基于Python的计算科学网格生成

wwtsj6pe  于 2023-03-16  发布在  Python
关注(0)|答案(4)|浏览(222)

我需要一个Python模块/包,提供一个网格,我可以在上面做计算科学?我不做图形,所以我不认为混合器包是我想要的。
有谁知道什么好货吗?

eqqqjvef

eqqqjvef1#

最有用的软件包可能是

此外,还有optimesh用于提高任何网格的质量。
(免责声明:我是pygmsh、pygalmesh、dmsh、meshzoo和optimesh的作者。)

wqnecbli

wqnecbli2#

如果你想在网格上求解FE或CFD类型的方程,你可以使用MeshPy在2维和3维上。Meshpy是现有工具tetgentriangle的很好的 Package 器。
如果你正在寻找更典型的图形风格的网格,在PyCon 2011 "Algorithmic Generation of OpenGL Geometry"上有一个有趣的演讲,它描述了一种实用的程序化网格生成方法。
如果您对根据数据重建表面感兴趣,那么您一定不能错过Standford 3D Scanning Repository,它是斯坦福大学Bunny的故乡

编辑:

一个无依赖性的替代方案可能是使用类似gmsh的东西,它是平台独立的,并且使用类似的工具在其后端进行meshpy。

iklwldmw

iklwldmw3#

这是改编自Kardontchik港口的代码

import numpy as np
from numpy import pi as pi
from scipy.spatial import Delaunay
import matplotlib.pylab as plt
from scipy.optimize import fmin
import matplotlib.pylab as plt

def ktrimesh(p,bars,pflag=0):
    # create the (x,y) data for the plot
    xx1 = p[bars[:,0],0]; yy1 = p[bars[:,0],1]
    xx2 = p[bars[:,1],0]; yy2 = p[bars[:,1],1]
    xmin = np.min(p[:,0])
    xmax = np.max(p[:,0])
    ymin = np.min(p[:,1])
    ymax = np.max(p[:,1])
    xmin = xmin - 0.05*(xmax - xmin)
    xmax = xmax + 0.05*(xmax - xmin)
    ymin = ymin - 0.05*(ymax - ymin)
    ymax = ymax + 0.05*(ymax - ymin)

    plt.figure()
    for i in range(len(xx1)):
        xp = np.array([xx1[i],xx2[i]])
        yp = np.array([yy1[i],yy2[i]])
        plt.plot(xmin,ymin,'.',xmax,ymax,'.',markersize=0.1)
        plt.plot(xp,yp,'k')
    plt.axis('equal')
    if pflag == 0:
        stitle = 'Triangular Mesh'
    if pflag == 1:
        stitle = 'Visual Boundary Integrity Check'
    #plt.title('Triangular Mesh')
    plt.title(stitle)
    plt.xlabel('x')
    plt.ylabel('y')
    plt.show()
    return 1

def ccw_tri(p,t):
    """
    orients all the triangles counterclockwise
    """
    # vector A from vertex 0 to vertex 1
    # vector B from vertex 0 to vertex 2
    A01x = p[t[:,1],0] - p[t[:,0],0]
    A01y = p[t[:,1],1] - p[t[:,0],1]
    B02x = p[t[:,2],0] - p[t[:,0],0]
    B02y = p[t[:,2],1] - p[t[:,0],1]
    # if vertex 2 lies to the left of vector A the component z of
    # their vectorial product A^B is positive
    Cz = A01x*B02y - A01y*B02x
    a = t[np.where(Cz<0)]
    b = t[np.where(Cz>=0)]
    a[:,[1,2]] = a[:,[2,1]]
    t = np.concatenate((a, b))
    return t

def triqual_flag(p,t):
    # a(1,0), b(2,0), c(2,1)
    a = np.sqrt((p[t[:,1],0] - p[t[:,0],0])**2 + (p[t[:,1],1] - p[t[:,0],1])**2)
    b = np.sqrt((p[t[:,2],0] - p[t[:,0],0])**2 + (p[t[:,2],1] - p[t[:,0],1])**2)
    c = np.sqrt((p[t[:,2],0] - p[t[:,1],0])**2 + (p[t[:,2],1] - p[t[:,1],1])**2)
    A = 0.25*np.sqrt((a+b+c)*(b+c-a)*(a+c-b)*(a+b-c))
    R = 0.25*(a*b*c)/A
    r = 0.5*np.sqrt( (a+b-c)*(b+c-a)*(a+c-b)/(a+b+c) )
    q = 2.0*(r/R)
    min_edge = np.minimum(np.minimum(a,b),c)
    min_angle_deg = (180.0/np.pi)*np.arcsin(0.5*min_edge/R)
    
