该文采用M OD IS N DV I时序数据对东北区土地覆盖分类进行研究,以验证M OD IS区域土地覆盖制图的可靠性。通过试验发现经过Sav izky-G o lay滤波处理能有效去除云、缺失数据及异常值的影响,使得N DV I时序曲线能更好的反映植被季相变...该文采用M OD IS N DV I时序数据对东北区土地覆盖分类进行研究,以验证M OD IS区域土地覆盖制图的可靠性。通过试验发现经过Sav izky-G o lay滤波处理能有效去除云、缺失数据及异常值的影响,使得N DV I时序曲线能更好的反映植被季相变化特征,分类结果表明N DV I时序数列能较好的区分植被与非植被、草本(一年生)与木本(多年生)覆盖类型。但研究区内一年一熟的农作物与高盖度草地、落叶针叶林与落叶阔叶林具有相似的物候特征,混分现象比较严重。该研究通过添加地表温度(land surface tem perature,LST)数据解决这一问题,利用所得温度/植被指数TV I对研究区进行土地覆盖分类。所得结果用363个野外调查样区进行验证,N DV I及TV I时序数据的分类精度分别为62.26%与71.63%。结果表明TV I比N DV I对土地覆盖类型中的植被类型识别更有效。展开更多
阐述了G7的定义、工艺原理及其应用领域,介绍了传统TVI(Tone Value Increase)法与四维CMYK转换法,将G7与它们进行了对比研究,分析了各自的优点和局限性,发现G7对于印刷工艺过程控制具有明显的优势。最后讨论了G7认证的真正价值,以给印...阐述了G7的定义、工艺原理及其应用领域,介绍了传统TVI(Tone Value Increase)法与四维CMYK转换法,将G7与它们进行了对比研究,分析了各自的优点和局限性,发现G7对于印刷工艺过程控制具有明显的优势。最后讨论了G7认证的真正价值,以给印刷企业提供帮助。展开更多
In this study,non-cavitating and cavitating flow around the benchmark DTMB 4119 model propeller are solved using both viscous and potential based solvers.Cavitating and non-cavitating propeller radiated noises are the...In this study,non-cavitating and cavitating flow around the benchmark DTMB 4119 model propeller are solved using both viscous and potential based solvers.Cavitating and non-cavitating propeller radiated noises are then predicted by using a hybrid method in which RANS(Reynolds-averaged Navier-Stokes)and FWH(Ffowcs Williams Hawkings)equations are solved together in open water conditions.Sheet cavitation on the propeller blades is modelled by using a VOF(Volume of Fiuld)method equipped with Schnerr-Sauer cavitation model.Nevertheless,tip vortex cavitation noise is estimated by using two different semi-empirical techniques,namely Tip Vortex Index(TVI,based on potential flow theory)and Tip Vortex Contribution(TVC).As the reference distance between noise source and receiver is not defined in open water case for TVI technique,one of the outputs of this study is to propose a reference distance for TVI technique by coupling two semi-empirical techniques and ITTC distance normalization.At the defined distance,the starting point of the tip vortex cavitation is determined for different advance ratios and cavitation numbers using potential flow solver.Also,it is examined that whether the hybrid method and potential flow solver give the same noise results at the inception point of tip vortex cavitation.Results show that TVI method based on potential flow theory is reliable and can practically be used to replace the hybrid method(RANS with FWH approach)when tip vortex cavitation starts.展开更多
文摘该文采用M OD IS N DV I时序数据对东北区土地覆盖分类进行研究,以验证M OD IS区域土地覆盖制图的可靠性。通过试验发现经过Sav izky-G o lay滤波处理能有效去除云、缺失数据及异常值的影响,使得N DV I时序曲线能更好的反映植被季相变化特征,分类结果表明N DV I时序数列能较好的区分植被与非植被、草本(一年生)与木本(多年生)覆盖类型。但研究区内一年一熟的农作物与高盖度草地、落叶针叶林与落叶阔叶林具有相似的物候特征,混分现象比较严重。该研究通过添加地表温度(land surface tem perature,LST)数据解决这一问题,利用所得温度/植被指数TV I对研究区进行土地覆盖分类。所得结果用363个野外调查样区进行验证,N DV I及TV I时序数据的分类精度分别为62.26%与71.63%。结果表明TV I比N DV I对土地覆盖类型中的植被类型识别更有效。
文摘In this study,non-cavitating and cavitating flow around the benchmark DTMB 4119 model propeller are solved using both viscous and potential based solvers.Cavitating and non-cavitating propeller radiated noises are then predicted by using a hybrid method in which RANS(Reynolds-averaged Navier-Stokes)and FWH(Ffowcs Williams Hawkings)equations are solved together in open water conditions.Sheet cavitation on the propeller blades is modelled by using a VOF(Volume of Fiuld)method equipped with Schnerr-Sauer cavitation model.Nevertheless,tip vortex cavitation noise is estimated by using two different semi-empirical techniques,namely Tip Vortex Index(TVI,based on potential flow theory)and Tip Vortex Contribution(TVC).As the reference distance between noise source and receiver is not defined in open water case for TVI technique,one of the outputs of this study is to propose a reference distance for TVI technique by coupling two semi-empirical techniques and ITTC distance normalization.At the defined distance,the starting point of the tip vortex cavitation is determined for different advance ratios and cavitation numbers using potential flow solver.Also,it is examined that whether the hybrid method and potential flow solver give the same noise results at the inception point of tip vortex cavitation.Results show that TVI method based on potential flow theory is reliable and can practically be used to replace the hybrid method(RANS with FWH approach)when tip vortex cavitation starts.
