Calculation of MoM interaction integrals in highly conductive media

The construction of the impedance matrix in the method of moments requires the calculation of interaction integrals between the expansion functions, through the Green's function and its derivatives. The singular behavior of the Green's function poses considerable problems for an accurate numerical evaluation of these integrals, requiring techniques such as singularity extraction or cancellation. In this contribution we will show why these methods fail when the medium is highly conductive. A novel technique is proposed to handle these highly challenging integrals. The complexity of the new method is independent of the conductivity

Time-dependent calculation of the velocity of a yarn launched by the main nozzle of an air-jet loom

In air-jet weaving looms the yarn is initially accelerated by the main nozzle. To obtain a high yarn velocity a high air velocity is required which results in complex flow patterns. Consequently, predicting the influence of a change in geometry or inlet pressure on the yarn velocity is not straightforward. In this research a fast time-dependent fluid-structure interaction framework is used to model the acceleration of a yarn during launch. Initially, the performance of the framework is assessed by considering a smooth monofilament yarn. A suggestion is also madeand tested to deal with the surface texture of hairy/multifilament yarns

The concept of segmented wind turbine blades : a review

There is a trend to increase the length of wind turbine blades in an effort to reduce the cost of energy (COE). This causes manufacturing and transportation issues, which have given rise to the concept of segmented wind turbine blades. In this concept, multiple segments can be transported separately. While this idea is not new, it has recently gained renewed interest. In this review paper, the concept of wind turbine blade segmentation and related literature is discussed. The motivation for dividing blades into segments is explained, and the cost of energy is considered to obtain requirements for such blades. An overview of possible implementations is provided, considering the split location and orientation, as well as the type of joint to be used. Many implementations draw from experience with similar joints such as the joint at the blade root, hub and root extenders and joints used in rotor tips and glider wings. Adhesive bonds are expected to provide structural and economic efficiency, but in-field assembly poses a big issue. Prototype segmented blades using T-bolt joints, studs and spar bridge concepts have proven successful, as well as aerodynamically-shaped root and hub extenders

MoM impedance integrals in conductive media

During the past decades, much research has been done towards the efficient calculation of impedance integrals in the Method of Moments. However, these results were almost always uniquely concerned with penetrable media. In this contribution, it will be shown how the integrals can be treated in highly conductive media as well. The rapid exponential decline of the Green's function, due to the losses, is the root of all additional complexities. The method as presented here takes care of these problems in a scalable way, i.e. the computation time becomes independent of the conductivity of the material. It is not meant as a replacement for techniques in penetrable media, due to some additional costs, but is - to our knowledge - the only approach that currently exists to efficiently handle conductive media. This paper presents the ideas and techniques in a fairly condensed manner. More information can be found in [1]

Three-dimensional fluid-structure interaction simulations of a yarn subjected to the main nozzle flow of an air-jet weaving loom using a Chimera technique

In air-jet weaving looms, the main nozzle pulls the yarn from the prewinder by means of a high velocity air flow. The flexible yarn is excited by the flow and exhibits high amplitude oscillations. The motion of the yarn is important for the reliability and the attainable speed of the insertion. Fluid-structure interaction simulations calculate the interaction between the air flow and the yarn motion and could provide additional insight into yarn behavior. However, the use of an arbitrary Lagrangian–Eulerian approach for the deforming fluid domain around a flexible yarn typically results in severe mesh degradation, vastly reducing the accuracy of the calculations or limiting the physical time that can be simulated. In this research, the feasibility of using a Chimera technique to simulate the motion of a yarn interacting with the air flow from a main nozzle was investigated. This methodology combines a fixed background grid with a moving component grid deforming along with the yarn. The component grid is, however, not constrained by the boundaries of the flow domain allowing for large deformations with limited mesh degradation. Two separate cases were investigated. In the first case, the yarn was considered to be clamped at the main nozzle inlet. For the second case, the yarn was allowed to move axially as the main nozzle pulled it from a drum storage system