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Set parameters for a whale strike simulation

Source: R/parameters.R
parameters.Rd

Assembles control parameters into a list suitable for passing to strike() and the functions that it calls. If file is provided, then all the other arguments are read from that source. Note that updateParameters() may be used to modify the results of parameters, e.g. for use in sensitivity tests.

Usage

parameters(
  ms = 45000,
  Ss = NULL,
  Ly = 1.15,
  Lz = 1.15,
  species = "N. Atl. Right Whale",
  lw = 13.7,
  mw = NULL,
  Sw = NULL,
  l = NULL,
  a = NULL,
  b = NULL,
  s = NULL,
  theta = 55,
  Cs = 0.01,
  Cw = 0.0025,
  logistic = list(logStressCenter = 5.38, logStressWidth = 0.349, tau25 = 1e+05, tau50 =
    241000, tau75 = 581000),
  file = NULL
)

Arguments

ms

Ship mass (kg).

Ss

Ship wetted area (m^2). This, together with Cs, is used by shipWaterForce() to estimate ship drag force. If Ss is not given, then an estimate is made by calling shipAreaFromMass() with the provided value of ms.

Ly

Ship impact horizontal extent (m); defaults to 1.15m if not specified, based on an analysis of the shape of the bow of typical coastal fishing boats of the Cape Islander variety.

Lz

Ship impact vertical extent (m); defaults to 1.15m if not specified, based on the same analysis as for Ly.

species

a string indicating the whale species. For the permitted values, see whaleMassFromLength(). (The species value can also set the lw and l values, as noted in their portions of this documentation.)

lw

either (1) whale length in metres or (2) the string "from_species". If the latter, then the length is determined from whaleMeasurements(). In either case, the length is used by whaleAreaFromLength() to calculate area, which is needed for the water drag calculation done by whaleWaterForce().

mw

either (1) the whale mass in kg or (2) NULL. In the latter case, the mass is calculated from whale length, using whaleMassFromLength() with type="wetted".

Sw

either (1) the whale surface area in m^2 or (2) NULL. If the latter case, the area is calculated from whale length using whaleAreaFromLength().

l

either (1) a numerical vector of length 4 that indicates the thicknesses in metres of skin, blubber, sublayer and bone; (2) NULL to set these four values to 0.025, 0.16, 1.12, and 0.1; or (3) the string "from_species", in which case these four values are determined by calling whaleMeasurements(). The default skin thickness of 0.025 m represents the 0.9-1.0 inch value stated in Section 2.2.3 of Raymond (2007). The blubber default of 0.16 m is a rounded average of the values inferred by whale necropsy, reported in Appendix 2 of Daoust et al., 2018. The sublayer default of 1.12 m may be reasonable at some spots on the whale body. The bone default of 0.1 m may be reasonable at some spots on the whale body. The sum of these default values, 1.40 m, is a whale radius that is consistent with a half-circumference of 4.4 m, reported in Table 2.2 of Raymond (2007). Note, however, that these values are not identical to those found in whaleMeasurements.

a, b

Numerical vectors of length 4, giving values to use in the stress-strain law stress=a*(exp(b*strain)-1), where a is in Pa and b is unitless. By construction, a*b is the local modulus at low strain (i.e. at low b*strain values), and that b is the efolding scale for nonlinear increase in stress with strain. This exponential relationship has been mapped out for whale blubber, using a curve fit to Figure 2.13 of Raymond (2007), and these values are used for the second layer (blubber); see the documentation for the raymond2007 dataset, to see for how that fit was done. If not provided, a defaults to c(17.8e6/0.1, 1.58e5, 1.58e5, 8.54e8/0.1) and b defaults to c(0.1, 2.54, 2.54, 0.1). The skin defaults are set up to give a linear shape (since b is small) with the a*b product being 17.8e6 Pa, which is the adult-seal value given in Table 3 of Grear et al. (2017). The blubber defaults are from a regression of the stress-strain relationship shown in Figure 2.13 of Raymond (2007). The sublayer defaults are set to match those of blubber, lacking any other information. The bone default for b is small, to set up a linear function, and a*b is set to equal 8.54e8 Pa, given in Table 2.3 of Raymond (2007) and Table 4.5 of Campbell-Malone (2007).

