Xiaowei Deng

Fluid–Structure Interaction Modeling of Vertical-Axis Wind Turbines

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/ )i s 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. [DOI: 10.1115/1.4027466]

Fluid–Structure Interaction Modeling for Fatigue-Damage Prediction in Full-Scale Wind-Turbine Blades

This work presents a collection of advanced computational methods, and their coupling, that enable prediction of fatigue-damage evolution in full-scale composite blades of wind turbines operating at realistic wind and rotor speeds. The numerical methodology involves: (1) a recently developed and validated fatigue-damage model for multilayer fiber-reinforced composites; (2) a validated coupled fluid–structure interaction (FSI) framework, wherein the 3D time-dependent aerodynamics based on the Navier–Stokes equations of incompressible flows is computed using a finite-element-based arbitrary Lagrangian–Eulerian–variational multiscale (ALE–VMS) technique, and the blade structures are modeled as rotation-free isogeometric shells; and (3) coupling of the FSI and fatigue-damage models. The coupled FSI and fatigue-damage formulations are deployed on the Micon 13M wind turbine equipped with the Sandia CX-100 blades. Damage initiation, damage progression, and eventual failure of the blades are reported.

Geometric design and mechanical behavior of a deployable cylinder with Miura origami

The folding and deployment of a cylinder with Miura origami patterns are studied in this paper. First, the geometric formulation of the design problem is discussed. Then the loading case of the axial strains and corresponding external nodal loads applied on the vertices of the top polygon during the motion is investigated analytically. The influence of the angle between the diagonal and horizontal fold lines α and β and the number of Miura origami elements n on the dynamic behavior of the basic segment is also discussed. Then the dynamic behavior is analyzed using numerical simulations. Finally, the deployment process of a cylinder with multi-stories is discussed. The numerical results agree well with the analytical predictions. The results show that the range of motion, i.e. the maximal displacement of top nodes, will also increase with the increase of angles α and β. This cylinder, with a smaller n, may have a bistable behavior. When n is larger, the influence of n on the axial strains and external nodal loads is slight. The numerical results agree well with the analytical predictions. Moreover, the deployment of the cylinder with multi-stories is non-uniform, which deploys from the upper story to the lower story.

Graphics processing unit (GPU) accelerated fast multipole BEM with level-skip M2L for 3D elasticity problems

GPU parallel algorithm of the fast multipole BEM with level-skip M2L is presented.A rigid body motion method for the fast multipole BEM is given.Different M2L schemes are compared and discussed in detail.Engineering examples demonstrate the efficiency and accuracy of the algorithm. In order to accelerate fast multipole boundary element method (FMBEM), in terms of the intrinsic parallelism of boundary elements and the FMBEM tree structure, a series of CUDA based GPU parallel algorithms for different parts of FMBEM with level-skip M2L for 3D elasticity are presented. A rigid body motion method (RBMM) for the FMBEM is proposed based on special displacement boundary conditions to deal with strongly singular integration and free term coefficients. The numerical example results show that our parallel algorithms obviously accelerates the FMBEM and can be used in large scale engineering problems with wide applications in the future.

Isogeometric Fatigue Damage Prediction in Large-Scale Composite Structures Driven by Dynamic Sensor Data

Copyright

Topology Optimization of Total Femur Structure: Application of Parameterized Level Set Method Under Geometric Constraints

Optimization of the femur prosthesis is a key issue in femur replacement surgeries that provide a viable option for limb salvage rather than amputation. To overcome the drawback of the conventional techniques that do not support topology optimization of the prosthesis design, a parameterized level set method (LSM) topology optimization with arbitrary geometric constraints is presented. A predefined narrow band along the complex profile of the original femur is preserved by applying the contour method to construct the level set function, while the topology optimization is carried out inside the cavity. The Boolean R-function is adopted to combine the free boundary and geometric constraint level set functions to describe the composite level set function of the design domain. Based on the minimum compliance goal, three different designs of 2D femur prostheses subject to the target cavity fill ratios 34%, 54%, and 74%, respectively, are illustrated.

Effects of the prestress levels on the stiffness of prismatic and star-shaped tensegrity structures:

On the basis of the introduction of the stiffness matrix of tensegrity structures, the eigenvalue analysis is carried out to study the influence of the prestress level on the stiffness of tensegrity structures. The triangular prismatic tensegrity structure, the star-shaped tensegrity structure and the star-shaped tensegrity structure with a central strut are selected as the numerical examples. The analytical results show that some eigenvalues increase linearly with the prestress level, whereas other eigenvalues firstly increase and then decrease or firstly decrease and then increase with the increase of the prestress level. This is because the stiffness matrix of the tensegrity structures is mainly composed of the material stiffness matrix and geometric stiffness matrix. As the contribution of these two parts of stiffness to eigenvalue models is different, the trends of eigenvalue variations are different with the increase of the prestressed level.

Wrinkling of Orthotropic Viscoelastic Membranes

This paper presents a simplified simulation technique for orthotropic viscoelastic films. Wrinkling is detected by a combined stress-strain criterion and an iterative scheme searches for the wrinkle angle using a pseudo-elastic material stiffness matrix based on a nonlinear viscoelastic constitutive model. This simplified model has been implemented in ABAQUS/Explicit and is able to compute the behavior of a membrane structure by superposition of a small number of response increments. The model has been tested against a published solution for a time-independent isotropic membrane under simple shear and also against experimental results on StratoFilm 420 under simple shear.

Computation of Partially Inflated Shapes of Stratospheric Balloon Structures

This paper studies the relationship between height, volume and stress distribution in a superpressure pumpkin balloon with the differential pressure applied to the balloon. Two different approaches are presented. A simple two-dimensional solution based on previous work and a novel, detailed finite element simulation that provides three-dimensional solutions are investigated. It is found that the finite element solution provides a much better agreement with experimental results for the case of a flat facet ULDB balloon. It is also found that a region of tensile hoop stress remains in the crown region of the balloon until the bottom pressure becomes negative. This region prevents the formation of clefts in the balloon and keeps its shape axisymmetric.

Motion analysis of a foldable barrel vault based on regular and irregular Yoshimura Origami

This paper investigates the geometry of a foldable barrel vault with Yoshimura Origami patterns during the motion. On the base of the geometry analysis of the origami unit, the radius, span, rise, and longitudinal length of the foldable barrel vault with regular Yoshimura Origami pattern in all configurations throughout the motion are determined. The results show that the radius of curvature and the span increase during deployment. But the rise increases first, followed by a decrease with increasing fold angle. Furthermore, the influence of the apex angle of the origami unit and the numbers of triangular plates in the span direction on the geometric parameters is also investigated. Finally, the method to obtain the rise and span of the barrel vault with irregular origami pattern is also given.