薄板样条法和泛克里金法在理论和应用方面的比较

研究插值方法以建立变量的数据场模型是科学计算可视化的重要内容。文中首先给出了薄板样条法和泛克里金法的插值原理,推导得出了泛克里金法的对偶形式,并论证了薄板样条法是泛克里金法的特例;然后对这两种方法在理论形式和实际应用方面进行了比较,得出的结论为泛克里金法的插值效果要优于薄板样条法的效果。     

浅析雷州半岛海域夏季溶解氧的分布特点

2012年7月对雷州半岛海域海水中溶解氧进行详细的调查和研究,同时测试其温度、盐度等水质指标,通过统计分析,得出流沙湾DO的分布特征,并与其它海区夏季的DO含量进行比较。结果显示:表层海水溶解氧均高于底层海水。雷州半岛海域的夏季DO含量相对其它海域较高,与长江口的夏季溶解氧含量最为接近,这说明海水受工业、养殖的污染程度较低。     

利用残缺样本声速重构声速剖面

用经验正交函数(experiential orthogonal functions,EOF)表示声速剖面受限于样本声速的测量深度,应用该方法重构声速剖面只能计算到样本中最浅剖面的深度。要想进行全海深声速剖面的重构,必须对残缺的样本声速进行合理地外延。为此,首先对样本中温度和盐度进行了外延,然后根据声速经验公式计算得到了全海深的样本声速。在此基础上,通过解多元方程组的办法求解经验正交函数系数达到了声速剖面重构的目的。结果表明,提出的声速剖面外延方法是有效的。另外,只要知道声速剖面变化较剧烈深度上的3个点的声速值就能重构声速剖面,对于文中的数据来说,重构的均方根误差可达到0.872 m/s;增加经验正交函数的阶数能提高重构精度,但5阶以上,阶数的继续增加对精度的提高将不会有显著的影响。     

低矮房屋屋面脉动风压的预测

利用实测手段研究结构表面风压时,因测点布置数量有限,整个风场面貌不能充分反映,通常用插值法,但直接对时间序列插值难以实现。基于POD技术并借鉴地理统计学中“网格化”思想,对各阶空间本征向量进行处理,引入克里金法插值方法,编制与Surfer软件接口的Matlab程序,利用Surfer软件强大空间插值功能,对结构表面各阶本征向量进行空间插值。通过对台风发生时实测得到的低矮房屋屋盖风压时序的预测及误差分析验证该方法的可行性。研究表明克里金法可弥补三角线性插值法无法外插测点连线范围以外数值的不足,在风压变化梯度较大区域具有优于距离反比法的预测效果。该方法具有较强的通用性,可广泛应用于风洞试验和现场实测。     

抛弃式光纤温深仪系统设计与实现

海水温度梯度是海洋调查、海洋研究的重要参数,抛弃式温度剖面测量系统(Expendable Bathy Thermograph,XBT)是一种可在测量船走航状态下进行海洋温度剖面测量的仪器,具有实时、快速和低成本的特点.传统XBT通常不使用深度传感器,而是根据探头入水时间利用经验公式推算所处深度,深度误差较大.文章介绍了...     

带插值最小二乘法在打印机色域边界描述中的应用研究

目前色域映射多在二维色相平面上进行,色域描述相应地转换为色调剖面上的边界线描述。 通过分析打印机色调剖面边界形状,结合考虑色域映射的精度和效率问题,提出了运用带插值条件的最小二乘模型分段拟合打印机色域边界。 实验结果表明:该技术的运用可以确保打印机色域边界的连续性,同时拟合效果也与分段线性插值方法很接近,从而保证了色域映射的精度,其最大的优势是提高了色域映射的效率,使色域映射的实施更加简单。     

