International Journal of Integrated Engineering Secial Issue on Electrical Electronic Engineering Vol. 9 No. 4 (07). 43-48 Finite Element Analysis for Acoustic Wave Transmission in Ultrasonic Tomograhy Alication J. Pusanathan, M. H. Satria, R. A. Rahim, Elmy Johana Mohd, N. M. Nor Ayob 3, P. L. Leow 3, F. A. Phang 4, M. S. Badri Mansor 3, M. H. Fazalul Rahiman 5, C.K. Seong Faculty of Biosciences and Medical Engineering, Universiti Teknologi Malaysia, 830 UTM Johor Bahru, Malaysia Faculty of Electrical Engineering, Universiti Tun Hussein Onn Malaysia, Universiti Teknologi Malaysia, 830 UTM Johor Bahru, Malaysia 3 Faculty of Electrical Engineering, Universiti Teknologi Malaysia, 830 UTM Johor Bahru, Malaysia 4 Centre of Engineering Education, Universiti Teknologi Malaysia, 830 UTM Johor Bahru, Malaysia 5 School of Mechatronic Engineering, Universiti Malaysia Perlis, Pauh Putra Camus, 000 Arau, Perlis, Malaysia. Evolusi Engineering Sdn. Bhd, Jalan Bukit Imian, Taman Imian Emas, 8300 Skudai Johor, Malaysia. Abstract: A study of acoustic wave transmission through obstacles and boundary surface for ultrasonic tomograhy alications has been carried out. Ultrasonic tomograhy for water crude oil two hase flow sensing relies uon the comlex ratio of sound ressure to article velocity which is the acoustic imedance matching. According to Snell s Law, the ultrasonic transmission roerties can be obtained on the basis of incidence angle, acoustic imedance and basic frequency of ultrasound, material and thickness of the ieline. These arameters corresond to maximum transmission of an ultrasonic wave from one medium to another when the characteristic imedance is matched. To investigate the wave s transmission and diffraction on water crude oil boundaries, several simulations using finite element method (FEM) have been carried out. The simulated result images successfully visualize the ultrasonic wave transmission and reflection characteristic in the two-hase liquid flow tomograhy system. Thus, the wave roagation behavior in the boundaries is also resented. The information and results obtained is useful for further develoment for ultrasonic tomograhy multihase flow measurement. Keywords: Renewable fuel, ethanol, numerical simulation, auto ignition, single-ste mechanism. Introduction Ultrasonic tomograhy is a measurement method using acoustic wave to investigate the activities inside the measurement subject [, ]. This method is widely alied in both the medical and rocess industry such as in oil exloitation and chemical rocess monitoring [3, 4]. This system is develoed with the caability to reconstruct the gas-liquid, liquid-liquid two hase flow over the cross section of a ie. This method is much comlex and costly due to the requirement of utilizing many transducers around the ieline to detect the echoes scattered around the measurement subject [5]. The aim of this aer is to investigate the acoustic ressure wave roagation behavior in water-crude oil two hase liquid flow in a ieline. The roblem raised is the strong mismatch between the acoustic imedance of the hases []. This condition creates a boundary level between two different material and hases which is; (i) Sensor and ie wall boundary. (ii) Water crude oil liquid boundary. These comlications will result in low efficiency and low accuracy in ultrasonic tomograhy flow system. Therefore, it has become necessary to get better understanding on the dynamic characteristics of acoustic wave roagation behavior in a ieline. *Corresonding author: jaysuman@utm.my 07 UTHM Publisher. All right reserved. enerbit.uthm.edu.my/ojs/index.h/ijie. Ultrasonic Sensor Configuration and Simulation Setu To investigate the ultrasonic wave transmission and reflection, the simulation ultrasonic sensor configuration 3D model setu is illustrated as in Figure. Fig. Ultrasonic sensor configuration on acrylic ieline A total of ultrasonic transducers are mounted on an acrylic ie circumference with a 0 mm of outer diameter as these tye of ies are transarent 43
