scholarly journals Methods for the Determination of Aerodynamic Parameters and Trajectory Reconstruction of the Orion Command Module from Scale Model Aeroballistic Flight Data

2009 ◽  
Author(s):  
Thomas Sebastian ◽  
Robert Tolson
Keyword(s):  
Scale Model ◽  
Flight Data ◽  
Trajectory Reconstruction ◽  
Aerodynamic Parameters

scholarly journals Alignment determination of the Hayabusa2 laser altimeter (LIDAR)

2021 ◽  
Vol 73 (1) ◽  
Author(s):  
Hirotomo Noda ◽  
Hiroki Senshu ◽  
Koji Matsumoto ◽  
Noriyuki Namiki ◽  
Takahide Mizuno ◽  
...  
Keyword(s):  
Altimeter Data ◽  
Gravity Assist ◽  
Laser Altimeter ◽  
Trajectory Error ◽  
Flight Data ◽  
Camera Image ◽  
Operation Period ◽  
The Cross ◽  
Along Track

AbstractIn this study, we determined the alignment of the laser altimeter aboard Hayabusa2 with respect to the spacecraft using in-flight data. Since the laser altimeter data were used to estimate the trajectory of the Hayabusa2 spacecraft, the pointing direction of the altimeter needed to be accurately determined. The boresight direction of the receiving telescope was estimated by comparing elevations of the laser altimeter data and camera images, and was confirmed by identifying prominent terrains of other datasets. The estimated boresight direction obtained by the laser link experiment in the winter of 2015, during the Earth’s gravity assist operation period, differed from the direction estimated in this study, which fell on another part of the candidate direction; this was not selected in a previous study. Assuming that the uncertainty of alignment determination of the laser altimeter boresight was 4.6 pixels in the camera image, the trajectory error of the spacecraft in the cross- and/or along-track directions was determined to be 0.4, 2.1, or 8.6 m for altitudes of 1, 5, or 20 km, respectively.

scholarly journals A parametric prediction of the Young’s modulus of polymers enhanced with ΜWCNTs

2018 ◽  
Vol 233 ◽  
pp. 00025
Author(s):  
P.V. Polydoropoulou ◽  
K.I. Tserpes ◽  
Sp.G. Pantelakis ◽  
Ch.V. Katsiropoulos
Keyword(s):  
Young’S Modulus ◽  
Elastic Properties ◽  
Young's Modulus ◽  
Experimental Results ◽  
Scale Model ◽  
Fe Model ◽  
Multi Scale ◽  
Unit Cells ◽  
Random Dispersion

In this work a multi-scale model simulating the effect of the dispersion, the waviness as well as the agglomerations of MWCNTs on the Young’s modulus of a polymer enhanced with 0.4% MWCNTs (v/v) has been developed. Representative Unit Cells (RUCs) have been employed for the determination of the homogenized elastic properties of the MWCNT/polymer. The elastic properties computed by the RUCs were assigned to the Finite Element (FE) model of a tension specimen which was used to predict the Young’s modulus of the enhanced material. Furthermore, a comparison with experimental results obtained by tensile testing according to ASTM 638 has been made. The results show a remarkable decrease of the Young’s modulus for the polymer enhanced with aligned MWCNTs due to the increase of the CNT agglomerations. On the other hand, slight differences on the Young’s modulus have been observed for the material enhanced with randomly-oriented MWCNTs by the increase of the MWCNTs agglomerations, which might be attributed to the low concentration of the MWCNTs into the polymer. Moreover, the increase of the MWCNTs waviness led to a significant decrease of the Young’s modulus of the polymer enhanced with aligned MWCNTs. The experimental results in terms of the Young’s modulus are predicted well by assuming a random dispersion of MWCNTs into the polymer.

Numerical Determination of Paris Law Constants for Carbon Steel Using a Two-Scale Model

2022 ◽  
pp. 1-15
Author(s):  
M. Mlikota
Keyword(s):  
Growth Rate ◽  
Stress Intensity Factor ◽  
Fatigue Crack ◽  
Stress Intensity ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Scale Model ◽  
Numerical Determination ◽  
Paris Law

For most engineering alloys, the long fatigue crack growth under a certain stress level can be described by the Paris law. The law provides a correlation between the fatigue crack growth rate (FCGR or da/dN), the range of stress intensity factor (ΔK), and the material constants C and m. A well-established test procedure is typically used to determine the Paris law constants C and m, considering standard specimens, notched and pre-cracked. Definition of all the details necessary to obtain feasible and comparable Paris law constants are covered by standards. However, these cost-expensive tests can be replaced by appropriate numerical calculations. In this respect, this paper deals with the numerical determination of Paris law constants for carbon steel using a two-scale model. A micro-model containing the microstructure of a material is generated using the Finite Element Method (FEM) to calculate the fatigue crack growth rate at a crack tip. The model is based on the Tanaka-Mura equation. On the other side, a macro-model serves for the calculation of the stress intensity factor. The analysis yields a relationship between the crack growth rates and the stress intensity factors for defined crack lengths which is then used to determine the Paris law constants.

