Mitigation of EDFA transient effects in variable duty cycle pulsed signals

We report the transient effects in Erbium Doped Fiber Amplifier (EDFA) systems for pulsed signals with different duty-cycles. The work includes the analysis using three different duty-cycles, 10%, 20% and 50%. A curve fitting technique is also proposed to predict the transients of any lesser duty-cycled pulse, once the transients of a larger duty-cycled pulse is known. Mathematical evaluation confirms the double exponential shape of transient distorted signal. Further, EDFA transient effect is experimentally verified on a Wavelength Division Multiplexed (WDM) link by multiplexing high and low bitrate modulated optical signals. We conclude the paper by proposing a transient suppression technique for variable dutycycle signals and analyzing its effectiveness with different wavelength spacing.

Resistance Torque Based Variable Duty-Cycle Control Method for a Stage Ⅱ Compressor

The resistance torque of a piston stage II com- pressor generates strenuous fluctuations in a rotational period, and this can lead to negative influences on the working performance of the compressor. To restrain the strenuous fluctuations in the piston stage II compressor, a variable duty-cycle control method based on the resistance torque is proposed. A dynamic model of a stage II com- pressor is set up, and the resistance torque and other characteristic parameters are acquired as the control tar- gets. Then, a variable duty-cycle control method is applied to track the resistance torque, thereby improving the working performance of the compressor. Simulated results show that the compressor, driven by the proposed method, requires lower current, while the rotating speed and the output torque remain comparable to the traditional vari- able-frequency control methods. A variable duty-cycle control system is developed, and the experimental results prove that the proposed method can help reduce the specific power, input power, and working noise of the compressor to 0.97 kW.m-3.min-1, 0.09 kW and 3.10 dB, respectively, under the same conditions of discharge pressure of 2.00 MPa and a discharge volume of 0.095 m3/rain. The proposed variable duty-cycle control method tracks the resistance torque dynamically, and improves the working performance of a Stage II Compressor. The pro- posed variable duty-cycle control method can be applied to other compressors, and can provide theoretical guidance for the compressor.

On Multi-Timescale Variability of Temperature in China in Modulated Annual Cycle Reference Frame

The traditional anomaly （TA） reference frame and its corresponding anomaly for a given data span changes with the extension of data length. In this study, the modulated annual cycle （MAC）, instead of the widely used climatological mean annual cycle, is used as an alternative reference frame for computing climate anomalies to study the multi-timescale variability of surface air temperature （SAT） in China based on homogenized daily data from 1952 to 2004. The Ensemble Empirical Mode Decomposition （EEMD） method is used to separate daily SAT into a high frequency component, a MAC component, an interannual component, and a decadal-to-trend component. The results show that the EEMD method can reflect historical events reasonably well, indicating its adaptive and temporally local characteristics. It is shown that MAC is a temporally local reference frame and will not be altered over a particular time span by an exten-sion of data length, thereby making it easier for physical interpretation. In the MAC reference frame, the low frequency component is found more suitable for studying the interannual to longer timescale variability （ILV） than a 13-month window running mean, which does not exclude the annual cycle. It is also better than other traditional versions （annual or summer or winter mean） of ILV, which contains a portion of the annual cycle. The analysis reveals that the variability of the annual cycle could be as large as the magnitude of interannual variability. The possible physical causes of different timescale variability of SAT in China are further discussed.

The influence of freeze-thaw cycles on the granulometric composition of Moscow morainic clay

The freeze-thaw cycling process considerably changes the composition, structure, and properties of soils. Since the grain size is the most important factor in determining soil characteristics, our current research primarily aims to investigate dynamic changes of the soil fraction when exposed to freeze-thaw conditions. We observed two series of Moscow morainic clayey specimens （gQⅡm）： （Ⅰ） the original series, and （Ⅱ） the remolded series. We subjected each series of soil specimens to different frequencies of freeze-thaw cycles （3, 6, 20, and 40 cycles）, and we used granulometric tests to analyze both series before and after exposure to freeze-thaw conditions. As a result of our experiments, the granulometric compositions tended to be distributed evenly after 40 freeze-thaw processes （i.e., content of fraction for 0.1-0.05 mm was increased after 40 freeze-thaw cycles） because the division of coarse grains and the aggregation of fine grains were synchronized during the freeze-thaw process. The soil grains in both series changed bi-directionally. In the original series, changes of the sand grains were conjugated with the clay grains, and in the remolded series, changes of the sand grains were conjugated with the silt grains, because potential energy difference caused the division and aggregation processes to relate to the counteraction process. The even distribution of soil grain size indicated the state of equilibrium or balance. The granulometric compositions were altered the most during the sixth freeze-thaw cycle, because the coefficient of the intensity variation of the grain fineness （Kvar） had its maximum value at that time.

