WO2023027616A1

WO2023027616A1 - Acoustic spectroscopy assembly and a method for determining a property of a fluid in a pipe using the acoustic spectroscopy assembly

Info

Publication number: WO2023027616A1
Application number: PCT/SE2021/050826
Authority: WO
Inventors: Amr ABBOUD; Frederik RIETDIJK; Andreas HENRIKSSON; Astrid LUNDGREN; ORRE. Filip GRÖNB]ÄCK; Jörgen SAHIBZADA
Original assignee: Acosense Ab
Priority date: 2021-08-25
Filing date: 2021-08-25
Publication date: 2023-03-02

Abstract

The invention relates to an acoustic spectroscopy assembly (100) for determining a property of a fluid in a pipe (102). The assembly comprising: an acoustic transmitter (104) arranged in contact with the pipe and configured to emit an acoustic signal propagating in the pipe; a first ring-shaped element (106) arranged around the pipe and in contact with the pipe on a first side of the acoustic transmitter; and a second ring-shaped element (108) arranged around the pipe and in contact with the pipe on a second side of the acoustic transmitter; wherein each of the first and second ring-shaped elements is configured to cause a mechanical impedance mismatch between a portion of the pipe encircled by the ring-shaped element and an adjacent portion of the pipe such that a reflection coefficient for the acoustic signal at the respective first and second ring shaped element is higher than a predetermined reflection threshold value for frequencies within a predetermined frequency range.

Description

ACOUSTIC SPECTROSCOPY ASSEMBLY AND A METHOD FOR DETERMINING A PROPERTY OF A FLUID IN A PIPE USING THE ACOUSTIC SPECTROSCOPY ASSEMBLY

Field of the Invention

The present invention relates to an acoustic spectroscopy assembly for determining a property of a fluid in a pipe and to a method of controlling the acoustic spectroscopy assembly.

Background of the Invention

Active Acoustic Spectroscopy is a measurement technique used to analyze fluids inside of a container or containment such as a pipe or a vat. The technique is currently mainly used in the process industry. The technique requires small sensors with high precision in order to achieve measurements with sufficient quality in the process industry.

However, when measuring and analyzing properties of fluids, solids and/or gases from the outside of containers such as a pipe by using vibration, acoustic and ultrasound techniques, there are many external influences that decrease the accuracy of the measurement. In particular, surrounding process noise in an industrial environment can result in a significantly decreased signal to noise ratio of a received signal. Continuous noise and vibration sources such as pumps, valves, cones and the like may exist which may introduce process related noise and vibrations in the pipe, thereby negatively influencing the measurements.

In view of the aforementioned problems related to the measurement of acoustic signals in an industrial context, it is desirable to improve on existing acoustic spectroscopy systems to facilitate process integration.

Summary

In view of above-mentioned and other drawbacks of the prior art, it is an object of the present invention to provide an improved acoustic spectroscopy assembly for determining a property of a fluid in a pipe. According to a first aspect of the invention, there is provided an acoustic spectroscopy assembly for determining a property of a fluid in a pipe. The assembly comprises: an acoustic transmitter arranged in contact with the pipe and configured to emit an acoustic signal propagating in the pipe; a first ring-shaped element arranged around the pipe and in contact with the pipe on a first side of the acoustic transmitter; and a second ring-shaped element arranged around the pipe and in contact with the pipe on a second side of the acoustic transmitter; wherein each of the first and second ring-shaped element is configured to cause a mechanical impedance mismatch between a portion of the pipe encircled by the ring-shaped element and an adjacent portion of the pipe such that a reflection coefficient for an acoustic signal emitted by the transmitter is higher than a predetermined threshold value for frequencies within a predetermined frequency range.

The operation of the acoustic transmitter is based on vibrations of the transmitter which in turn generates an acoustic signal propagating in the pipe, thereby providing a non-invasive measurement technique for determining properties of a fluid in a pipe. According to an example implementation the pipe is excited with broadband noise from the acoustic transmitter, the input force is measured with a force sensor, and the response is measured with an accelerometer. A transfer function is estimated between the force signal and the acceleration signal and based on the transfer function, properties of a fluid flowing in the pipe can be estimated.

