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Atmospheric turbulence is an intrinsic factor that causes uncertainty of wind speed and its power generation by wind turbine. The research of atmospheric turbulence characteristics of wind farms can be used to reduce this uncertainty. In this paper, enough measurement data getting from actual wind farms is used for information processing to quantitatively analyze the daily variation of wind speed and its power output characteristics. Furthermore, the concept of spatiotemporal diurnal modulation characteristics of atmospheric turbulence is proposed with a global scope, which is an intrinsic property of wind. Besides the daily variation characteristics, the average hourly wind speed has a short-term modulation effect on its turbulence and provides a modulation characteristic on wind speed uncertainty. Moreover, the long-term modulation process is affected by seasonal and regional factors, indicating that it has spatiotemporal characteristics. This atmospheric turbulence characteristic has similar effects on characteristic description parameters. However, the characteristics description parameters of wind speed and wind power variation fail to reflect such intrinsic characteristics that are not affected by the spatiotemporal diurnal modulation characteristics of atmospheric turbulence. This indicates that they do not have diurnal characteristics. Finally, a time-varying model combined with the spatiotemporal diurnal modulation characteristics of wind speed and its power generation is discussed by applying on the evaluation of frequency control in power systems. It is shown that the results obtained by measured data processing could improve the power generation quality of large-scale wind power effectively.

More wind and solar power will be integrated into future power systems in China. Assessing the complementarity of wind and solar resources helps to mitigate the fluctuation of renewable power output effectively. This study comprehensively assesses the complementarity of wind and solar resources over China based on MERRA-2 reanalysis dataset. The results show that the complementarity between two resources and that between different regions for a single resource are significantly affected by the time scales. The complementarity between wind and PV power plants is superior to that between wind or solar power plants in different regions. Furthermore, the complementarity between wind and PV power can be further improved by dispersing the locations of wind farms, especially when the PV power is significantly positively correlated with wind power at the same location. However, dispersing the locations of PV plants may not work since the diurnal and seasonal solar radiation are highly similar in different regions. Extreme value analysis is employed to assess the benefits obtained from the wind-solar complementarity. The duration of no power output and the hourly negative fluctuation in power output are significantly reduced due to the complementarity.

Turbulence intensity of wind speed is a viable uncertainty quantification for wind speed. This paper develops an innovative framework for multi-step wind speed prediction using Wind Speed and Turbulence Intensity-based Recursive Neural Network. In this study, real-time turbulence intensity is measured from actual wind speed, and multi-resolution features of wind speed and turbulence intensity are deployed as input for prediction model. Ensemble recursive neural network is designed to execute prediction on multiple prediction intervals ranging from 10 min to 12 h with two different integrating strategies. Experimental results indicate that: (1) The proposed model dramatically outperforms conventional machine learning models on multi-step wind speed prediction; (2) The reliable wind speed prediction requires that the maximum time-resolution of turbulence intensity should be longer than prediction interval; (3) Turbulence intensity features involved prediction will achieves higher accuracy than the approaches that apply signal processing on raw wind speed, especially on middle-long term prediction. Therefore, this innovative scheme for multi-step wind speed prediction can be of immense utility to apply data-driven methods for accurate long-term wind speed prediction.

The assessment of wind resource is the basis of wind power utilization. An accurate and comprehensive characterization of wind resource is of vital importance to site planning, wind turbine selecti ...

The wind power ramp event includes large fluctuations in wind power within a short period of time. To maintain grid stability, defining, identifying, and predicting the wind power ramp event is inevitable. Therefore, a comprehensive assessment method of wind power ramp events that combines the generalized information of the source, grid, and load sides is proposed. In this method, we put forward a channel self-selected multi-layer coefficient correction model (CSMCC) and wind power ramp threshold, according to the allowable value of a grid frequency change. Additionally, the availability of data-driven modeling methods is verified by performing autocorrelation analysis. Finally, the comprehensive evaluation method, which combines the back propagation (BP) neural network, supports the vector machine and CSMCC model is proved to be effective. This paper has a certain reference significance for basic research on large-scale wind power safety and efficient utilization.

