Patent Description:
Structural health monitoring apparatus and their methods are known from <CIT>, <CIT>, <CIT> and <CIT>. Usually a sensor is embedded in a wall of the container. Fluid diffusing into the wall is detected by the sensors and subsequently an alarm is triggered.

<CIT> discloses a sensor apparatus configured to detect the presence of a gas, such as a tracer gas and a leak detection apparatus configured to detect the present of a tracer gas and indicate the location of a leak. The sensor apparatus includes multiple sensors, each of which is a metal halide sensor. The leak detection apparatus may further be configured to quantify the leak rate at the leak location. There is, however, no indication that leak rates are compared with historical leak data.

<CIT> discloses an aircraft fuel oil leak detection system and method. A fuel measurement module gathers aircraft fuel oil data, an engine consumption measurement module gathers consumption data, and timing signal source provides a timing signal. A fuel leakage data processing center judges whether there is a leak based on the gathered data.

<CIT> discloses a protective composite liner for installation inside a vessel, such as a supertanker, that has an outer layer of high strength fibers, a middle layer of flexible, high strength, resilient film material, and an inner chemical resistant layer. Means for anchoring the protective composite liner and sensor means for detecting a leak are further provided for use with the liner.

It is the object of the invention to improve structural health monitoring apparatus and methods, preferably with respect to their reliability and sensitivity.

The object is achieved by the subject-matter of the independent claims. Preferred embodiments are subject-matter of the dependent claims.

The invention provides a computer implemented method for structural health monitoring of a fluid container that is configured to store fluids, preferably cryogenic fluids, the method comprising:.

Preferably, in step a) the fluid sensors are gas sensors and the gas sensors measure a gas level value of a gas that emanates from a fluid within the fluid container.

Preferably, the method further comprises a step: d) generating a leak signal based on the determination in step c), the leak signal being indicative of the type of gas leak and outputting the leak signal in order to cause maintenance or modify a repair plan.

Preferably, in step a) at least one additional fluid sensor measures a fluid level value in the vicinity and outside of the fluid container.

Preferably, in step a) the at least one additional fluid sensor is a gas sensor that measures a gas level value in the vicinity and outside the fluid container.

Preferably, in step a) the fluid sensors are integrated within a structure of the fluid container such as into a wall or double wall of the fluid container. Preferably, the fluid sensor is interposed between a first and second wall of the double wall, preferably in a vacuum. Preferably, the structure of the fluid container comprises a composite laminate structure having a plurality of layers, and the fluid sensors are integrated in different layers of the composite laminate structure, so as to allow monitoring incipient leakage. Preferably, the fluid sensor includes fiber optical gas sensor.

Preferably, in step b) before retrieving the gas leakage data, flight parameters are measured and associated with actual fluid consumption out of the fluid container in order to determine an estimate for fluid consumption. Preferably, the flight parameters include aircraft weight, air speed, altitude, air pressure, or temperature.

Preferably, in step a) with a fluid gauge apparatus: an amount of fluid remaining in the fluid container is measured. Preferably, in step b) a predicted fluid consumption is retrieved from the database. Preferably, the estimated fluid consumption is compared with at least one of the amount of remaining fluid and the predicted fluid consumption, in order to generate an adjustment value for at least one of the flight parameters, the adjustment value being configured to adjust for lost fluid.

Preferably, the fluid container is a liquid hydrogen tank for an aircraft, the fluid is liquid hydrogen, and the gas is hydrogen gas.

The invention provides a structural health monitoring system configured for structural health monitoring of a fluid container that is configured to store fluids, preferably cryogenic fluids, the system comprising:.

Preferably, the classifier apparatus is further configured for generating a leak signal that is indicative of the type of gas leak and outputting the leak signal in order to cause maintenance or modify a repair plan.

Preferably, the system further comprises at least one additional fluid sensor that is arranged in the vicinity and outside of the fluid container.

Preferably, the fluid sensor is interposed between a first and second wall of the double wall, preferably in a vacuum. Preferably, the structure of the fluid container comprises a composite laminate structure having a plurality of layers, and the fluid sensors are integrated in different layers of the composite laminate structure, so as to allow monitoring incipient leakage. Preferably, the fluid sensor includes fiber optical gas sensor. Preferably, the fluid container has a fluid gauge apparatus configured for measuring an amount of fluid remaining in the fluid container. Preferably, the database includes a predicted fluid consumption. Preferably, the system is configured for comparing an estimated fluid consumption with at least one of the amount of remaining fluid and a predicted fluid consumption, in order to generate an adjustment value for at least one of the flight parameters, the adjustment value being configured to adjust for lost fluid.

The invention provides an aircraft comprising a preferred structural health monitoring system.

The invention provides a computer program that includes instructions that, when executed by a preferred structural health monitoring system, cause the system to perform a preferred method.

