Research on Axial Mechanical Properties of the Grouted Connection Section Considering Installation Errors

[Introduction] With the development of offshore wind turbine works to deep sea areas, the challenging construction environment tends to result in errors in the installation of the grouted connection for the jacket foundation. These errors can subsequently affect the axial mechanical properties of the grouted connection. Therefore, it is necessary to study the impact laws of installation errors on the axial mechanical properties of the grouted connection section. [Method] The study was commenced by conducting axial static loading tests on reduced-scale test piece of the grouted connection section, which was followed by simulating the axial loading process of the corresponding test piece using the finite element analysis method. The simulation results were found to align well with the experimental data, indicating a successful outcome. [Result] According to the research findings, the increasing in longitudinal and transverse installation errors can lead to an increase in the axial stiffness of the grouted connection section. This, in turn, further alters the longitudinal strain distribution of the casing and pile pipe. Additionally, the increase in installation errors can lead to an increase in the maximum value of the third principal stress in the grouting materials during the axial loading process, as well as changes in its distribution location. [Conclusion] In conclusion, the influence of installation errors on the axial mechanical properties of the grouted connection section for the jacket foundation can cause alterations in failure modes of the grouted connection section. Therefore, it is needed to consider and evaluate the harm caused by the impact laws of installation errors based on their influence rules

Optimization for Offshore Prestressed Concrete–Steel Hybrid Wind Turbine Support Structure with Pile Foundation Using a Parallel Modified Particle Swarm Algorithm

The prestressed concrete–steel hybrid (PCSH) support structure, which replaces the lower part of the traditional support with a concrete segment, is a prospective support structure solution for ultrahigh wind turbines. Taking a 5.5 MW wind turbine support structure founded on a jacket substructure with pile foundation as an example, an optimized design of the corresponding PCSH support structure with pile foundation for offshore wind turbine is conducted considering the soil–structure interaction (SSI) and the effect of water pressure. The construction cost of the proposed structure is treated as the objective function and minimized with a parallel modified particle swarm optimization (PMPSO) algorithm where the physical dimensions of each part of the PCSH wind turbine support structure are treated as optimization variables. Eleven optimization constraints are considered under both the serviceability limit state (SLS) and the ultimate limit state (ULS) according to relevant specifications and industry standards. A penalty function strategy is introduced to make sure that these constraints are fulfilled. The mechanical behavior and the cost of the optimal PCSH support structure with pile foundation are analyzed and are compared with those of the original design with a traditional steel tube tower founded on a jacket substructure. The results show that the cost and levelized cost of energy (LCOE), a comprehensive evaluation, of the optimized PCSH support decrease obviously with the PMPSO algorithm, which can provide advanced mechanic behavior including natural frequency, top deformation, and anti-overturning capacity. Compared with the PSO algorithm, the PMPSO algorithm has better performance in the procedure of PCSH support for offshore wind turbine optimization

Fatigue evaluation of grouted connections subjected to Markov matrix based random loading

Grouted connections in offshore wind turbines often experience random cyclic loadings due to harsh marine environment and are prone to fatigue damage. It is significant to evaluate their fatigue life for the durability of the offshore wind turbine. In this study, a fatigue evaluation exercise of grouted connection of wind turbine structure with finite element method is completed based on standards of Det Norske Veritas, i.e., DNVGL-ST-0126 and DNVGL-RP-C203. Loadings of variable amplitude summarized in the format of Markov matrix are firstly separately applied to the grouted connection models, and refined finite element models were analyzed to obtain stress states of the materials at critical locations. Hot spot stresses of welded shear keys and nominal stresses of grout were calculated and their damage indices were then accumulated for predominant loading directions. Furthermore, an integrated program has been designed to make the process of fatigue assessment convenient and efficient. Finally, fatigue evaluation is conducted for the grouted connection based on the proposed method. The process was applied to the grouted connection of an actual wind turbine and the results indicated that the damage indices are less than 1/3. The proposed method can serve as a useful tool for the actual engineering design of grouted connections. •A fatigue evaluation method for grouted connections was proposed based on finite element analyses with Markov matrix loads.•An integrated program was developed to facilitate the extensive finite element modeling and fatigue damage evaluation.•Critical locations of the model under axial force, horizontal force, and bending moment were discussed.•Fatigue damage contours are plotted to show the extent of damage of the grouted connection in different directions

Experimental and numerical investigation of mixed mode fracture of high-performance grouting materials based on peridynamics

This paper investigates the fracture behavior of high-performance grouting materials in the grouted connection section of marine structures, where they are subjected to complex stress states. This study utilizes a combination of experimental and numerical simulation methods to establish a reliable numerical simulation technique for the fracture process of high-performance grouting materials. The mixed mode fracture behavior is analyzed using six different types of specimens, and the strain contour is analyzed using the Digital Image Correlation technique. An extended peridynamics model is proposed for the numerical simulation, which adopts a fracture criterion based on strain energy density. The accuracy of the model is verified qualitatively and quantitatively, and the simulation results are consistent with the experiments. Overall, this study provides insights into the fracture behavior of high-performance grouting materials in complex stress states and presents a reliable numerical simulation technique for the fracture process. © 2023 John Wiley & Sons Ltd

A Class of 2-Degree-of-Freedom Planar Remote Center-of-Motion Mechanisms Based on Virtual Parallelograms

Robot-assisted minimally invasive surgery (MIS) has shown tremendous advances over the traditional technique. The remote center-of-motion (RCM) mechanism is one of the main components of a MIS robot. However, the widely used planar RCM mechanism, with double parallelogram structure, requires an active prismatic joint to drive the surgical tool move in-out of the patient's body cavity, which restricts the dexterity and the back-drivability of the robot to some extent. To solve this problem, a two degree-offreedom (DOF) planar RCM mechanism type synthesis method is proposed. The basic principle is to construct virtual double parallelogram structure at any instant during the mechanism movements. Different with the existing ones, both of the actuated joints of the obtained RCM mechanism are revolute joints. Combining the proposed mechanism with a revolute joint whose axis passes through the RCM point to drive the whole mechanism out of the plane, the spatial RCM mechanisms to manipulate surgical tool in threedimension (3D) space can be obtained; and the 3D RCM mechanism can be used for manipulating multi-DOF instruments in a robot-assisted MIS or can be used as an external positioner in robotic single-port surgeries