共查询到20条相似文献,搜索用时 31 毫秒
1.
D. J. F. Ewing A. J. Fawkes J. R. Griffiths 《International journal for numerical methods in engineering》1970,2(4):597-600
In any mesh, rules exist that interrelate the number of internal and external sides, vertices, etc. and the total number of elements. These are given explicitly for plane meshes of triangles and quadrilaterals, and for solid meshes of tetrahedra and cuboidal elements. The method is quite general and discovers all such independent rules that exist. Thus, for a plane mesh of T elements having Vi internal and Vb boundary vertices and Si internal and Sb boundary sides, then where H is the number of internal boundaries (holes) there might be. For solid meshes, these two-dimensional equations relating elements to sides generalize to where there are Fb boundary and Fi internal faces. Unfortunately, there is no direct generalization of the two-dimensional equations relating vertices and elements: it is only possible to do this by including the Ei internal and Eb boundary edges: where there are H through holes and h cavities. 相似文献
2.
We study the reliability analysis of a repairable system with operating units, warm standby units and repairmen in which the balking and reneging of units are considered. It is assumed that failed units balk (refuse to join) with a constant probability ( ) and renege (leave the queue after joining) according to a negative exponential distribution with parameter . The failure times of the operating unit and of a standby unit are assumed to be exponentially distributed with parameters λ and α, respectively. The repair time distribution is also exponential. The repairable system is out of , in which . The reliability characteristics, such as the system reliability and the mean time to system failure (MTTF), in a repairable system are derived. Several cases are analysed graphically to study the effect of various parameters on the reliability and MTTF of the system. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
3.
Some simple and useful equations were obtained by experiments with a turbomolecular pump (TMP 340). After switching off the current of the motor the rotation frequenzy f decreases proportionally with the time t: f(t) = f0 ? αt . The coefficient α depends on the gasflow Q and the roughing pressure p vv . An other linear equation is obtained for the retarding factor Δf/Δt in dependance of the roughing pressure . With increasing molecular mass M the factor - m decreases exponentially by the ratio of tangential rotation speed u t to the most probable molecular speed c w . The equation shows the same parameters as the compression ratio of any turbomolecular pump. The parameter Γ is effected by the geometrical dimensions of the pump. These results are valid within the molecular mass range 2 ? M ? 130 . The energy consumption of the pump and other quantities can be calculated by the parameters – Δf/Δt and m. 相似文献
4.
J. Ziaja 《Materialwissenschaft und Werkstofftechnik》1991,22(11):422-426
Residual stresses as parameters of X-ray criterion of fracture and of fatigue life prediction Fatigue testing is notorious for considerable scatter in specimen life even if special measures are taken to precisely control parameters of stress cycling. The reason for that must be ascribed to variation in material microstructure existing prior to fatigue loading. Structural condition of material may be determined by the following function: Extensive fatigue tests on α-Ti and (α + β)-Ti alloy at temperatures 77 K and 295 K showed that failure did not occur until function V reached its critical value at a plane characteristic of each lattice type (failure plane). The condition V = K may be therefore regarded an X-Ray criterion and, once determined numerically, a sort of material constant. The life NB of fatigue tested specimen was found to be clearly depended on structural condition of virgin material exhibited natural variation of structural characteristics. The finite fatigue life was found to conform with the relationship The expression may be used for predicting life NB if prior to fatigue loading the material condition function V value is made known for a characteristic lattice plane. 相似文献
5.
