actuator failure compensation for nonlinear MIMO systems with an aircraft control application

Remote Sensing of Environment, Volume 114, Issue 11, 15

Purchase November 2010, Pages 25-2574

$ 31.50 Grey S. Nearing, M. Susan Moran, Kelly R. Thorp, Chandra D.

Holifield Collins, Donald C. Slack

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Abstract

Land surface model parameter estimation can be performed using soil moisture information provided by synthetic aperture radar imagery. The presence of speckle necessitates aggregating backscatter measurements over large (> 100 m × 100 m) land areas in order to derive reliable soil moisture information from imagery, and a model calibrated to such aggregated information can only provide estimates of soil moisture at spatial resolutions required for reliable speckle accounting. A method utilizing the likelihood formulation of a probabilistic speckle model as the calibration objective function is proposed which will allow for calibrating land surface models directly to radar backscatter intensity measurements in a way which simultaneously accounts for model parameter- and speckle-induced uncertainty. The method is demonstrated using the NOAH land surface model and Advanced Integral Equation Method (AIEM) backscatter model calibrated to SAR imagery of an area in the Southwestern United States, and validated against in situ soil moisture measurements. At spatial resolutions finer than 100 m × 100 m NOAH and AIEM calibrated using the proposed radar intensity likelihood parameter estimation algorithm predict surface level soil moisture to within 4% volumetric water content 95% of the time, which is an improvement over a 95% prediction confidence of 10% volumetric water content by the same models calibrated directly to soil moisture information derived from synthetic aperture radar imagery at the same scales. Results suggest that much of this improvement is due to increased ability to simultaneously estimate NOAH parameters and AIEM surface roughness parameters.

Article Outline

1. Introduction

2. Models, study site, and methods

2.1. The advanced integral equation backscatter model 2.2. The NOAH land surface model 2.3. The likelihood speckle model 2.4. Calibration methods

2.4.1. Multilook calibration (control) 2.4.2. Likelihood calibration (experimental) 2.5. Study site and SAR imagery 2.6. Simulated data tests 2.7. Real data tests 3. Results

3.1. Comparing simulated data tests 3.2. Comparing real data tests

3.3. The effects of the homogeneity assumption 4. Discussion on the handling of uncertainty 5. Conclusion Acknowledgements References

417

Creep failure of low pressure turbine blade of an

aircraft engine Original Research Article

Engineering Failure Analysis, In Press, Accepted Manuscript, Available online 31 March 2011 N. Ejaz, I.N. Qureshi, S.A. Rizvi

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Abstract

Abstract

A low pressure turbine blade of an aircraft engine was fractured during the ground test run. The failed as well as neighboring un-failed blades were studied during failure investigation. Microstructure of a virgin blade was also analyzed for reference.

The material of the blade was Udimet-500, a high strength Ni-base super alloy. The investigation revealed that the triple point creep cracks were initiated on the trailing edge of blade-airfoil near root region. Grain dropping was also observed within these cracks. One of these cracks was propagated under the high cycle fatigue mechanism, circumscribing almost 50% of the fracture area. When this fatigue crack might have propagated to a critical length, the airfoil of the blade fractured catastrophically under overload condition. The primary cracking was due to creep. Such cracks were also present on the same location of neighboring blades indicating that they were also prone to failure.

Microstrucural study of the failed and unused blades revealed that except the creep crack problem at specific location, there was no other microstructural degradation typical of high temperature exposure in the failed blade. Hardness of the failed blade was closer to that of unused blade as well. The edges of the airfoil of blades were found grinded which was carried out on the instructions of the OEM. It is assumed that the stresses in the turbine region might gone higher either due to engine operating parameter or due to the change in original design of blade.

418

US approves fuel cells, fuels for aircraft cabins

Fuel Cells Bulletin, Volume 2008, Issue 6, June 2008, Page 9

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$ 41.95

Abstract

The US Department of Transportation has approved the carriage of fuel cells and four specified fuels in aircraft passenger cabins, in a decision that is consistent with airline regulations internationally. Passengers and crew will be

permitted to carry fuel cell systems designed for portable electronic devices in carry-on baggage, and up to two spare fuel cartridges. The move has been welcomed by fuel cell industry bodies such as the US Fuel Cell Council and the Methanol Institute.

419

Fail-safe design of integral metallic aircraft structures

reinforced by bonded crack retarders Original Research

Article

Purchase Engineering Fracture Mechanics, Volume 76, Issue 1,

$ 35.95 January 2009, Pages 114-133

X. Zhang, M. Boscolo, D. Figueroa-Gordon, G. Allegri, P.E. Irving

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Abstract

This paper presents an investigation on the effectiveness of crack growth retarders bonded to integral metallic structures. The study was performed by both numerical modelling and experimental tests. It focuses on aluminium alloy panels reinforced by bonded straps made of carbon-epoxy, glass-epoxy composite materials or a titanium alloy. The goal was to develop a fail-safe design for integrally stiffened skin-stringer panels applicable to aircraft wing structures. The modelling strategy and finite element models are presented and discussed. The requirements that the models should meet are also discussed. The study has focused on establishing the extent of crack retarder benefits, in terms of fatigue crack growth life improvement, by numerical simulation and experimental tests of various crack retarders. The results of predicted fatigue crack growth retardation have been validated by tests of laboratory samples. This study concludes that by bonding discrete straps to an integral structure, the fatigue crack growth life can be significantly improved.