Wind speed turbulence intensity is crucial for wind turbine structure design and aerodynamic loads calculation. In the study, the actual turbulence intensity observations are compared with the Normal Turbulence Model defined by IEC standard. The results show that the Normal Turbulence Model overestimates the turbulence intensity. A new turbulence intensity model is proposed based on the actual observations, which shows better performance than the Normal Turbulence Model. Then the variation pattern of turbulence intensity during a day is analyzed. The turbulence intensity exhibits obvious daily periodicity in two wind farms. Furthermore, the causes of daily periodicity are discussed and verified by the wind speed dataset 3. Finally, an improved time-varying turbulence intensity model is developed according to the daily periodicity.

The sufficient actual big data analysis shows that wind speed has multi-scale amplitude & frequency modulation characteristics. There is an evident amplitude modulation effect between the average wind speed and the turbulence variance, and the modulation effect is also found with multi-scale characteristic. The turbulence intensity decreases with the wind speed in a certain range. However, when the wind speed is great in a certain degree, the turbulence intensity almost keeps stable. Simultaneously, both the average wind speed and the center frequency also have the multi-scale modulation effect. The center frequency increases with the wind speed in a certain range. However, when the wind speed is great in a certain degree, the center frequency almost keeps stable. The key discussion was given for this multi-scale amplitude and frequency modulation characteristic resulting from the cascade effect of turbulent energy transport. And the instantaneous model of wind speed and wind power is presented for its great significance of power system's real-time dispatch and optimization control.

As wind power provides an increasingly larger share of electricity supply, the challenges caused by wind power intermittency have become more and more prominent. A better understanding of wind powe ...

The uncertainty is a significant characteristic of wind speed in wind engineering field. Especially, it has brought much more problems to the grid in safe and efficient utilization of large scale wind power. And there is urgent need of systematic and perfect models that can describe windspeed uncertainty in grid scheduling and controlling. In this paper, a universal power-law model is proposed for properly depicting the uncertainty of both wind speed and wind power. According to the turbulence nature of wind uncertainty, the uncertainty model of wind speed is firstly obtained by using wavelet multi-scale transform algorithm for its tight supporting characteristic, which is more reasonable than the traditional algorithm of getting the mean valve and the variance valve of the time series. And the turbulent intensity model is further improved by a power-law model, which is suitable for much more kinds of turbulence on complex geographical conditions than that proposed in current international IEC standard with the sufficient actual data. In physically speaking, the model improvement with three parameters is consistent with turbulence development mechanism. Moreover, the uncertainty modeling method of wind power is developed based on the universal power-law model, which is not only suitable for the power of single wind turbine, but also suitable for the power of whole wind farm. It’s very importance that the wind speed uncertainty model is extended to model the power uncertainty of wind turbine and farm, in especial its or their power output is usually limited for human adjustment control. It has a certain significance to the real-time dispatch and optimal control of the renewable energy power system.

Variability and intermittency are the intrinsic nature of wind and solar resources. Expanded wind and solar power development in China requires a deeper understanding of their differences in variability and intermittency, both spatially and temporally. To address this issue, this study provides a systematic quantitative comparison of the variability and intermittency between wind and solar resources across China. Compared with wind resources, solar resources show regular spatial patterns and highly similar temporal characteristics. Solar resources usually have larger daily variation amplitudes (1.0–3.5 times) and are more intermittent (1.0–10.0 times) than wind resources in most regions. Solar resources fluctuate 1.0–8.0 times faster than wind resources in western Xinjiang, most of central and southern China, and north and east of northeast China. However, the variation rate of solar resources is approximately 0.1–0.5 times the wind resources in the Qinghai–Tibet plateau and East China Sea. In general, wind and solar resources fluctuate faster and are more intermittent in spring and autumn. Onshore wind resources are more variable and intermittent in the periods of 6:00–12:00 and 16:00–22:00. However, the variability and intermittency of offshore wind resources are weak and have very small intra-day changes compared with onshore wind resources. Solar resources are usually more variable and intermittent during the periods of 2–4 h after sunrise and 2–4 h before sunset. Furthermore, the intra-day changes in the variability and intermittency of solar resources are significantly greater than the inter-month changes. Those quantitative insights contribute to better and more efficiently mitigate the variability and intermittency of wind and solar resources.

