scholarly journals IMPLEMENTATION OF SEMI-EMPIRICAL MODELS TO ENHANCE THE ACCURACY OF PANEL METHODS FOR DRAG PREDICTION AT SUPERSONIC SPEEDS

2011 ◽  
Vol 12 (3) ◽  
Author(s):  
Abdulkareem Shafiq Mahdi Al-Obaidi
Keyword(s):  
Computer Program ◽  
Panel Method ◽  
Preliminary Design ◽  
Empirical Methods ◽  
Average Value ◽  
Panel Methods ◽  
Drag Prediction ◽  
Stall Angle ◽  
Semi Empirical ◽  
Base Drag

This paper introduces an attempt to enhance the accuracy of panel methods. A low-order panel method is selected and coupled with semi-empirical methods to enhance the accuracy of drag prediction of flying bodies at supersonic speeds. The semi-empirical methods are used to improve the accuracy of drag prediction by mathematical modelling of viscosity, base drag, and drag due to wing-body interference. Both methods were implemented by a computer program and validated against experimental and analytical results. The comparisons show that a considerable improvement has been achieved for the selected panel method for prediction of drag coefficients. In general, accuracy within an average value of -4.4% was obtained for the enhanced panel method. Such accuracy could be considered acceptable for the preliminary design stages of supersonic flying bodies such as projectiles and missiles. The developed computer program gives satisfactory results as long as the considered configurations are slender and the angles of attack are small (below stall angle).  ABSTRAK: Kertas kerja ini memperkenalkan percubaan untuk  mempertingkatkan ketepatan kaedah panel. Kaedah panel tertib rendah telah dipilih dan digabungkan dengan kaedah separa empirik untuk mempertingkatkan ketepatan ramalan seret objek terbang pada kelajuan supersonik. Kaedah semi empirikal yang digunakan untuk meningkatkan ketepatan jangkaan seret menggunakan model matematik bagi kelikatan, seretan dasar, dan  seretan disebabkan  oleh badan sayap interferens. Kedua-dua kaedah dijalankan menggunakan program komputer dan disah berdasarkan keputusan uji kaji dan analisis. Perbandingan keputusan menunjukkan peningkatan yang mendadak diperolehi melalui kaedah panel yang telah dipilih sebagai jangkaan pekali seret. Secara umumnya, ketepatan yang melingkungi nilai purata sebanyak -4.4% telah diperolehi daripada kaedah peningkatan panel. Keputusan sebegini boleh diterima untuk peringkat reka bentuk permulaan bagi objek terbang supersonik seperti projektil dan misil. Program komputer yang direka memberikan keputusan yang memuaskan selagi konfigurasi yang dipilih adalah kecil dan sudut serangan adalah rendah (di bawah sudut tegun).

Analysis of the internal stability of granular soils using different methods

2014 ◽  
Vol 51 (9) ◽  
pp. 1063-1072 ◽  
Author(s):  
N. Moraci ◽  
M.C. Mandaglio ◽  
D. Ielo
Keyword(s):  
Experimental Methods ◽  
Granular Soils ◽  
Internal Stability ◽  
Empirical Methods ◽  
Average Value ◽  
Key Factor ◽  
Experimental Approaches ◽  
Geotextile Filters ◽  
Semi Empirical

The knowledge of the internal stability of granular soils is a key factor in the design of granular or geotextile filters. To evaluate the internal stability of granular soils, different semi-empirical methods are generally used. Nevertheless, the results of these methods, on the same soil, can lead to different internal stability evaluations. In this paper, to evaluate the reliability of the semi-empirical methods available in literature, the internal stability of different granular soils, reconstituted by the authors and by other researchers, has been studied by means of theoretical and experimental approaches. In particular, the theoretical analysis of the internal stability was performed using the Simulfiltr method, developed recently by the authors, while the experimental evaluation of the internal stability was carried out by means of long-term filtration tests. The comparison of the internal stability analysis performed by means of semi-empirical, theoretical, and experimental methods showed that the semi-empirical methods are not always reliable. Therefore, on the base of these results, a new chart, in terms of minimum slope Smin (%) of the grain-size distribution and of average value of finer percentage F, has been proposed to evaluate the internal stability of granular soils.

scholarly journals Nonlinear vortex lattice method for stall prediction

2019 ◽  
Vol 304 ◽  
pp. 02006
Author(s):  
Hasier Goitia ◽  
Raúl Llamas
Keyword(s):  
Vortex Lattice ◽  
Design Parameters ◽  
Preliminary Design ◽  
Empirical Methods ◽  
Swept Wing ◽  
Lattice Method ◽  
Vortex Lattice Method ◽  
Narrow Scope ◽  
Novel Method ◽  
Semi Empirical

