Aerodynamic shape optimisation of hovering rotors using compressible CFD

PurposeLocally-advanced non-small cell lung cancer (NSCLC) patients may experience dramatic changes in anatomy during radiotherapy and could benefit from adaptive radiotherapy (ART). Deformable image registration (DIR) is necessary to accurately accumulate dose during plan adaptation, but current algorithms perform poorly in the presence of large geometric changes, namely atelectasis resolution. The goal of this work is to develop a DIR framework, named Consistent Anatomy in Lung Parametric imagE Registration (CALIPER), to handle large geometric changes in the thorax.MethodsRegistrations were performed on pairs of baseline and mid-treatment CT datasets of NSCLC patients presenting with atelectasis at the start of treatment. Pairs were classified based on atelectasis volume change as either full, partial, or no resolution. The evaluated registration algorithms consisted of several combinations of a hybrid intensity- and feature-based similarity cost function to investigate the ability to simultaneously match healthy lung parenchyma and adjacent atelectasis. These components of the cost function included a mass-preserving intensity cost in the lung parenchyma, use of filters to enhance vascular structures in the lung parenchyma, manually-delineated lung lobes as labels, and several intensity cost functions to model atelectasis change. Registration error was quantified with landmark-based target registration error and post-registration alignment of atelectatic lobes.ResultsThe registrations using both lobe labels and vasculature enhancement in addition to intensity of the CT images were found to have the highest accuracy. Of these registrations, the mean (SD) of mean landmark error across patients was 2.50 (1.16) mm, 2.80 (0.70) mm, and 2.04 (0.13) mm for no change, partial resolution, and full atelectasis resolution, respectively. The mean (SD) atelectatic lobe Dice similarity coefficient was 0.91 (0.08), 0.90 (0.08), and 0.89 (0.04), respectively, for the same groups. Registration accuracy was comparable to healthy lung registrations of current state-of-the-art algorithms reported in literature.ConclusionsThe CALIPER algorithm developed in this work achieves accurate image registration for challenging cases involving large geometric and topological changes in NSCLC patients, a requirement for enabling ART in this patient group.

High effective WENO scheme for transonic inviscid flow computation on a helicopter rotor in hover

Women have a higher rupture risk of intracranial aneurysms than men. One possible explanation is that aneurysm volume and shape irregularity, both linked to rupture risk, may differ between women and men. We investigated this with 3-dimensional morphological aneurysm parameters. In a random sample of consecutive patients with unruptured intracranial aneurysms diagnosed between 2008 and 2018, we quantified volume and shape parameters describing global (sphericity, elongation, and flatness) and local shape (shape index and curvedness) on CT or MR angiography scans. We compared these parameters between women and men (reference) with univariable and multivariable linear regression analysis (global parameters) and binary logistic regression analysis (local parameters). The multivariable analysis was adjusted for the confounders: age, hypertension, smoking status, aneurysm size, location, and imaging modality. We included 326 patients (239 women [73%], mean age 58 years [SD 12 years]). Women had smaller aneurysm volumes than men in multivariable analysis (β -0.30 SD, 95%CI -0.55 to -0.06). The global shape parameters sphericity, elongation, and flatness were comparable between sexes. Of the local shape parameters, women had higher aneurysm shape index (OR 2.38, 95%CI 1.03 to 5.49) and lower curvedness (OR 0.50, 95%CI 0.29 to 0.88) in multivariable analysis. Women have intracranial aneurysms with smaller volumes and shape characteristics associated with lower rupture risk. Therefore, factors other than aneurysm morphology are likely responsible for the higher risk of aneurysm rupture in women.

This paper describes measurements of chordwise distributions of unsteady pressure at three radial locations on a stiff two-bladed teetering model helicopter rotor in hover, with the blades executing simple harmonic pitch oscillations about the quarter-chord pitch axis. The objective of the present work is to provide a data base to correlate the measured unsteady blade pressure distributions with dynamic inflow to establish the validity or deficiencies of available analytical methods for predictions of unsteady aerodynamic phenomena. The effect of dynamic inflow on rotor unsteady surface pressure has been

In the present article, the authors are performing a comparison study between two vortex models for the rapid numerical computation of the static thrust of a helicopter rotor in hover. The aim of this study is to access the rapidity and accuracy of a vortex model, comprised of a series of vortex rings and a single semi-infinite vortex cylinder, compared to a helical wake model with straight-line segmentation. Studies are performed for the optimal number of vortex elements, as well as for their optimal positioning, in order to provide both fast computation and good agreement with the experimental data obtained from a wind tunnel test of a model rotor. The studied vortex model is shown to significantly reduce the amount of computational time required to evaluate the performance of the model rotor, when compared to the helical wake model, while offering a similar degree of accuracy.

The relationship between rotor-blade aeroelasticity and tip-vortex stability is investigated numerically. An aeroelastic framework based on the free-vortex wake and finite element methods is employed to model a subscaled helicopter rotor in hover and forward-tilted conditions. A linear eigenvalue stability analysis is performed on tip vortices to associate the coupled impact of aeroelastic effects and vortex evolution. Prior numerical investigations have shown that highly flexible wind turbine rotor-blades have the potential to decrease levels of the instability of tip vortices. The present work focuses on testing these findings against a subscaled rotor within the range of helicopter operational rotation frequencies. The presented work aims to develop further insight into rotor-wake interactions and blade-vortex interaction to explore the mitigation of adverse rotorcraft operational conditions, such as their effect on aerodynamic-induced airframe vibrations and the associated life-cycle fatigue performance.

