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    • 专利摘要:
    Non-intrusive device and method to detect cavitation in a vessel. The object of the present invention is a non-intrusive device and a method of automatic detection of cavitation in a ship, wherein said cavitation is produced by a ship's helix or the helix-helix interaction thereof. More specifically, this non-intrusive device comprises at least one accelerometer intended to be installed inside the ship's hull at an intersection of at least two primary elements of the case structure in the area near the propeller, a connector to be linked to the ship's tachometer, a control unit designed to receive information from the accelerometer and the tachometer to detect cavitation and notify a user through an interface. (Machine-translation by Google Translate, not legally binding)
    公开号:ES2615809A1
    申请号:ES201631097
    申请日:2016-08-16
    公开日:2017-06-08
    发明作者:Publio BELTRÁN PALOMO；Alfonso MORENO RODRÍGUEZ
    申请人:Tecn Y Servicios De Ingenieria S L；Tecnicas Y Servicios De Ingenieria Sl；
    IPC主号:
    专利说明:

    OBJECT OF THE INVENTION
    The object of the present invention is a non-intrusive device and an automatic cavitation detection method in a ship, wherein said cavitation is produced by a ship's propeller or the hull-helix interaction thereof. BACKGROUND OF THE INVENTION
    Currently, cavitation is the main cause of erosion on the propellers and on the rudders of ships. Cavitation is also one of the most important sources of noise radiated by the ship to the water, as well as the main generator of noise and / or vibration on board the ship.
    Additionally, cavitation causes a significant loss of energy efficiency of the ship's propulsion system with its corresponding negative economic impact on the operation of the ship.
    The cavitation phenomenon occurs in the ship's propeller, this phenomenon is due to the pressure drop generated on the front face of the propeller blades when the blades rotate around the axis that links the ship's propeller with the engine of propulsion.
    In this way, bubbles are formed that travel to areas of greater pressure where they implode spontaneously (the vapor returns to the liquid state suddenly) producing a wake of gas and a start of the metal of the surface of the blades in which it originates phenomenon. There are different types of cavitation depending on the flow conditions that can be found on the blades. According to the degree of development, it can be classified as non-cavitation flow, incipient cavitation and developed cavitation.


    In order to prevent such cavitation, studies of cavitant flows are performed to optimize the design of the ship's propeller. These studies entail great difficulty, since they take into account the biphasic and turbulent state of the water, there being a strong coupling between the turbulence state of the water and the pressure variations that this state induces.
    More specifically, these studies usually employ the following techniques: generation of theoretical models, carrying out tests with a scale model in cavitation tunnels, performing computational fluid dynamics analysis (CFD), and real-scale observation and measurement monitoring noise and vibrations outside the hull of the ship.
    Despite the advances made in the design of propeller and, in particular in the study of the generation of cavitation, these techniques do not allow to accurately predict the behavior of the propellant motor under real cavitation conditions.
    Typically, theoretical models become inconsistent when water flow becomes more complex, that is, when turbulence appears, trials with scale models have cost and time to prepare models, and simulation flow analysis entails the adoption of models (turbulence, multiphase, ...) and hypotheses (boundary conditions) that limit their application, especially for the analysis of cavitation.
    Therefore, at present, the real-scale observations of the behavior of the propeller against the phenomenon of cavitation are indispensable in the design of the propeller, as well as in the interpretation of the test results with the scale models and with the simulations .
    However, despite the great importance that these real-scale observations have in the understanding of cavitation, these techniques are not widely used due to their excessive cost since they require the realization of viewing windows in the helmet with a system of cameras and strobe lights linked to shaft rotation. This means taking the ship to a dike for the realization of these windows, with the economic cost that entails, and with the problems that can lead to the hull itself.