The stall behavior of an empennage is a crucial and conditioning factor for its design. Thus, the preliminary design of empennages requires a fast low-order method which reliably computes the stall behavior and which must be sensitive to the design parameters (taper, sweep, dihedral, airfoil, etc.). Handbook or semi-empirical methods typically have a narrow scope and low fidelity, so a more general and unbiased method is desired. This paper presents a nonlinear vortex lattice method (VLM) for the stall prediction of generic fuselage-empennage configurations which is able to compute complete aerodynamic polars up to and beyond stall. The method is a generalized form of the van Dam algorithm, which couples the potential VLM solution with 2.5D viscous data. A novel method for computing 2.5D polars from 2D polars is presented, which extends the traditional infinite swept wing theory to finite wings, relying minimally on empirical data. The method has been compared to CFD and WTT results, showing a satisfactory degree of accuracy for the preliminary design of empennages.

Semi-empirical methods versus dynamic load testing in piles

Geotecnia ◽  
2015 ◽  
Vol 135 ◽  
pp. 89-113
Author(s):  
Jean Felix Cabette ◽  
◽  
<br>Heloisa Helena Silva Gonçalves ◽  
<br>Fernando Antônio Marinho ◽  
◽  
...  
Keyword(s):  
Dynamic Load ◽  
Load Testing ◽  
Empirical Methods ◽  
Semi Empirical

Base drag prediction on missile configurations

1994 ◽  
Vol 31 (5) ◽  
pp. 759-765 ◽  
Author(s):  
F. G. Moore ◽  
F. Wilcox ◽  
T. Hymer
Keyword(s):  
Drag Prediction ◽  
Base Drag

Excited-state localization and energy transfer in pyrene core dendrimers with fluorene/carbazole as the dendrons and acetylene as the linkages

2016 ◽  
Vol 18 (5) ◽  
pp. 4134-4143 ◽  
Author(s):  
Linyin Yan ◽  
Yan Wan ◽  
Andong Xia ◽  
Sheng Hien Lin ◽  
Ran Huang
Keyword(s):  
Energy Transfer ◽  
Excited State ◽  
Theoretical Model ◽  
Empirical Methods ◽  
Multi Scale ◽  
Td Dft ◽  
Semi Empirical

Multi-scale theoretical model and spectra simulation for dendrimers combining TD-DFT/DFT and semi-empirical methods.

scholarly journals VERIFICAÇÃO DO DESEMPENHO DAS ESTACAS INJETADAS AUTOPERFURANTES EXECUTADAS EM SOLOS ARENOSOS PARA CONSTRUÇÃO DE USINA EÓLICA

2017 ◽  
Vol 13 (2) ◽  
Author(s):  
Rodrigo Cerqueira Rogerio
Keyword(s):  
Structural Characteristics ◽  
Load Capacity ◽  
The Self ◽  
Executive Processes ◽  
Empirical Methods ◽  
Deep Drilling ◽  
Load Tests ◽  
Different Diameters ◽  
Semi Empirical

RESUMO: Apresenta-se neste trabalho a solução adotada para execução das fundações do Parque de Usina Eólica localizado no Ceará, com a utilização das estacas injetadas autoperfurantes, executadas em presença de solos arenosos. No qual consiste em perfurar o solo com altíssima velocidade por rotação e “pull down”, através da injeção simultânea de nata de cimento com medias pressões. Ocasionando na estaca um diâmetro final que pode obter o dobro do bit de perfuração, de acordo com o tipo de solo, gerado pelo efeito do jato da nata de cimento. Detalhando os processos executivos, verificando os aspectos técnicos e operacionais, para melhor compreender as características estruturais deste elemento. De forma a verificar “in situ” o desempenho deste novo tipo de fundação profunda, foram realizadas provas de carga, em estacas com diferentes diâmetros e comprimentos, realizadas em perfis estratigráficos de solos arenosos, para melhor avaliação de sua capacidade de carga. Analisando-se os ensaios das provas de carga interpretados a base da extrapolação da curva carga versus recalque e das previsões da capacidade de carga, obtidas por meio dos métodos semi-empíricos de correlação com ensaios de penetração (SPT), avaliando os padrões de execução desta tipologia de estaca injetada para comunidade geotécnica. ABSTRACT: This paper aims to establish the selected solution to except the foundations of the Wind Energy Park in Ceará (Brazil), with an executive methodology of the self-drilling injection piles framed in loco in Sandy soil. In which the soil drilling is done with the highest speed by rotation and pull down, through the simultaneous injection of grouting with medium pressures. This kind of drilling causes in the pile a final diameter that can get the double bore bit, according to the type of soil, done by the grouting blast. The executive processes are detailed as a whole, and also presenting the pile materials composition, in order to understand the structural characteristics of this element. To verify the performance of this new kind of deep drilling, instrumentations were done: settlement control and load tests in constructions with different structural characteristics, in self-drilling injected piles with different diameters and length, done in stratigraphical sandy, for a better evaluation of its load capacity. Analyzing the essays of load tests interpreted in the basis of curve extrapolation load versus settlement and the previsions of the load capacity, obtained by semi-empirical methods correlating with the penetrations methods (SPT), offering information to the geotechnical community.

