WO2017157641A1

WO2017157641A1 - Natural frequency optimised propeller

Info

Publication number: WO2017157641A1
Application number: PCT/EP2017/054415
Authority: WO
Inventors: Max Dr. STEDEN
Original assignee: Thyssenkrupp Marine Systems Gmbh; Thyssenkrupp Ag
Priority date: 2016-03-16
Filing date: 2017-02-24
Publication date: 2017-09-21
Also published as: DE102016204393B3

Abstract

The invention relates to a method for adapting the frequency of a propeller (10), in which the propeller (10) comprises at least one propeller blade (30) that has at least one blind hole (50), one first body being inserted into at least one blind hole (50).

Description

Natural frequency optimized propeller

The invention relates to a method for frequency adjustment of a propeller, wherein the natural frequency of the propeller can be changed by introducing at least one body, so as to reduce the noise emission.

There are known so-called built-propeller, in which the wings are releasably mounted on a support body, typically a propeller hub. Such built propellers also allow the propeller to be constructed from a variety of materials, such as a metal hub and wings constructed of composite material. Such wings are particularly advantageous for use in military submarines because they have better damping properties and thus a lower signature than metallic wings.

From DE 10 2009 024 845 AI a propeller with a central support body and attached propeller blades is known.

From JP S61-181794 A a propeller with a cavity is known.

From US 5 304 038 A a propeller with propeller blades is known, wherein the propeller blades have cavities.

From US 7 144 222 B2 a propeller blade or a propeller blade with cavities is known.

Since the properties of a propeller can not be completely predicted, it usually happens that it resonates in the case of a manufactured propeller in the range of a wing or even a wing area. This phenomenon known as singing or humming leads to an increase in the acoustic radiation. Such a propeller must therefore be regularly rebuilt, which has proven to be very expensive, especially in the protracted production of composite propellers.

The object of the invention is to provide a propeller, in which a resonance can be subsequently remedied. This object is achieved by the method having the features specified in claim 1. Advantageous developments emerge from the subclaims, the following description and the drawings.

A propeller blade for a propeller of a watercraft for the method according to the invention has at least one first blind hole. The at least one first blind hole is arranged on an outer surface in contact with water. This is to be understood that the blind hole is not used for mounting the propeller blade on the hub and is not arranged on the hub facing surface. The at least one first blind hole is thus not used to attach the propeller blade to the hub of the propeller, but is also after attachment of the propeller blade to the hub with the water in connection. As a result, accessibility of the blind hole is given with mounted propeller blades. The at least one first blind hole is also within the meaning of the invention on the outer surface in contact with water when the at least one first blind hole is covered with a cover and thus the cover forms part of the outer surface in contact with water. As a result, the propeller blade is adapted to change by insertion of a body, the natural frequency of the propeller and thus to eliminate a resonance with occurring during operation frequencies without disassembling the propeller blades of the hub.

A blind hole is a depression, for example a hole that does not penetrate the workpiece. For example, a blind hole may be conical or cylindrical, may have an oval or rectangular basic shape. For example, a blind hole may have a thread, preferably a cylindrical shape. As a result, a body can be easily inserted into the blind hole.

In a further embodiment of the invention, the at least one first blind hole is arranged on the propeller blade tip. The propeller blade tip is preferably provided with a surface which preferably extends in the circumferential direction and forms an end face. The arrangement on the end face is particularly preferred, since on the one hand the strength requirements in this area are relatively easy to meet. On the other hand, the position causes the greatest possible change in the moment of inertia and the center of gravity with a comparatively small mass change. Furthermore, the at least one first blind hole is not hydrodynamically disadvantageous in this area. In a further embodiment of the invention, at least one second blind hole is arranged on the end face on the propeller blade tip. Here, the at least one first blind hole and the at least one second blind hole may be the same or different in shape and size. If the at least one first blind hole and the at least one second blind hole are the same in shape and size, then it is possible to introduce a first body into either the at least one first blind hole or the at least one second blind hole. This can be effected by changing the position of a first body, a different change in the natural frequency of the propeller blade. If the at least one first blind hole and the at least one second blind hole differ in shape and size, then it is possible to introduce different bodies. Preferably, a body introduced into the at least one first blind hole would have a different mass than a body inserted into the at least one second blind hole.

