A large eddy simulation （LES） of the flows around an underwater vehicle model at intermediate Reynolds numbers is performed. The underwater vehicle model is taken as the DARPA SUBOFF with full appendages, where the ...A large eddy simulation （LES） of the flows around an underwater vehicle model at intermediate Reynolds numbers is performed. The underwater vehicle model is taken as the DARPA SUBOFF with full appendages, where the Reynolds number based on the hull length is 1.0x 105, An immersed boundary method based on the moving-least-squares reconstruction is used to handle the complex geometric boundaries. The adaptive mesh refinement is utilized to resolve the flows near the hull, The parallel scalabilities of the flow solver are tested on meshes with the number of cells varying from 50 million to 3.2 billion, The parallel solver reaches nearly linear scalability for the flows around the underwater vehicle model, The present simulation captures the essential features of the vortex structures near the hull and in the wake, Both of the time-averaged pressure coefficients and srreamwise velocity profiles obtained from the LES are consistent with the characteristics of the flows pass an appended axisymmetric body. The code efficiency and its correct predictions on flow features allow us to perform the full-scale simulations on tens of thousands of cores with billions of grid points for higher-Reynolds-number flows around the underwater vehicles.展开更多
The inhomogeneous sound speed in seawater causes refraction of sound waves,and the elimination of the refraction effect is essential to the accuracy of underwater acoustic positioning.The raytracing method is an indis...The inhomogeneous sound speed in seawater causes refraction of sound waves,and the elimination of the refraction effect is essential to the accuracy of underwater acoustic positioning.The raytracing method is an indispensable tool for effectively handling problems.However,this method has a conflict between localization accuracy and computational quantity.The equivalent sound speed profile(ESSP)method uses a simple sound speed profile(SSP)instead of the actual complex SSP,which can improve positioning precision but with residual error.The residual error is especially non-negligible in deep water and at large beam incidence angles.By analyzing the residual error of the ESSP method through a simulation,an empirical formula of error is presented.The data collected in the sailing circle mode(large incidence angle)of the South China Sea are used for verification.The experiments show that compared to the ESSP method,the improved algorithm has higher positioning precision and is more efficient than the ray-tracing method.展开更多
A novel efficient track initiation method is proposed for the harsh underwater target tracking environment(heavy clutter and large measurement errors): track splitting, evaluating, pruning and merging method(TSEPM). T...A novel efficient track initiation method is proposed for the harsh underwater target tracking environment(heavy clutter and large measurement errors): track splitting, evaluating, pruning and merging method(TSEPM). Track initiation demands that the method should determine the existence and initial state of a target quickly and correctly.Heavy clutter and large measurement errors certainly pose additional difficulties and challenges, which deteriorate and complicate the track initiation in the harsh underwater target tracking environment. There are three primary shortcomings for the current track initiation methods to initialize a target:(a) they cannot eliminate the turbulences of clutter effectively;(b) there may be a high false alarm probability and low detection probability of a track;(c) they cannot estimate the initial state for a new confirmed track correctly. Based on the multiple hypotheses tracking principle and modified logic-based track initiation method, in order to increase the detection probability of a track,track splitting creates a large number of tracks which include the true track originated from the target. And in order to decrease the false alarm probability, based on the evaluation mechanism, track pruning and track merging are proposed to reduce the false tracks. TSEPM method can deal with the track initiation problems derived from heavy clutter and large measurement errors, determine the target’s existence and estimate its initial state with the least squares method. What’s more, our method is fully automatic and does not require any kind manual input for initializing and tuning any parameter. Simulation results indicate that our new method improves significantly the performance of the track initiation in the harsh underwater target tracking environment.展开更多
