钢丝绳罐道刚性系数检测与调整

为了更加科学的进行钢丝绳罐道刚性系数检测,介绍了刚性系数检测的三种检测方法,针对三种检测方法进行对比分析,制定振波频率法测试方案,设计出罐道刚性系数检测装置,进行最小刚性系数计算,满足钢丝绳罐道刚性系数检测要求,并给出罐道绳刚性系数调整措施和意见,为矿井提升系统安全运行提供科学的保障。

罐道钢丝绳张力检测装置研究设计与应用

阐述钢丝绳罐道在煤矿提升系统中的应用情况及面临解决的难题、通过对目前罐道钢丝绳张力检测方法的研究,结合最优检测方法,设计罐道钢丝绳张力检测装置,进行最小刚性系数计算,指导钢丝绳张力调整,为矿井提升系统安全运行提供科学的保障。

Nonlinear interactions among internal tidal waves in the northeastern South China Sea

We used a set of 75-day long ADCP data from the northeastern South China Sea(SCS) to investigate nonlinear interactions among freely propagating internal tidal waves.The kinetic energy spectra displayed significant peaks at some higher tidal frequencies,such as O1M2(O1+M2),and M4(M2 +M2),where O1 is the lunar diurnal internal tide,M2 is the lunar semidiurnal internal tide,and M4 is the first higher harmonic frequency of M2.These higher tidal harmonic frequency peaks,as well as the fundamental tidal harmonic peaks,show a σ-2.3 spectral falloff rate with frequency.In addition,we explored the possible generation mechanism of higher tidal harmonics.Analysis on the rotary and bicoherence spectra suggests that strong forced non-resonant interaction induced by nonlinear advections was the dominant physical mechanism that induced these higher tidal harmonics.Moreover,the energetic,freely propagating semidiurnal(M2) internal tidal wave played the most crucial role in these interactions.These results indicate that strong nonlinear forced non-resonant interactions among internal tides can be one of the processes responsible for the redistribution of energy in the internal wave spectrum.

Design of low-sidelobe circularly-polarized microstrip array for RFID readers

A low-sidelobe circularly-polarized(CP) microstrip patch array for 2.4 GHz radio frequency identification(RFID) readers is presented.The antenna array with a Chebyshev current distribution is composed of 6 microstrip elements.The CP operation is obtained by the quasi-square patch with difference in lengths of the two sides.The antenna has been investigated numerically and experimentally.Measured results show that the array has a Chebyshev pattern with the sidelobe level of-23 dB, the half-power beamwidth of 16° and an impedance bandwidth(S11≤-10 dB) of 130 MHz, which is suitable for RFID reader applications.

MICRO-MOTION TARGET SENSING BY STEPPED-FREQUENCY CONTINUOUS-WAVE RADAR

Mechanical micro-vibration of a target may induce phase modulations on the radar echo,and the vibration can be detected to identify micro-motion target. In this paper,a new method to detect a micro-motion target and obtain its range and micro-motion frequency is proposed in which multiple periods stepped-frequency continuous-wave signal and Moving Target Indication (MTI) filter are adopted. The simulation results illustrate the validity of this method and present the detection of the target range and the vibration frequency. The experiment gives promising results.

Experimental Studies on High-Frequency Performance of the Inverse Control Magneto-Rheological Damper

Severe vibration of underground structures may be induced under blast loads. According to the characteristics of the explosion-induced ground shock wave, a new-type damper, inverse control magneto-rheological（MR） damper was designed to control the vibration, The high-frequency performance test of the MR damper was carried out on the small shaking table. It is shown that the performance can be modeled by use of the modified Bouc-Wen model, and the Parameters of the model keep stable in the range of 15--50 Hz.

Interactions of Two Identical Wave Trains with a Relative Separation Angle of 24?

Interactions between two identical monochromatic wave trains with a relative separation angle of 24? were experimentally investigated in a well-designed ‘X' configuration.Wave trains with different amplitudes and frequencies were generated.The results demonstrated that the interaction was strongly dependent on both wave amplitude and frequency.For nonbreaking and lower-frequency cases,the wave trains can approximately reestablish their initial state following the interaction.However,for larger waves,the interaction was enhanced,distorting the surfaces significantly-the wave trains were no longer two-dimensional after the encounter.During the interaction process,there was an obvious increase in wave height,reaching a maximum amplification in the middle of the interaction region that was approximately 1.55 times the initial height.Furthermore,the images captured by high-speed cameras illustrated that two wave trains entered the interaction region at the same time and then merged during the interaction process,resulting in an increase in wave amplitude.The combined wave crest was initially composed of two straight segments with a relative angle of 24? and gradually morphed into a single segment as is evident in the plan view.The wave then broke in the downstream,still within the interaction region,exhibiting a crescent pattern along the crest.

The Analysis and Improving of the Microwave Exciter in the Lower Hybrid Wave System

When we carry out lower hybrid wave heating and current driving plasma experiment at tokamak, we need mega-watt order of microwave power. The microwave signal at frequency of 2450 MHz is generated by a microwave exciter. According to the experiment＇s demands, the microwave exciter must provide output power of 1.5～ 2. 5 W with stabilized frequency and amplitude tobe used as the klystron input. Being amplified by the klystron, the microwave signal is transmitted through the transmitting system to the antenna and is emitted into the HL-2A tokamak. So we can see that the microwave exciter＇s function is very important to the lower hybrid wave heating and current driving plasma experiment.

