Existence for constrained dynamic Griffith fracture with a weak maximal dissipation condition

The study of dynamic fracture is based on the dynamic energy-dissipation balance. It is easy to see that this condition is always satisfied by a stationary crack together with a displacement satisfying the system of elastodynamics. Therefore to predict crack growth a further principle is needed. In this paper we introduce a weak maximal dissipation condition that, together with elastodynamics and energy balance, provides a model for dynamic fracture, at least within a certain class of possible crack evolutions. In particular, we prove the existence of dynamic fracture evolutions satisfying this condition, subject to smoothness constraints, and exhibit an explicit example to show that maximal dissipation can indeed rule out stationary cracks.     

催化裂化装置仿真器的开发

根据流化催化裂化装置开工、停工和生产操作动态数学模型,开发了既可用于培训、也可用于研究的催化裂化仿真器。其硬件包括个人微机、接口、模拟仪表盘和教员操作台。运用这种仿真器对操作工进行技术培训、能摸拟装置的开工、停工、生产操作调节、干扰调节及事故处理等过程,并可对催化裂化装置的操作性能、控制方法和优化等进行考察研究。这种仿真器具有较低的价格/性能值。     

热载体再生(烧碳)动力学特点

对热载体再生(烧碳)动力学进行了研究,结果表明,与一般裂化催化剂对比,热载体的再生动力学有三个特点:(1)动力学仍可用一级反应(对碳)模型处理,但在含碳量较高时,用表面反应模型拟合得更好;(2)经水热老化处理的热载体的再生速度比新鲜热载体快;(3)再生反应活化能较低.     

含磷铸铁闸瓦断裂原因的实验分析

本文通过实验，分析了含磷铸铁闸瓦的致断原因。结果表明，裂纹萌生于工作表面或次表面，由工作表面向背面扩展。在使用过程中，高磷灰铁闸瓦有严重的断裂现象，蠕化良好的含磷蠕墨铸铁闸瓦与没有明显铸造缺陷的中磷灰铁闸瓦在使用过程中不会发生断裂。     

催化裂化装置烟机入口管线失效分析

对催化裂化装置烟机入口管线在操作过程中出现的开裂或皱折进行了失效分析研究.结果表明.由于管材lCR18 Ni9Ti中的铁素体含量偏高,长期在700℃高温下工作.析出大量σ相.导致材料脆化.在分析的基础上提出了对管材进行固溶处理.提高焊接工艺.选用耐高温膨胀节等改进措施.     

CRCP加HMA加铺层荷载应力分析

CRCP加HMA加铺层路面结构以其良好的整体性、耐久性和行车舒适性 ,在道路铺装中得到了广泛的应用 .但是由于CRCP中有钢筋和横向裂缝的存在 ,使得对这种路面结构的应力计算困难较大 .使用有限元方法 ,对CRCP加HMA加铺层这种路面结构化简为平面应变问题进行分析 ,采用等参八结点四边形单元作为基本的单元对路面结构进行离散化 ,用组合单元法模拟钢筋的单向加劲作用 ,用裂缝单元模拟裂缝的传荷作用 .得出了裂缝间距和配筋率对路面结构应力的影响     

Kinetics of Oxidative Cracking of n-Hexane to Light Olefins using Lattice Oxygen of a VOx/SrO-γAl2O3 Catalyst

