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1.
In this paper, we present some examples of sensitivity analysis for flows modeled by the standard k–ε model of turbulence with wall functions. The flow and continuous sensitivity equations are solved using an adaptive finite
element method. Our examples emphasize a number of applications of sensitivity analysis: identification of the most significant
parameters, analysis of the flow model, assessing the influence of closure coefficients, calculation of nearby flows, and
uncertainty analysis. The sensitivity parameters considered are closure coefficients of the turbulence model and constants
appearing in the wall functions. 相似文献
2.
The growth of mixed crystals of Ba
x
Ca1−x
(IO3)4 were carried out with simple gel method. The effect of various parameters such as pH of gel solution, gel concentration,
gel setting time, concentration of reactants on the growth was studied. Crystals having different morphologies and habits
were obtained. The grown crystals were characterized by XRD, FT-IR, EDAX, TGA, DTA and DSC. 相似文献
3.
4.
L. Lipiński A. Kowal A. Szmyrka-Grzebyk H. Manuszkiewicz P. P. M. Steur F. Pavese 《International Journal of Thermophysics》2007,28(6):1904-1912
It is well-known that, aside from its triple point, nitrogen exhibits a solid-to-solid transition at about 35 K that is of
some interest as a secondary reference temperature. During the recently published highly accurate measurements of the triple
point of nitrogen (Metrologia
43, 435 (2006)), an extensive study was made also of the solid α–β transition of nitrogen, using both the continuous heating method and the pulse-heating method. This transition is of significantly
lower quality than the triple point of nitrogen. A very high thermal resistance and a large time constant characterize the
transition. Therefore, even the determination of the self-heating of the thermometer requires a very long time. A value of
T
90 = 35.620 K with an expanded uncertainty U = 8 mK for the coverage factor k = 2 was found, differing by +6 mK from the published CCT-recommended value. The reproducibility of the value was better than
± 5 mK. In addition to the temperature value found for the transition, a comparison is made with previous measurements on
this point, and an overview is given of the available information about it. 相似文献
5.
Yoshiyuki Kawazoe 《Bulletin of Materials Science》2003,26(1):13-17
Ab initio treatment is becoming realistic to predict physical, chemical, and even mechanical properties of academically and industrially
interesting materials. There is, however, some limitation in size and time of the system up to the order of several hundred
atoms and ∼ 1 pico second, even if we use the fastest supercomputer efficiently. Therefore, it is very difficult to simulate
realistic materials with grain boundaries and important reactions like diffusion in materials. To improve this situation,
two ways have been invented. One way is to upgrade approximations to match the necessary levels according to inhomogeneous
electron gas theory beyond the present day standard, i.e. local density approximation (LDA). The reason is simply that the
system we are interested in is composed of many particles interacting with Coulomb forces governed by quantum mechanics. (Complete
knowledge is available, and only what we should do is to make better approximations to explain the phenomena!). Another is
to extract the necessary parameters from theab initio calculations on systems with limited number of atoms, and apply these results into cluster variation, direct, or any other
sophisticated methods based on classical concepts such as statistical mechanics. In this paper, several typical examples recently
worked out by our research group are introduced to indicate that these methodologies are actually possible to be successfully
used to predict materials properties before experiments based on the present day state-of-art supercomputing systems. It includes
scientific visualization of the results ofab initio molecular dynamics simulation on atom insertion process to C60 and to carbon nanotube, tight-binding calculation of single electron conductance properties in nanotube to create nano-scale
diode virtually by computer, which will be a base of future nanoscale electric device in nanometer size, Li + H reaction without
Born-Oppenheimer approximation, structural phase transitions in perovskite materials under very high pressure in earth by
direct method, and prediction of wavelength of emitted light from Na clusters with GW (G = Green function-vertex, W = screened
Coulomb interaction) approximation. 相似文献
6.
Paul Camion Jacques Patarin 《Applicable Algebra in Engineering, Communication and Computing》2008,19(2):99-133
The Wire-Tap Channel II introduced by L. H. Ozarow, A.D. Wyner was the first instance of a Partial Exposure Problem. General
Exposure-Resilient Functions (ℓ-ERF) are known to be appropriate to provide a solution to the Partial Exposure Problem as
long as random secret chains are to be protected. It is known that a perfect ℓ-ERF is nothing but a t-resilient function for t = n − ℓ, where n is the length of the exposed symbol-chain and t the largest number of symbols that an adversary is able to observe. We here manage to adapt the use of t-resilient functions for protecting messages against partial exposure. A solution to that problem had been given by the perfect
local pseudo-random generator introduced by Maurer and Massey which is based upon a t-resilient function, but its use needs a secret key shared by the sender and the receiver. We are able to provide solutions
to protect messages against Partial Exposure without using secret keys, for various ranges of parameters. Moreover low complexity
algorithms are devised to that end. 相似文献
7.
