Drag force acting on the biomimetic flow sensor based artificial hair cell using CFD simulation

Transcription

1 Indian Journal of Geo Marine Sciences Vol. 42 (8), December 2013, pp Drag force acting on the biomimetic flow sensor based artificial hair cell using CFD simulation Mohd Norzaidi Mat Nawi 1, Asrulnizam Abd Manaf 1, Mohd Rizal Arshad 1 & Othman Sidek 2 1 Underwater Robotics Research Group (URRG), School of Electrical and Electronic Engineering, University Sains Malaysia Engineering Campus, Nibong Tebal, Pulau Pinang, Malaysia. 2 Collaborative MicroElectronic Design Excellence Centre (CEDEC), Universiti Sains Malaysia Engineering Campus, Nibong Tebal, Pulau Pinang, Malaysia. [ eeasrulnizam@gmail.com; norzaidiurrg@gmail.com] Received 05 December 2012; revised 10 September 2013 This paper demonstrates the modeling of the biomimetic flow sensor based artificial hair cell using computational fluid dynamic (CFD) approach. Velocity of fluid, length of hair cell and also the angle of flow to the hair cell were varied in order to study the hydrodynamic parameter such as velocity and the drag distribution. Dag force acting on the hair cells linearly increased as the flow velocity and the length of hair cell increased. Maximum drag for hair cell length was 8 mm which equaled to 7 mn/ms -1 based on the drag force and the fluid velocity. For different angle of flow, the drag force is at maximum when the flow was parallel with the substrate and approaching zero when the flow angle was perpendicular. To improve the hair cell, the dome-shaped structure was proposed and discussed for multi directional flow measurement. [Keywords: Biomimetic flow sensor, Hair cell, Dome-shaped, CFD] Introduction Development of underwater sensor is increasingly being developed in a variety of design and applications. Many types of underwater sensor for underwater applications have been explored such as the acoustic sensor, optical sensor, electrochemical sensor and flow sensor. Acoustic sensor is widely used in sonar application for underwater communication and imaging. There are many factors that may affect the acoustic communication including attenuation, geometric spreading, noise, high and variable propagation delay 1. The new achievement in flow measurement for the underwater vehicle platform and aqua robotic is the development of the optical flow sensor and bio-inspired flow sensor for the detection and localization of moving object. Optical flow depends on the intensity patterns of the flow in consecutive images. This flow is caused by the movement of a pictorial object to a static observer 2. This concept also has been implemented on the robotic application for the elementary motion detectors of visual neurons in the housefly 3. For bio-inspired flow sensor, it has been widely developed by previous researchers for any underwater application where it is suitable for measuring the flow distribution around the vehicle especially for monitoring and surveillance. Bio-inspired flow sensor is a new alternative sensor design based on the function of organs at biological inspiration. Recently, the development of the artificial lateral line has been investigated where this system is widely found on the fish body for monitoring and insect pray detection 4. The lateral line system consists of about 100 to 1000 sense organs called neuromast that usually appears on the fish body and its flow sensing system is depends on the difference of freshwater and marine environment. In their basic features, there are two types of neuromasts present, canal and superficial where the canal neuromast has a dome-shaped structure and superficial neuromast is more like cilia (Fig. 1). Superficial neuromast located on the skin in direct contact with the stream while canal neuromasts exist in the sub-epidermal canals connecting pore openings on the skin surface. Each neuromast consists of the hair cell attached to a neuron encapsulated in a gelatinous cap known as a cupula. External fluid flow gives the drag force acting on the neuromast and leads the deflection of hair cell inside the cupula 5. Based on this biological behavior, many of the researchers have tried to design and fabricate the lateral line sensor by using different material and sensing principle.

