To clarify the mechanism for aerodynamic sound to be generated from a lifting surface placed in a flow with turbulence, wind-tunnel experiments and numerical simulations have been carried out for a flow around an airfoil subjected to the wake of a circular cylinder. The test airfoil has the NACA0012 profile with a chord length of 150 mm and a spanwise length of 500 mm, and it is set in a flow with the cylinder wake at angles of attack of 0 degree and 9 degrees. The wind velocity is set to 30 m/s, which results in an airfoil Reynolds number of 3.0×105. The circular cylinder is set 100 mm upstream of the leading edge of the airfoil, and its diameter as well as installation position in the transverse direction are varied. The numerical simulations are composed of large eddy simulation (LES) and aeroacoustical simulations that solves the Lighthill equation in the frequency domain with the Lighthill tensor computed by the above-mentioned LES as the acoustical source terms. The sound pressure level is also computed by the Curle’s equation with the fluctuation in the airfoil lift force computed by the LES as the acoustical source and compared with the experiments. The computed static-pressure distributions on the airfoil surfaces and aerodynamic sound spectra are in good agreement with the measured equivalents. The pressure fluctuation near the leading edge of the airfoil is remarkably high when the circular cylinder is placed upstream. When they flow near the leading edge of the airfoil, the vortices in the cylinder wake are stretched due to the acceleration of the main flow, form strong source of sound, and radiate intense sound in the upstream direction.
Experiments were performed on parallel-flow-type multiple-passage channel flows with five branch channels. To improve the performance of multiple-passage device, it is necessary to achieve a uniform flow distribution in each branch channel and reduce the pressure loss. In the present study, a dielectric barrier discharge plasma actuator (PA) is used to ensure a uniform flow distribution and to reduce pressure loss. A waveform with a constant voltage of 5 kV and a frequency of 1.0, 1.5, 2.0 or 2.5 kHz was applied to the actuator electrode, and the mounting position of the actuator was varied among six positions on the outer wall of the inlet and outlet manifolds. The Reynolds number Re based on the bulk velocity and hydraulic diameter at the inlet channel ranged from 6.0 × 102 to 2.0 × 103. The wall static pressure was measured, and the flow rate and the pressure loss were evaluated. The velocity profiles were measured using a particle image velocimetry system to clarify the change of the velocity field with and without PA actuation. The results show that the pressure loss decreases and the flow rate in each branch channel improves because of the effect of PA-induced flow. The effect becomes remarkable when the PA is installed near the first branch channel at the outlet manifold. Flow uniformity is related to the flow from the low-flow-rate channel to the PA. The preferred frequency depends on the Re, and the optimum velocity induced by PA is approximately four times the bulk velocity at the inlet channel.
This study investigated graphene oxide nanosheets, with excellent thermal conductivity and water dispersibility, as additives that could achieve a trade-off relationship between drag reduction and heat transfer improvement. We experimentally clarified the heat flow characteristics of graphene oxide nanosheet suspensions in a circular pipe. The graphene oxide nanosheets have a size of 0.8 nm × 3 μm × 3 μm. The test suspension concentrations were 0.1 wt%, 0.3 wt%, and 0.5 wt%. For a comparison, a 0.5 wt% TiO2 suspension showing an improvement in the heat transfer coefficient and a 15 ppm Peo solution with drag reduction were also prepared. The experimental results show that the frictional coefficient of the graphene oxide nanosheet suspensions was reduced by up to 36.5% compared to that of distilled water in the turbulent flow region. The amount of drag reduction increased with the increase of Reynolds number. After reaching the maximum value, it gradually approached a constant value. Meanwhile, the Nusselt number of the graphene oxide nanosheet suspensions increased by 10 – 20% in the range of the Reynolds number where the drag reduction occurred. This result indicates that the nanosheets improved the heat transfer performance, which increased with increasing concentration and Reynolds number. In conclusion, improvements in both drag reduction and heat transfer cannot be achieved in the TiO2 suspension and Peo solution, but these properties were found in the graphene oxide nanosheet suspensions used herein.
Oil film bearings are often used in large rotating machinery because they have large load capacity and damping coefficients. They, however, generate fluid forces and cause unstable vibrations such as oil whirl and oil whip at high rotational speed. Because the amplitudes of such self-excited vibrations are severe, it is important to predict the stability limit of rotational speed to avoid the unstable vibration problems in rotor systems supported by oil film bearings. This paper describes the vibration analyses of a flexible rotor system supported by oil film bearings and the simplified prediction method for the rotational speed limits of the self-excited vibration induced by the fluid force in oil film bearings. In the vibration analyses, the equations of motion for the rotor system are simplified and modeled as a two-degree-of-freedom system with parallel and flexural modes of vibration. The stability analyses are conducted by introducing the approximation equations instead of complex eigenvalue calculations. The rotational speed limits for the stability of the system obtained by the present method are compared with the calculation results in the references to discuss the validity of the present method. This paper also shows the importance of anisotropic properties of oil film bearings to increase the accuracy of stability prediction when the clearance of the oil film bearing is large.
Recently, wearable leg support systems that can be applied to people with lower limb disabilities have been developed by many researchers. This study aims to develop system that automatically prevents a user’s fall due to a sudden disturbance and manipulates a posture based on the user’s intention. To achieve the goal, automatic control was added to the manually controlled leg support system. In the system, the posture of the leg support robot is controlled on a master-slave mode by a control lever attached to the user’s hand. A grip in the lever is automatically controlled to stabilize the standing posture. Experiments using test equipment were performed; results showed that the system automatically prevents the user from falling on the manually controlled system.
