基于ANSYS的LNG船用超低温阀门的数值模拟分析

应用有限元分析软件分别对通径为DN15的LNG船用超低温阀门在管路中开启与关闭状态稳态热力分析。研究了阀颈长度,阀颈与阀杆之间的,阀颈的厚度对填料函温度的影响。研究结果表明,阀颈长度和阀颈厚度是影响填料函温度的主要因素,阀颈与阀杆之间的间隙尺寸对填料函温度影响很小。     

LNG储罐内翻滚现象临界判据的数值模拟

利用Fluent软件分别对160 000、30 000和5 000立方米LNG储罐内的翻滚现象进行了数值模拟,并将翻滚过程中的密度变化幅值与翻滚时间的比值定义为翻滚系数来表征翻滚的剧烈程度,得到了不同罐容LNG储罐内的翻滚现象随初始密度差的变化规律.研究结果发现:不同罐容的LNG储罐均存在一个翻滚的临界密度差,当初始密度差小于临界密度差时,储罐内相邻两层LNG的混合过程较为平稳;当储罐中相邻两层LNG的密度差大于临界密度差时,翻滚有明显的加速趋势.计算结果表明160 000立方米储罐的临界密度差区间为0.78-0.82千克每立方米,30 000和5 000立方米储罐的临界密度差区间为4-5千克每立方米.这些临界密度差区间值可作为不同罐容储罐的分层与翻滚判据,用于指导储罐设计和实际工程操作.     

Hydrodynamic modelling of flow over a spillway using a two-dimensional finite volume-based numerical model

Spillway flow, a classical problem of hydraulics, is generally a gravity-driven free surface flow. Spillway flows are essentially rapidly varying flows near the crest with pronounced curvature of the streamlines in the vertical direction. Two processes simultaneously occur in the flow over the crest, that is, formation and gradual thickening of the turbulent boundary layer along the profile, and gradual increase in the velocity and decrease in the depth of main flow. Spillway hydrodynamics can be obtained through physical modelling or numerical modelling. Physical modelling of spillways is expensive, cumbersome and time-consuming. The main difficulties in solving the spillway problem numerically are: rapidly varying flow, existence of both subcritical and supercritical flows, development of turbulent boundary layers, unknown free surface and air entrainment. Numerical simulation of such flows over spillways in all flow regimes is a challenging task. This paper describes a numerical model and its application to a case study to investigate the hydraulic characteristics of flow over spillway crest profiles by simulating the velocity distribution, pressure distribution and discharge characteristics. Results of the numerical modelling are compared with those from the physical modelling and found to be satisfactory.     

Numerical investigation of supercritical LNG convective heat transfer in a horizontal serpentine tube

The submerged combustion vaporizer (SCV) is indispensable general equipment for liquefied natural gas (LNG) receiving terminals. In this paper, numerical simulation was conducted to get insight into the flow and heat transfer characteristics of supercritical LNG on the tube-side of SCV. The SST model with enhanced wall treatment method was utilized to handle the coupled wall-to-LNG heat transfer. The thermal–physical properties of LNG under supercritical pressure were used for this study. After the validation of model and method, the effects of mass flux, outer wall temperature and inlet pressure on the heat transfer behaviors were discussed in detail. Then the non-uniformity heat transfer mechanism of supercritical LNG and effect of natural convection due to buoyancy change in the tube was discussed based on the numerical results. Moreover, different flow and heat transfer characteristics inside the bend tube sections were also analyzed. The obtained numerical results showed that the local surface heat transfer coefficient attained its peak value when the bulk LNG temperature approached the so-called pseudo-critical temperature. Higher mass flux could eliminate the heat transfer deteriorations due to the increase of turbulent diffusion. An increase of outer wall temperature had a significant influence on diminishing heat transfer ability of LNG. The maximum surface heat transfer coefficient strongly depended on inlet pressure. Bend tube sections could enhance the heat transfer due to secondary flow phenomenon. Furthermore, based on the current simulation results, a new dimensionless, semi-theoretical empirical correlation was developed for supercritical LNG convective heat transfer in a horizontal serpentine tube. The paper provided the mechanism of heat transfer for the design of high-efficiency SCV.     

