Structural and geomorphological analysis of the Martian surface in the visible spectral range using the NASA/Viking images in the 90’s,complemented by experimental modelling(Mège and Masson,1996a;Mège et al...Structural and geomorphological analysis of the Martian surface in the visible spectral range using the NASA/Viking images in the 90’s,complemented by experimental modelling(Mège and Masson,1996a;Mège et al.,2003)suggested that the Valles Marineris trough(chasma)system is aligned with a mafic dyke swarm,named the Syria Planum Dyke Swarm.Cross-cutting relationships展开更多
An extensive survey of dykes in the Valles Marineris troughs(chasmata)on Mars has been undertaken.Most dykes are observed along the chasma walls(Mège and Gurgurewicz,2016),in the spur-and-gully morphology
The rate of the total electron content(TEC)change index(ROTI)can be regarded as an effective indicator of the level of ionospheric scintillation,in particular in low and high latitude regions.An accurate prediction of...The rate of the total electron content(TEC)change index(ROTI)can be regarded as an effective indicator of the level of ionospheric scintillation,in particular in low and high latitude regions.An accurate prediction of the ROTI is essential to reduce the impact of the ionospheric scintillation on earth observation systems,such as the global navigation satellite systems.However,it is difficult to predict the ROTI with high accuracy because of the complexity of the ionosphere.In this study,advanced machine learning methods have been investigated for ROTI prediction over a station at high-latitude in Canada.These methods are used to predict the ROTI in the next 5 minutes using the data derived from the past 15 minutes at the same location.Experimental results show that the method of the bidirectional gated recurrent unit network(BGRU)outperforms the other six approaches tested in the research.It is also confirmed that the RMSEs of the predicted ROTI using the BGRU method in all four seasons of 2017 are less than 0.05 TECU/min.It is demonstrated that the BGRU method exhibits a high level of robustness in dealing with abrupt solar activities.展开更多
Interferometric phase filtering is one of the key steps in interferometricsynthetic aperture radar (InSAR/SAR). However, the ideal filtering results are difficult toobtain due to dense fringe and low coherence regions...Interferometric phase filtering is one of the key steps in interferometricsynthetic aperture radar (InSAR/SAR). However, the ideal filtering results are difficult toobtain due to dense fringe and low coherence regions. Moreover, the InSAR/SAR datarange is relatively large, so the efficiency of interferential phase filtering is one of themajor problems. In this letter, we proposed an interferometric phase filtering methodbased on an amended matrix pencil and linear window mean filter. The combination ofthe matrix pencil and the linear mean filter are introduced to the interferometric phasefiltering for the first time. First, the interferometric signal is analyzed, and theinterferometric phase filtering is transformed into a local frequency estimation problem.Then, the local frequency is estimated using an amended matrix pencil at a window. Thelocal frequency can represent terrain changes, thus suggesting that the frequency can beaccurately estimated even in dense fringe regions. Finally, the local frequency is filteredby using a linear window mean filter, and the filtered phase is recovered. The proposedmethod is calculated by some matrices. Therefore, the computational complexity isreduced, and the efficiency of the interferometric phase filtering is improved.Experiments are conducted with simulated and real InSAR data. The proposed methodexhibits a better filtering effect and an ideal efficiency as compared with the traditionalfiltering method.展开更多
We estimate the zonal drift velocity of small-scale ionospheric irregularities at low latitude by leveraging the spaced-receivers technique applied to two GNSS receivers for scintillation monitoring installed along th...We estimate the zonal drift velocity of small-scale ionospheric irregularities at low latitude by leveraging the spaced-receivers technique applied to two GNSS receivers for scintillation monitoring installed along the magnetic parallel passing in Presidente Prudente(Brazil,magnetic latitude 12.8°S).The investigated ionospheric sector is ideal to study small-scale irregularities,being located close to the expected position of the southern crest of the equatorial ionospheric anomaly.The measurement campaign took place between September 2013 and February 2014,i.e.equinox and summer solstice seasons under solar maximum,during which the probability of formation of small-scale irregularities