Application of BDRM Theory in the Two-AXIS Underwater Channel

Two-axis underwater channel often exists in deep ocean. Because of the coupling between surface channel and SOFAR channel, sound propagation in the two-axis underwater channel is complex and so its calculations of acoustic fields are difficult. The beam-displacement ray-mode （BDRM） theory is a normal mode method for propagation modeling in the common horizontally stratified shallow water. We improve the theory, proposing a new method for computing the upper boundary reflection coefficient, and apply it to calculate the acoustic fields of two-axis underwater channel. Transmission losses in the two-axis underwater channel are calculated by the BDRM theory. The results are in good agreement with the KRAKEN code and the computational speed excels those of the other methods.

A Novel Roll Compensation Method for Two-Axis Transportable Satellite Antennas

Two-axis transportable satellite antennas(TATSAs) have been widely adopted owing to its simple structure and low cost. However, by searching in a wide range, it will take a very long searching time. Under extreme conditions, it will even fail to work. In this paper, we propose a novel roll compensation(RC) method for the low-cost TATSAs to achieve faster tracking even if when the antenna has no azimuth sensor. By analyzing the influence of roll axis on the system performance, details of the compensation method are derived. Simulation and measurement results indicate that the proposed RC method can effectively reduce the initial searching time for satellite communication. In addition, tracking along with the ellipse path with the RC method provides the highest tracking efficiency.

Sound propagation in two-axis underwater channel based on beam-displacement ray-mode theory

Sound propagation in a deep ocean two-axis underwater channel is often complex and difficult to simulate between surface channel and sound fixing and ranging (SOFAR) channel. The beam-displacement ray-mode (BDRM) theory is a normal mode method for propagation modeling in horizontally stratified shallow water. An improved method for computing the upper boundary reflection coefficient in the BDRM is proposed and applied to calculate the acoustic fields of a two-axis underwater channel. Transmission losses in the two-axis underwater channel are calculated in the new BDRM. The corresponding results are in good agreement with those from the Kraken code, and furthermore the computed speed of the new BDRM excels the other methods.

Tunable two-axis spin model and spin squeezing in two cavities

Multi-mode cavities have now attracted much attention both experimentally and theoretically. In this paper, inspired by recent experiments of cavity-assisted Raman transitions, we realize a two-axis spin Hamiltonian H = q（J_x^2＋ χJ_y^2） ＋ ω_0J_z in two cavities. This realized Hamiltonian has a distinct property that all parameters can be tuned independently. For proper parameters, the well-studied one- and two-axis twisting Hamiltonians are recovered, and the scaling of N^（-1） of the maximal squeezing factor can occur naturally. On the other hand, in the two-axis twisting Hamiltonian, spin squeezing is usually reduced when increasing the atomic resonant frequency ω_0. Surprisingly, we find that by combining with the dimensionless parameter χ（-1）, this atomic resonant frequency ω_0 can enhance spin squeezing greatly. These results are beneficial for achieving the required spin squeezing in experiments.

Research of the Data Processing Method in Two-Axis Servo Drift Testing

The theory and algorithm of Singular Value Decomposition(SVD) is introduced.The advantage of Singular Value Decomposition used in system identification is studied,compared and illustrated through analyzing the data of navigational gyroscopes drift in two-axis servo testing.

Endoscopic Optical Doppler Tomography Based on Two-Axis Scanning MEMS Mirror

We study the feasibility of endoscopic optical Doppler tomography with a micro-electro-mechanical system(MEMS) mirror based probe. The additional phase shifts introduced by the probe are tracked and formulated.The suppression method of the probe phase shifts is proposed and validated by fluid flow detection experiments.In vivo blood flow detection is also implemented on a hairless mouse. The velocities of the blood flow in two directions are obtained to be-8.1 mm/s and 6.6 mm/s, respectively.

A new two-axis solar tracker based on the online optimization method:Experimental investigation and neural network modeling

This article presents a new two-axis solar tracker based on an online optimization algorithm so as to track the position of the sun without using its movement model.In this research,four well-known optimization algorithms are employed to find the two unknown parameters named azimuth and zenith angles,which determine the position of the sun.The magnitude of the sunray is considered as the cost function of all algorithms.Then,several experiments are carried out to find the best optimization algorithm with optimal population size,number of iterations,and also the best initialization method.Uniform initialization leads to faster convergence compared to random initialization.The results clearly show that the particle swarm optimization algorithm with a population size of 15 and 7 iterations using uniform initialization method has better performance than the other algorithms,with a convergence time of less than 40 s.The average fitness value or voltage received by the tracker is 2.4 Volts in this method,which is higher than other methods.TLBO also performs well with a population size of 15 and 7 iterations.Afterward,the artificial neural network with one hidden layer and 20 neurons is employed to predict these two parameters in each day and moment in a year in Shiraz city according to the experimental data extracted from PSO.Number of the day from January and the time are inputs and zenith and azimuth angles are considered the output of neural network modeling.The performance of the proposed ANN model is evaluated using regression plots,demonstrating a strong correlation between predicted and target outputs.Finally,the outcomes reveal the feasibility of using online optimization algorithms and neural network modeling in an effort to bypass the complex mathematical model of mechatronic systems and predict the movement of the sun automatically.

The WKBZ mode approach to sound propagation in the two-axis underwater channel

The two-axis underwater channel often exists in deep ocean. Sound propagation in the two-axis underwater channel is a benchmark problem for computational methods of underwater acoustics. In this paper, the generalized phase-integral (WKBZ) normal mo de approach is extended to deal with this kind of problem. Numerical results show that the extended WKBZ approach is effective.

LARGE-EDDY SIMULATION OF FLOW AROUND CYLINDER ARRAYS AT A SUBCRITICAL REYNOLDS NUMBER

The complex three-dimensional turbulent flows around a cylinder array with four cylinders in an in-line square configuration at a subcritical Reynolds number of 1.5 × 10^4 with the spacing ratio at L/D = 1.5 and 3.5 were investigated using the Large Eddy Simulation （LES）. The full field vorticity and velocity distributions as well as turbulent quantities were calculated in detail and the near wake structures were presented. The results show that the bi-stable flow nature was observed at L/D = 1.5 and distinct vortex shedding of the upstream cylinders occurred at L/D = 3.5 at Re = 1.5 × 10^4. The techniques of Laser Doppler Anemometry （LDA） and Digital Particle Image Velocimetry （DPIV） are also employed to validate the present LES method. The results show that the numerical predictions are in excellent agreement with the experimental measurements. Therefore, the full field instantaneous and mean quantities of the flow field, velocity field and vorticity field can be extracted from the LES results for further study of the complex flow characteristics.