Control design toolbox for large scale variable speed pitch regulated wind turbines

The trend towards large multi-MW wind turbineshas given new impetus to the development of wind turbine controllers.Additional objectives are being placed on the controllermaking the specification of the control system more complex. A new toolbox, which assists with most of the control design cycle,has been developed. Its purpose is to assist and guide the control system designer through the design cycle, thereby enabling faster design. With the choice of control strategy unrestricted,the toolbox is sufficiently flexible to support the design processfor the aforementioned more complex specifications

Corrections to the SU(3)×SU(3){\bf SU(3)\times SU(3)} Gell-Mann-Oakes-Renner relation and chiral couplings L8rL^r_8 and H2rH^r_2

Next to leading order corrections to the $SU(3) \times SU(3)$ Gell-Mann-Oakes-Renner relation (GMOR) are obtained using weighted QCD Finite Energy Sum Rules (FESR) involving the pseudoscalar current correlator. Two types of integration kernels in the FESR are used to suppress the contribution of the kaon radial excitations to the hadronic spectral function, one with local and the other with global constraints. The result for the pseudoscalar current correlator at zero momentum is $\psi_5(0) = (2.8 \pm 0.3) \times 10^{-3} GeV^{4}$, leading to the chiral corrections to GMOR: $\delta_K = (55 \pm 5)$. The resulting uncertainties are mostly due to variations in the upper limit of integration in the FESR, within the stability regions, and to a much lesser extent due to the uncertainties in the strong coupling and the strange quark mass. Higher order quark mass corrections, vacuum condensates, and the hadronic resonance sector play a negligible role in this determination. These results confirm an independent determination from chiral perturbation theory giving also very large corrections, i.e. roughly an order of magnitude larger than the corresponding corrections in chiral $SU(2) \times SU(2)$. Combining these results with our previous determination of the corrections to GMOR in chiral $SU(2) \times SU(2)$, $\delta_\pi$, we are able to determine two low energy constants of chiral perturbation theory, i.e. $L^r_8 = (1.0 \pm 0.3) \times 10^{-3}$, and $H^r_2 = - (4.7 \pm 0.6) \times 10^{-3}$, both at the scale of the $\rho$-meson mass.Comment: Revised version with minor correction

Dynamics of colloidal particles with capillary interactions

We investigate the dynamics of colloids at a fluid interface driven by attractive capillary interactions. At submillimeter length scales, the capillary attraction is formally analogous to two-dimensional gravity. In particular it is a non-integrable interaction and it can be actually relevant for collective phenomena in spite of its weakness at the level of the pair potential. We introduce a mean-field model for the dynamical evolution of the particle number density at the interface. For generic values of the physical parameters the homogeneous distribution is found to be unstable against large-scale clustering driven by the capillary attraction. We also show that for the instability to be observable, the appropriate values for the relevant parameters (colloid radius, surface charge, external electric field, etc.) are experimentally well accessible. Our analysis contributes to current studies of the structure and dynamics of systems governed by long-ranged interactions and points towards their experimental realizations via colloidal suspensions.Comment: Matches version accepted for publication. New refs. added, misprints corrected in figs.6,8,9,1

Analysis of tower/blade interaction in the cancellation of the tower fore-aft mode via control

With the increase in size of wind turbines, there is increasing interest in exploiting the pitch control capability of variable speed turbines to alleviate tower fatigue loads. The most direct method is to modify the blade pitch angle in response to a measurement of tower acceleration. It is shown that the ap mode has a central role in determining whether this approach is effective since there is a strong interaction between the blade ap-wise mode and the tower fore-aft mode. Several different approaches to the design of the controller for the tower speed feedback loop are investigated. It is concluded that a reduction in the tower loads of up to 18% is possible for multi-megawatt sized wind turbines

Alleviation of unbalanced rotor loads by single blade controllers

A novel approach to reducing the unbalance rotor loads by pitch control is presented in this paper. Each blade has its own actuator, sensors and controller. These localised blade control systems operate in isolation without need of communication with each other. This single blade control approach to regulation of unbalanced rotor loads has several advantages including being straightforward to design and easy to tune. Furthermore, it does not affect the operation of the central controller and the latter need not be re-designed when used in conjunction with the single blade controllers. Their performance is assessed using BLADED simulations

Skyrmions, Hadrons and isospin chemical potential

Using the Hamiltonian formulation, in terms of collective variables, we explore the evolution of different skyrmionic parameters as function of the isospin chemical potential ($\mu$), such as the energy density, the charge density, the isoscalar radius and the isoscalar magnetic radius. We found that the radii start to grow very fast for $\mu \gtrsim 140$ MeV, suggesting the occurrence of a phase transition.Comment: 10 pages, 5 figure

Numerical Analysis of Fatigue Crack Growth of Low Porosity Auxetic Materials using the Contour J-integral

Recent studies suggest that auxetic materials such as porous metals with orthogonal periodic void patterns have an increased fatigue life compared to non-auxetic materials. This study provides numerical solution to support the existing experiments with the use of contour J-integral as a parameter of stress intensity factor for computing the number of fatigue life cycle of the materials with auxetic structures. Representative volume elements (RVEs) were constructed to characterize the physical test specimens with void patterns such as ellipse, slot, and stop-hole. Extended finite element method (XFEM) was performed to verify the direction of crack propagation on auxetic materials. Sixty-five distinct RVEs were made for each void shape with increasing horizontal double notch to mimic the crack propagation. Using Abaqus, the contour J-integral was calculated automatically at the crack-tip region. Numerical computation showed that auxetics have lower rate of overall crack propagation compared to non-auxetics. Variation of geometric parameters were employed to the void patterns of the RVE which changed the porosity and the minimum hole distance of the auxetics. Computation on stress intensity factor for each crack increment showed that models with relatively larger negative Poisson’s ratio have faster crack initiation. XFEM and J-integral simulations were performed on aluminum plates with circular and stop-hole void patterns and compared with experimental data. Results were in good agreement to the experiment where stop-hole void model had lower rate of crack evolution compared to the circular void model

Patient Satisfaction Related to Noise in the Coronary Care Unit

Background The CCU staff recognized a department trend for low patient-satisfaction score related to environmental noise levels. Based on the Press Ganey score, the patient-satisfaction score plummeted in relation to noise level beginning in March 2014. Purpose To improve patient satisfaction regarding noise level in the CCU to 100% by November 21, 2014. Methods Senior & Fleming’s Hard System Model of Change guided this literature search of CINAHL and Fusion for articles published from 2009 to 2014. Specific terms used were noise, critical care, and sleep promotion. From September to November 2014, earplugs were offered to all alert/oriented patients entering the CCU. Data were analyzed using the tracking tool for earplugs and the CCU Press Ganey scores for noises in and around the patient room. Results A direct result of staff education, staff/patient awareness, and the availability of ear plugs resulted in a dramatic increase in patient perception of reduced noises on the Unit. CCU Press Ganey score increased to 93.8 compared to magnet mean for like hospitals of 79.4. While approximately half of the alert/oriented patient population in the CCU elected to use earplugs for sleep, patient perception of reduced noise levels increased. Patients declined use of the earplug for various reasons with the most common being hearing loss, visual loss, and anxiety. Nursing relevance Patients who elected not to utilize earplugs for sleep reported they were pleased that such an option existed and perceived the nursing staff as being interested in their overall wellbeing. Nursing staff also reported increased recognition of elevated noise (talking at nursing station) and worked to decrease loud talking amongst staff members