is expected to maximize.We found that the hourly average of the velocity increases up to 135 m/s right after the local sunset at ionospheric altitudes and then smoothly decreases in the next hours.Such measurements are in agreement with independent estimations of the velocity made by the Incoherent Scatter Radar located at the Jicamarca Radio Observatory(magnetic latitude 0.1°N),by the Boa Vista Ionosonde(magnetic latitude 12.0°N),and by applying a recently-developed empirical regional short-term forecasting model.Additionally,we investigated the relationship with the percentage occurrence of amplitude scintillation;we report that it is exponentially dependent on the zonal velocity of the irregularities that cause it.展开更多
Opening of the Red Sea started while the core of the lavas of the Ethiopian Large Igneous Province(LIP)was being erupted at^30 Ma(Hughes et al.,1991)and has continued to the Present.In the southern Red Sea。
Important international reports and a significant number of scientific publications have reported on the abrupt decline of Arctic sea ice and its impact on the Global Climate System. In this paper, we evaluated the ab...Important international reports and a significant number of scientific publications have reported on the abrupt decline of Arctic sea ice and its impact on the Global Climate System. In this paper, we evaluated the ability of the newly implemented Brazilian Earth System Model (BESM-OA) to represent Arctic sea ice and sensitivity to CO<sub>2</sub> forcing, using decadal simulations (1980-2012) and future scenarios (2006-2100). We validated our results with satellite observations and compared them to Coupled Model Intercomparison Project, Phase 5 (CMIP5) for the same numerical experiment. BESM results for the seasonal cycle are consistent with CMIP5 models and observations. However, almost all models tend to overestimate sea ice extent in March compared to observations. The correct evaluation of minimum record of sea ice, in terms of time, spatial and area remains a limitation in Coupled Global Climate Models. Looking to spatial patterns, we found a systematic model error in September sea ice cover between the Beaufort Sea and East Siberia for most models. Future scenarios show a decrease in sea ice extent in response to an increase in radiative forcing for all models. From the year 2045 onwards, all models show a dramatic shrinking in sea ice and ice free conditions at the end of the melting season. The projected future sea ice loss is explained by the combined effects of the amplified warming in northern hemisphere high latitudes and feedbacks processes.展开更多
The presence of wrinkles in the membrane is the main factor to induce the reflector surface inaccuracy of the space inflatable antenna.Based on the commercial finite element package ABAQUS,a numerical procedure for me...The presence of wrinkles in the membrane is the main factor to induce the reflector surface inaccuracy of the space inflatable antenna.Based on the commercial finite element package ABAQUS,a numerical procedure for membrane wrinkle analysis was set up and used to analyze a space inflatable antenna which was under inner pressure to evaluate its wrinkle characteristics.First,the inner pressure effect on the reflector's wrinkle pattern was studied thoroughly.As inner pressure increases,both the number and the amplitude of the wrinkles decrease,but the total deformation of the whole reflector surface increases much.Second,the influence of the interactions between antenna's parts was investigated comprehensively.Any kind of unwanted interaction deteriorates reflector's wrinkle characteristics.The works are valuable to the development and research of the space inflatable antenna.展开更多
The presence of wrinkles in a membrane is the main factor that induces surface errors on space planar film reflect-arrays. Based on the commercial finite element (FE) package ABAQUS, a numerical procedure for membrane...The presence of wrinkles in a membrane is the main factor that induces surface errors on space planar film reflect-arrays. Based on the commercial finite element (FE) package ABAQUS, a numerical procedure for membrane wrinkle analysis was set up, and used to analyze a square planar film reflect-array under pure shear force to evaluate its induced wrinkle characteristics. First, the effect of shear force on the wrinkle pattern of the array was studied and validated by experiment. Second, the effect of prestress was studied. When the prestress increases, the quantity of the wrinkles increases, and the amplitude of the wrinkles decreases. Third, the influence of the boundary conditions was investigated. A frame side edge structure has a relatively smooth surface, but also relatively high stress. Finally, the behavior of a joint seam was analyzed. The results indicate that a joint band has a significant influence on the wrinkle pattern of the membrane.展开更多