Marine current turbine(MCT),which is designed for the power supply of underwater mooring platform(UMP),is investigated in this article.To reduce its flow noise,the microgrooved surface is applied at the suction surfac...Marine current turbine(MCT),which is designed for the power supply of underwater mooring platform(UMP),is investigated in this article.To reduce its flow noise,the microgrooved surface is applied at the suction surface of the turbine blades.Comprehensive analyses of the effects of the UMP on MCT with microgrooved surface in different working conditions are presented.The transient turbulent flow field is obtained by incompressible large eddy simulation(LES),and then the Ffowcs Williams and Hawkings(FW-H)acoustic analogy is adopted to forecast the flow noise generated from the pressure fluctuations and loadings of the UMP shell and MCT blade surfaces.The numerical methods are first validated with experimental data and good agreements are obtained.Then,the influence of several key parameters on the performance of the MCT is then systematically studied,including interval distance,angle of pitch and angle of sideslip.For each case,the hydrodynamic parameters(thrust coefficient,torque coefficient and power coefficient),the vortical structures behind the model and the overall sound pressure level(OASPL)directionality are analyzed.Additionally,the noise reduction effect of the microgrooved surface is also presented.The present investigation could provide an overall understanding for the performance of MCT combined with UMP.展开更多
针对大深度环境水下发射技术需求,提出一种利用水压驱动两级提拉式水下新型发射方案。利用大深度环境高压水驱动两级活塞实现武器快速发射。建立武器出管过程动力学模型,开展高压水驱动方案原理验证试验,并与高压气体驱动方案进行了对...针对大深度环境水下发射技术需求,提出一种利用水压驱动两级提拉式水下新型发射方案。利用大深度环境高压水驱动两级活塞实现武器快速发射。建立武器出管过程动力学模型,开展高压水驱动方案原理验证试验,并与高压气体驱动方案进行了对比分析。研究结果表明:水压驱动与气体驱动方案的内弹道结果基本一致,高压水发射方案在大深度环境具有显著优势;加速度峰值出现在发射瞬时和级间转换过程,级间转换过程武器加速度存在显著的陡变现象;水下发射武器出管过程弹道预报结果得出,在发射水深100~500 m条件下,武器出管过程最大速度范围为7.4~15.3 m/s,最大加速度小于100 m/s 2;研究结果验证了水压驱动两级活塞式发射方案的可行性,为装置的进一步研制开发提供了设计依据。展开更多
针对在越江海高水压水下超大直径盾构隧道联络通道施工过程中缺乏足够的工程技术标准和案例经验、设计与施工面临众多挑战问题,以广州海珠湾超大直径盾构隧道区间的6条联络通道工程为例,对工程地质补勘资料及现场施工情况进行分析,揭示...针对在越江海高水压水下超大直径盾构隧道联络通道施工过程中缺乏足够的工程技术标准和案例经验、设计与施工面临众多挑战问题,以广州海珠湾超大直径盾构隧道区间的6条联络通道工程为例,对工程地质补勘资料及现场施工情况进行分析,揭示原矿山法设计施工方案存在的不足,并基于此提出“矿山法结合地层冻结加固方案”和“机械顶管法施工方案”2种优化方案;随后在安全性、经济性、施工工期等方面对不同工法进行综合优选分析,同时引入碳排放指标进行绿色低碳评估。研究结果表明:1)机械顶管法在安全性和施工效率上优于其他方案,能够显著缩短施工周期;2)相比矿山法结合地层冻结加固方案,机械顶管法方案碳排放量减少了2 747.51 t CO_(2e)。展开更多
该文开展了2.5 g TNT、RDX和B炸药在固支方板底部近距离起爆的水下爆炸试验,研究了固支方板在水下爆炸冲击波、气泡脉动、水射流载荷共同作用下的动态响应。试验结果表明:含能较低的TNT炸药使方板呈现整体上凸式永久变形,含能较高的B炸...该文开展了2.5 g TNT、RDX和B炸药在固支方板底部近距离起爆的水下爆炸试验,研究了固支方板在水下爆炸冲击波、气泡脉动、水射流载荷共同作用下的动态响应。试验结果表明:含能较低的TNT炸药使方板呈现整体上凸式永久变形,含能较高的B炸药和RDX炸药会使方板呈现中部上凸、边部下凹式永久变形。为了进一步探讨不同炸药对固支方板的毁伤特性,通过ABAQUS软件对水下爆炸全过程进行数值模拟,数值模拟结果显示:在气泡膨胀的过程中,气泡内部压力逐渐小于大气压力,固支方板在压力差的作用下向下凹陷,接着在气泡脉动和水射流的联合作用下向上凸起,在不同类型炸药产生的气泡作用下方板凸起过程中动态响应的差异是其呈现不同毁伤形态的根本原因。仿真结果还显示,固支方板的最大等效塑性应变发生在固支边界处;增加板厚可有效防止固支方板发生中凸边凹式变形。该文的工作可为水下战斗部设计提供参考。展开更多
基金supported by the National Natural Science Foundation of China (11302238, 11232011. and 11572331)support from the Strategic Priority Research Program (XDB22040104)+1 种基金the Key Research Program of Frontier Sciences of the Chinese Academy of Sciences (QYZDJ-SSW-SYS002)the National Basic Research Program of China (973 Program 2013CB834100: Nonlinear science)