Numerical modelling of fatigue crack initiation and growth of martensitic steels

This paper presents a numerical simulation of micro‐crack initiation that is based on Tanaka‐Mura micro‐crack nucleation model. Three improvements were added to this model. First, multiple slip bands where micro‐cracks may occur are used in each grain. Second improvement deals with micro‐crack coalescence by extending existing micro‐cracks along grain boundaries and connecting them into a macro‐crack. The third improvement handles segmented micro‐crack generation, where a micro‐crack is not nucleated in one step like in Tanaka‐Mura model, but is instead generated in multiple steps. High cycle fatigue testing was also performed and showed reasonably good correlation of proposed model to experimental results. Because numerical model was directed at simulating fatigue properties of thermally cut steel, edge properties of test specimens were additionally inspected in terms of surface roughness and micro‐structural properties.     

B型LNG模拟舱内低温流体两相流动与相变传热数值研究

本文以内容积为40 m³,绝热层(聚氨酯)厚度为400 mm的新型独立B型液化天然气船模拟舱为研究对象,对模拟舱内低温流体的两相流动及相变传热问题进行了非稳态三维CFD模拟。采用流体体积函数(VOF)模型追踪气液相界面,利用Lee模型作为相变模型,在相变模型中考虑了静压的影响,对模拟舱的温度分布及静态BOG生成速率进行了计算。研究了在不同液位以及绝热层存在破损的情况下模拟舱的温度分布及静态BOG生成速率的变化,同时研究了当模拟舱密闭时的增压特性。对比模拟结果与实验结果,偏差在10%以内,模型对模拟舱内的低温液体的蒸发过程模拟较好,可为新型独立B型液化天然气实船的设计和改进提供参考。     

Data-driven cardiovascular flow modelling: examples and opportunities

High-fidelity blood flow modelling is crucial for enhancing our understanding of cardiovascular disease. Despite significant advances in computational and experimental characterization of blood flow, the knowledge that we can acquire from such investigations remains limited by the presence of uncertainty in parameters, low resolution, and measurement noise. Additionally, extracting useful information from these datasets is challenging. Data-driven modelling techniques have the potential to overcome these challenges and transform cardiovascular flow modelling. Here, we review several data-driven modelling techniques, highlight the common ideas and principles that emerge across numerous such techniques, and provide illustrative examples of how they could be used in the context of cardiovascular fluid mechanics. In particular, we discuss principal component analysis (PCA), robust PCA, compressed sensing, the Kalman filter for data assimilation, low-rank data recovery, and several additional methods for reduced-order modelling of cardiovascular flows, including the dynamic mode decomposition and the sparse identification of nonlinear dynamics. All techniques are presented in the context of cardiovascular flows with simple examples. These data-driven modelling techniques have the potential to transform computational and experimental cardiovascular research, and we discuss challenges and opportunities in applying these techniques in the field, looking ultimately towards data-driven patient-specific blood flow modelling.     

Two-phase heat transfer and pressure drop of LNG during saturated flow boiling in a horizontal tube

Two-phase heat transfer and pressure drop of LNG (liquefied natural gas) have been measured in a horizontal smooth tube with an inner diameter of 8 mm. The experiments were conducted at inlet pressures from 0.3 to 0.7 MPa with a heat flux of 8–36 kW m⁻², and mass flux of 49.2–201.8 kg m⁻² s⁻¹. The effect of vapor quality, inlet pressure, heat flux and mass flux on the heat transfer characteristic are discussed. The comparisons of the experimental data with the predicted value by existing correlations are analyzed. Zou et al. (2010) correlation shows the best accuracy with 24.1% RMS deviation among them. Moreover four frictional pressure drop methods are also chosen to compare with the experimental database.     

工程计算可视化的几个热点问题

随着工程数值模拟的规模和复杂度的提高,可视化研究面临着发展机遇和挑战,结合国内外的技术发展情况,对于工程计算应用中的表达方式、算法优化、集成解决框架等几个热点问题展开讨论,指出可视化技术发展与应用学科结合的重要性.     

