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Example to show how to use the lumped mass approach
This example is a modified/simplified version of one of the tests we made. As this example is meant to show how to use this new functionality only, I didn't check the results of the example case thoroughly.
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| Original file line number | Diff line number | Diff line change |
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| @@ -0,0 +1,74 @@ | ||
| import moorpy as mp | ||
| import os | ||
| import numpy as np | ||
| from moorpy.helpers import lines2subsystem, lines2ss | ||
| try: | ||
| import pickle5 as pickle | ||
| except: | ||
| import pickle | ||
| import matplotlib.pyplot as plt | ||
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| def JONSWAP(ws, Hs, Tp, Gamma=None): | ||
| '''JONSWAP function copied from RAFT | ||
| ''' | ||
| # If peak shape parameter gamma is not specified, use the recommendation | ||
| # from IEC 61400-3 as a function of Hs and Tp. For PM spectrum, use 1. | ||
| if not Gamma: | ||
| TpOvrSqrtHs = Tp/np.sqrt(Hs) | ||
| if TpOvrSqrtHs <= 3.6: | ||
| Gamma = 5.0 | ||
| elif TpOvrSqrtHs >= 5.0: | ||
| Gamma = 1.0 | ||
| else: | ||
| Gamma = np.exp( 5.75 - 1.15*TpOvrSqrtHs ) | ||
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| # handle both scalar and array inputs | ||
| if isinstance(ws, (list, tuple, np.ndarray)): | ||
| ws = np.array(ws) | ||
| else: | ||
| ws = np.array([ws]) | ||
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| # initialize output array | ||
| S = np.zeros(len(ws)) | ||
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| # the calculations | ||
| f = 0.5/np.pi * ws # wave frequencies in Hz | ||
| fpOvrf4 = pow((Tp*f), -4.0) # a common term, (fp/f)^4 = (Tp*f)^(-4) | ||
| C = 1.0 - ( 0.287*np.log(Gamma) ) # normalizing factor | ||
| Sigma = 0.07*(f <= 1.0/Tp) + 0.09*(f > 1.0/Tp) # scaling factor | ||
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| Alpha = np.exp( -0.5*((f*Tp - 1.0)/Sigma)**2 ) | ||
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| return 0.5/np.pi *C* 0.3125*Hs*Hs*fpOvrf4/f *np.exp( -1.25*fpOvrf4 )* Gamma**Alpha | ||
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| current_dir = os.path.dirname(os.path.abspath(__file__)) | ||
| ms = mp.System(os.path.join(current_dir, 'volturn_chain.dat')) | ||
| ms.initialize() | ||
| ms.solveEquilibrium() | ||
| # ms = lines2ss(ms) # For cases with multisegment lines, need to convert each of them to a subsystem | ||
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||
| # Updates the dynamic matrices of all the lines in the system. | ||
| # This function can only properly update the inertia, added mass, and stiffness matrices of each line. | ||
| # Though it updates the damping matrix, this is done considering unitary amplitude motions of the nodes and | ||
| # no fluid kinematics, so it is not correct. | ||
| ms.updateSystemDynamicMatrices() | ||
| M, A, B, K_dyn = ms.getCoupledDynamicMatrices() # Get the dynamic matrices of the system | ||
| K_qsA = ms.getCoupledStiffnessA(lines_only=True) # We can also compute the stiffness matrix without the lumped mass model. K_dyn should be similar to K_qsa | ||
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| # Get the dynamic tension along the line | ||
| line = ms.lineList[0] # Get the line object | ||
| RAO_data = pickle.load(open(os.path.join(current_dir, 'RAO_fl.pkl'), 'rb')) # Read the nFreq x 3 RAO matrix (nFreq x 4 complex numpy array, first column are the frequencies in rad/s) | ||
| RAO_fl = RAO_data[:, 1:] # Motion RAOs of the fairlead | ||
| w = RAO_data[:, 0] # Frequencies of the RAO data | ||
| Sw = JONSWAP(ws = w, Hs = 6, Tp = 8) # Arbitrary wave spectrum | ||
| T_nodes_amp, T_nodes_psd,T_nodes_std,s,r_static,r_dynamic,r_total,X = line.dynamicSolve(w, Sw, RAO_A=0,RAO_B=RAO_fl, depth=np.abs(line.rA[2])) | ||
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| fig, ax = plt.subplots(1, 1) | ||
| ax.plot(w, T_nodes_psd[:,-1], '-k') | ||
| ax.set_xlabel('Frequency (rad/s)') | ||
| ax.set_ylabel('PSD fairlead tension (N^2.s/rad)') | ||
| plt.show() |
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|---|---|---|
| @@ -0,0 +1,248 @@ | ||
| --------------------- MoorDyn Input File ------------------------------------ | ||
| MoorDyn input file | ||
| ----------------------- LINE TYPES ------------------------------------------ | ||
| TypeName Diam Mass/m EA BA/-zeta EI Cd Ca CdAx CaAx | ||
| (name) (m) (kg/m) (N) (N-s/-) (N-m^2) (-) (-) (-) (-) | ||
| chain 3.33000e-01 6.85000e+02 3.27000e+09 -1.00000e+00 0 1.11000e+00 8.20000e-01 2.00000e-01 2.70000e-01 | ||
| ---------------------- POINT PROPERTIES -------------------------------- | ||
| ID Type X Y Z Mass Volume CdA Ca | ||
| (#) (-) (m) (m) (m) (kg) (m^3) (m^2) (-) | ||
| 1 Vessel -5.80000e+01 0.00000e+00 -1.40000e+01 0.00000e+00 0.00000e+00 0.00000e+00 0.00000e+00 | ||
| 2 Fixed -8.37600e+02 0.00000e+00 -2.00000e+02 0.00000e+00 0.00000e+00 0.00000e+00 0.00000e+00 | ||
| ---------------------- LINES ---------------------------------------- | ||
| ID LineType AttachA AttachB UnstrLen NumSegs LineOutputs | ||
| (#) (name) (#) (#) (m) (-) (-) | ||
| 1 chain 2 1 8.50000e+02 50 - | ||
| ---------------------- OPTIONS ----------------------------------------- | ||
| 2 writeLog Write a log file | ||
| 0.001 dtM time step to use in mooring integration (s) | ||
| 3.0e6 kBot bottom stiffness (Pa/m) | ||
| 3.0e5 cBot bottom damping (Pa-s/m) | ||
| 1025.0 WtrDnsty water density (kg/m^3) | ||
| 200.0 WtrDpth water depth (m) | ||
| 1.0 dtIC time interval for analyzing convergence during IC gen (s) | ||
| 60.0 TmaxIC max time for ic gen (s) | ||
| 4.0 CdScaleIC factor by which to scale drag coefficients during dynamic relaxation (-) | ||
| 0.001 threshIC threshold for IC convergence (-) | ||
| ------------------------ OUTPUTS -------------------------------------------- | ||
| FAIRTEN1 | ||
| POINT1PX | ||
| POINT1PY | ||
| POINT1PZ | ||
| POINT1FX | ||
| POINT1FY | ||
| POINT1FZ | ||
| POINT1T | ||
| POINT2PX | ||
| POINT2PY | ||
| POINT2PZ | ||
| POINT2FX | ||
| POINT2FY | ||
| POINT2FZ | ||
| POINT2T | ||
| LINE1N0PX | ||
| LINE1N0PY | ||
| LINE1N0PZ | ||
| LINE1N0T | ||
| LINE1N1PX | ||
| LINE1N1PY | ||
| LINE1N1PZ | ||
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| END | ||
| ------------------------- need this line -------------------------------------- |