A band-pass frequency selective surface with polarization rotation

A band-pass frequency selective surface(FSS) with polarization rotation property is proposed. The proposed polarization rotating FSS(PR-FSS) is a two-dimensional periodic structure, its unit cell is an antenna-filter-antenna(AFA) module,and the polarization directions of the upper and lower antennas in each AFA module are orthogonal to each other, so the PR-FSS can achieve frequency selection and 90 degrees polarization rotation at the same time. The numerical simulation demonstrate that the anticipated frequency selection and polarization rotation are realized by the PR-FSS in the frequency band from 8.84 GHz to 10.30 GHz with a relative bandwidth of 15.26%, and the maximum insertion loss in the pass band is only 0.17 d B. Finally, one effective experiment validation is carried out, a reasonable agreement is observed between the experimental and simulated results except for a slight deviation caused by fabrication error and measurement tolerance.

Rolling element bearing instantaneous rotational frequency estimation based on EMD soft-thresholding denoising and instantaneous fault characteristic frequency

The accurate estimation of the rolling element bearing instantaneous rotational frequency(IRF) is the key capability of the order tracking method based on time-frequency analysis. The rolling element bearing IRF can be accurately estimated according to the instantaneous fault characteristic frequency(IFCF). However, in an environment with a low signal-to-noise ratio(SNR), e.g., an incipient fault or function at a low speed, the signal contains strong background noise that seriously affects the effectiveness of the aforementioned method. An algorithm of signal preprocessing based on empirical mode decomposition(EMD) and wavelet shrinkage was proposed in this work. Compared with EMD denoising by the cross-correlation coefficient and kurtosis(CCK) criterion, the method of EMD soft-thresholding(ST) denoising can ensure the integrity of the signal, improve the SNR, and highlight fault features. The effectiveness of the algorithm for rolling element bearing IRF estimation by EMD ST denoising and the IFCF was validated by both simulated and experimental bearing vibration signals at a low SNR.

Time-frequency response spectrum of rotational ground motion and its application

The rotational seismic motions are estimated from one station records of the 1999 Jiji （Chi-Chi）, Taiwan, earthquake based on the theory of elastic plane wave propagation. The time-frequency response spectrum （TFRS） of the rotational motions is calculated and its characteristics are analyzed, then the TFRS is applied to analyze the damage mechanism of one twelve-storey frame concrete structure. The results show that one of the ground motion components can not reflect the characteristics of the seismic motions completely; the characteristics of each component, especially rotational motions, need to be studied. The damage line of the structure and TFRS of ground motion are important for seismic design, only the TFRS of input seismic wave is suitable, the structure design is reliable.

DEVELOPMENT OF VIRTUAL INSTRUMENT IN CHARACTERISTIC ANALYSIS OF ROTATING MACHINERY BASED ON INSTANTANEOUS FREQUENCY ESTIMATION

Based on the recently quick-developing time-frequency analysis (TFA)technique and virtual instrument (VI) technique, a virtual instrument in characteristic analysis ofrotating machinery is researched and developed successfully. By utilizing instantaneous frequencyestimation (IFE) theoretics of TFA technique, and based on IFE of peak searching on thetime-frequency spectrum, order analysis (OA) functions is put forward and implemented, such as orderspectrum, order spectrum matrix, order tracking, order tracking filtering, and order componentextraction, etc. Unlike the home and abroad existing popular characteristic analyzers, which needkey phasing devices such as shaft encoder, phase-locked loop (PLL), phase-locked multiple frequency,tachometer, etc, to implement constant angle sampling directly or indirectly, whereas thisinstrument only uses the vibration signal of rotating machinery to carry out OA. This instrumentmakes up the shortage of these traditional instruments in analyzing the non-stationary signal ofrun-up and run-down process of rotating machinery. Therefore, it is a great breakthrough for theexisting order analyzers.

