Página 1 dos resultados de 62812 itens digitais encontrados em 0.071 segundos

Stability region bifurcations of nonlinear autonomous dynamical systems: Type-zero saddle-node bifurcations

AMARAL, F. M.; ALBERTO, L. F. C.
Fonte: WILEY-BLACKWELL Publicador: WILEY-BLACKWELL
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
36.31%
The behavior of stability regions of nonlinear autonomous dynamical systems subjected to parameter variation is studied in this paper. In particular, the behavior of stability regions and stability boundaries when the system undergoes a type-zero sadle-node bifurcation on the stability boundary is investigated in this paper. It is shown that the stability regions suffer drastic changes with parameter variation if type-zero saddle-node bifurcations occur on the stability boundary. A complete characterization of these changes in the neighborhood of a type-zero saddle-node bifurcation value is presented in this paper. Copyright (C) 2010 John Wiley & Sons, Ltd.; Conselho Nacional de Desenvolvimento Cientfico e Tecnolgico (CNPQ)

Stability analysis of core-annular flow and neutral stability wave number

RODRIGUEZ, Oscar M. H.; BANNWART, Antonio C.
Fonte: JOHN WILEY & SONS INC Publicador: JOHN WILEY & SONS INC
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
36.31%
A general transition criterion is proposed in order to locate the core-annular flow pattern in horizontal and vertical oil-water flows. It is based on a rigorous one-dimensional two-fluid model of liquid-liquid two-phase flow and considers the existence of critical interfacial wave numbers related to a non-negligible interfacial tension term to which the linear stability theory still applies. The viscous laminar-laminar flow problem is fully resolved and turbulence effects on the stability are analyzed through experimentally obtained shape factors. The proposed general transition criterion includes in its formulation the inviscid Kelvin-Helmholtz`s discriminator. If a theoretical maximum wavelength is considered as a necessary condition for stability, a stability criterion in terms of the Eotvos number is achieved. Effects of interfacial tension, viscosity ratio, density difference, and shape factors on the stability of core-annular flow are analyzed in detail. The more complete modeling allowed for the analysis of the neutral-stability wave number and the results strongly suggest that the interfacial tension term plays an indispensable role in the correct prediction of the stable region of core-annular flow pattern. The incorporation of a theoretical minimum wavelength into the transition model produced significantly better results. The criterion predictions were compared with recent data from the literature and the agreement is encouraging. (C) 2007 American Institute of Chemical Engineers.

The effect of sodium fluoride preservative and storage temperature on the stability of cocaine in horse blood, sheep vitreous and deer muscle

Rees, Kelly A.; Jones, Nicola S.; McLaughlin, Poppy A.; Seulin, Saskia; Leyton, Vilma; Yonamine, Maurício; Osselton, M. David
Fonte: ELSEVIER IRELAND LTD; CLARE Publicador: ELSEVIER IRELAND LTD; CLARE
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
36.34%
The in vitro stability of cocaine in horse blood, sheep vitreous humour (VH) and homogenised deer muscle is described. The stability of cocaine in horse blood was of interest because many toxicology laboratories utilise horse blood for the preparation of calibration and check standards and the latter are typically stored during routine use. The storage stability of cocaine in human VH and muscle has not been previously reported. In the absence of blank human VH and muscle, cocaine stability under varying conditions was demonstrated in animal tissues. Blood and VH were stored with and without addition of NaF at room temperature (RT), 4 degrees C and -18 degrees C for 84 days. Muscle homogenates were prepared in water, water/2% NaF, and phosphate buffer (pH 6.0)/2% NaF, and stored for 31 days at RT, 4 degrees C and -18 degrees C. Cocaine stability in human muscle obtained from cocaine positive forensic cases was assessed following storage at -18 degrees C for 13 months. Cocaine and benzoylecgonine (BZE) were extracted using SPE and quantified by GC-MS/MS. Cocaine was stable for 7 days in refrigerated (4 degrees C) horse blood fortified with 1 and 2% NaF. In the absence of NaF, cocaine was not detectable by day 7 in blood stored at RT and 4 degrees C and had declined by 81% following storage at -18 degrees C. At 4 degrees C the rate of cocaine degradation in blood preserved with 2% NaF was significantly slower than with 1% NaF. The stability of cocaine in horse blood appeared to be less than that reported for human blood...

