Rapid gust response simulation of large civil aircraft using computational fluid dynamics

ABSTRACTSeveral critical load cases during the aircraft design process result from atmospheric turbulence. Thus, rapidly performable and highly accurate dynamic response simulations are required to analyse a wide range of parameters. A method is proposed to predict dynamic loads on an elastically trimmed, large civil aircraft using computational fluid dynamics in conjunction with model reduction. A small-sized modal basis is computed by sampling the aerodynamic response at discrete frequencies and applying proper orthogonal decomposition. The linear operator of the Reynolds-averaged Navier-Stokes equations plus turbulence model is then projected onto the subspace spanned by this basis. The resulting reduced system is solved at an arbitrary number of frequencies to analyse responses to 1-cos gusts very efficiently. Lift coefficient and surface pressure distribution are compared with full-order, non-linear, unsteady time-marching simulations to verify the method. Overall, the reduced-order model predicts highly accurate global coefficients and surface loads at a fraction of the computational cost, which is an important step towards the aircraft loads process relying on computational fluid dynamics.</jats:p

Model reduction for gust load analysis of free-flying aircraft

The coupling of computational fluid dynamics and rigid body dynamics promises enhanced multidisciplinary simulation capability for aircraft design and certification. Industrial application of such coupled simulations is limited however by computational cost. In this context, model reduction can retain the fidelity of the underlying model while decreasing the computational effort. A model reduction technique is presented herein based on modal decomposition and projection of the non-linear residual function. Flight dynamics eigenmodes are obtained with an operator-based identification procedure which is capable of calculating these global modes of the coupled Jacobian matrix also for an industrial use case with nearly 50 million degrees-of-freedom. Additional modes based on proper orthogonal decomposition to describe the aerodynamic response due to gust encounter are combined with the eigenmode basis. Results are presented for initial disturbance analysis using flight dynamics modes only and for gust encounter simulations using the combined modal basis. Overall, the reduced model is capable of predicting the full order results accurately

Frequency-Domain Gust Response Simulation using Computational Fluid Dynamics

The numerical investigation of dynamic responses to atmospheric turbulence is an important task during the aircraft design and certification process. Efficient methods are desirable because large parameter spaces spanned by, for example, Mach number, flight altitude, load case, and gust shape need to be covered. Aerodynamic nonlinearities such as shocks and boundary-layer separation should be included to account for transonic flight conditions. A linearized frequency-domain method is outlined to efficiently obtain gust responses using computational fluid dynamics. The Reynolds-averaged Navier–Stokes equations are linearized around a steady-state solution and solved for discrete frequencies. The resulting large but sparse system of linear equations can then be evaluated significantly faster than its time-domain counterpart. The method is verified analyzing sinusoidal gust responses for an airfoil and a large civil aircraft considering a broad range of reduced frequencies. Derivatives of aerodynamic coefficients and complex-valued surface pressures are compared for time- and frequency-domain approaches. Next, 1-cos gusts are investigated using an incomplete inverse Fourier transform in conjunction with a complex-valued weighting function to discuss time histories of lift coefficients as well as surface pressures. Finally, introduced techniques are applied to conditions arising from certification requirements to demonstrate the technical readiness. The methods discussed present an important step to establish computational fluid dynamics in the routine aircraft loads process

Investigation into gust load alleviation using computational fluid dynamics

Gust load alleviation has become an integral part of aircraft design to significantly decrease the impact of atmospheric turbulence on aircraft loads, handling qualities and also passenger comfort. During the design of an active control system, the aerodynamic response of the aircraft subjected to gust encounter and control surface deflection effects needs to be modelled. Current industrial practice is based on low-fidelity linear-potential panel methods which are repeatedly evaluated in frequency domain to obtain so-called frequency response functions. Even though rapid turnaround times are possible, important aerodynamic effects such as shock waves and resulting boundary layer separation which define transonic flow conditions are neglected. Typically, robust and adaptive control laws have been designed to account for the shortcomings of the underlying aerodynamic modelling fidelity. In contrast to this, we present initial results of a basic gust controller while using an enhanced aerodynamic modelling by solving the linearised Reynolds-averaged Navier–Stokes equations in frequency domain. Results are presented both for an aerofoil and a large aircraft configuration near transonic cruise conditions. Control laws derived from different levels of the aerodynamic hierarchy are scrutinised during unsteady simulations of realistic gust-encounter scenarios

