Measurement of Loads Acting on a Near-Wall Particle in Turbulent Water Flow by Using a 6-Dof MEMS-Based Sensor Anh Tuan Nguyen , Dzung Viet Dao*, Toshiyuki Toriyama, John C. Wells and Susumu Sugiyama Graduate School of Science and Engineering, Ritsumeikan University, * Center for promotion of the COE program, Ritsumeikan University, 1-1-1 Noji-Higashi, Kusatsu, Shiga, 525-8577 Japan, dzung@se.ritsumei.ac.jp Abstract: This paper presents the application of 6-degree of freedom (6-DOF) micro sensor in measuring force and moment acting on a particle in turbulent water flow. The experiments were performed with a particle whose center was mounted at the level of the channel bed. The diameter of the particle is 9.5 mm. All the components of force and moment have been measured. The three most important components: the lift (vertical force Fz), the drag (tangential force Fx) and the moment around particle’s spanwise-axis My have been compared with theoretical calculations and other experimental data taken from literatures. Acceptable agreements between them have been confirmed. Keywords: 6-DOF, force-moment sensor, turbulent flow, sediment transport, near-wall particle 1 INTRODUCTION Most flows occurring in the nature and engineering applications are turbulent. In hydraulic engineering, one of the most important phenomena associated with turbulence is the transport of sediment. Particularly, bedload sediment transport, in which a flow transports bed material in a thin layer above the bed, constitutes a large fraction of total sediment transport. We plan to study this phenomenon at the particle scale. In this situation, the initial motion of the particle is considered at high priority: once a particle overcomes the static resistance to motion, it can easily continue moving for a long distance. For this reason, forces and moments acting on the particle at the initial motion should be measured and analyzed. To measure forces and moments acting on objects in flow, several methods have been reported. Some of the common principles are: strain gauge [1-3], capacitance [4], micrometer-point-gage [5], and Dial-O-Gram [6]. However, they could measure one, or two components of force/moment. The other disadvantages of these methods are requirement of large space, complexity in calibration and setup. In this context, the development of a 6-DOF sensor based on Micro Electromechanical Systems (MEMS) technology is a new and promising direction. This sensor was designed based on piezoresitive effect in silicon and it can detect simultaneously 3 components of force and 3 components of moment at high sensitivity. Structure, working principle, fabrication process, and calibration result of the sensing chip can be found in [7]. The measurements of 6 components were conducted with a spherical particle whose center was at the level of the bottom plane, thus approximately a surface-mounted hemisphere. The experimental conditions and results will be detailed in coming sections. Figure 1. Configuration of the sensor 2 SENSOR CONFIGURATION The sensor configuration is shown in Fig. 1. The sensing chip is located inside a test particle so that its upper surface coincides with the center of the particle. This condition is necessary to measure exactly the moment around the center of the particle. The chip is overload-protected by a protection base located underneath. Forces and moments acting on the test particle are transmitted to the sensing chip via a transmission pillar attached at the center of the sensing chip (Fig. 2). The transmission pillar is a 3 mm diameter cylinder with 0.5 mm-diameter cylindrical pins on either end. The lower pin is attached to the central block of the sensing chip. The upper pin is inserted into the small hole of the test particle as shown in Fig. 3. A conical surface was machined at an angle of 45 o and has good smoothness. The inside assembling surface of the Force-mo ment receiver Force-mo ment receiver Force transmission pillar Force transmission pillar Silicone rubber Silicone rubber 6-DOF force sensing chip 6-DOF force sensing chip Overload protection base Overload protection base Gold wires Gold wires Lead-out cable Lead-out cable Base pillar Base pillar Force-mo ment receiver Force-mo ment receiver Force transmission pillar Force transmission pillar Silicone rubber Silicone rubber 6-DOF force sensing chip 6-DOF force sensing chip Overload protection base Overload protection base Gold wires Gold wires Lead-out cable Lead-out cable Base pillar Base pillar