a potentiometer with one given by an electromagnetic log, the difierence then directly actuating a slave motor controlling the pump motor input control elements. This feedback system may be completed by the addition of a conventional correction system where appropriate. It will be understood that the showings of the drawings are given by way of examples only and do not disclose all possible forms and applications of the invention as will be apparent to those skilled in the art. I claim: 1. A method of effecting optimum propulsion operating conditions in a jet propelled ship, comprising pumpiug water through a passage provided with a discharge orifice for the propelling jet of water capable of being modified in cross-sectional form, measuring the speed of the ship, providing a given input to the pump so that the water output thereof is at a rate in conformance with the speed of the ship, and then simultaneously modifying the cross-sectional area of the discharge orifice, said given input to the pump, and the output thereof under such modified input to provide an optimum combination of pump operation and discharge orifice configuration for the instantaneous speed of the ship. 2. The method defined in claim 1, comprising additionally providing an inlet orifice for the water for such jet capable of being modified in cross-sectional form, and when modifying the cross-sectional area of the discharge orifice, simultaneously modifying the cross-sectional area of the inlet orifice, to provide an optimum combination of the inlet and outlet orifice configurations and the pump operation for the instantaneous speed of the ship. 3. The method defined in claim 1, comprising additionally determining the thrust of the ship at said given input to the pump, and when modifying the pump operation and the cross-sectional area of the discharge orifice, compensating the optimum combination for maximum thrust of the ship at such instantaneous speed thereof. 4. A jet propulsion system for a ship comprising a discharge orifice for the propelling jet of water capable of being modified in cross-sectional form, an inlet orifice for the water for such jet, a motorized pump for pumping water from said inlet orifice and through said discharge orifice, means for measuring the speed of the ship, means for providing a given input to the pump so that the output thereof is at a rate in conformance with the speed of the ship, means for measuring the operation of the motorized pump, means for modifying the cross-sectional area of the discharge orifice to bring the cross-sectional area of the jet to an optimum value relevant to the speed of the ship and the rate of operation of the pump at that ships speed, and means for measuring the cross-sectional area of the discharge orifice as it is being modified and modifying the input to the motorized pump to effect said optimum value. 5. The system defined in claim 4, in which said means for providing a given input to the pump is controlled by said means for measuring the operation of the pump and is connected to and controls the rotational speed of the motor driving said motorized pump. 6. The system defined in claim 4, in which said motorized pump is provided with adjustable blades, and in which said means for providing a given input to the pump is controlled by said means for measuring the operation of the pump and is connected to and controls the setting of said adjustable blades. 7. The system defined in claim 4, in which said area measuring means controls the operation of said modifying means. 8. The system defined in claim 4, including a calculator connected to said modifying means, said speed measuring means and said pump measuring means, said calculator being responsive to values fed thereto by said speed measuring means and said pump measuring means to control the operation of said modifying means. 9. The system defined in claim 4, including a calculator connected to said means for providing an input to the pump and said area measuring means, said calculator being responsive to values fed thereto by said area measuring means to control the operation of said pump input means. 10. The system defined in claim 4, in which said inlet orifice is capable of being modified in cross-sectional form, and said modifying means is connected to and modifies the cross-sectional area of the inlet orifice to bring the cross-sectional area of such orifice to an optimum value relevant to the speed of the ship and the rate of operation of the pump at that ships speed, and including cal- .culator means connected to said speed measuring means and said pump measuring means and responsive to values fed thereto by such measuring means to control the operation of said modifying means. 11. The method defined in claim 1, comprising additionally measuring for a jet propelled ship designed for varying degrees of immersion, the depth of immersion of such ship at said measured speed thereof, and when modifying the pump operation and the cross-sectional area of the discharge orifice, compensating said optimum combination for said immersion of the ship at such instantaneous speed thereof. References Cited by the Examiner UNITED STATES PATENTS 2,411,895 12/1946 Poole 60356 2,540,594 2/1951 Price 6035.6 2,566,961 9/1951 Poole 6035.6 2,619,794 12/1952 Lombard 6035.5 3,002,486 10/1961 Jardmo 2301 14 3,145,780 8/1964 Kean. 3,151,596 10/1964 McMurtrey 6035.5 X 3,171,379 3/1965 Schell et al. 6035.5 X 3,214,903 11/1965 Cochran -14 X CARLTON R. CROYLE, Primary Examiner. Patent Citations
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