A Petri net-based approach to incremental modelling of flow and resources in service-oriented manufacturing systems

In order to overcome the myopia problem, routing strategies must be based on formal representations of flow that automatically account for modifications in the values of parameters of interest and in the model itself. This work addresses this problem and discusses how to automatically incorporate resources (e.g. workstations/transportation devices/storage) in a Petri-net-derived model of flow that is modifiable at runtime to reflect and influence the routing in a manufacturing line. The modelling approach takes into consideration scalability needs and was experimentally validated. The applicability of the models is shown for PN-based dynamic scheduling.     

磁性液体管道流动的数值模拟

通过将磁性液体的磁化曲线用一个反正切函数来模拟，并且将磁场体积力写成Az的函数形式来模拟磁性液体在圆管申的流动。结果表明，圆管内的磁性液体有最大流量时，磁性液体流在靠近永磁附近呈紊流状态流动，在圆管的最右端，大致呈层流状态流动；圆管内的磁性液体净流量为零时，靠近永磁的磁性液体在原地呈激烈的涡旋流动状态．     

PECVD反应室的气流场模拟分析

本文利用计算流体力学(CFD)方法对某等离子增强化学气相沉积(Plasma Enhanced Chemical Vapor Deposition,PECVD)反应室流场进行了数值模拟研究,通过改变匀流板布孔方式、进气管与匀流板距离、进气管出口形状和角度、压强等条件,研究反应器内流动的相应变化,给出了获得薄膜生长所需的最佳输运过程的条件,以形成稳定均匀的流场,从而保证薄膜的生长质量.根据本文优化后的匀流装置已实际加工应用,取得良好效果.     

Numerical Calculation of the Interaction of Superfluid Vortices and a Rigid Sphere

We implement a method for the calculation of the effects of a solid sphere on the dynamics of superfluid vortices. We present in detail the derivation of the mathematical formulae used in a computational algorithm which avoids numerical singularities, as well as an adaptive algorithm for convergence tests and diagnostics of the method’s accuracy.     

Numerical Simulation of Fluid-Structure Interaction of LNG Prestressed Storage Tank under Seismic Influence

Aim of this paper is to estimate the integrity of liquefied natural gas (LNG) prestressed storage tank under seismic influence. The coupled Eulerian-Lagrangian (CEL) analysis technique is used to simulate the fluid-structure interaction between LNG and the cylinder of LNG prestressed storage tank. The 3-D model of LNG has been dispersed by Eulerian mesh that is different from traditional analysis method which is called the added mass method. Meanwhile, both of the 3-D models of prestressed rebar and concrete structure are dispersed by Lagrangian mesh. Following conclusions are obtained: 1) Natural frequency of the whole model has been obtained by using the Block Lanczos algorithm in Abaqus; 2) Seismic waves of El Centro and Taft have been selected for time history analysis, and curves of displacement, stress and acceleration have been plotted under two seismic waves respectively. By comparing time points when the maximum displacement, stress and acceleration occurred to splash phenomena of LNG liquid surface, numerical results can fit splash phenomena of LNG very well. 3)When El Centro wave is imported, the maximum values of displacement and tension stress of concrete structure are 7.729mm and 2.16MPa respectively, and the maximum values of displacement and tension stress of concrete structure are 9.4mm and 0.24MPa respectively when Taft wave is applied. The values of maximum tension stress are less than the axial tensile strength of the standard value of concrete, which indicate that the structure of LNG prestressed storage tank is safe, and numerical results can provide a reference to monitor the liability of this kind of structures.     

