Molecular Dynamics Simulation of Barnacle Cement

Barnacle cement is an underwater adhesive that is used for permanent settlement. Its main components are insoluble protein complexes that have not been fully studied. In present article, we chose two proteins of barnacle cement for study, 36-KD protein and Mrcp-100K protein. In order to investigate the characteristic of above two proteins, we introduced the method of molecular modeling. And the simulation package GROMACS was used to simulate the behavior of these proteins. In this article, before the simulations, we introduce some theories to predict the time scale for polymer relaxation. During the simulation, we mainly focus on two properties of these two proteins: structural stability and adhesive force to substrate. First, we simulate the structural stability of two proteins in water, and then the stability of 36-KD protein in seawater environment is investigated.We find that the stability varies in the different environments. Next, to study adhesive ability of two proteins, we simulate the process of peeling the two proteins from the substrate (graphite). Then, we analyze the main reasons of these results. We find that hydrogen bonds in proteins play an important role in the protein stability. In the process of the peeling, we use Lennard–Jones 12-6 potential to calculate the van der Waals interactions between proteins and substrate.

Equivalent Model Of Expansion Of Cement Mortar Under Sulphate Erosion

The expansion property of cement mortar under the attack of sulfate ions is studied by experimental and theoretical methods. First, cement mortars are fabricated with the ratio of water to cement of 0.4, 0.6, and 0.8. Secondly, the expansion of specimen immerged in sulphate solution is measured at different times. Thirdly, a theoretical model of expansion of cement mortar under sulphate erosion is suggested by virtue of represent volume element method. In this model, the damage evolution due to the interaction between delayed ettringite and cement mortar is taken into account. Finally, the numerical calculation is performed. The numerical and experimental results indicate that the model perfectly describes the expansion of the cement mortar.

Variation Of Flexural Strength Of Cement Mortar Attacked By Sulfate Ions

Under the environment of seawater, durability of concrete materials is one of the chief factors considered in the design of structures. The decrease of durability of structures is induced by the evolution of micro-damage due to the erosion of chlorine and sulfate ions, which is characterized by the reduction of modulus, strength, and toughness of the material. In this paper, the variation of the flexural strength of cement mortar under sulfate erosion is investigated. The results obtained in present work indicate that the erosion time, concentration of sulfate solution, and water-to-cement ratio will significantly affect the flexural strength. Crown Copyright (c) 2008 Published by Elsevier Ltd. All rights reserved.

Damage Evolution In Cement Mortar Due To Erosion Of Sulphate

Ultrasonic technique is used to detect the velocity change of stress wave propagated in the cement mortar immersed in the solution of sodium sulfate for 425 days. Also the density change of specimens at different erosion time is measured. By curve fitting, the effect of solutions' concentration and water/cement ratio on the damage evolution is analyzed. The SEM observation on the growth of delayed ettringite is also performed. It shows that the damage evolution of specimens attacked by sulphate solution is dominantly induced by the nucleation and growth of delayed ettringite, and the average size of microvoids in cement mortar affects the damage evolution significantly. (c) 2008 Elsevier Ltd. All rights reserved.

Molecular Dynamics Simulation of Barnacle Cement

Barnacle cement is an underwater adhesive that is used for permanent settlement. Its main components are insoluble protein complexes that have not been fully studied. In present article, we chose two proteins of barnacle cement for study, 36-KD protein and Mrcp-100K protein. In order to investigate the characteristic of above two proteins, we introduced the method of molecular modeling. And the simulation package GROMACS was used to simulate the behavior of these proteins. In this article, before the simulations, we introduce some theories to predict the time scale for polymer relaxation. During the simulation, we mainly focus on two properties of these two proteins: structural stability and adhesive force to substrate. First, we simulate the structural stability of two proteins in water, and then the stability of 36-KD protein in seawater environment is investigated. We find that the stability varies in the different environments. Next, to study adhesive ability of two proteins, we simulate the process of peeling the two proteins from the substrate (graphite). Then, we analyze the main reasons of these results. We find that hydrogen bonds in proteins play an important role in the protein stability. In the process of the peeling, we use Lennard-Jones 12-6 potential to calculate the van der Waals interactions between proteins and substrate.