基于K-means聚类分析与单经验正交函数回归法的南海声速剖面估计方法研究

基于遥感参数和Argo历史数据对水体声速剖面(Sound Speed Profile, SSP)进行重构,对单经验正交函数回归(single Empirical Orthogonal Function-regression, sEOF-r)法在南海的适用性进行了研究。由于南海动力活动的复杂性,SSP扰动相对复杂,同时海域内SSP样本稀疏,相关的SSP统计学估计方法在南海区域还难以有效应用。文章基于K-means对样本进行聚类分析,讨论南海海域正交经验函数模态的一致性。通过扩大重构实验网格解决样本稀疏的问题。利用经典的sEOF-r对南海SSP进行反演,对重构SSP的误差分析说明了该方法在南海海域应用的有效性。SSP重构的均方根误差为2.341 1 m·s^-1,较大误差主要出现在深度40～200 m,其原因是海域内混合层深度发生变化。实验证明在南海区域内利用遥感参数可以有效地估计SSP。     

基于C~1自然邻近插值的曲面拟合

以C~0连续non-Sibsonian插值作为三次单纯形Bernstein-Bézier多项式的基坐标,构造C1连续自然邻近插值函数。介绍了高阶连续函数的构建原理和性质。将C1连续自然邻近插值函数应用于曲面拟合场合,由于Voronoi图能够自动调整数据点分布不规则和密度不均匀在空间上的差异,即使对于散乱数据点,也能获得较好的拟合结果。     

CTD校准结果在海洋调查中的应用

CTD是用于自动测量海水电导率、温度和深度剖面的仪器,具有测量精度高、测量速度快、性能稳定、数据容量大等优点,是现场海水温度、盐度(电导率)和深度测量的主要手段.然而由于使用环境的特殊性和仪器自身的漂移,需要定期对其校准以保证测量数据的准确性和可靠性.本文着重阐述了CTD校准的必要性和校准结果的应用,为海洋调查人员进一步确保仪器测量的可靠性提供了保障.     

浅海孤立子内波对海洋声传播损失与声源定位的影响研究

孤立子内波是浅海大陆架海域普遍存在的水文现象,它的存在将改变海水稳定分层的声速、密度剖面,引起声场结构的改变。文中应用抛物方程方法研究二维与三维情况下浅海孤立子内波对声传播损失的影响,并研究孤立子内波的存在对水平阵波束形成定位的影响。通过仿真结果,对常规波束形成、MVDR及MUSIC等波束形成方法进行比较。     

基于STL模型投影轮廓的EPS连续切割技术

针对目前EPS连续切割技术轮廓数据不易直接获取、不同角度轮廓数据之间存在干扰的情况,提出了基于STL模型投影轮廓的EPS连续切割技术.该方法用等距的平行平面直接切分某个角度的STL模型,然后对获得的轮廓求并而得到该角度下的投影轮廓,并配合STL模型固定角度的旋转,获得STL模型各个角度的投影轮廓,最后处理投影轮廓、加工EPS模型.对简单多边形求并的算法作了详细的阐述,对模型的精度也作了简单的分析.实验结果表明,基于投影轮廓的EPS连续切割技术稳定、准确、高效地切割了EPS模型.     

Injection technique for generating accurate adsorption isotherm data using the elution by characteristic points method

With the use of the elution by characteristic points (ECP) method, the adsorption isotherms are rapidly determined from the diffusive part of an overloaded elution profile. However, very large injection volumes are required, which lead to extremely tailed rears of the injection profiles. The ECP method is based on a theory assuming rectangular injection profiles and can therefore not account for such profiles. Consequently, the use of the ECP method in the traditional way, with classical full-loop injections, results in serious errors on the determined adsorption isotherm parameters which has not been demonstrated until this study. Therefore, we developed and validated a new experimental injection method, here denoted the "cut-injection" technique where instead nearly rectangular injection profiles are generated. The result convincingly shows that adsorption isotherms acquired by using the new cut-injection technique nearly totally coincide with adsorption isotherms determined using the accurate reference methods.     