文摘A large eddy simulation （LES） of the flows around an underwater vehicle model at intermediate Reynolds numbers is performed. The underwater vehicle model is taken as the DARPA SUBOFF with full appendages, where the Reynolds number based on the hull length is 1.0x 105, An immersed boundary method based on the moving-least-squares reconstruction is used to handle the complex geometric boundaries. The adaptive mesh refinement is utilized to resolve the flows near the hull, The parallel scalabilities of the flow solver are tested on meshes with the number of cells varying from 50 million to 3.2 billion, The parallel solver reaches nearly linear scalability for the flows around the underwater vehicle model, The present simulation captures the essential features of the vortex structures near the hull and in the wake, Both of the time-averaged pressure coefficients and srreamwise velocity profiles obtained from the LES are consistent with the characteristics of the flows pass an appended axisymmetric body. The code efficiency and its correct predictions on flow features allow us to perform the full-scale simulations on tens of thousands of cores with billions of grid points for higher-Reynolds-number flows around the underwater vehicles.
基金the Natural Science Foundation of Shandong Province of China(No.ZR2022MA051)the China Postdoctoral Science Foundation(No.2020M670891)the SDUST Research Fund(No.2019TDJH103)。
文摘The inhomogeneous sound speed in seawater causes refraction of sound waves,and the elimination of the refraction effect is essential to the accuracy of underwater acoustic positioning.The raytracing method is an indispensable tool for effectively handling problems.However,this method has a conflict between localization accuracy and computational quantity.The equivalent sound speed profile(ESSP)method uses a simple sound speed profile(SSP)instead of the actual complex SSP,which can improve positioning precision but with residual error.The residual error is especially non-negligible in deep water and at large beam incidence angles.By analyzing the residual error of the ESSP method through a simulation,an empirical formula of error is presented.The data collected in the sailing circle mode(large incidence angle)of the South China Sea are used for verification.The experiments show that compared to the ESSP method,the improved algorithm has higher positioning precision and is more efficient than the ray-tracing method.
基金financially supported by the Key Research Program of the Chinese Academy of Sciences(Grant No.KGFZD-125-014)the National Natural Science Foundation of China(Grant No.61273334)State Key Laboratory of Robotics Foundation(Grant No.2017-Z05)
文摘A novel efficient track initiation method is proposed for the harsh underwater target tracking environment(heavy clutter and large measurement errors): track splitting, evaluating, pruning and merging method(TSEPM). Track initiation demands that the method should determine the existence and initial state of a target quickly and correctly.Heavy clutter and large measurement errors certainly pose additional difficulties and challenges, which deteriorate and complicate the track initiation in the harsh underwater target tracking environment. There are three primary shortcomings for the current track initiation methods to initialize a target:(a) they cannot eliminate the turbulences of clutter effectively;(b) there may be a high false alarm probability and low detection probability of a track;(c) they cannot estimate the initial state for a new confirmed track correctly. Based on the multiple hypotheses tracking principle and modified logic-based track initiation method, in order to increase the detection probability of a track,track splitting creates a large number of tracks which include the true track originated from the target. And in order to decrease the false alarm probability, based on the evaluation mechanism, track pruning and track merging are proposed to reduce the false tracks. TSEPM method can deal with the track initiation problems derived from heavy clutter and large measurement errors, determine the target’s existence and estimate its initial state with the least squares method. What’s more, our method is fully automatic and does not require any kind manual input for initializing and tuning any parameter. Simulation results indicate that our new method improves significantly the performance of the track initiation in the harsh underwater target tracking environment.