Environmental issues and the prospect of an energy crisis inspire humans to exploit wind power. However, with the increase of wind power penetration level, operating power systems securely and reliably is a serious challenge due to the inherent nature of wind power intermittency. Wind power intermittency has been the major barrier for large scale wind power integration. This paper reviews past research on wind power intermittency, including its impacts on power system, how it is measured, and mitigation solutions. It has been found that as wind power integration increase, the system reverses and costs consequently increase, while the system reliability and CO2 reductions decrease. In order to mitigate wind power intermittency, studies on intermittency measurements and mitigation solutions are necessary. Existing measurements of wind power intermittency are summarized firstly. Considering the limitations of existing methods, new definitions and metrics are proposed based on our study. Then, various wind power intermittency mitigation solutions are comprehensively reviewed, including wind farms, generation-side, demand-side and energy storage. In the final part of this paper, the further work on wind power intermittency is discussed in detail. In summary, wind power intermittency can be effectively mitigated using various technological and managerial approaches based on an in-depth understanding of intermittency.

Developing the description and gaining an understanding of wind characteristics are important research tasks in wind engineering. Intermittency is one of the most important characteristics of wind. However, little literature is available on its quantitative measurement. In this study, wind speed intermittency is defined from the perspective of the physical nature of wind. According to this definition, the duty ratio of wind speed ramp (DRWSR) is proposed to quantitatively measure wind speed intermittency. Based on the measurement of wind speed intermittency, quantitative insights into intermittency can be obtained by analyzing the time series of the DRWSR, e.g., the intensity and variation pattern of wind speed intermittency in a day, which contributes to better understanding of wind characteristics.

Fluctuations of wind-power production are a significant hindrance to its high penetration in power systems. System operators have to provide complementary power and relevant control strategies to smooth out the fluctuations when large-scale wind power ones is injected into the grid. To better smooth the fluctuations, the change rate of the wind speed is a critical piece of information. In this study, the variogram function is introduced to measure the change rate of the wind speed. Based on the variogram time-series, some statistical analyses are conducted. These results contribute to a better understanding of the characteristics of the change rate of the wind speed, such as the chronological variation pattern of the change rate on a day, whether the future change rate can be forecasted, and whether there is a relationship between the change rate and wind speed.

Wind power is widely used as a type of clean and renewable energy source in recent years. However, large-scale wind power penetration brings lots of challenges due to the uncertainty of wind speed. As a result, the research of wind speed uncertainty plays an important role in large scale wind power integration. In this paper, the multi-scale amplitude modulation effect of wind speed random fluctuation is found based on actual wind speed data. And the physical mechanism of multi-scale characteristics are presented from the perspective of turbulence. This research has both certain physical academic meaning and engineering application value in wind speed uncertainty research.

Accurate prediction of ultra-short-term wind speed is important in many applications. Because of the different patterns of wind speed, researchers have indicated that a multi-scale prediction method based on wavelet algorithms could improve forecasting. However, traditional multi-scale methods that directly synthetize results of different-scale components may reduce forecasting accuracy because of error accumulation. In this paper, a multi-scale synthesis strategy that takes into account the predictability of different scales is proposed. As the correlation length of each frequency sub-series is different, prediction models are constructed for each frequency sub-series using different numbers of prediction steps. Finally, based on two wind farms in different regions of China and different basic forecast models, eight experiments are performed using real-world wind speed data. Experimental results show that the proposed multi-scale synthesis method has better performance than traditional multi-scale forecasting methods that use direct synthetizing strategies, indicating its utility in wind engineering applications.

Wan, J.; Yao, K.; Ren, G.R.; Cao, Y.; Wang, W.; Zhao, X.X., and Yu, J.L., 2020. Coastal wind speed's multi-parameter forecasting based on quantitative measurement of its predictability. In: Bai, X. and Zhou, H. (eds.), Advances in Water Resources, Environmental Protection, and Sustainable Development. Journal of Coastal Research, Special Issue No. 115, pp. 662-665. Coconut Creek (Florida), ISSN 0749-0208.Wind speed prediction has important significance and value to coastal wind power. And the statistical model based on historical data is one of the most common prediction methods, which has made great progress for hourly mean wind speed forecasting with almost no consideration of predictability. In this paper, the correlation analysis was introduced to analyze the optimal wind speed predictable length based on the non-stationarity analysis of wind speed time series. The experimental results based on a large number of measured wind speed data shown that there exists a specific correlation length for the nonlinear wind speed time series. With the increasing of the correlation length, the prediction error gradually decreased and then increased. Thus, the correlation length corresponding to the turning point could be recognized as the optimal predictable length. Therefore, correlation analysis could be used to measure the predictability of wind speed. Based on the results, the quantitative measurement and prediction strategy with multiple characterization parameters of wind speed uncertainty is also presented. And the SVR and DBN algorithms are selected for several tests to verify that this multi-parameter forecasting method is feasible in practice.