    min_q = np.min(q)
    min_ang = np.min(min_angle_deg)
    return min_q, min_ang

def triqual(p,t,fh,qlim=0.2):
    # a(1,0), b(2,0), c(2,1)
    a = np.sqrt((p[t[:,1],0] - p[t[:,0],0])**2 + (p[t[:,1],1] - p[t[:,0],1])**2)
    b = np.sqrt((p[t[:,2],0] - p[t[:,0],0])**2 + (p[t[:,2],1] - p[t[:,0],1])**2)
    c = np.sqrt((p[t[:,2],0] - p[t[:,1],0])**2 + (p[t[:,2],1] - p[t[:,1],1])**2)
    A = 0.25*np.sqrt((a+b+c)*(b+c-a)*(a+c-b)*(a+b-c))
    R = 0.25*(a*b*c)/A
    r = 0.5*np.sqrt( (a+b-c)*(b+c-a)*(a+c-b)/(a+b+c) )
    q = 2.0*(r/R)
    pmid = (p[t[:,0]] + p[t[:,1]] + p[t[:,2]])/3.0
    hmid = fh(pmid)
    Ah = A/hmid
    Anorm = Ah/np.mean(Ah)
    min_edge = np.minimum(np.minimum(a,b),c)
    min_angle_deg = (180.0/np.pi)*np.arcsin(0.5*min_edge/R)
    
    plt.figure()
    plt.subplot(3,1,1)
    plt.hist(q)
    plt.title('Histogram;Triangle Statistics:q-factor,Minimum Angle and Area')
    plt.subplot(3,1,2)
    plt.hist(min_angle_deg)
    plt.ylabel('Number of Triangles')
    plt.subplot(3,1,3)
    plt.hist(Anorm)
    plt.xlabel('Note: for equilateral triangles q = 1 and angle = 60 deg')
    plt.show()

    indq = np.where(q < qlim)  # indq is a tuple: len(indq) = 1
    if list(indq[0]) != []:
        print ('List of triangles with q < %5.3f and the (x,y) location of their nodes' % qlim)
        print ('')
        print ('q     t[i]      t[nodes]         [x,y][0]       [x,y][1]       [x,y][2]')
        for i in indq[0]:
            print ('%.2f  %4d  [%4d,%4d,%4d]     [%+.2f,%+.2f]  [%+.2f,%+.2f]  [%+.2f,%+.2f]' % \
              (q[i],i,t[i,0],t[i,1],t[i,2],p[t[i,0],0],p[t[i,0],1],p[t[i,1],0],p[t[i,1],1],p[t[i,2],0],p[t[i,2],1]))
        print ('')
        # end of detailed data on worst offenders    
    return q,min_angle_deg,Anorm

class Circle:
    def __init__(self,xc,yc,r):
        self.xc, self.yc, self.r = xc, yc, r
    def __call__(self,p):
        xc, yc, r = self.xc, self.yc, self.r
        d = np.sqrt((p[:,0] - xc)**2 + (p[:,1] - yc)**2) - r
        return d

class Rectangle:
    def __init__(self,x1,x2,y1,y2):
        self.x1, self.x2, self.y1, self.y2 = x1,x2,y1,y2
    def __call__(self,p):
        x1,x2,y1,y2 = self.x1, self.x2, self.y1, self.y2
        d1 = p[:,1] - y1    # if p inside d1 > 0
        d2 = y2 - p[:,1]    # if p inside d2 > 0
        d3 = p[:,0] - x1    # if p inside d3 > 0
        d4 = x2 - p[:,0]    # if p inside d4 > 0
        d =  -np.minimum(np.minimum(np.minimum(d1,d2),d3),d4)
        return d

