Implementation of innovative methods of Electrical Impedance Tomography to examine the flood embankment
View presentation: sa.netrix.com.pl/monitoring-walow
In the case of reversibility of flooding increases the danger of breaking the shaft. Ad-hoc testing their status, whether the current monitoring can prevent flood disasters or warn of impending danger. How important is this issue showed the floods in Poland and all over the world. The measuring system for monitoring can detect in advance in case of danger.
The aim of the project is to develop a modern system for testing and monitoring the flood embankment. The proposed solution is an innovative product, which is an innovative and modern way unprecedented in such a form today due to the applied technologies and the complexity and diversity of reconstruction algorithms (testing property objects).
Main elements of the project:
- performing new methods in Electrical Impedance Tomography to obtain electrical conductivity distribution,
- creating innovative methods to checking state of flood embankment system,
- creating new algorithms for on-line monitoring,
- constructing prototype of the system.
The Electrical Impedance Tomography (EIT) is a non-destructive imaging technique, which has various applications. Efficient algorithms for solving forward and inverse problem have to be developed in order to use this approach for practical tasks. Moreover, it is necessity to improve performance of selected numerical methods. The typical problem in EIT requires the identification of the unknown internal area from near-boundary measurements of the electrical potential.
The architecture of the flood embankment system (fig. 1):
- data acquisition,
- management system
- algorithms of image reconstruction,
Fig. 1. The architecture of the flood embankment system
The flood embankment dampness was examined by the electrical impedance tomography. The examples of embankment’s damage were presented on figure 1 such as: piping, erosion outer slope, micro instability, drifting ice, slip circle inner slop, slip circle outer slop, wave overtopping, overflow and liquefaction.
Figure 2. The examples of embankment’s damage
The architecture of the flood embankment system was shown in the figure 3. The measurement voltage is from node 1 to 57 – 28 items (27 electrodes from node 2 at the second node to node until the number 56, in addition to node 32 where it was applied 10V). The applications was depended on a specially built model. Surface potential measurements are performed at different angles of projection whereby the information needed to determine an approximate distribution of conductivity inside the object is obtained.
Figure 3. The distribution of elements on the edge of the flood embankment
The forward problem solution in EIT consists in determining potential distribution inside the region under given boundary conditions and full information about region under consideration, that is in solving Laplace’s equation. In this paper there was proposed combination the level set method and the finite element method to solve the inverse problem. The representation of the boundary shape and its evolution during an iterative reconstruction process is achieved by the level set method. The shape derivatives of this problem involve the normal derivative of the potential along the unknown boundary. The level set method relies on the shape derivative, while the topological gradient method is based on the topological derivative.
The proposed algorithm is iterative method, structured as follows:
- from the level set function at initial time, find necessary interface information,
- use the finite element method to solve the Laplace’s equation and next compute the difference of the obtained solution with the observed data,
- solve the Poisson’s equation (adjoint equation),
- find velocity in the normal direction,
- update the level set function,
- reinitialize the level set function.
Fig. 4. The model of typical flood embankment. Electrodes of the control system are indicated
Fig. 5. The 2D geometrical model of flood embankment with micro instability. This model has been prepared in order to solve the forward problem by means of the boundary element method. Nodes and normal vectors are indicated. Each subdomain has its own conductivity.
Concept of communication and data processing system
The assumptions of the system are determined by the area in which the system should work. Covering an area about 80m is provided by 16 electrodes arranged evenly in acting as electrodes and one electrode acts as a master in the present system. The whole measurement system connects to the server acting as the control and monitoring. Distribution of electrodes in the diagram below.
Fig.6. Schematic communication system
The system, due to the functions of roles, mainly includes:
- Source variable frequency,
- Data-acquisition system,
- Control unit with digital signal processor.
Fig.7. Diagram of the data acquisition system
Fig.8. The schematic diagram
The main elements of sixteen electrode data acquisition system for electrical impedance tomography system is following:
- A/D Converter (TI ADS1258)
- General Control System (TI OMAP L-137)
- Forming and Control Circurit for Power System (Base on MC34063 and amplifier TDA7056)
- Analog Multiplexers Team (TI CD4067)
- Measuring the tub with 16 measuring electrodes (chrome-nickel) and cables (50 Om, shielded)
- Operational amplifiers (TI OPA365)
Applied analog for digital converter is ADS1258. This is 24-bit, low-noise ADC optimized for fast multi-channel, high-resolution measurement systems. The converter provides a maximum channel scan rate of 23.7kSPS, providing a complete 16-channel scan in less than 700 s.