Nine kinds of structure systems were proposed for the flexible airship according to the inherent structural characteristics. On the basis of equilibrium configuration of the oating airship subjected to the ascent heli...Nine kinds of structure systems were proposed for the flexible airship according to the inherent structural characteristics. On the basis of equilibrium configuration of the oating airship subjected to the ascent helium buoyancy and gravity,the structural analysis procedure was developed and the computation models were presented for the airship. Then the systematic numerical analysis was carried out for a 25 m long airship,the comparison of principal stress of envelope was performed between the nonlinear numerical analysis result and the engineering elastic theory result. The structural performances were evaluated thoroughly. Finally,the reasonable structural systems were proposed. Accordingly,the results herein were valuable to structural design for flexible airship especially for large flexible airship.展开更多
As a new Ionosphere Associate Analysis Center(IAAC)of the International GNSS Service(IGS),Chinese Academy of Sciences(CAS)started the routine computation of the real-time,rapid,and final Global Ionospheric Maps(GIMs)i...As a new Ionosphere Associate Analysis Center(IAAC)of the International GNSS Service(IGS),Chinese Academy of Sciences(CAS)started the routine computation of the real-time,rapid,and final Global Ionospheric Maps(GIMs)in 2015.The method for the generation of CAS rapid and final GIMs and recent updates are presented in the paper.The quality of CAS post-processed GIMs is assessed during 2015-2018 after the maximum of solar cycle 24.To perform an independent and fair assessment,Jason-2/3 Vertical Total Electron Contents(VTEC)are first used as the references over the ocean.GPS differential Slant TECs(dSTEC)generated from 55 Multi-GNSS Experimental(MGEX)stations of the IGS are also employed,which provides a complementing way to evaluate the ability of electron content models to reproduce the spatial and temporal gradients in the ionosphere.During the test period,Jet Propulsion Laboratory(JPL)GIMs present significantly positive deviations compared to the Jason VTEC and GPS dSTEC.Technical University of Catalonia(UPC)rapid GIM UQRG exhibits the best performance in both Jason VTEC and GPS dSTEC analysis.The CAS GIMs show comparable performance with the results of the first four IAACs of the IGS.As expected,the poor performance of all GIMs is in equatorial regions and the high latitudes of the southern hemisphere.The consideration of generating multi-layer or three-dimensional ionospheric maps is emphasized to mitigate the inadequacy of ionospheric single-layer assumption in the presence of pronounced latitudinal gradients.The use of ionospheric observations from the new GNSS constellations and other space-or ground-based observation techniques is also suggested in the generation of future GIMs,given the sparse GPS/GLONASS stations in the southern hemisphere.展开更多
The prestress developing of tensile cable-net structures is a state transforming process from the initial unstressed state to the final prestressed state, and it is rather complicated because the elastic deformation i...The prestress developing of tensile cable-net structures is a state transforming process from the initial unstressed state to the final prestressed state, and it is rather complicated because the elastic deformation is normally coupled with the kinematic mechanism movement. Firstly, the basic equations of prestress developing by moving boundary joint are derived from the total potential energy equation. Secondly, the presumed initial tension is proposed to impose into the elements and avoid the singularity of global stiffness matrix. And the self-stress mode which is calculated from the equilibrium matrix with singular value decomposition is employed as basically presumed initial tension. By applying boundary movement increment, an iterative computation is developed to calculate the updating geometric configuration and tension evolution. Finally, the MATLAB program is coded from the presented method, and numerical examples indicate that this computational method is effective and has theoretical significance and valuable guide to design and construction of tensile cable-net structure.展开更多
