This paper investigates the hydrodynamic characteristics of floating truncated cylinders undergoing horizontal and vertical motions due to earthquake excitations in the finite water depth.The governing equation of the...This paper investigates the hydrodynamic characteristics of floating truncated cylinders undergoing horizontal and vertical motions due to earthquake excitations in the finite water depth.The governing equation of the hydrodynamic pressure acting on the cylinder is derived based on the radiation theory with the inviscid and incompressible assumptions.The governing equation is solved by using the method of separating variables and analytical solutions are obtained by assigning reasonable boundary conditions.The analytical result is validated by a numerical model using the exact artificial boundary simulation of the infinite water.The main variation and distribution characteristics of the hydrodynamic pressure acting on the side and bottom of the cylinder are analyzed for different combinations of wide-height and immersion ratios.The added mass coefficient of the cylinder is calculated by integrating the hydrodynamic pressure and simplified formulas are proposed for engineering applications.The calculation results show that the simplified formulas are in good agreement with the analytical solutions.展开更多
In order to accurately predict the on-wave resistance and responses to hull motions of ships in actual sea conditions,the k-εmethod of the RNG model is adopted on the basis of the unsteady RANS method.The two-formula...In order to accurately predict the on-wave resistance and responses to hull motions of ships in actual sea conditions,the k-εmethod of the RNG model is adopted on the basis of the unsteady RANS method.The two-formula turbulence model deals with the viscous flow,the VOF method captures the free surface,the velocity boundary method makes waves,the artificial damping method is used to eliminate waves,and the nested grid technology is used to deal with the motion response of ships on waves.Combined with the 6-DOF motion formula,a three-dimensional numerical wave cell for regular waves is established.For one example,taking a KCS Container ship and fishing boat sailing at a mid-high-speed,the increase of wave resistance and motion response at different wavelengths are analyzed,and the simulation results are compared with the experimental value,the content of strip theory in potential flow theory and the panel method to prove the reliability of CFD method in predicting ship motion.展开更多
传统的通信网络和计算机网络课程在涉及无线接入技术教学时,往往侧重于纯理论模型和相关原理的阐述,在实验环节更多依赖于计算机仿真手段,很少有基于真实硬件设备的实验教学。为丰富授课内容,使学生更直观且全面地了解无线局域网及移动...传统的通信网络和计算机网络课程在涉及无线接入技术教学时,往往侧重于纯理论模型和相关原理的阐述,在实验环节更多依赖于计算机仿真手段,很少有基于真实硬件设备的实验教学。为丰富授课内容,使学生更直观且全面地了解无线局域网及移动自组网(Ad Hoc Network)的媒体访问控制(Media Access Control,MAC)技术,掌握隐藏终端的概念,提出了一种基于CC2530的隐终端实验案例设计与实现方式。介绍了将CC2530作为实验平台硬件的优势,阐述了实验原理,说明了实验平台的搭建、实验的实施过程和结果分析的方法。通过学习实验原理并自主地完成实验,学生能够对无线网络中的隐终端现象有更加深刻的认识。该实验也为相关课程的教师提供了教学参考。展开更多
在无中心节点网络中可能存在不同类型的业务,部分高优先级业务具有严格的时延等服务质量(quality of service,QoS)需求。但当网络负载较重时,冲突概率明显提高,使得这些业务的需求难以得到保障,如何设计高效的多址接入协议以保证不同种...在无中心节点网络中可能存在不同类型的业务,部分高优先级业务具有严格的时延等服务质量(quality of service,QoS)需求。但当网络负载较重时,冲突概率明显提高,使得这些业务的需求难以得到保障,如何设计高效的多址接入协议以保证不同种类业务的服务质量是重要的研究方向。信道预约机制是保证QoS的重要方法,但现有信道预约机制对多种业务服务时,通常没有根据服务质量需求和网络状况精细调整预约参数。因此针对以上问题提出了一种面向差异化业务保障的信道预约MAC协议(differentiated service guarantee adaptive reservation mechanism,DSGARM),协议核心思想是针对每种业务的容忍时延需求和网络状况精细提供差异化服务,协议中通过建立的数学模型设计自适应算法,定量计算出满足时延需求的预约参数,能够根据网络状况自适应调整合适的预约参数以保障每一类业务的时延需求。仿真结果说明了提出协议的优势,具有较大的实际意义。展开更多
基金financially supported by the National Natural Science Foundation of China(Grant Nos.52078010 and 52101321)the National Key Research and Development Program of China(Grant No.2022YFC3004300).
