System and method for controlling hydrofoil boats; and hydrofoil boat comprising said control system

Abstract

The invention relates to a system for controlling a hydrofoil boat comprising at least three static pressure or dynamic pressure and water speed sensors submerged in the water and located on the submerged hydrofoils of the boat, an electronic controller on the boat, an actuator for each one of the submerged hydrofoils able to change an angle of attack of its respective hydrofoil. The control system allows boats on hydrofoils to sail in a safe and comfortable way in any wave condition within the sailing limits of traditional boats.

Claims

1. A control system for hydrofoil boats able to change an angle of attack thereof, or having ailerons, the system comprising: at least three sensors for measuring pressure and water speed, intended to be located on most submerged ends of the hydrofoils, an electronic controller intended to be placed on board, and one actuator for each one of the hydrofoils, each actuator connected to its respective hydrofoil to change the angle of attack or aileron of said hydrofoil, wherein the electronic controller is communicated with the sensors for periodically collecting the measurements taken by the sensors, as well as the electronic controller is connected to the actuators to act in real time on the actuators, in order to maintain constant values of total pressure of the water equal to a reference total pressure.

2. The control system for hydrofoil boats of claim 1, wherein the controller is configured to command the actuators of the hydrofoils to maintain the total pressure according to the following Bernoulli equation: $P_T=P_O+\rho .Math.g.Math.h_o+\frac{1}{2}.Math.\rho .Math.V_o^2$ where: P.sub.T≡Total pressure measured by the sensor, P.sub.O≡Atmospheric pressure, ρ≡Water density, h.sub.O≡Reference depth under the surface of the water without waves at which the sensor on the hydrofoil is located, g≡Gravitational acceleration, V.sub.O≡Reference speed.

3. A boat comprising: a hull, and at least two hydrofoils mounted with adjustable angles of attack, the boat further comprising the control system described in claim 1, wherein the sensors are located on the hydrofoils in positions intended to be submerged, as well as the electronic controller is on-board the hull, and wherein each one of the actuators is connected to its respective hydrofoil to change the angle of attack of said hydrofoil, and wherein the electronic controller is communicated with the sensors for periodically collecting the measurements taken by the sensors, as well as being connected to the actuators to act in real time on the actuators, to maintain the total pressure values constant.

4. A method for controlling a boat, wherein the boat is of the type comprising: a hull, at least two hydrofoils mounted with adjustable angles of attack, at least three sensors for measuring pressure and speed, located on the hydrofoils in positions intended to be submerged, an electronic controller placed on the hull, and one actuator for each one of the hydrofoils, each actuator connected to its respective hydrofoil to vary the angle of attack said hydrofoil, wherein the electronic controller is communicated with the sensors for periodically collecting the measurements taken by the sensors, as well as being connected to the actuators to act in real time on the actuators, wherein the method comprises the following steps: the controller receives pressure and water speed measurements taken by the sensors, and the controller sends the order to the actuators to modify the angle of attack of the hydrofoils to maintain a constant total pressure value.

5. The control method according to claim 4, wherein the total pressure is given by the following formula of the Bernoulli equation: $P_T=P_O+\rho .Math.g.Math.h_o+\frac{1}{2}.Math.\rho .Math.V_o^2$ where: P.sub.T≡Total pressure measured by the sensor, P.sub.O≡Atmospheric pressure, ρ≡Water density, h.sub.o≡Reference depth under the surface of the water without waves at which the sensor on the hydrofoil is located, g≡Gravitational acceleration, V.sub.O≡Reference speed while sailing without waves.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

(1) The previous advantages and features, in addition to others, shall be understood more fully in light of the following detailed description of embodiments, with reference to the following figures, which must be understood by way of illustration and not limitation, wherein:

(2) FIG. 1 shows a side view of a diagram of a flying moth-type boat of the state of the art, wherein the hydrofoils and the wand sensor for controlling the lift can be seen.

(3) FIG. 2 shows a front view of a diagram of the boat of FIG. 1.

(4) FIG. 3 shows two graphs with examples of the isobars of the total pressure (PT) under the wave, in other words, of the streamlines at different reference depths.

(5) FIG. 4 shows drawings with the two sailing modes of these types of vessels: constant height and following the shape of the wave.

(6) FIG. 5 shows a diagram of the high-level modules of the invention, including the controller, sensors and actuators forming the same.

(7) FIG. 6 shows a diagram of an example of the boat, type AC50, as well as the location of the pressure and speed sensors of the invention.

DESCRIPTION OF SPECIFIC EMBODIMENTS OF THE INVENTION

(8) The invention substantially improves the ability of hydrofoil boats (100) to sail on waves. The system is based on controlling the boat (100) from the measurements of several pressure (P.sub.L) sensors (201) and water speed (V.sub.L) sensors (201) located on the lowest part of each appendix; i.e. keels (102) and rudder (101).

