Comparison of delay compensation methods for real-time hybrid simulation using frequency-domain evaluation index

The delay compensation method plays an essential role in maintaining the stability and achieving accurate real-time hybrid simulation results. The effectiveness of various compensation methods in different test scenarios, however, needs to be quantitatively evaluated. In this study, four compensation methods （i.e., the polynomial extrapolation, the linear acceleration extrapolation, the inverse compensation and the adaptive inverse compensation） are selected and compared experimentally using a frequency evaluation index （FEI） method. The effectiveness of the FEI method is first verified through comparison with the discrete transfer fimction approach for compensation methods assuming constant delay. Incomparable advantage is further demonstrated for the FEI method when applied to adaptive compensation methods, where the discrete transfer function approach is difficult to implement. Both numerical simulation and laboratory tests with predefined displacements are conducted using sinusoidal signals and random signals as inputs. Findings from numerical simulation and experimental results demonstrate that the FEI method is an efficient and effective approach to compare the performance of different compensation methods, especially for those requiring adaptation of compensation parameters.

A Simple Method for Source Depth Estimation with Multi-path Time Delay in Deep Ocean

A method of source depth estimation based on the multi-path time delay difference is proposed. When the minimum time arrivals in all receiver depths are snapped to a certain time on time delay-depth plane, time delay arrivals of surface-bottom reflection and bottom-surface reflection intersect at the source depth. Two hydrophones deployed vertically with a certain interval are required at least. If the receiver depths are known, the pair of time delays can be used to estimate the source depth. With the proposed method the source depth can be estimated successfully in a moderate range in the deep ocean without complicated matched-field calculations in the simulations and experiments.

光纤应力延迟器的调节方法

以琼斯矩阵为工具分析了光纤应力延迟器作１／４波片应用的调节方法．

基于压缩感知的光控相控阵波束形成方法

针对光控相控阵在实现宽带宽角扫描时,所需要的光真延时器数目过多问题进行研究,提出了基于压缩感知的光控相控阵方向图形成方法。首先通过公式推导详细分析了影响光控相控阵波束偏移的因素,其次给出光真延时器稀疏排布方式,在此基础上基于压缩感知理论恢复出光控相控阵的方向图。所提方法能够在大幅减少光真延时器数目的条件下实现宽带宽角扫描。最后利用仿真实验验证了所提方法的有效性。

THE STABILITY ANALYSIS OF THE θ-METHODS FOR DELAY DIFFERENTIAL EQUMIONS

This paper deals with the stability analysis of θ-methods for the numericalsolution of delny dmerential equations (DDEs). We focus on the behavioux of suchmethods in the solution of the linear test equation y'(t) = a(t)y(t) + b(t)y(t - T),where T > o, a(t) and b(t) are functions from R to C. It is proved that the linearθ-method and the one-leg θ-method are TGP-stable if and only if θ = 1.

Parallel Techniques for Frame Synchronous Scrambler

In high speed transmission system such as SDH,parallel scrambling technique is re-quired.This paper presents a method of expanding matrix,which makes the traditional ma-trix method capable of realizing parallel scramblers of any size.A novel method called delayoperator method is also described in this paper.The 8-bit parallel scrambling circuitry ofSDH has been realized with the two methods.

Outboard abnormal noise source localization method with curved surface projection based on time delay matching and weighting criterion

An improved localization method consisting of ＂filtering-time delay estimationhyperbolic localization＂ is proposed. Combining the empirical mode decomposition（EMD）and time delay estimation method based on generalized average magnitude difference function,the original signals are decomposed into intrinsic mode function（IMF） components. The energy distribution criterion and spectrum consistency criterion are used to select the IMFs, which can represent the physical characteristics of the source signal. Several sets of signals are applied to estimate the time delay, and then a vector matching criterion is proposed to select the correct time delay estimation. Considering the hydrophones location, a shell model is established and projected to a plane according to the quadrant before the hyperbolic localization. Results of mooring and sailing tests show that the proposed method improves the localization accuracy,and reduces the error caused by time delay estimation.

Numerical study of air cavity characteristics of bow wave breaking of KCS ship under different speeds

Ship bow wave breaking contains complex flow mechanism,which is very important for ship performance.In this study,a practical numerical simulation scheme for bow wave breaking is proposed and the scheme is applied to the simulation of bow wave breaking of KCS ship model with Fr=0.26,0.30,0.35,0.40,analyzing the impact of speed on the bow wave breaking.The results indicate that an increase in speed leads to a significant rise in viscous pressure resistance and more pronounced bow wave breaking.Moreover,it is found that the traditional wave height function in OpenFOAM is not suitable for detailed studies of bow wave breaking.This study extracts different free surfaces through top and bottom views to further analyze the free surface overturning,droplet splashing,and cavity entrainment in bow wave breaking.Additionally,the spatial and temporal distribution of cavities at Fr=0.40 is analyzed,revealing that cavity distribution is closely related to vortex structures and exhibits a periodic pulsation characteristic of approximately 12 s.

Effect of a transverse plasma jet on a shock wave induced by a ramp

We conducted experiments in a wind tunnel with Mach number 2 to explore the evolution of a transverse plasma jet and its modification effect on a shock wave induced by a ramp with an angle of 24°. The transverse plasma jet was created by arc discharge in a small cylindrical cavity with a 2 mm diameter orifice. Three group tests with different actuator arrangements in the spanwise or streamwise direction upstream from the ramp were respectively studied to compare their disturbances to the shock wave. As shown by a time-resolved schlieren system, an unsteady motion of the shock wave by actuation was found： the shock wave was significantly modified by the plasma jet with an upstream motion and a reduced angle. Compared to spanwise actuation, a more intensive impact was obtained with two or three streamwise actuators working together. From shock wave structures, the control effect of the plasma jet on the shock motion based on a thermal effect, a potential cause of shock modification, was discussed. Furthermore, we performed a numerical simulation by using the Improved Delayed Detached Eddy Simulation（IDDES） method to simulate the evolution of the transverse plasma jet plume produced by two streamwise actuators. The results show that flow structures are similar to those identified in schlieren images. Two streamwise vortices were recognized, which indicates that the higher jet plume is the result of the overlap of two streamwise jets.

Dynamical System Analysis of Unsteady Phenomena inCentrifugal Compressor

Surge and rotating stall occurring in a centrifugal compressor system are investigated by using a phaseportrait reconstruction method. From experimentally measured time series of data, the method clari-fied the cyclic behavior of surge. For rotating stall, there still remain problems in the phase portraitdue to the chaotic behavior. However, the results obtained by the present method are able to providenew insights to the modelings for surge and rotating stall. Surge and rotating stall occurring in acentrifugal compressor system are investigated by using a phase portrait reconstruction method. Fromexperimentally measured time series of data, the method clarified the cyclic behavior of surge. Forrotating stall, there still remain problems in the phase portrait due to the chaotic behavior. However,the results obtained by the present method are able to provide new insights to the modelings for surgeand rotating stall.