J Pusanathan et al., Int. J. Of Integrated Engineering Secial Issue on Electrical Electronic Engineering Vol. 9 No. 4 (07). 43-48 and convenient to be used for laboratory exeriment [7]. These sensors will roduce a 335 khz ulse to measure the two-hase (water-crude oil) flow within the ie [7]. The ultrasonic sensor system is based uon interactions between the incident ultrasonic waves and the object to be imaged. In most non-destructive testing or medical alications, an object or field of interest is irradiated from a single viewoint. The transmitted ultrasonic wave has a wide beam angle of 5 0. Some ultrasonic rocess tomograhy utilizes a wide beam angle beam as shown in Figure and below. Receiver Fig. 3 Ultrasound wave behavior In multihase flow alications, ultrasonic tomograhy relies on the measurement of the ultrasonic wave transmission and reflection in a homogenous or nonhomogenous condition [8, 9]. To ensure sufficient wave energy roagates from one end to another, the wavelength is determined in transmission-mode that measures the transmitted signal amlitude according to equation (). () transmitter Receiver transmitter Where c is the seed of sound (m/s) in a medium, f is the ultrasonic frequency (Hz) and λ is the wavelength (m). The higher the frequency will result in shorter wavelength and vice versa. Therefore a 335 khz ultrasound is sufficient enough to roagate signal from one end to another through a ie with diameter of 0 mm. The ultrasonic roagation seed could be measured by using two tyes of configuration which is the through transmission method and ulse echo method which will only take effect if the ultrasonic wave able to transmitted through the ie wall into the liquid medium [0]. This system uses ultrasound to detect the changes of acoustic imedance (Z) which is closely related to density (ρ) of the medium. This can be a useful descritor to identify the comlex ratio of sound ressure to article velocity which is analogous to electrical imedance. The acoustic equivalent to this relation is given by below equation [, ]. Fig. Wave beam Wide beam rojection Narrow beam rojection Whether an ultrasonic beam is narrow or wide angel, it advances as a longitudinal wave front, in common with all sound waves. Z = ρ c () Where Z is the acoustic imedance (kg/m s), ρ is the density of the medium (kg/m3) and c is the sound velocity in the medium (m/s). When an ultrasonic beam reflects from the boundary, the acoustic reflection coefficient (R) and transmission coefficient (D) from material to material as in figure can be exressed as follows: Reflection coefficient, R r e Z Z Z Z () 44
J Pusanathan et al., Int. J. Of Integrated Engineering Secial Issue on Electrical Electronic Engineering Vol. 9 No. 4 (07). 43-48 Transmission coefficient, D d e Z Z Z Where e is the incident wave sound ressure, is the reflected wave sound ressure and d is the transmitted wave sound ressure [3]. This incident is illustrated as in figure 4 and. (3) ie) into liquid medium (water) as in figure 4. ii) Ultrasonic wave roagation from the water medium into the crude oil medium as in Figure 5. The wave roagation energy transmission from material (ie) into material (water) can be calculated as follows. Z = 3. x 0 kg/m s (Acrylic) Z =.5 x 0 kg/m s (Water) Material, (Z ) Material, (Z ) e d R D Z Z Z.50 Z.50 3.0 3.0 ( Acrylic / Water) 0.37 3.7% Z.50 Z Z.50 3.0 ( Acrylic / Water) 0.383 3.83% Boundary d Transmitter Water (Z ) Material Acrylic ie (Z ) Material Fig. 4 Wave roagation; From material to material. From ie section to liquid 3. Ultrasonic Wave at Boundaries Acoustic imedance is imortant to determine the acoustic transmission and reflection at the boundary of two different materials. Following are the two conditions to be considered before measurement is carried out: i) If D > R; Acoustic wave enetration through medium is ossible ii) If R > D; Acoustic wave will face difficulties to enetrate medium The greater the difference in acoustic imedance at the interface, the greater will be the amount of energy