Savonius drag-type wind turbine suffers from poor efficiency due to adverse negative torques on returning blades when they rotate against incoming flows. It was proven that using a suitable deflector system has potential to improve wind turbine efficiency. However, as previously identified in studies, the common drawback of using flat deflector is strong wake zone behind it. Present study aims to improve overall performance of drag-type wind turbine by using a cylinder deflector with wake splitter plate to manage and mitigate detrimental effect of wake zone behind deflector. Wake control and suppressing vortex shedding downstream of circular cylinder have been divided into active and passive flow control techniques. Amid latter control methods, adoption of splitter plates has proven to be highly effective for wake control and suppressing vortex shedding behind cylinder. Unlike previous studies, a cylinder deflector with the wake splitter plate will be utilized instead of conventional deflectors to improve efficiency of wind turbine by disturbing wake zone downstream of deflector. To obtain more efficient configuration, effect of variations of wake splitter length (Ls/D), attachment angle (θwsp), and count of wake splitters on outputs such as generated torque coefficient, power coefficient and wake zone on performance of Savonius rotor were investigated via Computational Fluid Dynamics simulation. The results revealed that cylinder deflector with wake splitter increased Savonius rotor's performance most for almost all Tip Speed Ratios. The average Cm and CP raised considerably up to 15% using deflector with two wake splitters at TSR=0.6 compared to case without deflectors.

The role of wake splitter deflector on performance enhancement of Savonius wind turbine

In recent years the increased rate of the aging population has become more serious. With aging, the elderly sometimes inevitably faces many problems which lead to slow walking, unstable or weak limbs and even fall-related injuries. So, it is very important to develop an assistive aid device. In this study, a fuzzy controller-based smart walker with a distributed robot operating system (ROS) framework is designed to assist in independent walking. The combination of Raspberry Pi and PIC microcontroller acts as the control kernel of the proposed device. In addition, the environmental information and user postures can be recognized with the integration of sensors. The sensing data include the road slope, velocity of the walker, and user's grip forces, etc. According to the sensing data, the fuzzy controller can produce an assistive force to make the walker moving more smoothly and safely. Apart from this, a mobile application (App) is designed that allows the user's guardian to view the current status of the smart walker as well as to track the user's location.

https://www.mdpi.com/1424-8220/21/7/2371/pdf

ROS-Based Smart Walker with Fuzzy Posture Judgement and Power Assistance.

Driven by technology or sociality? Use intention of service robots in hospitality from the human–robot interaction perspective

Traditional walkers are commonly used for the elderly in social life, which solves the basic problem of walking, but it is difficult to ensure safety when a fall occurs, and the human-computer interaction is poor. The image recognition method or the IMU sensor method fixed on the user, such as a wearable watch, is used by most of the current fall detection methods. Wearable sensors require the user’s wearing operation, which is a little troublesome, and the detection accuracy is related to the way of wearing. The image recognition method requires a high-priced camera and a fixed installation position, which is unable to adapt to outdoor activities. We investigated a low-cost method of mounting the sensor on the body of the walker. We propose in this paper an improved fall detection method, namely Precondition and Limit Threshold SPRT (PLT-SPRT), and a novel fall detection system on the smart walker based on PLT-SPRT. The signals of the upper and lower limb sensors are fused based on the Kalman filter algorithm, and the admittance control parameters are obtained through the system identification method. In this study, the improved sequential probability ratio test algorithm is used to set the null hypothesis and the alternative hypothesis, construct the likelihood ratio and optimize the decision function, which is used to judge whether falls occur. The system is simulated by Matlab software, the user intention after fusion is more accurate, and the optimized decision function is judged accurately. Verified by the embedded system based on STM32 of the smart walker equipment in the real world, it can accurately identify the fallen state, with low detection delay, and the fallen state is detected about 160ms earlier than the traditional threshold-based detection algorithm, at the same time, the accuracy is higher than 94.9%, which meets the high real-time requirements of fall detection and is the ideal solution for smart walkers.

https://ieeexplore.ieee.org/ielx7/6287639/6514899/09846990.pdf

Fall Detection System on Smart Walker Based on Multisensor Data Fusion and SPRT Method