In order to evaluate the vibration characteristics of non-rigid airship with suspended curtain,we introduce vibration characteristic analysis method of the inflatable membrane structure.Modal numerical method of the i...In order to evaluate the vibration characteristics of non-rigid airship with suspended curtain,we introduce vibration characteristic analysis method of the inflatable membrane structure.Modal numerical method of the inflatable membrane structure under the pressure difference is validated by the model testing of the inflatable cantilever tube.The finite element model of 75 m airships is established to simulate the vibration characteristics subjected to only pressure difference and the resultant force of weight and buoyancy.The nonlinear static deformation and stress analysis are investigated for two kinds of equilibrated configurations with various pressure differences,as well as the vibration characteristics.The structural efficiency of the suspended curtain is investigated through the force transfer ratio at the assumed equilibrated point.The effects of manufacture error of the suspended cable length on the structural behavior are analyzed.The results indicate that the local area of airship envelope connected to the suspended cable is a weak part.Various pressures and pressure gradients have significant effects on the global airship structure and the suspended curtain.The suspended curtain is effective to transfer the equilibrated force from the bottom to the top of airship envelope.Manufacture error of the suspended cable length could result in obvious deformation of local airship envelope.The presented work is valuable to the structural engineering design of stratospheric airship.展开更多
This paper presents the results of the application of mathematical morphology for the automatic quantification of the number of tents and the detection of changes in the Menik Farm IDP camp in Sri Lanka.The tents were...This paper presents the results of the application of mathematical morphology for the automatic quantification of the number of tents and the detection of changes in the Menik Farm IDP camp in Sri Lanka.The tents were retrieved using an area-constraint top-hat opening applied to WorldView-1 data.The counting of tents was based on the centroids of the automatically detected structures indicating an overall number of 25,150 tents on the 26 June 2009.The comparison with a visual interpretation produced an R2 of 0.97 with an error of 1.25%.In addition,an automated detection of changes inside a camp area was conducted.The comparison of the satellite image of 26 June 2009(WorldView-1)and an image of 28 February 2010(GeoEye-1)is based on mutual(mixed)information metric,after using morphological image processing techniques and previously specified criterion.Changes are observed on a terrain of around 15.2%of the total camp area and 3813 of previously detected structures disappeared in a period of 8 months.展开更多
文摘Structural and geomorphological analysis of the Martian surface in the visible spectral range using the NASA/Viking images in the 90’s,complemented by experimental modelling(Mège and Masson,1996a;Mège et al.,2003)suggested that the Valles Marineris trough(chasma)system is aligned with a mafic dyke swarm,named the Syria Planum Dyke Swarm.Cross-cutting relationships
文摘An extensive survey of dykes in the Valles Marineris troughs(chasmata)on Mars has been undertaken.Most dykes are observed along the chasma walls(Mège and Gurgurewicz,2016),in the spur-and-gully morphology
基金National Key Research Program of China(No.2017YFE0131400)National Natural Science Foundation of China(Nos.41674043,41704038,41874040)+2 种基金Beijing Nova Program(No.xx2017042)Beijing Talents Foundation(No.2017000021223ZK13)CUMT Independent Innovation Project of“Double-First Class”Construction(No.2018ZZ08)。
文摘The rate of the total electron content(TEC)change index(ROTI)can be regarded as an effective indicator of the level of ionospheric scintillation,in particular in low and high latitude regions.An accurate prediction of the ROTI is essential to reduce the impact of the ionospheric scintillation on earth observation systems,such as the global navigation satellite systems.However,it is difficult to predict the ROTI with high accuracy because of the complexity of the ionosphere.In this study,advanced machine learning methods have been investigated for ROTI prediction over a station at high-latitude in Canada.These methods are used to predict the ROTI in the next 5 minutes using the data derived from the past 15 minutes at the same location.Experimental results show that the method of the bidirectional gated recurrent unit network(BGRU)outperforms the other six approaches tested in the research.It is also confirmed that the RMSEs of the predicted ROTI using the BGRU method in all four seasons of 2017 are less than 0.05 TECU/min.It is demonstrated that the BGRU method exhibits a high level of robustness in dealing with abrupt solar activities.
