The effects of hurricane forward speed(V)and approach angle(θ)on storm surge are important and a systematic investigation covering possible and continuous ranges of these parameters has not been done before.Here we p...The effects of hurricane forward speed(V)and approach angle(θ)on storm surge are important and a systematic investigation covering possible and continuous ranges of these parameters has not been done before.Here we present such a study with a numerical experiment using the Finite Volume Community Ocean Model(FVCOM).The hurricane track is simplified as a straight line,such that V andθfully define the motion of the hurricane.The maximum surge is contributed by both free waves and a forced storm surge wave moving with the hurricane.Among the free waves,Kelvin-type waves can only propagate in the down-coast direction.Simulations show that those waves can only have a significant positive storm surge when the hurricane velocity has a down-coast component.The optimal values of V andθthat maximize the storm surge in an idealized semi-circular ocean basin are functions of the bathymetry.For a constant bathymetry,the maximum surge occurs when the hurricane approaches the coast from the normal direction when the free wave generation is minimal;for a stepped bathymetry,the maximum surge occurs at a certain acute approach angle which maximizes the duration of persistent wind forcing;a step-like bathymetry with a sloped shelf is similar to the stepped bathymetry,with the added possibility of landfall resonance when the free and forced waves are moving at about the same velocity.For other cases,the storm surge is smaller,given other parameters(hurricane size,maximum wind speed,etc.)unchanged.展开更多
An expression of the 3-D pulsating source of Michell type with forward speed for infinite water depth is derived in the present paper based on the Fourier transformation and contour integration technique. Emphases are...An expression of the 3-D pulsating source of Michell type with forward speed for infinite water depth is derived in the present paper based on the Fourier transformation and contour integration technique. Emphases are laid on the discussion of the mechanical feature of the source and the radiation behavior far from the source. The relative importance of each components of the pulsating source is discussed in detail. Compared with the commonly used pulsating source of Haskind type, the present expression has the merits of simplicity for numerical treatment and being more meaningful in its physical explanation. The Michell type expression of the 3-D pulsating source with forward speed can be widely used for the estimation of motions and wave forces for ships and offshore structures in waves with forward speed. The radiative behavior of the source in the far field may also give a reasonabel description of the radiation condition or the open boundary condition for other numerical methods, such as the Rankine source method etc.展开更多
The time-domain calculations of retard function and ship motions in waves by the direct time-domain method （DTM） and the frequency to time-domain transformation method （FTTM） are compared and analyzed. A Wigley-hu...The time-domain calculations of retard function and ship motions in waves by the direct time-domain method （DTM） and the frequency to time-domain transformation method （FTTM） are compared and analyzed. A Wigley-hull-form ship and an $60 ship moving in waves are examined, and the corresponding retard functions are in good agreement with those given by DTM and FTTM. The comparison of retard functions in different forward speeds by the two methods is observed, and the results of ship motions in forward speed are also compared with the experimental data. On this basis, the advantage and disadvantage of them are discussed.展开更多
The mechanical properties of the glue have great effects on the forward roll coating,which are analyzed here. The analysis shows that liquid viscosity,up and down rollers' speeds,diameters and the size of their ga...The mechanical properties of the glue have great effects on the forward roll coating,which are analyzed here. The analysis shows that liquid viscosity,up and down rollers' speeds,diameters and the size of their gap have major impacts on coating property.The pressure and the shear force increase with the increases of the roll rotation speed,the radii and the viscosity of the glue,while decrease with the increase of the size of the roller gap. At a position of about 0. 8 mm from the nip symmetry axis by removing dimensionality,the pressure produces a maximum or minimum value,and the direction of the shear force changes.展开更多
This article reports on track-monitoring and analyzing machine clearances during wood forwarding across seasons and weather, using ultrasonic distance sensors in combination with time-stamped GPS xy locations, at 10 s...This article reports on track-monitoring and analyzing machine clearances during wood forwarding across seasons and weather, using ultrasonic distance sensors in combination with time-stamped GPS xy locations, at 10 sec intervals. The resulting data, obtained from 54 harvesting blocks, were analyzed by machine type (two wood forwarders and one grapple skidder), stand type (softwood plantation versus natural hardwood stands), month, slope, cartographic depth-to-water (DTW) classes, number of passes along track, and machine speed. For the most part, clearances were highly variable, due to passing over stumps, rocks, harvest slash, brushmats, ruts, and snow cover when present. This variability was on average greater for the lighter-weight wood forwarders than for the heavier-weight skidder, with the former mostly moving along equally spaced lines on brushmats, while the paths of the latter spread away from central wood-landing sites. In terms of trends, machines moved 1) more slowly on wet ground, 2) faster during returning than forwarding, and 3) fastest along wood-landing roads, as to be expected. Low clearances were most notable during winter on snow-covered ground, and on non-frozen shallow DTW and wet multiple-pass ground. During dry weather conditions, clearances also increased from low-pass tracks to multi-pass tracks due to repeat soil compaction of broadened tracks. These results are presented block-by-block and by machine type. Each block-based clearance frequency pattern was quantified through regression analysis and using a gamma probability distribution function.展开更多
