This paper introduces the preparatory work and conducts an integrated review on the maiden voyage of a Chinese commercial ship on the Arctic Northeast Route. It puts forth expectations on the exploitation and utilizat...This paper introduces the preparatory work and conducts an integrated review on the maiden voyage of a Chinese commercial ship on the Arctic Northeast Route. It puts forth expectations on the exploitation and utilization of the Arctic Northeast Route in the aspects of safety, fastness, low costs, low consumption of energy and less pollution, knowledge of maritime law and navigation practice, building seaworthiness ships and making studies on the methods of sailing and maneuvering for navigation in polar waters, training qualified seafarers with navigation experiences in ice waters and establishing a safeguard system for the navigation in this route through the analysis on the weather, temperature, ice condition, route and hydrology encountered in the practice of a Chinese merchant ship in its maiden voyage in the route, and studies on the ice pilotage, convoy by icebreaker, practical condition of communication and navigation equipment in sea areas of high latitude and the economic benefit of the navigation in the Arctic Northeast Route.展开更多
To carry out the deep space exploration tasks near Sun-Earth Libration point L2, the CRTBP dynamic model was built up and the numerical conditional quasi-periodic orbit （Lissajons orbit） was computed near L2. Then, ...To carry out the deep space exploration tasks near Sun-Earth Libration point L2, the CRTBP dynamic model was built up and the numerical conditional quasi-periodic orbit （Lissajons orbit） was computed near L2. Then, a formation controller was designed with linear matrix inequality to overcome the difficuhy of parameter tuning. To meet the demands of formation accuracy and present thruster＇s capability, a threshold scheme was adopted for formation control. Finally, some numerical simulations and analysis were completed to demonstrate the feasibility of the proposed control strategy.展开更多
This paper intends to study Ezra Pound＇s early poetics and his modemist poetry through a close research of the Eastern elements in the shaping process of his poetics and the significance and influence of his poetic t...This paper intends to study Ezra Pound＇s early poetics and his modemist poetry through a close research of the Eastern elements in the shaping process of his poetics and the significance and influence of his poetic thoughts on the American New Poetry Movement. In order to clarify the essence of Pound＇s early poetics under the influence of Chinese classical poems, the paper starts from the discussion of the influence of Cathay （1915） and his translation of Cathay; then it provides a detailed analysis of the relationship between Chinese classical poems and Pound＇s creation; and finally it has given an analysis of ＂In a Station of the Metro＂. Pound absorbed different poetic concepts from all of them and transformed his poetry from the conventional Romanticism to the innovative Modemism. What Pound innovated in the poetry composition is of great importance if the new era wishes to shake off the banality and out-of-date tradition in literature. Pound changed a whole generation of poets and set a good example for those who desire to write in a new way展开更多
To meet the increasing research demand for deep space exploration,especially for the second libration point (L2) conditional periodic orbit (Halo orbit) in the Sun-Earth system,the methods to get analytical Halo orbit...To meet the increasing research demand for deep space exploration,especially for the second libration point (L2) conditional periodic orbit (Halo orbit) in the Sun-Earth system,the methods to get analytical Halo orbit and differential-correction Halo orbit were described firstly,and the corresponding orbits accuracy was analyzed.Then,based on the results of third-order and differential-correction Halo orbits,the formation form was studied.Analysis was carried out to discuss the influence of system amplitude,initial phase,and phase difference on the formation form,as well as that of initial orbit values on form accuracy.Finally,some simulation results demonstrate the validity of the proposed methods.展开更多
Based on the Ricatti technique, the methodology for preventing the limit cycle accomplished by adding a control function to the original equation of wing rock motion is presented in this paper. To analyze the state va...Based on the Ricatti technique, the methodology for preventing the limit cycle accomplished by adding a control function to the original equation of wing rock motion is presented in this paper. To analyze the state variables of the system, the complete set of nonlinear equations of motion including an effective linear control function was solved for A-4D and Mig-21 Aircraft. The roll angle responding to the linear control function for both models was estimated when the systems were tested under different damping ratios. The numerical re- suits show that a linear control function including both the roll attitude and the roll rate is sufficient to suppress the wing rock motion with an acceptable error in desired time. A good agreement between the numerical results and the published work is obtained for the limit cycle oscillation existence at different damping ratios.展开更多