基金The authors would like to thank the support by the State Key Program of National Natural Science Foundation of China under Grant[Number 41774026]the Satellite Mapping Technology and Application,National Administration of Surveying,Mapping and Geoinformation Key Laboratory under Grant[Number KLSMTA-201708].
文摘Interferometric phase filtering is one of the key steps in interferometricsynthetic aperture radar (InSAR/SAR). However, the ideal filtering results are difficult toobtain due to dense fringe and low coherence regions. Moreover, the InSAR/SAR datarange is relatively large, so the efficiency of interferential phase filtering is one of themajor problems. In this letter, we proposed an interferometric phase filtering methodbased on an amended matrix pencil and linear window mean filter. The combination ofthe matrix pencil and the linear mean filter are introduced to the interferometric phasefiltering for the first time. First, the interferometric signal is analyzed, and theinterferometric phase filtering is transformed into a local frequency estimation problem.Then, the local frequency is estimated using an amended matrix pencil at a window. Thelocal frequency can represent terrain changes, thus suggesting that the frequency can beaccurately estimated even in dense fringe regions. Finally, the local frequency is filteredby using a linear window mean filter, and the filtered phase is recovered. The proposedmethod is calculated by some matrices. Therefore, the computational complexity isreduced, and the efficiency of the interferometric phase filtering is improved.Experiments are conducted with simulated and real InSAR data. The proposed methodexhibits a better filtering effect and an ideal efficiency as compared with the traditionalfiltering method.
基金funded by FAPESP(Process 06/04008-2)funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Sk?odowska-Curie Actions grant agreement No 722023。
文摘We estimate the zonal drift velocity of small-scale ionospheric irregularities at low latitude by leveraging the spaced-receivers technique applied to two GNSS receivers for scintillation monitoring installed along the magnetic parallel passing in Presidente Prudente(Brazil,magnetic latitude 12.8°S).The investigated ionospheric sector is ideal to study small-scale irregularities,being located close to the expected position of the southern crest of the equatorial ionospheric anomaly.The measurement campaign took place between September 2013 and February 2014,i.e.equinox and summer solstice seasons under solar maximum,during which the probability of formation of small-scale irregularities is expected to maximize.We found that the hourly average of the velocity increases up to 135 m/s right after the local sunset at ionospheric altitudes and then smoothly decreases in the next hours.Such measurements are in agreement with independent estimations of the velocity made by the Incoherent Scatter Radar located at the Jicamarca Radio Observatory(magnetic latitude 0.1°N),by the Boa Vista Ionosonde(magnetic latitude 12.0°N),and by applying a recently-developed empirical regional short-term forecasting model.Additionally,we investigated the relationship with the percentage occurrence of amplitude scintillation;we report that it is exponentially dependent on the zonal velocity of the irregularities that cause it.
基金P & R Geological Consultants and the CNRS/INSU/Marges programme for funding this work
文摘Opening of the Red Sea started while the core of the lavas of the Ethiopian Large Igneous Province(LIP)was being erupted at^30 Ma(Hughes et al.,1991)and has continued to the Present.In the southern Red Sea。
文摘Important international reports and a significant number of scientific publications have reported on the abrupt decline of Arctic sea ice and its impact on the Global Climate System. In this paper, we evaluated the ability of the newly implemented Brazilian Earth System Model (BESM-OA) to represent Arctic sea ice and sensitivity to CO<sub>2</sub> forcing, using decadal simulations (1980-2012) and future scenarios (2006-2100). We validated our results with satellite observations and compared them to Coupled Model Intercomparison Project, Phase 5 (CMIP5) for the same numerical experiment. BESM results for the seasonal cycle are consistent with CMIP5 models and observations. However, almost all models tend to overestimate sea ice extent in March compared to observations. The correct evaluation of minimum record of sea ice, in terms of time, spatial and area remains a limitation in Coupled Global Climate Models. Looking to spatial patterns, we found a systematic model error in September sea ice cover between the Beaufort Sea and East Siberia for most models. Future scenarios show a decrease in sea ice extent in response to an increase in radiative forcing for all models. From the year 2045 onwards, all models show a dramatic shrinking in sea ice and ice free conditions at the end of the melting season. The projected future sea ice loss is explained by the combined effects of the amplified warming in northern hemisphere high latitudes and feedbacks processes.