HDPE厚壁管挤出过程的模拟

本文对HDPE厚壁管的口模定型部分以及后面的冷却定径部分的流动和传热问题进行了分析,建立了数学物理模型。在凝固区两相模型中,提出了求解比热的新的处理方法。运用SIMPLER有限差分程序,结合新编制的子程序,得出了该区域的速度场、压力场及温度场。利用破裂强度值原理,求出了模头后面冷却定径套的长度,该值与文献[5]的实验值吻合较好。本文还通过改变各种工艺条件,得出HDPE熔体在所研究区域的各种场值,用以描述不同条件下的熔体流动情况及冷却情况,为挤出口模定型和冷却定径部分的设计及厚壁管的最佳工艺控制提供了理论基础。     

CFRP拉挤过程非稳态温度场数值模拟与FBG实时检测

碳纤维增强聚合物基复合材料的拉挤成型过程是动态的,其固化度与温度变化为强耦合关系。温度场是工艺过程控制关键之一。根据固化动力学和传热学理论,建立了非稳态温度场与固化动力学数学模型。通过差示扫描量热仪（DSC）分析计算出模型中固化动力学参数。采用有限元与有限差分相结合的方法,依据ANSYS求解耦合场的间接耦合法,编制了计算程序,对拉挤工艺不同工况CFRP内部非稳态温度场进行数值模拟。采用专门设计制作的铝毛细管封装的布拉格光栅光纤(FBG),排除了非温度应变的干扰。通过试验确定了FBG温度传感特性表征及FBG温度灵敏度系数值,保障了CFRP内部温度场实时动态检测的准确度。模拟与实验结果基本吻合,为取代传统试凑性实验,优化CFRP拉挤工艺提供了科学快捷的理论依据。      

Scale effect on flow and thermal boundaries in micro‐/nano‐channel flow using molecular dynamics–continuum hybrid simulation method

The molecular dynamics (MD)–continuum hybrid simulation method has been developed in two aspects in the present work: (1) The energy equation has been combined into the coupling method in order to obtain the hybrid temperature profile and (2) the coupling method has been improved by the local linearization to obtain a smoother parametric profile. The developed method is primarily validated by analytical solutions and full MD results. Then, it is employed to study the scale effect on the flow and thermal boundaries in micro‐/nano‐channel flow. The hybrid velocity and temperature profiles are obtained with the channel height (H) ranging from 60σ to 2014σ and the solid–liquid coupling (β) ranging from 0.1 to 50. Scale effect has shown strong influence on the boundaries. Obvious slip characteristics can be found in the profiles, i.e. velocity slip and temperature jump, when H is small and β is large. However, the results also show that the profiles can be well predicted to converge to the macroscale non‐slip/non‐jump analytical solutions when H is large enough, where the effect of β can be omitted and the slip characteristics disappear. Correlations of relative slip length, relative temperature jump and pressure gradient with H are fitted from the simulation results. Copyright © 2009 John Wiley & Sons, Ltd.     

An inverse model for optimisation of laser heat flux distributions in an automated laser tape placement process for carbon-fibre/PEEK

High power diode lasers have enabled higher placement rates to be achieved in automated tape placement (ATP) of thermoplastic-based composite materials. Laser ATP heads in published literature employ homogeneous linear or rectangular laser spots, however a variety of solutions are available to produce customised irradiance profiles. No efforts to date have investigated what a more ideal heat flux profile would be for laser ATP in terms of length and distribution. This paper describes a method to determine the required laser heat flux profiles to achieve desired heating zone temperature profiles by means of an inverse thermal model. A bonding model was implemented to assess the performance of various heating zone temperature profiles for placement at 400 mm/s. Short beam strengths from experimental trials (Stokes-Griffin and Compston, 2015) were used to validate the bonding model. A two-stepped heating profile was found to provide a good balance of increased strength with a small increase in power requirement.     

