红层软岩软化的界面过程及其动力学模型

红层软岩灾变和界面上的水-岩相互作用密切相关,研究界面过程对于揭示其灾变机制具有重要的意义。目前针对红层软岩软化的研究主要是宏观唯象特征的研究,红层软岩软化界面过程的研究处于探索和起步阶段,仍需要进一步地完善。针对这一问题,通过分析红层软岩软化界面过程的特征,水-岩界面上的软岩颗粒不断溶解,水在软岩中扩散,形成新的水-岩界面,基于此建立软岩系统标准熵对软岩软化进行表征,发现软岩系统标准熵值随着时间的变化规律与软岩软化崩解具有一致性;同时,利用菲克扩散定律构建软岩软化界面过程的动力学模型,很好地描述水-岩界面的生成规律;最后在红层软岩的DEM-CFD（离散元-计算流体力学耦合）模型中,软岩软化过程颗粒连接断裂代表水-岩界面的生成,对比界面过程动力学模型,取得较好的拟合结果。该研究结果对软岩软化界面过程的探索具有一定的意义。     

An extensive analysis of numerical ship self-propulsion prediction via a coupled BEM/RANS approach

The paper deals with the self-propulsion problem, i.e. the solution of the flow around the hull that advances at uniform speed due to the action of its own propeller. A coupled BEM/RANS approach, previously proposed for a simpler case with only rudder and propeller, has been extensively analysed to highlight the strength and the weakness of the method. The proposed analyses consider the influence of different turbulence modelling, the role of the interpolating algorithm for the inclusion of body forces into the RANS domain, a mesh and simulation time step sensitivity study and the influence of the extrapolation procedure for the definition of the effective wake to the propeller in the light of the lightest and the most affordable computational setup for daily accurate calculations. At first, the well-known Kriso Container Ship (KCS) test case is considered. This ship has been widely investigated in the context of different research projects and a large amount of data (both measurements and numerical calculations) is available to validate the solution approach and to highlight the benefits, as well as the weaknesses, of the proposed coupled BEM/RANS approach versus established but computationally demanding calculations based only on RANS simulations. Once the approach has been developed and validated via the KCS test case, calculations have been repeated in the case of completely different ships, in order to evaluate its general applicability and to test the robustness and the reliability of the proposed procedure.     

基于CFD的自然通风对日光温室湿度分布模拟分析

以济南日光温室为研究对象,基于试验观测数据,采用计算流体力学（computational fluid dynamics, CFD）模拟技术,利用κ-ε湍流模型和离散坐标（DO）辐射模型,模拟自然通风条件下日光温室内空气相对湿度分布。结果表明：CFD能够较好地模拟自然通风条件下温室内湿度变化特征,湿度模拟值与实测值平均误差为5.5%;低风速条件下,自然通风降湿能力弱,温室内湿度呈现明显的下高上低的垂直分布,随着风速增大,降湿效果明显提高,温室内湿度呈现北侧湿度高南侧湿度低的分布特征;风向为温室自然通风降湿的主要动力因素,对降湿效果影响较大,风向为与温室建造走向一致的偏东风时,温室内湿度低且分布均匀,降湿效率高,北风时,温室内湿度空间差异大,降湿效果差。该研究可以为日光温室的结构优化设计和环境调控提供科学依据。     

CFD数值分析三体船片体位置对阻力及兴波干扰影响

三体船的水动力性能是目前水动力学研究的热门。对于中高速三体船来说,其静水阻力的很大一部分由兴波阻力构成,而对于兴波最大的影响因素就是片体位置的布局。以一艘圆舭型三体船为研究对象,运用黏流计算流体力学(CFD)方法模拟分析4种不同片体位置对三体船静水阻力和兴波干扰的影响。数值计算采用自主研发的黏流CFD求解器naoe-FOAM-SJTU。数值预报得到三体船静水阻力结果与模型试验结果吻合较好,验证了当前CFD方法预报三体船阻力的可靠性。通过不同片体位置三体船阻力计算发现,方案4的船型方案阻力最优,且通过细节的主片体间兴波干扰流场的结果给出了不同片体布置方案对三体船阻力和兴波的影响。     

Regular waves onto a truncated circular column: A comparison of experiments and simulations

Accurate prediction of hydrodynamic forces on offshore structures is critical for safe and cost effective design of fixed and floating offshore structures exposed to a harsh environment. In the present paper, nonlinear interactions between regular waves and a single surface-piercing truncated circular column have been investigated using a frequency domain potential flow solver (DIFFRACT) and a full CFD solver in OpenFOAM for direct comparisons. Both the predicted free surface elevation around the column and the total force acting on the column have been analysed and compared with experimental data from MOERI. The degree of non-linearity and the contribution of each harmonic to the free surface run-up and wave forces have been examined, and evaluations of the accuracy and computational efficiency of the potential flow solver and the full CFD solver are provided and compared in the paper. Also of note are the local forms of the scattered waves around the column in numerical simulations, which are consistent with the Type-1 and Type-2 patterns identified in physical experiments at Imperial College.     