基金the National Natural Science Foundation of China(Nos. 50878128 and 50808122)the Shanghai Committee of Science and Technology(No. 06DZ22105)
文摘The presence of wrinkles in the membrane is the main factor to induce the reflector surface inaccuracy of the space inflatable antenna.Based on the commercial finite element package ABAQUS,a numerical procedure for membrane wrinkle analysis was set up and used to analyze a space inflatable antenna which was under inner pressure to evaluate its wrinkle characteristics.First,the inner pressure effect on the reflector's wrinkle pattern was studied thoroughly.As inner pressure increases,both the number and the amplitude of the wrinkles decrease,but the total deformation of the whole reflector surface increases much.Second,the influence of the interactions between antenna's parts was investigated comprehensively.Any kind of unwanted interaction deteriorates reflector's wrinkle characteristics.The works are valuable to the development and research of the space inflatable antenna.
基金Project (Nos. 50878128 and 50808122) supported by the National Natural Science Foundation of China
文摘The presence of wrinkles in a membrane is the main factor that induces surface errors on space planar film reflect-arrays. Based on the commercial finite element (FE) package ABAQUS, a numerical procedure for membrane wrinkle analysis was set up, and used to analyze a square planar film reflect-array under pure shear force to evaluate its induced wrinkle characteristics. First, the effect of shear force on the wrinkle pattern of the array was studied and validated by experiment. Second, the effect of prestress was studied. When the prestress increases, the quantity of the wrinkles increases, and the amplitude of the wrinkles decreases. Third, the influence of the boundary conditions was investigated. A frame side edge structure has a relatively smooth surface, but also relatively high stress. Finally, the behavior of a joint seam was analyzed. The results indicate that a joint band has a significant influence on the wrinkle pattern of the membrane.
文摘Nine kinds of structure systems were proposed for the flexible airship according to the inherent structural characteristics. On the basis of equilibrium configuration of the oating airship subjected to the ascent helium buoyancy and gravity,the structural analysis procedure was developed and the computation models were presented for the airship. Then the systematic numerical analysis was carried out for a 25 m long airship,the comparison of principal stress of envelope was performed between the nonlinear numerical analysis result and the engineering elastic theory result. The structural performances were evaluated thoroughly. Finally,the reasonable structural systems were proposed. Accordingly,the results herein were valuable to structural design for flexible airship especially for large flexible airship.
基金the National Key Research Program of China(No.2017YFE0131400)the Alliance of International Science Organizations(No.ANSO-CR-KP-2020-12)+3 种基金the National Natural Science Foundation of China(42074043)the Scientific Instrument Developing Project of the Chinese Academy of Sciences(YJKYYQ20190071)AK acknowledges the financial support from Ministry of Science and Higher Education(MSHE),Poland(MSHE Decision Nos.DIR/WK/2016/2017/05-1 and 59/E-383/SPUB/SP/2019.1)the National Centre for Research and Development,Poland(Decision No.DWM/PL-CHN/97/2019,WPC1/ARTEMIS/2019).
