ANSYS软件中修正剑桥模型的二次开发

ANSYS软件具有很强的非线性计算功能和前、后处理能力,是目前世界上最强大的通用分析程序之一。标准ANSYS程序中包含众多的材料本构模型,但尚缺少岩土工程数值计算中常用的修正剑桥模型。为扩展ANSYS在岩土工程领域的计算能力,利用二次开发工具UPFs和数据接口将修正剑桥模型连接到标准ANSYS程序中。二次开发的核心是本构模型子程序UMAT.F的编制。子程序的编写一方面要符合修正剑桥模型的本构关系式和弹塑性有限元计算的特点;另一方面变量名和输入输出格式必须和标准ANSYS程序一致。对二次开发后的ANSYS程序进行了典型算例的验证。结果表明,在ANSYS中加入修正剑桥模型的方法是可行的,可推广到ANSYS对于其他材料本构模型的二次开发中。     

Book reviews

The Cambridge Companion to Historical Archaeology. Dan Hicks and Mary C. Beaudry (Editors), 2006, Cambridge University Press, New York, New York, xvi + 404 pp., $80 (hardcover), $34.99 (paper).     

海口红黏土的结构性本构模型研究

土体结构性的数学模型是21世纪土力学的核心问题。由于土体微观结构的变化造成了重塑土与原状土的力学特性上的差异。采用应变型和应力型结构性宏观参数来表征这种微观结构的变化,同时将应变性结构性参数引入到等向固结过程中去,用以描述常规三轴试验中剪切前的等向固结过程以及剪切时球应力对结构性土体的影响。实现应变型和应力型结构性宏观参数对整个三轴剪切过程的描述。修正剑桥模型对正常固结重塑黏土的三轴压缩试验能做出准确地描述,但对超固结黏土及原状土,即具有结构地土体,则不能给出准确地描述。将应变型和应力型结构性宏观参数引入到修正剑桥模型中,实现修正剑桥模型的结构化。该结构性修正剑桥模型参数的确定方法与常规修正剑桥模型参数的确定方法相差不多,只不过多了球应力与土体结构性体应变的关系式、偏应力与土体结构性广义剪应变的关系式。经过数值模拟比较,结构性修正的剑桥模型能较好地反映原状土的结构性演化过程,能描述原状土结构的整个破坏过程,在多种应力路径下具有很好的预测作用。     

基于旋转运动硬化理论的修正剑桥模型的改进

修正剑桥模型是最早建立和得到广泛承认的经典土体弹塑性模型之一,但不能模拟应力路径转折时土体的应力-应变特性以及应力引起的各向异性。将旋转运动硬化理论引入到剑桥模型中,给出了椭圆屈服面的旋转运动硬化机制,在不增加任何模型参数的情况下,把等向硬化的修正剑桥模型扩展为旋转运动硬化模型。扩展的新模型既保留了单调加载时的等向硬化的特性,又能反映应力路径转折时土体的本构特性与应力诱发的各向异性,初步验证了模型的有效性。     

扩展剑桥模型参数的优化选择及其应用

在有限元计算中合理选取土的本构关系与模型参数,对于计算成果的可靠性是十分重要的。剑桥模型是一个应用广泛的弹塑性模型,其参数一般是通过室内试验来确定的。通过建立扩展剑桥模型在三轴条件下的弹塑性本构关系的表达式,并以此为依据,利用数值模拟常规三轴试验和单向压缩试验过程并利用正反分析技术优化求解剑桥模型参数,在小浪底大坝固结计算的应用中证明了这种方法的合理性与实用性。     

Notice of nodosaur (Dinosauria,Ankylosauria) remains from the mid-Cretaceous of Cambridge,England, with comments on cervical half-ring armour

Three pieces from cervical half-rings of an immature nodosaur, part of a nodosaurid presacral rod and some post-cranial osteoderms from the Cretaceous of Cambridge were studied at the Booth Museum of Natural History, Brighton, UK. Two of the three half-ring elements show dorsal ridge morphologies distinct from each other, and all three have unfused sutured lateral borders. It is possible they may be derived from the same animal. Comparison with other material from the Cretaceous of Europe, USA and Asia indicates the presence of a large nodosaurid in the Cambridge Greensand fauna, with cervical half-ring morphologies similar to North American taxa, but unlike any previously known from the European Cretaceous.     