In recent years, different types of commercial rollators or gait-training devices have been widely used by elderly people, suffering from dementia, for their daily activities to avoid being bedridden. However, the effectiveness of most of these commercial devices has not been investigated thoroughly. In this study, a novel rollator with a freely rotating chest pad, integrated with two angular sensors and two load cells, was developed. Walk measurements were carried out on four young healthy subjects who performed walk tests using the developed rollator. To measure the motion of the lower limbs, two goniometers were attached to the exteriors of both the knees, and two more were attached to the exteriors of both the ankle joints of the subjects. The results of the pressing forces on the pad measured by the load cells, pad rotations, knee extensions, and ankle rotations were demonstrated. Frequency analyses were performed and correlation coefficients were computed for the obtained results. The relationship between the pad rotation and the motion of the lower limbs was investigated, and the effectiveness of the developed novel rollator in walk assistance was discussed.

Measurements and Analyses of Walk Using a Novel Rollator Equipped with a Rotatable Chest Pad

The elderly population has rapidly increased in past years, bringing huge demands for elderly serving devices, especially for those with mobility impairment. Present assistant walkers designed for elderly users are primitive with limited user interactivity and intelligence. We propose a novel smart robotic walker that targets a convenient-to-use indoor walking aid for the elderly. The walker supports multiple modes of interactions through voice, gait or haptic touch, and allows intelligent control via learning-based methods to achieve mobility safety. Our design enables a flexible, initiative and reliable walker due to the following: (1) we take a hybrid approach by combining the conventional mobile robotic platform with the existing rollator design, to achieve a novel robotic system that fulfills expected functionalities; (2) our walker tracks users in front by detecting lower limb gait, while providing close-proximity walking safety support; (3) our walker can detect human intentions and predict emergency events, e.g., falling, by monitoring force pressure on a specially designed soft-robotic interface on the handle; (4) our walker performs reinforcement learning-based sound source localization to locate and navigate to the user based on his/her voice signals. Experiment results demonstrate the sturdy mechanical structure, the reliability of multiple novel interactions, and the efficiency of the intelligent control algorithms implemented. The demonstration video is available at: https://sites.google.com/view/smart-walker-hku.

/pdf/a-smart-robotic-walker-with-intelligent-close-proximity-50715fvuqc.pdf

A Smart Robotic Walker With Intelligent Close-Proximity Interaction Capabilities for Elderly Mobility Safety

A flexible plate vertically clamped at the free-end leading edge was used to modulate the aerodynamic forces on a wall-mounted finite square cylinder. The side width (d) of the cylinder was 40 mm and the aspect ratio (H/d) was 5. The flexible plate was made of low-density polyethylene, with a width of d and thickness of 0.04 mm. The length of the flexible plate ranged from d/8 to d. All measurements were carried out in a low-speed wind tunnel with the free-stream velocity (U∞) ranging from 4 to 20 m/s, corresponding to a Reynolds number ranging from 10 960 to 54 800. It was found that the flexible plate behaves distinctly depending on its length and has significant effects on the aerodynamic forces on the finite square cylinder. When U∞ is smaller than the critical velocity Ucr, which is closely related to the length of the plate, the plate statically deforms, having a negligible influence on the aerodynamic forces on the cylinder. When U∞ exceeds Ucr, the plate flaps periodically, resulting in a significant reduction in the aerodynamic forces. The maximum reduction in the mean drag, fluctuating drag, and fluctuating lateral force reaches approximately 5%, 25%, and 60%, respectively. The reduction in the aerodynamic forces is insensitive to both the plate length and flapping frequency. Flow visualization and particle image velocimetry results point out that the flapping plate induces large-scale vortices in the free-end shear flow, which suppress the formation of spanwise vortex shedding and make the upper part of the near wake symmetrical. The flapping configuration of the flexible plate and the corresponding pressure fluctuation on the free end were also addressed. 

/pdf/control-of-the-flow-around-a-finite-square-cylinder-with-a-2xzixpyf.pdf

Chongyu Zhao

Papers

A Smart Robotic Walker With Intelligent Close-Proximity Interaction Capabilities for Elderly Mobility Safety

Control of the flow around a finite square cylinder with a flexible plate attached at the free end

Deep Learning-driven Front-Following within Close Proximity: a Hands-Free Control Model on a Smart Walker

Flow over a forward-facing step with a flexible membrane at its leading edge