Stereoselective pharmacokinetics of ketamine and norketamine after racemic ketamine or S-ketamine administration during isoflurane anaesthesia in Shetland ponies

Background The arterial pharmacokinetics of ketamine and norketamine enantiomers after racemic ketamine or S-ketamine i.v. administration were evaluated in seven gelding ponies in a crossover study (2-month interval). Methods Anaesthesia was induced with isoflurane in oxygen via a face-mask and then maintained at each pony's individual MAC. Racemic ketamine (2.2mgkg−1) or S-ketamine (1.1mgkg−1) was injected in the right jugular vein. Blood samples were collected from the right carotid artery before and at 1, 2, 4, 8, 16, 32, 64, and 128min after ketamine administration. Ketamine and norketamine enantiomer plasma concentrations were determined by capillary electrophoresis. Individual R-ketamine and S-ketamine concentration vs time curves were analysed by non-linear least square regression two-compartment model analysis using PCNonlin. Plasma disposition curves for R-norketamine and S-norketamine were described by estimating AUC, Cmax, and Tmax. Pulse rate (PR), respiratory rate (Rf), tidal volume (VT), minute volume ventilation (VE), end-tidal partial pressure of carbon dioxide (Pe′CO2), and mean arterial blood pressure (MAP) were also evaluated. Results The pharmacokinetic parameters of S- and R-ketamine administered in the racemic mixture or S-ketamine administered separately did not differ significantly. Statistically significant higher AUC and Cmax were found for S-norketamine compared with R-norketamine in the racemic group. Overall, Rf, VE, Pe′CO2, and MAP were significantly higher in the racemic group, whereas PR was higher in the S-ketamine group. Conclusions Norketamine enantiomers showed different pharmacokinetic profiles after single i.v. administration of racemic ketamine in ponies anaesthetised with isoflurane in oxygen (1 MAC). Cardiopulmonary variables require further investigatio

Geography of genetic structure in barley wild relative Hordeum vulgare subsp. spontaneum in Jordan

Informed collecting, conservation, monitoring and utilization of genetic diversity requires knowledge of the distribution and structure of the variation occurring in a species. Hordeum vulgare subsp. spontaneum (K. Koch) Thell., a primary wild relative of barley, is an important source of genetic diversity for barley improvement and co-occurs with the domesticate within the center of origin. We studied the current distribution of genetic diversity and population structure in H. vulgare subsp. spontaneum in Jordan and investigated whether it is correlated with either spatial or climatic variation inferred from publically available climate layers commonly used in conservation and ecogeographical studies. The genetic structure of 32 populations collected in 2012 was analyzed with 37 SSRs. Three distinct genetic clusters were identified. Populations were characterized by admixture and high allelic richness, and genetic diversity was concentrated in the northern part of the study area. Genetic structure, spatial location and climate were not correlated. This may point out a limitation in using large scale climatic data layers to predict genetic diversity, especially as it is applied to regional genetic resources collections in H. vulgare subsp. spontaneum

Stereoselective pharmacokinetics of ketamine and norketamine after racemic ketamine or S-ketamine administration during isoflurane anaesthesia in Shetland ponies