The kinetics of oxidative cracking of n-hexane to light olefins using the lattice oxygen of VO_x/SrO-γAl₂O₃ catalysts has been investigated. Kinetic experiments were conducted in a CREC Riser Simulator (CERC: Chemical Reactor Engineering Center), which mimics fluidized bed reactors. The catalyst's performance is partly attributed to the moderate interaction between active VO_x species and the SrO-γAl₂O₃ support. This moderate interaction serves to control the release of lattice oxygen to curtail deep oxidation. The incorporation of basic SrO component in the support also helped to moderate the catalyst's acidity to checkmate excessive cracking. Langmuir-Hinshelwood model was applied to formulate the rate equations. The intrinsic kinetic parameters were obtained by fitting the experimental data to the kinetic model using a nonlinear regression algorithm at a 95% confidence interval, implemented in MATLAB. n-Hexane transforms to olefins at a specific reaction rate of 1.33 mol/gcat.s and activation energy of 119.2 kJ/mol. These values when compared with other duplets (i. e., ki° and E_A) for paraffins to olefins, show that indeed olefins are stable products of the oxidative conversion of n-hexane over VO_x/SrO-γAl₂O₃ under a fluidized bed condition. Values of activation energy for all CO_x formation routes indicate that intermediate paraffins are likely to be cracked to form CH₄ than to be converted directly to CO_x. On the other hand, olefins may transform partly, and directly to CO_x (E₉=9.65 kJ/mol) than to form CH₄ (E₈=89.1 kJ/mol) in the presence of excess lattice oxygen. Overall, olefins appear to be stable to deep oxidation due to the role of SrO in controlling the amount of lattice oxygen of the catalyst at the reaction temperature.     

高熔点蜡合成技术的研究进展

高熔点蜡(熔点 > 80 ℃)具有高熔点、高稳定性、低针入度、低迁移率以及耐磨坚硬等特点,在食品化妆、材料加工、电子机械、国防航空以及医疗领域有着重要的应用。但目前市场上的蜡产品熔点(50–70 ℃)较低。而我国高熔点蜡和特种蜡的需求量日益增加,预计缺口将突破70万吨。本文详细综述国内外合成高熔点蜡(熔点 > 80 ℃)的技术和工艺,包括聚乙烯蜡、费托蜡和生物质基蜡等,尤其对工艺涉及的催化剂和反应机理等进行了分析。聚乙烯裂解制备具有成本低、可以有效解决“白色污染”等优点,并且可以直接利用现有的催化裂化装置。但这一过程需要在高温的苛刻条件下进行,得到的蜡产品碳数分布较广、杂质较多,性能和色泽等方面不如直接乙烯聚合工艺的蜡产品。乙烯聚合蜡工艺则主要受限于复杂的工艺和昂贵的茂金属及非茂金属的配合物催化剂。高熔点费托蜡虽然性能优异并且技术也逐渐成熟,但其不同熔点的产品是通过不同长度碳链的精馏得到,产品是混合碳链的烷烃,仍然存在相对较宽的熔程。虽然生物质基蜡的合成研究刚起步,但其产物碳数单一,具有更窄的熔程;在合成过程中可根据需求选取特殊官能团的生物质平台小分子,还可根据特殊的使用场景对产品进行官能团化等。更重要的是,生物质基高熔点蜡更加契合世界各国的能源绿色可再生化和低碳化政策。展望了高熔点合成蜡的未来发展趋势,以期促进新的工艺和技术路线的涌现。     

Leaning towers

Masonry, as a unilateral material, can resist compressive stresses but has feeble tensile strength. A masonry wall or tower, subjected to uneven foundation settlements, will crack, and these cracks may lead to overall structural collapse. Of particular interest is the leaning tower, in which a fissure (of a shape to be determined) develops progressively up to the point of critical stability. A practical rule is developed for the maximum inclination that may be regarded as safe for a masonry tower.

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Sommario La muratura, materiale a comportamento unilaterale, puo' sopportare sforzi di compressione ma ha una modesta resistenza a trazione. Una parete od una torre in muratura, soggette a cedimenti fondali, si fessurano e tali lesioni possono condurre al collasso globale. Un caso di particolare interesse e' quello di una torre inclinata nella quale una lesione (la cui forma e' da determinare) si sviluppa progressivamente fino al punto di stabilita' critica. Nel presente studio si sviluppa un criterio pratico di sicurezza per la massima inclinazione ammissibile per una torre in muratura.

     

新型螯合配体BPMPHD的质谱特性研究

通过质谱分析法、理论计算等首次对新型螯合配体BPMPHD的质谱特性进行了较系统的研究 ,并对其基峰、分子离子峰以及主要特征碎片离子形成的机制和规律进行了研讨