TYPE-ZERO SADDLE-NODE BIFURCATIONS AND STABILITY REGION ESTIMATION OF NONLINEAR AUTONOMOUS DYNAMICAL SYSTEMS

Amaral, Fabiolo M.; Alberto, Luís Fernando Costa
Fonte: WORLD SCIENTIFIC PUBL CO PTE LTD; SINGAPORE Publicador: WORLD SCIENTIFIC PUBL CO PTE LTD; SINGAPORE
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
36.31%
A complete characterization of the stability boundary of a class of nonlinear dynamical systems that admit energy functions is developed in this paper. This characterization generalizes the existing results by allowing the type-zero saddle-node nonhyperbolic equilibrium points on the stability boundary. Conceptual algorithms to obtain optimal estimates of the stability region (basin of attraction) in the form of level sets of a given family of energy functions are derived. The behavior of the stability region and the corresponding estimates are investigated for parameter variation in the neighborhood of a type-zero saddle-node bifurcation value.; FAPESP [2010/00574-9, 2011/06938-5]; FAPESP; CNPq; CNPq; IFBA; IFBA

Estabilidade e adaptabilidade fenotípica através da reamostragem "Bootstrap" no modelo AMMI.; Phenotypic stability and adaptability via ammi model with bootstrap re-sampling.

Lavoranti, Osmir José
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Tese de Doutorado Formato: application/pdf
Publicado em 28/08/2003 Português
Relevância na Pesquisa
36.31%
As posições críticas dos estatísticos, que atuam em programas de melhoramento genético, referem-se à falta de uma análise criteriosa da estrutura da interação do genótipo com o ambiente (G x E) como um dos principais problemas para a recomendação de cultivares. Tradicionalmente, a análise dessa estrutura á superficial não detalhando os efeitos da complexidade da interação. Com isso, os ganhos genéticos podem ser diminutos, pela não seleção de genótipos superiores melhores indicados a um ambiente específico. A busca constante por novos métodos e algoritmos, visando eliminar ou minimizar esse problema, tem proporcionado uma inegável evolução científica, com a geração de tecnologias de ponta que envolvem grande capacidade de processamento computacional. Atualmente, a metodologia AMMI (additive main efects and multiplicative interaction analysis) propõe ser mais eficiente que as análises usuais na interpretação e compreensão da interação G x E. Entretanto, os principais pontos negativos dessa metodologia dizem respeito à dificuldade de se interpretar a interação quando há baixa explicação do primeiro componente principal; à dificuldade de se quantificar os escores como baixos, considerando estável os genótipos e/ou ambientes...

Caracterização, estimativas e bifurcações da região de estabilidade de sistemas dinâmicos não lineares; Characterization, estimates and bifurcations of stability region of nonlinear dynamical systems