J. Ewald 《Materialwissenschaft und Werkstofftechnik》1991,22(10):359-369
Degradation of the Deformation Capacity under Creep due to Multiaxial States of Stress A method is proposed, which describes the degradation of the uniform true (rupture) strain φ due to the multiaxial stress states in creep. The method is based on the formulas of Siebel which describe the ratios of the uniform true strains in the 3 principle stress directions for any given states of stress: σm is the hydrostatic stress. These values for different given stress states are normalized by the principle stress σIZV for uniaxial tension with the same amount as for the multiaxial stress states. From such ratios it is possible to find out the real uniform true (rupture) strains φ for the different stress states in taking the uniform true (rupture) strain for uniaxial tension, φIBZV, as a basis: The comparison of predicted and tested φ-values proves that the formulas describe the toughness-degradations with the right tendency. For multiaxial states of stress it has to be kept in mind that we have two counterbalancing influences which are on the one hand the reduction of the creep rate due to lower v. Mises equivalent stresses and on the other hand the reduction of the deformation capacity, described above. A model ist proposed to estimate these influences of the states of stress on the creep rupture times. 相似文献
6.
G. H. Lin W. L. Pearn Y. S. Yang 《Quality and Reliability Engineering International》2005,21(6):655-668
The Taguchi capability index Cpm, which incorporates the departure of the process mean from the target value, has been proposed to the manufacturing industry for measuring manufacturing capability. A Bayesian procedure has been considered for testing process performance assuming , which was generalized without assuming . Statistical properties of the natural estimator of the index Cpm for normal processes have been investigated extensively. However, the investigation was restricted to processes with symmetric tolerances. Recently, a generalized Cpm, referred to as , was proposed to cover processes with asymmetric tolerances. Under the normality assumption, the statistical properties of the estimated including the exact sampling distribution, the rth moment, expected value, variance, and the mean‐squared error were obtained. In this paper, we use a Bayesian approach to obtain the interval estimation for the generalized Taguchi capability index . Consequently, the manufacturing capability testing can be performed for quality assurance. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
7.
J. C. Lee H. N. Hung W. L. Pearn T. L. Kueng 《Quality and Reliability Engineering International》2002,18(2):111-116
This paper considers an asymptotic distribution for an estimate of the process yield index proposed by Boyles (1994). The asymptotic distribution of is useful in statistical inferences for . An illustrative example is given for hypothesis testing and for interval estimation on the yield index . Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
8.
W. A. Gruver N. H. Engersbach 《International journal for numerical methods in engineering》1976,10(5):1047-1056
This paper concerns the implementation of a recent idea, attributed to Hestenes and Powell, based on solving the equality constrained finite dimensional minimization problem via the unconstrained problem where ? is a non-linear functional, g is a non-linear mapping into Rp, K is a prescribed matrix of penalty constants and λ is the Lagrange multiplier. The computational algorithm is based on restoring active constraints to first order and adjusting x in the remaining necessary conditions by gradient projection. The minimization is performed by the variable metric rank-two BGFS update with linear search by cubic interpolation. Computational results using the algorithm include two problems of minimum fuel trajectory optimization—two impulse rendezvous with Comet Encke and three impulse constrained positioning of a geostationary satellite. 相似文献
9.
Wagner de Souza Borges Linda Lee Ho 《Quality and Reliability Engineering International》2001,17(6):447-458
Two problems greatly affect the use of capability indices such as , and : the lack of affinity with the process fraction defective π and the difficulty of dealing with the sampling distributions of their natural estimators. In this paper, a capability index which is in one‐to‐one correspondence with π is introduced and simple inferential procedures under a Bayesian perspective are developed to facilitate its use in industrial applications. Copyright © 2001 John Wiley & Sons, Ltd. 相似文献
10.
Greenwich and Jahr‐Schaffrath (1995) introduced the process incapability index , which provides an uncontaminated separation between information concerning the process precision and process accuracy . In this paper, we consider the three indices, and investigate the statistical properties of their natural estimators. For the three indices, we obtain their UMVUEs and MLEs, and compare the reliability of the two estimators based on the relative mean square errors. In addition, we construct 90%, 95%, and 99% upper confidence limits, and the maximum values of for which the process is capable 90%, 95%, and 99% of the time. The results obtained in this paper are useful to the practitioners in choosing good estimators and making reliable decisions on judging process capability. Copyright © 2001 John Wiley & Sons, Ltd. 相似文献
11.