Centerwell Water Motions and Hydrodynamic Loading Using Viscous Flow Calculations

2008 ◽  
Author(s):  
Samuel Holmes ◽  
Joseph Gebara ◽  
Allan Magee
Keyword(s):  
Scale Effects ◽  
Vertical Motion ◽  
Scale Model ◽  
Navier Stokes ◽  
Open Area ◽  
Flow Models ◽  
Free Surface Waves ◽  
Natural Response ◽  
Termination Point

Most Spar platforms have a wet centerwell which provides a termination point for umbilicals and risers. The column of water in the centerwell is a dynamic system which can be excited by the wave action around the Spar as well as the platform’s own motions. When the exciting frequencies are close to the natural frequency of the water column, the vertical motion of the water in the centerwell can become large in large seastates. This might damage structures within the centerwell. A natural response to this problem is to restrict the fluid flow at the bottom of the centerwell by adding a plated structure to partially close the opening. The remaining open area in the centerwell determines the amount of damping as well as the loads on the plating which can be quite large in heavy seas. The problem addressed in this paper is the determination of the appropriate open area in the centerwell plate that will control the fluid vertical motion without requiring expensive reinforcements to the plating beyond the riser guide structure already present. Traditional design tools based on potential flow models appear to perform poorly for this problem because they do not model the viscous damping in the flow correctly. In this paper we use a Navier-Stokes solver to study the centerwell motions and centerwell plate loads for three centerwell plate geometries. It is found that the Spar motions and the free surface waves need to be included in these simulations. The centerwell water motions and centerwell plate loads are compared with those measured in a scale model experiment. Full-scale calculations are also carried out to determine the corresponding centerwell plate loads and centerwell water motions to assess scale effects.

Forced Oscillation Model Tests for Determination of Hydrodynamic Coefficients of Large Subsea Blowout Preventers

2015 ◽  
Author(s):  
Xavier Arino ◽  
Jaap de Wilde ◽  
Massimiliano Russo ◽  
Guttorm Grytøyr ◽  
Michael Tognarelli
Keyword(s):  
Large Scale ◽  
Forced Oscillation ◽  
Model Tests ◽  
Scale Model ◽  
Hydrodynamic Coefficients ◽  
Lumped Mass ◽  
Towing Tank ◽  
Steady Current ◽  
Large Scale Model

Large scale model tests have been conducted in a towing tank facility for the determination of the hydrodynamic coefficients of subsea blowout preventers. A subsea blowout preventer (BOP) is a large, complex device 10–15 [m] tall, weighing 200–450 [ton]. The BOP stack consists of two assemblies, the ‘lower marine riser package’ (LMRP) connected to the riser string and the BOP itself, connected to the wellhead. Together they represent a large lumped mass, which directly influences the natural frequencies and vibration modes of the riser system, particularly those of the BOP-wellhead-casing assembly. Large uncertainties in the estimates of the hydrodynamic coefficients (added mass, lift and drag or damping) result in large uncertainties in the fatigue damage predictions of the riser and wellhead system. The trend toward larger and heavier BOPs, which could place BOP-wellhead-casing oscillation frequencies in the range of wave frequencies, has motivated Statoil and BP to start a new research project on this subject. The project involves a large scale model test for experimental determination of hydrodynamic coefficients. Two different BOP designs were tested in a towing tank at model scale 1:12. The models weighed about 50 [kg] in air and were about 1.2–1.5 [m] tall. A six-degree-of-freedom oscillator was mounted under the carriage of the towing tank for oscillation of the models in different directions. Static tow tests and forced oscillation tests with and in the absence of steady current were carried out. Keulegan-Carpenter (KC) numbers ranged between 0.2 and 2.0, while the Sarpkaya frequency parameter β was in the range from 4,000 to 50,000. The Reynolds numbers of the static tow tests ranged between 50,000 and 150,000. This paper focuses particularly on tests in the surge direction with and in the absence of a steady current. Results indicate that the hydrodynamic coefficients for BOP stacks are quite different from those of simpler geometries like a circular cylinder. In addition, they provide new insight for analytical modeling of global hydrodynamic forces on BOPs in many configurations and scenarios.

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