本文采用特征线方法和激波装配法,对磁流体中间激波在行星际空间的演化过程进行数值模拟。主要结论如下:(1) 2→4型中间激波通过向下游发出后向慢压缩波使下游态磁场减幅,通过向上游发出前向快压缩波使上游态磁场增幅,以致2→4型中间激...本文采用特征线方法和激波装配法,对磁流体中间激波在行星际空间的演化过程进行数值模拟。主要结论如下:(1) 2→4型中间激波通过向下游发出后向慢压缩波使下游态磁场减幅,通过向上游发出前向快压缩波使上游态磁场增幅,以致2→4型中间激波迅速经导灭激波向慢激波转化;所发出的前向快压缩波经非线性变陡形成快激波。(2)1→3型中间激波首先通过向下游发出前向慢稀疏波而很快变成1→3=4型临界中间激波,并瞬间转变为由前向快激波和前向2→4型中间激波构成的激波系统。其中,2→4型中间激波可在其前导快激波的下游传播较远的距离,有可能为 IAU 附近的飞船观测到,但最终导灭激波转变为慢激波。展开更多
The Bit Error Rate (BER) caused by Inter Carrier Interference (ICI) increases greatly with the increase of frequency offset in Orthogonal Frequency Division Multiplexing (OFDM) systems. According to a typical OFDM sig...The Bit Error Rate (BER) caused by Inter Carrier Interference (ICI) increases greatly with the increase of frequency offset in Orthogonal Frequency Division Multiplexing (OFDM) systems. According to a typical OFDM signal model, this letter proves that the coefficient matrix of ICI is a unitary matrix whose inverse matrix is much easier to get, and then proposes a new ICI cancellation method with less computation complexity by sending typical pilot symbols. Compared with two existing ICI cancellation methods, self-cancellation and windowing cancellation, it is shown that the proposed algorithm can cancel ICI better and overcome the limitation of the two traditional methods.展开更多
A new method based on the material removal and cross-section optical scanning is investigated.The advantage of this method is that the internal and external information of the specimen can be obtained at same precisio...A new method based on the material removal and cross-section optical scanning is investigated.The advantage of this method is that the internal and external information of the specimen can be obtained at same precision. In order to eliminate the pulse and Gaussian noise, the multi-scale dyadic wavelet methods are presented and discussed. The experimental results show that the multi-scale dyadic wavelet methods can successfully extract the features from noise image.The accuracy of 2D edge detection is 5.4 μm with the resolution of 2.7 μm.展开更多
A mathematical model for constant pressure filtration is established. The distribution of hydraulic pressure within the cake and the medium resistance are measured. The medium resistance Rm is calculated from the supp...A mathematical model for constant pressure filtration is established. The distribution of hydraulic pressure within the cake and the medium resistance are measured. The medium resistance Rm is calculated from the suppositional filtration time θm. It is demonstrated that Rm is nearly a constant for a given filter cloth.展开更多
The variations of ocean environmental parameters invariably result in variations of local modal wave numbers of a sound pressure field. The asymptotic Hankel transform with a short sliding window is applied to the com...The variations of ocean environmental parameters invariably result in variations of local modal wave numbers of a sound pressure field. The asymptotic Hankel transform with a short sliding window is applied to the complex sound pressure field in the water containing a mesoscale eddy to examine the variation of local modal wave numbers in such a range-dependent environment. The numerical simulation results show that modal wave number spectra obtained by this method can reflect the location and strength of a mesoscale eddy, therefore it can be used to monitor the strength and spatial scale of ocean mesoscale eddies.展开更多
Downtime due to adverse wave conditions for vessels at berth is an important commercial aspect in the planning and development of a sea port or a berthing terminal. This paper describes a practical technique for preli...Downtime due to adverse wave conditions for vessels at berth is an important commercial aspect in the planning and development of a sea port or a berthing terminal. This paper describes a practical technique for preliminary assessment of operational downtime at a proposed bulk terminal. Time-series wind and wave data at an offshore location was purchased. Numerical modelling was then carried out using the MIKE21 SW （spectral wave） model developed by DHI （Deutsches Hydrographisches Institut） to transform these offshore waves into inshore in order to derive wave conditions at the berth. Both wind-waves and swell-waves were considered. Waves affecting the head and beam of a vessel were considered separately for a wide range of vessel sizes with DT （displacement tonnage） ranging from 5,000 tons to 〉 200,000 tons. The limiting wave height H5% was used. Operational downtime was also calculated using significant wave height, Hs as a criterion with limits ofHs = 1.0 m for beam seas and Hs = 1.5 m for head seas. The methodology and lessons learnt from the study can be applied for the development of any sea port worldwide.展开更多