Article Outline

1. Introduction 2. Problem statement

2.1. Strap reinforced skin-stringer panels 2.2. Scope of this investigation

3. Modelling approach

3.1. Stress intensity factor for bonded structures under static load 3.2. FE modelling of disbond damage 3.3. Damage growth under fatigue loading

4. Development of properties to input into the model 4.1. Material properties – Coupon test data

4.2. Residual stress developed during strap bond cure 5. Fatigue crack growth tests 5.1. Test samples and test procedure 5.2. Fatigue crack growth results 5.2.1. M(T) samples 5.2.2. SENT samples

6. Comparison of experimental and predicted fatigue crack growth behaviour 6.1. M(T) sample 6.2. SENT samples 7. Conclusions Acknowledgements Appendix A. Appendix

A.1. Two methods for calculating ΔK in the presence of residual stress field A.2. Comparison of the two methods References

420

Underwater blast loading of sandwich beams:

Regimes of behaviour Original Research Article

International Journal of Solids and Structures, Volume 46,

Purchase Issue 17, 15 August 2009, Pages 3209-3221

$ 31.50 M.T. Tilbrook, V.S. Deshpande, N.A. Fleck

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Abstract

Finite element (FE) calculations are used to develop a comprehensive understanding of the dynamic response of sandwich beams subjected to underwater blast loading, including the effects of fluid–structure interaction. Design maps are constructed to show the regimes of behaviour over a broad range of loading intensity, sandwich panel geometry and material strength. Over the entire range of parameters investigated, the time-scale associated with the initial fluid–structure interaction phase up to the instant of first cavitation in the fluid is much smaller than the time-scales associated with the core compression and the bending/stretching responses of the sandwich beam. Consequently, this initial fluid–structure interaction phase decouples from the subsequent phases of response. Four regimes of behaviour exist: the period of sandwich core compression either couples or decouples with the period of the beam bending, and the core either densifies partially or fully. These regimes of behaviour are charted on maps using axes of blast impulse and core strength. The simulations indicate that continued loading by the fluid during the core compression phase and the beam bending/stretching phase cannot be neglected. Consequently, analyses that neglect full fluid–structure interaction during the structural responses provide only estimates of performance metrics such as back face deflection and reaction forces at the supports. The calculations here also indicate that appropriately designed sandwich beams undergo significantly smaller back face deflections and exert smaller support forces than monolithic beams of equal mass. The optimum transverse core strength is determined for minimizing the back face deflection or support reactions at a given blast impulse. Typically, the transverse core strength that minimizes back face deflection is 40% below the value that minimizes the support reaction. Moreover, the optimal core strength depends upon the level of blast impulse, with higher strength cores required for higher intensity blasts.

Article Outline

1. Introduction

2. Overview of the dynamic response of sandwich beams 2.1. Coupling of stages I and II 2.2. Coupling of stages II and III 3. Finite element simulations 3.1. Constitutive models 3.2. Applied loading 3.3. Non-dimensional groups

4. Underwater blast response of sandwich beams 4.1. Identification of the four regimes

4.1.1. Regime A: decoupled regime with partial core densification

4.1.2. Regime B: decoupled regime with full core densification

4.1.3. Regime C: coupled regime with partial core densification 4.1.4. Regime D: coupled regime with full core densification 4.2. Regime maps

4.3. Comparison with monolithic beams

4.4. Optimal performance of the sandwich beams

5. Discussion: decoupled versus coupled fluid structure interaction simulations 6. Concluding remarks Acknowledgements References

421

Real Time Monitoring and Forecasting of Full Scale

Aircraft Static Test Original Research Article

Tsinghua Science & Technology, Volume 14, Supplement

Purchase 2, December 2009, Pages 38-42

Xiuhua Chen, Haitao Fan, Jinli Pei, Hai Wang, Junfeng $ 31.50

Zhao, Weiyi Guo, Lin'gang Zhu, Guangrong Zhu

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Abstract

To meet the airworthiness certification requirement of the full scale static test for ARJ21-700 commercial aircraft, a real time monitoring and forecasting software is presented. The software contains a database which stores all the material data, finite element analysis (FEA) model and results, strain gages and displacement transducers' information, etc. The software can also compare the test data with the FEA and theoretical results, and forecast the next and the final test results based on the analytical and test data in real time. With the support of this software, aircraft designers can monitor the strain and displacement data through distributed monitors and calculate the structure stress and safety margin in real time and can prevent unexpected accidents. Now this software has already been successfully used in the static test of ARJ21 with its high accuracy and reliability.

