A Note on Hydroelasticity

1960 ◽  
Vol 4 (01) ◽  
pp. 9-29
Author(s):  
David A. Jewell
Keyword(s):  
High Density ◽  
Small Range ◽  
Mass Ratio ◽  
Aeroelastic Stability ◽  
Lifting Surfaces ◽  
Range Of Values ◽  
Theory And Experiment

This note is essentially a discussion of a paper, "Aeroelastic Stability of Lifting Surfaces in High-Density Fluids," by Henry, Dugundji, and Ashley [1].2 Additional viewpoints are presented which indicate that flutter phenomena are not unlikely in hydrodynamic operation; that the discrepancy between theory and experiment in a small range of values of the "mass ratio" is due to a transitional nature of flutter; and that either of two revisions to the theoretical oscillatory lift and moment expressions might provide better correlation with experiment.

Aeroelastic Stability of Lifting Surfaces in High-Density Fluids

1959 ◽  
Vol 3 (01) ◽  
pp. 10-21 ◽  
Author(s):  
Charles J. Henry ◽  
John Dugundji ◽  
Holt Ashley
Keyword(s):  
Degrees Of Freedom ◽  
Three Dimensional ◽  
Separated Flow ◽  
High Density ◽  
Aeroelastic Stability ◽  
Free Surfaces ◽  
Elastic Systems ◽  
Static Instability ◽  
Theoretical Evidence ◽  
Lifting Surfaces

The large increases anticipated in speeds of vehicles towed or propelled underwater suggests a re-examination of the problem of stability of flexible lifting surfaces mounted thereon. Experimental and theoretical evidence is assembled which suggests that oscillatory aeroelastic instability (flutter) is very unlikely at the structural-to-fluid mass ratios typical of hydrodynamic operation. It is shown that static instability (divergence) is the more important practical problem but that its occurrence can be predicted with greater confidence. Flutter data obtained in high-density fluids are reviewed, and various sources of inaccuracy in their theoretical prediction are analyzed. The need is expressed for more precise means of analytically representing both dynamic-elastic systems and three-dimensional unsteady hydrodynamic loads. For a simple hydrofoil with single degrees of freedom in bending and torsion, the theoretical influence of several significant parameters on high-density flutter is calculated and discussed. Recommendations are made for refinements to existing techniques of analysis to include the presence of channel boundaries, free surfaces, cavitation or separated flow.

scholarly journals Clay-organic complexes in a Polish loess soil

2017 ◽  
Vol 31 (3) ◽  
pp. 447-452 ◽  
Author(s):  
Ewa A. Czyż ◽  
Jerzy Rejman ◽  
Anthony R. Dexter ◽  
Jan Jadczyszyn ◽  
Anna Rafalska-Przysucha ◽  
...  
Keyword(s):  
Loess Soil ◽  
Soil Samples ◽  
Mass Ratio ◽  
Loessial Soil ◽  
Soil Physical Quality ◽  
Organic Complexes ◽  
Carbon Mass ◽  
Predicted Values ◽  
Strip Tillage ◽  
Range Of Values

AbstractComplexes formed between clay and soil organic matter are important for carbon sequestration and for soil physical quality. Here, we use samples of loessial soil from South-East Poland to explore the phenomenon of complexing in loess. Soil samples were collected from a single catchment 8 years after the introduction of strip tillage and their compositions were characterized by traditional methods. Complexing was characterized in terms of the content of non-complexed clay which was estimated in two ways: firstly, by measurement of the content of readily-dispersible clay (which was assumed to be the non-complexed clay); and secondly, by calculation using algorithms that had been developed and evaluated previously. The calculations were based on the concept that, at carbon saturation, the clay/organic carbon mass ratio is equal ton. The calculations were done with a range of values ofn. It was assumed that the correct value ofnwas that which gave the greatest coefficient of correlation between the measured values of clay dispersion and the predicted values of non-complexed clay. For the loess used, the optimum value wasn= 14.