Background. The arterial pharmacokinetics of ketamine and norketamine enantiomers after racemic ketamine or S-ketamine i.v. administration were evaluated in seven gelding ponies in a crossover study (2-month interval). Methods. Anaesthesia was induced with isoflurane in oxygen via a face-mask and then maintained at each pony's individual MAC. Racemic ketamine (2.2 mg kg-1) or S-ketamine (1.1 mg kg-1) was injected in the right jugular vein. Blood samples were collected from the right carotid artery before and at 1, 2, 4, 8, 16, 32, 64, and 128 min after ketamine administration. Ketamine and norketamine enantiomer plasma concentrations were determined by capillary electrophoresis. Individual R-ketamine and S-ketamine concentration vs time curves were analysed by non-linear least square regression two-compartment model analysis using PCNonlin. Plasma disposition curves for R-norketamine and S-norketamine were described by estimating AUC, Cmax, and Tmax. Pulse rate (PR), respiratory rate (Rf), tidal volume (VT), minute volume ventilation (VE), end-tidal partial pressure of carbon dioxide (Pe′CO2), and mean arterial blood pressure (MAP) were also evaluated. Results. The pharmacokinetic parameters of S- and R-ketamine administered in the racemic mixture or S-ketamine administered separately did not differ significantly. Statistically significant higher AUC and Cmax were found for S-norketamine compared with R-norketamine in the racemic group. Overall, Rf, VE, Pe′CO2, and MAP were significantly higher in the racemic group, whereas PR was higher in the S-ketamine group. Conclusions. Norketamine enantiomers showed different pharmacokinetic profiles after single i.v. administration of racemic ketamine in ponies anaesthetised with isoflurane in oxygen (1 MAC). Cardiopulmonary variables require further investigation.Facultad de Ciencias Veterinaria

Influence of Pacing Mode and Rate on Peripheral Levels of Atrial Natriuretic Peptide (ANP)

The effect of acute modifications of pacing mode and rate on plasma ANP levels was evaluated. ANP was determined in ten resting patients with ODD pacemokers due to binodal disease or intermittent second- and third-degree AV block. At 82/minute pacing rate the ANP plasma levels (normal range 2 to 30 fmol/mL) corresponded to those under AAI (4.05 ± 2.10 fmol/mL) and DDD (4.18 ± 2.02 fmol/mL) pacing, but increased significantly (P < 0.05) during VVI pacing (6.96 ± 3.70 fmol/mL). Acceleration of DDD stimulation frequency from 82 to 113/minutes led to significant increases of ANP levels by the factor of three in all chosen AV delays. The lowest ANP plasma levels were measured of 175 msec AV delay under 82/minute pacing rate in DDD mode. Under 113/minutes the differences of ANP concentration after variations of AV delays were less pronounced. The influences of altered atrial pressure and tension on ANP release are discussed to account for changes in ANP plasma levels following different modes and rates of pacemaker stimulation.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/75366/1/j.1540-8159.1989.tb01862.x.pd

Stereoselective pharmacokinetics of ketamine and norketamine after racemic ketamine or S-ketamine administration during isoflurane anaesthesia in Shetland ponies

Background. The arterial pharmacokinetics of ketamine and norketamine enantiomers after racemic ketamine or S-ketamine i.v. administration were evaluated in seven gelding ponies in a crossover study (2-month interval). Methods. Anaesthesia was induced with isoflurane in oxygen via a face-mask and then maintained at each pony's individual MAC. Racemic ketamine (2.2 mg kg-1) or S-ketamine (1.1 mg kg-1) was injected in the right jugular vein. Blood samples were collected from the right carotid artery before and at 1, 2, 4, 8, 16, 32, 64, and 128 min after ketamine administration. Ketamine and norketamine enantiomer plasma concentrations were determined by capillary electrophoresis. Individual R-ketamine and S-ketamine concentration vs time curves were analysed by non-linear least square regression two-compartment model analysis using PCNonlin. Plasma disposition curves for R-norketamine and S-norketamine were described by estimating AUC, Cmax, and Tmax. Pulse rate (PR), respiratory rate (Rf), tidal volume (VT), minute volume ventilation (VE), end-tidal partial pressure of carbon dioxide (Pe′CO2), and mean arterial blood pressure (MAP) were also evaluated. Results. The pharmacokinetic parameters of S- and R-ketamine administered in the racemic mixture or S-ketamine administered separately did not differ significantly. Statistically significant higher AUC and Cmax were found for S-norketamine compared with R-norketamine in the racemic group. Overall, Rf, VE, Pe′CO2, and MAP were significantly higher in the racemic group, whereas PR was higher in the S-ketamine group. Conclusions. Norketamine enantiomers showed different pharmacokinetic profiles after single i.v. administration of racemic ketamine in ponies anaesthetised with isoflurane in oxygen (1 MAC). Cardiopulmonary variables require further investigation.Facultad de Ciencias Veterinaria