DE2342287A1 - Ship rudder or stabiliser force sensor - determines normal force by measuring flow speed electromagnetically at two surface points - Google Patents

Abstract

Transverse force of a ship's rudder or fin stabiliser is determined by measuring the local water speed with electromagnetic flow sensors at two opposed points on the surface of the rudder or stabiliser. The force is derived from the measurements, by forming their sum and difference and taking the product of the differences. The normal pressure at each sensor is given by pn = po - dVn2/2, whence the normal force on the body = N = f(p1-p2) = (d/2).f(V1 + V2)(V1 - V2) with n = 1 or 2, d = specific mass of sea water, and po = static pressure around the rudder or fin. The force thus derived is independent of external disturbances, and may be used for regulation.

Description

LICENTIA PATENT-VERWALTUNGS-GMBH. 6 Frankfurt / Main, Theodor-Stern-Kai 1

HH 73/22

Mb / rö ^{l6 AUGUST 1973}

"Procedure for determining the transverse force of underwater transverse drive bodies"

The invention relates to a method for determining the transverse force of hydrofoil-shaped transverse drive bodies on the ship are arranged under water, in particular of ship rudders and tail stabilizers.

The transverse force is that component of the hydropower resultant that is perpendicular to the axis of rotation of the transverse drive body and perpendicular to the direction of the relative flow. A transverse force that acts preferably in the vertical direction, is called buoyancy.

In the case of the transverse drive bodies mentioned, it is from control engineering Reasons advantageous to determine the existing transverse force and a signal corresponding to it to the control device · For example, the autopilot can be a The ship's rudder in this way receive a subordinate control loop, which change the rudder lateral force according to a predetermined one Setpoint reacts quickly and regulates the disturbance variables

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connects cheaply. Despite these undoubted advantages, it will the transverse force determination is only carried out in practice in a few cases, since the known methods are either too expensive or are too susceptible to failure.

The simplest known method is to use the axis of rotation of the transverse drive body well in front of the pressure point area of the profile to arrange to measure the steeping torque and from it to derive the existing shear force (DRP 706 352). The process makes the entire system more expensive, since larger ones are used when adjusting Torques occur and therefore a more powerful drive machine (e.g. rowing machine) is required than with a conventional one Transverse drive body that is fully or approximately "balanced"

In a known fin stabilizer, the elastic deformation of the fin shaft is measured and the existing transverse force is derived from this (DBP 1 lkk 612). To carry out the process, you need a highly sensitive extensometer on the fin shaft, i.e. at a point that is practically inaccessible for maintenance. In addition, the measurement result is falsified by the fact that the elastic deformation is not only generated by the force of water, but also by dynamic mass forces of the fin, which can be particularly large when the current is completely or partially torn.

From the same patent it is also known to measure the radial deflection of an elastically built-in fin bearing (DBP 1 lkk 612). Such a bearing can give way by several millimeters as a result of the transverse force, so that a less sensitive measuring device is required. However, the elastic installation of a fin bearing would make the system much more expensive.

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According to this patent specification it is also known to the fin surface to measure vertical water pressure with a membrane, the deflection of which as a result of the water pressure is an output variable generated, which is proportional to the transverse force · This known method has the following disadvantages: If the membrane is very large, then it can be easily damaged by solids floating in the water. If the membrane is small, its Elasticity can be changed, so that the measurement result is falsified.

The object of the invention is to provide a method for determining the transverse force that is suitable for control purposes create that is largely independent of disruptive external influences.

For this purpose, it is proposed according to the invention, on two each other opposite points of the surface of the transverse drive body with the help of electromagnetic flow sensors the local Measure water speed and derive the transverse force from it.

According to a further feature of the invention, the sum and the difference of the two speeds are multiplied with one another and derived the transverse force from the product.

An electromagnetic flow sensor is a device that detects an electrical and a magnetic element in the flowing liquid Force field generated, whereby the lines of force of the two fields cross each other. The flow affects the electrical Field in such a way that a signal is tapped at the field electrodes

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which corresponds to the flow velocity · Such sensors are used as electromagnetic LOG probes Measurement of the speed of a ship known.

The proposed method is based on the idea that the difference between the two measured flow velocities the normal surface pressures acting at the measuring points can be derived * From the normal surface pressures, Derive the normal force and from it, after multiplication with the cosine of the geometric angle of attack, the transverse force. The non-linear dependence of the normal force on the difference between the two pressures can be determined by model tests will. The following derivation should serve as an explanation:

f (P ₁ - P ₂ ) (ι)

P ₁ - P ₀ ■ £ // P ₂ = P _O -E ₁ ^ / (2)

N = JL

N * 5.

Therein mean:

f (,,,) = function of

N = normal force on the transverse drive body P ₁ P ₂ = normal surface pressure at measuring points 1 and 2

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ρ β static ambient pressure

VV ₂ = flow velocity at measuring points 1 and 2 ^ = specific mass of the sea water.

The proposed method has the advantage that it uses sensors that are insensitive to growth and incrustation and cannot be damaged by solids floating in the water. It also does not require any special construction costs the storage or the pitch drive of the transverse drive body.

The derived equation 5 contains the sum and the difference of the two measured speeds. Their electronic replication leads to particularly precise results because two are adjacent electromagnetic flow sensors can measure the difference between the two speeds much more accurately than the absolute magnitudes of the speeds. The speed difference is small compared to the at small angles of attack medium speed. A circuit according to equation 5 is therefore superior to a circuit according to equation 4, for example.

The drawing shows in FIG. 1 a cross section through an airfoil-shaped transverse drive body 1, with the two flow sensors 2 and 3 which measure _{the speeds V and V 2.} In addition, the normal surface pressures p. and p _o and the static ambient pressure ρ are entered.

ώ O

In Figure 2 is a block diagram for the proposed method shown. The two flow sensors 2 and

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3 speed signals V and V ₀ supplied are fed to a summing amplifier 4 and a differential amplifier 5. These form the signals (V _± + V ₃ ) and (V _± -V ₃ ), which are fed to the multiplier 6. Since (V -V ₀ ) is significantly smaller than (V + V ₀ ), the differential amplifier 5 has a larger terminal gain than the summing amplifier 4, so that the two signals fed to the multiplier 6 are of the same order of magnitude. The multiplier 6 forms the product (V + V ₀ ). (V - V ₀ ), which is converted into a signal in the function generator 7 «, which corresponds to the normal force N. N is multiplied in multiplier 8 by the cosine of the geometric angle of attack OC . A signal corresponding to the transverse force L is present at the output of the multiplier 8.

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Claims (2)

HH 73/22 PATENT CLAIMS 1. Procedure for determining the transverse force of an underwater transverse drive body, in particular a ship's rudder or fin stabilizer, characterized in that two opposite points of the surface of the transverse drive body (l) with the help of electromagnetic Flow sensors (2, 3) measured the local water speed and derived the transverse force from this will. 2. The method according to claim 1, characterized in that the sum and the difference of the two measured speeds are multiplied with each other and the transverse force is derived from the product. 509809/0220 Blank page