Thanks for your precious attention. I have read that section of the book but it contains nothing about ordinary differential equations describing motion of the tail. Thanks again for your attention.
Dr. El-Badawy was the first one i asked but with no response. I have followed all the references that he cited but with no benefit. Even Dr. Bauomy, Dr. El-Bassiouny and Dr. Y. Amer didn't provide any derivation of the model and just cited his papers only.