class Polygon:
    def __init__(self,verts):
        self.verts = verts
    def __call__(self,p):
        verts = self.verts
        # close the polygon
        cverts = np.zeros((len(verts)+1,2))
        cverts[0:-1] = verts
        cverts[-1] = verts[0]
        # initialize
        inside = np.zeros(len(p))
        dist = np.zeros(len(p))
        Cz = np.zeros(len(verts))  # z-components of the vectorial products
        dist_to_edge = np.zeros(len(verts))
        in_ref = np.ones(len(verts))
        # if np.sign(Cz) == in_ref then point is inside
        for j in range(len(p)):
            Cz = (cverts[1:,0] - cverts[0:-1,0])*(p[j,1] - cverts[0:-1,1]) - \
                 (cverts[1:,1] - cverts[0:-1,1])*(p[j,0] - cverts[0:-1,0])
            dist_to_edge = Cz/np.sqrt( \
                (cverts[1:,0] - cverts[0:-1,0])**2 + \
                (cverts[1:,1] - cverts[0:-1,1])**2)

            inside[j] = int(np.array_equal(np.sign(Cz),in_ref))
            dist[j] = (1 - 2*inside[j])*np.min(np.abs(dist_to_edge))
        return dist

class Union:
    def __init__(self,fd1,fd2):
        self.fd1, self.fd2 = fd1, fd2
    def __call__(self,p):
        fd1,fd2 = self.fd1, self.fd2
        d = np.minimum(fd1(p),fd2(p))
        return d

class Diff:
    def __init__(self,fd1,fd2):
        self.fd1, self.fd2 = fd1, fd2
    def __call__(self,p):
        fd1,fd2 = self.fd1, self.fd2
        d = np.maximum(fd1(p),-fd2(p))
        return d

class Intersect:
    def __init__(self,fd1,fd2):
        self.fd1, self.fd2 = fd1, fd2
    def __call__(self,p):
        fd1,fd2 = self.fd1, self.fd2
        d = np.maximum(fd1(p),fd2(p))
        return d

class Protate:
    def __init__(self,phi):
        self.phi = phi
    def __call__(self,p):
        phi = self.phi
        c = np.cos(phi)
        s = np.sin(phi)
        temp = np.copy(p[:,0])
        rp = np.copy(p)
        rp[:,0] = c*p[:,0] - s*p[:,1]
        rp[:,1] = s*temp + c*p[:,1]
        return rp

class Pshift:
    def __init__(self,x0,y0):
        self.x0, self.y0 = x0,y0
    def __call__(self,p):
        x0, y0 = self.x0, self.y0
        p[:,0] = p[:,0] + x0
        p[:,1] = p[:,1] + y0
        return p

def Ellipse_dist_to_minimize(t,p,xc,yc,a,b):
    x = xc + a*np.cos(t)    # coord x of the point on the ellipse
    y = yc + b*np.sin(t)    # coord y of the point on the ellipse
    dist = (p[0] - x)**2 + (p[1] - y)**2
    return dist

class Ellipse:
    def __init__(self,xc,yc,a,b):
        self.xc, self.yc, self.a, self.b = xc, yc, a, b
        self.t, self.verts = self.pick_points_on_shape()

    def pick_points_on_shape(self):
        xc, yc, a, b = self.xc, self.yc, self.a, self.b        
        c = np.array([xc,yc])
        t = np.linspace(0,(7.0/4.0)*pi,8)
        verts = np.zeros((8,2))
        verts[:,0] = c[0] + a*np.cos(t)
        verts[:,1] = c[1] + b*np.sin(t)
        return t, verts
        
    def inside_ellipse(self,p):
        xc, yc, a, b = self.xc, self.yc, self.a, self.b
        c = np.array([xc,yc])
        r, phase = self.rect_to_polar(p-c)
        r_ellipse = self.rellipse(phase)
        in_ref = np.ones(len(p))
        inside = 0.5 + 0.5*np.sign(r_ellipse-r)
        return inside

    def rect_to_polar(self,p):
        r = np.sqrt(p[:,0]**2 + p[:,1]**2)
        phase = np.arctan2(p[:,1],p[:,0])
        # note: np.arctan2(y,x) order; phase in +/- pi (+/- 180deg)
        return r, phase

    def rellipse(self,phi):
        a, b = self.a, self.b
        r = a*b/np.sqrt((b*np.cos(phi))**2 + (a*np.sin(phi))**2)
        return r