The Successive Overrelaxation (SOR) and the Cyclic Chebyshev Semi-Iterative (CCSI) methods are considered for solving the non-symmetric linear systems Ax = b when A has the form with D 1 and D 2 symmetric positive definite (SPD). The D 1/2-norms of both methods are determined and it is shown that, though the SOR method is better based on the spectral radius, the CCSI scheme is far better than SOR according to the D 1/2-norm. 相似文献
12.
Don R. Holcomb W. Matthew Carlyle 《Quality and Reliability Engineering International》2002,18(4):299-304
Supersaturated designs offer a potentially useful way to investigate many factors with few experiments. A super‐saturated design evaluates factors with experiments, where . In some supersaturated designs the number of factors being investigated may exceed the number of experiments by a factor of three or more. The problem of developing a supersaturated design is described in computational complexity terms and methods of construction are discussed. Using standard combinatorial formulation may permit researchers to use additional methods to develop additional designs. Designs are generated with a modified method and compared with published designs using existing criteria and a new criterion. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
13.
Z. H. Jia D. J. Shippy F. J. Rizzo 《International journal for numerical methods in engineering》1989,28(10):2257-2273
A multi-domain method of solving three-dimensional elastic crack problems in an infinite elastic body using the boundary element method is proposed. The displacement and traction behaviours near a crack front are incorporated in special crack elements. The elimination of singularities arising from the term combined with Kelvin's kernel for displacement in the integrals is discussed in detail. Stress intensity factors of modes I, II and III are obtained directly from crack-front nodal values, without any extrapolation as in some other methods. No differentiation of conventional boundary integral equations (with Kelvin's tensor kernels) is necessary in the current approach. This method is applicable to cracks of arbitrary shape. Infinite bodies are modelled precisely as such, not approximated as large finite bodies. Numerical solutions of stress intensity factors are given for several problems involving a penny-shaped crack. 相似文献
14.
J. Jirousek A. Wrblewski B. Szybiski 《International journal for numerical methods in engineering》1995,38(15):2619-2638
This paper presents a simple quadrilateral 12 DOF plate bending element based on a modified version of the hybrid-Trefftz approach. This element makes use of two independent fields of generalized displacements:
- i a non-conforming field (11 Trefftz terms for transverse displacement w and the corresponding rotations Θx, Θy) satisfying the governing differential equations of Reissner-Mindlin theory;
- ii an auxiliary conforming field with displacements w? linked to rotations $ \tilde \Theta _x,\tilde \Theta _y$, by the requirement of constant boundary distribution of the corresponding tangential component S?t, of the transverse shear. This allows quadratic w? and linear $ \tilde \Theta _x,\tilde \Theta _y $, at the element boundary to be obtained with only 3 DOF at the corner nodes.
15.
Double sampling (DS) ‐control charts are designed to allow quick detection of a small shift of process mean and provides a quick response in an agile manufacturing environment. However, the DS ‐control charts assume that the process standard deviation remains unchanged throughout the entire course of the statistical process control. Therefore, a complementary DS chart that can be used to monitor the process variation caused by changes in process standard deviation should be developed. In this paper, the development of the DS s‐charts for quickly detecting small shift in process standard deviation for agile manufacturing is presented. The construction of the DS s‐charts is based on the same concepts in constructing the DS ‐charts and is formulated as an optimization problem and solved with a genetic algorithm. The efficiency of the DS s‐control chart is compared with that of the traditional s‐control chart. The results show that the DS s‐control charts can be a more economically preferable alternative in detecting small shifts than traditional s‐control charts. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
16.
This study presents an integrated model for the joint economic design of ‐control charts and maintenance schedules and, simultaneously, determines the economic production quantity and production run length for a deteriorating production system. The operating state of the production process is classified as either in control or out of control. In the latter state, the process produces some defective items. An ‐control chart is used to monitor the process mean. Both uniform and non‐uniform inspection schemes are adopted. Inspection and maintenance are performed simultaneously. Replacement cost is assumed to be very high. The process failure mechanism is assumed to follow a general probability distribution with an increasing failure rate. The concept of a truncated production cycle is introduced. The production cycle begins when a new component is installed and ends with a repair after the detection of a failure or after a specified number of inspection intervals, , whichever occurs first. The effects of preventive maintenance on quality control are discussed. Numerical examples are provided to evaluate the performance of the model. Sensitivity analyses are conducted to study the effects of various model parameters. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
17.