    On the other hand, there are also cavitation detection technologies based on pressure, noise and vibration measurement methods in the areas near the ship's propeller. These cavitation detection methods are based on the measurement and analysis of signals induced by the behavior of the propeller. Currently the installation of vibration, pressure or noise sensors are installed in external areas of the ship's hull, usually in the areas closest to the propeller. Due to this they also require the realization of holes in the hull and therefore to remove the ship to dike with the associated cost.
    In this way, all known techniques have a slow installation, a high cost, pierce the hull of the ship and do not allow the detection of cavitation in real time and differentiating form for each ship. DESCRIPTION OF THE INVENTION
    A first aspect of the invention is a non-intrusive device for detecting the appearance of cavitation in a ship, wherein the ship comprises:
    - a helmet,
    - apropulsion unit thattoitstimeunderstand thelessaengine of
    propulsion, a transmission system and at least one propeller with a plurality
    of blades, where the propulsion engine and the propeller are linked to each other by
    the transmission system,
    - a tachometer coupled with the ship's transmission system, and -a navigation system.
    More specifically, the device comprises:
    - at least one accelerometer, intended to be installed inside the ship's hull at an intersection of at least two primary elements of the case structure in the area near the propeller, to detect a first signal comprising vibrations in the hull and that when there is cavitation it is modulated by the frequency of the blade's pitch,
    - at least one connector intended to be linked to the tachometer and / or the ship's navigation system, 4


    - a control unit, linked with accelerometer and with said connector, which in turn comprises:
    - acquisition means intended to acquire the first signal and to acquire from the tachometer or the navigation system of the vessel the frequency of rotation of the propulsion engine to determine the frequency of pitch of the propeller blade,
    - high frequency filtering means intended to filter the first signal to obtain a second signal comprising the high frequency components, between 1 kHz and 20 kHz, of the first signal,
    - signal processing means intended to calculate the envelope of the second signal by applying the Hilbert transform and subsequently performing its complex sum with the second signal, obtaining a third signal that is complex and whose module is the envelope of the second signal ,
    - means of spectral analysis to obtain a spectrum that quantifies the intensity of the third signal at several frequencies to compare the intensity of the spectrum component to the frequency of shoveling with a specific limit value obtained for each vessel, which when exceeded indicates the appearance of cavitation produced by the propeller, and
    - calculation means to obtain a fourth signal, which collects a historical series, in the time domain, of the value of the intensity of the spectrum component at the blade pitch frequency.
    Said control unit is linked to an interface intended to notify the appearance of cavitation to a user.
    Preferably, the device comprises three accelerometers intended to be installed in the junction areas of the primary elements of the hull structure.
    Preferably, the high frequency filtering means filters the first signal at frequencies between 8 kHz and 10 kHz.
    Optionally, the control unit through the vessel's navigation system records at least some operating conditions of the particular vessel, a speed


    of the ship, the passage of the propeller and a power developed by the engine. These ship operating conditions are used in determining the limit value that determines the appearance of cavitation and the alarm signal. These navigation conditions allow the user to be informed of the conditions in which there is an alarm in the cavitation signal.
    Optionally, these conditions of operation of the vessel allow to know the condition of non-cavitation of the vessel in navigation. Specifically, by means of a correlation between the fourth signal and the ship's speed, to adjust the specific limit value of the cavitation detection method obtained for each ship.
    A second aspect of the invention is a non-intrusive method of detecting cavitation.
    comprising: -acquiring, by means of the accelerometer, the first signal, -acquiring, by means of the tachometer and / or the ship's navigation system, the
    frequency of rotation of the propulsion engine to determine the pitch of the propeller blade,
    - apply a filter to the first signal, by means of high frequency filtering means, to obtain the second signal comprising the high frequency components, between 1 kHz and 20 kHz, of the first signal,
    - apply a Hilbert transform to the second signal and make its complex sum with the second signal obtaining a third signal that is complex and whose module is the envelope of the second signal,
    - generate a spectral analysis of the third signal, by means of the analysis, to quantify the intensities of each frequency of the third signal, - locate the intensity of the component in the frequency in the spectral analysis
    of blade pitch, -generate the fourth signal, which collects in the time domain the value of the intensity of the spectrum component in the blade pitch frequency,
    - establish at least a limit of amplitude of the intensity of the fourth signal at the frequency of the ship's specific blade pitch which, when exceeded, indicates the appearance of cavitation produced by the propeller,
    - send real-time information about the fourth signal to the interface, and -notify, through said interface, the user of the appearance of cavitation. 6