This paper introduces a mobile robot system that follows a human target, in particular, a robot system designed to follow a smartphone user. The proposed system integrates a global following method based on Wi-Fi radio intensity maps and a local following method based on matching walking states.“ Global following ”means that the robot follows the global trajectory of the human target. Because it is important to keep following when the target is lost in a crowded environment, we propose a global following system that uses Wi-Fi radio intensity and occupancy grid maps. This paper presents some experimental results for a robot being called to follow a human target using a Wi-Fi radio intensity map. “ Local following ”means that the robot always keeps close to the human target and keeps tracking the target without losing it. The human target is detected by cross-correlating the signals indicating the target ’s walking motion, including vertical acceleration data measured by the target user’s smartphone and the horizontal velocity of the legs measured by an LRF installed in the robot. The results show that the system produces a higher cross-correlation coefficient for the human target than for other pedestrians in the vicinity. The paper introduces a method for calculating the cross-correlation coefficients online and presents experimental results which show that the target can be identified from an online calculation of the cross-correlation coefficients.
Injection molding machines are one of the industrial machines producing plastic products. They have been required to improve repeatability for quality stability and speed up for mass production. Injection molding machines consist of a mold clamping device and an injection device. In particular, it is required that the mold clamping devices have operation with not only repeatability but also methods to avoid collisions between the molds. The devices perform positioning control for opening and closing operations and force control for clamping with specified force. If optimal switching is not possible, the molds will collide and cause damage. Therefore, it is essential to design a controller that switches the control systems appropriately. In addition, speeding up cause strains of the machine’s frame. Positioning control is required to suppress strain of frame while maintaining high speed operation. In this paper, positioning and force control is smoothly switched by hybrid control. It was demonstrated that using optimized hybrid signal which was one of the switching signals improved force response. Furthermore, strain of frame was suppressed using modified Bang-Bang control which was one of the minimum time controls. Finally, it was confirmed that the similar effects can be obtained in the control system that combining hybrid control and modified Bang-Bang control.
2D-like indentations are performed by molecular dynamics simulation as “nanometric indentation cutting”. A 90 degree triangle rigid bcc-Fe indenter with (001) or (110) surfaces is continuously drove into single crystalline fcc-Ni and Cu with free side surface, on three different top surfaces of (001), (110) and (111) of the work materials. Despite of large difference in the elastic constants, there is little difference in the repulsive force between Ni and Cu during cutting. This is because the plastic deformation or dislocation emission immediately occurs without large elastic deformation under the 2D-like infinite-length sharp blade, in contrast to spherical indenter in 3D indentation. Ni(001) work material shows drastic change in the cutting morphology by the tool surface; cleavage cracking occurs from a line defect ahead of the (001) tool while smooth cut at the tool end is observed on the (110) tool. The key of this difference is the atomic roughness of the tool surface; the rough (001) tool leads drag and rotation of the work surface, nucleating complicated small grains around the tool. The smooth (110) tool shows growth of single grain, in which the (111) plane is parallel to the cutting direction, at the front of the contact surface. Ni work also shows various deformation mode compared to Cu work, e.g. deformation by large grain growth normal to tool surface in the (110) work and kink formation by dislocation array in the (111) work, due to the high stacking fault energy.
In this study, the tribofilm formation process lubricated with an engine formulated oil was investigated using a lab-built in-situ Raman-SLIM (Spacing Layer Imaging Method) multi-analytical tribometer. The tribometer can simultaneously analyze the chemical composition and film thickness of tribofilms on the worn surface. The tribological test was conducted at DLC/Steel (disk/ball) tribopairs lubricated with the fully-formulated oil with zinc dialkyldithiophosphate and molybdenum dithiocarbamate. From the results, there is a distribution of the tribofilms and a difference of the tribofilm thickness on the steel surface. It should be noted that the chemical characterization of the tribofilms depends on their film thickness. The thicker tribofilms have richer MoS2 and higher P-O-P rate phosphate glasses. On the other hand, the thinner tribofilms have richer MoOx and lower P-O-P rate phosphate glasses. Therefore, there is a correlation between the film thickness and the chemical characterization of the tribofilms, and in-situ Raman-SLIM analysis method is an effectiveness for monitoring for the factors.
In order to assess anterior position of a cane tip for prevention of anterior fall during walking with a cane by the elderlies, this paper presents an investigation of three evaluation indices for determination of the cane tip’s position based on analysis model with dynamic pair. The dynamic pair expresses moveable and spring-damper characteristics between a human hand and a cane in consideration of hand grip weakness of the elderlies. A human body and a cane were modeled as a planar 4-link mechanism with the dynamic pair. Using this model, dynamic simulation was conducted. From the results, energy dissipation by damping effect of dynamic pair and magnitude of force applied to a human hand from a cane were proposed as the evaluation indices. In addition to this proposal, the simulation result also suggested that an ability to perform negative work (ANW) depending on a margin to a limit of torque and angular displacement at each joint of a human body played an important role in fall prevention. Experiment of walking with a cane by three subjects under three conditions concerning cane tip’s positions had been conducted. Through the experiment, joint torque and angular displacement of each joint for calculating values of the ANW, and the result of organoleptic evaluation for safety were obtained. Since magnitude of the values of the ANW mostly corresponded with a level of the organoleptic evaluation for a subject according to the cane tip’s position, effectiveness of the ANW as the evaluation index was validated in the subject and thus the ANW was proposed as another index. Finally, it was shown that by using the proposed indices, an optimal anterior position of a cane tip from a human toe could be determined according to physical characteristics of each of the elderlies.