This study makes a comparison between China and foreign countries about the ＂supportive shipping policies＂ in the period of late Qing Dynasty, from 1840 to 1911. After the first opium war, China was forced to open t...This study makes a comparison between China and foreign countries about the ＂supportive shipping policies＂ in the period of late Qing Dynasty, from 1840 to 1911. After the first opium war, China was forced to open the gate of the old oriental country to the world. As more treaty ports opened, the import and export of goods increased the growing trade that brought about the increased demands of shipping transportation. In the same period, British, France, America, Germany and Japan governing bodies instated various kinds of laws, regulations and other policies encouraging their national shipping companies to grab shipping market share. As a result, foreign steamship companies monopolized Chinese shipping market quickly. Faced with this situation, in 1872, the China Merchants＇ Steam Navigation Company was the fisst steamship company of China to be formed. It was a government-supervised and merchant-managed company, and the Qing Dynasty government took a series of measures to support it under the fierce competition, these measures were different from foreign countries＇.展开更多
This paper describes a campaign of WEC （wave energy converter） testing and presents a selection of the results related to the measured motions and mooring tensions. A 1：20 physical model has been successfully deplo...This paper describes a campaign of WEC （wave energy converter） testing and presents a selection of the results related to the measured motions and mooring tensions. A 1：20 physical model has been successfully deployed using a three point mooring installed at sea （Strangford Lough, NI） in 10 m depth. In calm weather the overall dynamics of mooring tensions is dominated by the tidal cycle due to the progressive lifting of the heavy chain with the increase in water depth on the flood and gradual lowering on the ebb. In flesh winds the dynamics is very complex, but can be studied with the aid of mathematical modelling. A simulation model was used to assess the dynamics of the mooring lines, and the results of open water tests have been compared with the model＇s performance. The results indicate that, in general, the model shows a reasonable agreement with the observations. The WEC＇s motions and the measured loads on the leading mooring line appear to relate to the concurrent environmental conditions. The data obtained can therefore be used for the model＇s calibration and further improvements, which is valuable for improving the WEC＇s design and operational characteristics. This may be important not only in relation to the issues of reliability and power take off, but also in terms of minimising the adverse effects of mooring lines on bottom sediments, as well as indirect effects of the eroded particles on a wide range of aquatic processes.展开更多
Existing optimization methodologies for intersection operations assumes a fixed geometric design, however the geometry and operational system should be simultaneously optimized to produce the best performance. Signali...Existing optimization methodologies for intersection operations assumes a fixed geometric design, however the geometry and operational system should be simultaneously optimized to produce the best performance. Signalized crosswalks are complex and critical pedestrian facilities. Their geometry and configuration directly affect the safety, cycle length and resulting delays for all users. As crosswalks become wider or they are placed further upstream, the cycle length will increase due to the all-red time requirement, which deteriorates the overall mobility levels of signalized intersections. In contrast, when crosswalk width decreases, the required minimum pedestrian crossing time increases due to the bi-directional pedestrian flow effects, which leads to longer cycle length. Furthermore, existing manuals and guidelines do not offer any specification for the required crosswalk width under various pedestrian demand conditions. This study aims to propose new criteria for designing crosswalk width at signalized intersections, which can optimize the performance from the viewpoint of vehicular traffic and pedestrians. The proposed methodology considers pedestrian demand and its characteristics （such as bi-directional flow effects）, vehicle demand and the geometric characteristics of the intersection The concept of optimized crosswalk width is proposed and demonstrated through a case study. Moreover, a comprehensive discussion regarding the merits and drawbacks of existing strategies on positioning crosswalks is presented. It was found that at signalized intersections, which are characterized by low pedestrian and high vehicle demands, crosswalk width of 2 meters is appropriate to minimize cycle length and resulting delays for all users including pedestrians.展开更多