基于广义位势理论的弹塑性模型的修正方法

广义位势理论为岩土材料的本构关系研究指出了更开阔的数学背景。基于广义位势理论可以构造出基于应力空间的模型,也可构造出基于应变空间的模型,利用两者之间的对称关系,把常规基于应力空间的模型直接转换到应变空间中,对本构模型自身无需做任何改动。基于广义位势理论也可以对已有的本构模型进行修正,比如,可基于广义位势理论对剑桥模型进行修正,这种修正可使模型利用三轴试验的部分成果,比单纯使用压缩试验的成果要好一些。另外,也初步探讨了模型的三维化问题。     

考虑初始结构性影响的吹填软土应力应变关系

正常沉积的土体一般具有结构性。目前土的本构模型大多数是以非结构性土为基础建立和发展起来的,用它们直接描述结构性土体应力应变关系与实际出入很大。本文以修正的剑桥模型为基础,建立了可考虑初始结构性影响的结构性吹填软土应力应变关系。与修正的剑桥模型相比,只增加了参数的个数,但参数种类不变,其值通过室内常规试验即可求得。对天津滨海新区吹填场地经过真空预压处理后有结构强度的吹填土体进行了三轴试验,通过试验值与模拟值分析比较,初步验证了本文建立的模型可以考虑吹填软土初始结构性影响。     

非饱和土剑桥模型的基本框架

分析了用有效应力原理和用两个应力变量建立非饱和土力学理论的区别与联系，借助于有效应力原理将饱和土的剑桥模型推广到非饱和土，并与现有的几种塑性模型作了对比分析。     

Soiling of limestone in an urban environment characterized by heavy vehicular exhaust emissions

The inorganic and organic chemical composition of weathering sulphate patinas on the limestone walls of Emmanuel College, Cambridge, UK, have been analysed by FT-IR spectroscopy, pyrolysis gas-chromatography/mass spectrometry and scanning electron microscopy. The College location is characterized by heavy vehicular exhaust emissions including those from diesel powered public transport vehicles due to its proximity to the main Cambridge coach station. A complex mixture of gaseous and particulate air pollutants are found deposited in the weathering patinas including organic compounds (such as PAHs), which represent markers for present-day vehicular pollution. Slight differences in composition between patinas collected at different heights on the building facades with, in particular, more evidence for a biogenic overprint in samples collected at roof level as opposed to ground (street) level are found. Analytical results confirm how building stones in urban areas acted in the past and still do today as passive repositories for any kind of gaseous and particulate air pollutant present in the surrounding atmosphere; accordingly, weathering patinas are slowly changing their composition to accommodate new classes of present-day air pollutants.     

Rapid expansion of a cylindrical cavity in a rate-type soil

An analytical solution for rapid (undrained) expansion of a long cylindrical cavity from initially zero radius is presented. A simple rate-type soil model possessing the salient features of the modified Cambridge critical state model is used. Application of the solution to determination of the stress field surrounding a pile immediately after driving is discussed.     

某国际机场试验区软基固结沉降的过程模拟

随着计算技术的发展与普及，土体的固结沉降数据解法已在实际工程中得到推广应用，并取得了较好效果。本文借助剑桥本构模式，对某国际机构试验区软基进行固结沉降的过程模拟研究，并对试验区不 均匀沉降作出评价。     

泥水盾构泥膜形成二维理论分析

在各种复杂环境下采用泥水盾构法修建隧道工程,需要解决在开挖面上如何及时形成安全有效的泥膜支护问题。采用修正的剑桥模型中正常固结黏土各向等压固结曲线规律,建立泥膜固含率与有效应力之间的关系,结合圆球形颗粒孔隙理想模型的渗透率以及泥膜固含率、渗透率和比阻三者之间的关系,确立新的泥膜形成本构关系模型。将泥膜形成一维模型拓展为二维模型,基于增量分析方法分析泥膜的增长规律,给出泥膜滤失量和厚度分别与位置、时间、重度比和盾构直径等因素的关系。结果表明,修正的剑桥模型能够较好地表征泥膜压缩固结特性;对于高压泥浆,泥浆重度对泥膜增长的影响较小,但对超大直径的盾构其影响不可忽略。     

砂井地基平面问题转换及其应用

考虑砂井地基的井阻和涂抹区效应，建立了轴对称砂井和平面砂墙之间渗透系数以及几何尺寸的关系式，使砂井地基等效成平面砂墙处理。采用修正剑桥模型的二维平面应变Biot(比奥特)固结有限元对一高速公路塑料排水板路基的沉降预测，显示结果与实测沉降结果比较接近。     

Knowledge makes the money go round: Conflicts of interest and corporate finance in London’s financial district