A comparison of theory and experiment for high density, high temperature germanium spectra

2010 ◽  
Vol 6 (1) ◽  
pp. 95-98 ◽  
Author(s):  
J.W.O. Harris ◽  
L.M. Upcraft ◽  
D.J. Hoarty ◽  
B.J.B. Crowley ◽  
C.R.D. Brown ◽  
...  
Keyword(s):  
High Temperature ◽  
High Density ◽  
Theory And Experiment

Aerodynamics of slot-film cooling: theory and experiment

1985 ◽  
Vol 160 ◽  
pp. 15-27 ◽  
Author(s):  
A. D. Fitt ◽  
J. R. Ockendon ◽  
T. V. Jones
Keyword(s):  
Integral Equation ◽  
Film Cooling ◽  
Nonlinear Integral Equation ◽  
Free Stream ◽  
Inviscid Fluid ◽  
Two Dimensional ◽  
Total Head ◽  
Slot Film Cooling ◽  
Range Of Values ◽  
Theory And Experiment

A simple model is proposed for the two-dimensional injection of irrotational inviscid fluid from a slot into a free stream. In a certain range of values of the ratio of free-stream to injection total heads, the film thickness satisfies a nonlinear integral equation whose solution enables the mass flow in the film to be found. Some experiments are described which both agree with this theory when it is relevant and indicate its deficiencies at other values of the total head ratio.

scholarly journals Selecting the Suitable Resampling Strategy for Imbalanced Data Classification Regarding Dataset Properties. An Approach Based on Association Models

2021 ◽  
Vol 11 (18) ◽  
pp. 8546
Author(s):  
Mohamed S. Kraiem ◽  
Fernando Sánchez-Hernández ◽  
María N. Moreno-García
Keyword(s):  
Imbalanced Data ◽  
Data Classification ◽  
General Nature ◽  
Small Range ◽  
Minority Class ◽  
Unequal Distribution ◽  
Imbalanced Data Classification ◽  
Wide Range ◽  
The Impact ◽  
Range Of Values

In many application domains such as medicine, information retrieval, cybersecurity, social media, etc., datasets used for inducing classification models often have an unequal distribution of the instances of each class. This situation, known as imbalanced data classification, causes low predictive performance for the minority class examples. Thus, the prediction model is unreliable although the overall model accuracy can be acceptable. Oversampling and undersampling techniques are well-known strategies to deal with this problem by balancing the number of examples of each class. However, their effectiveness depends on several factors mainly related to data intrinsic characteristics, such as imbalance ratio, dataset size and dimensionality, overlapping between classes or borderline examples. In this work, the impact of these factors is analyzed through a comprehensive comparative study involving 40 datasets from different application areas. The objective is to obtain models for automatic selection of the best resampling strategy for any dataset based on its characteristics. These models allow us to check several factors simultaneously considering a wide range of values since they are induced from very varied datasets that cover a broad spectrum of conditions. This differs from most studies that focus on the individual analysis of the characteristics or cover a small range of values. In addition, the study encompasses both basic and advanced resampling strategies that are evaluated by means of eight different performance metrics, including new measures specifically designed for imbalanced data classification. The general nature of the proposal allows the choice of the most appropriate method regardless of the domain, avoiding the search for special purpose techniques that could be valid for the target data.

Numerical Changes and Population Regulation in Brook Trout Salvelinus fontinalis

1967 ◽  
Vol 24 (7) ◽  
pp. 1425-1459 ◽  
Author(s):  
James T. McFadden ◽  
Gaylord R. Alexander ◽  
David S. Shetter
Keyword(s):  
Sex Ratio ◽  
Population Size ◽  
Brook Trout ◽  
Egg Production ◽  
Age Groups ◽  
Small Range ◽  
Age Group ◽  
Density Dependent ◽  
Group I ◽  
Range Of Values

