Dynamic Characteristics Analysis And Structural Dynamic Modification Technology Of HJJ45046 Offshore Drilling Rig

In recent years,with the stable improvement of industrial level, to oil, natural gas energy demand has increased dramatically, and our country to speed up the pace of the offshore oil and gas field exploration and exploitation. As the key bearing structure of Marine oil and gas field exploitation, offshore derrick plays an important role in the process of oil and gas field exploitation. The safety of offshore derrick is related to the whole platform is safe and effective production and the life safety of the staff.Offshore derrick is in a very bad working environment, which is not only affected by the static load, but also a large number of dynamic loads such as wind load, wave load and so on,the stress situation is very complicated.The action of these loads is a great test of the stability and reliability to the derrick.But the current derrick design method is using the static design method which increases the safety factor just to calculate the dynamic load conditions of the derrick at the static level.Obviously, it is not enough to consider the dynamic characteristics of the derrick;When the natural frequency of the derrick is close to or in agreement with the working frequency of the drilling and repairing power equipment or the frequency of the external dynamic load, the natural frequency of the derrick will occur,the drilling machine can not normally start the work.Under the complicated working conditions such as dynamic load, the load bearing capacity of the derrick will change.But these dynamic factors are not in the scope of the static design considerations. Therefore, for the protection of the marine derrick structure can more safe and reliable service, the design method more perfect and reasonable, to study the dynamic characteristics of offshore derrick and to put forward the research and method of structural dynamic modification is very necessary and significant.In this paper, the author collects and studies the relevant literature of the derrick at home and abroad, and summarizes the research contents, steps and advantages and disadvantages of the static design method of the derrick;The method of analyzing the dynamic characteristics of derrick at home and abroad is collected and sorted out and the historical background and the development status of the research on the dynamic characteristics of the derrick are analyzed and summarized.Proposed the research ideas, the overall technical route and the structure of the article.On the basis of introducing the theory of dynamic characteristic analysis, the research object of HJJ45046 offshore drilling rig derrick is introduced,after reasonable simplification and hypothesis, the finite element software is used to model the model directly,the grid is divided into 2 beam 188 node beam elements. According to the section shape of the derrick,16 section properties are defined, which are divided into 4255 units and 7255 nodes;After verifying the static strength of the derrick under the maximum load condition, the dynamic characteristic simulation analysis is carried out on the derrick;Subsequently, the sensitivity analysis is made on the basis of the mast member in the derrick, By selecting equipment parameters to avoid the first two order modal frequency and the maximum structural parameters are directly searched for the frequency of the first 3,4;On the basis of introducing the basic theory of structural dynamic modification technology, this paper puts forward the structural dynamic modification scheme with the aim of the structural parameters as the target.Analysis of dynamic characteristics of derrick.Including modal analysis, harmonic response analysis and transient dynamic analysis.The first is the modal analysis;The analysis results show that under the influence of prestress effect, the first 10 orders of the derrick have a smaller decline, which shows that the influence of the prestress on the vibration characteristics of the derrick, but very small.In addition, the first 4 modal frequency of the derrick corresponds to the speed of the rotating speed of the derrick in the normal speed range, and the derrick is equipped with power equipment to avoid the four modal frequencies;The modal frequency is in the range of 1.56Hz to 11.63Hz, which is in accordance with the low frequency vibration characteristics of large structure engineering, which is consistent with the engineering practice;The vibration characteristic of derrick is better;Harmonic response analysis. Results show that displacement response peak were in the corresponding natural frequency, and the theory and the actual situation coincide, the derrick in the X direction (left-right direction) stiffness difference than in Z direction (anterior posterior direction); derrick at work does not produce forced vibration analysis.Transient dynamic analysis, the analysis results show that the X direction stiffness is the weakest, which is consistent with the results of modal analysis. Under the impact load, the load capacity of the derrick is poor.Sensitivity analysis and structural dynamic modification. Based on the results of the sensitivity analysis, the influence of the parameters on the performance of the derrick and the cost of modification are analyzed, and two kinds of structural dynamic modification schemes are proposed, and the two schemes are adopted to carry out the modal analysis. The modal frequency of the derrick is obtained:it is found that the frequency of the derrick is improved, the second order of the 3,4 is improved, and the structural dynamic modification effect is better.