Frequency modulation of body waves to improve performance of sidewinding robots

Sidewinding is a form of locomotion executed by certain snakes and has been reconstructed in limbless robots; the gait is beneficial because it is effective in diverse terrestrial environments. Sidewinding gaits are generated by coordination of horizontal and vertical traveling waves of body undulation: the horizontal wave largely sets the direction of sidewinding with respect to the body frame while the vertical traveling wave largely determines the contact pattern between the body and the environment. When the locomotor’s center of mass leaves the supporting polygon formed by the contact pattern, undesirable locomotor behaviors (such as unwanted turning or unstable oscillation of the body) can occur. In this article, we develop an approach to generate desired translation and turning by modulating the vertical wave. These modulations alter the distribution of body–environment contact patches and can stabilize configurations that were previously statically unstable. The approach first identifies the spatial frequency of the vertical wave that statically stabilizes the locomotor for a given horizontal wave. Then, using geometric mechanics tools, we design the coordination between body waves that produces the desired translation or rotation. We demonstrate the effectiveness of our technique in numerical simulations and on experiments with a 16-joint limbless robot locomoting on flat hard ground. Our scheme broadens the range of movements and behaviors accessible to sidewinding locomotors at low speeds, which can lead to limbless systems capable of traversing diverse terrain stably and/or rapidly.

Continuous Gravitational Waves from Neutron Stars: Current Status and Prospects

Gravitational waves astronomy allows us to study objects and events invisible in electromagnetic waves. It is crucial to validate the theories and models of the most mysterious and extreme matter in the Universe: the neutron stars. In addition to inspirals and mergers of neutrons stars, there are currently a few proposed mechanisms that can trigger radiation of long-lasting gravitational radiation from neutron stars, such as e.g., elastically and/or magnetically driven deformations: mountains on the stellar surface supported by the elastic strain or magnetic field, free precession, or unstable oscillation modes (e.g., the r-modes). The astrophysical motivation for continuous gravitational waves searches, current LIGO and Virgo strategies of data analysis and prospects are reviewed in this work.

Radial Decomposition of Blade Vibration to Identify a Stall Flutter Source in a Transonic Fan

This paper investigates the three dimensionality of the unsteady flow responsible for stall flutter instability. Nonlinear unsteady Reynolds-averaged Navier–Stokes (RANS) computations are used to predict the aeroelastic behavior of a fan blade at part speed. Flutter is experienced by the blades at low mass flow for the first flap mode at nodal diameter 2. The maximal energy exchange is located near the tip of the blade, at 90% span. The modeshape is radially decomposed to investigate the main source of instability. This decomposition method is validated for the first time in 3D using a time-marching nonlinear solver. The source of stall flutter is finally found at 65% span where the local vibration induces an unstable oscillation of the shock-wave of large amplitude. This demonstrates that the radial migration of the pressure fluctuations must be taken into account to predict stall flutter.

Weathervane Performance and Stability of Single Point Moored FOWTs Under Wind-Current Coexisting Field

The objective of this study is to understand the weathervane performance and stability of FOWTs moored to SPM systems under wind and current coexisting field. Two types of FOWT systems, a semi-submersible and a spar (1/200 scale) are designed and manufactured based on Froude’s scaling law. A series of scaled model experiments are conducted and compared during wind-current coexisting field in a circulating water tank at Osaka Prefecture University, Osaka, Japan. Weathervane performance is evaluated under various conditions of wind and current. It is found during experiments that the weathervane performance of the SPM-FOWT systems is acceptable in rated wind and slow current condition. However, in the rated wind and high speed current condition, the weathervane performance is found to be not acceptable and unstable oscillation is observed. A numerical program is also developed to understand the behavior using the maneuvering equations. Further, attempts are made to understand the stability of SPM-FOWT systems based on Eigenvalue analysis.

