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1.
Comparison of finite element reliability methods 总被引:7,自引:0,他引:7
The spectral stochastic finite element method (SSFEM) aims at constructing a probabilistic representation of the response of a mechanical system, whose material properties are random fields. The response quantities, e.g. the nodal displacements, are represented by a polynomial series expansion in terms of standard normal random variables. This expansion is usually post-processed to obtain the second-order statistical moments of the response quantities. However, in the literature, the SSFEM has also been suggested as a method for reliability analysis. No careful examination of this potential has been made yet. In this paper, the SSFEM is considered in conjunction with the first-order reliability method (FORM) and with importance sampling for finite element reliability analysis. This approach is compared with the direct coupling of a FORM reliability code and a finite element code. The two procedures are applied to the reliability analysis of the settlement of a foundation lying on a randomly heterogeneous soil layer. The results are used to make a comprehensive comparison of the two methods in terms of their relative accuracies and efficiencies. 相似文献
2.
Yurii S. Borovikov Daria D. Andreeva Stanislava V. Avrova Vladimir V. Sirenko Armen O. Simonyan Charles S. Redwood Olga E. Karpicheva 《International journal of molecular sciences》2021,22(12)
Point mutations in the genes encoding the skeletal muscle isoforms of tropomyosin can cause a range of muscle diseases. The amino acid substitution of Arg for Pro residue in the 90th position (R90P) in γ-tropomyosin (Tpm3.12) is associated with congenital fiber type disproportion and muscle weakness. The molecular mechanisms underlying muscle dysfunction in this disease remain unclear. Here, we observed that this mutation causes an abnormally high Ca2+-sensitivity of myofilaments in vitro and in muscle fibers. To determine the critical conformational changes that myosin, actin, and tropomyosin undergo during the ATPase cycle and the alterations in these changes caused by R90P replacement in Tpm3.12, we used polarized fluorimetry. It was shown that the R90P mutation inhibits the ability of tropomyosin to shift towards the outer domains of actin, which is accompanied by the almost complete depression of troponin’s ability to switch actin monomers off and to reduce the amount of the myosin heads weakly bound to F-actin at a low Ca2+. These changes in the behavior of tropomyosin and the troponin–tropomyosin complex, as well as in the balance of strongly and weakly bound myosin heads in the ATPase cycle may underlie the occurrence of both abnormally high Ca2+-sensitivity and muscle weakness. BDM, an inhibitor of myosin ATPase activity, and W7, a troponin C antagonist, restore the ability of tropomyosin for Ca2+-dependent movement and the ability of the troponin–tropomyosin complex to switch actin monomers off, demonstrating a weakening of the damaging effect of the R90P mutation on muscle contractility. 相似文献
3.
Abbas Rastgoo Armen Amirian 《International Journal of Mechanics and Materials in Design》2006,3(3):253-264
This study presents three mathematical methods namely the polynomial stress function approach, the Fourier series form approach
and the approximated equations form approach for finding the stress distribution in a cantilever beam with rectangular cross
section loaded by a parabolically distributed load. By taking the stress function as a polynomial of the seventh degree, it
is attempted to find the coefficients either in complete or in full shape of the polynomial. In the Fourier series approach,
the load is discreted to unlimited series of harmonic loads and superposing resultant stresses is the affect of parabolically
distributed load on the beam. The resultant stresses are compared with some approximated stress formulas which have been provided
before. Finite element analysis are done for square, short, medium and long cantilever beams and the mathematical results
of stress distribution in five different height of the beam was compared with FEM results. It was found good results for τ
yy
and τ
xy
in all cross section of the beams and acceptable results for τ
xx
only in y = 0. It is found that discreting loads to even a limit number of harmonic loads and superposing the resultant stresses can
give the distribution of τ
yy
and τ
xy
with the acceptable precision in medium and long cantilever beams with rectangular cross section. 相似文献
4.
The first-passage probability, describing the probability that a scalar process exceeds a prescribed threshold during an interval of time, is of great engineering interest. This probability is essential for estimating the reliability of a structural component whose response is a stochastic process. When considering the reliability of an engineering system composed of several interdependent components, the probability that two or more response processes exceed their respective safe thresholds during the operation time of the system is an equally essential quantity. This paper proposes simple and accurate formulas for approximating this joint first-passage probability of a vector process. The nth order joint first-passage probability is obtained from a recursive formula involving lower order joint first-passage probabilities and the out-crossing probability of the vector process over a safe domain. Interdependence between the crossings is approximately accounted for by considering the clumping of these events. The accuracy of the proposed formulas is examined by comparing analytical estimates with those obtained from Monte Carlo simulations for stationary Gaussian processes. As an example application, the reliability of a system of interconnected equipment items subjected to a stochastic earthquake excitation is estimated by linear programming bounds employing marginal and joint component fragilities obtained by the proposed formulas. 相似文献
5.
