Damping Characteristic Analysis and Optimization of Wind-thermal-bundled Power Transmission by LCC-HVDC Systems

With the rapid development of renewable energy,wind-thermal-bundled power transmission by line-commutated converter based high-voltage direct current(LCC-HVDC)systems has been widely developed.The dynamic interaction mechanisms among permanent magnet synchronous generators(PMSGs),synchronous generators(SGs),and LCC-HVDC system become complex.To deal with this issue,a path analysis method(PAM)is proposed to study the dynamic interaction mechanism,and the damping reconstruction is used to analyze the damping characteristic of the system.First,based on the modular modeling,linearized models for the PMSG subsystem,the LCC-HVDC subsystem,and the SG subsystem are established.Second,based on the closed-loop transfer function diagram of the system,the disturbance transfer path and coupling relationship among subsystems are analyzed by the PAM,and the damping characteristic analysis of the SG-dominated oscillation mode is studied based on the damping reconstruction.Compared with the PAM,the small-signal model of the system is obtained and eigenvalue analysis results are presented.Then,the effect of the control parameters on the damping characteristic is analyzed and the conclusions are verified by time-domain simulations.Finally,the penalty functions of the oscillation modes and decay modes are taken as the objective function,and an optimization strategy based on the Monte Carlo method is proposed to solve the parameter optimization problem.Numerical simulation results are presented to validate the effectiveness of the proposed strategy.

Analysis and Research on Aerodynamic Characteristics of Quad Tilt Rotor Aircraft

For the quad tilt rotor aircraft, a computational fluid dynamics method based on multiple reference frames (MRF) was used to analyze the influence of aerodynamic layout parameters on the aerodynamic characteristics of the quad tilt rotor aircraft. Firstly, a numerical simulation method for the interference flow field of the quad tilt rotor aircraft is established. Based on this method, the aerodynamic characteristics of isolated rotors, rotor combinations at different lateral positions on the wing, and rotor rotation directions under different inflow velocities were calculated and analyzed, in order to grasp their aerodynamic interference laws and provide reference for the design and control theory research of such aircraft.

Detection and characteristics analysis of the western subarctic front using the high-resolution SST product

Oceanic front plays a significant role in the ocean vertical mixing and the regulation of air-sea interaction,among others.The western branch of the subarctic front(WSAF)located in the Northwest Pacific has attained lots of attention given its strong intensity and widespread influence on this region.In this study,we take advantage of the merged sea surface temperature(SST)at a high spatial resolution of 0.05°to investigate the characteristics of WSAF.The front detection algorithm that combines the Sobel operator and histogram analysis is adopted.It is advantageous in both preserving the front intensity represented by the SST gradient as well as reducing the detection noise level.We systematically applied this algorithm to the daily SST products for front detection,based on which the WSAF characteristics including its intensity,occurrence of frequency,latitudinal position and coverage area are then extracted.WSAF is mostly located within a small latitude range between 40°N and 41°N with a clear seasonal trend in its intensity that peaks in the winter and troughs in the summer.The seasonal variation of WSAF intensity is almost consistent throughout the temporal period of interest from 2010 to 2018.Similar seasonality is observed for its occurrence of frequency with the winter-summer contrast reaching up to5%.The findings presented here shall help better interpret the WSAF characteristics in the long-term run as well as their impact on the regional weather and climate patterns at high spatial resolution.

Analysis on Climatic Characteristics of High Temperature Weather in Longdong Region

Using meteorological data from 8 national basic meteorological observation stations in Qingyang City of Longdong region from 1972 to 2021,the causes and change characteristics of high-temperature weather were analyzed,and targeted countermeasures and suggestions were proposed for residents' production,life,and energy security supply affected by high-temperature weather.The results showed that①affected by global warming,the annual average temperature,annual average maximum temperature,annual extreme maximum temperature,days of daily maximum temperature≥30℃,and days of daily maximum temperature≥35℃in Longdong region were all showing an upward trend;②due to the different terrain and soil properties of the underlying surface,the increase in high temperature weather varied in different regions.Due to the influence of desert and hilly terrain,the frequency and days of high temperature occurrence were relatively high in the central and northern parts of Qingyang City.Due to the climate regulation of the Ziwuling Mountains,the days of high temperature in the central and southern parts was significantly less than that in the central and northern parts;③if the warm high pressure ridge on the Qinghai-Tibet Plateau developed strongly in summer,the temperature of the closed warm center reached 0-4℃on the 500 hPa of high-altitude weather map.If the warm air mass developed eastward,it often led to sustained high temperature weather in Longdong region;④when the El Nino phenomenon occurred,the subtropical high in the western Pacific developed strongly in summer,with a center located northward,which was stable,with little movement.It was dry,sunny,hot,and rainless in Longdong region,and the high temperature weather was more significant than that in normal years.