2 NAWI et al.: DRAG FORCE ACTING ON THE BIOMIMETIC FLOW SENSOR BASED ARTIFICIAL HAIR CELL 981 The same principle of sensing has been implemented to the biomimetic flow sensor which consists of single hair cell and integrated with strain gages. When the fluid flow is applied, the hair cell will bend and induce the strain. The strain is measured by using conventional strain gage. The validation has been made between simulation and experiment and it shows that the experiment is aligned with the simulation 6. In this paper, the modeling of the sensor was based on the sensor structure and the angle of the flow rate effect. The Computational Fluid Dynamic (CFD) approach was used when related to the fluid where it is a computer-based simulation that increasingly being used in a variety of applications by solving a set of field equations describing the dynamics of the fluid flow. Parameters used in this modeling were various flow rates, different length of the hair cell and the angle of flow. Also, the dome-shaped structure was proposed for the flow sensor that was inspired by the canal neuromast for measuring the flow in multi direction. Materials and Methods The schematic of the biomimetic flow sensor was shown in Fig. 2 where it consisted of hair cell and strain gage used as a sensing element. When the fluid flow imparted the hair cell, it deflected and produced the strain due to the rigid connection between hair cell and substrate.rectangular shape of hair cell was chosen because this shape will allow the installation of strain gage and this shape is usually used based on the previous research 7. The details of sensor parameter were listed in Table 1. There were two types of analysis that have previously presented namely hydrodynamic analysis and structural analysis 6. In this paper, the work only focuses on the hydrodynamic analysis which were the effect of structure, different length of the hair cell and angle of flow. Hair cell with different length of 2 mm, 4 mm, 6 mm and 8 mm were simulated using the computational fluid dynamic (CFD) approach. The dimension of width and thickness of the hair cell was fixed to 2 mm and 0.1 mm. Relationship between Reynolds Number and the velocity, u is directly proportional as long as the density, ρ and leading edge, x are constant. ux Re = ν (1) Reynolds Number can be used to determine either the flow is laminar, transient or turbulent. Flow is considered to be laminar when the Reynolds Number is less than Theoretically, the drag force depends on the velocity, flow direction, object position, object size, fluid density and fluid viscosity. Larger the drag force will optimize the performance of the sensor. Given that the basic equation of drag force is Fig. 2 Schematic of the biomimetic flow sensor based artificial hair cell Fig. 1 The lateral line system in the fish body; consist of canal neuromast and superficial neuromast Table 1 List of parameters for biomimetic flow sensor Parameter Dimension Thickness of the hair cell, t 0.1 mm Width of the hair cell, w 2.0 mm Length of the hair cell, L L Leading edge, x 30 mm

3 982 INDIAN J MAR SCI, VOL. 42, NO.8, DECEMBER 2013 Table 2 Properties of liquid Fluent Liquid Density (kgm -3 ) Viscosity (kgms -1 ) water e-4 F D 1 = C D ρ 2 u A 2 (2) where C D and A are the drag coefficient and surface area of the hair cell (width length). The density and viscosity of the fluid used is listed in Table 2. The purpose of simulation to study the flow characteristic including velocity and pressure acting on the hair cell by using different velocity and dimension of hair cell. Also, from this simulation the drag force can be determined. The common CFD software that is usually used in modeling is the ANSYS Fluent. Fluent is commercial software based on the finite volume method that enables to calculate the laminar/turbulent, 2D/3D, steady/unsteady flows, and to run on a personal computer. Fluent solves the equation of the mass and momentum conservation equations in terms of primitive variable velocity and pressure for a constant property fluid 8. U = 0 (3) U 2 t 1 + U U = P + v ρ U (4) where ρ and v are the density and kinematic viscosity of water respectively. U is the vector velocity and P is the pressure. The whole ANSYS Fluent software package includes the Fluent and the pre-processor Gambit. Gambit software is used to create the volume and mesh generation. Fluent is used for the simulation setup, the solving process and the post-processing of the results 9. The height of the boundary is usually three times the length of hair cell while the leading edge is fixed. Velocity inlet is applied parallel to the substrate and the hair cell was set as a wall. Also, other boundary was set as the pressure outlet. By using Gambit, the geometry is easily modified because it is user friendly and also easy to generate the mesh. In mesh generation, the quality of meshing scheme will give different effect to the simulation result. The best comparable result with the experimental data depends on the best quality of mesh 10. The Tet/hybrid was selected due to the design geometry and the mesh volumes were Fig. 3 Grid generation; meshing bottom of hair cell generated using this method. The meshing structure was shown in Fig. 3 for the bottom of hair cell.input of velocity was 0 until 0.5 ms -1 and the flow directions were perpendicular to the hair cells. Iteration stopped at 950 because it has already met the criteria. This simulation was limited to 1E-5 for convergence criterian. Results and Discussion Drag force acting on the biomimetic flow sensor Hair cell structure The biomimetic flow sensor based hair cell was successfully simulated using the laminar model in ANSYS Fluent. For the initial, the velocity behavior and pressure acting on the hair cell were discussed. Hair cell with dimension of 8 mm length, 2 mm width and 0.1 mm thickness was chosen for that purpose. Velocity of fluid 0.05 ms -1 to 0.5 ms -1 has been applied to the hair cell which parallel to the substrate (0 angle of flow). Fig. 4 shows the velocities contour for three different velocity of fluid which were 0.1 ms -1, 0.3 ms -1 and 0.5 ms -1. Two critical points were observed, first was the boundary layer thickness which was produced by leading edge that decrease as the flow rate increase. Another point was the number of contours in the recirculation of the flow right after the hair cell that increased where the turbulence occurred in this area. Meanwhile, Fig. 5 shows the pressure distribution, the front surface that facing the flow always has high pressure because the maximum velocity drops. Red contour represented the high pressure coefficient region in which the maximum pressure was about 863 Pa. The same phenomenon occurred either for different dimension or shape of hair cell simulated.