In a further embodiment of the invention, the at least one first blind hole is cylindrically shaped. Particularly preferably, the at least one first blind hole on a thread.

In a further embodiment of the invention, the propeller blade consists of a composite material. Examples of composite materials are glass fiber or carbon fiber reinforced plastics.

The composite material may be constructed, for example, in the form of a fiber reinforced composite of eight layers, the eight layers having a layer sequence D-C-B-A-A-B-C-D. The layer A consists of a unidirectionally fiber-reinforced composite material, the layer B of a biaxial fiber-reinforced composite, wherein the two axes of the layer B is rotated by 45 ° relative to the axis of the layer A. The layer C consists of a unidirectionally fiber-reinforced composite, wherein the axis of the layer C is rotated by 90 ° relative to the axis of the layer A. The layer D has properties to protect the composite against damage. By this symmetrical position arrangement, a composite material with optimal mechanical properties can be obtained.

In a further embodiment, at least one first body is introduced into the blind hole, wherein the at least one first body has approximately the same density of the propeller material. Particularly preferably, the body consists of the same material and thus has the same density. In a further embodiment, at least partially a first body of higher density is at least partially introduced into the blind hole. Preferably, the body has a mass of from 0.05% to 10% of the propeller blade, more preferably the body has a mass of from 1% to 5% of the propeller blade.

In a further embodiment, at least partially a first body of lower density is at least partially introduced into the blind hole. This embodiment is advantageous when propeller blades are made of metal. This embodiment also includes closing the blind hole with a lid and thereby forming a low density air body within the blind hole. According to the invention, at least partially a first body is introduced into the blind hole, wherein the at least one first body has damping properties. The at least one first body preferably has a metallic core embedded in an elastic shape.

In a further embodiment, at least one first body is introduced into the blind hole, wherein the at least one first body is designed in the form of a lid. The blind hole is closed in this embodiment by the lid. At least a second body may have been introduced into the cavity that results under the cover. The at least one second body introduced into the blind hole does not have to be directly in communication with the water bypassing the propeller, but particularly preferably the cover prevents the second body from being in direct communication with the surrounding water. As a result, the second body is protected by the lid from corrosion.

In another embodiment, the blind hole is filled with a liquid before closing with a lid. As a liquid, for example, water, oil or glycerol can be used. The advantage of backfilling with a liquid is the low compressibility of the liquid, so that no deforming forces act on the lid even under high external pressure. The liquid should be chosen so that it does not cause any change to the propeller blade, the lid and / or a second body. In particular, the second liquid should have no corrosive properties. Particularly preferably, the liquid has a higher viscosity than water. This is preferred when a second body is freely movably inserted into the blind hole under the lid. As another selection criterion For the liquid, the miscibility or solubility in water can be used. If liquid escapes from a blind hole, it is thus avoided that an insoluble phase in water reveals the presence of the boat using the propeller.

In another embodiment, the blind hole is cylindrical and 5 cm to 15 cm, preferably 10 cm deep and has a diameter of 2 cm to 10 cm, preferably 5 cm.

A propeller for a watercraft for the inventive method has at least one propeller blade according to the invention. As a result, the propeller is adapted to change by introducing a body, the natural frequency of the propeller and thus to eliminate resonance with frequencies occurring during operation.

In the method according to the invention for frequency adaptation of a propeller, a propeller according to the invention is first selected in method step a), and in method step b) at least one first body is introduced into at least one blind hole. This procedure is performed if, contrary to the calculation, a resonance occurs at a certain frequency. Due to the additional mass of the at least one first body, the natural frequency and thus the resonance frequency is changed in order to prevent the occurrence of resonance at the specific frequency.

As a body, any object can be used, which can be introduced into at least one blind hole. Preferably, the body is shaped so that it fits precisely into at least one blind hole. For example, at least one blind hole has a thread, the body has a thread which fits into the thread of the at least one blind hole. Preferably, among a plurality of bodies may be selected, wherein the different bodies have different masses. Particularly preferably, the bodies each have the same outer shape. For example, bodies may be made of plastic, steel or lead. The body may have a corresponding coating, in particular on the side which later comes into contact with water. Likewise, the body may be a body constructed of a core, such as a metal core, and a plastic sheath.

In a further embodiment of the invention, the method additionally comprises the method steps c) removing the at least one first body from at least one blind hole, d) selecting at least one secondary body, wherein the mass of the at least a second body is selected differently from the mass of the at least one first body, and e) introducing the at least one second body into at least one blind hole.