Choon Keat Kuan Dominic Chwan Yee Foo Raymond R. Tan Sivakumar Kumaresan Ramlan Abdul Aziz 《Clean Technologies and Environmental Policy》2007,9(3):225-234
Life cycle assessment (LCA) is often used to compare alternative process options in terms of their overall impact on the environment
to easily identify the most environmentally friendly alternative. In this work, a streamlined LCA study was conducted to assess
three different residue utilization schemes for Tongkat Ali (Eurycoma longifolia) extract production. The case study was firstly simulated using a batch process simulation software. The results of mass
and energy balances obtained from the simulation software were then subjected to life cycle analysis. By evaluating the different
schemes for using the fibrous residue from the extraction process, the potential for environmental process improvement was
identified. Overall, use of the residue as process fuel was found to be the most environmentally friendly option. It produces
the least emissions and reduces resource usage per unit of product than the other options evaluated. 相似文献
8.
A. P. Fröba L. Penedo Pellegrino A. Leipertz 《International Journal of Thermophysics》2004,25(5):1323-1337
Light scattering by thermally excited capillary waves on liquid surfaces or interfaces can be used for the investigation of viscoelastic properties of fluids. In this work, the simultaneous determination of surface tension and liquid kinematic viscosity of n-pentane by surface light scattering (SLS) on a gas–liquid interface was carried out. The experiments are based on a heterodyne detection scheme and signal analysis by photon correlation spectroscopy (PCS). Measurements were performed under saturation conditions over a wide temperature range from about 233 to 363 K. For the whole temperature range the total uncertainty of the liquid kinematic viscosity and surface tension is estimated to be better than 1.0 and 1.2, respectively. The results obtained corroborate the reliability of the SLS technique for the determination of thermophysical properties. 相似文献
9.
In this paper, we present an rp-discretization strategy for physically non-linear problems based on a high order finite element formulation. In order to
achieve convergence, the p-version leaves the mesh unchanged and increases the polynomial degree of the shape functions locally or globally, whereas
the r-method moves nodes and edges of an existing FE-mesh. The basic idea of our rp-version approach is to adjust the finite element mesh to the shape of the elastic–plastic interface in order to take into
account the loss of regularity which arises along the curve of the plastic front. Numerical examples will demonstrate that
this approach leads to an exponential rate of convergence and highly accurate results. 相似文献
10.
K. B. Broberg 《International Journal of Fracture》2005,131(1):1-14
In general, numerical determination of T-stresses requires careful handling, because of their location in the vicinity of singular points. Discretization methods, such as common finite element methods, may not lead to accurate results. However, the well known technique of using dislocation arrays for determination of stress intensity factors may also be used for determination of T-stresses. Except for a few simple cases, this technique leads to a Fredholm equation, that can be solved very accurately. The general method is described and the technique is demonstrated by examples. 相似文献
11.
We present an hp-adaptive strategy that is based on estimating the decay of the expansion coefficients when a function is expanded in L
2-orthogonal polynomials on a triangle or a tetrahedron. We justify this approach by showing that the decay of the coefficients
is exponential if and only if the function is analytic. Numerical examples illustrate the performance of this approach, and
we compare it with two other hp-adaptive strategies. 相似文献
12.
Kjell Eriksson 《International Journal of Fracture》2004,130(4):L201-L203
In a recent work Z.-H. Jin and C. T. Sun (2004) presented a derivation of the J-integral from the potential energy of a system, which is thought to circumvent previous cumbersome or flawed derivations. Two items in this work call for discussion; one is related to the effect of a singularity upon different types of contour integrals and the other to the strain energy difference term. 相似文献
13.
A modified 3ω technique is designed for measurement of the thermal conductivity of polymers. In this study, samples are prepared by pressing
a platinum (Pt) hot wire into melt polymers, and a LabVIEW-based virtual lock-in amplifier is employed to collect the third
harmonic of the voltage across the hot wire, which has proved to overcome the disadvantages of the commercial lock-in amplifier,
such as inaccuracy at low frequency, lack of flexibility/scalability, and high cost. Three kinds of commercial polymers are
measured at room temperature, and the results are checked against data from the literature, which demonstrates that the modified
technique can be used with high accuracy and good reproducibility. 相似文献
14.
We have developed an effective approach to the solution of problems on geometrically nonlinear vibrations of orthotropic multilayer
plates of irregular shapes in a classical statement based on the use of the R-function theory, Ritz variational method and
Bubnov-Galerkin method. Using the proposed method, problems of vibrations of both multilayer rectangular plates and plates
of complex geometries have been solved. The effect of the domain geometry and boundary conditions on the amplitude-frequency
characteristics has been investigated.
__________
Translated from Problemy Prochnosti, No. 5, pp. 101–113, September–October, 2007. 相似文献
15.
This paper investigates interfacial crack tip stress fields and the J-integral for bi-materials with plastic hardening mismatch via detailed elastic-plastic finite element analyses. For small
scale yielding, the modified boundary layer formulation with the elastic T-stress is employed. For fully plastic yielding, plane strain single-edge- cracked specimens under pure bending are considered.