The present invention is based on the realization that the acoustic spectroscopy measurements can be improved by introducing the described mechanical impedance mismatch at respective sides of the acoustic transmitter. By arranging the ring-shaped elements so that the reflection coefficient for frequencies within the first frequency range is higher than a predetermined threshold value, measured resonant peaks will be more pronounced which in turn facilitates and simplifies the following analysis of the acquired acoustic spectra. A further advantage of the described assembly is that external noise in the measurement will be reduced. Since acoustic noise may be introduced into the pipe in the form of elastic wave propagation caused by noise and vibrations in the equipment to which the pipe is attached, the ring-shaped elements will act as reflectors preventing or reducing noise reaching the measurement setup between the ring-shaped elements, thereby improving the overall signal-to-noise ratio of the measured signal.

In the present context, the ring-shaped element may be any element which is arranged around the pipe and which causes a mechanical impedance mismatch, where mechanical impedance is a measure of how much a structure resists motion when subjected to a harmonic force. Thereby, the portion of the pipe surrounded by the ring-shaped element will respond differently to the generated acoustic signal compared to portions of the pipe which are outside of the ring-shaped element. More particularly, in a rigid pipe such as a steel pipe the change in mechanical impedance comes from the change in mass and cross section caused by the ring-shaped elements, which may be a steel ring arranged around the pipe.

The mechanical impedance mismatch will cause an acoustic signal propagating in the pipe to be at least partially reflected when reaching the position of the ring-shaped element. Moreover, the reflection coefficient can be assumed to be frequency dependent and it is therefore advantageous to configure the ring-shaped elements so that the reflection coefficient is higher than a predetermined threshold value for the specific frequency range used by the acoustic transmitter.

According to one embodiment of the invention, the first and second ring-shaped elements are further arranged and configured to create resonances in the pipe for specific frequencies within the first frequency range. Thereby, specific frequencies of interest for determining certain material properties can be selected.

According to one embodiment of the invention, the first and second ring-shaped elements are arranged and configured such that the modal density for frequencies within the predetermined frequency range is reduced compared to for a pipe without the first and second ring-shaped elements. In a practical application, a pipe transporting a fluid can be assumed to be connected to or attached by elements or objects giving rise to reflections of an acoustic signal so that for a given acoustic signal emitted by the transmitter, resonances will occur in the pipe which are subsequently detected by the measurement circuitry. However, in an uncontrolled system, there may be many resonances and the resonances may also be close to each other in frequency, making it difficult to identify and monitor specific resonances and also to detect a change in resonance frequency which may arise from a change of properties of a fluid flowing in the pipe. It is therefore desirable to reduce the number of resonant modes within the predetermined frequency range, i.e. to reduce the modal density, in order to more easily detect and identify specific resonant modes. The reduction in density of the resonant modes can be achieved through a suitable arrangement of the first and second ring shaped element. The resonance frequency can then be used to determine a density of the fluid and the bandwidth can be used to estimate the viscosity of the fluid.

According to one embodiment of the invention, the first and second ring-shaped elements are arranged and configured such that the resonant modes for frequencies within the predetermined frequency range are shifted to higher frequencies compared to for a pipe without the first and second ring- shaped elements. As a general relation, resonant modes are shifted to higher frequencies with a decreasing distance between the ring-shaped elements. However, if the rings are too close to each other there may not be any resonant modes within the predetermined frequency range since the resonant modes have been pushed to higher frequencies. There is also a practical aspect to consider since there must be sufficient room for the measurement equipment such as the transmitter between the first and second ring-shaped elements, thereby limiting how close to each other the first and second ring- shaped element can be placed.

According to one embodiment of the invention, the first and second ring-shaped elements are arranged at a distance from each other such that a predetermined number of resonant modes within the predetermined frequency range occur in the pipe. Here, resonant modes should be interpreted to mean resonant modes having an amplitude above a threshold value, i.e. resonant modes which are clearly detectable by the measurement equipment. The number of resonant modes for a given system and frequency can for example be controlled by controlling the distance between the first and second ring-shaped elements.

