Polar Carriers operate in both open water and brash ice areas,where differing navigation environments impose varying requirements on hull form design.Determining the proportion of these navigation areas is crucial for...Polar Carriers operate in both open water and brash ice areas,where differing navigation environments impose varying requirements on hull form design.Determining the proportion of these navigation areas is crucial for achieving a balanced hull form that optimizes both open water performance and ice-going capabilities.This paper proposes a Navigation State Recognition Model(NSRM)that utilizes GPS data from ship tracks to distinguish between different navigation states,allowing for an assessment of the proportion of open water and brash ice encountered during voyages.Based on the NSRM,a rapid hull form optimization method is developed for polar ships,aiming to minimize total resistance across both open water and brash ice areas.The total resistance is calculated using a weighted sum of the resistances in ice-covered and open-water sections of the route,as determined by the NSRM.The Rankine source and Reynolds-Averaged Navier-Stokes(RANS)methods are employed to calculate open-water resistance,while Juva and Riskas formula is used to estimate ice resistance in brash ice conditions.Additionally,the optimization method is applied to a parent ship with an invisible bulbous bow,resulting in an optimized bow hull form.This demonstrates the applicability of the NSRM-based optimization method for the design of Polar Carrier hull forms.展开更多
Vehicle positioning with the global navigation satellite system （GNSS） in urban environments faces two problems which are attenuation and dynamic. For traditional GNSS receivers hardly able to track dynamic weak sig...Vehicle positioning with the global navigation satellite system （GNSS） in urban environments faces two problems which are attenuation and dynamic. For traditional GNSS receivers hardly able to track dynamic weak signals, the coupling between all visible satellite signals is ignored in the absence of navigation state feedback, and thermal noise error and dynamic stress threshold are contradictory due to non-coherent discriminators. The vector delay/frequency locked loop （VDFLL） with navigation state feedback and the joint vector tracking loop （JVTL） with coherent discriminator which is a synchronization parameter tracking loop based on maximum likelihood estimation （MLE） are proposed to improve the tracking sensitivity of GNSS receiver in dynamic weak signal environments. A joint vector position tracking loop （JVPTL） directly tracking user position and velocity is proposed to further improve tracking sensitivity. The coherent navigation parameter discriminator of JVPTL, being able to ease the contradiction between thermal noise error and dynamic stress threshold, is based on MLE according to the navigation parameter based linear model of received baseband signals. Simulation results show that JVPTL, which combines the advantages of both VDFLL and JVTL, performs better than both VDFLL and JVTL in dynamic weak signal environments.展开更多
基金funded by the National Natural Science Foundation of China(No.52301330)the Fundamental Research Funds for the Central Universities.
文摘Polar Carriers operate in both open water and brash ice areas,where differing navigation environments impose varying requirements on hull form design.Determining the proportion of these navigation areas is crucial for achieving a balanced hull form that optimizes both open water performance and ice-going capabilities.This paper proposes a Navigation State Recognition Model(NSRM)that utilizes GPS data from ship tracks to distinguish between different navigation states,allowing for an assessment of the proportion of open water and brash ice encountered during voyages.Based on the NSRM,a rapid hull form optimization method is developed for polar ships,aiming to minimize total resistance across both open water and brash ice areas.The total resistance is calculated using a weighted sum of the resistances in ice-covered and open-water sections of the route,as determined by the NSRM.The Rankine source and Reynolds-Averaged Navier-Stokes(RANS)methods are employed to calculate open-water resistance,while Juva and Riskas formula is used to estimate ice resistance in brash ice conditions.Additionally,the optimization method is applied to a parent ship with an invisible bulbous bow,resulting in an optimized bow hull form.This demonstrates the applicability of the NSRM-based optimization method for the design of Polar Carrier hull forms.
基金supported by the National Natural Science Foundation for Young Scientists of China(61201190)
文摘Vehicle positioning with the global navigation satellite system （GNSS） in urban environments faces two problems which are attenuation and dynamic. For traditional GNSS receivers hardly able to track dynamic weak signals, the coupling between all visible satellite signals is ignored in the absence of navigation state feedback, and thermal noise error and dynamic stress threshold are contradictory due to non-coherent discriminators. The vector delay/frequency locked loop （VDFLL） with navigation state feedback and the joint vector tracking loop （JVTL） with coherent discriminator which is a synchronization parameter tracking loop based on maximum likelihood estimation （MLE） are proposed to improve the tracking sensitivity of GNSS receiver in dynamic weak signal environments. A joint vector position tracking loop （JVPTL） directly tracking user position and velocity is proposed to further improve tracking sensitivity. The coherent navigation parameter discriminator of JVPTL, being able to ease the contradiction between thermal noise error and dynamic stress threshold, is based on MLE according to the navigation parameter based linear model of received baseband signals. Simulation results show that JVPTL, which combines the advantages of both VDFLL and JVTL, performs better than both VDFLL and JVTL in dynamic weak signal environments.
