Mechanics Parameters (mechanic + parameter)

Distribution by Scientific Domains

Selected Abstracts

Numerical simulation of rotating bending process for U-tubes in heat exchangers

ABSTRACT Heat exchangers comprise thousands of tubes having U-shaped portions. Rotating bending method has been widely utilized to make U-bends. Although this method shows an excellent performance, cracks have been frequently detected in the U-bends due to residual stresses induced by bending. In this paper, the bending process is simulated based on elastic,plastic finite element analyses in order to investigate the magnitude and distribution of the residual stresses including the effects of operating pressure. Analyses results show that the residual stress increases as the radius of U-bend decreases and that operating pressure has a detrimental effect in terms of stress corrosion cracking at the intrados of U-bend. It is thought that these results can be utilized for the estimations of fracture mechanics parameters such as limit load, stress intensity factor and J-integral, prevention of the cracking, and establishment of the optimum inspection strategy for the heat exchanger tubes. [source]

Molecular mechanics (MM4) study of amines,

Kuo-Hsiang Chen
Abstract The MM4 force field has been extended to include aliphatic amines. About 20 amines have been examined to obtain a set of useful molecular mechanics parameters for this class. The vibrational spectra of seven amines (172 frequencies) calculated by MM4 have an overall rms error of 27 cm,1, compared with corresponding MM4 value of 24 cm,1 for alkanes. The rms and signed average errors of the moments of inertia of nine simple amines compared with the experimental data were 0.18% and ,0.004%, respectively. The heats of formation of 30 amines were also studied. The MM4 weighted standard deviation is 0.41 kcal/mol, compared with experiment. Electronegativity effects occur in the hydrocarbon portion of an amine from the nitrogen, and are accounted for by including electronegativity induced changes in bond lengths and angles, and induced dipole,dipole interactions in the molecule. Negative hyperconjugation results from the presence of the lone pair of electrons on nitrogen, and leads to the Bohlmann bands in the infrared, and also to strong and unusual geometric changes in the molecules (Bohlmann effect), all of which are fairly well accounted for. The conformational energies in amines appear to be less straightforward than those for most other classes of molecules, apparently because of the Bohlmann effect, and these are probably not yet completely understood. In general, the agreement between the MM4 calculated results and the available data is reasonably good. © 2007 Wiley Periodicals, Inc. J Comput Chem, 2007 [source]

Fountain flow revisited: The effect of various fluid mechanics parameters

AICHE JOURNAL, Issue 5 2010
Evan Mitsoulis
Abstract Numerical simulations have been undertaken for the benchmark problem of fountain flow present in injection-mold filling. The finite element method (FEM) is used to provide numerical results for both cases of planar and axisymmetric domains under laminar, isothermal, steady-state conditions for Newtonian fluids. The effects of inertia, gravity, surface tension, compressibility, slip at the wall, and pressure dependence of the viscosity are all considered individually in parametric studies covering a wide range of the relevant parameters. These results extend previous ones regarding the shape of the front, and in particular the centerline front position, as a function of the dimensionless parameters. The pressures from the simulations have been used to compute the excess pressure losses in the system (front pressure correction or exit correction). Inertia leads to highly extended front positions relative to the inertialess Newtonian values, which are 0.895 for the planar case and 0.835 for the axisymmetric one. Gravity acting in the direction of flow shows the same effect, while gravity opposing the flow gives a reduced bulge of the fountain. Surface tension, slip at the wall, and compressibility, all decrease the shape of the front. Pressure-dependence of the viscosity leads to increased front position as a corresponding dimensionless parameter goes from zero (no effect) to higher values of the pressure-shift factor. The exit correction increases monotonically with inertia, compressibility, and gravity, while it decreases monotonically with slip and pressure-dependence of the viscosity. Contour plots of the primary variables (velocity-pressure) show interesting trends compared with the base case (zero values of the dimensionless parameters and of surface tension). © 2009 American Institute of Chemical Engineers AIChE J, 2010 [source]

Beanspruchungsanalyse von Holzbauteilen durch 2D-Photogrammetrie

BAUTECHNIK, Issue 2 2005
Bettina Franke Dipl.-Ing.
Für die Bewertung der Tragsicherheit von Bauteilen aus Voll- und Brettschichtholz in Lasteinleitungs- und Störbereichen mittels der Bruchmechanik ist die Kenntnis von kritischen Bruchkennwerten Voraussetzung. Realitätsnahe Kennwerte können aus der Kombination experimenteller Untersuchungen zur Bestimmung der Rißaufweitung und der Rißlänge mit daran anschließender FE-Simulation gewonnen werden. Aufgrund der, bisher bei konventionellen Meßverfahren, nicht ausreichenden Zuordnung der Meßwerte taktil applizierter Meßaufnehmer lag es nahe das Rißwachstum mit Hilfe der Photogrammetrie zu untersuchen. Mit dem entwickelten Meßsystem ist nunmehr die Möglichkeit der exakten Vermessung der Rißgeometrie zur Bestimmung von bruchmechanischen Kennwerten gegeben. Zusätzlich ermöglicht der Einsatz der Photogrammetrie die Verdichtung der Anzahl variierender diskreter Meßpunkte, so daß ein deutlich vollständigeres Bild der örtlichen Verformungen gewonnen, und damit die Aussagekraft eines Versuchs wesentlich verbessert werden kann. Strain analysis of solid wood and glued laminated timber members by close range photogrammetry. The assumption of critical fracture mechanics parameters for the evaluation of the load-bearing safety of structural units of full and board laminated timber in loaded areas and disturbance ranges the use of fracture mechanics is required. Realistic parameters can be gained only from experimental investigations that are transferred to the determination of the crack opening and the crack length with subsequent FE-simulation. Due to the insufficient appropriation of measured data gained by tactile position encoders in conventional measuring procedures it is advisable to investigate crack growth with the help of the photogrammetry. Using the developed measuring system it is now possible to measure the crack geometry exactly for the determination of fracture mechanics parameters. Additionally a complete picture of the local deformations and the validity of a test can be improved considerably by the possibility of the varying number of discrete measuring points. [source]