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41.
In this paper, we propose a new compact fourth-order accurate method for solving the two-dimensional fourth-order elliptic boundary value problem with third-order nonlinear derivative terms. We use only 9-point single computational cell in the scheme. The proposed method is then employed to solve Navier–Stokes equations of motion in terms of streamfunction–velocity formulation, and the lid-driven square cavity problem. We describe the derivation of the method in details and also discuss how our streamfunction–velocity formulation is able to handle boundary conditions in terms of normal derivatives. Numerical results show that the proposed method enables us to obtain oscillation-free high accuracy solution. 相似文献
42.
43.
In some previous geometric nonlinear finite element formulations, due to the use of axial displacement, the contribution of
all the elements lying between the reference node of zero axial displacement and the element to the foreshortening effect
should be taken into account. In this paper, a finite element formulation is proposed based on geometric nonlinear elastic
theory and finite element technique. The coupling deformation terms of an arbitrary point only relate to the nodal coordinates
of the element at which the point is located. Based on Hamilton principle, dynamic equations of elastic beams undergoing large
overall motions are derived. To investigate the effect of coupling deformation terms on system dynamic characters and reduce
the dynamic equations, a complete dynamic model and three reduced models of hub-beam are prospected. When the Cartesian deformation
coordinates are adopted, the results indicate that the terms related to the coupling deformation in the inertia forces of
dynamic equations have small effect on system dynamic behavior and may be neglected, whereas the terms related to coupling
deformation in the elastic forces are important for system dynamic behavior and should be considered in dynamic equation.
Numerical examples of the rotating beam and flexible beam system are carried out to demonstrate the accuracy and validity
of this dynamic model. Furthermore, it is shown that a small number of finite elements are needed to obtain a stable solution
using the present coupling finite element formulation. 相似文献
44.
Flexible-body modeling with geometric nonlinearities remains a hot topic of research by applications in multibody system dynamics
undergoing large overall motions. However, the geometric nonlinear effects on the impact dynamics of flexible multibody systems
have attracted significantly less attention. In this paper, a point-surface impact problem between a rigid ball and a pivoted
flexible beam is investigated. The Hertzian contact law is used to describe the impact process, and the dynamic equations
are formulated in the floating frame of reference using the assumed mode method. The two important geometric nonlinear effects
of the flexible beam are taken into account, i.e., the longitudinal foreshortening effect due to the transverse deformation,
and the stress stiffness effect due to the axial force. The simulation results show that good consistency can be obtained
with the nonlinear finite element program ABAQUS/Explicit if proper geometric nonlinearities are included in the floating
frame formulation. Specifically, only the foreshortening effect should be considered in a pure transverse impact for efficiency,
while the stress stiffness effect should be further considered in an oblique case with much more computational effort. It
also implies that the geometric nonlinear effects should be considered properly in the impact dynamic analysis of more general
flexible multibody systems. 相似文献
45.
Marco Franchini 《Water Resources Management》1994,8(3):225-238
With reference to the kinematic wave theory coupled with the hypothesis of constant linear velocity for the rating curve, rising limb analytical solutions have been calculated for overland flow, over an Hortonian-infiltrating surface, and sediment discharge. These analytical solutions are certainly easier to use than the numerical integration of the basic equations and they may be used to obtain an initial evaluation of the parameters of more complex models generally devised for complicated cases.Notation
a
exponent of the Horton law [T–1]
-
b
exponent of the rill erosion equation
-
B
inter-rill erosion coefficient [ML–m–2T
m–1]
-
c
sediment concentration [ML–3]
-
c
o
reference sediment concentration [ML–3]
-
E
I
inter-rill erosion [ML–2T–1]
-
E
R
rill erosion [ML–2T–1]
-
f
c
final infiltration rate of the soil [LT–1]
-
f
o
initial infiltration rate of the soil [LT–1]
-
h
flow depth [L]
-
h
o
reference flow depth [L]
-
i
infiltration rate [LT–1]
-
k
rill erosion coefficient [ML–1–b
T–1]
-
K
integration constant
-
L()
Laplace transformation
-
m
exponent of the inter-rill erosion equation
-
n
Manning's coefficient [L–1/3T]
-
p
rainfall intensity [LT–1]
-
q
water discharge per unit width [L2T–1]
-
q
s
sediment discharge per unit width [ML–1T–1]
-
t
time [T]
-
t
p
ponding time [T]
-
x
distance along the flow direction [L]
Greek Letters
coefficient of the stage-discharge equation [L2–T–1]
-
exponent of the stage-discharge equation
-
rill erosion coefficient [L–1] 相似文献
46.
47.
Given an undirected network with positive edge costs and a positive integer , the minimum-degree constrained minimum spanning tree problem is the problem of finding a spanning tree with minimum total cost such that each non-leaf node in the tree has a degree of at least . This problem is new to the literature while the related problem with upper bound constraints on degrees is well studied. Mixed-integer programs proposed for either type of problem is composed, in general, of a tree-defining part and a degree-enforcing part. In our formulation of the minimum-degree constrained minimum spanning tree problem, the tree-defining part is based on the Miller–Tucker–Zemlin constraints while the only earlier paper available in the literature on this problem uses single and multi-commodity flow-based formulations that are well studied for the case of upper degree constraints. We propose a new set of constraints for the degree-enforcing part that lead to significantly better solution times than earlier approaches when used in conjunction with Miller–Tucker–Zemlin constraints. 相似文献
48.
Small package delivery companies offer services where packages are guaranteed to be delivered within a given time-frame. With variability in travel time, the configuration on the hub-and-spoke delivery network is vital in ensuring a high probability of meeting the service-level guarantee. We present the stochastic p-hub center problem with chance constraints, which we use to model the service-level guarantees. We discuss analytical results, propose solution heuristics, and present the results from computational experiments. 相似文献
49.
In mean–variance (M–V) analysis, an investor with a holding period [0,T] operates in a two-dimensional space—one is the mean and the other is the variance. At time 0, he/she evaluates alternative portfolios based on their means and variances, and holds a combination of the market portfolio (e.g., an index fund) and the risk-free asset to maximize his/her expected utility at time T. In our continuous-time model, we operate in a three-dimensional space—the first is the spot rate, the second is the expected return on the risky asset (e.g., an index fund), and the third is time. At various times over [0,T], we determine, for each combination of the spot rate and expected return, the optimum fractions invested in the risky and risk-free assets to maximize our expected utility at time T. Hence, unlike those static M–V models, our dynamic model allows investors to trade at any time in response to changes in the market conditions and the length of their holding period. Our results show that (1) the optimum fraction y*(t) in the risky asset increases as the expected return increases but decreases as the spot rate increases; (2) y*(t) decreases as the holding period shortens; and (3) y*(t) decreases as the risk aversion parameter-γ is larger. 相似文献
50.
In an array of problem solving methods, one can traditionally distinguish two kinds of problems: one is a problem that has solutions in a search space and the other is a problem that does not have solutions in a given space. The later problem so called solutionless problem or inventive problem requires an inventive approach to reformulate the problem and dialectical thinking brings benefits in the process. The framework used to formulate problems in a dialectical approach is contradiction. Identification of contradictions plays an important role in distinguishing solutionless problems: a contradiction exists when no solution can be found, and a solution exists when no contradiction can be found. In this article, the inadequacy of existing frameworks in satisfying this requirement is demonstrated and a framework that fits this requirement is proposed. 相似文献