reflected. Conversely, if the imedances are similar, most of the energy is transmitted [4-]. Two case studies were carried out; i) Ultrasonic wave roagation from exerimental ieline (acrylic From above calculation, more than half of the transmitted ultrasonic wave able to enetrate through the acrylic iesection into the liquid medium which is 3.83% the rest 3.7% is reflected and scattered on the ieline surface. This means, the ultrasound signal intensity is sufficient enough to enetrate through the acrylic ie wall. The wave roagation which enetrated through acrylic ie material into the water medium will have to roagate through the water crude oil boundary into the second hase material which is crude oil. To determine the amount of transmitted and reflected ultrasonic wave in the water crude oil medium, the transmission coefficient and the reflection coefficient are calculated using equation and 3. R D Z Z Z 3. 0 Z 3. 0.7 0.7 0 ( Water / CrudeOil) 0.0847 8.47% Z.7 0 Z Z.7 0 3. 0 ( Water / CrudeOil) 0.95 9.5% From above calculation, the ultrasonic wave transmission through the water-crude oil boundary is 9.5% while only 8.47% will be reflected back to the water medium. Meaning, the receiver located on the oosite side will be anticiating incoming signals. 45
J Pusanathan et al., Int. J. Of Integrated Engineering Secial Issue on Electrical Electronic Engineering Vol. 9 No. 4 (07). 43-48 A certain amount of the wave will be able to transmit through the water-crude oil boundary while the rest will be reflected and scattered back in the water medium. This condition is illustrated in below figure 5. Receiver The finite element analysis (FEM) setu for the UT sensors is develoed using ressure acoustics (PA) hysics interface module. In PA, the roagation of sound waves in the domain is described by Helmholtz wave equation as follows. d (4) Ultrasonic Transmitter Crude Oil, Z Water, Z where is the acoustic ressure (Pa), is the density of material (kgm -3 ), denotes the angular frequency of incident wave (rad/s), is the seed of sound (m/s) of the material and is the monoole source (/s ). Table tabulates the arameters for the material used for the water-crude oil flow measurement [9]. Table Materials arameter for two hase liquid flow measurement Material Density [kg/m 3 ] Seed of Sound [m/s] Figure 5 Ultrasonic wave roagation from water to crude oil. It is mathematically roven that the 335 khz ultrasonic wave is able to transmit through the ie surface into the water medium and further transmit through the watercrude oil boundary. Somehow, the transmitted and reflected waves will contact with one another in the ieline. It is imortant to take this henomenon into consideration before designing the tomograhy system. When the ultrasonic waves roagate in the cylinder ie, it reflects off the surface wall. This leads to a distribution of ultrasonic energy in different forms that deend basically on the geometry of the ieline and the location of sensors lacing. The occurrence of these overlaing waves will roduce inaccurate results if the measurement system fails to differentiate between transmitted signal and overlaed signal [7]. The direction of this sound roagation is determined by the sound seed gradients in the liquid medium. Therefore, a theoretical model of acoustic wave scattering from the liquid boundary is required to determine the acoustic ressure distribution in the mixture water/crude oil for ultrasonic tomograhy alications. This case, a finite element method using COMSOL Multihysics is imlemented to visualize the acoustic wave roagation and the scattering effects. 