According to one embodiment of the invention, the first and/or the second ring-shaped element is a pipe flange. A pipe is often attached to another pipe or to a container by means of a pipe flange. Such a flange can result in a reflection coefficient higher than a threshold value and may in that case be regarded as a ring-shaped element providing the described functionality.

According to one embodiment of the invention, the acoustic spectroscopy assembly may further comprise a vibration damping material located adjacent to at least one of the first and second ring-shaped element and arranged around a portion of the pipe which is not between the first and second ring-shaped element. The vibration damping material will reduce the amount of external noise reaching the region between the ring-shaped elements. It should be noted that acoustic damping and vibration damping in many cases can be considered to be equivalent in the sense that low frequency vibrations in the audible range often gives rise to sound. Accordingly, acoustic damping and vibration damping can in many cases be seen as equivalent.

According to a second aspect of the invention, there is provided a method of controlling an acoustic spectroscopy assembly for determining a property of a fluid in a pipe. The assembly comprises: an acoustic transmitter arranged in contact with the pipe and configured to emit an acoustic signal propagating in the pipe; a receiver arranged in contact with the pipe and configured to receive a signal propagating in the pipe; a first ring-shaped element arranged around the pipe an in contact with the pipe on a first side of the acoustic transmitter; and a second ring-shaped element arranged around the pipe and in contact with the pipe on a second side of the acoustic transmitter, wherein each of the first and second ring-shaped element is configured to cause a mechanical impedance mismatch between a portion of the pipe encircled by the ring-shaped element and an adjacent portion of the pipe such that a reflection coefficient for an acoustic signal emitted by the transmitter is higher than a predetermined threshold value for frequencies within a predetermined frequency range

The method comprises: by the transmitter, emitting an acoustic signal into the pipe; by the receiver, acquire an acoustic signal propagating in the pipe; and determining a property of a fluid flowing in the pipe based on the acquired acoustic signal. The acquired acoustic signal can for example be an acoustic spectrum of the signal propagating in the pipe. Moreover, a plurality of receivers may be arranged at different locations of the pipe to acquire a plurality of spectra from different locations.

Features and advantages of the second aspect of the invention are largely analogous to those discussed above in relation to the first aspect of the invention.

Further features of, and advantages with, the present invention will become apparent when studying the appended claims and the following description. The skilled person realize that different features of the present invention may be combined to create embodiments other than those described in the following, without departing from the scope of the present invention.

Brief Description of the Drawings

These and other aspects of the present invention will now be described in more detail, with reference to the appended drawings showing an example embodiment of the invention, wherein:

Fig. 1 schematically illustrates an acoustic spectroscopy assembly according to an embodiment of the invention;

Fig. 2 schematically illustrates an acoustic spectroscopy assembly according to an embodiment of the invention; Figs. 3A-C schematically illustrate various features of an acoustic spectroscopy assembly according to an embodiment of the invention;

Fig. 4 schematically illustrates features of an acoustic spectroscopy assembly according to an embodiment of the invention; and

Fig. 5 is a flow chart outlining steps of a method of controlling the acoustic spectroscopy assembly according to an embodiment of the invention.

Detailed Description of

Embodiments

The present invention will now be described more fully hereinafter with reference to the accompanying drawings, in which currently preferred embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided for thoroughness and completeness, and fully convey the scope of the invention to the skilled person. Like reference characters refer to like elements throughout.

The present invention will be described with reference to an acoustic spectroscopy system suitable for characterizing a fluid. However, the described acoustic spectroscopy assembly and control method could also be used to determine properties of a semi-solid or granular material being transported in a pipe or the like.

