Nonlinear behaviors of a free-floating body in waves were experimentally investigated in the present study. The experiments were carried out for 6 different wave heights and 6 different wave periods to cover a relativ...Nonlinear behaviors of a free-floating body in waves were experimentally investigated in the present study. The experiments were carried out for 6 different wave heights and 6 different wave periods to cover a relatively wide range of wave nonlinearities. A charge-coupled device （CCD） camera was used to capture the real-time motion of the floating body. The measurement data show that the sway, heave and roll motions of the floating body are all harmonic oscillations while the equilibrium position of the sway motion drifts in the wave direction. The drift speed is proportional to wave steepness when the size of the floating body is comparable to the wavelength, while it is proportional to the square of wave steepness when the floating body is relatively small. In addition, the drift motion leads to a slightly longer oscillation period of the floating body than the wave period of nonlinear wave and the discrepancy increases with the increment of wave steepness.展开更多
长线阵TDI(time delay and integration)CCD空间相机通过机动成像可以获得更宽的地面幅宽,缩短重访周期。由于角度变换和地球曲率等因素,相机不同视场位置的像移速度和偏流角存在差异,TDICCD焦面越长,机动角度越大,差异越大。通过像移...长线阵TDI(time delay and integration)CCD空间相机通过机动成像可以获得更宽的地面幅宽,缩短重访周期。由于角度变换和地球曲率等因素,相机不同视场位置的像移速度和偏流角存在差异,TDICCD焦面越长,机动角度越大,差异越大。通过像移解析模型计算像面上各点像速矢量,定量分析空间相机在侧摆和俯仰成像时视场上各点像移速度和偏流角差异对调制传递函数(MTF)的影响,并以MTF为约束确定各工况下的像速匹配模式和参数指标。分析结果表明:侧摆成像时,以沿TDICCD积分方向上的MTF退化为主;俯仰成像时,垂直于TDICCD积分方向上的MTF退化较多。以某工程实例计算:以传函下降5%为约束,以最大侧摆角40°成像时,可采用32级积分级数。俯仰30°成像时,可用积分级数不能超过8级;俯仰10°成像时,积分级数不超过16级。展开更多
基金financially supported by the National Natural Science Foundation of China(Grant No.11272079)the National Basic Research Program of China(973 Program,Grant No.2011CB013702)
文摘Nonlinear behaviors of a free-floating body in waves were experimentally investigated in the present study. The experiments were carried out for 6 different wave heights and 6 different wave periods to cover a relatively wide range of wave nonlinearities. A charge-coupled device （CCD） camera was used to capture the real-time motion of the floating body. The measurement data show that the sway, heave and roll motions of the floating body are all harmonic oscillations while the equilibrium position of the sway motion drifts in the wave direction. The drift speed is proportional to wave steepness when the size of the floating body is comparable to the wavelength, while it is proportional to the square of wave steepness when the floating body is relatively small. In addition, the drift motion leads to a slightly longer oscillation period of the floating body than the wave period of nonlinear wave and the discrepancy increases with the increment of wave steepness.
文摘太湖北部重度水华暴发时,在夏季盛行风推动下,漂浮的席状水华可由大太湖漂移进入位于太湖北部的梅梁湾,使湾内的水华加剧.本文通过室内风箱水槽实验和野外观测,对水华的风力漂移作了定量研究,建立了风速与水华漂移速度的指数相关方程.并据此对2004年夏季太湖北部发生席状水华的6d分别计算了水华风力漂移入湾量.6d中,只有2004-07-31水华漂移是由湾内向大太湖输出,且量很小,只有0.05 km2;其余5d水华漂移进入梅梁湾的面积占整个梅梁湾面积的3.7%～13.3%,进入量最大的是2004-06-11,达17.4km2,最少的是2004-07-30,为4.8 km2.
文摘长线阵TDI(time delay and integration)CCD空间相机通过机动成像可以获得更宽的地面幅宽,缩短重访周期。由于角度变换和地球曲率等因素,相机不同视场位置的像移速度和偏流角存在差异,TDICCD焦面越长,机动角度越大,差异越大。通过像移解析模型计算像面上各点像速矢量,定量分析空间相机在侧摆和俯仰成像时视场上各点像移速度和偏流角差异对调制传递函数(MTF)的影响,并以MTF为约束确定各工况下的像速匹配模式和参数指标。分析结果表明:侧摆成像时,以沿TDICCD积分方向上的MTF退化为主;俯仰成像时,垂直于TDICCD积分方向上的MTF退化较多。以某工程实例计算:以传函下降5%为约束,以最大侧摆角40°成像时,可采用32级积分级数。俯仰30°成像时,可用积分级数不能超过8级;俯仰10°成像时,积分级数不超过16级。
