The cantilever beam model

We are interested in the vertical deviation of a diving board created by a child diver. We consider a child whose weight generates a force approximately equal to 300N (i.e. almost 30 kg). Because of the uncertainties in the weight of the person, we consider that the force is a random variable. The length of the diving board is between 2.5 m and 2.6 m. The Young modulus is uncertain and between 65 and 75 GPa, which corresponds to the fiberglass material, a material often used for diving boards. Uncertainties in the production of the material are taken into account in the Young modulus and the section modulus of the board.

We consider a cantilever beam defined by its Young’s modulus E, its length L and its section modulus I. One end of the cantilever beam is built in a wall and we apply a concentrated bending load F at the other end of the beam, resulting in a deviation Y.

beam geometry

The beam geometry

Inputs

  • E : Young modulus (Pa), Beta(\alpha = 0.9, \beta = 3.5, a = 65.0 \times 10^9, b = 75.0 \times 10^9)

  • F : Loading (N), Lognormal(\mu_F=300.0, \sigma_F=30.0, shift=0.0)

  • L : Length of beam (m), Uniform(min=2.5, max= 2.6)

  • I : Moment of inertia (m^4), Beta(\alpha = 2.5, \beta = 4.0, a = 1.3 \times 10^{-7}, b = 1.7 \times 10^{-7}).

In the previous table \mu_F=E(F) and \sigma_F=\sqrt{V(F)} are the mean and the standard deviation of F.

We assume that the random variables E, F, L and I are dependent and associated with a gaussian copula which correlation matrix is:

R = \begin{pmatrix}
    1 & 0 & 0 & 0 \\
    0 & 1 & 0 & 0 \\
    0 & 0 & 1 & -0.2 \\
    0 & 0 & -0.2 & 1
    \end{pmatrix}

In other words, we consider that the variables L and I are negatively correlated: when the length L increases, the moment of inertia I decreases.

Output

The vertical displacement at free end of the cantilever beam is:

Y  = \dfrac{F\, L^3}{3 \, E \, I}

A typical event of interest is when the beam deviation is too large which is a failure:

Y \ge 0.30 (m)

API documentation

class CantileverBeam

Data class for the cantilever beam example.

Examples

>>> from openturns.usecases import cantilever_beam
>>> # Load the cantilever beam model
>>> cb = cantilever_beam.CantileverBeam()
Attributes:
dimThe dimension of the problem

dim=4.

EBeta distribution

ot.Beta(0.9, 3.5, 65.0e9, 75.0e9)

FLogNormal distribution

ot.LogNormalMuSigma()([300.0, 30.0, 0.0])

LUniform distribution

ot.Uniform(2.5, 2.6)

IBeta distribution

ot.Beta(2.5, 4.0, 1.3e-7, 1.7e-7)

modelSymbolicFunction, the physical model of the cantilever beam.
RCorrelationMatrix

Correlation matrix used to define the copula.

copulaNormalCopula

Copula of the model.

distributionComposedDistribution

The joint distribution of the parameters.

independentDistributionComposedDistribution

The joint distribution of the parameters with independent copula.

Examples based on this use case

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