Numerical Bichromatic Wave Generation Using Designed Mass Source Function

A mass source wave-maker method is generalized as the two-wave-source wave-maker method to generate bichromatic waves in the numerical model, whose governing equations are Navier–Stokes equations with the continuity equation. The Fluent software is taken as the calculation platform. In the numerical model, the waves at both the left and right ends of the numerical wave flume are absorbed with the momentum sources added in Navier–Stokes equations. The numerical simulation of bichromatic waves propagation with different frequencies in uniform deep, intermediate, and shallow water has been conducted. The numerical solutions are compared with the theoretical solutions obtained on the basis of Stokes waves theory. The frequency spectrum analyses of the results are conducted and discussed, and the differences between the weakly nonlinear theoretical solutions and the fully nonlinear numerical results are investigated in detail. It is found that the numerical model can effectively simulate the nonlinear effect of bichromatic waves in water with different depths, and the theoretical solutions only adapt the deep and intermediate water. The results indicate that the present numerical model is valuable in the aspect of practical application.

Generation of Direct-, Retrograde-, and Source-Wave Gaits in Multi-Legged Locomotion in a Decentralized Manner via Embodied Sensorimotor Interaction

Multi-legged animals show several types of ipsilateral interlimb coordination. Millipedes use a direct-wave gait, in which the swing leg movements propagate from posterior to anterior. In contrast, centipedes use a retrograde-wave gait, in which the swing leg movements propagate from anterior to posterior. Interestingly, when millipedes walk in a specific way, both direct and retrograde waves of the swing leg movements appear with the waves' source, which we call the source-wave gait. However, the gait generation mechanism is still unclear because of the complex nature of the interaction between neural control and dynamic body systems. The present study used a simple model to understand the mechanism better, primarily how local sensory feedback affects multi-legged locomotion. The model comprises a multi-legged body and its locomotion control system using biologically inspired oscillators with local sensory feedback, phase resetting. Each oscillator controls each leg independently. Our simulation produced the above three types of animal gaits. These gaits are not predesigned but emerge through the interaction between the neural control and dynamic body systems through sensory feedback (embodied sensorimotor interaction) in a decentralized manner. The analytical description of these gaits' solution and stability clarifies the embodied sensorimotor interaction's functional roles in the interlimb coordination.

023 Sleep in a Brainless Animal - The Relationship Between Centralization and Sleep in the Upside-down Jellyfish

Introduction Though sleep is pervasive in animals, its fundamental roles, and the processes involved in generating the behavior, remain poorly understood. A key outstanding question in sleep regulation is whether sleep is controlled strictly by a top-down mechanism via activity of specific central nervous system (CNS) neurons or is controlled partially by bottom-up signals from neural and non-neural tissue. Recently, we showed that the upside-down jellyfish Cassiopea sleeps, providing an opportunity to study sleep control, regulation, and function in an animal without a CNS. Methods Cassiopea have a decentralized nervous system (DNS) of radially spaced interconnected ganglia called rhopalia along their bell margin that control muscle contractions. The signal to contract is sent to muscle fibers local to the initiating ganglion, and the contraction propagates outwards as a point source wave. We have developed computer programs to detect the controlling ganglion, which allows us to non-invasively determine ganglia activity, and to understand how a simple network of ganglia controls behavior. We are also using immunofluorescence, in situ hybridization, qPCR, and RNAseq to characterize the effect of sleep deprivation (SD) on the jellyfish nervous system. Results We have discovered a temporally centralized form of behavioral control that changes between day and night, and during SD. A subset of ganglia share behavioral control—while some almost never initiate contractions, others are active both day and night, or are mostly day-active or night-active, and SD drastically changes ganglia usage. Regions that increase activity at night are less active the following day, perhaps evidence of homeostatic regulation. Using RNAseq we found that during SD, one nAChRα subunit increases expression ~3.8-fold and we are studying its role in arousal and sleep. Conclusion We are investigating a different kind of nervous system, one that is morphologically decentralized (a network of discrete ganglia), and yet temporally centralized (a subset of ganglia dominate activity control). Wake, sleep, and SD involve different ganglia activity patterns, different levels of centralization, and different gene expression. Thus, temporal centralization could provide a mechanism to explain how local sleep, via a bottom-up mechanism, can result in organismal sleep behavior. Support (if any) UC Berkeley Miller Postdoctoral Fellowship

Generating Water Waves on Steady Currents Using Mass Source Wave Maker Coupled with Analytical Relaxation Wave Absorber