Modelling of multi-bodies in close proximity under water waves——Fluid resonance in narrow gaps

Viscous fluid model and potential flow model with and without artificial damping force(f=-μV,μ the damping coefficient and V the local averaging flow velocity) are employed in this work to investigate the phenomenon of fluid resonance in narrow gaps between multi-bodies in close proximity under water waves.The numerical results are compared with experimental data available in the literature.The comparison demonstrates that both the viscous fluid model and the potential flow model are able to predict the resonant frequency reasonably well.However the conventional potential flow model(without artificial damping term) significantly over-predicts the wave height in narrow gaps around the resonant frequency.In order to calibrate the appropriate damping coefficient used for the potential model and make it work as well as the viscous fluid model in predicting the resonant wave height in narrow gaps but with little computational efforts,the dependence of damping coefficient μ on the body geometric dimensions is examined considering the parameters of gap width Bg,body draft D,body breadth ratio Br and body number n(n = 2,3),where Br = BB/BA for the case of two bodies(Body A and Body B) with different breadths of BA and BB,respectively.It was confirmed that the damping coefficient used for the potential flow model is not sensitive to the geometric dimensions and spatial arrangement.It was found that μ∈ [0.4,0.5] may guarantee the variation of Hg/H0 with kh to be generally in good agreement with the experimental data and the results of viscous fluid model,where Hg is the excited wave height in narrow gaps under various dimensionless incident wave frequencies kh,H0 is the incident wave height,k = 2π/L is the wave number and h is the water depth.

Selective excitation of resonances in gammadion metamaterials for terahertz wave manipulation

A gammadion terahertz(THz) metamaterial embedded with a pair of splits is experimentally investigated. By introducing the pair of splits at different arms, the transmitted amplitude at the resonance frequency can be manipulated from 61% to 24%. Broadband static resonance tunability from 1.11 to 1.51 THz is also demonstrated via varying the relative split positions at certain arms. The amplitude change and static resonance tunability are attributed to the introduced split pairs, which enable selective excitation of different resonance modes in the gammadion metamaterials. This work promises a new approach to design THz functional devices.

Frequency/time domain modeling of a direct drive point absorber wave energy converter

Two different methods to model a point absorber wave energy converter （WEC） with direct drive linear power take-off （PTO） are proposed in the present study： the frequency domain （FD） method and the time domain （TD） method. In the FD analysis, the frequency response function （FRF） of the WEC device is obtained via the equation of motion, and the expressions of power capture width in regular and random waves are derived as well. In the TD modeling, based on a state space approximation of the convolution term in the motion equation, both regular wave and random wave simulations are carded out. The regular wave simulation results indicate that the state space approximation is sufficiently accurate and the capture width reaches the maximum in the vicinity of the natural frequency. In the random wave simulations, the effects of buoy size, the PTO damping and wave climate on the power capture width are discussed in detail, which leads to the conclusion that the capture widths are influenced by the natural frequency of the WEC device, peak frequency of the wave spectrum, the amplitude of FRF and PTO damping. Furthermore, the increase of the capture width is at the cost of a relatively large buoy size and PTO damping when control is not included.

Controlled fabrication and microwave absorbing mechanism of hollow Fe3O4@C microspheres

Uniform core-shell SiO2@Fe_3O_4@C microspheres were prepared by a one-step hydrothermal method with SiO_2 microspheres as the template, and the hollow Fe_3O_4@C(HFC) microspheres were achieved via etching SiO_2 template. By changing the sizes of SiO_2 microspheres, a series of HFC microspheres with variable cavity sizes were obtained to study the relationship between cavity size and microwave absorbing(MA) performance for the first time. The morphology and structure of samples were characterized in detail. The results showed that the MA performance of HFC sample depended on its cavity size. In particular, the hollow structure was good for improving MA performance and could make MA move to the high-frequency region. More importantly, as the cavity size increases, the resonance frequency of HFC-i(i=1,2, 3, 4) samples moved to a low frequency, and the optimal matching thickness of HFC-i samples was increasing. Among all HFC-i samples, HFC-3 showed the most excellent MA performance,which could be mainly explained by the quarter-wavelength matching model, intrinsical magnetic and dielectric loss. Furthermore,the MA performance of HFC mixture blended by the equal mass fraction of HFC-2, HFC-3 and HFC-4 was the comprehensive results of three HFC-i samples. All the above suggested that the cavity size in HFC sample had a great influence on the MA performance.

On-Line Adaptive Repetitive Controller for Power Factor Correction Systems

When the fundamental frequency is shifting, it is hard for traditional repetitive controller to work at the resonant frequencies. In this paper, a novel adaptive repetitive controller for power factor correction systems is proposed to suppress the current harmonics. Through the controller, the shifting sampling times of the repetitive controller in a fundamental period can be obtained. Mathematical analysis, simulations and physical experiments have validated the effectiveness of the adaptive repetitive controller.