Fire cycle of the Canada's boreal region and its potential response to global change

Interactions of fire cycle and plant species＇ reproductive characteristics could determine vegetation distribution pattern of a landscape. In Canada＇s boreal region, fire cycles before the Little Ice Age （c. 1850s） ranged from 30-130 years and 25-234 years afterwards until the settlement period （c. 1930s） when longer fire cycles occurred in response to climatic change and human interference. Analysis indicated that fire cycles were correlated with growing season （April-October） temperature and precipitation departure from the 1961-1990 normal, varying by regions. Assuming that wildfires will respond to future warming similar to the manner during the past century, an assessment using climatic change scenarios CGCMI, CGCM2 and HadCM2 indicates fire cycles would divert to a range of 80-140 years in the west taiga shield, more than 700 years for the east boreal shield and east taiga shield, and 300-400 years for the boreal plains in 2050.

Variations in the annual cycle of the East Asian monsoon and its phase-induced interseasonal rainfall anomalies in China

The East Asian monsoon(EAM)exhibits a robust annual cycle with significant interannual variability.Here,the authors find that the EAM annual cycle can be decomposed into the equinoctial and solstitial modes in the combined sea level pressure,850-hPa low-level wind,and rainfall fields.The solstitial mode shows a zonal pressure contrast between the continental thermal low and the western Pacific subtropical high,reaching its peak in July and dominating the East Asian summer monsoon.The equinoctial mode shows an approximate zonal contrast between the low-level cyclone over the east of the Tibetan Plateau and the western Pacific anticyclone over the east of the Philippines.It prevails during the spring rainy season in South China and reaches its peak in April.The interannual variations of the lead–lag phase of the two modes may result in the negative correlation of rainfall anomalies in North China between spring and fall and in South China between winter and summer,which provides a potential basis for the across-seasonal prediction of rainfall.The warm phase of ENSO in winter could give rise to the reverse interseasonal rainfall anomalies in South China,while the SST anomaly in the Northwest Pacific Ocean may regulate the rainfall anomaly in North China.

Feedforward Variable Structural Proportional-Integral-Derivative for Temperature Control of Polymerase Chain Reaction

To track the rapidly changing temperature profiles of thermal cycling of polymerase chain reaction （PCR） accurately, an innovative feedforward variable structural proportional-integral-derivative （FVSPID） controller was developed. Based on the step response test data of the heat block, a reduced first order model was estabfished at different operating points. Based on the reduced model, the FVSPID controller combined a feedforward path with the variable structural proportional-integral-derivative （PID） control. The modified feedforward action provided directly the optimal predictive power for the desired setpoint to speed up the dynamic response. To cooperate with the feedforward action, a variable structural PID was applied, where the P mode was used in the case of the largest errors to speed up response, whereas the PD mode was used in the case of larger errors to suppress overshoot, and finally the PID mode was applied for small error conditions to eliminate the steady state offset. Experimental results illustrated that compared to the conventional PID controller, the FVSPID controller can not only reduce the time taken to complete a standard PCR protocol, but also improve the accuracy of gene amplification.