Effect of Clearance and Friction in Revolute Imperfect Joints on Dynamic Behaviors of a Slider-Crank Mechanism with Two Sliders

Friction and clearance always present in any mechanical system. Hence, the effects of friction and clearance on a dynamic system are so critical. This paper aims to investigate their effects on the dynamic response of a slider-crank mechanism with two sliders and imperfect joints. Firstly, the mechanism is created in Solidworks and then it is simulated via finite element method in ANSYS. The dynamic simulation are conducted to evaluate the mentioned effects. The results revealed that the effect degree of clearance on the dynamic behaviors of the proposed mechanisms is significantly higher than that of friction. Also, the results indicated that the velocities, acceleration, and contact force graph are almost same at different friction coefficient. However, compared with ideal joint case, they had a maximum value and an unstable oscillation. This problem is due to journal collide into bearing induced the maximum values of contact force. The results of this study are a helpful guidance to practitioners, scientists, and engineers. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Objects, Fragments, Scenes, and the Construction of Narrative

This chapter interrogates the construction of narrative out of lyrical and musical fragments and scenes. Tracing displacements and condensations in the blues reveals a metonymic structure underpinning narrative articulations. Close examination of the contexts of reception—including the minstrel show, the juke joint, and most especially the print advertising of race record labels—unearths a system that guides listeners to construct narrative cohesion out of fragments and pieces. Analyzing Charley Patton’s “High Water Everywhere,” Blind Lemon Jefferson’s “Competition Bed Blues,” and Robert Johnson’s “Hellhound on my Trail” uncovers an unstable oscillation between synchronic and diachronic understandings of time that is foregrounded by the blues’ fundamentally fragmentary structure.

EFFECT OF LOADING RATE ON VISCOELASTIC PROPERTIES AND LOCAL MECHANICAL HETEROGENEITY OF FRESHLY ISOLATED MUSCLE FIBER BUNDLES SUBJECTED TO UNIAXIAL STRETCHING

To investigate the effect of viscoelastic behavior on instantaneous muscle mechanics, the passive mechanical properties for the range of physiologically relevant rates should be clarified. Therefore, a series of uniaxial extension tests were conducted at various stretching rates using the muscle fiber bundles, which contained extracellular matrix (ECM) and interfibrillar microstructural components. We revealed that the tensile strength is strain rate-sensitive over the examined range, i.e., the muscle fiber bundle failed at 109[Formula: see text][Formula: see text][Formula: see text]34, 122[Formula: see text][Formula: see text][Formula: see text]44, and 179[Formula: see text][Formula: see text][Formula: see text]61[Formula: see text]kPa (mean[Formula: see text][Formula: see text][Formula: see text]SD) for strain rates of 0.02, 0.1, and 0.5[Formula: see text]s[Formula: see text], respectively. Moreover, we found that the applied stretch was not distributed uniformly even in relaxed conditions; the ratio between maximum and minimum local strains within a specimen was 2–3 on average during stretching and increased up to approximately four just before failure, indicating local mechanical heterogeneity along a fiber bundle and its exaggeration by stretching. Macroscopically, however, the tensile strain at failure was almost constant, [Formula: see text]50%. The local heterogeneity of muscle strain distribution can lead to unstable oscillation in a computational model. Thus, in addition to the intrinsic viscous effects of the muscle fiber itself, those of ECM and interfibrillar microstructural components should be considered in mathematical modeling of skeletal muscle.

Accelerometer Performance for Maker Faire Quadrotor with Kalman Filtering Using PID Controller

This paper presents a study on quadrotor using PID controller together with the application of Kalman Filter. Purpose of this project is to study effect of separate Kalman filter in overcoming the signal noise and gyro drift in the attitude sensors and simulate the PID controller which controlling the quadrotor dynamics through damping the vehicle oscillation. In this research, simulation of Kalman Filter in filtering the noise from the inertial moment unit (IMU) and PID controller in damping on unstable oscillation has been conducted to observe the performance of the quadrotor.