Although in principle the natural frequencies can be calculated, in practice it has been shown that this can not be done completely reliably. Therefore, trying out different bodies with different masses, Thal and Error, is often effective.

In addition to the above-mentioned process variant is as a further process variant often expedient, if several blind holes, optimally with identical shape, to introduce a body successively in different blind holes and then observe the change in the occurring resonance. As a result, the best position of the body can be found out empirically.

Below, the propeller according to the invention is explained in more detail with reference to exemplary embodiments illustrated in the drawings.

Fig. 1 view of a propeller with a propeller blade, and enlargement of the end face of the propeller blade

Fig. 2 propeller blades with several blind holes

Fig. 3 propeller blades with several blind holes and introduced bodies

In Fig. 1, the propeller 10 is shown with a hub 20 and a propeller blade 30. Usually, the propeller 10 has approximately three to nine propeller blades 30, which are arranged on the hub 20. For simplicity, however, only one propeller blade 30 is shown here. The propeller blade 30 has an end face 40 in the circumferential direction, the end face 40 has a blind hole 50. The blind hole 50 is executed in the example shown approximately rectangular. In the blind hole 50, a body, not shown, are introduced to change the natural frequency and thus the resonance frequency of the propeller blade 30 and thus the propeller 10.

FIG. 2 shows a further propeller blade 30, wherein the propeller blade 30 has six cylindrical blind holes 50 on the end face 40. This makes it possible to introduce one to six bodies in these blind holes 50. As a result, a more targeted change in the natural frequency can be achieved. FIG. 3 shows the propeller blade 30 partly shown in FIG. 2. The blind holes 50 are normally filled with first bodies 60, which has approximately the density of the propeller blade 30. For simplicity, only one introduced first body 60 is shown. To change the natural frequency and thus the resonance frequency, a first body 60 is removed and a second body 62 introduced, wherein the second body 62 has a higher density than the first body 60 and has more weight for the same dimensions. In the propeller blade 30 shown, it is possible to introduce one to six first and / or second bodies in the blind holes 50. As a result, a more targeted change in the natural frequency and thus the resonance frequency can be achieved.

Of course, if the targeted change of the natural frequency can not be achieved satisfactorily with a second body 62 of higher density, the second body 62 may also have a same density but different damping behavior or a lower density than the first body 60.

Advantageously, 50 first body 60 would be introduced into the four blind holes shown still empty.

reference numeral

10 propellers

20 hub

30 propeller blades

40 face

50 blind hole

60 first body with a first density

62 second body with a second density

Claims

claims

A method of frequency adjusting a propeller (10), the method comprising

the following method steps include:

a) selecting a propeller (10) for a watercraft with at least one

A propeller blade (30), wherein a propeller blade (30) with at least one first blind hole (50) is selected as the propeller blade (30), wherein the at least one first blind hole (50) is arranged on an outer surface in contact with water,

b) introducing at least one first body into at least one blind hole (50), wherein the at least one first body has damping properties.

2. The method according to claim 1, characterized in that the method additionally comprises the following method steps:

c) removing the at least one first body from at least one blind hole (50), d) selecting at least one second body, wherein the mass of the at least one second body is chosen to be different from the mass of the at least one first body,

e) introducing the at least one second body into at least one blind hole (50).

3. The method according to any one of the preceding claims, characterized in that as a propeller blade (30) a propeller blade is selected from a composite material.

4. The method according to any one of the preceding claims, characterized in that the at least one first body is designed in the form of a lid.

5. The method according to claim 1, characterized in that in the blind hole first at least a second body and then at least a first body is introduced, wherein as at least one first body, a body is selected in the form of a lid.

6. The method according to any one of claims 1 to 4, characterized in that in the

Blind hole filled first with a liquid, wherein as a liquid, for example, water, oil or glycerol is selected, then at least a first body is introduced into the blind hole, wherein as at least a first body, a body is selected in the form of a lid.

7. The method according to any one of the preceding claims, characterized in that the method is carried out when a resonance occurs at a certain frequency.

8. The method according to any one of the preceding claims, characterized in that the natural frequency of the propeller is changed by the introduction of a body such that a resonance is eliminated with occurring during operation frequencies.