China has different topographic conditions and multiple weather systems due to its vast geographic areas. As a result, the geographic diversity between different provinces is potential to mitigate wind power variability. This study analyzes the spatial and temporal correlations of wind power on the province level. The results show that a lower correlation is observed for greater distances and smaller time scales. Correlation between different provinces is stronger than that between different wind farms within the same distance. The correlation coefficient of wind power decays more rapidly in China than in Europe and North America within the same distance. The correlation coefficients of wind power variation are generally smaller than the correlation coefficients of instantaneous wind power, and a positive linear relationship is observed between these coefficients. The temporal correlations of wind power between different provinces are analyzed as well. The time lags of wind power between different province pairs are obtained.

Turbulent wind speed is a vital component of wind speed, corresponding to the small-scale uncertainty of wind speed. The wind power output and aerodynamic loads are significantly influenced by turbulent wind speed. The present paper concentrates on the study of turbulent wind speed prediction, which is hardly addressed in previous studies and is a novel approach to understand turbulent wind speed in advance. In the present study, turbulent wind speed is measured by turbulence standard deviation. Although turbulent wind speed itself is unpredictable, the correlation analysis proves that the turbulence standard deviation is predictable within a proper time horizon. As a result, the turbulent wind speed can be understood ahead of time by predicting turbulence standard deviation. The 10-min ahead, 30-min ahead and 60-min ahead predictions of turbulence standard deviation are provided by Support Vector Regression and Kernel Ridge Regression. Furthermore, the average wind speed is fused into the forecasting model to improve the prediction accuracy of turbulence standard deviation.

As large scale integration of wind power generation into grid, the fluctuation of wind power must be stabilized with fast response complementary power source such as gas and oil power generation. However entire power system is dominated by thermal power plant in China, moreover the proportion of heating units is more and more high. Therefore, expanding the peak regulating capacity of heating units to take in wind power on a large-scale is an inevitable choice. This research proposed the heat load and wind power forecast approach, meanwhile, the analysis strategy of forecasting uncertainty is also be put forward. Then, a thermal electricity combined (TEC) operation technology, which based on making the best use of the heat transfer and thermal storage characteristics of heating network and electric heating, is proposed in this paper to enhance the utilization of wind power. Final, a practical system block diagram is proposed for practical application.

At present, with the development of wind’s energy application and disaster prevention, the windspeed uncertainty must be estimated because of the existing large gap between the requirement of prediction performance and current techniques owing to it’s strong random fluctuation. In this paper, a new method for windspeed uncertainty estimation is proposed on the base of physical mechanism, the inherent amplitude modulation effect in windspeed. According to the the atmosphere motion power spectrum in low-layers, the actual windspeed is usually decomposed into the hourly average windspeed and the turbulent residual error by many researchers. And the turbulent residual error and the turbulent standard deviation is modulated by the hourly average windspeed. Moreover experiments further show that the confidence interval of windspeed random fluctuation uncertainty based on it’s amplitude modulation effect is more rigorous than that obtained by general statistical model. As a result, this uncertainty estimation method has certain physical academic meaning and engineering application value both in the electric system and the other wind domain.

In order to stabilize the uncertainty of large-scale new energy power’s random fluctuation in the grid, there is an increasing number of large thermal power generating unit needing to do deep variable load operation. However, the pattern of steam inlet on turbine’s part load has a very significant impact on the unit operation condition of safety, stability and economy. In this paper the HP-valve’s body vibration fault of large steam turbines caused by unsteady steam flow under partial arc admission operating at part of their full load is researched, and an economic solution based on analysis and diagnosis of fault mechanism is provided by designing of complex HP-valve opening sequence rules. This solution solves the safety problem of valve vibration and avoids the economic loss by using full arc admission or replacing the valve body equipment directly, which is of great effective and practical verified by units’s actual operating experiment. As a result, it demonstrates that the optimization of HP-valve iadmission mode can not only change the stress state of high pressure rotor and prevent its vibration caused by the force of unbalanced flow to improve the shafting stability of the unit when running with variable load, but also can improve the steam instability and solve the resulting vibration problem in HP-valve. And it is of great engineering practical value to improve high-power thermal power unit depth secure efficient load operation.