Fig. 1 is a schematic illustration of an acoustic spectroscopy assembly 100 for determining a property of a fluid in a pipe 102. The assembly 100 comprises an acoustic transmitter 104 arranged in contact with the pipe 102 and configured to emit an acoustic signal propagating in the pipe 102, a first ring-shaped element 106 arranged around the pipe 102 and in contact with the pipe on a first side of the acoustic transmitter 104 and a second ring- shaped element 108 arranged around the pipe 102 and in contact with the pipe 102 on a second side of the acoustic transmitter 104. The ring-shaped elements 106, 108 may also be referred to as rings for simplicity. The acoustic spectroscopy assembly 100 further comprises a receiver 110 arranged in contact with the pipe 102 and located between the first and second ring 106, 108. The receiver 110 may for example be an accelerometer configured to detect acoustic signals in the pipe, and the receiver 110 and transmitter 104 are both coupled to readout circuitry 112. The readout circuitry 112 is configured to determine a transfer function between an input force resulting from the emitted acoustic signal and the received signal from the receiver 110. Based on the estimated transfer function, properties of a fluid flowing in the pipe can be estimated. The general principles of acoustic spectroscopy are known to the skilled person and will not be discussed in further detail herein.

That the elements are ring-shaped should be interpreted to mean that they are configured to encircle at least a major portion of the pipe circumference. It should however be noted that there may be gaps or the like in the rings and they may still provide the desired functionality of introducing an impedance mismatch. A potential drawback of not having the rings fully encircle the pipe is that noise from the pipe outside of the rings more easily reach the receiver 110 and also that reflections occurring in the rings will not be homogeneous in a circumferential direction, potentially leading to measurement results which are more difficult to interpret. Although the illustrated ring-shaped elements 106, 108 represent a straight-forward alternative, structures having a different shape such as a square, rectangular or irregular shaped elements may also be coupled to the pipe 102 to achieve the desired effect of impedance mismatch.

Fig. 2 illustrates an acoustic spectroscopy assembly 100 further comprising a vibration damping material 202, 204 located adjacent to each of the first and second ring-shaped elements 106, 108 and arranged around a portion of the pipe 102 which is not between the first and second ring-shaped elements. The vibration damping material 202, 204 can for example be provided in the form of a sleeve, tape or the like which is attached to the pipe adjacent to or in the vicinity of the rings 106, 108 in order to dampen vibrations in the pipe 102. As outlined above, the ring-shaped elements 106, 108 are configured to introduce a mechanical impedance mismatch at the position of the pipe 102 where they are placed. Starting from an infinite uniform pipe 300 as an illustrative example as illustrated in Fig. 3A, a signal generated by the transmitter 104 would propagate in the pipe unhindered and without reflection. The theoretical transfer function 302 for the pipe with infinite length illustrated in Fig. 3A does not contain any resonances and the response is therefore smooth as a function of frequency.

Fig. 3B schematically illustrates a “long” but finite pipe 204 and the corresponding transfer function 306 as a function of frequency. Here it can be seen that a number of resonance peaks are observable, and that the density of resonance peaks is increasing with increasing frequency.

In a practical application, the pipe is obviously not infinite and there will often be many different features of the pipe leading to reflections due to impedance mismatch. This will cause the resulting acquired signal to be influenced by features outside of the measurement system as such, thereby leading to a signal which may be distorted, and which may vary over time, thereby making it difficult to determine if a change in signal properties is due to a change of the fluid in the pipe or due to external factors.

By placing ring-shaped elements 106, 108 on respective sides of the transmitter, the acoustic “environment” can be better controlled resulting in that the number and position of resonance peaks can be controlled, and the signal-to-noise ratio can be improved.

With the introduction of the ring-shaped elements 106, 108, as illustrated in Fig. 3C, the experienced difference in mechanical acoustic impedance will lead to a reflection of a portion of the signal at the respective ring which in turn will cause the resonant modes arising in the region between the ring-shaped elements 106, 108 to be more sparsely distributed and thereby more easily discernible. Thereby, there will be fewer resonance peaks within a given frequency range, making it easier to detect and monitor individual resonance peaks. Moreover, the amplitude of the resonance peaks will be increased, further facilitating detection and monitoring of the resonance peaks.

The specific details of how to configure the ring-shaped elements 106, 108 and where to place them is determined based on various parameters of the measurement setup such as the properties of the pipe, i.e. the pipe material, diameter and wall thickness. The placement and properties of the rings also depend on the selected frequency range and on the existing environment of the pipe where for example the space around the pipe may be limited. Accordingly, it is not possible to provide a specific answer on how to arrange and configure the ring-shaped elements in any given situation, but general relations and considerations will be described in the following.