The outage performance of the multihop free-space optical(FSO) communication system with decode-and-forward(DF) protocol is studied by considering the joint effects of nonzero boresight pointing errors and atmospheric...The outage performance of the multihop free-space optical(FSO) communication system with decode-and-forward(DF) protocol is studied by considering the joint effects of nonzero boresight pointing errors and atmospheric turbulence modeled by exponentiated Weibull(EW) distribution. The closed-form analytical expression of outage probability is derived, and the results are validated through Monte Carlo simulation. Furthermore, the detailed analysis is provided to evaluate the impacts of turbulence strength, receiver aperture size, boresight displacement, beamwidth and number of relays on the outage performance for the studied system.展开更多
文摘本文采用特征线方法和激波装配法,对磁流体中间激波在行星际空间的演化过程进行数值模拟。主要结论如下:(1) 2→4型中间激波通过向下游发出后向慢压缩波使下游态磁场减幅,通过向上游发出前向快压缩波使上游态磁场增幅,以致2→4型中间激波迅速经导灭激波向慢激波转化;所发出的前向快压缩波经非线性变陡形成快激波。(2)1→3型中间激波首先通过向下游发出前向慢稀疏波而很快变成1→3=4型临界中间激波,并瞬间转变为由前向快激波和前向2→4型中间激波构成的激波系统。其中,2→4型中间激波可在其前导快激波的下游传播较远的距离,有可能为 IAU 附近的飞船观测到,但最终导灭激波转变为慢激波。
文摘The Bit Error Rate (BER) caused by Inter Carrier Interference (ICI) increases greatly with the increase of frequency offset in Orthogonal Frequency Division Multiplexing (OFDM) systems. According to a typical OFDM signal model, this letter proves that the coefficient matrix of ICI is a unitary matrix whose inverse matrix is much easier to get, and then proposes a new ICI cancellation method with less computation complexity by sending typical pilot symbols. Compared with two existing ICI cancellation methods, self-cancellation and windowing cancellation, it is shown that the proposed algorithm can cancel ICI better and overcome the limitation of the two traditional methods.
文摘A new method based on the material removal and cross-section optical scanning is investigated.The advantage of this method is that the internal and external information of the specimen can be obtained at same precision. In order to eliminate the pulse and Gaussian noise, the multi-scale dyadic wavelet methods are presented and discussed. The experimental results show that the multi-scale dyadic wavelet methods can successfully extract the features from noise image.The accuracy of 2D edge detection is 5.4 μm with the resolution of 2.7 μm.
文摘A mathematical model for constant pressure filtration is established. The distribution of hydraulic pressure within the cake and the medium resistance are measured. The medium resistance Rm is calculated from the suppositional filtration time θm. It is demonstrated that Rm is nearly a constant for a given filter cloth.
文摘The variations of ocean environmental parameters invariably result in variations of local modal wave numbers of a sound pressure field. The asymptotic Hankel transform with a short sliding window is applied to the complex sound pressure field in the water containing a mesoscale eddy to examine the variation of local modal wave numbers in such a range-dependent environment. The numerical simulation results show that modal wave number spectra obtained by this method can reflect the location and strength of a mesoscale eddy, therefore it can be used to monitor the strength and spatial scale of ocean mesoscale eddies.
文摘Downtime due to adverse wave conditions for vessels at berth is an important commercial aspect in the planning and development of a sea port or a berthing terminal. This paper describes a practical technique for preliminary assessment of operational downtime at a proposed bulk terminal. Time-series wind and wave data at an offshore location was purchased. Numerical modelling was then carried out using the MIKE21 SW （spectral wave） model developed by DHI （Deutsches Hydrographisches Institut） to transform these offshore waves into inshore in order to derive wave conditions at the berth. Both wind-waves and swell-waves were considered. Waves affecting the head and beam of a vessel were considered separately for a wide range of vessel sizes with DT （displacement tonnage） ranging from 5,000 tons to 〉 200,000 tons. The limiting wave height H5% was used. Operational downtime was also calculated using significant wave height, Hs as a criterion with limits ofHs = 1.0 m for beam seas and Hs = 1.5 m for head seas. The methodology and lessons learnt from the study can be applied for the development of any sea port worldwide.
基金supported by the Fundamental Research Funds for the Central Universities(No.JB160105)the“111 Project”of China(No.B08038)
文摘The outage performance of the multihop free-space optical(FSO) communication system with decode-and-forward(DF) protocol is studied by considering the joint effects of nonzero boresight pointing errors and atmospheric turbulence modeled by exponentiated Weibull(EW) distribution. The closed-form analytical expression of outage probability is derived, and the results are validated through Monte Carlo simulation. Furthermore, the detailed analysis is provided to evaluate the impacts of turbulence strength, receiver aperture size, boresight displacement, beamwidth and number of relays on the outage performance for the studied system.