针对双PWM变频器整流侧与逆变侧独立控制时,直流侧必须利用大电容稳压,导致系统成本增加且寿命缩短的问题,提出一种整流侧采用引入新型开关矢量表的直接功率控制(Direct Power Control,DPC)方案。该方案逆变侧采用转子磁场定向矢量控制...针对双PWM变频器整流侧与逆变侧独立控制时,直流侧必须利用大电容稳压,导致系统成本增加且寿命缩短的问题,提出一种整流侧采用引入新型开关矢量表的直接功率控制(Direct Power Control,DPC)方案。该方案逆变侧采用转子磁场定向矢量控制,并采用负载功率前馈控制策略,以实现双PWM变频器的协调控制。仿真实验结果表明,相比独立控制的双PWM变频调速系统,采用该一体化协调控制策略的双PWM变频调速系统,不仅能减小网侧电流的谐波,还可较好地抑制负载突变时直流电压的波动,加快整流侧和逆变侧的动态响应,大大提高系统的抗扰能力,从而减小电容体积并降低成本。展开更多
基金The National Key R&D Project under contract No.2017YFC1404201
文摘The effects of hurricane forward speed(V)and approach angle(θ)on storm surge are important and a systematic investigation covering possible and continuous ranges of these parameters has not been done before.Here we present such a study with a numerical experiment using the Finite Volume Community Ocean Model(FVCOM).The hurricane track is simplified as a straight line,such that V andθfully define the motion of the hurricane.The maximum surge is contributed by both free waves and a forced storm surge wave moving with the hurricane.Among the free waves,Kelvin-type waves can only propagate in the down-coast direction.Simulations show that those waves can only have a significant positive storm surge when the hurricane velocity has a down-coast component.The optimal values of V andθthat maximize the storm surge in an idealized semi-circular ocean basin are functions of the bathymetry.For a constant bathymetry,the maximum surge occurs when the hurricane approaches the coast from the normal direction when the free wave generation is minimal;for a stepped bathymetry,the maximum surge occurs at a certain acute approach angle which maximizes the duration of persistent wind forcing;a step-like bathymetry with a sloped shelf is similar to the stepped bathymetry,with the added possibility of landfall resonance when the free and forced waves are moving at about the same velocity.For other cases,the storm surge is smaller,given other parameters(hurricane size,maximum wind speed,etc.)unchanged.
文摘An expression of the 3-D pulsating source of Michell type with forward speed for infinite water depth is derived in the present paper based on the Fourier transformation and contour integration technique. Emphases are laid on the discussion of the mechanical feature of the source and the radiation behavior far from the source. The relative importance of each components of the pulsating source is discussed in detail. Compared with the commonly used pulsating source of Haskind type, the present expression has the merits of simplicity for numerical treatment and being more meaningful in its physical explanation. The Michell type expression of the 3-D pulsating source with forward speed can be widely used for the estimation of motions and wave forces for ships and offshore structures in waves with forward speed. The radiative behavior of the source in the far field may also give a reasonabel description of the radiation condition or the open boundary condition for other numerical methods, such as the Rankine source method etc.
文摘The time-domain calculations of retard function and ship motions in waves by the direct time-domain method （DTM） and the frequency to time-domain transformation method （FTTM） are compared and analyzed. A Wigley-hull-form ship and an $60 ship moving in waves are examined, and the corresponding retard functions are in good agreement with those given by DTM and FTTM. The comparison of retard functions in different forward speeds by the two methods is observed, and the results of ship motions in forward speed are also compared with the experimental data. On this basis, the advantage and disadvantage of them are discussed.
文摘The mechanical properties of the glue have great effects on the forward roll coating,which are analyzed here. The analysis shows that liquid viscosity,up and down rollers' speeds,diameters and the size of their gap have major impacts on coating property.The pressure and the shear force increase with the increases of the roll rotation speed,the radii and the viscosity of the glue,while decrease with the increase of the size of the roller gap. At a position of about 0. 8 mm from the nip symmetry axis by removing dimensionality,the pressure produces a maximum or minimum value,and the direction of the shear force changes.
文摘This article reports on track-monitoring and analyzing machine clearances during wood forwarding across seasons and weather, using ultrasonic distance sensors in combination with time-stamped GPS xy locations, at 10 sec intervals. The resulting data, obtained from 54 harvesting blocks, were analyzed by machine type (two wood forwarders and one grapple skidder), stand type (softwood plantation versus natural hardwood stands), month, slope, cartographic depth-to-water (DTW) classes, number of passes along track, and machine speed. For the most part, clearances were highly variable, due to passing over stumps, rocks, harvest slash, brushmats, ruts, and snow cover when present. This variability was on average greater for the lighter-weight wood forwarders than for the heavier-weight skidder, with the former mostly moving along equally spaced lines on brushmats, while the paths of the latter spread away from central wood-landing sites. In terms of trends, machines moved 1) more slowly on wet ground, 2) faster during returning than forwarding, and 3) fastest along wood-landing roads, as to be expected. Low clearances were most notable during winter on snow-covered ground, and on non-frozen shallow DTW and wet multiple-pass ground. During dry weather conditions, clearances also increased from low-pass tracks to multi-pass tracks due to repeat soil compaction of broadened tracks. These results are presented block-by-block and by machine type. Each block-based clearance frequency pattern was quantified through regression analysis and using a gamma probability distribution function.
文摘针对双PWM变频器整流侧与逆变侧独立控制时,直流侧必须利用大电容稳压,导致系统成本增加且寿命缩短的问题,提出一种整流侧采用引入新型开关矢量表的直接功率控制(Direct Power Control,DPC)方案。该方案逆变侧采用转子磁场定向矢量控制,并采用负载功率前馈控制策略,以实现双PWM变频器的协调控制。仿真实验结果表明,相比独立控制的双PWM变频调速系统,采用该一体化协调控制策略的双PWM变频调速系统,不仅能减小网侧电流的谐波,还可较好地抑制负载突变时直流电压的波动,加快整流侧和逆变侧的动态响应,大大提高系统的抗扰能力,从而减小电容体积并降低成本。