4. Acoustic wave behavior simulation The ultrasonic tomograhy geometry model secification and setu consist of an acrylic ie with diameter of 0 mm and 0 mm ultrasonic transducers at 335 khz transmitting frequency. Acrylic ie is the commonly used material for investigation uroses due to the imedance matching with the internal bulk medium [8]. Crude oil 85 300 Water 000 500 Air.5 343 By using FEM, the cross-section region of the hardware needs to be discretized as triangular elements with mesh element size 0.00 mm to 0.8 mm. Figure shows the cross-sectional meshed image. Figure Cross-sectional meshed image with mesh element size range 0.008mm.5mm homogeneous inhomogeneous From the meshed element image, the total acoustic ressure field (Pa) for acrylic/water boundary is roduced. The simulated result visualizes the ultrasonic wave roagating from acrylic medium into water medium and its scattering effect due to the reflection on acrylic ie inner wall. This result is arallel with the mathematical results earlier where 3.83% of the ultrasonic wave able to 4
J Pusanathan et al., Int. J. Of Integrated Engineering Secial Issue on Electrical Electronic Engineering Vol. 9 No. 4 (07). 43-48 enetrate through the acrylic ie while 3.7% of it will be reflected and scattered along the ie wall. The residual ultrasonic wave is sufficient enough to roagate to the next boundary; water crude oil boundary. The simulated ultrasonic wave roagation in homogeneous (full water) and non-homogeneous (water crude oil) mixture is deicted in Figure 8 below. the arrival time measured between the starting oint to the first eak of the received ultrasound wave on the oosite osition [0]. Caturing signals after this time eriod will result in false signal due to overlaing waves. Crude Oil Water Full Water Figure 8 Ultrasonic wave transmission in homogeneous and inhomogeneous condition The simulated result visualizes the ultrasonic wave behavior roagating from water into crude oil medium. This result is also arallel with the mathematical results where 9.5% of the ultrasonic wave enetrating through the acrylic ie while 8.47%% of it will be reflected and scattered along the ie wall. Due to the high amount of acoustic wave able to enetrate through the water-crude oil boundary, the 8.47% amount of reflection can be seen at t=0 µs. This small amount of losses due to the interaction behavior is comlex and deends not simly uon the differences in acoustic imedance, but also on the size and shae of the interface or boundary [8]. To verify and evaluate the reflected and scattered acoustic wave, the sound ressure level was comuted and comared as in Figure 9. The simulated wave roagation is carried out on homogeneous and inhomogeneous condition using timedeendent study in COMSOL. At t= 40us, the wave roagation (homogeneous) arrives at the center of the sensing region. While at t=0us, the waves fully arrive at the oosite end-wall. At this oint, the signal strength is the highest. After this time eriod, reflected waves will mingle and overla with each other. The simulation exeriment shows that the receiver should cature receiving signal best at t=0us which is Figure 9 Sound ressure level (SPL) transmission, reflection and scattering effect; Water / Crude oil mixture Full water 5. CONCLUSION In the resent study, the acoustic wave ressure and sound ressure roagation behavior in mixing flow of water and crude oil in acrylic ie has been simulated using COMSOL Multihysics. Mathematically, it is roven that the greater the difference of imedance in the materials, the higher the wave will be reflected and scattered and vice versa. This can be determined by calculating the reflection and transmission coefficients. To investigate the transmission and reflection behavior, the total acoustic wave ressure distribution, ultrasonic wave roagation, reflection and scattering effect was simulated and resented using FEM generated images. 47