EQUIVALENT MODEL OF EXPANSION OF CEMENT MORTAR UNDER SULPHATE EROSION

The expansion property of cement mortar under the attack of sulfate ions is studied by experimental and theoretical methods. First, cement mortars are fabricated with the ratio of water to cement of 0.4, 0.6, and 0.8. Secondly, the expansion of specimen immerged in sulphate solution is measured at different times. Thirdly, a theoretical model of expansion of cement mortar under sulphate erosion is suggested by virtue of represent volume element method. In this model, the damage evolution due to the interaction between delayed ettringite and cement mortar is taken into account. Finally, the numerical calculation is performed. The numerical and experimental results indicate that the model perfectly describes the expansion of the cement mortar.

Variation of flexural strength of cement mortar attacked by sulfate ions

Under the environment of seawater, durability of concrete materials is one of the chief factors considered in the design of structures. The decrease of durability of structures is induced by the evolution of micro-damage due to the erosion of chlorine and sulfate ions, which is characterized by the reduction of modulus, strength, and toughness of the material. In this paper, the variation of the flexural strength of cement mortar under sulfate erosion is investigated. The results obtained in present work indicate that the erosion time, concentration of sulfate solution, and water-to-cement ratio will significantly affect the flexural strength. Crown Copyright (c) 2008 Published by Elsevier Ltd. All rights reserved.

Failure process analysis of cement under explosive loading with a generalized driven nonlinear threshold model

The microstructural heterogeneity and stress fluctuation play important roles in the failure process of brittle materials. In this paper, a generalized driven nonlinear threshold model with stress fluctuation is presented to study the effects of microstructural heterogeneity on continuum damage evolution. As an illustration, the failure process of cement material under explosive loading is analyzed using the model. The result agrees well with the experimental one, which proves the efficiency of the model.

Long-Term Evolution Of Delayed Ettringite And Gypsum In Portland Cement Mortars Under Sulfate Erosion

The magnitude evolution of ettringite and gypsum in hydrated Portland cement mortars due to sulfate attack was detected by X-ray powder diffraction. The influences of sulfate concentration and water-to-cement ratio on the evolution of ettringite and gypsum were investigated. Experimental results show that the magnitude of ettringite formation in sodium sulfate solution follows a three-stage process, namely, the 'penetration period', 'enhance period of strength', and 'macro-crack period'. The cracking of concrete materials is mainly attributed to the effect of ettringite. The gypsum formations occurred in two stages, the 'latent period' and the 'accelerated period'. The gypsum formation including ettringite formation was relative to the linear expansion of mortars to some extend. Both water-to-cement ratio and sulfate concentration play important roles in the evolution of ettringite and gypsum. (C) 2008 Elsevier Ltd. All rights reserved.

A simple method to simulate shrinkage-induced cracking in cement-based composites by lattice-type modeling

A new numerical procedure is proposed to investigate cracking behaviors induced by mismatch between the matrix phase and aggregates due to matrix shrinkage in cement-based composites. This kind of failure processes is simplified in this investigation as a purely spontaneous mechanical problem, therefore, one main difficulty during simulating the phenomenon lies that no explicit external load serves as the drive to propel development of this physical process. As a result, it is different from classical mechanical problems and seems hard to be solved by using directly the classical finite element method (FEM), a typical kind of "load -> medium -> response" procedures. As a solution, the actual mismatch deformation field is decomposed into two virtual fields, both of which can be obtained by the classical FEM. Then the actual response is obtained by adding together the two virtual displacement fields based on the principle of superposition. Then, critical elements are detected successively by the event-by-event technique. The micro-structure of composites is implemented by employing the generalized beam (GB) lattice model. Numerical examples are given to show the effectiveness of the method, and detailed discussions are conducted on influences of material properties.

