Updating MoorProps_default.yaml

- Using Brian's old code, reran numbers for mass, buoyancy, (and MBL) for chain and polyester
- - Masses of chain (studlink and studless) were similar to old coefficients
- - Had to adjust MBLs from Brian's numbers (d^2 term AND d term)
- - Updated chain dvol/dnom values (pretty close)
- Implemented the option for a user to specify either dvol/dnom, material density, or specific gravity
- - specific gravity was given in the polyester catalogs, and rather than try to calculate dvol from that, you can now just input the specific gravity
- - Updated mass and MBL of polyester (much different than before)
- Changed getLineProps in helpers.py to support the new dvol implementations
- Still need to update the EA and cost values for chain and polyester - (in progress)

moorpy/MoorProps_default.yaml

@@ -22,6 +22,9 @@
 #    EAd_MBL_Lm:     # dynamic stiffness per MBL per fraction of mean load (not %) [N/N] (aka or Krd_beta)
 #
 #    dvol_dnom :     # volume-equivalent diameter per nominal diameter [-]
+#    density   :     # density of the line material [kg/m^3] (e.g., chain density = 7850 kg/m^3)
+#    spec_grav :     # specific gravity of the line material [-] (relative to a reference density, usually water)
+#    NOTE: Only one of the above three variables can be used as input!
 #    
 #    cost_0    :     # cost offset [$/m]
 #    cost_d    :     # cost per diameter [$/m^2]
@@ -31,36 +34,43 @@
 #    cost_EA   :     # cost per stiffness [$/m/N]
 #    cost_MBL  :     # cost per MBL [$/m/N]
 
+# Chain Notes
+# - The MBLs between studless and studlink chains are the same, for every grade
+# - The masses between different grades of chain are the same (for now...different grades might correspond to different material densities)
+# - If the user needs a different grade of chain, they will have to add another section and include those properties here. This default file only considers R4 chain
+
+
 
 lineProps: 
 
-  chain       :            # R4 grade studless chain
-    mass_d2   :  19.9e3    # linear mass density per diameter^2 [kg/m^3]    
-    EA_d2     :  85.4e9    # stiffness per diameter^2 [N/m^2]    
-    MBL_d     :  66.72e6   # minimum breaking load per diameter [N/m]   
-    MBL_d2    : 482.2e6    # minimum breaking load per diameter^2 [N/m^2]   
-    dvol_dnom :   1.8      # volume-equivalent diameter per nominal diameter [-]    
-    cost_mass :   2.585    # cost per mass [$/kg]
-
+  water_density: 1025
+
+  chain       :     # R4 grade studless chain
+    mass_d2   :  20.01e3    # linear mass density per diameter^2 [kg/m^3]    
+    EA_d2     :  85.4e9     # stiffness per diameter^2 [N/m^2]    
+    MBL_d     :  37.34e6    # minimum breaking load per diameter [N/m]   
+    MBL_d2    : 602.47e6    # minimum breaking load per diameter^2 [N/m^2]   
+    dvol_dnom :   1.801     # volume-equivalent diameter per nominal diameter [-] (assumes 7,850 kg/m^3 material density)
+    cost_mass :   2.585     # cost per mass [$/kg]
 
-  chain_studlink :         # R4 grade studlink chain
-    mass_d2   :  19.9e3    # linear mass density per diameter^2 [kg/m^3]    
-    EA_d2     :  85.4e9    # stiffness per diameter^2 [N/m^2]    
-    MBL_d     :  66.72e6   # minimum breaking load per diameter [N/m]   
-    MBL_d2    : 482.2e6    # minimum breaking load per diameter^2 [N/m^2]   
-    dvol_dnom :   1.89     # volume-equivalent diameter per nominal diameter [-]    
-    cost_mass :   2.585    # cost per mass [$/kg]           
+
+  chain_studlink :  # R4 grade studlink chain
+    mass_d2   :  21.9e3     # linear mass density per diameter^2 [kg/m^3]    
+    EA_d2     :  85.4e9     # stiffness per diameter^2 [N/m^2]    
+    MBL_d     :  37.34e6    # minimum breaking load per diameter [N/m]   
+    MBL_d2    : 602.47e6    # minimum breaking load per diameter^2 [N/m^2]   
+    dvol_dnom :   1.885     # volume-equivalent diameter per nominal diameter [-] (assumes 7,850 kg/m^3 material density)
+    cost_mass :   2.585     # cost per mass [$/kg]           
 