Modified Omega-K algorithm for processing helicopter-borne frequency modulated continuous waveform rotating synthetic aperture radar data

With appropriate geometry configuration, helicopter- borne rotating synthetic aperture radar （ROSAR） can break through the limitations of monostatic synthetic aperture radar （SAR） on forward-looking imaging. With this capability, ROSAR has extensive potential applications, such as self-navigation and self-landing. Moreover, it has many advantages if combined with the frequency modulated continuous wave （FMCW） technology. A novel geometric configuration and an imaging algorithm for helicopter-borne FMCW-ROSAR are proposed. Firstly, by per- forming the equivalent phase center principle, the separated trans- mitting and receiving antenna system is equalized to the case of system configuration with antenna for both transmitting and receiving signals. Based on this, the accurate two-dimensional spectrum is obtained and the Doppler frequency shift effect in- duced by the continuous motion of the platform during the long pulse duration is compensated. Next, the impacts of the velocity approximation error on the imaging algorithm are analyzed in de- tail, and the system parameters selection and resolution analysis are presented. The well-focused SAR image is then obtained by using the improved Omega-K algorithm incorporating the accurate compensation method for the velocity approximation error. FJnally, correctness of the analysis and effectiveness of the proposed al- gorithm are demonstrated through simulation results.

Frequency-selective microwave polarization rotator using substrate-integrated waveguide cavities

A frequency selective polarization rotator that can rotate the polarization angle of an incident electromagnetic wave at the microwave frequency by 45 is presented. The polarization rotator is based on a two-dimensional periodic array of substrate integrated waveguide cavities, realizing the polarization rotation by coupling the input signal to the output wave through three metallic slots. Two layers of frequency selective surfaces are cascaded by substrate and form the polarization rotator. A vertical slot on the top layer is used to select the horizontal polarization from the incident wave, the vertical and the horizontal slots on the bottom layer are, respectively, used to obtain horizontally and vertically polarized outgoing waves. The two orthogonal outgoing waves are combined to result in the 45~ polarized wave. Both full wave simulation and experimental measurement are carried out, together validating the proposed method.

EFFECT OF THE GUIDES ON THE LOWEST CRITICAL ROTATIONAL FREQUENCIES OF CIRCULAR SAW

The effects of the location,number and stiffness of guide pads on the lowest critical rotational frequencies of the rotating circular saw damped at the inside and free at the perimeter are discussed by the non linear theory and the perturbation theory of structural vibration analysis The influence of the centrifugal force and the cutting temperature are considered in the course of the analysis The results of the analysis and the calculation show that the introduction of one guide does not stably raise critical rotational frequencies of the circular saw The two guides can raise lowest critical rotational frequency of the circular saw when the angle between the two guides fixed on the direction of the circumference satisfies the certain conditions

A simplified method for analyzing the fundamental frequency of monopile supported offshore wind turbine system design

Preliminary design of offshore wind turbines requires high precision simplified methods for the analysis of the system fundamental frequency. Based on the Rayleigh method and Lagrange’s Equation, this study establishes a simple formula for the analysis of system fundamental frequency in the preliminary design of an offshore wind turbine with a monopile foundation. This method takes into consideration the variation of cross-section geometry of the wind turbine tower along its length, with the inertia moment and distributed mass both changing with diameter. Also the rotational flexibility of the monopile foundation is mainly considered. The rigid pile and elastic middle long pile are calculated separately. The method is validated against both FEM analysis cases and field measurements, showing good agreement. The method is then used in a parametric study, showing that the tower length Lt, tower base diameter d0, tower wall thickness δt, pile diameter db and pile length Lb are the major factors influencing the fundamental frequency of the offshore wind turbine system. In the design of offshore wind turbine systems, these five parameters should be adjusted comprehensively. The seabed soil condition also needs to be carefully considered for soft clay and loose sand.

Effect of Rotation on the Propagation of Waves in Hollow Poroelastic Circular Cylinder with Magnetic Field

Employing Biot’s theory of wave propagation in liquid saturated porous media,the effect of rotation and magnetic field on wave propagation in a hollow poroelastic circular of infinite extent is investigated.An exact closed form solution is presented.General frequency equations for propagation of poroelastic cylinder are obtained when the boundaries are stress free.The frequencies are calculated for poroelastic cylinder for different values of magnetic field and rotation.Numerical results are given and illustrated graphically.The results indicate that the effect of rotation,and magnetic field are very pronounced.Such a model would be useful in large-scale parametric studies of mechanical response.

Frequency domain polarization weighted ESPRIT method for bearing angle

The signal to noise ratio （SNR） of seismic waves is usually very low after long distance transmission. For this condition, to improve the bearing estimation capability in the low SNR, a frequency domain polarization weighted ESPRIT method using a single vector device is proposed. The frequency domain polari- zation parameters extracted from the signals are used to design the weighted function which is applied to the received signals. The bearing angle and the target frequency are estimated through ESPRIT using the weighted signals. The simulation and experiment results show that the presented method can obtain accurate estimation values under the low SNR with little prior information.