The analysis of a two-phase zone with condensation in a porous medium

The one-dimensional steady-state heat and mass transfer in a two-phase zone of a water-saturated porous medium is studied. The system consists of a sand-water-vapour mixture in a tube that is heated from above and cooled from below. Under certain conditions, a two-phase zone of both vapour and water exists in the middle of the tube. A model problem for the temperature and the liquid saturation profiles within this two-phase zone is formulated by allowing for an explicit temperature dependence for the saturation vapour pressure together with an explicit saturation dependence for the capillary pressure. A boundary-layer analysis is performed on this model in the asymptotic limit of a large vapour-pressure gradient. This asymptotic limit is similar to the large-activation-energy limit commonly used in combustion problems. In this limit, and in the outer region away from any boundary layers, it is shown that the temperature profile is slowly varying and that the corresponding saturation profile agrees very well with that obtained in the previous model of Udell [J. Heat Transfer 105 (1983) p. 485] where strict isothermal conditions were assumed. The condensation and evaporation occurring within the boundary layers near the edges of the two-phase zone is examined. Finally, an iterative method is described that allows the temperature profile in the two-phase zone to be coupled to the temperature profiles in the two single-phase zones consisting of either water or vapour. This allows for the computation of the locations of the edges of the two-phase zone within the tube. Numerical computations are performed with realistic values of the parameters.     

A method to estimate local deposition conditions using film profiles in features

A method to estimate the local partial pressures and temperature during low pressure chemical vapor deposition (LPCVD) proceses using film profile data is demonstrated using the chemistry of blanket tungsten deposition by the hydrogen reduction of tungsten hexafluoride. EVREST, the computer program which performs the estimates, uses EVOLVE, a physically based process simulator for ballistic transport and heterogeneous reactions in features on patterned wafers, to compute film profiles for a given set of deposition conditions. In order to validate the estimation method and to demonstrate EVREST, test calculations are performed using film profiles generated by EVOLVE instead of experimental scanning electron microscopy cross-sections. Calculated films profiles are compared with the generated film profiles (the data) and the simulated deposition conditions are adjusted using an algorithm based on Marquardt's method to minimize the sum of squared differences between points on the calculated and generated profiles. Test calculations confirm that film profiles in more than one feature can be used to improve the reliability of the partial pressure and temperature estimates.     

Pairwise Estimation of Multivariate Gaussian Process Models With Replicated Observations: Application to Multivariate Profile Monitoring

Profile monitoring is often conducted when the product quality is characterized by profiles. Although existing methods almost exclusively deal with univariate profiles, observations of multivariate profile data are increasingly encountered in practice. These data are seldom analyzed in the area of statistical process control due to lack of effective modeling tools. In this article, we propose to analyze them using the multivariate Gaussian process model, which offers a natural way to accommodate both within-profile and between-profile correlations. To mitigate the prohibitively high computation in building such models, a pairwise estimation strategy is adopted. Asymptotic normality of the parameter estimates from this approach has been established. Comprehensive simulation studies are conducted. In the case study, the method has been demonstrated using transmittance profiles from low-emittance glass. Supplementary materials for this article are available online.     

Thermal Resistance Formulation of Fourier Equation and Its Application in the Study of Inhomogeneous Materials and Inverse Problems

In this work, considering that all the thermal properties of a sample depend on the position, it is shown that the Fourier heat transport equation can be written in terms of just the square of the thermal effusivity, by introducing the thermal resistance as a new variable. The conditions, in which analytical solutions of this equation can be obtained, are discussed. Based on these results, an inversion method is proposed to retrieve the profile of the thermal property profiles, if the surface temperature is provided. The method requires the assumption of a local thermal-effusivity profile, such that the temperature profile can be analytically obtained, to generate a global thermal-effusivity profile, which is independent of the initial assumed profile. Applying this method to a pair of simple but representative cases of one-dimensional layered systems, the accuracy and stability of the method is verified. In particular, the noise sensitivity is investigated by carrying out the inversion procedure with white Gaussian noise added to the simulated experimental data. The proposed approach could be useful for the development of methodologies to interpret experimental data and to retrieve the in-depth variations of thermal properties of materials.