In recent years, a novel optical zooming technique has been paid much attention. With the help of optical leveraging effect, it is possible to alter the system focal length dramatically without moving elements involved in by only changing the curvature radius of VCM (variable curvature mirror) slightly. With no doubt, VCM is the key to realize non-moving element optical zooming and it has to provide large enough saggitus variation while still maintaining the high surface figure accuracy to ensure high quality imaging. In our previously published paper, an annular force based VCM has been designed, fabricated and tested. Experiments demonstrate that with the aperture of 100mm and thickness of 2mm, the VCM could generate a large saggitus variation exceeding 30λ (λ=632.8nm). However, the optical quality degrades very fast and this makes such a VCM unsuitable for optical imaging in visible band. Therefore in this manuscript, a multipoint actuation array, which is composed of totally 49 piezoelectric actuators, is embedded into the annular structure to aim to correct the surface figure distortion caused by large saggitus variation. The new structure model has been designed and numerical simulation indicates that the surface figure distortion could be well corrected as long as the degraded surface figure accuracy is better than 1.8λ (λ=632.8nm) (RMS). Based on this, a new prototype VCM is being fabricated and intermediate results are reported here.

In this paper, a new type of lightweight passive deployment mechanism based on the tape spring and the shape memory alloy is presented for the secondary mirror of a deployable space telescope. In this passive deployment mechanism for the secondary mirror, the high elastic potential energy of the folded tape springs is used as driving force when the support structure is extended, and the high stiffness characteristics of the circular arc cross section of the tape spring can be used to achieve structure self-locking after deployment. Then a deployable space telescope combined with lightweight passive deployable mechanism for the secondary mirror is designed for applying to nanosatellite imaging. Furthermore, a lock-release device is designed to achieve the function of locking the folded structure and releasing on orbit by taking advantage of the phase transformation characteristics of shape memory alloy with temperature changing. Finally, the correction method for the deployment error of secondary mirror is discussed. The temperature of the tape springs is controlled respectively to make a required length change. This can achieve the purpose of adjusting the position of the secondary mirror and improve the deployment accuracy.

A Φ600mm SiC primary mirror subsystem of a space-borne Ritchey-Chretien telescope was designed. The open-back primary mirror was made of pressure-less sintering silicon carbide (SiC), light-weighted at a ratio of approximately 70%. Minimizing the optical surface astigmatism was critical for the mirror, the astigmatism is caused mainly by gravity effects, temperature variation and the bonding process. Three invar flexure bipods were fixed on the baseplate of the telescope at first, and the posture of the primary mirror was adjusted precisely for 0.2mm gap to the bipods. 3M 2216 B/A grey adhesive was then injected into the gap between the mirror and bipod flexure, the curing process was last 72 hours in the room temperature. So the mirror was affected only by curing stress of the adhesive during the assembly process. Structural strength and dynamic stiffness of the mirror subsystem in the thermal- structural coupling state were analyzed with finite element method. Analyzed results show that the optical surface distortion is less than 1/50λ at 632.8nm RMS with three points support and less than 1/200λ RMS with 2°C temperature variation because of the flexure support and compatible support and mirror material, The optical performance test with interferometer show that the optical surface distortion caused by the curing stress of the adhesive is less than 1/50λRMS, the overall optical surface of the primary mirror is less than 1/30λ rms, which met the critical requirements for the primary mirror of the telescope.

Cadmium (Cd) is an environmental contaminant showing a variety of deleterious effects, including the potential threat for the ecological environment and human health via food chains. Low molecular weight chitosan (LMWC) has been demonstrated to be an effective antioxidant. Metallothionein (MT) mRNA levels and activities of glutathione-S-transferase (GST), superoxide dismutase (SOD), acid phosphatase (ACP), Na+,K+-ATPase, and Ca2+-ATPase as well as malondialdehyde (MDA) contents in the gills of the freshwater crab Sinopotamon yangtsekiense were analyzed in vivo in order to determine the injury of Cd exposure on the gill tissues as well as the protective effect of LMWC against this injury. The results showed that there was an apparent accumulation of Cd in the gills, which was lessened by the presence of LMWC. Moreover, Cd2+ significantly increased the gill MT mRNA levels, ACP activity and MDA content while decreasing the activities of SOD, GST, Na+,K+-ATPase, and Ca2+-ATPase in the crabs relative to the control. Cotreatment with LMWC reduced the levels of MT mRNA and ACP but raised the activities of GST, Na+,K+-ATPase, and Ca2+-ATPase in gill tissues compared with the crabs exposed to Cd2+ alone. These results suggest that LMWC may exert its protective effect through chelating Cd2+ to form LMWC-Cd2+ complex, elevating the antioxidative activities of GST, Na+,K+-ATPase, and Ca2+-ATPase as well as alleviating the stress pressure on MT and ACP, consequently protecting the cell from the adverse effects of Cd. © 2012 Wiley Periodicals, Inc. Environ Toxicol 29: 298–309, 2014.

