# Parallel Analysis of Offshore Wind Turbine Structures under Ultimate Loads
###### Abstract  
This paper investigates efficient design of offshore wind turbine (OWT) support structures under ultimate loads and proposes three schemes to overcome excessive computer time due to many required external loads. The first is the assumption of a rigid support structure to find blade wind forces, so that these forces are only dependent on wind profiles, which limits different cases in the structural analyses. Since the blade information is often confidential in turbine companies, this two-stage analysis allows the hub force to be the input data for the support structure design. The second is using a few control loads to perform the steel design between the second and the second-last design cycles. The third is using parallel computational procedures, since all loading cases can be independently executed in different CPU cores and computers. The test cases, with 5044 loading cases, indicate that the proposed method is fully parallel and can complete the design procedures using a few personal computers within several days. Test cases include IEC 61400-3, tropical cyclone, and seismic loads; although there are many loads to be considered, steel design is governed by a limited number of load cases, which are discussed in this paper. t pacs: 32.30.-c, 32.30.  
turbines, and the results showed that this approach can be useful for jacket structures. The work of [PERSON] et al. [10] established an optimal design process for the sub-structure of floating-type OWTs, using the neuro-response surface method, and confirmed the usefulness of the constructed framework in hydrodynamic performance. [PERSON] and [PERSON] [11] presented a design optimization framework for OWT support structures, taking uncertainties into consideration. A numerical case of a tripod-type OWT was built for formal optimization. The work of [PERSON] et al. [12] performed structural optimization, assuming that changing the dimensions of a structural member does not affect other members, which allows for a simple sizing algorithm. The work of [PERSON] et al. [13] developed a structural optimization model for OWT, based on a coupled parametric finite element analysis and genetic algorithm, and the results showed a 19.8% reduction in the global mass of the support structure. The work of [PERSON] et al. [14] studied the effects of blade pitch and rotor yaw, as well as wind-wave misalignment. The results showed that the effects of blade pitch and rotor yaw on turbine structural dynamics are significant, whereas the effect of wind-wave misalignment is small. The work of [PERSON] et al. [15] used a genetic algorithm to conduct structural design optimization for an OWT, and the results showed the proposed method to be superior in terms of finding optimal solutions. The work of [PERSON] et al. [16] used multiple tuned mass dampers to control vibrations from the fundamental and higher modes of an OWT tower, under combined wind, sea wave, and earthquake excitations. The work of [PERSON] et al. [17] presented an optimal design for a floating wind turbine tower, while the steel tower was compared to the composite materials tower, and the results demonstrated that the composite can significantly reduce the tower mass. [PERSON] and [PERSON] [18] investigated the response of a jacket supporting an OWT with the Define SSI, where the effect of the SSI became predominant for an OWT in loose sands. The work of [PERSON] et al. [19] carried out ultimate load analyses, and determined the optimum design for a jacket-type OWT support structure under tropical cyclone and IEC loads. The work of [PERSON] et al. [20] presented a nonlinear finite element model to simulate the interface behavior of a concrete grouted connection in a monopile OWT structure, and the results showed good agreement with the experimental results. The work of [PERSON] et al. [21; 22] proposed the coupled dynamic analysis of the tripod and jacket structures for OWTs with piles-oil-structure interaction (PSSI), by using X-SEA and FAST v8 programs.