Amaral, Fabíolo Moraes
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Tese de Doutorado Formato: application/pdf
Publicado em 24/09/2010 Português
Relevância na Pesquisa
36.37%
Estimar a região de estabilidade de um ponto de equilíbrio assintoticamente estável é importante em aplicações tais como sistemas de potência, economia e ecologia. A compreensão da estrutura qualitativa da fronteira da região de estabilidade é fundamental para estimar com eficiência a região de estabilidade. Caracterizações topológicas e dinâmicas da fronteira da região de estabilidade foram desenvolvidas ao longo das últimas décadas. Estas caracterizações foram desenvolvidas sob hipóteses de hiperbolicidade dos pontos de equilíbrio na fronteira e transversalidade. Para sistemas que dependem de parâmetros, a condição de hiperbolicidade pode ser violada em pontos de bifurcações. Estaremos interessados em estimar a região de estabilidade, para sistemas sujeitos a variações de parâmetros, onde ocorre a violação da condição de hiperbolicidade dos pontos de equilíbrio na fronteira da região de estabilidade devido ao aparecimento de uma bifurcação sela-nó do tipo zero nesta fronteira. Apresentaremos neste trabalho uma caracterização completa da fronteira da região de estabilidade na presença de um ponto de equilíbrio não hiperbólico sela-nó do tipo zero. Motivados também em oferecer um algoritmo conceitual para obter estimativas da região de estabilidade perturbada via conjunto de nível de uma dada função energia na vizinhança de um parâmetro de bifurcação sela-nó do tipo zero...

Estabilidade da carne de cordeiro em diferentes condições de armazenamento; Stability of lamb meat at different storage conditions

Fernandes, Rafaella de Paula Paseto
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: dissertação de mestrado Formato: application/pdf
Publicado em 15/04/2011 Português
Relevância na Pesquisa
36.33%
Atualmente no Brasil a carne ovina é comercializada quase exclusivamente congelada. No entanto, praticamente não existem estudos no país sobre alterações na qualidade desta carne durante seu armazenamento. Com a crescente demanda do consumidor por produtos de maior conveniência, surge a necessidade de maiores estudos em relação à estabilidade de cortes cárneos ovinos estocados sob refrigeração, principalmente em decorrência de sua curta vida útil. Os objetivos deste trabalho foram avaliar a estabilidade da carne ovina quando estocada sob refrigeração e congelamento e se diferentes sistemas de acondicionamento em atmosfera modificada poderiam aumentar a estabilidade desta carne quando armazenada sob refrigeração. Foram realizados dois experimentos. No primeiro, lombos ovinos foram embalados a vácuo e armazenados sob refrigeração (4±1ºC) por 28 dias e congelamento (-18±1ºC) por 12 meses. No segundo, os cortes foram acondicionados individualmente em 3 diferentes sistemas de embalagem com atmosfera modificada: 1) Á vácuo (sistema tradicional); 2) Com injeção de gases na proporção 75% O2 e 25% CO2 e 3) Com injeção de 100% de CO2). Neste segundo experimento as carnes foram armazenadas sob refrigeração (1±1ºC) por um período de 28 dias. A estabilidade dos cortes foi avaliada por meio de análises físicas...

Contribuição à avaliação da estabilidade global e pré-dimensionamento de pórticos planos em concreto pré-moldado; Contribution to the assessment of global stability and preliminary design of precast concrete frames

Lins, Fernando de Faria Vecchio
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: dissertação de mestrado Formato: application/pdf
Publicado em 01/07/2013 Português
Relevância na Pesquisa
36.39%
O presente trabalho tem como objetivo desenvolver processos analíticos e programas computacionais para avaliação da estabilidade global e pré-dimensionamento de pórticos planos em concreto pré-moldado com base na garantia da estabilidade global. Em relação à avaliação da estabilidade global, são propostas duas expressões. A primeira está relacionada à expressão do limite do parâmetro de estabilidade aplicada a pórticos planos em concreto pré-moldado. A segunda expressão tem o objetivo determinar o deslocamento horizontal de topo de pórticos planos em concreto pré-moldado de um pavimento. A expressão do limite alternativo do parâmetro de estabilidade é deduzida a partir dos valores obtidos da relação entre o deslocamento horizontal médio e de topo de 1320 pórticos. A expressão é função do fator de restrição da ligação, contemplando, dessa forma, os efeitos causados pela semirrígidez das ligações no comportamento da estabilidade global desse sistema estrutural. A equação de determinação do deslocamento horizontal de topo de pórticos planos em concreto pré-moldado de um pavimento é deduzida com base no método dos deslocamentos. Em relação ao pré-dimensionamento de pórticos planos em concreto pré-moldado...