(9) The objective of the control is for the boat (100) to follow the shape of the wave without the hull touching the water. With this objective, the control will act on the hydrofoils of the boat (100) to keep the total pressure constant at the points where the pressure and water speed are measured. This means that, as will be shown, the depth h(t) of the measuring points with respect to the water surface will be maintained within a range that allows the boat to follow the shape of the wave without the wave touching the hull. By applying Bernoulli's principle, the total pressure to be kept constant at one measuring point is:

(10) $P_T=P_L+\frac{1}{2}.Math.\rho .Math.V_L^2=P_o+\rho .Math.g.Math.h_o+\frac{1}{2}.Math.\rho .Math.V_o^2$
Where:

(11) P.sub.L≡Local Static Pressure measured by the sensor (201) at the measuring point.

(12) V.sub.L≡Local Speed measured by the sensor (201) at the measuring point.

(13) P.sub.O≡Atmospheric Pressure.

(14) ρ≡Water density.

(15) h.sub.O≡Reference depth below the surface of the water without waves.

(16) V.sub.O≡Reference speed while sailing without waves. This speed can be matched at all times to the V.sub.L.

(17) g≡gravitational acceleration.

(18) The total pressure is kept constant along the streamlines. One of the streamlines is a tangent to the profile where the sensor (201) is located. Supposing that the boat (100) maintains its speed with respect to the water (V.sub.O), in the case that the hydrofoils are moving and thereby providing energy to the system, the total pressure at any point where the sensor (201) is located will be:

(19) $P_T\approx P_o+\rho .Math.g.Math.h\left(t\right)-\rho .Math.g.Math.\zeta \left(t\right)\left\{1-\frac{h_w}{2}.Math.e^{\frac{2.Math.\pi }{{\lambda }_w}.Math.\left(\zeta \left(t\right)-h\left(t\right)\right)}\right\}+ℒ\left(h\left(t\right),\alpha \left(t\right)\right)+ℳ\left(h\left(t\right),\alpha \left(t\right),\stackrel{.}{\alpha }\left(t\right)\right)+\frac{1}{2}.Math.\rho .Math.V_o^2$$\zeta \left(t\right)=\mp \frac{h_w}{2}.Math.\sin \left(\beta .Math.t\right)$$\beta =\frac{2\pi V_o}{{\lambda }_W}\mp \sqrt{\frac{2\pi g}{{\lambda }_W}}$$c=\mp \sqrt{\frac{{\lambda }_W.Math.g}{2\pi }}$
Where:

(20) t≡Time variable.

(21) h(t)≡Depth of the measuring point below the surface of the water.

(22) ζ(t)≡Equation of the wave.

(23) h.sub.w≡Semi-amplitude of the wave.

(24) λ.sub.w≡Wavelength of the wave.

(25) ≡Contribution to total pressure due to the influence of the lift of the hydrofoil.

(26) α(t)≡Configuration of the angles of attack of the hydrofoils that affect the measurement of the sensor (201).

(27) {dot over (α)}(t)≡Derivative of the configuration of the angles of attack of the hydrofoils that affect the measurement of the sensor (201).

(28) ≡Contribution to total pressure due to the influence of the torque that is applied to the hydrofoil to change the angle of attack thereof.

(29) +≡The negative sign (−) corresponds to the case in which the boat advances in the direction of the wave, and the positive sign (+) when the boat sails against the wave.

(30) β≡Wave frequency.

(31) c≡Speed of the wave train.

(32) The contribution to the kinetic energy coming from the wave-induced water speed has been disregarded, due to the fact that it is of a smaller degree than the kinetic energy of the boat (100).

(33) By identifying all terms, the following results:

(34) $P_L=P_o+\rho .Math.g.Math.h\left(t\right)-\rho .Math.g.Math.\zeta \left(t\right)\left\{1-\frac{h_w}{2}.Math.e^{\frac{2.Math.\pi }{{\lambda }_w}.Math.\left(\zeta \left(t\right)-h\left(t\right)\right)}\right\}+{ℒ}_P\left(h\left(t\right),\alpha \left(t\right)\right)+{ℳ}_P\left(h\left(t\right),\alpha \left(t\right),\stackrel{.}{\alpha }\left(t\right)\right)$$\frac{1}{2}.Math.\rho .Math.V_L^2\approx {ℒ}_V\left(h\left(t\right),\alpha \left(t\right)\right)+{ℳ}_V\left(h\left(t\right),\alpha \left(t\right),\stackrel{.}{\alpha }\left(t\right)\right)+\frac{1}{2}.Math.\rho .Math.V_o^2$
Where:

(35) .sub.P≡Contribution to the potential energy term of the total pressure due to the influence of the lift of the hydrofoil.

(36) .sub.V≡Contribution to the kinetic energy term of the total pressure due to the influence of the lift of the hydrofoil.

(37) .sub.P≡Contribution to the potential energy term of the total pressure due to the influence of the torque that is applied to the hydrofoil to change the angle of attack thereof.