The physiological impact of Cd(2+) on Sinopotamon yangtsekiense was evaluated through changes of selected parameters considered as key elements of carbohydrate and protein metabolisms. Crab were exposed to 0.725, 1.45, 2.9mg·L(-1) Cd(2+) for 7, 14 and 21 days. A time- and/or concentration- dependent decrease in muscle glycogen and increase in LDH activity suggested that glycolysis was accelerated during the treatments. Increased protease activity, lowering of FAA and the initially increased and subsequently decreased aminotransferase activities suggest an enhanced protein mobilization during early Cd(2+) exposure followed by a metabolic impairment during late exposure. Decreased hemolymph glucose level was observed in the crabs treated with 2.9mg·L(-1) Cd(2+) for 21d, suggesting an impaired gluconeogenesis. Ammonia level barely changed during the 14d Cd(2+) exposure most likely due to the increased urea and glutamine production; After 1.45 and 2.9mg·L(-1) Cd(2+) treatment for 21d, ammonia was observed increased followed by an exclusive increase in glutamine. Taken together, our results indicate that carbohydrate and protein are mobilized to a varying degree as a compensatory metabolism to response to the energy stress during acute Cd(2+) exposure. As the time lapsed, some symptoms on metabolism obstacle reflect the toxic effect of sublethal Cd(2+).

Cadmium (Cd) has been shown to induce oxidative stress. Low-molecular-weight-chitosan (LMWC) has been demonstrated to exhibit potent antioxidant effects. We investigated the regulation role in Cd²⁺-induced oxidative damage in the hepatopancreas of the freshwater crab Sinopotamon yangtsekiense and the protective effect of LMWC. The results showed that Cd²⁺ significantly increased the hepatopancreatic metallothionein (MT) mRNA levels and protein kinase C (PKC) activity while decreasing the activities of Na⁺,K⁺-ATPase and Ca²⁺-ATPase in crabs relative to the control group. Co-treatment with LMWC suppressed the levels of MT and PKC but raised the activities of Na⁺,K+-ATPase and Ca²⁺-ATPase in hepatopancreatic tissues compared with the crabs exposed to Cd²⁺ alone. We postulate that LMWC may exert its protective effect through regulating the expressions of MT, PKC, Na⁺,K⁺-ATPase and Ca²⁺-ATPase, thereby enhancing antioxidant defense. These observations suggest that LMWC may be beneficial because of its ability to alleviate the Cd²⁺-induced damages to the crabs.

Recently, a new kind of optical zooming technique in which no moving elements are involved has been paid much attention. The elimination of moving elements makes optical zooming suitable for applications which has exacting requirements in space, power cost and system stability. The mobile phone and the space-borne camera are two typical examples. The key to realize non-moving elements optical zooming lies in the introduction of variable curvature mirror (VCM) whose radius of curvature could be changed dynamically. When VCM is about to be used to implement optical zoom imaging, two characteristics should be ensured. First, VCM has to provide large enough saggitus variation in order to obtain a big magnification ratio. Second, after the radius of curvature has been changed, the corresponding surface figure accuracy should still be maintained superior to a threshold level to make the high quality imaging possible. In this manuscript, based on the elasticity theory, the physical model of the annular force based variable curvature mirror is established and numerically analyzed. The results demonstrate that when the annular force is applied at the half-the-aperture position, the actuation force is reduced and a smaller actuation force is required to generate the saggitus variation and thus the maintenance of surface figure accuracy becomes easier during the variation of radius of curvature. Besides that, a prototype VCM, whose diameter and thickness are 100mm and 3mm respectively, have been fabricated and the maximum saggitus variation that could be obtained approaches more than 30 wavelengths. At the same time, the degradation of surface figure accuracy is weakly correlated to the curvature radius variation. Keywords: optical zooming; variable curvature mirror; surface figure accuracy; saggitus

