Attenuation module for a trailing antenna

Abstract

The present invention relates to a damping module 20 for a trailing antenna, wherein the damping module 20 has an outer shell 22, wherein a stretchable tensile element 26 is arranged in the outer shell 22, characterized in that the shell 22 is filled with a granulate 24.

Description

The invention relates to a damping module for a trailing antenna. Towed antennas are designed to be towed behind a vessel. This allows sonar receivers to be positioned at a greater distance from the vessel's sonar emitters. Furthermore, the greater distance between the receivers facilitates precise location tracking. Towed antennas can also be deployed at a different depth than the vessel, further enhancing their capabilities. Additionally, a towed antenna can incorporate an active sound-emitting component, thereby creating a separation between the vessel and the sound source. A trailing antenna is known from EP 1 033 588 A2. The trailing antenna has a damping module in front of and behind the acoustic part. The damping module has soft, gel-filled sections. When the towed antenna is launched, it is unwound by a winch. Until the first section of the antenna is in the water, it must be actively guided on board to prevent it from simply unwinding onto the deck and remaining there. This active guidance is usually achieved using two rollers, one on top and one on the bottom, to actively transport the antenna. Therefore, the rear damping module of the towed antenna is crucial for the initial deployment. If this damping module is too soft, the force transmission may not be effective, resulting in the antenna unwinding on board without actually being launched into the water. At the same time, the trailing antenna must be flexible enough to be wound onto a winch, even one with a large diameter. A seismic detection system is known from US 020060239117 A1. A continuous strengthening element is known from US 000005844860 A. A module for vibration isolation is known from DE 000069312791 T2. From DE 000068902311 T2 a signal receiver insensitive to static pressure variations is known. From DE 000010311245 A1 an acoustic part made of a composite foam is known. A damping element is known from DE 000009307059 U1. A sound-dampening or sound-absorbing composite material is known from WO 002016113241 A1. A vibration damping system is known from WO 002002035004 A1. The object of the invention is to provide a damping module that, on the one hand, has good damping properties, but also optimally fulfills the other requirements for winding and application. This problem is solved by a damping modulus with the features specified in claim 1. Advantageous further developments are described in the dependent claims, the following description, and the drawings. The damping module according to the invention is integrated into, or is a component of, a trailing antenna. The damping module according to the invention is particularly preferably located behind the acoustic section of the trailing antenna, i.e., at the end of the trailing antenna. Of course, the damping module according to the invention can also be used in front of the acoustic section. The damping module has an outer casing. The outer casing is typically made of a flexible plastic to allow, for example, the trailing antenna to be wound up. At the same time, the outer casing must protect the electronic components, especially in the acoustic section, from moisture. Flexibility is also advantageous to compensate for the different pressures at different depths. A stretchable tension element is arranged in or inside the outer casing.The outer shell incorporates both the fact that the elastic tension element is an integral part of the outer shell and that the elastic tension element is arranged within the outer shell, i.e., in the interior space formed by the outer shell. This space serves both for force transmission and, due to its elasticity, as damping for longitudinal vibrations. According to the invention, the shell is filled with granules. In contrast to simply filling it with a liquid, filling it with granules offers several advantages. Firstly, a bed of granules is movable yet more solid than a liquid filling. This allows the damping module to be reliably moved from the outside, for example, by rollers, enabling safe deployment until the towed sonar reaches the water. Additionally, a bed of granules provides damping both longitudinally and transversely.This also significantly improves the damping properties, which in turn improves the accuracy of the acoustic part and thus increases the overall performance of the trailing antenna. In a further embodiment of the invention, the granules have a density of 0.8 to 1.2 kg / dm³. Since the trailing antenna is preferably towed horizontally in the water, a significant deviation from the density of the water would be problematic, as the greater the difference, the more difficult it is for the other components to compensate for it. In a further embodiment of the invention, the space between the granules is filled with a liquid. The granules and liquid together have a density of 0.95 to 1.05 kg / dm³. Oil or water, preferably oil, can be used as the liquid. In a bulk granule, depending on the shape and surface properties of the particles, 30 to 65% of the volume is filled by the solid and the corresponding remainder by the liquid. Therefore, the bulk volume of the granules must also be taken into account when adjusting the density of the liquid used. The density of the liquid can also be adjusted, for example, by adding soluble components. Furthermore, this can optionally also be used to adapt the rheological behavior of the liquid to the damping characteristics, for example, by using starch dissolved in water. Thus, the damping properties can be adjusted as a function of frequency.To adjust the density, the flow properties of the granules can also be modified, particularly through their shape and surface finish, as this alters the solid-to-liquid ratio. Furthermore, the density of the granules can be controlled by selecting the appropriate material. In a further embodiment of the