谱归一化CycleGAN的轴承故障迁移诊断研究

深度学习无需先验特征提取的优点使其受到了工业设备的智能故障诊断领域研究的青睐,但深度学习的低鲁棒性和较高的数据要求阻碍其实际应用。为适应在工业现场复杂多变的工况,该文提出了一种基于谱归一化(spectral normalization, SN)和循环一致对抗网络(cycle-consistent adversarial networks, CycleGAN)的SN-1DCycleGAN网络用于变工况条件下的故障数据迁移生成和诊断。首先,搭建一种适应振动数据生成的1DCycleGAN网络,用于获得同种工况下正常信号与故障信号的映射关系。使用谱归一化对网络进行改进,有效的防止CycleGAN网络训练过程中训练不稳定情况。其次,通过不同工况的正常数据生成自适应的故障数据,实现变工况迁移生成的目的。最后,3种评价指标以及分类器准确率对数据生成质量进行定量评估,并使用仿真与试验信号进行验证。试验结果表明,SN-1DCycleGAN在一维振动信号上具备一定迁移效果,可对变工况数据进行增强,提升分类器的准确率。

Geophysical methods for the study of sedimentary cycles

We present the wavelet depth-frequency analysis and variable-scale frequency cycle analysis methods to study sedimentary cycles. The spectrum analysis, variable-scale frequency cycle analysis, and wavelet depth-frequency analysis methods are mainly discussed to distinguish sedimentary cycles of different levels. The spectrum analysis method established the relationship between the spectrum characteristics and the thickness and number of sedimentary cycles. Both the variable-scale frequency cycle analysis and the wavelet depth-frequency analysis are based on the wavelet transform. The variable-scale frequency cycle analysis is used to obtain the relationship between the periodic changes of frequency in different scales and sedimentary cycles, and the wavelet depth-frequency analysis is used to obtain the relationship between migration changes of frequency energy clusters and sedimentary cycles. We designed a soft-ware system to process actual logging data from the Changqing Oilfield to analyze the sedimentary cycles, which verified the effectiveness of the three methods, and good results were obtained.

Performance Assessment of a Heat Recovery Unit Utilizing Turbine with Variable Inlet Guide Vanes Configuration for Application in Passenger Vehicles

This study explores the potentials of employing an Organic Rankine Cycle (ORC) system with variable inlet guide vanes (VIV) turbine geometry designed on a GT-Suite platform for effective exhaust heat recovery (EHR) application onboard passenger vehicles. The ORC model simulation was based on vehicle speed mode using R245fa as working fluid to assess the thermal performance of the ORC system when utilizing modified turbine geometry. Interestingly, the model achieved a very improved performance in contrast to the model without a modified turbine configuration. The results revealed the average 2.32 kW ORC net output, 4.93% thermal efficiency, 6.1% mechanical efficiency, and 5.0% improved brake specific fuel consumption (BSFC) for the developed model. As determined by the performance indicators, these promising results from the model study show the prospect of EHR technology application in the transportation sector for reduction in exhaust emissions and fuel savings.

Interannual variability of carbon cycle implied by a 2-D atmospheric transport model

A 2-dimensional atmospheric transport model is deployed in a simplified CO 2 inverse study. Calculated carbon flux distribution for the interval from 1981 to 1997 confirms the existence of a terrestrial carbon sink in mid-high latitude area of North Hemisphere. Strong interannual variability exists in carbon flux patterns, implying a possible link with ENSO and other natural episodes such as Pinatubo volcano eruption in 1991. Mechanism of this possible link was investigated with statistic method. Correlation analysis indicated that in North Hemisphere, climatic factors such as temperature and precipitation, to some extend, could influence the carbon cycle process of land and ocean, thus cause considerable change in carbon flux distribution. In addition, correlation study also demonstrated the possible important role of Asian terrestrial ecosystems in carbon cycle.

A numerical model of wire melting rate in variable-polarity submerged arc welding

Based on the pre-existing wire melting rate model of direct-current submerged arc welding （ DC-SAW） , a new numerical model of wire melting rate was developed for variable-polarity submerged are welding （VP-SAW） by accounting for the combined effects of duty cycle β and offset α. The experimental measurements are in a good agreement with the results calculated by this new wire melting rate model, with the maximum discrepancy being less than 10%. Therefore it is evident that this new numerical model can successfully describe the dependence of wire melting rate on the duty cycle β and offset α.