One space-based astronomy telescope will observe astronomy objects whose brightness should be lower than 23th magnitude. To ensure the telescope performance, very low system noise requirements need extreme low CCD operating temperature (lower than -65°C). Because the satellite will be launched in a low earth orbit, inevitable space external heat fluxes will result in a high radiator sink temperature (higher than -65°C). Only passive measures can’t meet the focal plane cooling specification and active cooling technologies must be utilized. Based on detailed analysis on thermal environment of the telescope and thermal characteristics of focal plane assembly (FPA), active cooling system which is based on thermo-electric cooler (TEC) and heat rejection system (HRS) which is based on flexible heat pipe and radiator have been designed. Power consumption of TECs is dependent on the heat pumped requirements and its hot side temperature. Heat rejection capability of HRS is mainly dependent on the radiator size and temperature. To compromise TEC power consumption and the radiator size requirement, thermal design of FPA must be optimized. Parasitic heat loads on the detector is minimized to reduce the heat pumped demands of TECs and its power consumption. Thermal resistance of heat rejection system is minimized to reject the heat dissipation of TECs from the hot side to the radiator efficiently. The size and surface coating of radiator are optimized to compromise heat reject ion requirements and system constraints. Based on above work, transient thermal analysis of FPA is performed. FPA prototype model has been developed and thermal vacuum/balance test has been accomplished. From the test, temperature of key parts and working parameters of TECs in extreme cases have been acquired. Test results show that CCD can be controlled below -65°C and all parts worked well during the test. All of these verified the thermal design of FPA and some lessons will be presented in this paper.

In recent years, how to eliminate moving elements while realizing optical zoom imaging has been paid much attention. Compared with the conventional optical zooming techniques, removing moving elements would bring in many benefits such as reduction in weight, volume and power cost and so on. The key to implement non-moving-element optical zooming lies in the design of variable curvature mirror (VCM). In order to obtain big enough optical magnification, the VCM should be capable of generating a large variation of saggitus. Hence, the mirror material should not be brittle, in other words the corresponding ultimate strength should be high enough to ensure that mirror surface would not be broken during large curvature variation. Besides that, the material should have a not too big Young’s modulus because in this case less force is required to generate a deformation. Among all available materials, for instance SiC, Zerodur and et.al, CFRP (carbon fiber reinforced polymer) satisfies all these requirements and many related research have proven this. In this paper, a CFRP VCM is designed, fabricated and tested. With a diameter of 100mm, a thickness of 2mm and an initial curvature radius of 1740mm, this component could change its curvature radius from 1705mm to 1760mm, which correspond to a saggitus variation of nearly 23μm. The work reported further proves the suitability of CFRP in constructing variable curvature mirror which could generate a large variation of saggitus.

Variable curvature mirror (VCM) is a simplified active optical component being capable of changing its curvature radius. Curvature radius variation within a wide range requires that the VCM should be able to generate a large saggitus variation. Besides that, the surface form accuracy should be maintained above a reasonable level. In this paper, a piezoelectric actuation based prototype VCM is designed, constructed and experimentally tested. The thickness of the K9 plane mirror is only 3mm over the full aperture of 100mm. Six piezoelectric actuators are fixed into a base plate and the head of each actuator is connected to an annular ring through the screw thread. With such a structure, the force provided by each actuator can be transformed to the mirror backside through this annular ring. With each actuator generating the same force, the curvature radius can be changed in a uniform way. At the mean time, the surface form accuracy could be adjusted one point by point to compensation asymmetric modes as well. Mathematical analysis and FEA (finite element analysis) are used together to demonstrate the theoretical correctness. Besides that, the prototype VCM is successfully constructed and experiments have been carried out to give a quantitative assessment on the saggitus variation..

The key to realize non-moving-element optical zooming lies in VCM (variable curvature mirror). In order to obtain a large optical magnification, VCM should be capable of providing a large center deflection and this requires that the mirror material should be robust enough, require less force to deform and have a high ultimate strength. In this paper, CFRP (carbon-fiber-reinforced-polymer) is selected as the mirror material and a prototype VCM has been fabricated. With diameter of 100mm, thickness of 2mm and initial curvature radius of 1740mm, this VCM can provide a center deflection approaching nearly 23um, which proves the feasibility of CFRP in constructing VCM. Compared with the work reported in [Proc. of SPIE, 8725, 87250W, 2013], the center deflection obtained here becomes even larger.

