102 lines
2.8 KiB
Python
102 lines
2.8 KiB
Python
"""
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FTCS (Forward-Time Centered-Space) explicit finite difference solver
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for the 1D heat equation with a movable point heat source:
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dT/dt = alpha * d²T/dx² + Q(t) * alpha / (k * dx) * delta(x - x_src)
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Boundary conditions (both ends Robin / convective):
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- x=0 (Robin): convective exchange with ambient
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- x=L (Robin): convective exchange with ambient
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Returns T_matrix of shape (NX, NT).
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"""
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import sys
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import os
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import numpy as np
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import pandas as pd
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sys.path.insert(0, os.path.dirname(os.path.dirname(os.path.abspath(__file__))))
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import config
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def solve():
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"""Run the FTCS solver and return (T_matrix, x_vals, t_vals).
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Returns
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-------
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T_matrix : np.ndarray, shape (NX, NT)
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x_vals : np.ndarray, shape (NX,)
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t_vals : np.ndarray, shape (NT,)
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"""
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alpha = config.ALPHA
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k = config.K
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L = config.L
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T0 = config.T0
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Q_val = config.Q_VAL
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t_step = config.T_STEP
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h = config.H_CONV
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T_amb = config.T_AMB
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T_end = config.T_END
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NX = config.NX
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NT = config.NT
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x_src = config.X_SRC
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x_vals = np.linspace(0.0, L, NX)
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t_vals = np.linspace(0.0, T_end, NT)
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dx = x_vals[1] - x_vals[0]
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dt = t_vals[1] - t_vals[0]
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r = alpha * dt / dx**2
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if r > 0.5:
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print(
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f"[FDM WARNING] Stability condition violated: "
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f"r={r:.4f} > 0.5 (dt={dt:.6g}, dx={dx:.6g}). "
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"Solution may diverge."
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)
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i_src = int(np.argmin(np.abs(x_vals - x_src)))
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robin_coeff = dx * h / k
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T_matrix = np.zeros((NX, NT), dtype=np.float64)
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T_matrix[:, 0] = T0
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T_cur = np.full(NX, T0, dtype=np.float64)
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for n in range(NT - 1):
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t_now = t_vals[n]
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T_new = T_cur.copy()
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# Interior FTCS (nodi 1 .. NX-2)
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T_new[1:-1] = T_cur[1:-1] + r * (T_cur[2:] - 2.0 * T_cur[1:-1] + T_cur[:-2])
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# Robin BC a x=0
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T_new[0] = (T_cur[1] + robin_coeff * T_amb) / (1.0 + robin_coeff)
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# Robin BC a x=L
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T_new[-1] = (T_cur[-2] + robin_coeff * T_amb) / (1.0 + robin_coeff)
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# Sorgente puntuale al nodo i_src — applicata dopo le BCs per non essere sovrascritta
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Q_now = Q_val if t_now >= t_step else 0.0
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T_new[i_src] += Q_now * alpha * dt / (k * dx)
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T_cur = T_new
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T_matrix[:, n + 1] = T_cur
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return T_matrix, x_vals, t_vals
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def save_csv(T_matrix, x_vals, t_vals, path: str) -> None:
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"""Save FDM solution to CSV with columns: x, t, T."""
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xs, ts = np.meshgrid(x_vals, t_vals, indexing="ij")
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df = pd.DataFrame({
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"x": xs.ravel(),
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"t": ts.ravel(),
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"T": T_matrix.ravel(),
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})
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os.makedirs(os.path.dirname(os.path.abspath(path)), exist_ok=True)
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df.to_csv(path, index=False)
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print(f"Salvato: {path} ({len(df)} righe)")
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