Mechanism of adjusting bypass ratio by front variable area bypass injector for a variable cycle engine

The Front Variable Area Bypass Injector(FVABI)is a key to bypass ratio adjustment for a Variable Cycle Engine(VCE).In order to study the role of the FVABI with the Core Driven Fan Stage(CDFS)duct,firstly,the engine bypass with the CDFS duct model and the equivalent engine bypass without the CDFS duct model are designed using the concept of a jet boundary line.By comparing the difference between airflow driving forces in the two engine bypass models,the quantitative effects of the injection from the CDFS duct on the mass flow rate of the engine bypass airflow are obtained under different combinations of pressure difference and area ratios.Then,the CDFS duct injection characteristic map is obtained through the typical experiment of the FVABI.Based on this map,the performance model of the FVABI is developed.Finally,the turbofan engine model with the Variable Inlet Guide Vane(VIGV),the First Variable Cycle Engine model(VCE1)with the CDFS duct and without the VIGV,and the Second Variable Cycle Engine model(VCE2)with the CDFS duct and VIGV are built.The gain on the engine bypass ratio adjustment range caused by the injection from the CDFS duct is clarified by comparing the three engine models.It is concluded that the bypass ratio adjustment range of the variable cycle engine with the FVABI is about twice that of the traditional turbofan engine.

Thermodynamic Performance Analysis of E/F/H-Class Gas Turbine Combined Cycle with Exhaust Gas Recirculation and Inlet/Variable Guide Vane Adjustment under Part-Load Conditions

Exhaust gas recirculation control(EGRC),an inlet air heating technology,can be utilized in combination with inlet/variable guide vane control(IGV/VGVC) and fuel flow control(FFC) to regulate the load,thereby effectively improving the part-load(i.e.,off-design) performance of the gas turbine combined cycle(GTCC).In this study,the E-,F-,and H-Class EGR-GTCC design and off-design system models were established and validated to perform a comparative analysis of the part-load performance under the EGR-IGV-FFC and conventional IGV-FFC strategies in the E/F/H-Class GTCC.Results show that EGR-IGV-FFC has considerable potential for the part-load performance enhancement and can show a higher combined cycle efficiency than IGV-FFC in the E-,F-,and H-Class GTCCs.However,the part-load performance improvement in the corresponding GTCC was weakened for the higher class of the gas turbine because of the narrower load range of EGR action and the deterioration of the gas turbine performance.Furthermore,EGR-IGV-FFC was inferior to IGV-FFC in improving the performance at loads below 50% for the H-Class GTCC.The results obtained in this paper could help guide the application of EGR-IGV-FFC to enhance the part-load performance of various classes of GTCC systems.

变周期RP-EKF时延纯方位角目标跟踪算法

针对声传感器纯方位目标跟踪应用,提出了一种基于静态多模型的距离参数化变周期扩展卡尔曼滤波算法,将时延影响转换为模型的可变周期,并通过参数在线估计的方法,估计该可变周期。距离参数化方法将整个距离空间分成若干个区间,分区间对距离进行估计,进而搜索出目标与观测平台之间的正确距离值。仿真结果表明变周期距离参数化扩展卡尔曼滤波算法能有效解决经典扩展卡尔曼滤波算法在纯方位角目标跟踪时可能出现的滤波发散现象,并能处理声音信号的传输时间延迟问题。

Integration of high-fidelity model of forward variable area bypass injector into zero-dimensional variable cycle engine model

Forward Variable Area Bypass Injector(FVABI)is one of key components which contributes to modulate the cycle parameters of Variable Cycle Engine(VCE)under various operation conditions.The modeling method of zero-dimensional FVABI was reviewed and its deficiency was analyzed based on FVABI flow characteristic.In order to improve the accuracy of VCE performance simulation,the high-fidelity modeling method of FVABI was developed based on its working characteristics.Then it was coupled with the zero-dimensional VCE model and the multi-level VCE model was built.The results indicate that the geometric and aerodynamic parameters can affect the interaction between the two airflows and the zero-dimensional FVABI model is too simple to predict the component performance accurately,especially when the FVABI inner bypass is chocked.Based on the performance curves for single bypass mode and the regression model of multi-scale support vector regression for double bypass mode,the high-fidelity model can predict FVABI performance accurately and rapidly.The integration of high-fidelity FVABI model into zerodimensional VCE model can be done by adjusting iterative variables and balance equations.The multi-level model has good convergence and it can predict VCE performance when the FVABI inner bypass is chocked.