Short-time maritime target detection based on polarization scattering characteristics

In this paper,a detection method combining Cameron decomposition based on polarization scattering characteristics in sea clutter background is proposed.Firstly,the Cameron decomposition is exploited to fuse the radar echoes of full polarization channels at the data level.Due to the artificial material structure on the surface of the target,it can be shown that the non-reciprocity of the target cell is stronger than that of the clutter cell.Then,based on the analysis of the decomposition results,a new feature with scattering geometry characteristics in polarization domain,denoted as Cameron polarization decomposition scattering weight(CPD-SW),is extracted as the test statistic,which can achieve more detailed descriptions of the clutter scattering characteristics utilizing the difference between their scattering types.Finally,the superiority of the proposed CPD-SW detector over traditional detectors in improving detection performance is verified by the IPIX measured dataset,which has strong stability under short-time observation in threshold detection and can also improve the separability of feature space zin anomaly detection.

Characteristic analysis and design of near moon abort trajectory for manned lunar landing mission

The safety of astronauts would be severely threatened if the lunar-landing spacecraft were under an emergency during the near moon phase of flight, which was far from the Earth. For the problem of mission abort caused by the main engine (service propulsion system, SPS) failure during lunar orbit insertion, firstly, the family of trajectories resulted from SPS premature shutdown and corresponding abort trajectories were analyzed; then an algorithm that can be applied to the near moon abort trajectories was proposed using patched-conic technique. The characteristics of the abort trajectory, such as energy consumption and return time of flight, were analyzed and presented. Finally, simulation examples were given to demonstrate various cases of near moon SPS failure. The results of the simulation have validated the approach proposed.

Characteristic analysis of a Smith–Purcell terahertz source

We investigate a novel Smith–Purcell terahertz source. This device is composed of an electron gun, a cylindrical resonator, a metallic grating, and a collector. The characteristics of the Smith–Purcell terahertz source are discussed with the help of three-dimensional particle-in-cell simulation. In this device, coherent and high-power Smith–Purcell radiation(SPR) at the terahertz frequency range can be produced for the reasonable parameters of charge energy and grating. Our results indicate that coherent SPR at 506.529 GHz with a power around 1000 W can be obtained for a grating of period l=0.3 mm operating at the beam energy E=50 keV and beam current I=10 A.

Dynamics Response and Non⁃linear Characteristics Analysis of Complex Planar 2⁃DOF Mechanism with Revolute Clearances

There are clearances in mechanism because of manufacture and assembly error,which reduces operation life and working accuracy of mechanism and has a great impact on dynamical responses.At the moment,research in this area mainly focuses on single degree⁃of⁃freedom mechanism considering one clearance,while research of multi⁃DOF mechanism considering multi⁃clearance is less.With the purpose of studying the dynamical characteristics of complex multi⁃DOF mechanism with multi⁃clearances,a dynamic model was developed.The dynamic responses of 2⁃DOF mechanism with two clearances under different positions,values,and numbers of clearance were analyzed.The displacement,velocity,acceleration,collision force,and the axis trajectory at clearance were then given.In addition,there is a limited amount of literature on chaotic phenomena,which mainly focuses on the chaotic phenomena of end⁃effector of mechanism.But in this paper,the non⁃linear characteristics were analyzed by chaotic phenomenon of clearance joint,then chaotic phenomenon was identified by Poincarémappings and phase diagrams.Bifurcation diagrams were given.The results will offer a reliable technical support for the study of dynamical responses of planar mechanisms and the analysis of chaotic phenomena.

