The Vibration Response on Body of Pile Gripper

Abstract

Underwater skirt pile gripper is a kind of hydraulic fixture which is widely used in the installation of offshore oil platform. In the construction of offshore oil platform, the widely used installation method abroad is to fix it to the seabed by using steel piles. Leveled through the leveling equipment, the jacket legs are not clamped with skirt pile grippers until grouting is over. The pile gripper is composed of a body, several hydraulic cylinders and two hydraulic system. The upper end of the body is welded on the skirt pile sleeve. Under the action of circle-distributed hydraulic cylinders, the pressure block coupled with the piston rod will provide radial clamping force to clamp the tubular pile. Harbin Engineering University collaborated on 84-inch pile gripper with Offshore Oil Engineering Co., Ltd. The 84-inch pile gripper with twelve hydraulic cylinders equispaced radially on the body can withstand the impact of pile hammer under construction. When piling, the positive pressure $N^{\prime}$ on each pressure block caused by tubular pile is fixed on the annular surface of the main body by hydraulic cylinder. The upper end of the main body is fixed. The annular surface of the twelve uniformly distributed holes is subjected to surface load (i.e., the force applied to the cylinder by the pile). At present, driven pile foundation is still the most reliable foundation of offshore oil and gas platforms. During the construction process, the pile hammer piles 30 to 40 times per minute. The body of pile gripper will undergo forced vibration under the impact of the pile hammer. In this paper, the 8-node brick structure 8node45 (i.e., solid brick 8node 45) of ANSYS software was selected as computing unit of the body. The samcef solver was used for modal analysis of pile body, which worked out modal value between one and six order, and the natural frequency corresponding to the modal. The forced vibration analysis of the pile gripper body subjected to external excitation was carried out in the article. With the analysis result, the stress and strain cloud and the failure mode of the pile gripper body were obtained. In addition, the static analysis method was also used in this paper. Other force situation of the body is consistent with the aforementioned vibration analysis. The analysis results show that the maximum stress and strain in the body of the pile gripper is in the position of the annular hole of the body, and there is no obvious deformation in other parts. Comparing the results of the two methods, it is found that the stress and strain of pile gripper body increases obviously when the impact of vibration is considered, and the structure is more prone to damage. With small excitation in this paper, the results of static analysis and the dynamic analysis are not much different, while the dynamic analysis apparently can better simulate the deformation of the object to meet the actual engineering requirements. The finite element analysis is useful for the design of the pile gripper body. In the article, the results of finite element analysis were used to optimize the force condition of the pile gripper body to ensure that it would not fail under the impact of pile hammer.