A multi-fidelity simulation method research on front variable area bypass injector of an adaptive cycle engine

Front Variable Area Bypass Injector(Front-VABI) is a component of the Adaptive Cycle Engine(ACE) with important variable-cycle features. The performance of Front-VABI has a direct impact on the performance and stability of ACE, but the current ACE performance model uses approximate models for Front-VABI performance calculation. In this work, a multi-fidelity simulation based on a de-coupled method is developed which delivers a more accurate calculation of the Front-VABI performance based on Computational Fluid Dynamics(CFD) simulation. This simulation method proposes a form of Front-VABI characteristic and its matching calculation method between it and the ACE performance model, constructs a coupling method between the(2-D) Front-VABI model and the(0-D) ACE performance model. The result shows, when ACE works in triple bypass mode, the approximate model cannot account for the effect of FrontVABI pressure loss on Core Driven Fan Stage(CDFS) design pressure ratio, and the calculated error of high-pressure turbine inlet total temperature is more than 40 K in mode transition condition(the transition operating condition between triple bypass mode and double bypass mode). In double bypass mode, the approximate model can better simulate the performance of FrontVABI by considering the local loss of area expansion. This method can be applied to the performance-optimized design of Front-VABI and the ACE control law design during mode transition.

Designing method of acceleration and deceleration control schedule for variable cycle engine

Studies show that different geometries of a Variable Cycle Engine(VCE)can be adjusted during the transient stage of the engine operation to improve the engine performance.However,this improvement increases the complexity of the acceleration and deceleration control schedule.In order to resolve this problem,the Transient-state Reverse Method(TRM)is established in the present study based on the Steady-state Reverse Method(SRM)and the Virtual Power Extraction Method(VPEM).The state factors in the component-based engine performance models are replaced by variable geometry parameters to establish the TRM for a double bypass VCE.Obtained results are compared with the conventional component-based model from different aspects,including the accuracy and the convergence rate.The TRM is then employed to optimize the control schedule of a VCE.Obtained results show that the accuracy and the convergence rate of the proposed method are consistent with that of the conventional model.On the other hand,it is found that the new-model-optimized control schedules reduce the acceleration and deceleration time by 45%and 54%,respectively.Meanwhile,the surge margin of compressors,fuel–air ratio and the turbine inlet temperature maintained are within the acceptable criteria.It is concluded that the proposed TRM is a powerful method to design the acceleration and deceleration control schedule of the VCE.

Analytical redundancy of variable cycle engine based on variable-weights neural network

In this paper, variable-weights neural network is proposed to construct variable cycle engine’s analytical redundancy, when all control variables and environmental variables are changing simultaneously, also accompanied with the whole engine’s degradation. In another word,variable-weights neural network is proposed to solve a multi-variable, strongly nonlinear, dynamic and time-varying problem. By making weights a function of input, variable-weights neural network’s nonlinear expressive capability is increased dramatically at the same time of decreasing the number of parameters. Results demonstrate that although variable-weights neural network and other algorithms excel in different analytical redundancy tasks, due to the fact that variableweights neural network’s calculation time is less than one fifth of other algorithms, the calculation efficiency of variable-weights neural network is five times more than other algorithms. Variableweights neural network not only provides critical variable-weights thought that could be applied in almost all machine learning methods, but also blazes a new way to apply deep learning methods to aeroengines.

Flow control of double bypass variable cycle engine in modal transition

To study the change mechanism and the control of the variable cycle engine in the process of modal transition,a variable cycle engine model based on component level characteristics is established.The two-dimensional CFD technology is used to simulate the influence of mode selection valve rotation on the engine flow field,which improves the accuracy of the model.Furthermore,the constant flow control plan is proposed in the modal transition process to reduce the engine installed drag.The constant flow control plan adopts the augmentation linear quadratic regulator control method.Simulation results indicate that the control method is able to effectively control the bypass ratio and demand flow of the variable cycle engine,and make the engine transform smoothly,which ensures the stable operation of the engine in modal transition and the constant demand flow of the engine.