A hybrid Navier-Stokes/Free Wake methodology is applied to helicopter rotors in hover. Three tip planforms were analyzed: the S-76 rotor with a swept tip, a rectangular planform, and a swept tip with anhedral. The solidity of the three rotors was matched. A pitch sweep was conducted. Computed thrust, power, and figure of merit values have been compared with test data. Where available, comparisons with other calculations for these quantities and the near wake tip vortex trajectory have been done. The simulations are in reasonable agreement with published data for the thrust, power, and figure of merit. The simulations differ from full Navier-Stokes calculations in the predictions for tip vortex descent rate and contraction rate. The simulations correctly predicted the trends. The swept tapered anhedral tip had the highest figure of merit, followed by the swept tapered tip. The rectangular planform had the lowest figure of merit.

Pressure-sensitive paint (PSP) has become an important technique for global pressure measurement on rotating surfaces such as helicopter rotor blades. Due to the temperature sensitivity of PSP, it is essential to apply accurate temperature correction method in PSP measurements. In previous studies, one-dimensional (1D) correction methods were generally adopted which only considered the radial temperature gradient on the blade. However, in the current study, it was found that the systematic error of this 1D assumption was non-negligible in large-scale experiments due to the growing chordwise temperature gradient. Accordingly, a two-dimensional (2D) temperature correction method considering both radial and chordwise temperature gradients was developed to improve the accuracy of PSP. In this method, a 2D temperature map was firstly generated based on the TSP results. Calibrations were then conducted under a series of temperature and pressure values to generate a calibration surface. According to the calibration results, the pressure and temperature fields on the rotor blade were solved directly. The proposed 2D method was validated through PSP measurements on a 2 m diameter BO-105 helicopter rotor in hover. Compared with 1D temperature correction, the results from the current method showed clearly improved agreement with the CFD results and reduced overall measurement error.

In this paper, the results of a correlation study using a new higher-order, free-wake method, applied to the problem of hovering rotors, are presented. The predictions of the free-wake method are compared with the experimental data from three different studies focusing on sectional force distributions, aggregate performance parameters such as figures of merit and downwash distributions. The correlations provide a good amount of confidence as to the ability of the new free-wake method in predicting the challenging aerodynamics of a helicopter rotor in hover.

A procedure for the computation of transonic steady and unsteady flow around helicopter rotors is presented. The algorithm is based on the Euler equations and allows the computation of anisotropic rotational flow and thus an implicitly accurate calculation of shocks. In addition the capturing of the rotor wake and the tip vortex is provided for arbitrary tip shapes. The code for the computation of steady, fully 3-D rotor flow is derived from the EUFLEX procedure originated by A. Eberle, that has successfully been applied to a lot of fixed wing configurations up to now. A finite-volume scheme based on the method of characteristic flux averaging solves the Euler equations formulated in the conservation form. The discretizatlon of the flow field is carried out in two different manners concerning the grid topology and the size of the physical domain. Calculations are presented for a non-lifting case and for a helicopter rotor in hover. The comparisons of the method in its present stage show good agreement with experimental data.

Image segmentation based on hierarchical belief propagation with variable weighting parameters

The area‐perimeter allometric scaling is an important approach for researching fractal cities, and the basic ideas and models have been researched for a long time. However, the fractal parameters based on this scaling relation have not been efficiently utilized in urban studies. This paper is devoted to developing a description method of urban evolution using the fractal parameter sets based on the area‐perimeter measure relation. The novelty of this methodology is as follows: first, the form dimension and boundary dimension are integrated to characterize the urban structure and texture; second, the global and local parameters are combined to characterize an urban system and individual cities; third, an entire analytical process based on the area‐perimeter scaling is illustrated. Two discoveries are made in this work: first, a dynamic proportionality factor can be employed to estimate the local boundary dimension; second, the average values of the local fractal parameters are approximately equal to the corresponding global fractal parameters of cities. By illustrating how to carry out the area‐perimeter scaling analysis of Chinese cities in Yangtze River Delta in the case of remote sensing images with low resolution, we propose a possible new approach to exploring fractal systems of cities.

This paper deals with some recent developments of a boundary element methodology for the unified aerodynamic/aeroacoustic analysis of subsonic and transonic potential flows past helicopter rotors in hover and forward flight. In this methodology, first the potential solution is derived on the rotor-blade surfaces. Then, the boundary integral representation gives the potential everywhere in the field, and the Bernoulli theorem yields the acoustic pressure. Numerical results are presented for helicopter rotors in hover and forward flight at both subsonic and transonic rotor speeds. Comparisons with existing numerical results and experimental data are included.

A new method to improve estimation of uncertain parameters in the Ensemble Kalman filter by re-parameterization employing prior statistics correction

In vitro (humans, animals) or in vivo (animals) hemilarynx experiments are still the only way to visualize and analyze 3-D vibrations of the entire medial surface of the vocal fold. However, to date, only a few studies have been performed. For three different larynges during sustained phonation, vibrational output was statistically analyzed as a function of glottal airflow (800 to 1800 ml/s), adductory forces (10, 50, 100 g), and two different anterior–posterior pre-stress conditions (10, 50 g). Using a homogeneous grid of 30 microsutures sewn along the medial surface of the vocal fold, global parameters (empirical eigenfunctions/EEF, f0, subglottal pressure, and sound intensity level) were computed. Similarly, local parameters (displacements, velocities, and accelerations) were analyzed at the 30 different suture locations. The recordings were obtained using a digital high-speed camera (2000 and 4000 fps). Increased airflow resulted in significant statistical changes in all parameter values except the empirical eigenfunctions. For increased adduction and a lower pre-stress (10 g), the local parameters increased more than for the higher pre-stress condition (50 g). For the two pre-stress conditions and an increased adductional force, most global parameters exhibited significant changes (f0, sound intensity, EEF2), while other global parameters (subglottal pressure) did not.