    def find_closest_vertex(self,point):
        t, verts = self.t, self.verts
        
        dist = np.zeros(len(t))
        for i in range(len(t)):
            dist[i] = (point[0] - verts[i,0])**2 + (point[1] - verts[i,1])**2
        ind = np.argmin(dist)
        t0 = t[ind]
        return t0   
    
    def __call__(self,p):
        xc, yc, a, b = self.xc, self.yc, self.a, self.b
        t, verts = self.t, self.verts
        dist = np.zeros(len(p))
        inside = self.inside_ellipse(p)
        for j in range(len(p)):
            t0 =  self.find_closest_vertex(p[j])  # initial guess to minimizer
            opt = fmin(Ellipse_dist_to_minimize,t0, \
                       args=(p[j],xc,yc,a,b),full_output=1,disp=0)
            # add full_output=1 so we can retrieve the min dist(squared)
            # (2nd argument of opt array, 1st argument is the optimum t)
            min_dist = np.sqrt(opt[1])
            dist[j] = min_dist*(1 - 2*inside[j])
        return dist

def distmesh(fd,fh,h0,xmin,ymin,xmax,ymax,pfix,ttol=0.1,dptol=0.001,Iflag=1,qmin=1.0):
    geps = 0.001*h0; deltat = 0.2; Fscale = 1.2
    deps = h0 * np.sqrt(np.spacing(1))

    random_seed = 17

    h0x = h0; h0y = h0*np.sqrt(3)/2  # to obtain equilateral triangles
    Nx = int(np.floor((xmax - xmin)/h0x))
    Ny = int(np.floor((ymax - ymin)/h0y))
    x = np.linspace(xmin,xmax,Nx)
    y = np.linspace(ymin,ymax,Ny)
    # create the grid in the (x,y) plane
    xx,yy = np.meshgrid(x,y)
    xx[1::2] = xx[1::2] + h0x/2.0   # shifts even rows by h0x/2
    p = np.zeros((np.size(xx),2))
    p[:,0] = np.reshape(xx,np.size(xx))
    p[:,1] = np.reshape(yy,np.size(yy))

    p = np.delete(p,np.where(fd(p) > geps),axis=0)

    np.random.seed(random_seed)
    r0 = 1.0/fh(p)**2
    p = np.concatenate((pfix,p[np.random.rand(len(p))<r0/max(r0),:]))

    pold = np.inf
    Num_of_Delaunay_triangulations = 0
    Num_of_Node_movements = 0  # dp = F*dt

    while (1):
        Num_of_Node_movements += 1
        if Iflag == 1 or Iflag == 3:  # Newton flag
            print ('Num_of_Node_movements = %3d' % (Num_of_Node_movements))
        if np.max(np.sqrt(np.sum((p - pold)**2,axis = 1))) > ttol:
            Num_of_Delaunay_triangulations += 1
            if Iflag == 1 or Iflag == 3:   # Delaunay flag
                print ('Num_of_Delaunay_triangulations = %3d' % \
                      (Num_of_Delaunay_triangulations))
            pold = p
            tri = Delaunay(p)  # instantiate a class
            t = tri.vertices
            pmid = (p[t[:,0]] + p[t[:,1]] + p[t[:,2]])/3.0
            t = t[np.where(fd(pmid) < -geps)]
            bars = np.concatenate((t[:,[0,1]],t[:,[0,2]], t[:,[1,2]]))
            bars = np.unique(np.sort(bars),axis=0)
            if Iflag == 4:
                min_q, min_angle_deg = triqual_flag(p,t)
                print ('Del iter: %3d, min q = %5.2f, min angle = %3.0f deg' \
                      % (Num_of_Delaunay_triangulations, min_q, min_angle_deg))
                if min_q > qmin:
                    break
            if Iflag == 2 or Iflag == 3:
                ktrimesh(p,bars)

        # move mesh points based on bar lengths L and forces F
        barvec = p[bars[:,0],:] - p[bars[:,1],:]
        L = np.sqrt(np.sum(barvec**2,axis=1))
        hbars = 0.5*(fh(p[bars[:,0],:]) + fh(p[bars[:,1],:]))
        L0 = hbars*Fscale*np.sqrt(np.sum(L**2)/np.sum(hbars**2))
        F = np.maximum(L0-L,0)
        Fvec = np.column_stack((F,F))*(barvec/np.column_stack((L,L)))
        Ftot = np.zeros((len(p),2))
        n = len(bars)
        for j in range(n):
            Ftot[bars[j,0],:] += Fvec[j,:]  # the : for the (x,y) components