Moreover, the environment of the acoustic spectroscopy assembly also influences the preferable configuration of the ring-shaped elements 106, 108 since in some cases only a minor enhancement of resonant peaks is required while in other situations the signal may be very noisy and/or comprising densely located resonance peaks in which case the ring-shaped elements may be required to have a higher mass and to be placed closer to each other to achieve the desired effects.

Based on the description provided herein, the skilled person can relatively easily find a suitable arrangement of ring-shaped elements achieving the described effects in a given system.

A general relation is that an increasing mass and stiffness of the ring- shaped element 106, 108 is correlated with an increasing reflection coefficient, at least up to a certain point. Accordingly, the mass of the rings is preferably controlled to achieve the desired reflection coefficient, where the mass can be controlled by controlling the diameter of the ring-shaped elements 106, 108 and/or the extension of the ring-shaped elements 106, 108 in the axial direction of the pipe. The stiffness of the ring-shaped element 106, 108 depends on the material of the ring and also on if the ring is solid or if it has an internal structure. As a general rule, a solid metallic ring can be used.

Moreover, a reduced distance between the ring-shaped elements 106, 108 leads to a higher resonance frequency which in turn leads to a reduced modal density. The overlap of resonant frequencies will thus be reduced with a reduced distance between the ring-shaped elements 106, 108. However, this is only true down to a certain distance between the ring-shaped elements 106, 108 since if the distance is too low, the standing waves may coalesce causing an increased overlap of resonant modes.

Fig. 4 illustrates a measured transfer function for a practical example with and without ring-shaped elements. The pipe is a steel pipe having a diameter of 156 mm and a wall thickness of 3 mm. In the setup using ring- shaped elements, the first and second ring-shaped elements are steel rings both having the same properties with an axial thickness of 40 mm and a radial extension of 50 mm, thereby having an inner radius of 156 mm and an outer radius of 206 mm. The axial distance between the first and second ring is approximately 70 cm. In the present configuration, the acoustic transmitter and receiver are arranged at approximately equal distance from the respective first and second ring in the same circumferential plane and with a 90° separation between the two. It should be noted that various positions of the acoustic transmitter and receiver are possible. Moreover, the desired reflection coefficient at the respective ring-shaped element can also be achieved by stacking a number of rings which may simplify installation of the rings. Moreover, it may also be easier to achieve a homogenous surface contact between the ring and the pipe when using smaller rings, i.e. rings having a lower thickness in the axial direction and thereby a smaller contact area towards the pipe.

Furthermore, a ring-shaped element may consist of a plurality of separate parts, forming sections along the circumference of the ring, which when joined together will form a complete ring around the pipe, thereby simplifying installation of the rings. To improve the mechanical contact between the ring-shaped elements and the pipe, a film can be arranged between the ring and the pipe. The film may for example be a thin metallic film.

In Fig. 4, the dashed line 400 represents the measurement taken without any rings and the solid line 402 is a measurement taken with ring- shaped elements located on respective sides of the transmitter and receiver as illustrated above. As described above, it can be seen that the resonance peaks are more separated in frequency and also that the peak amplitude of the resonance peaks has increased with the introduction of the ring-shaped elements.

Fig. 5 is a flow chart outlining the general steps of a method of controlling the above-described acoustic spectroscopy assembly 100. The method comprises, by the transmitter 104, emitting 500 an acoustic signal into the pipe 102, by the receiver, acquiring 502 an acoustic signal propagating in the pipe 102, and determining 504 a property of a fluid flowing in the pipe 102 based on the acquired acoustic signal.

Even though the invention has been described with reference to specific exemplifying embodiments thereof, many different alterations, modifications and the like will become apparent for those skilled in the art.

Additionally, variations to the disclosed embodiments can be understood and effected by the skilled person in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims. In the claims, the word "comprising" does not exclude other elements or steps, and the indefinite article "a" or "an" does not exclude a plurality. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.

