SUMMARYIn this paper, we target more advanced fluid-structure interaction (FSI) simulations of wind turbines than reported previously. For this, we illustrate how the recent advances in isogeometric analysis of thin structures may be used for efficient structural mechanics modeling of full wind turbine structures, including tower, nacelle, and blades. We consider both horizontal axis and vertical axis wind turbine designs. We enhance the sliding-interface formulation of aerodynamics, previously developed to handle flows about mechanical components in relative motion such as rotor-tower interaction to allow nonstationary sliding interfaces. To accommodate the nonstationary sliding interfaces, we propose a new mesh moving technique and present its mathematical formulation. The numerical examples include structural mechanics verification for the new offshore wind turbine blade design, FSI simulation of a horizontal axis wind turbine undergoing yawing motion as it turns into the wind and FSI simulation of a vertical axis wind turbine. The FSI simulations are performed at full scale and using realistic wind conditions and rotor speeds.

Full-scale, 3D, time-dependent aerodynamics and fluid-structure interaction (FSI) simulations of a Darrieus-type vertical-axis wind turbine (VAWT) are presented. A structural model of the Windspire VAWT (Windspire energy, http://www.windspireenergy.com/) is developed, which makes use of the recently proposed rotation-free Kirchhoff-Love shell and beam/cable formulations. A moving-domain finite-element-based ALE-VMS (arbitrary Lagrangian-Eulerian-variational-multiscale) formulation is employed for the aerodynamics in combination with the sliding-interface formulation to handle the VAWT mechanical components in relative motion. The sliding-interface formulation is augmented to handle nonstationary cylindrical sliding interfaces, which are needed for the FSI modeling of VAWTs. The computational results presented show good agreement with the field-test data. Additionally, several scenarios are considered to investigate the transient VAWT response and the issues related to self-starting.

Background The relationship between disturbances of the gut microbiota and 1,25(OH) 2 D 3 deficiency has been established both in humans and animal models with a vitamin D poor diet or a lack of sun exposure. Our prior study has demonstrated that Cyp27b1 − / − ( Cyp27b1 knockout) mice that could not produce 1,25(OH) 2 D 3 had significant colon inflammation phenotypes. However, whether and how 1,25(OH) 2 D 3 deficiency due to the genetic deletion controls the gut homeostasis and modulates the composition of the gut microbiota remains to be explored. Results 1,25(OH) 2 D 3 deficiency impair the composition of the gut microbiota and metabolite in Cyp27b1 − / − mice, including Akkermansia muciniphila, Solitalea Canadensis , Bacteroides - acidifaciens , Bacteroides plebeius and SCFA production. 1,25(OH) 2 D 3 deficiency cause the thinner colonic mucus layer and increase the translocation of the bacteria to the mesenteric lymph nodes. We also found 1,25(OH) 2 D 3 supplement significantly decreased Akkermansia muciniphila abundance in fecal samples of Cyp27b1 − / − mice. Conclusion Deficiency in 1,25(OH) 2 D 3 impairs the composition of gut microbiota leading to disruption of intestinal epithelial barrier homeostasis and induction of colonic inflammation. This study highlights the association between 1,25(OH) 2 D 3 status, the gut microbiota and the colonic mucus barrier that is regarded as a primary defense against enteric pathogens.

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