-
-  polyester   :            # polyester synthetic rope
-    mass_d2   :  797.8     # linear mass density per diameter^2 [kg/m^3]    
-    #EA_d2     :  1.09e9    # stiffness per diameter^2 [N/m^2]    
-    MBL_d2    :  170.5e6   # minimum breaking load per diameter^2 [N/m^2]   
-    dvol_dnom :  0.86      # volume-equivalent diameter per nominal diameter [-]    
+
+  polyester   :     # polyester synthetic rope
+    mass_d2   :  678.75     # linear mass density per diameter^2 [kg/m^3]       
+    MBL_d2    :  308.2e6    # minimum breaking load per diameter^2 [N/m^2]     
     cost_MBL  :  1.65e-05  # cost per MBL [$/m/N]
     EA_MBL    :   14       # quasi-static stiffness per MBL [N/N]
     EAd_MBL   :   14       # dynamic stiffness per MBL [N/N]
     EAd_MBL_Lm :  0.34     # dynamic stiffness per MBL per fraction of mean load (not %) [N/N]
+    spec_grav :  1.38       # specific gravity of polyester used to calculate the volume-equivalent diameter, relative to the reference density of water [-]
 
   nylon       :            # nylon synthetic rope
     mass_d2   :  647.6     # linear mass density per diameter^2 [kg/m^3]

moorpy/helpers.py

@@ -679,13 +679,28 @@ def getLineProps(dnommm, material, lineProps=None, source=None, name="", rho=102
 
     # calculate the relevant properties for this specific line type
     mat = lineProps[material]       # shorthand for the sub-dictionary of properties for the material in question    
-    d = dnommm*0.001                # convert nominal diameter from mm to m    
-    d_vol = mat['dvol_dnom']*d    
+    d = dnommm*0.001                # convert nominal diameter from mm to m      
     mass = mat['mass_0'] + mat['mass_d']*d + mat['mass_d2']*d**2 + mat['mass_d3']*d**3 
     MBL  = mat[ 'MBL_0'] + mat[ 'MBL_d']*d + mat[ 'MBL_d2']*d**2 + mat[ 'MBL_d3']*d**3 
     EA   = mat[  'EA_0'] + mat[  'EA_d']*d + mat[  'EA_d2']*d**2 + mat[  'EA_d3']*d**3 + mat['EA_MBL']*MBL 
     cost =(mat['cost_0'] + mat['cost_d']*d + mat['cost_d2']*d**2 + mat['cost_d3']*d**3 
                          + mat['cost_mass']*mass + mat['cost_EA']*EA + mat['cost_MBL']*MBL)
+
+    # internally calculate the volumetric diameter using one of three options
+    if 'dvol_dnom' in mat and 'density' not in mat and 'spec_grav' not in mat:      # if only 'dvol_dnom' is specified in the source
+        d_vol = mat['dvol_dnom']*d                                          # [m]
+    elif 'density' in mat and 'dvol_dnom' not in mat and 'spec_grav' not in mat:    # if only 'density' is specified in the source
+        material_density = mat['density']                                   # [kg/m^3]
+        d_vol = np.sqrt((mass/material_density)*(4/np.pi))                  # [m]
+    elif 'spec_grav' in mat and 'dvol_dnom' not in mat and 'density' not in mat:    # if only 'spec_grav' is specified in the source
+        water_density = lineProps['water_density']                          # [kg/m^3]
+        print('Warning: Is this water density the same that is specified in MoorPy?')
+        material_density = (mat['spec_grav']/(water_density/1000))*1000     # [kg/m^3]
+        d_vol = np.sqrt((mass/material_density)*(4/np.pi))                  # [m]
+    else:
+        raise ValueError("Only one parameter can be specified to calculate the volumetric diameter. Choose either 'dvol_dnom', 'density', or 'spec_grav'")
+
+    # use the volumetric diameter to calculate the weight per unit length (could have also used mass, water density, and material density)
     w = (mass - np.pi/4*d_vol**2 *rho)*g
 
     # stiffness values for viscoelastic approach