In order to reduce product development cycle time, aerospace companies tend to develop various correlations integrating geometric and performance parameters. This paper covers the development of a parameterization mod...In order to reduce product development cycle time, aerospace companies tend to develop various correlations integrating geometric and performance parameters. This paper covers the development of a parameterization modeling, to be used in the preliminary design phase, for the turbine cover plate of an aero-engine. The parameterization modeling of the turbine cover plate is achieved by using commercial CAD （computer aided design） software processing in batch mode. Two main approaches are presented the outer face and the skeleton models. These models can then be integrated into an iterative process for designing optimal shapes. Both models are capable of reproducing existing cover plate with reasonable accuracy in relatively shorter time periods. However, the skeleton approach provides probably the best results in terms of flexibility and accuracy, but increases programming complexity and requires greater run times.展开更多
Period estimation of X-ray pulsars plays an important role in X-ray pulsar based navigation （XPNAV）. The fast Lomb periodogram is suitable for period estimation of X-ray pulsars, but its performance in terms of freq...Period estimation of X-ray pulsars plays an important role in X-ray pulsar based navigation （XPNAV）. The fast Lomb periodogram is suitable for period estimation of X-ray pulsars, but its performance in terms of frequency resolution is limited by data length and observation time. Longer observation time or oversampling can be employed to improve frequency analysis results, but with greatly increased computational complexity and large amounts of sampling data. This greatly restricts real-time autonomous navigation based on X-ray pulsars. To resolve this issue, a new method based on frequency subdivision and the continuous Lomb periodogram （CLP） is proposed to improve precision of period estimation using short-time observation data. In the proposed method, an initial frequency is first calculated using fast Lomb periodogram. Then frequency subdivision is per- formed near the initial frequency to obtain frequencies with higher precision. Finally, a refined period is achieved by calculating the CLP in the obtained frequencies. Real data experiments show that when observation time is shorter than 135 s, the proposed method improves period estimation precision by 1-3 orders of magnitude compared with the fast Lomb periodogram and fast Fourier transform （FFT） methods, with only a slight increase in computational complexity. Furthermore, the proposed method performs better than efsearch （a period estimation method of HEAsoft） with lower computational complexity. The proposed method is suitable for estimating periods of X-ray pulsars and obtaining the rotation period of variable stars and other celestial bodies.展开更多
The tropospheric delay is one of the main error sources for radio navigation technologies and other ground-or space-based earth observation systems. In this paper, the spatial and temporal variations of the zenith tro...The tropospheric delay is one of the main error sources for radio navigation technologies and other ground-or space-based earth observation systems. In this paper, the spatial and temporal variations of the zenith tropospheric delay (ZTD), especially their dependence on altitude over China region, are analyzed using ECMWF (European Centre for Medium-Range Weather Forecast) pressure-level atmospheric data in 2004 and the ZTD series in 1999-2007 measured at 28 GPS stations from the Crustal Movement Observation Network of China (CMONC). A new tropospheric delay correction model (SHAO) is derived and a regional realization of this model for China region named SHAO-C is established. In SHAO-C model, ZTD is modeled directly by a cosine function together with an initial value and an amplitude at a reference height in each grid, and the variation of ZTD along altitude is fitted with a second-order polynomial. The coefficients of SHAO-C are generated using the meteorology data in China area and given at two degree latitude and longitude interval, featuring regional characteristics in order to facilitate a wide range of navigation and other surveying applications in and around China. Compared with the EGNOS (European Geostationary Navigation Overlay Service) model, which has been used globally and recommended by the European Union Wide Area Augmentation System, the ZTD prediction (in form of spatial and temporal projection) accuracy of the SHAO-C model is significantly improved over China region, especially at stations of higher altitudes. The reasons for the improvement are: (1) the reference altitude of SHAO-C parameters are given at the average height of each grid, and (2) more detailed description of complicated terrain variations in China is incorporated in the model. Therefore, the accumulated error at higher altitude can be reduced considerably. In contrast, the ZTD has to be calculated from the mean sea level with EGNOS and other models. Compared with the direct estimation of ZTD from the 28 GPS stations, the accuracy of the derived ZTD using the SHAO-C model can be improved by 60.5% averagely compared with the EGNOS model. The overall bias and rms are 2.0 and 4.5 cm, respectively, which should be sufficient to satisfy the requirements of most GNSS navigation or positioning applications in terms of the tropospheric delay correction.展开更多