DESIGN AND ANALYSIS OF NOVEL ACTIVE ACTUATOR TO CONTROL LOW FREQUENCY VIBRATIONS OF SHAFT SYSTEM

Aiming at providing with high-load capability in active vibration control of large-scale rotor system, a new type of active actuator to simultaneously reduce the dangers of low frequency flexural and torsional vibrations is designed. The actuator employs electro-hydraulic system and can provide a high and circumferential load. To initialize new research, the characteristics of various kinds of active actuators to control rotor shaft vibration are briefly introduced. The purpose of this paper is to introduce the preliminary results via presenting the structure, functions and operating principles, in particular, the working process of the electro-hydraulic system of the new actuator which includes a set of high speed electromagnetic valves and a series of sloping cone-shaped openings, and presenting the transmission relationships among the control parameters from control signals into the valves to active load onto shaft. The course of the work is dynamic, and a series of spatial forces and moments are put on the shaft to get an external resultant force to reduce excitations that induce vibration of shafts. By checking states of vibration, the actuator can control the impulse width and the interval of injection time for applying different control force to a vibration shaft in two circumference directions through the regulating action of a set of combination directional control valves. The results from simulating analysis and experiment show evidence of that this design can satisfy the case of active process of decreasing of flexural and torsional vibrations.

Synchronization for the Environment of OFDM Cooperative Communications Based on Preamble Design and Phase Rotation

Timing and carrier frequency offset estimation are critical issue for OFDM cooperative communications. In view of the complexity and high accuracy requirement, 1/2 and 1/4 pilot symbol cycle CAZAC sequence structures are defined as the pilot frequency sequence. Estimation within one symbol cycle is carried out through averaging samples of two neighboring symbol cycles, after which the operation is expanded to all the symbol cycles in one band group. Taking multipath effect into account, the concept of phase rotation is proposed for a further step. Adjust the phase difference of estimated symbols by phase rotation, and cross estimation could be done. Meanwhile, timing scheme works within one cycle training sequence. Theoretical and simulation analysis indicate that CRLB does not only relate to estimation symbol length, but also be influenced by phase difference of estimation symbols seriously. In the condition that the length of estimation is fixed, the bigger the phase rotation angle is, the smaller the CRLB is. The complexity of proposed algorithm is less than full cycle average estimation method for almost 50%. Meanwhile, the estimation accuracy is approximate with the full cycle average estimation method as well. Timing scheme with the defined preamble structure is also proposed. Simulation proves its efficiency.

Rotational analysis and line intensities of the HCO ~2A′-~2A′3_1~1 band at 296 K

This paper computes the rotational energy levels of the HCO B^2A＇-X^2A＇31^1 transition, especially, the higher values of the rotational quantum numbers NKa Kc and Ka, with the rotational constants which are obtained via B3LYP method with 6-311G basis set, and the results show that the calculated frequencies using the computed vibration-rotation energy levels are in reasonable agreement with the data from the experiment. Meanwhile, the line intensities of HCO are first reported, the results are of significance for the studying HCO.

Natural frequencies of rotating functionally graded cylindrical shells

Love＇s first approximation theory is used to analyze the natural frequencies of rotating functionally graded cylindrical shells. To verify the validity of the present method, the natural frequencies of the simply supported non-rotating isotropic cylindrical shell and the functionally graded cylindrical shell are compared with available published results. Good agreement is obtained. The effects of the power law index, the wave numbers along the x- and O-directions, and the thickness-to-radius ratio on the natural frequencies of the simply supported rotating functionally graded cylindrical shell are investigated by several numerical examples. It is found that the fundamental frequencies of the backward waves increase with the increasing rotating speed, the fundamental frequencies of the forward waves decrease with the increasing rotating speed, and the forward and backward waves frequencies increase with the increasing thickness-to-radius ratio.