A brook trout population in a stable stream environment was studied for 14 years. Population estimates were made each September, the catch of fish by anglers was recorded, and collections of fish were made to determine sex ratio, age at sexual maturity, and fecundity.The sex ratio was close to 1:1 for all age-groups. Some male trout were sexually mature at the end of the 1st year of life, most were mature at the end of the 2nd year, and all were mature at the end of the 3rd. No females were mature at the end of their 1st year, most were mature at the end of the 2nd, and all were mature at the end of the 3rd year of life. The regression of egg content on total length of female trout was determined.On the average 132,000 eggs were produced annually by the population in the study area, from which 4813 fish survived to the end of the 1st year; 1966 to the end of the 2nd; 356 to the 3rd; 29 to the 4th; and 0.6 to the end of the 5th year.The growth rate of the fish varied little during the period of study. Annual egg production varied between 80,000 and 212,000; the number of age-group 0 fish between 2809 and 6703; age-group I fish between 1589 and 2653; age-group II between 175 and 685; age-group III between 13 and 68; and age-group IV fish between 0 and 2.During the 14 years of observation, survival of adult fish tended to increase, leading to larger numbers of spawners. The larger egg complements which resulted tended to experience lower survival, thus largely preventing substantial increases in population size. Positive serial correlations exist in some of the series of estimates of numbers and of survival. No biological explanation is advanced for these serial correlations.Life tables and age-specific fecundity rates were calculated for 11 successive cohorts of brook trout. Net reproduction rates varied from 0.74 to 1.88, averaging 1.14. The lx components were about three times as variable as the mx components, indicating that changes in death rates rather than changes in birth rates have been the principal immediate cause of fluctuations in the population.The mx values were not related to population density in any way that would tend to regulate population size. Survival from the 12th to the 24th month of life was directly density-dependent. The pattern of survival from the 24th to the 36th month of life suggested an inverse density-dependent relationship.The number of 12-month-old progeny surviving varied from 2809 to 6703, and the parental egg complement varied from 80,000 to 212,000. The form of the relationship between these two variables could not be defined, partly because of the relatively small range of values of parental egg complement.Even though the form of the density-survival relationship was defined for several stages of the life history, no relationship between the size of a parental egg complement and the lifetime egg production of the progeny could be established, again partly because of the small range of values of the former variable.

Propeller influence on the aeroelastic stability of High Altitude Long Endurance aircraft

2020 ◽  
Vol 124 (1275) ◽  
pp. 703-730 ◽  
Author(s):  
P.C. Teixeira ◽  
C.E.S. Cesnik
Keyword(s):  
High Altitude ◽  
Data Series ◽  
Aeroelastic Stability ◽  
Time Data ◽  
Lattice Method ◽  
Vortex Lattice Method ◽  
Lifting Surfaces ◽  
Structural Case ◽  
The Stability ◽  
Long Endurance

AbstractThis work investigates the propeller’s influence on the stability of High Altitude Long Endurance aircraft, incorporating all resultant loads at the propeller hub, propeller slipstream, and gyroscopic loads. Such effects are usually neglected in the aeroelastic simulation of HALE aircraft. For that goal, a previously developed framework, which couples a geometrically nonlinear structural solver with an Unsteady Vortex Lattice method (uVLM) for lifting surfaces and a Viscous Vortex Particle (VVP) method for propeller slipstream, was employed to generate time-data series. Also, a method, based on a combination of Proper Orthogonal Decomposition and system identification, to extract dynamic information (frequencies, damping, and modes) of the aircraft from a time-series signal is proposed and successfully tested for a purely structural case, for which reference data is available. The method is then applied to investigate the stability of aeroelastic cases. The results demonstrate that the presence of propellers can influence the aeroelastic stability of a Very Flexible Aircraft.

