简述二阶斯托克斯波的特征？
参考答案：
斯托克斯2阶波波形与微幅波的比较：波峰处，波面抬高，因而变为尖陡；波谷处，波面抬高，因而变得平坦。波峰波谷不再对称于静水面。随着波陡增大，峰谷不对称将加剧。斯托克斯波不适于浅水情况，因为波面中的二阶项与一阶项的比值趋于无穷大。
速度不对称：斯托克斯2阶波正向（向岸）历时变短，波峰时水平速度增大；负向（离岸）历时增长，波谷时水平速度减小。
二阶斯托克斯波与微幅波另一个明显的差别是其水质点的运动轨迹不封闭.水质点运动一个周期后有一净水平位移，这种净水平位移造成一种水平流动，称为漂流或质量输移。一个波周期内质点平均漂流速度，称传质速度。
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| Gabriel Oak was a sensible man of good character who had been brought up by his father as a shepherd (牧羊人). He became a 1 like his father after growing up and was then managing to save enough money to 2 his own farm on Norcombe Hill in Dorset. He was twenty-eight, a tall, handsome 3 man, who didn't seem to think his appearance was very important. One 4 morning he was in one of his fields on the side of Norcombe Hill. 5 over his gate, Gabriel could see a yellow cart loaded with furniture and 6 , coming up the road. Right on top of the pile sat a handsome 7 . As Gabriel was watching, the cart stopped at the top of the 8 , and the driver climbed 9 to go back and 10 something that had fallen off. The woman sat 11 in the sunshine for a few minutes. Then she picked up a parcel(包袱) 12 next to her, and she looked 13 to see if the driver was coming back. There was no sign of him. She unwrapped(解开)the parcel and took out the 14 it contained. The sun shone on her 15 face and hair. 16 it was December, she looked almost summery, sitting there in her bright red jacket with the 17 green plants around her. She looked at 18 in the mirror and smiled, thinking that only the birds could see her. 19 behind the gate Gabriel Oak was 20 too. | ||||
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