Bifurcações da região de estabilidade induzidas por bifurcações locais do tipo Hopf; Bifurcations of the stability region induced by type-Hopf local bifurcations

Gouveia Júnior, Josaphat Ricardo Ribeiro
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Tese de Doutorado Formato: application/pdf
Publicado em 19/03/2015 Português
Relevância na Pesquisa
36.36%
Pontos de equilíbrio assintoticamente estáveis de sistemas dinâmicos não lineares geralmente não são globalmente estáveis. Na maioria dos casos, há um subconjunto de condições iniciais, chamada região de estabilidade (ou área de atração), cujas trajetórias tendem ao ponto de equilíbrio quando o tempo tende ao infinito. Devido à importância das regiões de estabilidade em aplicações, e motivado principalmente pelo problema de analise de estabilidade transitória em sistemas elétricos de potência, uma caracterização completa da fronteira da região de estabilidade foi desenvolvida. Esta caracterização foi desenvolvida sob a suposição de que o sistema dinâmico é bem conhecido e que os parâmetros de seu modelo são constantes. Na prática, variações de parâmetros ocorrem e bifurcações desta podem ocorrer. Nesta tese, desenvolveremos uma caracterização completa da fronteira da região de estabilidade de sistemas dinâmicos autônomos não lineares admitindo a existência de pontos de equilíbrio não hiperbólicos do tipo Hopf na fronteira da região de estabilidade. Sob certas condições de transversalidade, apresentaremos uma caracterização completa da fronteira da região de estabilidade admitindo tanto a presença de pontos de equilíbrio não hiperbólicos do tipo Hopf como também a existência de órbitas periódicas na fronteira. Ofereceremos também uma caracterização da fronteira da região de estabilidade fraca do ponto de equilíbrio não hiperbólico Hopf supercrítico do tipo zero e uma caracterização topológica da sua região de atração. Além disso...

Transient stability indices from a hybrid approach

Padilha, A.; Denis, E. F.
Tipo: info:eu-repo/semantics/conferencepaper Formato: 474-478
Português
Relevância na Pesquisa
36.33%
This paper deals with hybrid method for transient stability analysis combining time domain simulation and a direct method. Nowadays, the step-by-step simulation is the best available tool for allowing the uses of detailed models and for providing reliable results. The main limitation of this approach involves the large time of computational simulations and the absence of stability margin. On the other hand, direct methods, that demand less CPU time, did not show ample reliability and applicability yet. The best way seems to be using hybrid solutions, in which a direct method is incorporated in a time domain simulation tool. This work has studied a direct method using the transient potential and kinetic energy of the critical machine only. In this paper the critical machine is identified by a fast and efficient method, and the proposal is new for using to get stability margins from hybrid approaches. Results from systems, like 16-machine, show stability indices to dynamic security assessment. © 2001 IEEE.

Stability analysis of core-annular flow and neutral stability wave number

RODRIGUEZ, Oscar M. H.; BANNWART, Antonio C.
Fonte: JOHN WILEY & SONS INC Publicador: JOHN WILEY & SONS INC
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
36.31%
A general transition criterion is proposed in order to locate the core-annular flow pattern in horizontal and vertical oil-water flows. It is based on a rigorous one-dimensional two-fluid model of liquid-liquid two-phase flow and considers the existence of critical interfacial wave numbers related to a non-negligible interfacial tension term to which the linear stability theory still applies. The viscous laminar-laminar flow problem is fully resolved and turbulence effects on the stability are analyzed through experimentally obtained shape factors. The proposed general transition criterion includes in its formulation the inviscid Kelvin-Helmholtz`s discriminator. If a theoretical maximum wavelength is considered as a necessary condition for stability, a stability criterion in terms of the Eotvos number is achieved. Effects of interfacial tension, viscosity ratio, density difference, and shape factors on the stability of core-annular flow are analyzed in detail. The more complete modeling allowed for the analysis of the neutral-stability wave number and the results strongly suggest that the interfacial tension term plays an indispensable role in the correct prediction of the stable region of core-annular flow pattern. The incorporation of a theoretical minimum wavelength into the transition model produced significantly better results. The criterion predictions were compared with recent data from the literature and the agreement is encouraging. (C) 2007 American Institute of Chemical Engineers.