Benefiting from low cost, light weight and reduced volume in launch, deployable optical telescopes will be extensively applied in microsatellites. As a result of manufactured tolerance and external disturbance, the secondary mirror can’t arrive at designed position precisely after a deployable telescope is unfolded. We investigate an adjustment system with six degrees of freedom based on hexapod structure to solve this problem. There are mainly four parts in this paper. Firstly, the adjustment methods of deployable telescopes for microsatellites are introduced. Generally several kinds of optical components can be adjusted to align a deployed telescope: primary mirror, tip/tilt mirror and secondary mirror. Due to its high sensitivity and convenience, the secondary mirror is chosen to collimate the optical system of the telescope. Secondly, an adjustment system with hexapod structure is designed for a secondary mirror with 85 mm diameter. After comparing the characteristics of step motors, piezo actuators and voice coil motors (VCMs), VCMs are selected as the linear actuators. By using optical gratings as displacement sensors in the system, we can make closed-loop control come true. The hexapod structure mainly consists of 6 VCMs, 6 optical gratings and 6 oblique legs with flexible hinges. The secondary mirror adjustment system is 83 mm in diameter and 55 mm high. It has tip/tilt rotational ranges of ±2.205° with resolution of better than ±0.007°, and translational ranges of ±1.545 mm with resolution of better than ±0.966 μm. Thirdly, the maximum stress and the maximum deformation in the adjustment system are computed with finite element method. At last, the kinematics problems of the adjustment system are discussed.

Based on optical zooming used to capture images with variable resolution and field of view (FOV), an all-reflective non-coaxial optical zooming system without moving elements is designed for space camera application. In this prototype design, a deformable mirror (DM) whose curvature radius can be changed is introduced. By carefully selecting the optical power of conventional reflective mirrors surrounding the DM, the overall focal length of the imaging system can be greatly changed with slight variation of curvature radius of DM. The focal length of the system can be changed from 48mm to 192mm and the system performance is approaching diffraction-limited with diverse criteria and the maximum stoke of DM is still within its physical limits at the same time. The experimental results prove the effectiveness of DM based optical zooming and will provide a new routine for new type of space camera design in the future.

Day-ahead prediction of wind speed is a basic and key problem of large-scale wind power penetration. Many current techniques fail to satisfy practical engineering requirements because of wind speed's strong nonlinear features, influenced by many complex factors, and the general model's inability to automatically learn features. It is well recognized that wind speed varies in different patterns. In this paper, we propose a deep feature learning (DFL) approach to wind speed forecasting because of its advantages at both multi-layer feature extraction and unsupervised learning. A deep belief network (DBN) model for regression with an architecture of 144 input and 144 output nodes was constructed using a restricted Boltzmann machine (RBM). Day-ahead prediction experiments were then carried out. By comparing the experimental results, it was found that the prediction errors with respect to both size and stability of a DBN model with only three hidden layers were less than those of the other three typical approaches including support vector regression (SVR), single hidden layer neural networks (SHL-NN), and neural networks with three hidden layers (THL-NN). In addition, the DBN model can learn and obtain complex features of wind speed through its strong nonlinear mapping ability, which effectively improves its prediction precision. In addition, prediction errors are minimized when the number of DBN model's hidden layers reaches a threshold value. Above this number, it is not possible to improve the prediction accuracy by further increasing the number of hidden layers. Thus, the DBN method has a high practical value for wind speed prediction.

A space telescope containing two CCD cameras is being built for scientific observation. The CCD detectors need to operate at a temperature below -65°C in order to avoid unacceptable dark current. This cooling is achieved through detailed thermal design which minimizes the parasitic load to 2K×4K array with 13.5 micron pixels and cools this detector with a combination of thermo electric cooler(TEC). This paper will describe detailed thermal design necessary to maintain the CCD at its cold operating temperature while providing the means to reject the heat generated by the TECs. It will focus on optimized techniques developed to manage parasitic loads including material selection, surface finishes and thermal insulation. The paper will also address analytical techniques developed to characterize TEC performance. Finally, analysis results have been shown the temperature of key parts.