Nearfield acoustic holography in a moving medium based on particle velocity input using nonsingular propagator

Nearfield acoustic holography in a moving medium is a technique which is typically suitable for sound sources identification in a flow. In the process of sound field reconstruction, sound pressure is usually used as the input, but it may contain considerable background noise due to the interactions between microphones and flow moving at a high velocity. To avoid this problem, particle velocity is an alternative input, which can be obtained by using Laser Doppler Velocimetry in a non-intrusive way. However, there is a singular problem in the conventional propagator relating the particle velocity to the pressure, and it could lead to significant errors or even false results. In view of this, in this paper nonsingular propagators are deduced to realize accurate reconstruction in both cases that the hologram is parallel to and perpendicular to the flow direction. The advantages of the proposed method are analyzed, and simulations are conducted to verify the validation. The results show that the method can overcome the singular problem effectively, and the reconstruction errors are at a low level for different flow velocities, frequencies, and signal-to-noise ratios.

COMPLETE LOCOMOTION ANALYSIS OF A SMALL DIFFERENTIALDRIVE MOBILE ROBOTIC PLATFORM

Mobile robots are becoming a part of more and more research areas due to their structural advantages and the increase in usage areas. Differential drive mobile robots are among the most preferred of this type of robots due to the convenience that they provide in engineering studies. It is quite important to test and structurally investigate primary parts such as motors and its sensors before being used in research applications. Before proceeding to further studies, it is very useful to do such tests as they may provide critical information about the robot which can be quite beneficial in terms of time, effort, and cost. To achieve this task, variety of methods are available in the literature such as structural locomotion tests and system identifiaction. In the first part of this study, locomotion tests of a small mobile robot driven by servo motors and operating with a single microcontroller was performed using the velocity propulsion mode. Three different predefined routes were determined for the robot and the accuracy of the robot moving along these routes was investigated. Through these tests, it is aimed to examine how the robot interprets the basic movements such as rectilinear forward motion, curvilinear motion, and rotation around its own axis. The next part focuses on the system identification of the robot. A data-driven model for the robotic platform was developed to make a mobile robot perform the desired movements and system identification. Various step input commands were sent to the robot under consideration and the responses of the robot wheels to these inputs were examined. Circular movements were made to the robot with a range of velocity input values and the relationship between input and output was examined for both wheels of the robot. In the locomotion tests, it was observed that the robot completed the predetermined routes with minor errors. As a result of these tests, theoretical calculations and experimental results were compared and the reasons for the error parameters were discussed. Through system identification tests, it was observed that the right wheel of the robot was more consistent and produced closer to the expected value for each test performed.

Modelling of tribological responses of composites using integrated ANN-GA technique

In the present article, artificial neural networks (ANNs) and genetic algorithm (GA) methodology were integrated to model tribological characteristics of stir-cast Al-Zn-Mg-Cu matrix composites under two-body abrasion considering large numbers of experimentally generated results. Tribo-responses of wear rate (Wrt), coefficient of friction (COF) and roughness of abraded surface (RAS) were evaluated under wide range of intrinsic ( i.e., particle quantity) and extrinsic ( i.e., abrasive size, load, distance and velocity) input parameters. Characteristics of Wrt, COF and RAS are often mutually contradictory in nature and so, multi-objective optimization technique becomes imperative for selection and design of machine components. Accordingly, those were optimized through Pareto solutions. Sensitivity of different factors was analyzed on each of the tribo-performances and validated via experimental evidences. Amongst the input variables, particle quantity and abrasive size dominated significantly over other variables except load which imparted modest influences. The role of various input parameters was explained through determination of different micromechanisms via exhaustive post wear characterizations, microstructural and surface topography attributes. Lowest values of Wrt and COF with a modest value of RAS were identified at 15 ± 2 wt.% particle quantity.

Sources of path integration error in young and aging humans

Path integration is a vital function in navigation: it enables the continuous tracking of one’s position in space by integrating self-motion cues. Path integration abilities vary across individuals but tend to deteriorate in old age. The specific causes of path integration errors, however, remain poorly characterized. Here, we combined tests of path integration performance with a novel analysis based on the Langevin diffusion equation, which allowed us to decompose errors into distinct causes that can corrupt path integration computations. Across age groups, the dominant errors were due to noise and a bias in speed estimation. Noise-driven errors accumulated with travel distance not elapsed time, suggesting that the dominant noise originates in the velocity input rather than within the integrator. Age-related declines were traced primarily to a growth in this unbiased noise. Together, these findings shed light on the contributors to path integration error and the mechanisms underlying age-related navigational deficits.

