AlternateSWMM6

Wave Speed in Innovyze H2OCalc – Alternative? for SWMM6


Note for SWMM6 – this may be useful for any discussion of a Slot in SWMM6.  A Preissmann Slot is used in InfoWorks ICM, XPSWMM and one of the solutions of SWMM4

Wave Speed

The wave speed, c, is influenced by the elasticity of the pipe wall. For a pipe system with some degree of axial restraint a good approximation for the wave propagation speed is obtained using

where Ef = elastic modulus of the fluid (for water, 2.19 GN/m2, 0.05 Glb/ft2)

ρ = density of the fluid (for water, 998 kg/m3, 1.94 slug/ft3)

Ec = elastic modulus of the conduit (GN/m2, Glb/ft2)

D = pipe diameter (mm, inch)

t = pipe thickness (mm, inch)

KR = coefficient of restraint for longitudinal pipe movement.

The constant KR takes into account the type of support provided for the pipeline. Typically, three cases are recognized with KR defined for each as follows (m is the Poisson’s ratio for the pipe material):

Case a: The pipeline is anchored at the upstream end only.

KR = 1 – m / 2

Case b: The pipeline is anchored against longitudinal movement.

KR = 1 – m2

Case c: The pipeline has expansion joints throughout.

KR = 1

The following table provides physical properties of common pipe materials.

Table 3-8: Physical Properties of Common Pipe Materials

Material Young’s Modulus (Ec) Poisson’s Ratio, μ
GN/m2 Glb/ft2
Asbestos Cement 23 – 24 0.53 – 0.55
Cast Iron 80 – 170 1.8 – 3.9 0.25 – 0.27
Concrete 14 – 30 0.32 – 0.68 0.1 – 0.15
Reinforced Concrete 30 – 60 0.68 – 1.4
Ductile Iron 172 3.93 0.3
PVC 2.4 – 3.5 0.055 – 0.08 0.46
Steel 200 – 207 4.57 – 4.73 0.30

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