J Pusanathan et al., Int. J. Of Integrated Engineering Secial Issue on Electrical Electronic Engineering Vol. 9 No. 4 (07). 43-48 The result obtained could aid in detection and measurement of two hase liquid flow regime articularly in the ultrasonic tomograhy alications. Understanding the acoustic imedance matching oint will determine the aroriate sensory technique to be used on a articular flow condition. From the simulated exeriment, it is shown that ultrasonic tomograhy can hardly measure the resence of water-crude oil comosition due to its very close acoustic imedance. On the other hand, it can detect the resents of liquid-gas comosition. Acknowledgement This research is suorted under the Research University Grant Scheme (GUP) 0K97, 03G77, 4B3, 4C and H50 of Universiti Teknologi Malaysia. We would like to extend our areciation to Evolusi Engineering Sdn. Bhd co-oeration and consultation. References [] Taylor, S.H. and S.V. Garimella, Design of electrode arrays for 3D caacitance tomograhy in a lanar domain. International Journal of Heat and Mass Transfer, 07. 0:. 5-0. [] Seong, C.K., et al., Hardware Develoment of Electrical Caacitance Tomograhy (ECT) System with Caacitance Sensor for Liquid Measurements. Jurnal Teknologi, 05. 73(). [3] Goncharsky, A.V., S.Y. Romanov, and S.Y. Seryozhnikov, A comuter simulation study of soft tissue characterization using low-frequency ultrasonic tomograhy. Ultrasonics, 0. 7:. 3-50. [4] Wahab, Y.A., et al., Alication of transmissionmode ultrasonic tomograhy to identify multihase flow regime, in Electrical, Control and Comuter Engineering (INECCE), 0 International Conference on. 0, IEEE: Pahang, Malaysia. [5] Wada, S., H. Kikura, and M. Aritomi, Pattern recognition and signal rocessing of ultrasonic echo signal on two-hase flow. Flow Measurement and Instrumentation, 00. 7(4):. 07-4. [] Inoue, Y., et al., A study of ultrasonic roagation for ultrasonic flow rate measurement. Flow Measurement and Instrumentation, 008. 9(3-4):. 3-3. [7] N. M. Nor Ayob, et al., Design Consideration for Front-End System in Ultrasonic Tomograhy. Jurnal Teknologi (Secial Edition), 03. 4(5):. 53-58. [8] Rahiman, M.H.F., R.A. Rahim, and Z. Zakaria, Design and modelling of ultrasonic tomograhy for two-comonent high-acoustic imedance mixture. Sensors and Actuators A: Physical, 008. 47():. 409-44. [9] J. Pusanathan, et al., Study on Single Plane Ultrasonic and Electrical Caacitance Sensor for Process Tomograhy System. Sensors & Transducers, 03. 50(3):. 40-45. [0] Ayob, N.M.N., et al., Detection of small gas bubble using ultrasonic transmission-mode tomograhy system, in Industrial Electronics & Alications (ISIEA), 00 IEEE Symosium on. 00, IEEE: Penang, Malaysia. [] Pallás-Areny, R., Process tomograhy, rinciles, techniques and alications. Flow Measurement and Instrumentation, 99. 7():. 55-5. [] Murakawa, H., H. Kikura, and M. Aritomi, Alication of ultrasonic multi-wave method for two-hase bubbly and slug flows. Flow Measurement and Instrumentation, 008. 9(3-4):. 05-3. [3] Wachinger, C., R. Shams, and N. Navab. Estimation of acoustic imedance from multile ultrasound images with alication to satial comounding. in 008 IEEE Comuter Society Conference on Comuter Vision and Pattern Recognition Workshos. 008. [4] Rahiman, M.H.F., et al., An evaluation of single lane ultrasonic tomograhy sensor to reconstruct three-dimensional rofiles in chemical bubble column. Sensors and Actuators A: Physical, 0. 4:. 8-7. [5] Rahiman, M.H.F., et al., Gas Hold-U Profiles Determination by means of Ultrasonic Transducer. Secial Issue on Advanced Measurement and Sensor Alications, 04. 9(8). [] Faramarzi, M., et al., Image Reconstruction Methods for Ultrasonic Transmission Mode Tomograhy in Bubbly Flow Regime. Secial Issue on Advanced Sensors and Instrumentation Systems, 04. 70(3). [7] Rahiman, M.H.F., et al., Modelling ultrasonic sensor for gas bubble rofiles characterization of chemical column. Sensors and Actuators B: Chemical, 03. 84(0):. 00-05. [8] Goh, C.L., et al., Ultrasonic Tomograhy System for Flow Monitoring: A Review. IEEE Sensors Journal, 07. 7(7):. 538-5390. [9] Pusanathan, J., et al., Single-Plane Dual Modality Tomograhy for Multihase Flow Imaging by Integrating Electrical Caacitance and Ultrasonic Sensors. IEEE Sensors Journal, 07. 7(9):. 38-377. [0] Halim, M.H.A., N. Buniyamin, and Z. Mohamad. Ultrasound B-model imaging using adated time of flight for ultrasound fat measurement sensor. in 05 International Conference on Information & Communication Technology and Systems (ICTS). 05. 48