爆炸载荷对水泥试样损伤破坏规律研究

从实验和数值模拟两方面对爆炸载荷对水泥试样的损伤破坏进行了研究。首先，在水中利用爆炸产生的爆炸冲击波对水泥试样进行损伤破坏，模拟“层内爆炸”采油技术中激波使岩石损伤开裂的现象；然后，利用波动力学理论，对激波在实验条件下对水泥试样的损伤破坏进行了数值模拟。结果表明，在冲击载荷作用下，水泥试样的损伤破坏可分为压实破坏、压实损伤、拉伸损伤、拉伸破坏4个区域，在压实损伤区水泥试样也具有较好的渗透性。数值模拟可以用来确定各种裂纹形成的应力条件，并可通过预制剖面上的裂纹分布来预测水泥试样内部裂纹分布的基本规律。

固井工程中的流动问题

同井是油气在建过程中的重要工程，一般分下套管和注水泥两个过程．本文结合作者近年来的研究，着重阐述了钻井液、前置液、水泥浆在环形空间中流动的流体力学问题，包括：高温高压下的水泥浆流变性、偏心环形空间中浆液的流动特性、钻井液-前置液和前置液-水泥浆界面的稳定性等，介绍了国内外学者对这些问题的研究进展，提出了今后应深入研究的问题.

饱和水泥试样被爆炸激波损伤破碎的尺度研究

利用水中爆炸冲击波使水泥试样损伤破坏,模拟爆炸采油时激波使岩石损伤开裂的现象.实验获得了适合本实验条件的激波峰压衰减规律p_m≈8.2(~3√W/R~(1.46)),得知压碎区尺度为集中装药特征尺度的2～5倍、拉伸损伤区尺度为集中装药特征尺度的20～30倍,激波使水泥试样破碎、拉裂的能量占总能量的2%～7%.

激波作用下水泥试样内部损伤试验方法研究

通过优化试验方案，实现了爆炸激波对水泥试样内部的损伤破坏试验，观察到激波对试样的损伤破坏现象。根据试验需求，设计、制作和标定了可用于测量水泥试样内部激波压力（或速度）的传感器，并在水中与商业传感器一起进行了测试，发现两种传感器获得的波形一致，并且该传感器的尺度可以满足试验的需要。利用量纲分析的方法，得到了激波在水泥试样中的衰减规律模型，通过比较相同条件下实测压力与模型计算的压力，发现计算压力要比实测压力高5％～15％。

水泥回转窑热工控制模型研究及其仿真

水泥回转窑是建材工业发展的方向，我国是水泥生产大国，而国内回转窑与发达国家相差甚大，尤其在热工控制方面。由于水泥回转窑具有时变、分布参数和非线性特性，是一个典型的复杂过程，因而水泥回转窑控制系统是一个很有意义且困难的研究方向，本论文在借鉴国内外同类研究的基础上，提出了模糊专家系统控制模型，进行了深入地研究，并且对该模型进行了计算机仿真，希望通过这项研究，提高我国在水泥回转窑先进智能技术的控制水平。主要研究内容有：对水泥回转窑的热工过程进行了详细分析，对其不同控制方法进行全面的综述，对水泥回转窑实现控制的人工智能方法进行了全面的综述，并介绍了国内外的研究现状；研究了对水泥回转窑控制的模糊控制模型、专家系统设计方法，以及利用模糊控制与专家系统相结合的方法对水泥回转窑进行安全而有效控制的方法：研究了专家系统的实时性问题，提出了静态排列专家系统的推理时间模型、优化排列专家系统的时间估计模型与排列准则；利用计算机仿真方法，实现对水泥回转窑这种复杂而昂贵系统控制进行实验研究，以较低的代价实现对其分析。本论文的主研究成果如下：1. 详细研究了水泥回转窑的技术发展与结构演化过程，分析了水泥回转窑的热工过程以及影响水泥生产的各种因素，总结了影响水泥生产质量的主要因素与次要因素，确定了控制水泥回转窑的主要并且可测量的过程参数。2. 用推理全成方法研究模糊控制模型，实现从模糊的角度研究水泥回转窑的控制：从专家 系统角度研究水泥回转窑的控制问题，并提取了有关的专家系统控制规则；在模糊控制与专家系统的基础上，将水泥回转窑的模糊控制与专家系统相结合，利用层次化的控制器结构，底层为模糊控制器，顶层为专家系统，实现了水泥回转窑的安全与有效控制。3. 从定量的角度研究了专家系统的推理时间问题，给出了三种相应的时间估计模型，这不仅可以分析水泥回转窑系统中的专家系统的实时性，而且也可以分析一般专家系统的推理时间和问题。4. 本文提出的计算机仿真工具，为三组数据分别进行计算机仿真，以此研究水泥回转窑控制策略的性能以及对其动态过程进行分析，为水泥回转窑这样的复杂且昂贵的控制系统研究提供有效的手段。