            Ftot[bars[j,1],:] -= Fvec[j,:]
            
        # force = 0 at fixed points, so they do not move:
        Ftot[0: len(pfix),:] = 0

        # update the node positions
        p = p + deltat*Ftot

        # bring outside points back to the boundary
        d = fd(p); ix = d > 0   # find points outside (d > 0)
        dpx = np.column_stack((p[ix,0] + deps,p[ix,1]))
        dgradx = (fd(dpx) - d[ix])/deps
        dpy = np.column_stack((p[ix,0], p[ix,1] + deps))
        dgrady = (fd(dpy) - d[ix])/deps
        p[ix,:] = p[ix,:] - np.column_stack((dgradx*d[ix], dgrady*d[ix]))

        # termination criterium: all interior nodes move less than dptol:

        if max(np.sqrt(np.sum(deltat*Ftot[d<-geps,:]**2,axis=1))/h0) < dptol:
            break

    final_tri = Delaunay(p)  # another instantiation of the class
    t = final_tri.vertices
    pmid = (p[t[:,0]] + p[t[:,1]] + p[t[:,2]])/3.0
    # keep the triangles whose geometrical center is inside the shape
    t = t[np.where(fd(pmid) < -geps)]
    bars = np.concatenate((t[:,[0,1]],t[:,[0,2]], t[:,[1,2]]))
    # delete repeated bars
    #bars = unique_rows(np.sort(bars))
    bars = np.unique(np.sort(bars),axis=0)
    # orient all the triangles counterclockwise (ccw)
    t = ccw_tri(p,t)
    # graphical output of the current mesh
    ktrimesh(p,bars)
    triqual(p,t,fh)
    return p,t,bars

def boundary_bars(t):
    # create the bars (edges) of every triangle
    bars = np.concatenate((t[:,[0,1]],t[:,[0,2]], t[:,[1,2]]))
    # sort all the bars
    data = np.sort(bars)
    # find the bars that are not repeated
    Delaunay_bars = dict()
    for row in data:
        row = tuple(row)
        if row in Delaunay_bars:
            Delaunay_bars[row] += 1
        else:
            Delaunay_bars[row] = 1
    # return the keys of Delaunay_bars whose value is 1 (non-repeated bars)
    bbars = []
    for key in Delaunay_bars:
        if Delaunay_bars[key] == 1:
            bbars.append(key)
    bbars = np.asarray(bbars)
    return bbars   

def plot_shapes(xc,yc,r):
    # circle for plotting
    t_cir = np.linspace(0,2*pi)
    x_cir = xc + r*np.cos(t_cir)
    y_cir = yc + r*np.sin(t_cir)

    plt.figure()
    plt.plot(x_cir,y_cir)
    plt.grid()
    plt.title('Shapes')
    plt.xlabel('x')
    plt.ylabel('y')
    plt.axis('equal')
    #plt.show()
    return

plt.close('all')

xc = 0; yc = 0; r = 1.0

x1,y1 = -1.0,-2.0
x2,y2 = 2.0,3.0

plot_shapes(xc,yc,r)

xmin = -1.5; ymin = -1.5
xmax = 1.5; ymax = 1.5
h0 = 0.4 

pfix = np.zeros((0,2))   # null 2D array, no fixed points provided

fd = Circle(xc,yc,r)

fh = lambda p: np.ones(len(p))

p,t,bars = distmesh(fd,fh,h0,xmin,ymin,xmax,ymax,pfix,Iflag=4)
8cdiaqws

8cdiaqws4#

我推荐使用NumPy(特别是如果你以前用过MATLAB的话),许多用python工作的计算科学家/机械工程师可能会同意,但我有偏见,因为我发现它在我去年的研究中占据了很大一部分,它是SciPy的一部分:Link我很喜欢numpy.linspace(a,b,N),它可以生成一个长度为N的向量,这些向量的值从a到B是等间距的。您可以使用numpy.ndarray生成一个N x M矩阵,或者如果您想要二维数组,则使用numpy.meshgrid

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