Rapid In Situ Reactive Sintering and Properties of ZrO2-ZrW2O8 Composites

2012 ◽  
Vol 535-537 ◽  
pp. 42-46
Author(s):  
Xiang Yang Guo ◽  
Chun Zhen Fan ◽  
Xian Sheng Liu ◽  
Wen Bo Song ◽  
Chun Xiao Cheng ◽  
...  
Keyword(s):  
Phase Transition ◽  
Thermal Expansion ◽  
Transition Temperature ◽  
Phase Transition Temperature ◽  
High Density ◽  
Reactive Sintering ◽  
Mass Ratio ◽  
Sintering Additive

ZrO2-ZrW2O8 diphasic composites with controllable coefficients of thermal expansion (CTEs) are synthesized by rapid in-situ reactive sintering with ZrO2 and WO3 as reactants. High density of ZrO2-ZrW2O8 composites without decomposition of ZrW2O8 is obtained with Y2O3 sintering additive. The CTEs of specimen with ZrO2 to ZrW2O8 mass ratio 1:1.0, 1:1.3, 1:1.5 and 1:2.0 are measured to be about 1.20×10−6, 0.31×10−6, -0.78×10−6 and -1.13×10−6 K−1, respectively. Raman mappings demonstrate homogenous dispersions of ZrO2 and ZrW2O8 in the ZrO2-ZrW2O8 composites. In addition to the role as sintering additive, some Y3+ cations enter the lattice to substitute Zr4+ in ZrW2O8, leading to an increase in disorder and a decrease in phase transition temperature of ZrW2O8 in the composites.

Planar defects in ordered (Ga,In)P

1988 ◽  
Vol 46 ◽  
pp. 902-903
Author(s):  
S. McKernan ◽  
C. B. Carter ◽  
D. Bour ◽  
J. R. Shealy
Keyword(s):  
Electron Diffraction ◽  
Vapor Phase ◽  
Growth Direction ◽  
High Density ◽  
Ordered Structure ◽  
Planar Defects ◽  
Diffraction Patterns ◽  
Ternary Semiconductors ◽  
Anion Species ◽  
Metallic Vapor

The growth of ternary III-V semiconductors by organo-metallic vapor phase epitaxy (OMVPE) is widely practiced. It has been generally assumed that the resulting structure is the same as that of the corresponding binary semiconductors, but with the two different cation or anion species randomly distributed on their appropriate sublattice sites. Recently several different ternary semiconductors including AlxGa1-xAs, Gaxln-1-xAs and Gaxln1-xP1-6 have been observed in ordered states. A common feature of these ordered compounds is that they contain a relatively high density of defects. This is evident in electron diffraction patterns from these materials where streaks, which are typically parallel to the growth direction, are associated with the extra reflections arising from the ordering. However, where the (Ga,ln)P epilayer is reasonably well ordered the streaking is extremely faint, and the intensity of the ordered spot at 1/2(111) is much greater than that at 1/2(111). In these cases it is possible to image relatively clearly many of the defects found in the ordered structure.

Quantitative defect studies in semiconductor TEM samples prepared by low angle ion milling

1995 ◽  
Vol 53 ◽  
pp. 512-513
Author(s):  
L. Mulestagno ◽  
J.C. Holzer ◽  
P. Fraundorf
Keyword(s):  
Sample Preparation ◽  
Milling Time ◽  
High Density ◽  
Low Density ◽  
Ion Milling ◽  
High Quality ◽  
Variable Angle ◽  
Major Disadvantage ◽  
Induced Defects

Due to the wealth of information, both analytical and structural that can be obtained from it TEM always has been a favorite tool for the analysis of process-induced defects in semiconductor wafers. The only major disadvantage has always been, that the volume under study in the TEM is relatively small, making it difficult to locate low density defects, and sample preparation is a somewhat lengthy procedure. This problem has been somewhat alleviated by the availability of efficient low angle milling.Using a PIPS® variable angle ion -mill, manufactured by Gatan, we have been consistently obtaining planar specimens with a high quality thin area in excess of 5 × 104 μm2 in about half an hour (milling time), which has made it possible to locate defects at lower densities, or, for defects of relatively high density, obtain information which is statistically more significant (table 1).

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