Interfacial crack tip stress fields are explained by modified Prandtl slip-line fields. It is found that, for bi-materials
consisting of two elastic-plastic materials, increasing plastic hardening mismatch increases both crack-tip stress constraint
in the lower hardening material and the J-contribution there. The implication of asymmetric J-integral in bi-materials is also discussed. 相似文献
16.
This paper presents a Bayesian diagnostic procedure for examining change-point assumption in the competing risks model framework.
It considers the family of distributions arising from the cause-specific model as reported by Chiang (Introduction to stochastic
processes in biostatistics. Wiley, New York, 1968) upon which change-points are added to accommodate possible distributional
heterogeneity. Model departure, due to misspecification of change-points associated with either the overall survival distribution
or cause-specific probabilities, is quantified in terms of a sequence of cumulative-sum statistics between each pair of adjacent
change-points assumed. When assessing the asymptotic behavior of each sequence of cumulative-sum statistics using its posterior
predictive p-values, see Rubin (Ann Stat 12:1151–1172, 1984) and partial posterior predictive p-values as reported by Bayarri and Berger (J Am Stat Assoc 95:1127–1142, 2000), we show that both types of p-values attain their greatest departure from 0.5 at the change-point that is missed in the assumed model, from which a diagnostic
procedure is formalized. Statistical power of these two types of p-values is discussed.
相似文献
17.
Pellets of ceramic Na1−xKxNbO3 (x = 0, 0.2 and 0.5), were prepared by conventional solid-state reaction method. Prepared samples were characterized using
XRD and SEM. The frequency and temperature variation of dielectric constant, loss tangent and dielectric conductivity of prepared
samples were measured in the frequency range from 10 KHz-1 MHz, and in the temperature range from 50–250°C for x = 0.2 and
0.5, and between 50 and 480°C for x = 0 compositions. It was observed that the dielectric constant and loss tangent decrease,
and conductivity increases with increasing frequency. Near the transition temperature the material shows anomalous behaviour
for the observed properties, and the peaks of dielectric constant and loss tangent were observed shifting towards lower temperature
with increasing frequency. 相似文献
18.
John D. Landes 《International Journal of Fracture》2007,145(4):285-297
The multiple specimen J
0.2/BL initiation fracture toughness test procedure from the ISO standard, ISO 12135:2002, is evaluated using the EURO fracture
toughness data set. This standard is also compared with the ASTM standard, ASTM E 1820, multiple specimen J
Ic procedure. The EURO round robin data set was generated to evaluate the transition fracture toughness methods for steels.
However, many of the tests resulted in ductile fracture behavior giving final J versus ductile crack extension points. This is the information that is measured in a multiple specimen J initiation fracture toughness test. The data set has more than 300 individual points of J versus crack extension with four different specimen sizes. It may be the largest data set of that type produced for one material.
Therefore, its use to determine J initiation values can provide an important evaluation of the standard procedures. The results showed that a J
0.2/BL value could be determined from the ISO standard for three of the four specimen sizes, the smallest size did not meet the
specimen size requirement on J. The construction line slopes in this method are very steep compared with the ASTM construction line slopes. This resulted
in low J initiation values, about a factor of two lower than the one from the ASTM method. Of the various criteria imposed to determine
a valid J
0.2/BL value, the one limiting the maximum J value was the most questionable. It had an effect of eliminating small specimen data that was identical to acceptable large
specimen data. 相似文献
19.
M.?Ahmetoglu G.?Kaynak I.?A.?Andreev E.?V.?Kunitsyna M.?P.?Mikhailova Yu.?P.?Yakovlev 《Technical Physics Letters》2008,34(11):937-940
We have studied the electrical characteristics of photodiodes based on p-GaSb/p-GaInAsSb/N-GaAlAsSb heterojunctions and investigated the mechanisms of current transfer in these heterostructures at various temperatures.
A comparison of the theoretical results and experimental data showed that the tunneling charge transfer mechanism dominates
at low temperatures (T < 150 K) under both forward and reverse bias conditions. The tunneling current becomes a determining factor at an electric
field strength in the p-n junction of no less that 105 V/cm, which is related to a small bandgap width of the materials studied and low effective masses of electrons and holes. 相似文献
20.
The traditional probability density evolution equations of stochastic systems are usually in high dimensions. It is very hard
to obtain the solutions. Recently the development of a family of generalized density evolution equation (GDEE) provides a
new possibility of tackling nonlinear stochastic systems. In the present paper, a numerical method different from the finite
difference method is developed for the solution of the GDEE. In the proposed method, the formal solution is firstly obtained
through the method of characteristics. Then the solution is approximated by introducing the asymptotic sequences of the Dirac
δ function combined with the smart selection of representative point sets in the random parameters space. The implementation
procedure of the proposed method is elaborated. Some details of the computation including the selection of the parameters
are discussed. The rationality and effectiveness of the proposed method is verified by some examples. Some features of the
numerical results are observed. 相似文献