    Preferably, the high frequency filtering means filters the first signal at frequencies between 8 kHz and 10 kHz. DESCRIPTION OF THE DRAWINGS
    To complement the description that is being made and in order to help a better understanding of the characteristics of the invention, according to a preferred example of practical implementation thereof, a set of drawings is attached as an integral part of said description. where, for illustrative and non-limiting purposes, the following has been represented:
    Figure 1.- Shows a schematic view of the connection between the elements of a preferred embodiment of the non-intrusive device for detecting cavitation in the vessel.
    Figure 2.- Shows an overview of a spectrogram of the third signal.
    Figure 3.- Shows an overview of the fourth signal where the cavitation phenomenon appears. PREFERRED EMBODIMENT OF THE INVENTION
    A preferred embodiment, as shown in Figure 1, is a non-intrusive device (1) for detecting cavitation in a ship, not shown, wherein the ship comprises:
    - a helmet, and
    - a propulsion unit which in turn comprises a propulsion engine coupled to a tachometer, a transmission system and a propeller with three blades, wherein the propulsion engine and the propeller are linked to each other by the transmission system. This vessel, without limitation, has undergone a test at sea where engine revolutions have increased to produce cavitation in the propeller.
    More specifically, the device (1) comprises:


    - three accelerometers (2), intended to be installed inside the ship's hull at an intersection of at least two primary elements of the hull structure in the area near the propeller,
    - a connector intended to be linked with the tachometer (3), -a control unit (4), linked with the accelerometers (2) and with said connector, to detect cavitation, and
    - an interface (5), linked to the control unit (4), intended to notify the appearance of cavitation to a user and navigation conditions, as well as a visual alarm that is activated when the cavitation phenomenon appears.
    Additionally, the device (1) comprises a connector intended to link the control unit (4) with a ship navigation system so that the control unit (4) records the ship's operating conditions.
    These operating conditions of the ship include information about the speed of the ship, the pitch of the propeller and the power developed by the engine.
    More specifically, the control unit (4) executes an algorithm comprising a non-intrusive method to detect cavitation comprising:
    - Acquire, by means of the accelerometers (2), the first signal relative to the vibrations modulated by the frequency of the propeller blade when there is cavitation,
    - acquire, by means of the tachometer (3) the frequency of rotation of the propulsion motor to determine the frequency of the pitch of the propeller blade,
    - apply a high pass filter to the first signal to obtain a second signal comprising the high frequency components, between 8 kHz and 10 kHz, of the first signal,
    - apply to the second signal a Hilbert transform and its complex sum with the second signal obtaining a third signal that is complex and whose module is the envelope of the high frequency signal,
    - generate a spectral analysis comprising a series of spectra in the frequency domain associated with different time moments, using segments of the second signal defined by a time window


    preferably of up to 8 seconds in duration and centered on the moment of time associated with the spectrum, and thus obtaining the different intensities of each frequency of the segments of the third signal (Figure 2),
    - generating a fourth signal, from the series of spectra, comprising the historical series of intensities of the spectral component at the frequency of the blade pitch for each spectrum, specifically, when the propeller does not cavitate the fourth signal would be equivalent to a “ white noise ”with a constant variance. However, when the cavitation phenomenon begins to appear, the fourth signal changes and its amplitude increases depending on the speed of rotation of the propeller, that is, depending on the volume of cavitation. This phenomenon is shown in figure 2, where the spectrogram of the third signal is represented, where initially (region I), at low speed of rotation of the propeller and in a non-cavitation regime. When cavitation begins to develop (region II), not only the component corresponding to the blade pitch frequency begins to be distinguished, but also some of its harmonics, and when the cavitation is fully developed (region III) the modulations are clearly distinguished corresponding to the blade pitch frequency. The phenomenon of cavitation, in this case in particular and not non-limiting, appears around 300 rpm of rotation of the propeller,
    - establish at least a limit of amplitude of the intensity of the fourth signal at the specific frequency of the ship's shovel which, when exceeded, indicates the appearance of cavitation produced by the propeller. Specifically, from the fourth signal, an algorithm determines the specific limits for each vessel. The algorithm comprises a previous learning phase to detect the “white noise” and establish the characteristics of the fourth signal (mean and variance). More specifically, when the propeller does not cavitate the fourth signal is a white noise that does not depend on ship speed. This is detected by the correlation between the fourth signal and the ship's speed when it is statistically zero, and from the mean and variance of the fourth signal the control limit is established. When the propeller begins to cavitate, the fourth signal, as shown in figure 3, begins to depend significantly on the ship's speed, therefore the correlation of this indicator with the speed is no longer statistically zero, which serves to


    setting the cavitation detection limit during the condition of
    no cavitation, -send real-time information about the fourth signal to the interface (5), and -notify, by means of said interface (5), the user of the appearance of cavitation