Modelling of underwater bubble plumes and gas dissolution with an Eulerian-Lagrangian CFD model

Underwater bubble plumes emerge from subsea releases of gas. They can be studied by mathematical models. Here an Eulerian-Lagrangian CFD model is presented. It accounts for relevant physics including buoyancy, turbulence, gas expansion and gas dissolution. The model is compared against three sets of experiments. There is consistency between model and experiments. Special focus is given to the effect of gas dissolution. It is demonstrated how the choice of mass transfer coefficient strongly affects the amount of gas dissolution. Since it is not apparent which mass transfer correlation is applicable, it is argued that more experimental data is needed.     

水平轴海流能发电机叶片设计与性能分析

全球海洋蕴藏着丰富的海流能,合理利用海流能可以有效缓解能源危机。以额定工况下获能系数达到最大值为目标,利用叶素-动量理论设计了150 kW水平轴海流能发电机的叶片。使用叶素-动量理论结合普朗特修正和葛劳渥修正的方法,预测了海流机在不同尖速比以及不同桨距角下的水动力性能,分析了攻角和载荷沿着叶片径向的分布规律。使用CFD方法计算了海流机在不同尖速比下的水动力性能,并与理论方法的计算结果进行了比较。理论方法和CFD方法的结果均表明,所设计的海流机最大获能系数位于设计尖速比处,证明基于叶素-动量理论的水平轴海流机叶片设计方法是有效的。     

液动锤射流元件喷嘴临界流速预测与验证

应用CFD动态分析技术,对SC71B型液动锤内部流场进行了仿真分析,结果表明,其射流元件临界流速为20.305～22.565 m/s,大大低于凭经验预测的40 m/s。为检验这一理论预测结果,对SC71B型液动锤射流元件临界流速进行了实验测定,为21.83 m/s,表明理论预测结果与实测结果高度吻合,证明了基于CFD动态分析的液动锤射流元件临界流速理论预测方法的可行性;同时通过理论分析和实测获得了至今为止液动锤射流元件临界流速的最低值,可为研制油气钻井用低速射流元件驱动控制的液动锤提供重要参考。     

台特玛湖干涸湖盆两种典型风蚀坑的三维流场特征及对风蚀的影响

台特玛湖干涸湖盆区风蚀沙漠化快速发展,发育了以新月形沙丘和风蚀坑（主要为槽状坑和碟状坑）为主的风沙地貌。风蚀坑的发育不仅受来流风影响,还与坑内三维流场有关。基于风洞实验和计算机流体力学（Computational fluid dynamics, CFD）数值模拟,对风蚀坑三维流场进行了探究。结果表明：（1） 从入风侧到出风侧,槽状风蚀坑和碟状风蚀坑底面的风速均呈减速—加速—减速—加速的变化模式,上口所在水平面的风速变化呈加速—减速—加速变化模式,上口气流压强也相应地发生变化,槽状风蚀坑和碟状风蚀坑整体呈低压—高压—低压变化模式,其中槽状坑变化更为明显。（2） 两种形状风蚀坑对气流均具有一定的吸附效应,使坑外一定范围的风沙流被吸入坑内,聚集能量和风沙流,加剧风蚀坑风蚀发育。（3） 风蚀坑加剧了地表侵蚀,侵蚀程度与风蚀坑尺度有关,风蚀坑尺度越大,对地表侵蚀越强。本文直观展示了两种典型风蚀坑中的三维速度、压力、风沙流流向分布,揭示了风蚀坑的风沙流吸附机制,研究结果可加深对风蚀坑形态动力学的理解,也可为内陆干涸湖盆沙漠化防治提供理论指导。     

Effects of Street-Bottom and Building-Roof Heating on Flow in Three-Dimensional Street Canyons

Using a computational fluid dynamics(CFD)model,the effects of street-bottom and building-roof heating on flow in three-dimensional street canyons are investigated.The building and street-canyon aspect ratios are one.In the presence of street-bottom heating,as the street-bottom heating intensity increases,the mean kinetic energy increases in the spanwise street canyon formed by the upwind and downwind buildings but decreases in the lower region of the streamwise street canyon.The increase in momentum due to buoyancy force intensifies mechanically induced flow in the spanwise street canyon.The vorticity in the spanwise street canyon strengthens.The temperature increase is not large because relatively cold above-roof-level air comes into the spanwise street canyon.In the presence of both street-bottom and building-roof heating,the mean kinetic energy rather decreases in the spanwise street canyon.This is caused by the decrease in horizontal flow speed at the roof level,which results in the weakening of the mean flow circulation in the spanwise street canyon.It is found that the vorticity in the spanwise street canyon weakens.The temperature increase is relatively large compared with that in the street-bottom heating case,because relatively warm above-roof-level air comes into the spanwise street canyon.