Nonparametric stability methods for interpreting genotype by environment interaction of bread wheat genotypes (Triticum aestivum L.)

Akcura,Mevlut; Kaya,Yuksel
Fonte: Sociedade Brasileira de Genética Publicador: Sociedade Brasileira de Genética
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/12/2008 Português
Relevância na Pesquisa
36.34%
Evaluation of performance stability and high yield is essential for yield trials conducted in different environments. We determined the stability of 10 bread wheat (Triticum aestivum L.) genotypes (5 cultivars and 5 advanced lines) using nonparametric stability measures and compared nonparametric stability statistics across 19 environments in the Central Anatolian Region of Turkey. Experiments were setup in a randomized complete block design with four replications. Nonparametric stability measures revealed that AL-2, Karahan-99 and Altay-2000 were the most stable and well adapted genotypes across the 19 environments. In addition, it was concluded that graphs of mean grain yield (t ha-1) vs. nonparametric measures (Si(¹), Si(²), S(³), Si(6) and ?gy) values and kr vs. ?r values could enhance visual efficiency of genotype selection based on genotype by environment interaction. Furthermore, high TOP values, Si(³) and Si(6) were associated with high grain yield, but the other nonparametric stability measures were not positively correlated with grain yield and instead characterized a static concept of stability. Choice of genotype for increased grain yield in bread wheat would, therefore, be expected to change yield stability by increasing the values of the Si(³)...

Nonparametric stability methods for interpreting genotype by environment interaction of bread wheat genotypes (Triticum aestivum L.)

Akcura,Mevlut; Kaya,Yuksel
Fonte: Sociedade Brasileira de Genética Publicador: Sociedade Brasileira de Genética
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/12/2008 Português
Relevância na Pesquisa
36.34%
Evaluation of performance stability and high yield is essential for yield trials conducted in different environments. We determined the stability of 10 bread wheat (Triticum aestivum L.) genotypes (5 cultivars and 5 advanced lines) using nonparametric stability measures and compared nonparametric stability statistics across 19 environments in the Central Anatolian Region of Turkey. Experiments were setup in a randomized complete block design with four replications. Nonparametric stability measures revealed that AL-2, Karahan-99 and Altay-2000 were the most stable and well adapted genotypes across the 19 environments. In addition, it was concluded that graphs of mean grain yield (t ha-1) vs. nonparametric measures (Si(¹), Si(²), S(³), Si(6) and ?gy) values and kr vs. ?r values could enhance visual efficiency of genotype selection based on genotype by environment interaction. Furthermore, high TOP values, Si(³) and Si(6) were associated with high grain yield, but the other nonparametric stability measures were not positively correlated with grain yield and instead characterized a static concept of stability. Choice of genotype for increased grain yield in bread wheat would, therefore, be expected to change yield stability by increasing the values of the Si(³)...

Accelerated chemical stability data of O/W fluid emulsions containing the extract of Trichilia catigua Adr. Juss (and) Ptychopetalum olacoides Bentham

