The time domain simulation was setup with the LoRa611Pro wireless transceiver data transmission module properties. LoRa611Pro is a commercial radio frequency module for data transmission. In order to observe whether attenuation of the electromagnetic wave crossing the steel wall of the storage tank will be detected at the receiver the electric field, signals were studied with different types of medium such as vegetable oil and petroleum (diesel fuel and kerosene). The simulation medium was selected with Table 5.5 e.g. vegetable oil permittivity or dielectric constant is in range of crude oil same for kerosene and jet fuel with a tinny difference. Real dimension of petrochemical storage tank was setup with an appropriate tank wall thickness in this simulation. Figure 5.13 shows a 2D drawing of the storage tank, two wireless transceivers were used, one of the transceivers located at 25 meters submerged in steel tank with petroleum medium or vegetable oil and the other transceiver located at 3 meters from the tank wall in the air. The thickness of the steel tank wall was setup to be 6.35 mm and the size of the tank was 50 meters in diameter. The tank properties were selected using the American Petroleum Institute standard (API 650 section 5.6.1.1) which specifies the range of petrochemical storage tank sizes and defines the minimum wall thickness required to avoid tank stress.
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Figure 5. 14 shows two sets of simulation in the air, with propagation of electromagnetic wave in the air with no steel wall between both transceivers and another set with a steel. Propagation in the air with no steel wall shows that the maximum electric field strength is 0.0024 V/m at about 35 seconds compared to propagation in the air with steel wall where the maximum electric field strength was 0.85 x10-3 at about 46 seconds. The presence of the steel wall attenuates the electromagnetic wave which is evidenced by the reduction in the electric field strength.
Figure 5. 14: Electric field propagation between two 433 MHz transceivers antenna beacon in air.
The simulation results for the electric field strength for vegetable oil, diesel fuel and kerosene medium. The electric field strength was tested with electromagnetic wave transmission in both directions from air to the medium and medium to air through the steel tank wall. Electromagnetic wave propagation through vegetable oil as medium (Figure 5. 15) has average electric field strength in both direction of 5.1 x10-4 V/m compared to electric field
strength in the air with steel wall stated in Figure 5. 14 which was 0.85 x10-3 V/m. Similarly, the average of the electric field strength (Figure 5. 16) of the electromagnetic wave propagation in diesel fuel in both directions is 6.3 x10-4 V/m compared to Figure 5. 14 where the electromagnetic wave propagation in the air with steel tank wall the electric field strength was 0.85 x10-3 V/m. Finally, the average electric field strength (Figure 5. 17) in kerosene fuel medium is 6.95 x10-4 V/m compared to 0.85 x10-3 V/m for electric field strength in the air with steel tank wall in Figure 5. 14. The simulation shows the time that it takes the electromagnetic wave to get to the maximum electric field strength. The electromagnetic wave travels faster in the air than diesel fuel, kerosene fuel and vegetable oil medium. The simulation conforms to the calculation of propagation speed and absorption coefficient of matter in Table 5.6.
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Figure 5. 15: Electric field propagation between two 433 MHz transceivers antenna beacon in vegetable oil used as a medium.
Figure 5. 16: Electric field propagation between two 433 MHz transceivers antenna beacon in diesel fuel used as a medium.
Figure 5. 17: Electric field propagation between two 433 MHz transceivers antenna beacon in kerosene fuel used as a medium.
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5.11 Chapter summary
This chapter presented a simulation and of radio frequency wireless communication through oil medium and through oil/steel/air interfaces. The simulation of electromagnetic wave radiation through petroleum products and vegetable oil has shown some attenuation of the wave through study of directivity patterns and surface currents. The time domain simulation shows faster propagation in petroleum medium than vegetable oil medium. The simulations and calculations have shown that the electromagnetic wave travels at lower speed in vegetable oil compared to other petroleum medium. Therefore, radio frequency could propagate better in petroleum products than vegetable oil with less dispersion and path loss.
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Chapter 6
Results and analysis
The objective is to be able to propagate very low power wireless radio frequency signals which complies with regulations and standards in the petroleum storage tank. The internal structure of a petrochemical storage tank makes a robot with umbilical cable difficult to move inside the tank for corrosion inspection and NDT data collection. Another aspect is related to the robot localisation for online inspection which has not been investigated in this work but offers the opportunity for further work. The reason for using wireless RF communication was due to the advantages presented by radio frequency such as faster data transmission, low cost implementation over other communication media such as optical and acoustic shown. In this experiment, non-conducting vegetable oil is used to evaluate the data transmission from air to medium and medium to air. Vegetable oil medium was used due its dielectric property (Du and Li, 2017) and (Paranjpe and Deshpande, 1935) and to its similar properties with petroleum medium as stated in Table 5.5.
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6.1 Electromagnetic wave propagation in vegetable oil