Surplus Torque Elimination Control of Electro-Hydraulic Load Simulator Based on Actuator Velocity Input Feedforword Compensating Method

Electro-hydraulic load simulator (EHLS) is a typical closed-loop torque control system. It is used to simulate the load of aircraft actuator on ground hardware-in-the-loop simulation and experiments. In general, EHLS is fixed with actuator shaft together. Thus, the movement of actuator has interference torque named the surplus torque on the EHLS. The surplus torque is not only related to the velocity of the actuator movement, but also related to the frequency of actuator movement. Especially when the model of the actuator and EHLS is dissimilar, the surplus torque is obviously different on different frequencies. In order to eliminate the surplus torque for accurate load simulation, the actuator velocity input feedforword compensating method (AVIFC) is proposed in this paper. In this strategy, the actuator velocity synchronous signals are used for compensation of different frequency actuator movement to eliminate surplus torque on different frequencies. First, the mathematical model of EHLS and the actuator system is established. Based on the models, the AVIFC method is proposed. It reveals the reason that generates surplus torque on different frequencies of actuator. For verification, simulations and experiments are conducted to prove that the new strategy performs well against low, medium, and high frequency movement interference. The results show that this method can effectively suppress the surplus torque with different frequencies and improve precision of EHLS with actuator movement.

Equivalent Source Method-Based Nearfield Acoustic Holography in a Moving Medium

To identify sound sources situated in a fluid flow, an equivalent source method (ESM)-based nearfield acoustic holography (NAH) in a moving medium is proposed, and two types of acoustic inputs, pressure and particle velocity, are considered. In particular, an analytical relationship between the particle velocity perpendicular to the flow direction and the equivalent source strength is deduced, which makes it possible to realize the reconstruction with particle velocity input. Compared to the planar NAH in a moving medium, the proposed method is applicable to sound sources with more complicated geometries. Numerical simulations with sound sources distributed over two types of geometries including planar geometry and nonplanar one are conducted to test the performances of the proposed method. The results indicate that the proposed method provides satisfactory reconstructed results whatever with pressure input or with particle velocity input, and it is valid and robust over a wide range of flow velocities and frequencies and under different levels of background noise.

Controlling the Movement of a TRR Spatial Chain With Coupled Six-Bar Function Generators for Biomimetic Motion

This paper describes a synthesis technique that constrains a spatial serial chain into a single degree-of-freedom mechanism using planar six-bar function generators. The synthesis process begins by specifying the target motion of a serial chain that is parameterized by time. The goal is to create a mechanism with a constant velocity rotary input that will achieve that motion. To do this, we solve the inverse kinematics equations to find functions of each serial joint angle with respect to time. Since a constant velocity input is desired, time is proportional to the angle of the input link, and each serial joint angle can be expressed as functions of the input angle. This poses a separate function generator problem to control each joint of the serial chain. Function generators are linkages that coordinate their input and output angles. Each function is synthesized using a technique that finds 11 position Stephenson II linkages, which are then packaged onto the serial chain. Using pulleys and the scaling capabilities of function generating linkages, the final device can be packaged compactly. We describe this synthesis procedure through the design of a biomimetic device for reproducing a flapping wing motion.

Controlling the Movement of a TRR Spatial Chain With Coupled Six-Bar Function Generators for Biomimetic Motion

This paper describes a synthesis technique that constrains a spatial serial chain into a single degree-of-freedom mechanism using planar six-bar function generators. The synthesis process begins by specifying the target motion of a serial chain that is parameterized by time. The goal is to create a mechanism with a constant velocity rotary input that will achieve that motion. To do this we solve the inverse kinematics equations to find functions of each serial joint angle with respect to time. Since a constant velocity input is desired, time is proportional to the angle of the input link, and each serial joint angle can be expressed as functions of the input angle. This poses a separate function generator problem to control each joint of the serial chain. Function generators are linkages that coordinate their input and output angles. Each function is synthesized using a technique that finds 11 position Stephenson II linkages, which are then packaged onto the serial chain. Using pulleys and the scaling capabilities of function generating linkages, the final device can be packaged compactly. We describe this synthesis procedure through the design of a biomimetic device for reproducing a flapping wing motion.