文摘This paper investigates the hydrodynamic characteristics of floating truncated cylinders undergoing horizontal and vertical motions due to earthquake excitations in the finite water depth.The governing equation of the hydrodynamic pressure acting on the cylinder is derived based on the radiation theory with the inviscid and incompressible assumptions.The governing equation is solved by using the method of separating variables and analytical solutions are obtained by assigning reasonable boundary conditions.The analytical result is validated by a numerical model using the exact artificial boundary simulation of the infinite water.The main variation and distribution characteristics of the hydrodynamic pressure acting on the side and bottom of the cylinder are analyzed for different combinations of wide-height and immersion ratios.The added mass coefficient of the cylinder is calculated by integrating the hydrodynamic pressure and simplified formulas are proposed for engineering applications.The calculation results show that the simplified formulas are in good agreement with the analytical solutions.
文摘In order to accurately predict the on-wave resistance and responses to hull motions of ships in actual sea conditions,the k-εmethod of the RNG model is adopted on the basis of the unsteady RANS method.The two-formula turbulence model deals with the viscous flow,the VOF method captures the free surface,the velocity boundary method makes waves,the artificial damping method is used to eliminate waves,and the nested grid technology is used to deal with the motion response of ships on waves.Combined with the 6-DOF motion formula,a three-dimensional numerical wave cell for regular waves is established.For one example,taking a KCS Container ship and fishing boat sailing at a mid-high-speed,the increase of wave resistance and motion response at different wavelengths are analyzed,and the simulation results are compared with the experimental value,the content of strip theory in potential flow theory and the panel method to prove the reliability of CFD method in predicting ship motion.
文摘传统的通信网络和计算机网络课程在涉及无线接入技术教学时,往往侧重于纯理论模型和相关原理的阐述,在实验环节更多依赖于计算机仿真手段,很少有基于真实硬件设备的实验教学。为丰富授课内容,使学生更直观且全面地了解无线局域网及移动自组网(Ad Hoc Network)的媒体访问控制(Media Access Control,MAC)技术,掌握隐藏终端的概念,提出了一种基于CC2530的隐终端实验案例设计与实现方式。介绍了将CC2530作为实验平台硬件的优势,阐述了实验原理,说明了实验平台的搭建、实验的实施过程和结果分析的方法。通过学习实验原理并自主地完成实验,学生能够对无线网络中的隐终端现象有更加深刻的认识。该实验也为相关课程的教师提供了教学参考。
文摘在无中心节点网络中可能存在不同类型的业务,部分高优先级业务具有严格的时延等服务质量(quality of service,QoS)需求。但当网络负载较重时,冲突概率明显提高,使得这些业务的需求难以得到保障,如何设计高效的多址接入协议以保证不同种类业务的服务质量是重要的研究方向。信道预约机制是保证QoS的重要方法,但现有信道预约机制对多种业务服务时,通常没有根据服务质量需求和网络状况精细调整预约参数。因此针对以上问题提出了一种面向差异化业务保障的信道预约MAC协议(differentiated service guarantee adaptive reservation mechanism,DSGARM),协议核心思想是针对每种业务的容忍时延需求和网络状况精细提供差异化服务,协议中通过建立的数学模型设计自适应算法,定量计算出满足时延需求的预约参数,能够根据网络状况自适应调整合适的预约参数以保障每一类业务的时延需求。仿真结果说明了提出协议的优势,具有较大的实际意义。