Explosive Welding as a Technique for Cladding of Precious Metals The method of explosive welding and the importance of the cladding parameters are described. The “Explosive Weldability Window” is experimentally determined for the material combination AgCu 10/Fe. The behaviour of explosive claddings produced under different conditions during rolling is investigated. Best results are obtained with samples with a wavy interphase, produced under the following cladding parameters: It is shown, that in comparison with conventional methods explosive cladding has advantages both in processing and quality. 相似文献
18.
K. Mayrhofer F. D. Fischer 《International journal for numerical methods in engineering》1992,33(5):1027-1047
An exact expression is derived for the general finite-part integral over an inclined ellipticaldomain Ω. r denotes the distance of a point in Ω to the singular point $\left({x,y} \right).f = x_{^0 }^i y_0^j \sqrt {Z\left({x_{0,} y_0 }\right)}$ is a general function of the Cartesian co-ordinates x0,y0. The boundary of the region Ω represents the equation Z(x0, y0)=O. These integrals appear during the numerical solution of plane crack problems in three-dimensional elasticity where they are the dominant part of a hypersingular integral equation. The availability of exact expressions for the integrals with arbitrary integers i and j will increase the accuracy of the numerical results and, simultaneously, lead to quicker numerical results. The considered finite-part integral can be expressed in closed form as function of complete elliptical integrals or Gauss hypergeometric functions, respectively. Formuias for special cases and some i, j values and their numerical verification are given in Appendices II and III. 相似文献
19.
Charles W. Champ Shou‐Peng Chou 《Quality and Reliability Engineering International》2003,19(2):161-170
Phase I control charts are used as aids in bringing a process into and defining the meaning of a process being in a state of statistical in‐control. This is done by looking at the data in retrospect to answer the question ‘were these data taken from an in‐control process?’ Typically the data is collected as independent random samples taken periodically from the output of the process. Commonly it is recommended that each sample be compared via a statistic(s) to a control limit(s) that is (are) function(s) of all the data. We refer to these charts as ‘standard limits’ charts. An alternative method is to compare each sample with all or some subcollection of the remaining samples. These charts are referred to as ‘individual’ limits charts. The individual limits charts appear to be attractive in detecting a sample from an out‐of‐control process when the other samples were taken when the process was in‐control. We demonstrate using a simple probability analysis that a standard limits Phase I Shewhart chart performs better than the individual limits Phase I Shewhart chart. Furthermore, it is shown that the individual limits Phase I Shewhart charts can be designed to be equivalent. This also holds for the individual and standard limits Phase I Shewhart charts. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
20.
G. Marci 《Materialwissenschaft und Werkstofftechnik》1979,10(5):158-166
A fatigue crack growth rate (FCGR) equation, had been proposed which predicts the observed R-ratio effects correctly. Conceptually, this equation accounts for spectrum loading effects via the parameter “K”. The work presented deals with the temperature effect on the fatigue parameters entering the above FCGR-equation. For materials which do not experience a microstructural or a fracture mode transition within the temperature range of interest, the effect of temperature on the fatigue parameters “C” and “ΔKT” can be interpolated or extrapolated from relatively few experimental data. Extrapolation of these fatigue parameters for Inconel X-750 measured between 300° K and 900° K allowed a very accurate prediction of the FCGR at 4° K. At higher temperatures the end of fatigue controlled crack growth is clearly indicated by a rapid increase of the fatigue parameter “C”. There, the fatigue parameter “C” increases withing a temperature span of 100° K by a factor of 102. This kind of information is of utmost importance for materials application at elevated temperatures as in nuclear systems. 相似文献