The forecast of growing air transport in the upcoming decades faces the challenge of an increasing environmental impact.Aviation industry is working on promising technologies to mitigate this environmental impact.Ligh...The forecast of growing air transport in the upcoming decades faces the challenge of an increasing environmental impact.Aviation industry is working on promising technologies to mitigate this environmental impact.Lightweight design is a strong lever to lower the fuel consumption and,consequently,with it the emissions of aviation.High performance composites are a key technology to help achieve these aims thanks to their favourable combination of mechanical properties and low weight in primary structures.However,mainly synthetic materials such as petrol based carbon fibres and epoxy resins are used nowadays to produce composite in aviation.Renewable materials like bio-based fibres and resin systems offer potential environmental advantages.However,they have not found their way into aviation,yet.The reasons are reduced mechanical properties and,especially for the use of natural fibres,their flammability.Improvements of these shortcomings are under investigation.Therefore the application of bio-based and recycled materials in certain areas of the aircraft could be possible in the future.Good examples for applications are furnishings and secondary structures.The motivation for this paper is to give an overview of potential environmental properties by using such eco-materials in aviation.Life cycle assessment(LCA) is a tool to calculate environmental impacts during all life stages of a product.The main focus is laid on the bio-fibres flax and ramie,recycled carbon fibres and bio-based thermoset resin systems.Furthermore an overview of environmental aspects of existing composite materials used in aviation is given.Generally,a lack of LCA results for the substitution of synthetic materials by bio-based/recycled composite materials in aviation applications has been identified.Therefore,available information from other transport areas,such as automotive,has been summarized.More detailed LCA data for eco-composite materials and technologies to improve their properties is important to understand potential environmental effects in aviation.展开更多
Above ground gas storage devices for compressed air energy storage(CAES) have three types:air storage tanks,gas cylinders,and gas storage pipelines.A cost model of these gas storage devices is established on the basis...Above ground gas storage devices for compressed air energy storage(CAES) have three types:air storage tanks,gas cylinders,and gas storage pipelines.A cost model of these gas storage devices is established on the basis of whole life cycle cost(LCC) analysis.The optimum parameters of the three types are determined by calculating the theoretical metallic raw material consumption of these three devices and considering the difficulties in manufacture and the influence of gas storage device number.The LCCs of the three types are comprehensively analyzed and compared.The result reveal that the cost of the gas storage pipeline type is lower than that of the other two types.This study may serve as a reference for designing large-scale CAES systems.展开更多
文摘This paper introduces the preparatory work and conducts an integrated review on the maiden voyage of a Chinese commercial ship on the Arctic Northeast Route. It puts forth expectations on the exploitation and utilization of the Arctic Northeast Route in the aspects of safety, fastness, low costs, low consumption of energy and less pollution, knowledge of maritime law and navigation practice, building seaworthiness ships and making studies on the methods of sailing and maneuvering for navigation in polar waters, training qualified seafarers with navigation experiences in ice waters and establishing a safeguard system for the navigation in this route through the analysis on the weather, temperature, ice condition, route and hydrology encountered in the practice of a Chinese merchant ship in its maiden voyage in the route, and studies on the ice pilotage, convoy by icebreaker, practical condition of communication and navigation equipment in sea areas of high latitude and the economic benefit of the navigation in the Arctic Northeast Route.
文摘To carry out the deep space exploration tasks near Sun-Earth Libration point L2, the CRTBP dynamic model was built up and the numerical conditional quasi-periodic orbit （Lissajons orbit） was computed near L2. Then, a formation controller was designed with linear matrix inequality to overcome the difficuhy of parameter tuning. To meet the demands of formation accuracy and present thruster＇s capability, a threshold scheme was adopted for formation control. Finally, some numerical simulations and analysis were completed to demonstrate the feasibility of the proposed control strategy.