(38) .sub.V≡Contribution to the potential energy term of the total pressure due to the influence of the torque that is applied to the hydrofoil to change the angle of attack thereof.

(39) Thus, if a control strategy is implemented that maintains the total pressure constant and equal to a reference, the pressure sensor (201) will continue the path of a streamline corresponding to a Total Pressure equal to the reference.

(40) $P_{\mathrm{Tref}}=P_o+\rho .Math.g.Math.h_o+\frac{1}{2}.Math.\rho .Math.V_L^2$

(41) The previous equation indicates that for a speed of the boat V.sub.L, if the reference total pressure is increased, the sensor (201) will follow a deeper streamline and if the reference total pressure is decreased, it will be shallower.

(42) FIG. 3 shows the streamlines for different total pressures for different reference depths h.sub.O: 1, 1.2, 1.4, 1.6 and 1.8 metres. Due to the exponential in the pressure differential formula, it is observed that as the reference depth increases, the streamlines or sensor (201) paths are flatter.

(43) Based on FIG. 3 it can be concluded that a control system that has the aim of keeping the total pressure of a point of the hydrofoil constant will force the path of that hydrofoil to follow a streamline and thus follow the shape of the wave. To be able to implement this system, the pressure and speed sensors (201) must be located on the submerged hydrofoils, as shown in FIG. 6. If these sensors (201) are on all of the hydrofoils, the points of the hull where the appendixes, i.e. heels (102) and rudder (101), are attached, by being integrally joined to the hydrofoils, will follow paths parallel to the isobars of the hydrofoils, and thus, with the proper configuration of the controller, the boat (100) will be able to follow a path that follows the shape of the wave. If there are no waves, the boat (100) will maintain a constant height, given that the depth will be equal to the reference h.sub.O. If the control is given a total pressure range, it will be able to maintain a constant height with respect to the free surface when the waves are small.

(44) With respect to the foregoing, the error signal of the control will be the following:

(45) $\begin{array}{c}\mathrm{.Math.}=P_T-P_{\mathrm{ref}}=\\ =P_L+\frac{1}{2}.Math.\rho .Math.V_L^2-P_{\mathrm{ref}}=P_o+\rho .Math.g.Math.h\left(t\right)-\rho .Math.g.Math.\\ \zeta \left(t\right)\left\{1-\frac{h_w}{2}.Math.e^{\frac{2.Math.\pi }{{\lambda }_w}.Math.\left(\zeta \left(t\right)-h\left(t\right)\right)}\right\}+\frac{1}{2}.Math.\rho .Math.V_L^2-P_0-\rho .Math.g.Math.h_o-\\ \frac{1}{2}.Math.\rho .Math.V_L^2\\ =\rho .Math.g.Math.\left[h\left(t\right)-h_o-\zeta \left(t\right)\left\{1-\frac{h_w}{2}.Math.e^{\frac{2.Math.\pi }{{\lambda }_w}.Math.\left(\zeta \left(t\right)-h\left(t\right)\right)}\right\}\right]\end{array}\hspace{1em}$

(46) Thus, in the aim of keeping the error signal at zero, the control will try to cancel the effect of the wave.

(47) Based on the error signal of the control, several types of controls can be implemented. The simplest one is a PD, relating the angle of attack of the hydrofoils to the error signal, such that:
α(t)=K.sub.p.Math.ε+K.sub.d.Math.{dot over (ε)}
Kp being the constant of proportionality of the control and Kd being the derivative constant of the control.

(48) FIG. 3 shows a sinusoidal wave, when the waves of the sea are a wave spectrum. However, given that the streamlines represent a spectrum, they are very similar to those of FIG. 4, and thus the boat (100) sailing on waves of the sea will also follow the shape of the wave.

(49) Furthermore, the equation corresponding to the total pressure of a wave spectrum has the same form as the previously mentioned equation. Thus, by having three pressure and speed measuring points, the larger amplitudes of the wave spectrum can be characterised. In other words, while sailing with waves, the control system can always calculate what the approaching wave train will be.

(50) By having the wave spectrum of the wave on which the boat (100) is sailing, the controller can be adjusted such that the variation of the angles of attack of the hydrofoils with time allows the hydrodynamic forces to respond with enough time to lift or lower the bow/stern, following the shape of the wave, and thus the hull of the boat (100) will not touch the water.

(51) The control system necessary for implementing this control method requires at least three sensors (201) situated on the hydrofoils that are submerged, an on-board processor in which the control algorithm and the actuators run in real time. The pressure and speed sensors (201) do not lose the measurement and provide a continuous signal; this is not the case for height sensors currently being used. FIG. 5 shows a high-level diagram of the location of the pressure sensors (201) of the invention in a typical boat (100). Nowadays there are several sensors (201) options for calculating pressure and speed: pitot tubes, ultrasonic sensors, infrared, etc., all of which are valid for this type of control.