    权利要求:
    Claims (6)
    [1]
    1.-Non-intrusive device (1) to detect cavitation in a ship, where the ship comprises:
    - a helmet,
    - apropulsion unit thattoitstimeunderstand thelessaengine of
    propulsion, a transmission system and at least one propeller with a plurality
    of blades, where the propulsion engine and the propeller are linked to each other by
    the transmission system,
    - a tachometer (3) coupled with the transmission system, and
    - a ship navigation system,
    wherein, the device (1) is characterized in that it comprises:
    - at least one accelerometer (2), intended to be installed inside the ship's hull at an intersection of at least two primary elements of the case structure in the area near the propeller, to detect a first signal comprising vibrations in the hull and that when there is cavitation it is modulated by the frequency of pitch of the propeller blade,
    - at least one connector intended to be linked with the tachometer (3) and / or with the ship's navigation system,
    - a control unit (4), linked with accelerometer (2), with said connector and with an interface intended to notify the appearance of cavitation to a user, which in turn comprises:
    - acquisition means intended to acquire the first signal and to acquire from the tachometer (3) or the ship's navigation system the frequency of rotation of the propulsion engine to determine the pitch of the propeller blade,
    - high frequency filtering means intended to filter the first signal to obtain a second signal comprising the high frequency components, between 1 kHz and 20 kHz, of the first signal,
    - signal processing means intended to calculate the envelope of the second signal by applying the Hilbert transform and subsequently performing its complex sum with the second signal, obtaining a third signal that is complex and whose module is the envelope of the second signal ,

    - means of spectral analysis to obtain a spectrum that quantifies the intensity of the third signal at several frequencies to compare the intensity of the spectrum component to the frequency of shoveling with a specific limit value obtained for each vessel, which when exceeded indicates the appearance of cavitation produced by the propeller, and
    - calculation means to obtain a fourth signal, which collects a historical series, in the time domain, of the value of the intensity of the spectrum component at the blade pitch frequency.
    [2]
    2. Device (1), according to claim 1, characterized in that it comprises three accelerometers (2) intended to be installed at the intersection of at least two primary elements of the case structure in the area near the ship's propeller.
    [3]
    3. Device (1) according to claim 1, characterized in that it comprises a connector intended to link the control unit (4) with the navigation system of the vessel so that the control unit (4) records the operating conditions of the ship
    [4]
    4. Device (1), according to claim 3, characterized in that the operating conditions of the ship comprise information about a ship speed, the propeller passage and a power developed by the engine.
    [5]
    5. Device (1), according to claim 1, characterized in that the high frequency filtering means are intended to filter the first signal to obtain a second signal comprising the high frequency components between 8 kHz and 10 kHz.
    [6]
    6. Non-intrusive method to detect cavitation in a ship, which uses the device (1) described in any preceding claim, characterized in that the method comprises:
    - acquire, by means of the accelerometer (2), the first signal,
    - Acquire, by means of the tachometer (3) and / or the ship's navigation system, the frequency of rotation of the propulsion engine to determine the pitch of the propeller blade,

    - apply a filter to the first signal, by means of high frequency filtering means, to obtain the second signal comprising the high frequency components, between 1 kHz and 20 kHz, of the first signal,
    - apply a Hilbert transform to the second signal and make its complex sum 5 with the second signal obtaining a third signal that is complex and whose module is the envelope of the second signal,
    - generate a spectral analysis of the third signal, by means of the analysis, to quantify the intensities of each frequency of the third signal, - locate the intensity of the component in the frequency in the spectral analysis
    10 blade pitch,
    - generate the fourth signal, which collects in the time domain the value of the intensity of the spectrum component at the blade pitch frequency, -set at least one amplitude limit of the intensity of the fourth signal in
    the frequency of specific shovel passing for the vessel that when exceeded
    15 indicates the appearance of cavitation produced by the propeller, -sending in real time information about the fourth signal to the interface, and -notifying, through said interface, the user of the appearance of cavitation.

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    ES201631097A|ES2615809B1|2016-08-16|2016-08-16|NON-INTRUSIVE DEVICE AND METHOD FOR DETECTING CAVITATION IN AVESSEL|ES201631097A| ES2615809B1|2016-08-16|2016-08-16|NON-INTRUSIVE DEVICE AND METHOD FOR DETECTING CAVITATION IN AVESSEL|
    PCT/ES2017/070580| WO2018033656A1|2016-08-16|2017-08-11|Non-intrusive device and method for detecting cavitation in a ship|
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