Hydraulics of a submerged weir and applicability in navigational channels: basic flow structures

This paper presents the basic flow structures in a river bend in a physical model with and without a submerged weir. The CCHE2D model and the CCHE3D model for free surface and turbulent flows, which have been extensively validated and verified in recent years, are combined to study the flow in the channel in both the presence and absence of a submerged weir, where the water surface elevations and velocities are measured for certain flow conditions and in certain ranges. A 2D model is used to determine the water edge and to calibrate the bed roughness for the 3D model. A 3D model, after calibration and validation with the physical model data, is used to investigate the flow structure in the channel both in the presence and absence of a submerged weir. The agreement between the measured velocities (surface elevations) and the simulated velocities is reasonably good, which indicates that the CCHE3D model is capable of investigating the flow structure of such a channel. It is found that the submerged weir has a significant effect on the flow in the channel, and that the largest influence appears in the vicinity of the weir. Secondary flows, which are key to navigational conditions, undergo a process of break up when the flow approaches the weir, and develop into single, two, and three secondary flow zones downstream of the weir and then decay from three to two secondary flow zones and finally revert to a single secondary flow zone. Copyright © 2006 John Wiley & Sons, Ltd.     

LNG储罐产生翻滚现象的原因及防治措施

结合某30万m3／d天然气液化项目中LNG储罐的设计及运行实践,分析LNG储罐中LNG产生翻滚的现象、原因及过程,提出预防和解决翻滚现象的方法。     

Numerical modelling of honeycomb core crush behaviour

In this work several numerical techniques for modelling the transverse crush behaviour of honeycomb core materials were developed and compared with test data on aluminium and Nomex™ honeycomb. The methods included a detailed honeycomb micromechanics model, a homogenised material model suitable for use in FE code solid elements, and a homogenised discrete/finite element model used in a semi-adaptive numerical coupling (SAC) technique. The micromechanics model is shown to be suitable for honeycomb design, since it may be used to compute crush energy absorption for different honeycomb cell sizes, cell wall thicknesses and cell materials. However, the very fine meshes required make it unsuitable for analysis of large sandwich structures. The homogenised FE model may be used for such structures, but gives poor agreement when failure is due to core crushing. The SAC model is shown to be most appropriate for use in structural simulations with extensive compression core crushing failures, since the discrete particles are able to model the material compaction during local crushing.     

自控系统在犍为LNG装置的应用

在总结和回顾四川犍为LNG装置一年来自动控制系统运行情况的基础上,对该装置自动控制的功能设置和安全放散等提出了认识和建议。     

灯泡贯流式水轮发电机通风系统流场的数值模拟

以计算流体力学(CFD)软件FLUENT为工具,对灯泡贯流式水轮发电机通风系统的流场进行数值模拟。建立了灯泡贯流式水轮发电机通风系统的三维几何通风模型,用标准κ-ε湍流模型作为气流的物理模型,并对计算出的电机空气风量分配情况与实测数据进行比较,验证了数值模拟的可靠性。研究表明,在合理的简化条件下,采用CFD能准确地模拟灯泡贯流式水轮发电机的通风系统流场,为进行灯泡贯流式水轮发电机通风系统设计和优化提供有效的依据。     

Numerical study of flow in a constricted curved annulus: An application to flow in a catheterised artery

The flow of an incompressible Newtonian fluid in a curved annulus with a local constriction at the outer wall is investigated numerically. The three-dimensional nonlinear elliptic partial differential equations governing the flow are simplified by use of small curvature and mild constriction approximations. The simplified equations of motion, which are locally two-dimensional elliptic in nature at each cross-section, are solved numerically by means of the finite-difference method described by Collins and Dennis [Quart. Jour. Mech. Appl. Math. 28 (1975) 133–156]. Although the results are restricted to small curvature and mild constriction, these are valid for all Dean numbers D in the entire laminar flow regime. The numerical results show that, for higher values of radii ratio k, the pressure gradient, pressure drop, and frictional resistance increase considerably and they vary markedly across the constricted length. These results are used to estimate the increase in frictional resistance in an artery when a catheter is inserted into it. In the absence of constriction (₁=0) and depending on the value of k ranging from 01 to 07, the frictional resistance increases by a factor ranging from 132 to 2391 for D=500 and 120 to 1656 for D=2000. But, in the presence of constriction (₁ = 01) with the same range for k, the increase in frictional resistance is by a factor ranging from 134 to 4232 for D=500 and 118 to 295 for D=2000. In a straight annulus, the increased factor ranges from 174 to 3261 for ₁=0 and 178 to 5827 for ₁ = 01 (for all Dean numbers D).