Claims

1 . An acoustic spectroscopy assembly (100) for determining a property of a fluid in a pipe (102), the assembly comprising: an acoustic transmitter (104) arranged in contact with the pipe and configured to emit an acoustic signal propagating in the pipe; a first ring-shaped element (106) arranged around the pipe and in contact with the pipe on a first side of the acoustic transmitter; and a second ring-shaped element (108) arranged around the pipe and in contact with the pipe on a second side of the acoustic transmitter; wherein each of the first and second ring-shaped elements is configured to cause a mechanical impedance mismatch between a portion of the pipe encircled by the ring-shaped element and an adjacent portion of the pipe such that a reflection coefficient for the acoustic signal at the respective first and second ring shaped element is higher than a predetermined reflection coefficient threshold value for frequencies within a predetermined frequency range.

2. The acoustic spectroscopy assembly according to claim 1 , wherein the first and second ring-shaped elements are further arranged and configured to create resonances in the pipe for selected frequencies within the first frequency range.

3. The acoustic spectroscopy assembly according to claim 1 or 2, wherein the transmitter is configured to emit a signal within the predetermined frequency range.

4. The acoustic spectroscopy assembly according to any one of the preceding claims, wherein the predetermined frequency range is 1 kHz to 20 kHz.

5. The acoustic spectroscopy assembly according to any one of the preceding claims, wherein the first and second ring-shaped elements are arranged and configured such that the modal density for frequencies within the predetermined frequency range is reduced compared to for a pipe without the first and second ring-shaped elements.

6. The acoustic spectroscopy assembly according to any one of the preceding claims, wherein the first and second ring-shaped elements are arranged and configured such that the resonant modes for frequencies within the predetermined frequency range are shifted to higher frequencies compared to for a pipe without the first and second ring-shaped elements.

7. The acoustic spectroscopy assembly according to any one of the preceding claims, wherein the first and second ring-shaped elements are arranged at a distance from each other such that a predetermined number of resonant modes within the predetermined frequency range occur in the pipe.

8. The acoustic spectroscopy assembly according to any one of the preceding claims, wherein the ring-shaped element consists of at least two parts which joined together forms a ring around the pipe.

9. The acoustic spectroscopy assembly according to any one of the preceding claims, wherein the first and/or the second ring-shaped element is a pipe flange.

10. The acoustic spectroscopy assembly according to any one of the preceding claims, further comprising a film arranged between the ring- shaped elements and the pipe.

11 . The acoustic spectroscopy assembly according to claim 10, wherein the film is a metallic film. 15

12. The acoustic spectroscopy assembly according to any one of the preceding claims, further comprising a vibration damping material (202, 204) located adjacent to at least one of the first and second ring-shaped element and arranged around a portion of the pipe which is not between the first and second ring-shaped element.

13. The acoustic spectroscopy assembly according to any one of the preceding claims, further comprising at least one receiver (110) arranged in contact with the pipe in a location between the first and second ring-shaped element.

14. Method of controlling an acoustic spectroscopy assembly (100) for determining a property of a fluid in a pipe (102), the assembly comprising: an acoustic transmitter (104) arranged in contact with the pipe and configured to emit an acoustic signal propagating in the pipe; a receiver (110) arranged in contact with the pipe and configured to receive a signal propagating in the pipe; a first ring-shaped element (106) arranged around the pipe an in contact with the pipe on a first side of the acoustic transmitter; and a second ring-shaped element (108) arranged around the pipe and in contact with the pipe on a second side of the acoustic transmitter, wherein each of the first and second ring-shaped element is configured to cause a mechanical impedance mismatch between a portion of the pipe encircled by the ring-shaped element and an adjacent portion of the pipe such that a reflection coefficient for the acoustic signal at the respective first and second ring shaped element is higher than a predetermined reflection coefficient threshold value for frequencies within a predetermined frequency range, wherein the method comprises: by the transmitter, emitting (500) an acoustic signal into the pipe; by the receiver, acquiring (502) an acoustic signal propagating in the pipe; and 16 determining (504) a property of a fluid flowing in the pipe based on the acquired acoustic signal.