文摘This paper intends to study Ezra Pound＇s early poetics and his modemist poetry through a close research of the Eastern elements in the shaping process of his poetics and the significance and influence of his poetic thoughts on the American New Poetry Movement. In order to clarify the essence of Pound＇s early poetics under the influence of Chinese classical poems, the paper starts from the discussion of the influence of Cathay （1915） and his translation of Cathay; then it provides a detailed analysis of the relationship between Chinese classical poems and Pound＇s creation; and finally it has given an analysis of ＂In a Station of the Metro＂. Pound absorbed different poetic concepts from all of them and transformed his poetry from the conventional Romanticism to the innovative Modemism. What Pound innovated in the poetry composition is of great importance if the new era wishes to shake off the banality and out-of-date tradition in literature. Pound changed a whole generation of poets and set a good example for those who desire to write in a new way
文摘To meet the increasing research demand for deep space exploration,especially for the second libration point (L2) conditional periodic orbit (Halo orbit) in the Sun-Earth system,the methods to get analytical Halo orbit and differential-correction Halo orbit were described firstly,and the corresponding orbits accuracy was analyzed.Then,based on the results of third-order and differential-correction Halo orbits,the formation form was studied.Analysis was carried out to discuss the influence of system amplitude,initial phase,and phase difference on the formation form,as well as that of initial orbit values on form accuracy.Finally,some simulation results demonstrate the validity of the proposed methods.
文摘Based on the Ricatti technique, the methodology for preventing the limit cycle accomplished by adding a control function to the original equation of wing rock motion is presented in this paper. To analyze the state variables of the system, the complete set of nonlinear equations of motion including an effective linear control function was solved for A-4D and Mig-21 Aircraft. The roll angle responding to the linear control function for both models was estimated when the systems were tested under different damping ratios. The numerical re- suits show that a linear control function including both the roll attitude and the roll rate is sufficient to suppress the wing rock motion with an acceptable error in desired time. A good agreement between the numerical results and the published work is obtained for the limit cycle oscillation existence at different damping ratios.
文摘This study makes a comparison between China and foreign countries about the ＂supportive shipping policies＂ in the period of late Qing Dynasty, from 1840 to 1911. After the first opium war, China was forced to open the gate of the old oriental country to the world. As more treaty ports opened, the import and export of goods increased the growing trade that brought about the increased demands of shipping transportation. In the same period, British, France, America, Germany and Japan governing bodies instated various kinds of laws, regulations and other policies encouraging their national shipping companies to grab shipping market share. As a result, foreign steamship companies monopolized Chinese shipping market quickly. Faced with this situation, in 1872, the China Merchants＇ Steam Navigation Company was the fisst steamship company of China to be formed. It was a government-supervised and merchant-managed company, and the Qing Dynasty government took a series of measures to support it under the fierce competition, these measures were different from foreign countries＇.
文摘This paper describes a campaign of WEC （wave energy converter） testing and presents a selection of the results related to the measured motions and mooring tensions. A 1：20 physical model has been successfully deployed using a three point mooring installed at sea （Strangford Lough, NI） in 10 m depth. In calm weather the overall dynamics of mooring tensions is dominated by the tidal cycle due to the progressive lifting of the heavy chain with the increase in water depth on the flood and gradual lowering on the ebb. In flesh winds the dynamics is very complex, but can be studied with the aid of mathematical modelling. A simulation model was used to assess the dynamics of the mooring lines, and the results of open water tests have been compared with the model＇s performance. The results indicate that, in general, the model shows a reasonable agreement with the observations. The WEC＇s motions and the measured loads on the leading mooring line appear to relate to the concurrent environmental conditions. The data obtained can therefore be used for the model＇s calibration and further improvements, which is valuable for improving the WEC＇s design and operational characteristics. This may be important not only in relation to the issues of reliability and power take off, but also in terms of minimising the adverse effects of mooring lines on bottom sediments, as well as indirect effects of the eroded particles on a wide range of aquatic processes.