s

Numerical vector of length 4, giving the ultimate strengths (Pa) of skin, blubber, sublayer, and bone, respectively. If not provided, the value is set to 1e6 * c(19.600,0.255,0.255,22.900) with reasoning as follows. The skin default of 19.6 MPa is a rounded value from Table 3 of Grear et al. (2018) for adult seal skin strength at an orientation of 0 degrees. The blubber and sublayer values were chosen as the central point of a logistic fit of whale collision damage to maximal stress during a default impact simulation. (For comparison, a strength of 0.437 MPa may be inferred by multiplying Raymond's (2007) Figure 2.13 elastic modulus of 0.636 MPa by the ratio 0.97/1.41 determined for adult seal strength/modulus, as reported in Table 3 of Grear et al. (2018).) The bone default o 22.9 MPa is from Table 2.3 of Raymond (2007) and Table 4.5 of Campbell-Malone (2007).

theta

Whale skin deformation angle (deg); defaults to 55 degrees, if not supplied, because that angle produces a good match to Raymond's (2007) Figure 6.1 for the total force as a function of vessel speed, for large vessels. Note that the match works almost as well in the range 50 deg to 70 deg.

Cs

Drag coefficient for ship (dimensionless), used by shipWaterForce() to estimate ship drag force. Defaults to 1e-2, which is 4 times the frictional coefficient of 2.5e-3 inferred from Figure 4 of Manen and van Oossanen (1988), assuming a Reynolds number of 5e7, computed from speed 5m/s, lengthscale 10m and viscosity 1e-6 m^2/s. The factor of 4 is under the assumption that frictional drag is about a quarter of total drag. The drag force is computed with shipWaterForce().

Cw

Drag coefficient for whale (dimensionless), used by whaleWaterForce() to estimate whale drag force. Defaults to 2.5e-3, for Reynolds number 2e7, computed from speed 2 m/s, lengthscale 5m which is chosen to be between radius and length, and viscosity 1e-6 m^2/s. The drag force is computed with whaleWaterForce().

logistic

a list containing logStressCenter and logStressWidth, which define an empirical logistic fit of an index of whale injury in observed strikes (ranging from 0 for no injury to 1 for fatal injury), as a function of the base-10 logarithm of compressive stress, as well as tau25, tau50 and tau75, which are the stresses in that fit that yield index values of 0.25, 0.50 and 0.75, respectively; these values set colour boundaries in plot.strike() plots that have which="threat".

file

Optional name a comma-separated file that holds all of the previous values, except Cs and Cw. If provided, then other parameters except Cs and Cw are ignored, because values are sought from the file. The purpose of this is in shiny apps that want to save a simulation framework. The file should be saved write.csv() with row.names=FALSE.

Value

A named list holding the parameters, with defaults and alternatives reconciled according to the system described above, along with some items used internally, including lsum, which is the sum of the values in l, and stressFromStrain(), a function created by stressFromStrainFunction() that computes compression force from engineering strain.

References

Campbell-Malone, Regina. "Biomechanics of North Atlantic Right Whale Bone: Mandibular Fracture as a Fatal Endpoint for Blunt Vessel-Whale Collision Modeling." PhD Thesis, Massachusetts Institute of Technology and Woods Hole Oceanographic Institution, 2007. doi:10.1575/1912/1817 .

Daoust, Pierre-Yves, Emilie L. Couture, Tonya Wimmer, and Laura Bourque. "Incident Report. North Atlantic Right Whale Mortality Event in the Gulf of St. Lawrence, 2017." Canadian Wildlife Health Cooperative, Marine Animal Response Society, and Fisheries and Oceans Canada, 2018. https://publications.gc.ca/site/eng/9.850838/publication.html.

Grear, Molly E., Michael R. Motley, Stephanie B. Crofts, Amanda E. Witt, Adam P. Summers, and Petra Ditsche. "Mechanical Properties of Harbor Seal Skin and Blubber - a Test of Anisotropy." Zoology 126 (2018): 137-44. doi:10.1016/j.zool.2017.11.002 .

Raymond, J. J. "Development of a Numerical Model to Predict Impact Forces on a North Atlantic Right Whale during Collision with a Vessel." University of New Hampshire, 2007. https://scholars.unh.edu/thesis/309/.

Author

Dan Kelley

Examples

parms <- parameters()
epsilon <- seq(0, 1, length.out = 100) # strain
sigma <- parms$stressFromStrain(epsilon) # stress
plot(epsilon, log10(sigma), xlab = "Strain", ylab = "log10(Stress [MPa])", type = "l")
mtext("Note sudden increase in stress, when bone compression starts")