The invention provides a data storage having stored thereon a preferred computer program. The ideas disclosed herein can be used as a way to monitor the structural integrity of hydrogen tanks. Picking up structural defects, degradation as well as detecting early risk of leakage Even if planned for aircraft this system will also work on tanks used in other applications. Further the use of the system is also possible for container with another content.

The invention provides the possibility to improve integrated structural health measuring systems in hydrogen tanks. The monitoring of the hydrogen tanks supports the acceptance of new fuels for aircraft in particular by the authorities, airlines and general public. The system can improve the safety level by picking up initial damage or degradation of the monitored fluid tanks at a very early stage. In addition, the system may - by using data analysis in combination with monitoring measurements - pick-up unknown unknowns. The ideas presented herein may help in reducing costs of such fluid (e.g. liquid hydrogen) containers. In addition to tested and proven materials, the safety can be increased by the system. With this, the need for novel and/or expensive materials, expensive manufacturing methods, and high test effort before usage can be at least reduced, if not avoided. Furthermore, aircraft operators are able to reduce maintenance effort, due to the system being capable of replacing the task of manual inspection. This is particularly advantageous, if tanks are difficult to reach and should be inspected by special non-destructive testing (NDT).

As during maintenance and overhaul the tanks might be swapped or replaced, the quality of the newly installed tanks can be checked using the structural health monitoring (SHM) system. Another effect can be that the design of the tank may be further optimized against weight with the help of this system. Furthermore, the system allows a longer usage of the tanks, due to (more or less continuously) monitoring of the tank's integrity.

A fluid sensor is to be used to measure in-situ the hydrogen concentration in the tank wall. With this, the integrity of composite / fiber reinforced plastic (FRP) hydrogen tanks can be checked by detecting incipient leakage.

The hardware part comprises fiber optical sensors embedded in the FRP laminate, preferable at different depths. Such Fiber optical sensors with a cladding changing optical properties with hydrogen concentration are known in the art.

Potential material degradation will start at chemical-physical level or microscopic level and lead to increased diffusion of hydrogen through the FRP tank wall, thus changing the concentration profile over the thickness.

Anomaly detection and trend monitoring can be performed by statistical methods, whereas the ability of fiber optical sensors to also measure additional factors of the diffusion and the degradation processes, like temperature and strain, are advantageous in the analysis. Furthermore the incorporation of physical models using the laws of diffusion are an option.

The fiber optical sensors can be also used for structural health monitoring for damages at a macroscopic level of the tank or its attachment points, as well as for detection of thermal isolation degradation by in-situ temperature monitoring.

It should be noted that while the invention is explained with a liquid hydrogen tank as an example for a fluid container, the ideas presented herein are applicable to most other fluid containers that are able to store fluids or cryogenic fluids.

Embodiments of the invention are described in more detail with reference to the accompanying schematic drawings; therein the Fig. depicts an embodiment of a structural health monitoring system.

The Fig. schematically depicts a structural health monitoring system <NUM> for a fluid container. The fluid container may be a pressure container, such as a liquid hydrogen tank for an aircraft. The system <NUM> comprises a plurality of sensors <NUM>. One type of sensor is a gas sensor <NUM> that is configured to detect hydrogen gas that emanates from the liquid hydrogen stored in the fluid container. The gas sensor <NUM> is an example for a fluid sensor. The gas sensors <NUM> are integrated into several layers of a wall of the fluid container. In addition, temperature sensors <NUM> may be integrated in the wall as well. Furthermore, there can be additional gas sensors <NUM> that are arranged in the vicinity of the fluid container but outside to monitor the immediate surroundings of the fluid container. The additional gas sensors <NUM> are an example for additional fluid sensors.

The sensors <NUM> measure a hydrogen gas level. The location of the sensors <NUM> is known so the measured hydrogen gas levels can be determined locally. Furthermore, it is possible to detect a hydrogen gradient within the tank wall and temperature changes (either caused by external temperature changes or leaking hydrogen gas). Local temperature changes are also possible due to operation of the fluid container, e.g. by change of fluid level, maintenance, sloshing of the fluid, etc. These gas leakage data are stored in a database <NUM> for future reference. It should be noted that in the database <NUM>, the gas leak data can be structured so that they are indicative not only for a specific fluid container, but for similar types of fluid containers.

The system <NUM> further comprises a classifier apparatus <NUM>. The classifier apparatus <NUM> is configured to classify a gas leak in the wall of the fluid container. The classifier apparatus <NUM> may do this by comparing the gas leak rate with thresholds that are derived from historic gas leakage data, which are - as previously mentioned - stored in the database <NUM>.

The classifier apparatus <NUM> determines that the gas leak is a large gas leak <NUM>, if individual gas sensors <NUM> report a hydrogen gas level value increase above a first threshold. The first threshold is determined by the gas leakage data. Furthermore, the location of the specific sensor <NUM> reporting the increase can be used to immediately determine an area of the wall of the fluid container that is affected by the leak. The first threshold is preferably set such that it is only exceeded in case of a mandatory repair of the fluid container.

