FLOW3D铸造_进阶培训_数值

U n+1
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Incremental Solution Steps增量解决方案的步骤
Solution at each time step only approximates the true solution. Smaller time step sizes and tighter convergence make the numerical solution more accurate.在每个时间步解决方案的唯一接近的解决办法。更小的时间步长和更紧密的融合，使更
敛在一个时间步长到所需的解决方案国家-由于不是太大的时间步长或流量的迅速变化。在这种情况下，重要的 是解决方案能够在随后的恢复时间步
recovery恢复
no recovery
没有恢复
If convergence fails but the solution stays within the convergence area, then it can catch up with the desired solution in a few time steps.
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认识收敛失败
图形用户界面的模拟选项卡提供了一个模拟进展情况的界面，它包括收敛速度（迭代次数）和 收敛程度(epsi and residual).
收敛失败
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收敛失败诊断
pressure iteration did not converge in itmax= 1000 iterations压力迭代不衔接itmax = 1000迭代
动量方程解决了使用上的时间步长n已知的解决办法获取时间步长为n +1的速度第一猜想：
The corrector step iteratively adjusts pressure and velocities to satisfy the continuity equation, which for the incompressible flow is the zero velocity divergence condition: div u = 0.校正步骤的反复调整的压力和速度，以满足连续性方程，对不可压缩流动速度是零分
占用更多的内存;
最有可能不是为了恢复收敛失败 .
SOR 求解: 收敛变化速率间的问题,可能非常慢； parallel scaling is uninspiring; 占用最少量的内存 ; recovers well from failures.
ADI solver: convergence rate better than SOR, but slower than GMRES; parallel scaling is poor; usually recovers from failures, but not always; is not generally recommended unless prompted by the preprocessor in cases of large cell aspect ratios or periodic mesh boundaries.
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Signs of Poor Convergence差收敛的迹象
Poor pressure convergence results in significant non-zero velocity divergence field, which in turn translates into an unphysical numerical compressibility of the metal. Persistent failures may also result in an unstable solution.可怜的压力重要的非收
骤都必须留在解决这方面的衔接，在校 正步骤
t
true solution真正的解决办法 numerical solution数值解
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压力收敛失败排除
Sometimes pressure iterations may not converge during a time step to the desired solution state – due to either too large a time step size or rapid changes in the flow. In that case, it is important for the solution to be able to recover during the subsequent time steps.有时压力的迭代不收
cpu --clock -----
22 4.99E-04/cz 2.79E-04 3.29E+01 3.4E-01 5.3E+01 17:24:16 23 4.57E-04/cz 4.57E-04 6.81E+01 2.1E-01 7.1E+01 17:24:34 20 4.54E-04/cz 4.54E-04 1.03E+02 2.1E-01 8.6E+01 17:24:49
VOF solvers - available options可用选项 VOF求解 - volume conservation体积守恒 - volume errors体积误差 Implicit options
隐式选项
- implicit/explicit approximations隐式/显式 - time step stability controls时间步长的稳定控制 - implicit solvers隐式求解 - pressure convergence failures压力收敛失败原因 - convective flux failures对流失败原因 - diagnostic output诊断输出信息
歧条件：
Once complete, the corrector step provides the new solution for pressure and velocity at V n+1 time step n+1.一旦完成，校正步骤提供了时间步长n +1的压力和速度的新解决方案
P n+1
1.62E-02
51
23 4.53E-04/cz 4.53E-04 1.38E+02 2.1E-01 1.0E+02 17:25:04
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压力迭代次数: 步长的预测校正
Predictor step solves the momentum equation using the known solution from the previous time step n to obtain the first guess for the velocity for time step n+1:预估步
b. repeat if fails again;重复如果再次失败 c. if still fails after three tries, continue with the simulation and increment the failure counter.如果仍然不能三次尝试后，继续
进行模拟和失败计数器递增。
failure失败 counter
A typical convergence failure is when the solution has not converged in a certain number of iterations – default or user defined. The solver will take one of the following actions:一个典型
求解信息文件
at t= 2.1063E-01 cycle=
1302 block= 1 epsi= 5.6360E-01 resid= 5.6433E-01 delt=6.03465E-06 nocon= 11
time时间
time-step时间步长 convergence收敛 iteration迭代(法), 循环 time step number数字 criterion标准 residual剩余的 size大小
GMRES 求解 (默认): • •
•
fast convergence for a wide range of problems;快速收敛的广泛的问题 scales well on shared-memory computers (SMP);
规模以及对共享内存的计算机处理（SMP
ቤተ መጻሕፍቲ ባይዱ
•
• • • • • • • • •
pressure iteration did not converge in itmax= 1000 iterations压力迭代不衔接itmax = 1000迭代 at t= 4.1523E-01 cycle= 2308 block= 1 epsi= 3.7088E-01 resid= 1.8004E+00 delt=9.14405E-06 restarting cycle with smaller time step重新启动与更小的时间周期步
数值选项
实用选项 常遇问题 诊断细目
U in 1 U in t
n 1 n 1 P i 1 P i x
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内容
Pressure solvers
压力求解
- available options可用选项 - convergence control收敛控制
的收敛失败时，没有融合的解决方案在一定数目的迭代-默认或用户自定义。规划求解将采取以下行动之一
1. 2.
resid < 2.0* epsi resid > 2.0* epsi
减少大小两个循环
- no action, continue with the simulation不采取行动，继续与仿真 - a. restart cycle with time step size cut by two:重新启动的时间逐步
Diagnostics 诊断
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图形用户界面
每个选项组都有默认的选择，尽可能使用默认设置。
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压力迭代
对于不可压缩流体压力方程式，必须保持近似隐式求解数值的稳定性。
因此，压力求解在每一时间步长是反复的迭代的。在FLOW-3D中有三种迭代方法可以 利用。每一方法都有其优缺点，一个理想的方法是：
和解决两端以外地区的融合，这样，它可能永远不会恢复 和产生非物理结果。
For the SOR pressure solver, the convergence area is the largest.
对于长远发展策略的压力求解，收敛面积最大的
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压力求解
如果失败，但融合的解决方案融合区域内停留，便可以赶 上在几个步骤，时间所需的解决方案
If convergence fails and the solution ends up outside the convergence area, then it may never recover and produce unphysical results.如果收敛失败
准确的数值解
time
corrector step校正步骤 predictor step预测步骤 n n+1 convergence area: the predictor step must stay within this area for the solution to converge in the corrector step融合领域：预测步
1. 2. 3.
大多数时间易于收敛 收敛快速 收敛失败易于恢复
给定时间步长的迭代 (或循环)
t --3.85E-03 7.99E-03 1.21E-02 cycle iter ----- ---22 33 42 dtstbl/code ----------delt ---vl -epsi ----
求解的输出信息