文摘Existing optimization methodologies for intersection operations assumes a fixed geometric design, however the geometry and operational system should be simultaneously optimized to produce the best performance. Signalized crosswalks are complex and critical pedestrian facilities. Their geometry and configuration directly affect the safety, cycle length and resulting delays for all users. As crosswalks become wider or they are placed further upstream, the cycle length will increase due to the all-red time requirement, which deteriorates the overall mobility levels of signalized intersections. In contrast, when crosswalk width decreases, the required minimum pedestrian crossing time increases due to the bi-directional pedestrian flow effects, which leads to longer cycle length. Furthermore, existing manuals and guidelines do not offer any specification for the required crosswalk width under various pedestrian demand conditions. This study aims to propose new criteria for designing crosswalk width at signalized intersections, which can optimize the performance from the viewpoint of vehicular traffic and pedestrians. The proposed methodology considers pedestrian demand and its characteristics （such as bi-directional flow effects）, vehicle demand and the geometric characteristics of the intersection The concept of optimized crosswalk width is proposed and demonstrated through a case study. Moreover, a comprehensive discussion regarding the merits and drawbacks of existing strategies on positioning crosswalks is presented. It was found that at signalized intersections, which are characterized by low pedestrian and high vehicle demands, crosswalk width of 2 meters is appropriate to minimize cycle length and resulting delays for all users including pedestrians.
文摘In order to reduce product development cycle time, aerospace companies tend to develop various correlations integrating geometric and performance parameters. This paper covers the development of a parameterization modeling, to be used in the preliminary design phase, for the turbine cover plate of an aero-engine. The parameterization modeling of the turbine cover plate is achieved by using commercial CAD （computer aided design） software processing in batch mode. Two main approaches are presented the outer face and the skeleton models. These models can then be integrated into an iterative process for designing optimal shapes. Both models are capable of reproducing existing cover plate with reasonable accuracy in relatively shorter time periods. However, the skeleton approach provides probably the best results in terms of flexibility and accuracy, but increases programming complexity and requires greater run times.
基金Project supported by the National Basic Research Program(973)of China(No.2014CB340205)the National Natural Science Foundation of China(Nos.61301173 and 61473228)the Aerospaced TT&C Innovation Program of 704 Research Institute of China(No.201405B)
文摘Period estimation of X-ray pulsars plays an important role in X-ray pulsar based navigation （XPNAV）. The fast Lomb periodogram is suitable for period estimation of X-ray pulsars, but its performance in terms of frequency resolution is limited by data length and observation time. Longer observation time or oversampling can be employed to improve frequency analysis results, but with greatly increased computational complexity and large amounts of sampling data. This greatly restricts real-time autonomous navigation based on X-ray pulsars. To resolve this issue, a new method based on frequency subdivision and the continuous Lomb periodogram （CLP） is proposed to improve precision of period estimation using short-time observation data. In the proposed method, an initial frequency is first calculated using fast Lomb periodogram. Then frequency subdivision is per- formed near the initial frequency to obtain frequencies with higher precision. Finally, a refined period is achieved by calculating the CLP in the obtained frequencies. Real data experiments show that when observation time is shorter than 135 s, the proposed method improves period estimation precision by 1-3 orders of magnitude compared with the fast Lomb periodogram and fast Fourier transform （FFT） methods, with only a slight increase in computational complexity. Furthermore, the proposed method performs better than efsearch （a period estimation method of HEAsoft） with lower computational complexity. The proposed method is suitable for estimating periods of X-ray pulsars and obtaining the rotation period of variable stars and other celestial bodies.