In order to numerically simulate the wave-current interaction problems frequently encountered by aquaculture structures, a two-dimensional numerical wave-current tank model was established here based on a mass source wave maker coupled with an analytical relaxation wave absorber. The wave-maker model and the wave-absorber model were embedded into a two-dimensional RANS solver, which was closed with RSM turbulence scheme. The volume of fluid (VOF) method was adapted to accurately capture the free surface between water and air. To generate a steady uniform current flow, the uniform current flow velocity was calculated at the left-hand-side (LHS) and right-had-side (RHS) outflow boundaries, respectively. Once the steady uniform current flow was generated over the whole computational domain, the target water wave was marked within a specified region by embedding the mass source function based on wave theory into the mass conservation equation and then propagated on the generated uniform current flow. To verify the accuracy of the numerical wave-current tank established here, some of the obtained numerical results were then compared with the experimental results and the analytical solutions, and they agreed well with each other, indicating that the model developed here has great ability in simulating water waves on uniform currents over constant water depth. The established numerical wave-current tank was then used to study the optimal layout of the mass source region and the effects of water current velocity on water surface wave parameters during regular wave coupling with uniform water currents. Meanwhile, the established model was extended to generate steep wave and apply in deep water conditions. Finally, the proposed methods were applied to investigate the wave-current-structure interaction problems and the propagation of solitary waves traveling with coplanar/counter currents. Model-data comparisons show that the developed model here is potentially useful and efficient for investigating the inevitable wave-current-structure interaction problems in aquaculture technologies.

Development and Validation of Passive Yaw in the Open-Source WEC-Sim Code

A passive yaw implementation is developed, validated, and explored for the WEC-Sim, an open-source wave energy converter modeling tool that works within MATLAB/Simulink. The Reference Model 5 (RM5) is selected for this investigation, and a WEC-Sim model of the device is modified to allow yaw motion. A boundary element method (BEM) code was used to calculate the excitation force coefficients for a range of wave headings. An algorithm was implemented in WEC-Sim to determine the equivalent wave heading from a body’s instantaneous yaw angle and interpolate the appropriate excitation coefficients to ensure the correct time-domain excitation force. This approach is able to determine excitation force for a body undergoing large yaw displacement. For the mathematically simple case of regular wave excitation, the dynamic equation was integrated numerically and found to closely approximate the results from this implementation in WEC-Sim. A case study is presented for the same device in irregular waves. In this case, computation time is increased by 32x when this interpolation is performed at every time step. To reduce this expense, a threshold yaw displacement can be set to reduce the number of interpolations performed. A threshold of 0.01° was found to increase computation time by only 22x without significantly affecting time domain results. Similar amplitude spectra for yaw force and displacements are observed for all threshold values less than 1°, for which computation time is only increased by 2.2x.

Single Phase Power Factor Improvement Based Instantaneous Power P Q Theorm

This paper presents how to harmonic disturbance reduce on single phase power system. One of the most popular method is harmonic signal extraction with instantaneous power p q theorm. This algorithm implemented to harmonic cencellation by active power filter circuit be paralled with the non linier load. This filter generates of current compensation that are injected into the grid to improve power quality. This Filter is built by an inverter circuit that consists of a mosfet switch array and capasitor mounted on DC link side. Two types of loads are resitive inductive and resistive capasitive produce of current source wave form that close pure sinusoid. Simulation results show the THD index fell to the level of 2.7% in accordance with IEEE 519 standard rules which states that the harmonics content of the power system may occur below 4%, indicating that the power system can be categorized as having good quality.

Generation of Water Waves Using Momentum Source Wave-Maker Applied to a RANS Solver

Nowadays, as the development of Computational Fluid Dynamics (CFD) and the numerical wave tank (NWT) has advanced, numerical analysis has become increasingly useful and powerful for the ship designing and ship hydrodynamics. In this study, a momentum source wave-maker and an analytical relaxation wave absorber were embedded into 2D RANS equation model with RSM turbulence closure scheme to establish the NWT for ship designing and hydrodynamics. The VOF (volume-of-fluid) method was applied to accurately capture the water free surface. The body force-weighted scheme is chosen for pressure interpolation and the second order upwind scheme for discretization of the momentum equation. In order to calculate convection and diffusion fluxes through the control volume faces, PISO algorithm is adopted for pressure-velocity coupling. The momentum source function for wave generation and the analytical relaxation function for wave absorption were deduced for constructing the NWT (numerical wave tank). The proposed NWT was then validated by the laboratory measurements of Umeyama and the analytical solution, indicating that the constructed NWT is effective and accurate.

Numerical Simulation of Wave Transformation Over Deep-Sea Platform Reef Using SPH Method

A non-reflective SPH (Smoothed Particle Hydrodynamics) wave flume is developed to study wave transformation over the deep-sea platform reef with a steep reef-face. The left and right boundaries of the flume are modeled using the periodic boundary conditions and a water circulation technology, and a momentum source wave maker is applied to generate the required wave. Wave transformation over the reef-flat is analyzed and compared with the experimental data. The results show that the present SPH model can effectively overcome the non-physical rise of the mean water level in the lagoon and over the reef-flat, which can be observed in the long time simulation with the traditional vertical two-dimensional numerical model. Furthermore, the present model can accurately reproduce the wave breaking process and give a good agreement with the experimental data in terms of the spatial distribution of wave height and wave setup on the reef flat.