定义薄体区域特征值最小尺寸与最大尺寸之比 为狭长比。表1列出了不同狭长比下,边界点 和内点 上温度的计算结果。表2和表3分别给出了不同狭长比下, 点热流和 点温度梯度 的计算结果。表4给出了当狭长比 时,直线 上内点温度梯度的计算结果。图34描绘了当 时,边界点 处的热流与内点 点温度梯度 的收敛曲线。
  
表1表明,即使狭长比达到1.0E-10,本文在边界点与内点处的温度数值解与精确解仍十分地吻合。从表2可看出,当狭长比为1.0E-02时,常规边界元法所算得的边界点处的热流已开始失效,随着狭长比的继续减小,计算结果则完全失真。相比较,即使狭长比为1.0E-10,本文在边界点 处的热流数值解与精确解仍十分地接近。表明,本文方法求解狭长比达 的超薄涂层结构十分地有效。
从表3可看出,在计算内点温度梯度时,常规边界元法求解狭长比为1.0E-02的结构已失效,而本文算法可准确计算到狭长比为1.0E-10的结构。表4的数据进一步表明,本文方法对内点位置不加限制,即使狭长比为1.0E-09时,不同内点上的温度梯度的计算精度相近而且很高。图34的温度梯度 与热流误差曲线表明,即使狭长比达到1.0E-09,方法仍具有良好的收敛特性。
例2矩形涂层结构的热流问题,涂层的厚度为 ,基体的厚度为 ,宽度为 ,涂层与基体的导热率分别为 , ,边界条件如图45所示。将边界离散成40个线性单元,边界函数采用二次不连续插值逼近。
当涂层厚度 从1.0E-01~1.0E-10变化时,表5列出了边界点 处的热流数值解,图56与表6分别给出了内点 处的温度与梯度的计算结果。当涂层厚度 时,表7给出了直线 上内点处的梯度数值解,图7给出了内点 上的梯度 ,边界点 上的热流的收敛曲线。
从表5可看出,当涂层的厚度 时,常规边界元法在边界点 处的热流解的精度已经比较差,随着 的继续减小,结果则完全失真。相比较,即使 时,本文在边界点 处的热流解与精确解仍十分地吻合。
 
图56与表6的数据表明,当涂层厚度小到 时,常规边界元法的内点 处的温度数值解已经偏离精确解,内点 处的梯度数值解已完全失效。对厚度小到 的结构,本文在内点 处的温度与梯度数值解与精确解仍十分地接近。
图7的误差曲线表明,当涂层的厚度为 时,本文方法具有良好的收敛特性。
   
img3
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4结论
本文对涂层结构材料的温度场进行了研究,成功地计算了涂层表面的温度、热流及内点的温度、梯度。在关键的涂层域计算中,采用二次单元逼近几何边界,使得准确计算超薄的涂层结构成为可能;基于规则化边界积分方程计算奇异积分;对求内点物理量及边界量时产生的几乎奇异拟奇异积分,采用一类非线性变量替换法,有效地改善了几乎奇异拟奇异核的特性,使几乎奇异拟奇异积分的计算可以通过普通的高斯求积公式精确地完成。从算例可看出,即使对厚度小到 或者狭长比达 的涂层结构,本文方法依然可准确地求解。表明了方法的可行性和有效性。
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