scholarly journals STRUCTURAL AND ELECTRONIC PROPERTIES OF BRIDGED BITHIOPHENE S-OXIDES (BTO) WITH S, S=O, O, SiH2 and BH2 BRIDGE: SEMI-EMPIRICAL AND AB INITIO STUDY

2010 ◽  
Vol 18 (18) ◽  
pp. 1-10
Author(s):  
Banjo Semire ◽  
Isaiah Ajibade Adejoro ◽  
Olusegun Ayobami Odunola
Keyword(s):  
Density Functional Theory ◽  
Thermodynamic Properties ◽  
Ab Initio ◽  
Density Functional ◽  
Ab Initio Study ◽  
Empirical Methods ◽  
Functional Theory ◽  
Structural And Electronic Properties ◽  
Semi Empirical ◽  
Good Agreement

In this paper, we theoretically studied the geometries, stabilities, electronic and thermodynamic properties of bridged bithiophene S-oxide (BTO-X) derivates (with X = BH2, SiH2, S, S=O, and O) by using semi-empirical methods, ab-initio, and Density functional theory. The geometries and thermodynamic parameters calculated by PM3 were in good agreement with that of B3LYP/6-31G(d). The bandgap calculated by B3LYP/6-31G(d) ranged from 3.94eV (BTO-O)-3.16eV (BTO-BH2). The absorption λmax calculated suing B3LYP/6-31G(d) shifted to longer wavelength with X=BH2, SiH2, and S=O due to enhancement of π-conjugated system whereas, BTO-S and BTO-O shifted to shorter wavelengths as compared to dimmer thiophene S-oxide (2TO).

scholarly journals Experimental and Computational Vibration Study of Amino Acids

2013 ◽  
Vol 15 ◽  
pp. 1-17 ◽  
Author(s):  
Musa E. Mohamed ◽  
Abdelhafeez M.A. Mohammed
Keyword(s):  
Amino Acids ◽  
Glutamic Acid ◽  
Ab Initio ◽  
Vibrational Frequencies ◽  
Empirical Methods ◽  
Vibrational Studies ◽  
Semi Empirical

Vibrational studies of amino acids experimentally and theoretically have been performed. The Semi-empirical methods optimization by PM6 and RM1 on the l- and d-amino acids (alanine, phenylalanine, aspartic and glutamic acid), showed no difference in energy between l-and d-isomers. The vibrational frequencies were calculated by semi-emprical methods (PM6 and RM1) and Ab Initio methods (B3LYP/6-31+G(d) and were scaled down by factors of 0.925 (RM1), 1.09 (PM6) and 0.89 (B3LYP/6-31+G(d)). The calculated and experimental vibrational frequencies have shown good general agreement.

Ship Roll Motion Damping Using Bilge Keels – A Detailed CFD Investigation

2015 ◽  
Author(s):  
Joshua Counsil ◽  
Kevin McTaggart ◽  
Dominic Groulx ◽  
Kiari Boulama
Keyword(s):  
Experimental Studies ◽  
The Body ◽  
Navier Stokes ◽  
Roll Motion ◽  
Empirical Methods ◽  
Viscous Effects ◽  
Vortex Interactions ◽  
Ship Roll ◽  
Semi Empirical ◽  
Bilge Keel

A study has been undertaken to test the value of unsteady Reynolds-averaged Navier-Stokes (URANS) and traditional semi-empirical methods in the face of complex ship roll phenomena, and provide insight into the selection of bilge keel span for varying roll amplitudes. The computational fluid dynamics (CFD) code STAR-CCM+ is employed and two-dimensional submerged bodies undergoing forced roll motion are analyzed. The spatial resolution and timestepping scheme are validated by comparison with published numerical and experimental studies. The model is then applied to a fully-submerged circular cylinder with bilge keels of varying span and undergoing roll motion at varying angular amplitudes. Extracted hydrodynamic coefficients indicate that in general, increasing displacement amplitude and bilge keel span yields increased added mass and increased damping. The relationship is complex and highly dependent upon vortex interactions with each other and the body. The semi-empirical methods used for comparison yield good predictions for simple vortex interactions but fail where viscous effects are strong. Hence, URANS methods are shown to be necessary for friction-dominated flows while semi-empirical methods remain useful for initial design considerations.

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