文摘As a new Ionosphere Associate Analysis Center(IAAC)of the International GNSS Service(IGS),Chinese Academy of Sciences(CAS)started the routine computation of the real-time,rapid,and final Global Ionospheric Maps(GIMs)in 2015.The method for the generation of CAS rapid and final GIMs and recent updates are presented in the paper.The quality of CAS post-processed GIMs is assessed during 2015-2018 after the maximum of solar cycle 24.To perform an independent and fair assessment,Jason-2/3 Vertical Total Electron Contents(VTEC)are first used as the references over the ocean.GPS differential Slant TECs(dSTEC)generated from 55 Multi-GNSS Experimental(MGEX)stations of the IGS are also employed,which provides a complementing way to evaluate the ability of electron content models to reproduce the spatial and temporal gradients in the ionosphere.During the test period,Jet Propulsion Laboratory(JPL)GIMs present significantly positive deviations compared to the Jason VTEC and GPS dSTEC.Technical University of Catalonia(UPC)rapid GIM UQRG exhibits the best performance in both Jason VTEC and GPS dSTEC analysis.The CAS GIMs show comparable performance with the results of the first four IAACs of the IGS.As expected,the poor performance of all GIMs is in equatorial regions and the high latitudes of the southern hemisphere.The consideration of generating multi-layer or three-dimensional ionospheric maps is emphasized to mitigate the inadequacy of ionospheric single-layer assumption in the presence of pronounced latitudinal gradients.The use of ionospheric observations from the new GNSS constellations and other space-or ground-based observation techniques is also suggested in the generation of future GIMs,given the sparse GPS/GLONASS stations in the southern hemisphere.
基金the National Natural Science Foundation of China (Nos. 50878128 and 51278299)
文摘The prestress developing of tensile cable-net structures is a state transforming process from the initial unstressed state to the final prestressed state, and it is rather complicated because the elastic deformation is normally coupled with the kinematic mechanism movement. Firstly, the basic equations of prestress developing by moving boundary joint are derived from the total potential energy equation. Secondly, the presumed initial tension is proposed to impose into the elements and avoid the singularity of global stiffness matrix. And the self-stress mode which is calculated from the equilibrium matrix with singular value decomposition is employed as basically presumed initial tension. By applying boundary movement increment, an iterative computation is developed to calculate the updating geometric configuration and tension evolution. Finally, the MATLAB program is coded from the presented method, and numerical examples indicate that this computational method is effective and has theoretical significance and valuable guide to design and construction of tensile cable-net structure.
基金the National Natural Science Foundation of China(No.51278299)
文摘In order to evaluate the vibration characteristics of non-rigid airship with suspended curtain,we introduce vibration characteristic analysis method of the inflatable membrane structure.Modal numerical method of the inflatable membrane structure under the pressure difference is validated by the model testing of the inflatable cantilever tube.The finite element model of 75 m airships is established to simulate the vibration characteristics subjected to only pressure difference and the resultant force of weight and buoyancy.The nonlinear static deformation and stress analysis are investigated for two kinds of equilibrated configurations with various pressure differences,as well as the vibration characteristics.The structural efficiency of the suspended curtain is investigated through the force transfer ratio at the assumed equilibrated point.The effects of manufacture error of the suspended cable length on the structural behavior are analyzed.The results indicate that the local area of airship envelope connected to the suspended cable is a weak part.Various pressures and pressure gradients have significant effects on the global airship structure and the suspended curtain.The suspended curtain is effective to transfer the equilibrated force from the bottom to the top of airship envelope.Manufacture error of the suspended cable length could result in obvious deformation of local airship envelope.The presented work is valuable to the structural engineering design of stratospheric airship.
文摘This paper presents the results of the application of mathematical morphology for the automatic quantification of the number of tents and the detection of changes in the Menik Farm IDP camp in Sri Lanka.The tents were retrieved using an area-constraint top-hat opening applied to WorldView-1 data.The counting of tents was based on the centroids of the automatically detected structures indicating an overall number of 25,150 tents on the 26 June 2009.The comparison with a visual interpretation produced an R2 of 0.97 with an error of 1.25%.In addition,an automated detection of changes inside a camp area was conducted.The comparison of the satellite image of 26 June 2009(WorldView-1)and an image of 28 February 2010(GeoEye-1)is based on mutual(mixed)information metric,after using morphological image processing techniques and previously specified criterion.Changes are observed on a terrain of around 15.2%of the total camp area and 3813 of previously detected structures disappeared in a period of 8 months.
