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Critical structures in transport, power industry, mining and processing industries require monitoring of their technical condition. Periodic control implemented by means of NDT methods usually requires stopping the object or even a complete withdrawal from the operation, which reduces the efficiency of its use. The fact is that most of the non-destructive testing methods do not work under the conditions of significant external effects. But if the test of the helicopter blades condition, wind turbine or the existing pipeline is possible, even with economic losses, then for some important objects, such as transport facilities, the stopping is difficult. In the case of offshore platforms and onshore facilities it is impossible to get rid of environmental impact.
A new approach to the monitoring of such structures is in tune with the aphorism from an old comedy film: "He, who hinders us, will help us!". Powerful external loads exerted in the form of air flow on the helicopter blades or wind turbine, in the form of liquid or gas flow in the existing pipeline, or in the form of wind and waves on offshore structures prevent the use of non-destructive testing methods. However, these loads provide the use of advanced load monitoring methods for structures by controlling their dynamic properties. These properties define, in fact, unlimited range of forms (modes) of normal vibrations, which each structure possesses. Methods of Operational Modal Analysis (OMA) allow to define the parameters of these vibrations (shape, frequency, and damping).
Dynamic properties are determined by a ratio of mass and stiffness of structural parts, so any change in their condition changes the said ratio, causing a change in the vibration parameters. In composite helicopter blades the separation of materials into layers may begin, indiscernible from the outside, in the wind turbine blades – fatigue changes.
Thus, the control over the parameters of structure vibration enables to detect a change in its condition without interrupting its operation. The systems we develop that implement the new approach to the monitoring of structures are collectively known as SenSmart, which reflects the content of the main components: sensor, peripheral and intellectual.
The sensor layer is being formed mainly by the sensors of dynamic strains integrated into flexible tapes which are installed on the surface of the object in accordance with its model. Each sensor includes a sensor and electronics. All sensors of one group are connected to the same hub.
Hubs, constituting the peripheral level, perform the functions of:
The intellectual component of the system provides the reception and processing of data by OMA methods in accordance with the object model and algorithms of defect identification within the Vibropassport of the object
DID YOU KNOW ...
Even the tinyest inner crack can evolve into a serious fault and become a cause for a tragedy.
Experimental systems of vibration-based monitoring and diagnostics of existing objects have been developed and used for:
It has been implemented in cooperation with the Aviation Research Center and functions at Riga International Airport. It operates as a test bed comprising:
The experimental system demonstrates the possibility of in flight monitoring of the condition of not only the blades but also other parts of the rotor, including the rotor shaft, swash plate bearings, driven gear of the output shaft of the gearbox and its bearings.
It is a full-scale layout of the functioning pipeline with a total length of 80 m, which consists of separate pipes of 6 m long and 88mm in diameter, connected with flanges or welded. The pump station provides the liquid flow in the pipeline at the pressure up to 39 ATM, and the rate of 5m/s. The data acquisition system includes 168 dynamic strain sensors and provides measurement of above-ground (5 pipes) and underground (2 pipes) sections. The pipeline design allows creating static deformations and make local defects, as well as provides starting up and flowing of the tool inside the pipeline.
Condition of the pipe walls of full-scale installation is controlled by the parameter of MPV (Modal Parameters Variation), measured in % of relative deformation. When creating a test action on the pipeline, MPV assesses the change in shape and other parameters of the vibration, compared with those which the pipe had at the initial state. Parameter output beyond the initial state, which for non-defective installation of the pipeline does not exceed 0.2%, means a change in its condition, requiring localization and identification of the defect.
As a result of the test defect simulating static deformation of the pipeline due to support damage, the MPV parameter increased to 0.72%. The test defect simulating corrosion or shallow weld, caused an increase of MPV to 0.6%. The experimental system provides not only the monitoring with the MPV parameter, but also the defect location, which is provided by a set of other parameters, indicating the area of the greatest change in dynamic properties.
The automatic station of monitoring of buildings and facilities has been designed to provide object vibration level monitoring for a long time without human intervention. The automatic station provides measurement of a given parameter of vibration in three directions, control and signalling in case of exceeding the allowed values, automatic readout of the measured values. Signalling in case of exceeding the allowed values and data transfer are carried out automatically according to a predetermined program through the local telephone network operator. The control program provides the ability to store and issue monitoring reports.