Article Outline

Introduction

1. System Overview 1.1. Hardware overview 1.2. Software overview 1.3. Server software design 1.4. Client software design 1.5. Database design

2. Real Time Monitoring and Forecasting of Full Scale Static Test of ARJ21 Aircraft 3. Conclusions

References

422

Experimental parametric study of forced and mixed

convection in a passenger aircraft cabin

mock-up Original Research Article

Building and Environment, Volume 44, Issue 5, May 2009, Purchase

$ 31.50 Pages 961-970

Matthias Kühn, Johannes Bosbach, Claus Wagner

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Abstract

Forced and mixed convection has been investigated experimentally in a full scale passenger aircraft cabin mock-up. The mock-up represents a generic cabin section of the A380 upper deck. Large scale particle image velocimetry (PIV) and temperature field measurements were conducted in a cross sectional plane of the cabin mock-up. The flow fields for two different air inlet configurations were measured and analysed under isothermal and cooling conditions. Furthermore the flow rates at the different air inlet positions were varied while keeping the air exchange rate constant. Our extensive experimental parametric study demonstrates that the flow field in aircraft cabins is affected by various fluid mechanical phenomena. Interaction between the supplied air jets, negative buoyancy forces acting on these air jets and interaction of thermal plumes with the supplied air jets, all influence the flow field inside the cabin. The impact of these effects differs considerably depending on the ventilation configuration and relative mass flow settings at the supply inlets.

Article Outline

1. Introduction

2. Passenger aircraft cabin model

2.1. Aircraft cabin mock-up

2.2. Boundary conditions and varied parameters 3. Experimental set-up

3.1. Set-up for air flow measurement using particle image velocimetry 3.2. Set-up for temperature field measurements

4. Results and discussion of the systematic parametric study 4.1. Configuration A 4.1.1. Isothermal conditions 4.1.2. Cooling conditions 4.2. Configuration B 4.2.1. Isothermal conditions 4.2.2. Cooling conditions

4.2.3. Configuration B 50/50 under cooling case conditions 5. Summary and conclusions References

423

What shall we do with the drunken sailor?: Effects of

alcohol on the performance of ship operators Original

Research Article

Forensic Science International, Volume 156, Issue 1, 6 Purchase

$ 31.50 January 2006, Pages 16-22

Stefanie Ritz-Timme, Mark Thome, Geertje Grütters, Martin Grütters, Jan A. Reichelt, Norbert Bilzer, Hans-Jürgen Kaatsch

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Abstract

The purpose of this study was to specify the effects of alcohol on the performance of ship operators as a contribution to the development of new strategies against the risks of alcohol in water traffic. The nautical performance of 21 captains before and after alcohol consumption was assessed on a ship

piloting simulator. The simulated scenarios represented passages of a container vessel through the German Bight. Performance was examined by nautical instructors according to standardised protocols. Mean (S.D.) blood alcohol concentrations (BACs) of 0.100 (0.024) g/dl before and 0.100 (0.017) g/dl after the performance trial resulted in striking effects on the nautical performance. The categories most severely affected were foresight and analysis of situation (impairment in 18 of 21 cases), concentration (impairment in 16 of 21 cases), accurateness, risk disposition and navigation (impairment in 15 of 21 cases). Chart work, preparation and communication were impaired in 12, 11 and 10 of 21 cases, respectively. None of the participants were capable to operate the simulated ship with an adequate safety after ingestion of alcohol. From these findings, and in consideration of the well-established impairment of a multitude of mental and physical functions by alcohol, it can be concluded that even low BACs bear high risks in water traffic, a concentration above 0.1 g/dl will hinder a sufficiently safe

performance of ship operators. This should be considered in alcohol education and legislation.

Article Outline

1. Introduction 2. Method

2.1. The participants 2.2. The simulator

2.3. The simulated scenarios 2.4. The experiments

2.5. The assessment of the nautical performance 3. Results 3.1. The BACs

3.2. Effects of alcohol on nautical performance 3.3. Heart rates

3.4. The subjective impressions of the participants 4. Discussion

4.1. To what extent does the performance on ship simulators predict performance on real vessels?

4.2. The effects of alcohol on the performance of ship operators 5. Conclusion Acknowledgements References

424

Characteristics of rainstorms over a temperate region

derived from multiple time series of weather radar

images Original Research Article

Purchase Journal of Hydrology, Volume 307, Issues 1-4, 9 June

$ 39.95 2005, Pages 126-144

Gabriëlle J.M. De Lannoy, Niko E.C. Verhoest, François P. De Troch

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425

Human factors evaluations of Free Flight: Issues solved and

issues remaining Original

Purchase Research Article

Applied Ergonomics, Volume 38, $ 31.50 Issue 4, July 2007, Pages 437-455 Rob C.J. Ruigrok, Jacco M. Hoekstra

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