Baby,André Rolim; Migliato,Ketylin Fernanda; Maciel,Carolina Penteado Moraes; Zague,Vivian; Pinto,Claudinéia Aparecida Sales de Oliveira; Salgado,Hérida Regina Nunes; Kaneko,Telma Mary; Velasco,Maria Valéria Robles
Fonte: Divisão de Biblioteca e Documentação do Conjunto das Químicas da Universidade de São Paulo Publicador: Divisão de Biblioteca e Documentação do Conjunto das Químicas da Universidade de São Paulo
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/09/2007 Português
Relevância na Pesquisa
36.31%
Development of topical dosage forms requires physical, physicochemical and chemical assays that provide, as soon as possible, the formulation with the best stability profiles. This study evaluated the stability of O/W fluid emulsions, by total flavonoids determination, expressed in rutin, containing the standardized extract of Trichilia catigua Adr. Juss (and) Ptychopetalum olacoides Bentham. Samples were evaluated for 90 days stored at 24.0 ± 2.0 ºC, 5.0 ± 0.5 ºC and 40.0 ± 0.5 ºC, following a protocol for the assessment of accelerated chemical stability assay, also known as Normal Stability Test. A sensitive UV-spectrophotometric method at 361.0 nm was previously validated for the determination of the active substance. By Normal Stability Test, the O/W fluid emulsions presented acceptable chemical stability, for at least 90 days, when the samples were stored at 24.0 ± 2.0 ºC and 5.0 ± 0.5 ºC. The storage condition at 40.0 ± 0.5 ºC has accelerated the degradation process of the total flavonoids, consequently, those O/W emulsions containing this kind of natural active substance or a similar preparation must not be stored at elevated temperatures.

The influence of pH, polyethylene glycol and polyacrylic acid on the stability of stem bromelain

Novaes,Letícia Celia de Lencastre; Jozala,Angela Faustino; Mazzola,Priscila Gava; Júnior,Adalberto Pessoa
Fonte: Universidade de São Paulo, Faculdade de Ciências Farmacêuticas Publicador: Universidade de São Paulo, Faculdade de Ciências Farmacêuticas
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/06/2014 Português
Relevância na Pesquisa
36.33%
Enzyme stability is critical in biotechnology, pharmaceutical and cosmetic industries. Investigations on this subject have drawn attention because of its practical application. Bromelain is a thiol-endopeptidase, obtained from pineapple (Ananas comosus), known for its clinical and therapeutic applications, particularly to selective burn debridement and improvement of antibiotic action and anti-inflammatory activities. To date, the use of bromelain in pharmacological or industrial applications is limited, due to commercial availability, costs, and sensitivity to pH and temperature. Therefore, a better understanding of enzyme stability would be of great interest. The aim of this study was to evaluate bromelain activity and stability in several pH (2.0 to 8.0) and in polyethylene glycol and polyacrylic acid solutions. We observed that bromelain was able to maintain its stability at pH 5.0 for the temperatures studied. PEG solutions increased bromelain stability, but PAA solutions had the opposite effect.

Investigation of Stability and Control Characteristics of a 1/10-scale Model of a Canadian Tailless Glider in the Langley Free-flight Tunnel

Johnson, Joseph L.
Tipo: naca-rm-sl9c28 Formato: application/pdf
Português
Relevância na Pesquisa
36.31%
An investigation of the stability and control characteristics of a 1/10-scale model of a Canadian tailless glider has been conducted in the 10 Langley free-flight tunnel. The glider designated the N.R.L. tailless glider has a straight center section and outboard panels sweptback 43 deg. along the leading edge of the wing. The aspect ratio is 5.83 and the taper ratio is 0.323. From the results of the investigation and on the basis of comparison with higher-scale static tests of the National Research Council of Canada, it is expected that the longitudinal stability of the airplane will be satisfactory with flap up but unsatisfactory near the stall with flap down. The airplane is expected to have unsatisfactory lateral stability and control characteristics in the design configuration with either flap up or flap down. The model flights showed very low damping of the lateral oscillation. Increasing the vertical-tail area improved the lateral stability, and it appeared that a value of the directional-stability parameter C(sub n beta) of at least 0.002 per degree would probably be necessary for satisfactory lateral flying characteristics. A comparison of the calculated dynamic lateral stability characteristics of the N.R.L. tailless glider with those of a conventional-type sweptback airplane having a similar wing plan form and about the same inclination of the principal longitudinal axis of inertia showed that the tailless glider had poorer lateral stability because of the relatively larger radius of gyration in roll and the smaller damping-in-yaw factor C(sub nr).