Experimental Study on Flow past A Rotationally Oscillating Cylinder

A series of experiments was carried out to study the flow behaviour behind a rotationally oscillating cylinder at a low Reynolds number （Re=300） placed in a recirculation water channel. A stepper motor was used to rotate the cylinder clockwise- and- counterclockwise about its longitudinal axis at selected frequencies. The particle image velocimetry （PIV） technique was used to capture the flow field behind a rotationally oscillating cylinder. Instantaneous and time-averaged flow fields such as the vorticity contours, streamline topologies and velocity distributions were analyzed. The effects of four rotation angle and frequency ratios Fr （Fr=fn/fv, the ratio of the forcing frequency fn to the natural vortex shedding frequency fv） on the wake in the lee of a rotationally oscillating cylinder were also examined. The significant wake modification was observed when the cylinder undergoes clockwise-and-counterclockwise motion with amplitude of π, especially in the range of 0.6≤Fr≤1.0.

SIMULTANEOUS FREQUENCY AND DIRECTION ESTIMATION OF COHERENT SIGNALS

A new method is proposed in this paper for simultaneous frequency and direction estimation of coherent signals. The method is based on the rotational invariance techniques and uses an array triplet in motion to estimate the central frequencies and azimuths of coherent signals from narrowband sources. Without searching in the space of frequency-direction, the computational efficiency of the method is improved significantly. Simulation resultsin the typical examples demonstrate the performance of this new method.

Plane Vibrations in a Transversely Isotropic Infinite Hollow Cylinder Under Effect of the Rotation and Magnetic Field

The aim of this paper is to study the effects of rotation and magnetic field on the plane vibrations in a transversely isotropic material of an infinite hollow cylinder.The natural frequency of the plane vibrations in the case of harmonic vibrations has been obtained.The natural frequencies are calculated numerically and the effects of rotation and magnetic field are discussed.The numerical results obtained have been illustrated graphically to understand the behavior of frequency equation with different values of frequencyωunder effects the rotation and magnetic field.Comparison was made with the results obtained in the presence and absence of the rotation and magnetic field.The results indicate that the effect of rotation and magnetic field are very pronounced.

Wave Propagation Model in a Human Long Poroelastic Bone under Effect of Magnetic Field and Rotation

This article is aimed at describing the way rotation and magnetic field affect the propagation of waves in an infinite poroelastic cylindrical bone.It offers a solution with an exact closed form.The authors got and examined numerically the general frequency equation for poroelastic bone.Moreover,they calculated the frequencies of poroelastic bone for different values of the magnetic field and rotation.Unlike the results of previous studies,the authors noticed little frequency dispersion in the wet bone.The proposed model will be applicable to wide-range parametric projects of bone mechanical response.Examining the vibration of surface waves in rotating cylindrical,long human bones under the magnetic field can have an impact.The findings of the study are offered in graphs.Then,a comparison with the results of the literature is conducted to show the effect of rotation and magnetic field on the wave propagation phenomenon.It is worth noting that the results of the study highly match those of the literature.

Effects of Density—Dependent Bag Constant and Strange Star Rotation

With the emphasis on the effects of the density-dependent bag constant and the rotation of strange star the limiting mass of strange star is calculated. The obtained results show that the limiting mass and the corresponding radius of strange star increase as the rotation frequency increases, and tend to be lowered when the density-dependent bag constant is considered.

High Frequency Ultrasound in Determining the Causes of Acute Shoulder Joint Pain

Shoulder ultrasonography is approved as the examination of choice for rotator cuff abnormality in many centers around the world since it is an inexpensive and safe tool for investigation of rotator cuff abnormalities. The goal of this study was to determine the ultrasound findings in patients with acute shoulder joint pain, and also to identify possible predictors of shoulder pain, as well as to compare the ultrasound diagnostic performance to that of MRI in such condition. A total of 65 (mean age 28 ± 1.2 years) consequential patients were recruited for a period of six months between July 2015 and June 2016 in this study. Collected data were confined on age, medical history, and clinical symptoms. Shoulder ultrasound was performed with a linear array transducer (10 - 15 MHz) connected to HI vision Avius ultrasound unit;Hitachi. MRI for the shoulder joint was performed in all cases to confirm the ultrasound results, using 1.5-T MRI system (Magnetom Espree);Siemens. Statistical analysis was completed using the standard Statistical Package for the Social Sciences (SPSS Inc., Chicago, IL, USA) version 20 for windows. Ultrasound manages to determine the causes of acute shoulder joint pain in 98% of the patients. Fitted achievement values for shoulder ultrasound in the diagnosis the causes of shoulder joint pain were 100% sensitivity and a range of 96% to 100% of accuracy. Ultrasound presents a high sensitivity and accuracy in diagnosis a wide spectrum of shoulder joint lesions, with a diagnostic performance near to that of MRI.