Analysis on the Characteristics of Rainstorm in Hanbin District of Ankang City during 1961-2003

[Objective] The research aimed to analyze the rainstorm characteristics in Hanbin District of Ankang City in 43 years. [Method] By using the daily and hourly precipitation data in Hanbin District of Ankang City during 1961-2003, the occurrence rule and variation characteristics of rainstorm weather in 43 years in the zone were analyzed. [Result] The distribution of rainstorm days in Hanbin District of Ankang City had the obvious season characteristic. The earliest rainstorm days occurred in May and started to increase in June. It frequently happened in July, August and gradually decreased in September. The latest rainstorm finished in the middle ten-day of October. The storm rainfall and days in Hanbin District of Ankang City during 1961-2003 both presented the obvious linear increase trend. From the 1970s to the end of 1980s, it was the period when the storm rainfall was more. The rainstorm days during the 1960s-early 1970s and early 1990s were fewer. The rainstorm days were more from the metaphase of 1970s to late 1980s and after the metaphase of 1990s. The time distribution characteristic of hourly precipitation in the rainstorm days was obvious and based mainly on the single peak type. The time mainly concentrated in the daytime, and the short-time strong precipitation was more. [Conclusion] The research provided the reference basis for accurately forecasting the rainstorm occurrence, disaster prevention and reduction work.

Analysis on the Change Characteristics of Climate in Suizhong in Recent 55 Years

[Objective] The research aimed to study the variation characteristics of climate in Suizhong in recent 55 years.[Method] Based on the meteorological observation data (temperature,sunshine,precipitation,etc.) in Suizhong County during 1956-2010,the variation trend,the time and stability which stably passed one threshold of meteorological factors were analyzed by using the linear regression,five-day sliding average and deviation coefficient.The change characteristics of climate in Suizhong County in recent 55 years were grasped.[Result] In recent 55 years,the temperature in Suizhong presented the rise trend.In recent 25 years (1986-2010),the temperature rise was obvious.The rise ranges of winter average temperature and average minimum temperature were big.Moreover,the variation range was big,and the stability was bad.The variation trends of frost-free period and ≥10 ℃ accumulated temperature were basically consistent with that of temperature.The sunshine hours overall presented the decline trend,which wasn't obvious.It presented the rise trend in winter half year and the decline trend in summer half year.The decline trend in summer was obvious.The rainfall overall presented the decline trend.Spring precipitation presented the rise trend.The precipitation in summer and autumn presented the decline trend.The variation range of precipitation in winter was big,and the stability was bad.The variation range of precipitation in summer was small,and the stability was good.[Conclusion] The research provided the basis for management department understanding and grasping the variation characteristics of local climate,disaster prevention and reduction.

Quantitative Characteristics Analysis of FY4A Satellite Products during a Thunderstorm Weather Process

Based on the lightning monitoring and FY4A satellite data in 12 periods during a thunderstorm,the relationship between lightning activity and four satellite digital products:blackbody radiation brightness temperature(TBB),cloud top temperature(CTT),cloud top height(CTH)and cloud top pressure(CTP)was quantitatively analyzed.The following conclusions were obtained:(1)at lightning location,90.5%of TBB values were less than 214.1 K;88.5%of CTT values were less than 207.7 K;88.5%of CTP values were less than 137.7 hPa,and 88.5%of CTH values were greater than 14872 m.At location without lightning,92.5%of TBB values were greater than 214.1 K;90.4%of CTT values were greater than 207.7 K;89%of CTP values were greater than 137.7 hPa,and 92%of CTH values were less than 14872 m.(2)Lightning activity was concentrated in the cloud area with TBB between 190-210 K,CTT between 185-210 K,CTP between 50-150 hPa and CTH between 12-18 km.Lightning intensity was roughly positively correlated with TBB,CTT and CTP,and negatively correlated with CTH.With the increase of CTH,lightning intensity decreased.(3)TBB,CTT,CTP and CTH can well indicate the location and activity frequency of lightning in thunderstorm weather.

Nonlinear dynamic characteristic analysis of speech for Chinese

Nonlinear dynamic method is used in studying Chinese spoken in normal speed, and the improved correlation dimension algorithm are made for the characterization of speech signal. The reconstructed phase space and correlation dimension curves of unvoiced fricative consonants and vowels are also given. It is found that the correlation dimension algorithm can distinguish fricative from vowel because of the different mechanism between them. And the study shows that it can provide information for distinguishing four basic tones in mandarin.

