RACE and Calculations of Three-dimensional Distributed Cavity Phase Shifts

The design for RACE, a Rb-clock flight experiment for the ISS, is described. The cold collision shift and multiple launching (juggling) have important implications for the design and the resulting clock accuracy and stability. We present and discuss the double clock design for RACE. This design reduces the noise contributions of the local oscillator and simplifies and enhances an accuracy evaluation of the clock. As we try to push beyond the current accuracies of clocks, new systematic errors become important. The best fountain clocks are using cylindrical TE(sub 011) microwave cavities. We recently pointed out that many atoms pass through a node of the standing wave microwave field in these cavities. Previous studies have shown potentially large frequency shifts for atoms passing through nodes in a TE(sub 013) cavity. The shift occurs because there is a small traveling wave component due to the absorption of the copper cavity walls. The small traveling wave component leads to position dependent phase shifts. To study these effects, we perform Finite Element calculations. Three-dimensional Finite Element calculations require significant computer resources. Here we show that the cylindrical boundary condition can be Fourier decomposed to a short series of two-dimensional problems. This dramatically reduces the time and memory required and we obtain (3D) phase distributions for a variety of cavities. With these results, we will be able to analyze this frequency shift in fountain and future space clocks

Numerical simulation of exploring fish motion by a series of linked rigid bodies

Propulsion and manoeuvring ability are parts of the most common and complicated mechanisms in nature, such as fish swimming in the water and birds flying in the sky. In order to get a deep understanding of these problems, a comprehensive and completed replication of fish movements is carried out in this project. Present work is based on a robotic fish named Amphibot III, which is a bio-inspired swimming robot. It is composed of 8 elements and the last part has a caudal fin attached as a tail. By using CFD method, the caudal fin is omitted in order to simplify the model. These elements in the model are connected by hinges. Commercial software FLUENT is used to solve flow field. Swimming tests are performed under two different conditions by varying the frequency and amplitude of the angular motion at the hinges. The motion curve at the head of fish is presented under both conditions

A study of vortex ring generation by a circular disc with its application in bionic investigation

Numerical simulation on a vortex ring generated by an impulsive started disc is studied. Commercial CFD software is used for the numerical simulation. Modelling results are compared with previous experimental data. The circulation, vortex core position and symmetric breaking time are discussed at two different velocities. Results show that a larger velocity leads to a greater vortex ring circulation, a shorter developing time for occurring asymmetry phase comparing with a smaller velocity

Multi-body dynamics modelling on a self-propelled pufferfish with its application in AUV

We developed a Computational Fluid Dynamics (CFD) based tool coupled with a Multi-Body Dynamics (MBD) technique to investigate a self-propelled pufferfish motion within a still water environment. The 3D pufferfish model consists of body, caudal, dorsal and anal fins. The locomotion of fish is entirely determined by the computation and fully induced by the oscillation motion of fish fins. The influence of the phase angle difference on the fish swimming behaviour is examined by varying the angle difference between the caudal, dorsal, and anal fins. The swimming displacement, hydrodynamic force and the wake pattern are analysed

Using the Great Lakes Environmental and Economic Data Visualization Tool

In 2015, the Great Lakes Regional Pollution Prevention Roundtable (GLRPPR) began a project to analyze public data sets to determine the impact of manufacturing on the economy and environment of the six states in U.S. EPA Region 5. The project’s goal was to use the analyzed results to assist pollution prevention technical assistance programs (P2 TAPs) with targeting their assistance efforts. The project resulted in a report, a series of fact sheets, and a data visualization tool. This guide provides information about how to use the tool.Funded by the U.S. Environmental Protection AgencyOpe

The application of multi-body dynamics theory on fish locomotion

Propulsion and manoeuvring ability are parts of the most common and complicated mechanisms in nature, such as fish swimming in the water and birds flying in the sky. In order to get a deep understanding of these problems, a comprehensive and completed replication of fish movements is carried out in this project. By combining with multi-body dynamic theory, the fish can be composed by a few serial elements as main body and two symmetric elements as pectoral fins, one for each side. All the elements are connected by hinges. Commercial software FLUENT is used to solve flow field. For propulsion part, swimming tests are performed under two different conditions by varying the frequency and amplitude of the angular motion at the hinges. In terms of manoeuvring ability, 3D cases will be carried out. The motion of pectoral fins is prescribed in order to simulate the up and down motion of fish in the water. Modelling results will be presented with detailed analysis on the hydrodynamic forces, vortex structure near fish body/fins and the related fish propulsion and manoeuvre performance

Bio-inspired propulsion in ocean engineering : learning from nature

In this paper, the CFD technology widely used in biomimetic applications is firstly reviewed in a brief manner. We then present two types of computational models employed in studies of ray-finned fishes: single-fin model and body-fin model. The single-fin models capture some key features possessed by real fish fins, such as anisotropic property, flexible rays and actively controlled curvature. In the body-fin models, the fish motion can be either prescribed or predicted. Fish models with prescribed motions are usually employed to provide insights in the hydrodynamics while those models with predicted motions can be used to investigate the stability and maneuvering problems

Numerical simulation of a multi-body system mimicking coupled active and passive movements of fish swimming

A multi-body system model is proposed for the mimicking of swimming fish with coupled active and passive movements. The relevant algorithms of the kinematics and dynamics of the multi-body system and coupled fluid solver are developed and fully validated. A simplified three-body model is applied for the investigation of the hydrodynamic performance of both an active pitch motion and passive movement. In general, there is an optimal stiffness, under which the model swims with the fastest velocity. The effect of the damper can be drawn only when the stiffness is small. Comparing with the rigid tail, the flexible tail leads to a faster speed when the stiffness and damping coefficients are in a suitable range