The classifier apparatus <NUM> determines that the gas leak is a small gas leak <NUM>, if individual gas sensors <NUM> report a hydrogen gas level value increase that exceeds a second threshold but is below a first threshold. The second threshold is determined by the gas leakage data. Furthermore, the location of the specific sensor <NUM> can again be used to immediately determine the affected area. The second threshold is preferably set such that operation of the aircraft is still possible, but the gas leak may increase operating costs. The second threshold can define how much gas leakage is acceptable from an economic point of view, while still maintaining operational safety.

The classifier apparatus <NUM> determines the fluid container to have degradation <NUM>, if the gas sensors <NUM> globally register an increase of hydrogen gas levels that exceed a third threshold. In this case, there is not an individual leak but rather a general decline in the capability of the tank wall to contain the hydrogen gas.

The first to third thresholds can also be influenced by the current hydrogen price <NUM> and/or the specific cost <NUM> of the type of repair that is indicated (large, small, degradation).

In case the classifier apparatus <NUM> determines the presence of a large or small gas leak, the classifier apparatus <NUM> may generate a leak signal that can be sent to an automated maintenance system <NUM> or be used to determine a repair plan. In turn the automated maintenance system <NUM> may automatically generate a material order <NUM> for the parts required for the repair.

The system <NUM> also includes various data sources that include gas leakage data that are relevant for determining the type of gas leakage or intensity of gas leakage. The system <NUM> may include a shared data source <NUM> that is shared between aircraft operator and aircraft manufacturer. The gas leakage data and data generated by the automated maintenance system <NUM> are stored in the shared data source <NUM>. Furthermore, the measurements of the sensors <NUM>, <NUM>, <NUM>, <NUM> can be transmitted to the shared data storage <NUM>. In addition, the database <NUM> may extract from or synchronize with the shared data source <NUM> so as to always include current data.

The system <NUM> also includes flight parameters <NUM> as an additional data source. The flight parameters <NUM>, such as aircraft weight, air speed, altitude, air pressure, and (ambient) temperature can also be fed into the database <NUM> and analyzed with respect to their influence on gas leakage data.

In another prong, the system <NUM>, can be used to infer changes of the flight parameters <NUM>, that allow to reduce or eliminate gas leakage or that allow reduction of wear on the hydrogen tank, thereby increasing its lifetime. After filling the hydrogen tank from a hydrogen source <NUM>, the actual hydrogen consumption <NUM> and the remaining hydrogen fluid <NUM> in the fluid container are measured.

The actual hydrogen consumption <NUM> can be compared by the classifier apparatus <NUM> to previous hydrogen consumption, that can be retrieved from the database <NUM>. From this, an estimated hydrogen consumption <NUM> for the remaining flight can be determined. Furthermore, the database <NUM> can be updated with the new estimate, so that the entire system <NUM> is continually learning.

The classifier apparatus <NUM> can then retrieve from the database <NUM> a predicted hydrogen loss <NUM> for the remaining flight and compare it to the estimated hydrogen consumption <NUM> and the remaining hydrogen fluid <NUM>. The predicted hydrogen loss <NUM> can also be transferred to the hydrogen source <NUM> in order to give a rough estimate for the hydrogen needed to be transferred into the hydrogen tank. Based on these input parameters, the classifier apparatus <NUM> determines recommended changes <NUM> to the flight parameters <NUM> that allow to reduce or eliminate gas leakage or that allow reduction of wear on the hydrogen tank. The recommended changes <NUM> can be put on a display <NUM> in the cockpit for the pilot to review.

Claim 1:
A computer implemented method for structural health monitoring of a fluid container that is configured to store fluids, the method comprising:
a) with a plurality of fluid sensors (<NUM>, <NUM>) that are distributed around and/or within a structure of the fluid container: measuring a gas level value of a gas that emanates from a fluid within the fluid container;
b) from a database (<NUM>): retrieving gas leakage data that are indicative of a gas leakage rate of the fluid container; and
c) with a classifier apparatus (<NUM>): classifying a gas leak of the fluid container by determining the gas leak to be a large gas leak (<NUM>), if individual fluid sensors (<NUM>, <NUM>) report a gas level value increase above a first threshold determined by the gas leakage data, or determining the gas leak to be a small gas leak (<NUM>), if individual fluid sensors (<NUM>, <NUM>) report a gas level value increase below the first threshold but above a second threshold that is non-zero and lower than the first threshold, characterized in that in step c) the classifier apparatus (<NUM>) determines the fluid container to have degraded, if a predetermined number or a majority of individual fluid sensors (<NUM>) reports a gas level value increase above a third threshold that is derived from the gas leak data.