4 NAWI et al.: DRAG FORCE ACTING ON THE BIOMIMETIC FLOW SENSOR BASED ARTIFICIAL HAIR CELL 983 Fig. 4 The velocity contour for different flow rate Fig. 6 shows the velocity profile for the velocity before and after passing the sensor. Before passing the hair cell, the velocity profile was normal where the boundary layer was formed. It can also be seen that the velocity close to the wall channel was approximately zero. Velocity profile after passing the hair cell apparently became not stable due to the turbulence effect. Fig. 7 shows the pressure coefficient with respect to the position of the hair cell for variation of velocity. The highest pressure coefficient was about 750 for the maximum of 1 ms -1. Therefore, the increasing of fluid velocity will increase the pressure coefficient on the hair cell surface. Using CFD Fluent, the total drag force which equaled to the summation to viscous and pressure force can be obtained for each different size of the hair cell. As mentioned before, the different length of hair cell namely 2 mm, 4 mm, 6 mm and 8 mm were chosen for this simulation. Fig. 8 shows the graph for the drag force versus velocity with different length of hair cells. Drag force acting on each different length has the same behavior which increased when the fluid velocity increased. Highest length gave maximum drag force equaled to 2.5 mn for velocity of 1 ms -1. The value of drag force also depends on the width of the hair cell but in this simulation the value of width was fixed due to the minimum size of strain gage that installed. For underwater platform, the hair cell flow sensor should be able to detect the moving object by mimicking the function of neuromast around the fish body to localize the moving object. In order to realize this function of the hair cell, the capability of the sensor for different angles of flow was studied by simulating the hair cell for different flow angle. The angle was varied starting from 0 o until 90 o and it eventually gave a significant effect to the drag force acting on the hair cell as shown in Fig. 9. Graph showed that the drag decreased as the flow angle increased at constant velocity. Because the structure of the hair cell is symmetric, then the graph pattern for the drag force should be the same for the flow angle starting from 180 o to 90 o. Therefore, the fluid velocity which was parallel to the substrate gave the maximum drag force to the sensor. Meanwhile, the drag force of the hair cell for the flow perpendicular to the substrate was approaching zero and consequently the sensor was unable to predict the flow velocity. This limitation also happened to the hair cell with cylinder structure. Due to that, the dome-shaped structure was proposed to replace the hair cell which is more suitable for multi directional flow measurement. Dome-shaped structure The proposed dome-shaped structure was inspired from the canal neuromast inside fish lateral line (see Fig. 1). Previously, the dome shaped structure by implementation of fluid technology as a sensing element was discussed by Nawi, 2013 for the flow sensor where the fluid inside dome-shaped can replace the function of biological hair cells to sense the cupula movement 11. However, the CFD analysis was needed in order to prove the capability of the dome-shaped structure in measuring the flow in multi

5 984 INDIAN J MAR SCI, VOL. 42, NO.8, DECEMBER 2013 Fig. 5 Pressure distribution on the front surface of hair cell Fig. 6 Velocity profile for the velocity before and after passing the hair cell direction. The dome-shaped with radius of 2.5 mm was chosen and simulated using the same procedure as before. The fluid velocity of 0.1 ms -1 was applied to the dome which was parallel to the substrate and the distribution of pressure coefficient on the surface of the dome can be observed as shown in Fig. 10. Red contour showed the highest pressure of P= 69 Pa and it was located in the front of the dome. The top center of the dome surface on the side view showed that the pressure was very low in that region. Next, the radius of the dome was varied from 1.9 mm to 2.5 mm for fluid velocity of 0.1 ms -1 until 0.5 ms -1. Drag force acting on the dome surface increased as the fluid velocity and the radius of the dome increased as shown in Fig. 11. The largest radius of dome of 2.5 mm radius gave the maximum drag force of about 0.72 mn. Pattern for the drag force based on the applied flow rate was similar to the hair cell which increased as the fluid velocity increased.