Dynamic impact experiment and response characteristics analysis for 1:2 reduced-scale model of hydraulic support

It is significant to research the impact resistance properties of hydraulic support due to its key support role in the fully mechanized mining face.However,it is difficult for the entire hydraulic support to implement the impact experiment underground and analyze the response characteristic.Therefore,a dynamic impact experiment for the entire hydraulic support was proposed in this paper,where a 1:2 reducedscale model of hydraulic support was designed and its response characteristics under dynamic impact load were analyzed.Firstly,a comprehensive monitoring scheme was proposed to achieve an effective monitoring for dynamic response of hydraulic support.Secondly,a multi-scale impact experiment was carried out for the entire hydraulic support and dynamic behaviors of hydraulic support under the multi-scale impact load were revealed by experimental data.Then a dynamic impact experiment of the entire hydraulic support was simulated in ADAMS with the same experiment conditions,and the experimental and simulation data were verified mutually.Finally,the characteristics of energy conversion and dissipation of the entire experiment system after impact were analyzed.The experiment results showed that the impact resistance properties of hydraulic support largely depended on the initial support conditions and different vertical rigidities affected energy distribution proportion of the entire support system.

Characteristic mode analysis of wideband high-gain and low-profile metasurface antenna

A wideband high-gain and low-profile metasurface antenna is proposed by analyzing characteristic quantities and parameters in the characteristic modes(CMs). The detailed modal current and modal weighting coefficient are analyzed to explain the broadband operation and high gain. A dominant characteristic mode is well excited, leading to a broadband operation. The mode behaviors of the excitation are changed to suppress the unwanted higher-order modes and improve the radiation performance by changing the widths of two patches. The measured impedance bandwidth for-10 dB is 39.8%(5.3 GHz–7.94 GHz) with a gain of 7.8 dBi–10.04 dBi over the operating bandwidth.

A quasi-isentropic model of a cylinder driven by aluminized explosives based on characteristic line analysis

A quasi-isentropic study on the process of driving a cylinder with aluminized explosives was carried out to examine the influence of the aluminum(Al) reaction rate on cylinder expansion and the physical parameters of the detonation products. Based on the proposed quasi-isentropic hypothesis and relevant isentropic theories, the characteristic lines of aluminized explosives driving a cylinder were analyzed,and a quasi-isentropic model was established. This model includes the variation of the cylinder wall velocity and the physical parameters of the detonation products with the Al reaction degree. Using previously reported experimental results, the quasi-isentropic model was verified to be applicative and accurate. This model was used to calculate the physical parameters for cylinder experiments with aluminized cyclotrimethylenetrinitramine explosives with 15.0 % and 30.0 % Al content. The results show that this quasi-isentropic model can be used not only to calculate the cylinder expansion rule or Al reaction degree, but also to calculate the physical parameters of the detonation products in the process of cylinder expansion. For explosives with 15.0 % and 30.0 % Al, 24.3 % and 18.5 % of the Al was found to have reacted at 33.9 μs and 34.0 μs, respectively. The difference in Al content results in different reaction intensity, occurrence time, and duration of two forms of reaction(diffusion and kinetic) between the Al powder and the detonation products;the post-detonation burning reaction between the Al powder and the detonation products prolongs the positive pressure action time, resulting in a continuous rise in temperature after detonation.

Analysis of the VWP Product Characteristics in One Strong Rainstorm Process

[Objective] The aim was to study the characteristics in VWP period characteristics in one strong rainstorm process.[Method] Based on the previous studies,the VWP product characteristics in early period of strong rainstorm,during the development and the end period in Hunan Province on April 8,2008 were studied.[Result] Before the occurrence of rainstorm,the destruction of low layer "ND" layer indicated the increase of water vapor content layer.The intrusion of cold and dry air in the middle layer led to unstable layer;during the maintaining period of rainstorm,the strong vertical shear in the low layer led to the occurrence of strong rainstorm.The cold air in the boundary layer penetrated and led the rainstorm to the most prevailing stage.There was hailstorm on the ground.Before the disappearance of rainstorm(after 17:59),the entire wind field changed into consecutive "ND" layer and it suggested that the strong convective cloud was far away from the location of radar,and indicated the end of rainstorm.[Conclusion] The study provided reference and basis for the pre-warning of rainstorm for temporary reporter.