基金supported by the Scientific Research Start-up Fund of Nanjing University of Science and Technology(Grant No.AE89991/383)the National Natural Science Foundation of China(Grant Nos.51809214,10672136 and 61572404).
文摘Marine current turbine(MCT),which is designed for the power supply of underwater mooring platform(UMP),is investigated in this article.To reduce its flow noise,the microgrooved surface is applied at the suction surface of the turbine blades.Comprehensive analyses of the effects of the UMP on MCT with microgrooved surface in different working conditions are presented.The transient turbulent flow field is obtained by incompressible large eddy simulation(LES),and then the Ffowcs Williams and Hawkings(FW-H)acoustic analogy is adopted to forecast the flow noise generated from the pressure fluctuations and loadings of the UMP shell and MCT blade surfaces.The numerical methods are first validated with experimental data and good agreements are obtained.Then,the influence of several key parameters on the performance of the MCT is then systematically studied,including interval distance,angle of pitch and angle of sideslip.For each case,the hydrodynamic parameters(thrust coefficient,torque coefficient and power coefficient),the vortical structures behind the model and the overall sound pressure level(OASPL)directionality are analyzed.Additionally,the noise reduction effect of the microgrooved surface is also presented.The present investigation could provide an overall understanding for the performance of MCT combined with UMP.
文摘针对大深度环境水下发射技术需求,提出一种利用水压驱动两级提拉式水下新型发射方案。利用大深度环境高压水驱动两级活塞实现武器快速发射。建立武器出管过程动力学模型,开展高压水驱动方案原理验证试验,并与高压气体驱动方案进行了对比分析。研究结果表明:水压驱动与气体驱动方案的内弹道结果基本一致,高压水发射方案在大深度环境具有显著优势;加速度峰值出现在发射瞬时和级间转换过程,级间转换过程武器加速度存在显著的陡变现象;水下发射武器出管过程弹道预报结果得出,在发射水深100~500 m条件下,武器出管过程最大速度范围为7.4~15.3 m/s,最大加速度小于100 m/s 2;研究结果验证了水压驱动两级活塞式发射方案的可行性,为装置的进一步研制开发提供了设计依据。
文摘针对在越江海高水压水下超大直径盾构隧道联络通道施工过程中缺乏足够的工程技术标准和案例经验、设计与施工面临众多挑战问题,以广州海珠湾超大直径盾构隧道区间的6条联络通道工程为例,对工程地质补勘资料及现场施工情况进行分析,揭示原矿山法设计施工方案存在的不足,并基于此提出“矿山法结合地层冻结加固方案”和“机械顶管法施工方案”2种优化方案;随后在安全性、经济性、施工工期等方面对不同工法进行综合优选分析,同时引入碳排放指标进行绿色低碳评估。研究结果表明:1)机械顶管法在安全性和施工效率上优于其他方案,能够显著缩短施工周期;2)相比矿山法结合地层冻结加固方案,机械顶管法方案碳排放量减少了2 747.51 t CO_(2e)。
文摘该文开展了2.5 g TNT、RDX和B炸药在固支方板底部近距离起爆的水下爆炸试验,研究了固支方板在水下爆炸冲击波、气泡脉动、水射流载荷共同作用下的动态响应。试验结果表明:含能较低的TNT炸药使方板呈现整体上凸式永久变形,含能较高的B炸药和RDX炸药会使方板呈现中部上凸、边部下凹式永久变形。为了进一步探讨不同炸药对固支方板的毁伤特性,通过ABAQUS软件对水下爆炸全过程进行数值模拟,数值模拟结果显示:在气泡膨胀的过程中,气泡内部压力逐渐小于大气压力,固支方板在压力差的作用下向下凹陷,接着在气泡脉动和水射流的联合作用下向上凸起,在不同类型炸药产生的气泡作用下方板凸起过程中动态响应的差异是其呈现不同毁伤形态的根本原因。仿真结果还显示,固支方板的最大等效塑性应变发生在固支边界处;增加板厚可有效防止固支方板发生中凸边凹式变形。该文的工作可为水下战斗部设计提供参考。
