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            Offshore wind turbines based collision analysis and protective measures

            Views: 876  Add time: 11/11/2015

              With the rapid development of wind power technology, the land development and utilization of wind farm fewer and fewer, and more attention paid to the offshore wind power development. Offshore wind turbines infrastructure as a basis for offshore wind power development, the long-term work under the harsh environment at sea, will inevitably encounter various collision problem. Tender and foundation, for example, collision, the upper structure of falling objects to the base platform and the impact of ice on basis. These accidents often whole bending or local buckling in the foundation, the structure bearing capacity is reduced, directly affect the safety and durability, and may even cause catastrophic consequences such as wind turbines collapsed.

              According to Tebbett the last five years experience in repair of steel platform for the world's 100 needs to be repaired in Marine structures damage reason carries on the analysis results, about 25% of the damage is caused by collision of Marine structures. According to the HSE organization of investigation, the damage for the offshore platform in the investigation of the cause of the damage occurred offshore platform of collision (11.2%), is one of the main reasons. According to the north sea in Norway DNV Marine industry report, ten years from 2001 to 2001, a total of 26 ship and Marine platform collision accident, six of them have serious consequences.

              Offshore wind turbine foundation platform with similar structures to the sea, but by sea wind turbines at the fledgling stage, technology is not yet mature, the corresponding sea wind turbine foundation physics research is not enough, also there are few standards for reference. In this paper, the Marine foundation and reference for research of collision of the offshore platform collision standard and experience. Based on ANSYS/ls-dyna software, through structure modeling and numerical simulation calculation, and analyzes the ship bridge collision force, energy conversion, the wind generator and the basic structure of the general rules and characteristics of shock response, thus for offshore wind turbine foundation design, maintenance and anti-collision measures such as to provide theoretical support.

              Development of ship and ocean platform based collision theory

              As early as the 1960 s, Minorsky in more than 20 ship collision accident and platform or experimental data analysis, obtained the impact kinetic energy loss of the ship was struck with platform linear relationship between structural damage, and in the form of empirical formula is given. MartinJ. Petersen research work is also a representative, collision of two dimensional case movement process is analyzed. In the 1970 s, McDermott and others according to the basic theory and method of plastic statics for cruise ship and platform structure problems for low-energy collisions is studied. With the development of the finite element technology, Reckling, Minorsky and Yang and others that have adopted finite element technology platform for ship collision problems are analyzed. In the 1990 s, upkeep and Che and Jang use showed a nonlinear analysis program MSC/DYTRAN for supertankers structure in the collision response are analyzed in numerical simulation, according to the finite element method (LSDYNA3D) analysis of the impact the structure of the ship's bow and collision platform deformation, damage and assumed in the calculation of rigid body collision.

              All in all, as to the problem of collision further research and development of finite element technology, both at home and abroad on ships and offshore collision problems more and more numerical simulation method, the result is more reliable. Through to the previous case data statistical analysis and theoretical derivation, the results of the analysis in the offshore platform design and maintenance has also played an increasingly important role.

              Ships and offshore structures collision simulation method

              A, common analysis method

              Due to the collision of deformation damage degree and the ship safety and accident consequence is directly related to, so you need to pay attention to the study of internal collision theory. The method of the present study internal collision mechanics statistical analysis method, experimental method, simplified analysis method and the finite element method.

              (a) statistical analysis

              Statistical analysis of ship collision problem is divided into relatively independent structural damage and kinetic energy loss, research of the relationship between them, use the fully nonlinear theory to solve the kinetic energy loss in the process of collision, with the influence of the entrained water quality to replace the water in the collision. With statistical analysis methods will finally damage volume and kinetic energy loss, a linear relationship. This on the basis of a large number of similar type of collision data summed up the experience formula application is very convenient, but it was clear from the consideration on the cost is not too realistic. In addition, this method a lot of simplified, accuracy is not high, so seldom used now.

              (2) test method

              For more complex theoretical models can't describe the problem, often more reliable conclusions can be obtained through experiment. On the ship and ocean platform collision problem, the Netherlands, Denmark, Germany, Japan and other countries' scholars have conducted a lot of collision simulation test, and summarizes a lot of conclusions with reference value.

              But as we all know, the test requires a lot of time and money, and Marine structures collision problem itself is strong nonlinear characteristics and the diversity of collision conditions on the results of application in practice have a great limitations, combined with the construction of the Marine structures is very expensive, such trials are costly and difficult to implement, so this method was very difficult to implement.

              (3) the analytical method

              Simplified analysis method is the characteristic of failure process of general study, through analysis of the theory calculation, thus provide the designer with the overall and local structure design and calculation tools. This method is mainly based on the theory of plastic mechanics of the upper limit and some important assumptions for the analysis of collision problem. These assumptions are mainly from the observation of the collision accident and experimental study on the analysis. But often due to it will impact the ship made a lot of simplified process, so the precision is relatively low.

              (4) the finite element numerical simulation method

              Numerical simulation method is virtual reappearance of ship collision scene, with the aid of some finite element analysis software, a collision in the process of various physical quantities can be as a result the output, can be a real simulation collision phenomenon, part instead of testing result or crash test of the model, the realization of "virtual collision". So the finite element method is powerful structural impact response analysis tools, also is the research of collision problem is the most effective method.

              But now in engineering applications, due to the establishment of the simulation model needs certain knowledge, experience, and processing techniques, the calculation precision of model is not always satisfactory, a collision of nonlinear finite element method (fem) for analysis of the collision of ship structure is not fully mature, the results of numerical simulation method of still need to test or calculation results of other researchers to test.