Study on the Variation Characteristic of Precipitation in Liaoning Province in Recent 48 Years

[Objective] The aim was to study the variation characteristic of precipitation in Liaoning Province in recent 48 years. [Method] According to monthly precipitation data from meteorological observation station in Liaoning Province from 1961 to 2008, the variation characteristic of precipitation in Liaoning was analyzed by means of one-dimensional linear estimation, 5-year moving average and wavelet transform method in our paper. [Result] Annual mean precipitation in Liaoning from 1961 to 2008 showed decrease trend on the whole, and there was great difference in variation in each season; there was more rainfall in 1960s, 1970s and 1990s and less rainfall in 1980s; spring precipitation showed increase trend on the whole, with great annual variation, while precipitation in other seasons reduced; the main fluctuation period of precipitation was 7-9 years which included the shorter variation period of 2-3 years. [Conclusion] The study could provide scientific references for the rational utilization of water resources, disaster prevention and reduction in Liaoning Province.

The Analysis on the Temporal and Spatial Variation of Strong Precipitation Caused Flood and Agricultural Disaster Loss in Huaihe River Basin of Anhui Province during Meiyu Period of 2007

[Objective] The research aimed to analyze temporal and spatial variation of strong precipitation caused flood and agricultural disaster loss in Huaihe River basin of Anhui Province during Meiyu period of 2007.[Method] On the basis of rainfalls of each station in Huaihe River basin of Anhui,rainfall data during Meiyu period of 2007 and flood disaster data in the same period,the temporal and spatial distribution characteristics of strong precipitation caused flood during Meiyu period of 2007 and its harm on agriculture were analyzed.The variation rule,distribution characteristics of strong precipitation during Meiyu period in Huaihe River basin of Anhui and its relationship with agricultural disaster loss were discussed.[Result] During Meiyu period of 2007 in Huaihe River basin of Anhui,the rainstorm was more,and the rainfall was large.The precipitation variation showed "three-peak" trend.Rainfall in Huaihe River basin during Meiyu period of 2007 was greatly more than that homochronously in Yangtze River basin.The rain area over 400.0 mm during Meiyu period mainly located in Huaihe River basin,and the rain area over 600.0 mm mainly located from area along Huaihe River to central Huaibei.The rainfall during Meiyu period gradually decreased toward south and north by the north bank of Huaihe River as the symmetry axis.The rainfall in area along Huaihe River showed wavy distribution in east-west direction.The flood disaster loss index and disaster area of crops in Huaihe River basin of Anhui both increased as rainfall in Meiyu period.[Conclusion] The research provided theoretical basis for flood prevention,disaster reduction and agricultural flood-avoiding development in Huaihe River basin.

PRELIMINARY ANALYSIS OF EFFECTS OF OLR FIELDS ON ANNUAL FREQUENCY OF TROPICAL CYCLONE IN FUJIAN

Outgoing Longwave Radiation (OLR) has been shown to play an important role in climatic diagnosis and long-term prediction and research. With the OLR data 1974 ~ 1997 as observed by satellites, the characteristics are computed. The results are used to depict the location and intensity of the subtropical high in the study of the relationship between the annual frequency of tropical cyclones affecting the Fujian province and ITCZ / subtropical high. It is shown that in years of fewer (more) tropical cyclones, the ITCZ is southward (northward) located with weaker (stronger) intensity, and the subtropical high is southward (northward). As shown in the relationship between the anomalous years of tropical cyclones and characteristics of preceding OLR fields, the OLR anomalies are just oppositely distributed in the Pacific Ocean for years of more (fewer) tropical cyclones. In other words, the years of fewer (more) tropical cyclones are associated with positive anomalies of OLR in the tropical west Pacific but negative (positive) anomalies in the equatorial central and eastern Pacific. It is hoped that our study be setting foundation for short-term climatological prediction of tropical cyclones.