Elasto-plastic wave propagation in a one dimensional rod is treated by utilizing finite element analysis. The time dependence is handled by means of a variable time step numerical integration method. Elasto-plastic reflections from a fixed boundary and interaction of plastic waves are discussed.
Theoretical expressions are presented for determining the stress response for a material exhibiting bilinear hardening behavior during elasto-plastic wave interaction and boundary reflection. These expressions are employed to evaluate predictions made by the numerical procedure.
In the computations, steep wave fronts are approximated by ramps. The steepness of these ramps may be increased by refining the finite element grid. Excellent agreement is obtained between numerical and theoretical elastic and inelastic stress response levels. 相似文献
6.
Surface and phased array receiving coils in MRI typically require that RF excitation be accomplished using the body coil.
This process requires that the receiving coils contain blocking circuitry to increase the overall circuit impedance during
RF excitation and withstand the electromotive force induced by the applied electromagnetic field. The aim of this study was
to determine the optimal impedance range required during RF excitation based on an assessment of image quality. The experimental
results are fit by an exponential model and establish criteria that can be applied for general receiver coil design. 相似文献
7.
8.
Karen Trchounian Anna Poladyan Armen Trchounian 《International Journal of Hydrogen Energy》2017,42(10):6590-6597
Escherichia coli growth and H2 production were followed in the presence of heavy metal ions and their mixtures during glycerol or glucose fermentation at pH 5.5–7.5. Ni2+ (50 μM) with Fe2+ (50 μM) but not sole metals stimulated bacterial biomass during glycerol fermentation at pH 6.5. Ni2++Fe3+ (50 μM), Ni2 +Fe3++Mo6+ (20 μM) and Fe3++Mo6+ (20 μM) but not sole metals enhanced up to 3-fold H2 yield but Cu+ or Cu2+ (100 μM) inhibited it. At pH 7.5 stimulating effect on biomass was observed by Ni2++Fe2++Mo6+. H2 production was enhanced 2.7 fold particularly by Ni2++Fe3++Mo6+ at the late stationary growth phase. Whereas at pH 5.5 increased biomass was when Fe2++Mo6+ or Mo6+ were added. H2 yield was decreased compared with that at pH 6.5, but metal ions again enhanced it. During glucose fermentation at pH 6.5 biomass was increased by the mixtures of metal ions, and 1.2 fold increased H2 yield was observed. At pH 7.5 Ni2++Fe2+ increased biomass but Cu+ or Cu2+ had suppressing effect; Fe3++Mo6+ stimulated H2 production. At pH 5.5 biomass also was raised by Ni2++Fe2++Mo6+; H2 yield was increased upon Mo6+ and Mo6++Fe2+ or Mo6++Fe3+ additions. The results point out the importance of Ni2+, Fe2+, Fe3+ and Mo6+ and some of their combinations for E. coli bacterial growth and H2 production mostly during glycerol but not glucose fermentation and at acidic conditions (pH 5.5 and 6.5). They can be used for optimizing fermentation processes on glycerol, controlling bacterial biomass and developing H2 production biotechnology. 相似文献
9.
Andrei Shchegrov John Khaydarov Stepan Essaian Greg Nemet Suren Soghomonyan Hakob Danielyan Armen Poghosyan Gevorg Gabrielyan 《Journal of the Society for Information Display》2010,18(8):589-595
Abstract— A novel green laser source, based on a monolithic cavity microchip laser platform, has been developed. The laser is designed to be a part of a miniature and efficient RGB light source for microdisplay‐based mobile projector devices. The use of highly efficient, periodically poled MgO‐doped lithium niobate as the non‐linear frequency doubler allows for a significant increase in the overall efficiency of the green microchip laser. Specifically, a 50–150‐mW green output with a wall‐plug efficiency exceeding 10% in the temperature range of greater than 40°C has been demonstrated. A compact package for this laser source with a volume less than 0.33 cm3 is discussed and results of performance tests are presented. 相似文献
10.
Levels of biopterin derivatives in urine, serum, milk, cerebrospinal fluid, brain, and liver have been measured with the Crithidia fasciculata assay. Normal levels in serum and urine have been given and compared with those in a number of benign and malignant proliferative disorders, phenylketonuria, kidney disease, Parkinson's disease, schizophrenia, controlled epilepsy, rheumatoid arthritis, and pernicious anaemia. The active component of Crithidia factor in serum was 7,8-dihydrobiopterin. Tissue, urine, and some serum samples contained two active materials, the principal one being 7,8-dihydrobiopterin; a minor constituent was probably tetrahydrobiopterin. Serum biopterin levels following methotrexate administration were raised and subsequent administration of folic acid and 5-formyltetrahydrofolic acid further increased serum levels of biopterin derivatives; this was in contrast to the total absence of response to oral folates without prior methotrexate and to 5-methyltetrahydrofolic acid either with or without methotrexate being given. 相似文献