This paper argues that the conflicts of interest cases brought against Wall Street investment banks in the early 2000s were neither geographically nor institutionally isolated events. Rather, by combining recent work on financial knowledges in both economic geography and the social studies of finance with the growing interest in topological spatial imaginaries, I explore how London’s corporate finance industry was unable to distance itself from both the conflicts of interest allegations and the ensuing regulatory changes of the ‘Global Settlement’ in the US. Analysis of 36 semi-structured interviews conducted in London in the early 2000s is used to explore how a range of individual interests, institutional demands and structural changes within London’s financial district affected analysts’ ability to produce ‘objective’ research. As well as pointing to the problematic nature of certain aspects of knowledge rich ‘communities of practice’ [Wenger, E., 1998. Communities of practice: learning, meaning and identity. Cambridge University Press, Cambridge], I explore how the resulting contingent and situated nature of research practice is at odds with a weakly defined notion of ‘objective’ research that underpins the Financial Services Authority’s regulatory response.     

Edentulous pterosaurs from the Cambridge Greensand (Cretaceous) of eastern England with a review of Ornithostoma Seeley, 1871

A re-examination of fossil material from the Late Cretaceous Cambridge Greensand Member (CGM) of the West Melbury Marly Chalk Formation revealed a number of new specimens of edentulous pterosaur jaw fragments previously identified as shark fin spines and fish jaws and accessioned under the epithet ‘cestraciontid finray’ and ‘jaws of fish’. These are now recognised as pterosaurian jaw tips and referred to Ornithostoma sedgwicki Seeley, 1891 and Azhdarchoidea indet. This material increases the diversity of edentulous pterosaurs from the CGM.The edentulous pterosaur Ornithostoma sedgwicki Seeley, 1891 from the Cretaceous Cambridge Greensand of eastern England is reviewed. The holotype specimen is confirmed as a fragment of a premaxilla/maxilla of a non-tapejarid azhdarchoid on account of the conspicuous curvature of the dorsal and occlusal margins posteriorly and the presence of small neural foramina on the lateral margins. Neural foramina are not seen on jaws of members of the Pteranodontia, a group to which O. sedgwicki was included previously. The referral of O. sedgwicki to Azhdarchoidea eliminates the single known Lower Cretaceous occurrence of Pteranodontidae, restricting the temporal range of this taxon to the Upper Cretaceous. Postcranial material referred to O. sedgwicki from the type horizon is regarded as indeterminate Pterosauria.     

Dr Woodward's 350‐year legacy

Almost three hundred and fifty years ago, on 1 May 1667, in Draycott, Derbyshire, northern England, John Woodward was born. Although we know precious little about his early life, he left a legacy that has resonated down the centuries. In a letter written in 1723 to a physician friend, John Allen of Bridgewater, five years before he died, Woodward confided that ‘I have bequeathd … an Hundred & Fifty Pounds per annum to the University of Cambridge, which I intreat [sic] you to keep secret …’     

The transformation behaviour of bornite

Phase transformations in bornite have been observed dynamically by in situ experiments in a transmission electron microscope. A series of superstructure phases is formed with decreasing temperature and a new polymorph with a 3a supercell is described. Ordering behaviour with the formation of antiphase domains is proposed as an alternative to the generally accepted twinning mechanism for the transformation to the 2a type.Work carried out while on leave at Department of Mineralogy and Petrology, Cambridge     

Upper Wisconsinan submarine end moraines off Cape Ann,Massachusetts

Seismic profiles across the southwest end of Jeffreys Ledge, a bathymetric high north of Cape Ann, Massachusetts, reveal two end moraines. The moraines overlie upper Wisconsinan glacialmarine silty clay and are composed mostly of subaqueous ice-contact deposits and outwash. They were formed below sea level in water depths of as much as 120 m during fluctuations of a calving ice front. The moraines are late Wisconsinan in age and were formed after the Cambridge readvance, about 14,000 yr B.P., and before the Kennebunk readvance, about 13,000 yr B.P. They represent fluctuations of the ice front during overall retreat of Laurentide ice from the Gulf of Maine and New England.     

结构性吹填软土蠕变模型研究

以天津滨海新区吹填场地经过真空预压处理的吹填软土为试验材料,对原状土及其重塑土基本性质与蠕变特性进行了试验研究。试验结果表明：经过真空预压处理后的吹填软土同时具有结构性和蠕变性,结构性的存在,对土体蠕变具有重要的影响。在修正的剑桥模型的基础上,对其进行改进,使其考虑结构性的影响,并以此作为蠕变屈服函数,建立了考虑结构性影响的吹填软土半经验半理论蠕变模型。计算结果表明,该模型符合结构性吹填软土实际,可在工程实践中应用。