On-Line Robust Modal Stability Prediction using Wavelet Processing

Brenner, Martin J.; Lind, Rick
Tipo: nas 1.15:206550; icas-98-4,9,1; h-2246; nasa/tm-1998-206550; 14-17 sep. 1998; melbourne; australia Formato: application/pdf
Português
Relevância na Pesquisa
36.31%
Wavelet analysis for filtering and system identification has been used to improve the estimation of aeroservoelastic stability margins. The conservatism of the robust stability margins is reduced with parametric and nonparametric time- frequency analysis of flight data in the model validation process. Nonparametric wavelet processing of data is used to reduce the effects of external disturbances and unmodeled dynamics. Parametric estimates of modal stability are also extracted using the wavelet transform. Computation of robust stability margins for stability boundary prediction depends on uncertainty descriptions derived from the data for model validation. The F-18 High Alpha Research Vehicle aeroservoelastic flight test data demonstrates improved robust stability prediction by extension of the stability boundary beyond the flight regime. Guidelines and computation times are presented to show the efficiency and practical aspects of these procedures for on-line implementation. Feasibility of the method is shown for processing flight data from time- varying nonstationary test points.

Wavelet Filtering to Reduce Conservatism in Aeroservoelastic Robust Stability Margins

Lind, Rick; Brenner, Marty
Tipo: aiaa paper 98-1896; nasa/tm-1998-206545; nas 1.15:206545; h-2222; structures, structural dynamics and materials conference; 20-23 apr. 1998; long beach, ca; united states Formato: application/pdf
Português
Relevância na Pesquisa
36.31%
Wavelet analysis for filtering and system identification was used to improve the estimation of aeroservoelastic stability margins. The conservatism of the robust stability margins was reduced with parametric and nonparametric time-frequency analysis of flight data in the model validation process. Nonparametric wavelet processing of data was used to reduce the effects of external desirableness and unmodeled dynamics. Parametric estimates of modal stability were also extracted using the wavelet transform. Computation of robust stability margins for stability boundary prediction depends on uncertainty descriptions derived from the data for model validation. F-18 high Alpha Research Vehicle aeroservoelastic flight test data demonstrated improved robust stability prediction by extension of the stability boundary beyond the flight regime.

Flight Determination of the Static Longitudinal Stability Boundaries of the Bell X-5 Research Airplane with 59 Deg Sweepback

Walker, Joseph A; Finch, Thomas W
Tipo: naca-rm-l53a09b Formato: application/pdf
Português
Relevância na Pesquisa
36.35%
During the flight program on the Bell X-5 airplane with 59 deg sweepback to determine the practical Mach number and normal-force coefficient limits of this configuration, a reduction in static longitudinal stability was encountered in maneuvering flight. A determination of the boundary for reduction of longitudinal stability extending to a Mach number of 0.98 is presented in this paper. A reduction of static longitudinal stability existed for all elevator and all stabilizer-executed maneuvers. The reduction of stability existed for maneuvers executed with elevator near a normal-force coefficient of 0.6 for a Mach number range of about 0.31 to 0.76. Above a Mach number of 0.76 the normal-force coefficient for reduction of stability gradually decreased to a value of 0.2 at a Mach number of 0.98. For stabilizer-executed maneuvers the stability boundary was the same as for elevator maneuvers up to a Mach number of 0.88. Above this Mach number the reduction of stability occurred at slightly higher normal-force coefficients decreasing from about 0.51 at a Mach number of 0.92 to a value of 0.311 at a Mach number of 0.97. The airplane has been flown to a Mach number of 1.04 at a normal-force coefficient of about 0.15 without encountering any reduction of stability. The pilot did not consider the reduction of stability to be dangerous at altitudes above 30...