6 NAWI et al.: DRAG FORCE ACTING ON THE BIOMIMETIC FLOW SENSOR BASED ARTIFICIAL HAIR CELL 985 Fig. 7 Pressure coefficient with respect to the position of the hair cell for variation of velocity Fig. 8 Drag force-fluid velocity for different hair cell length Fig. 9 Drag force-angle of flow for hair cell structure Fig. 10 Pressure distributions for dome-shaped for flow 0.1 ms -1 with radius of 2.5 mm

7 986 INDIAN J MAR SCI, VOL. 42, NO.8, DECEMBER 2013 other words the increasing of the hair cell length has increased the drag force. Angle of flow imparted the hair cell also gave significant effect where the drag force was nearly becoming zero when the flow was applied directly perpendicular to the substrate. The proposed dome-shaped structure proved that it was able to detect and measure the drag force in a multi direction compared to the hair cell structure. Fig. 11 Drag force-fluid velocity for different dome radius Fig. 12 Drag force-angle of flow for dome-shaped structure Then, the simulation was done for different angles of flow starting 0 o until 90 o. The drag force for the dome-shaped is increased when the angle of flow increases as shown in Fig. 12. It is proven that the dome-shaped was able to detect the flow even if the flow direction is perpendicular. The dome-shaped structure is more convenient compare with the hair cell which is the hair cell cannot be perform in roughness flow condition and only measured the flow in a single direction 12. However, both hair cell and dome-shaped structure can give excellent performance for underwater application depends on each function and usage. Conclusion Biomimetic flow sensor based artificial hair cell has been successfully simulated using CFD software ANSYS Fluent. The flow parameters including velocity and pressure coefficient have been presented. Drag force acting on the hair cell was obtained for different length of the hair cell and angle of flow. Drag force depended on the surface area or in Acknowledgments This study was supported by USM fellowship grant and grant number 1001/PELECT/ References 1 Akyildiz I.F., Pompili D., Melodia T., Challenges for Efficient Communication in Underwater Acoustic Sensor Networks, ACM Sigbed Review 1(2) (2004). 2 Chan R.P.M, Mulla A.H., and Stol K.A., Characterisation of low-cost optical flow sensors, in Proceeding of the Australasian Conference on Robotics and Automation, Brisbane, Australia (Dec 2010) Fabrice A. and Nicolas F., Bio-inspired optic flow sensors based on FPGA: Application to Micro-Air-Vehicles. Journal of Microprocessors and Microsystems 31(6) (2007) Coombs S., Smart Skins: Information Processing by Lateral Line Flow Sensors, Autonomous Robots, 11 (2001) Faucher K., Aubert A., Lagardere J., Spatial distribution and morphological characteristics of the trunk lateral line neuromasts of the sea bass (Dicentrarchus labrax, L.; Teleostei, Serranidae). Brain Behav Evol 62 (2003) Nawi M.N.M., Manaf A.A., Arshad M.R., Sidek O., Modeling of Biomimetic Flow Sensor based on Artificial Hair Cell using CFD and FEM Approach, in Proceeding Conference on Simulation of Semiconductor Processes and Devices (SISPAD 2012), Denver, CO, USA (2012) Nawi M.N.M., Manaf A.A., Arshad M.R., Sidek O., Review of MEMS flow sensors based on artificial hair cell sensor, Microsystem technologies 17 (9) (2011) Barbier C. and Humprey J.A.C., Drag force acting on a neuromast in the fish lateral line trunk canal. I. Numerical modeling of external internal flow coupling. Journal of The Royal Society Interface 6 (36) (2009) Thomas G., Christian L., Claudio C., Timo L., Christian M., Remigius N., Wolfgang S., Roland Z., Peter K., Computational fluid dynamics (CFD) software tools for microfluidic applications A case study, Computers and Fluids 37 (3) (2008) Zukas J.A. and Scheffler D.R., Practical aspects of numerical simulations of dynamic events: effects of meshing. International Journal of Impact Engineering 24 (9) (2000) Nawi M.N.M., Manaf A.A., Arshad M.R., Sidek O., Modeling of Novel Microfluidic based flow sensor inspired from fish canal neuromast, Jurnal Teknologi (Science and Engineering), 62 (2013) Tao J. and Yu X.B. Hair flow sensors: from bio-inspiration to bio-mimicking a review. Smart Materials and Structures, 21(11) (2012) 1-23.