              Second, ship and Marine platform collision problem of finite element numerical simulation

              Most of collision of the numerical simulation with nonlinear finite element method, not only can considering large deformation and contact structure, material nonlinearity and the structure failure, and so on and so forth, damage deformation of collision zone structure and the collision force, and combined with external mechanism analysis and calculation.

              At present commonly used 3 d nonlinear dynamic response analysis program MSC/Dytran and ls-dyna can be used to simulate the collision response, such as using the display or implicit method to solve dynamic control equation of fluid - structure, can better solve the large deformation of collision, damage, such as contact, hydrodynamic problems.

              Third, this article analysis method

              By two step analysis method of the ship collisions with wind turbines offshore base for numerical simulation.

              According to the experience of the analysis, proposed using ls-dyna and ANSYS software are analyzed. With ANSYSWorkbench good interface and powerful model with SolidWorks software before processing capabilities, to the analysis of hull and wind turbines for the grid division and handling, will produce the import ls-dyna finite element model of rigid body collision analysis and extract the required results. Finally the collision analysis results as input conditions on the basis of wind turbines local model is analyzed in detail, for infrastructure damage.

              Finite element analysis based collision of ships and wind turbines

              A structure model based, offshore wind turbines

              According to the scheme design of a wind turbines offshore infrastructure, six of foundation pile jacket model is set up. Each steel pipe pile foundation has six root, structure bottom diameter of 24 m; Steel pipe pile using Q345C steel, jacket to Q345D steel type, as shown in figure 1.

              Assuming the impact for the 5000 - ton ship, simplified model 20 m, long type 16 m wide and 15 m deep, line 5 m. Computational model of collision area using shell element model, the fore peak tank after the hull, because its far away from the collision area, practice is not deformation, only provides rigidity and quality effect, thus to omit it.

              Second, the finite element model

              According to the simplified geometric model of finite element model is set up, to reduce the computation time and ensure accuracy of the results, in this project and the hull using shell element modeling SHELL163 element; Collision area grid refinement, and concern for the overall structure finite element model is shown in figure 2 and figure 3.

              Third, contact algorithm

              Collision component interactions between done through contact algorithm. Defined in possible contact effect between the structure of contact area, contact surface collided can effectively simulate the interaction between the structure, and allows continuous contact between the structure and sliding.

              , this article USES the master-slave surface contact algorithm in solving each time step, check the position of slave node coordinates, to see if it has been through the primary side, if you haven't penetrate, continued the calculation work is not affected; If it has been through in places a force perpendicular to the direction of the primary side, to prevent the further penetration of slave node, this reaction is the contact force. Depends on the size of the contact force through quantity and unit on either side of the contact surface properties.

              Fourth, analysis condition

              The project is to simulate the various conditions of the collision of ship bow and foundation, and according to the calculation results and summing rules by analysis of ship collisions with wind turbine foundation general rules.

              (a) constraints

              For wind turbines all based at the bottom of the steel pipe pile position constraint; Ship stem constraints, in order to ensure the ship bow direction along the vertical direction of degrees of freedom.

              (2) analysis of working condition

              In this project according to the initial velocity and direction of the ship, respectively to calculate the various working condition analysis of the collision.

              Five, the collision analysis results

              List all operating conditions, the analysis results are shown in table 2. Can be seen from the above analysis, the energy absorption structure, equivalent stress and plastic deformation increase with the increase of the parameter as the initial kinetic energy of the ship, but due to the setting of anti-collision facilities effectively reduce, the three parameters are the important indicators of wind turbine foundation to resist the impact performance. Therefore, in the wind turbine foundation design can be set by anticollision structure, effectively reduce the structures such as ship collision the effects on the infrastructure.

              Six, protective measures

              According to the study found that occurred in the process of ship collisions with platform, ops ships is the main factor causing collisions, so for offshore wind turbine foundation, must fully consider ops ships to bring the damaging effects of infrastructure; Also can see through the above analysis, some protective measures were taken, support structure is the basis of force will decrease greatly, can reduce the damage to support structure of the ship. Currently available methods are: in the process of by ship, the ship upstream near the base platform; Increase the buffer device and so on rubber, tire, reduce operational ship impact force; On the foundation support structure Settings, by ship, reduce shipping direct impact to the infrastructure, etc.


              From the above analysis results can be obtained after the ship collisions with wind turbine foundation response, including wind turbine foundation design concerned parameters such as stress, strain and acceleration, energy change. By analysis and comparison of these results parameters,

              Can get a preliminary conclusion is as follows:

              Ship - based collision mechanical process and structural damage of wind turbines can be used ANSYS/LS_DYNA software simulation in detail, the results of numerical calculation the wind generator can be used as effective to the evaluation of the basic structure design, at sea.

              Endergonic structure, equivalent stress and plastic deformation increase with the increase of the parameter as the initial kinetic energy of the ship, but due to the setting of anti-collision facilities effectively reduce, the three parameters are the important indicators of wind turbine foundation to resist the impact performance. Therefore, in the wind turbine foundation design can be set by anticollision structure, effectively reduce the structures such as ship collision the effects on the infrastructure.

              Also can be made for other results from the collision analysis (e.g., collision force, after the collision parameters such as velocity and acceleration curve), as a condition of the local structure detailed analysis of the input, can evaluate the strength of foundation or ship structure.

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