invention, the granules have a particle size of 0.5 to 10 mm, preferably 1 to 8 mm, and particularly preferably 1.5 to 6 mm. If the granules are too coarse, proper filling of the casing is not possible. If the granules are too fine, the damping element becomes too stiff and can no longer be bent sufficiently to be wound onto the winch. Therefore, this size fraction is particularly suitable. In a further embodiment of the invention, the granules have a bimodal size distribution, wherein the coarser granules have a particle size of 0.5 to 10 mm, preferably 1 to 8 mm, and particularly preferably 1.5 to 6 mm. The finer granules have a particle size between 10 µm and 500 µm. The challenge here is that the bimodal size distribution must be selected, in particular depending on the roughness of the particles, to prevent segregation during operation, where the finer granules collect at the bottom and the coarser granules at the top. The advantage of the bimodal size distribution is that it allows the solids loading to be adjusted, in particular up to 80 vol.%, which is achievable and thus far exceeds the densest sphere packing. In the context of the invention, bimodal also includes multimodal size divisions with three or more size fractions.The density can ultimately be adjusted again by changing the solids loading. In a further embodiment of the invention, the granules contain cellulose. In this form, they are primarily a wood product. For example, ground walnut shells or cork oak can be used. These natural products have the advantage of being extremely irregularly shaped due to the manufacturing process and are therefore particularly suitable as granules for this application in damping modules. In another alternative embodiment of the invention, an injection molding granulate made of PE, PU or TPU is used. The advantage is that these granulates are available in large quantities and at low cost for industrial production. In a further embodiment of the invention, the granules have an aspect ratio of at least 2. This means that the particles of the granules are at least twice as long along their longest dimension as along their shortest dimension perpendicular to it. The granules are therefore more rod- or disc-shaped. In a further embodiment of the invention, the damping module comprises a non-stretchable tensile element. The non-stretchable tensile element is longer than the stretchable tensile element in its unloaded state. The effect is that, under normal circumstances, only the stretchable tensile element carries the force. Only when the stretchable tensile element is extended to the length of the non-stretchable tensile element does the non-stretchable tensile element take over the force transmission and prevent further elongation. This reduces the damping effect, but in particular, it protects the outer shell from overstretching and thus from damage, especially to the stretchable tensile element and ultimately to the outer shell itself, and thus to the entire trailing antenna. In a further embodiment of the invention, a towing body is arranged behind the damping module, wherein the towing body is designed to stabilize the end of the towing antenna and to tension the entire towing antenna so that it assumes as straight and as horizontal a course as possible in the water. A trailing antenna with an attenuation module according to the invention is explained in more detail below with reference to an embodiment illustrated in the drawings. Fig. 1 Start of deployment Fig. 2 Partially deployed trailing antenna Fig. 3 Cross-section Figure 1 shows the beginning of the deployment of a towed antenna from a watercraft 10. First, the damping module 20 must be unwound from the winch 30. Since the towed antenna is not yet in the water, it does not pull itself into the water at this early stage; instead, the water is pumped by the drive roller 40. Once the towed antenna has been unwound far enough that, for example, the damping module 20 is already in the water, as shown in Figure 2, tension is exerted on the towed antenna. Therefore, the ease of handling, as shown in Figure 1, is very important. Figure 3 shows a cross-section through the damping module 10. An outer shell 22 made of plastic surrounds an interior filled with granules 24 and oil arranged in the spaces between them. A stretchable tension element 26 runs along the center, fulfilling both the tensile and spring functions. A longer, non-stretchable tension element 28 serves to limit the maximum longitudinal expansion of the damping element 20 or 26. Reference sign 10 Watercraft 12 Water surface 20 Damping module 22 Outer shell 24 Granules 26 Stretchable tension element 28 Non-stretchable tension element 30 Winch 40 Drive roller 50 Acoustic part

Claims

Damping module (20) for a trailing antenna, wherein the damping module (20) has an outer shell (22), wherein a stretchable tensile element (26) is arranged in or in the interior of the outer shell (22), characterized in that the shell (22) is filled with a granulate (24). Damping module (20) according to claim 1, characterized in that the granules (24) have a density of 0.8 to 1.2 kg / dm3. Damping module (20) according to one of the preceding claims, characterized in that the space between the granules (24) is filled with a liquid, wherein the granules (24) and the liquid together have a density of 0.95 to 1.05 kg / dm3. Damping module (20) according to one of the preceding claims, characterized in that the granules (24) have a particle size of 0.5 to 10 mm, preferably of 1 to 8 mm, particularly preferably of 1.5 to 6 mm. Damping module (20) according to one of the preceding claims, characterized in that the granules (24) comprise cellulose. Damping module (20) according to one of the preceding claims, characterized in that the granules (24) have an aspect ratio of at least 2. Damping module (20) according to one of the preceding claims, characterized in that the damping module (20) has a non-stretchable tensile element (28), wherein the non-stretchable tensile element (28) is longer than the stretchable tensile element (26) in the unloaded state.

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