基金supported by the National Natural Science Foundation of China (Grant No.10603011 and 41174023)the National High Technology Research and Development Program of China (Grant No.2009AA12Z307)+2 种基金Science and Technology Commission of Shanghai Municipality (Grant Nos.05QMX1462 and 08ZR1422400)the Youth Foundation of Knowledge Innovation Project of the Chinese Academy of SciencesShanghai Astronomical Observatory (Grant No.5120090304)
文摘The tropospheric delay is one of the main error sources for radio navigation technologies and other ground-or space-based earth observation systems. In this paper, the spatial and temporal variations of the zenith tropospheric delay (ZTD), especially their dependence on altitude over China region, are analyzed using ECMWF (European Centre for Medium-Range Weather Forecast) pressure-level atmospheric data in 2004 and the ZTD series in 1999-2007 measured at 28 GPS stations from the Crustal Movement Observation Network of China (CMONC). A new tropospheric delay correction model (SHAO) is derived and a regional realization of this model for China region named SHAO-C is established. In SHAO-C model, ZTD is modeled directly by a cosine function together with an initial value and an amplitude at a reference height in each grid, and the variation of ZTD along altitude is fitted with a second-order polynomial. The coefficients of SHAO-C are generated using the meteorology data in China area and given at two degree latitude and longitude interval, featuring regional characteristics in order to facilitate a wide range of navigation and other surveying applications in and around China. Compared with the EGNOS (European Geostationary Navigation Overlay Service) model, which has been used globally and recommended by the European Union Wide Area Augmentation System, the ZTD prediction (in form of spatial and temporal projection) accuracy of the SHAO-C model is significantly improved over China region, especially at stations of higher altitudes. The reasons for the improvement are: (1) the reference altitude of SHAO-C parameters are given at the average height of each grid, and (2) more detailed description of complicated terrain variations in China is incorporated in the model. Therefore, the accumulated error at higher altitude can be reduced considerably. In contrast, the ZTD has to be calculated from the mean sea level with EGNOS and other models. Compared with the direct estimation of ZTD from the 28 GPS stations, the accuracy of the derived ZTD using the SHAO-C model can be improved by 60.5% averagely compared with the EGNOS model. The overall bias and rms are 2.0 and 4.5 cm, respectively, which should be sufficient to satisfy the requirements of most GNSS navigation or positioning applications in terms of the tropospheric delay correction.
基金supported by the European Union's Horizon 2020 research and innovation programme(Grant No.690638)the Ministry for Industry and Information of the People's Republic of China(Grant No.[2016]92)
文摘The forecast of growing air transport in the upcoming decades faces the challenge of an increasing environmental impact.Aviation industry is working on promising technologies to mitigate this environmental impact.Lightweight design is a strong lever to lower the fuel consumption and,consequently,with it the emissions of aviation.High performance composites are a key technology to help achieve these aims thanks to their favourable combination of mechanical properties and low weight in primary structures.However,mainly synthetic materials such as petrol based carbon fibres and epoxy resins are used nowadays to produce composite in aviation.Renewable materials like bio-based fibres and resin systems offer potential environmental advantages.However,they have not found their way into aviation,yet.The reasons are reduced mechanical properties and,especially for the use of natural fibres,their flammability.Improvements of these shortcomings are under investigation.Therefore the application of bio-based and recycled materials in certain areas of the aircraft could be possible in the future.Good examples for applications are furnishings and secondary structures.The motivation for this paper is to give an overview of potential environmental properties by using such eco-materials in aviation.Life cycle assessment(LCA) is a tool to calculate environmental impacts during all life stages of a product.The main focus is laid on the bio-fibres flax and ramie,recycled carbon fibres and bio-based thermoset resin systems.Furthermore an overview of environmental aspects of existing composite materials used in aviation is given.Generally,a lack of LCA results for the substitution of synthetic materials by bio-based/recycled composite materials in aviation applications has been identified.Therefore,available information from other transport areas,such as automotive,has been summarized.More detailed LCA data for eco-composite materials and technologies to improve their properties is important to understand potential environmental effects in aviation.
基金supported by grants from the National High-Tech Research and Development Projects(863)of China(No.2013AA050801)the International S&T Cooperation Projects of China(No.2014DFA60600)
文摘Above ground gas storage devices for compressed air energy storage(CAES) have three types:air storage tanks,gas cylinders,and gas storage pipelines.A cost model of these gas storage devices is established on the basis of whole life cycle cost(LCC) analysis.The optimum parameters of the three types are determined by calculating the theoretical metallic raw material consumption of these three devices and considering the difficulties in manufacture and the influence of gas storage device number.The LCCs of the three types are comprehensively analyzed and compared.The result reveal that the cost of the gas storage pipeline type is lower than that of the other two types.This study may serve as a reference for designing large-scale CAES systems.
