Computational fluid dynamics modeling of rapid pyrolysis of solid waste magnesium nitrate hydrate under different injection methods

This study developed a numerical model to efficiently treat solid waste magnesium nitrate hydrate through multi-step chemical reactions.The model simulates two-phase flow,heat,and mass transfer processes in a pyrolysis furnace to improve the decomposition rate of magnesium nitrate.The performance of multi-nozzle and single-nozzle injection methods was evaluated,and the effects of primary and secondary nozzle flow ratios,velocity ratios,and secondary nozzle inclination angles on the decomposition rate were investigated.Results indicate that multi-nozzle injection has a higher conversion efficiency and decomposition rate than single-nozzle injection,with a 10.3%higher conversion rate under the design parameters.The decomposition rate is primarily dependent on the average residence time of particles,which can be increased by decreasing flow rate and velocity ratios and increasing the inclination angle of secondary nozzles.The optimal parameters are injection flow ratio of 40%,injection velocity ratio of 0.6,and secondary nozzle inclination of 30°,corresponding to a maximum decomposition rate of 99.33%.

Computational Fluid Dynamics Approach for Predicting Pipeline Response to Various Blast Scenarios: A Numerical Modeling Study

Recent industrial explosions globally have intensified the focus in mechanical engineering on designing infras-tructure systems and networks capable of withstanding blast loading.Initially centered on high-profile facilities such as embassies and petrochemical plants,this concern now extends to a wider array of infrastructures and facilities.Engineers and scholars increasingly prioritize structural safety against explosions,particularly to prevent disproportionate collapse and damage to nearby structures.Urbanization has further amplified the reliance on oil and gas pipelines,making them vital for urban life and prime targets for terrorist activities.Consequently,there is a growing imperative for computational engineering solutions to tackle blast loading on pipelines and mitigate associated risks to avert disasters.In this study,an empty pipe model was successfully validated under contact blast conditions using Abaqus software,a powerful tool in mechanical engineering for simulating blast effects on buried pipelines.Employing a Eulerian-Lagrangian computational fluid dynamics approach,the investigation extended to above-surface and below-surface blasts at standoff distances of 25 and 50 mm.Material descriptions in the numerical model relied on Abaqus’default mechanical models.Comparative analysis revealed varying pipe performance,with deformation decreasing as explosion-to-pipe distance increased.The explosion’s location relative to the pipe surface notably influenced deformation levels,a key finding highlighted in the study.Moreover,quantitative findings indicated varying ratios of plastic dissipation energy(PDE)for different blast scenarios compared to the contact blast(P0).Specifically,P1(25 mm subsurface blast)and P2(50 mm subsurface blast)showed approximately 24.07%and 14.77%of P0’s PDE,respectively,while P3(25 mm above-surface blast)and P4(50 mm above-surface blast)exhibited lower PDE values,accounting for about 18.08%and 9.67%of P0’s PDE,respectively.Utilising energy-absorbing materials such as thin coatings of ultra-high-strength concrete,metallic foams,carbon fiber-reinforced polymer wraps,and others on the pipeline to effectively mitigate blast damage is recommended.This research contributes to the advancement of mechanical engineering by providing insights and solutions crucial for enhancing the resilience and safety of underground pipelines in the face of blast events.

Application of computational fluid dynamics in design of viscous dampers-CFD modeling and full-scale dynamic testing

Computational fluid dynamics(CFD)provides a powerful tool for investigating complicated fluid flows.This paper aims to study the applicability of CFD in the preliminary design of linear and nonlinear fluid viscous dampers.Two fluid viscous dampers were designed based on CFD models.The first device was a linear viscous damper with straight orifices.The second was a nonlinear viscous damper containing a one-way pressure-responsive valve inside its orifices.Both dampers were detailed based on CFD simulations,and their internal fluid flows were investigated.Full-scale specimens of both dampers were manufactured and tested under dynamic loads.According to the tests results,both dampers demonstrate stable cyclic behaviors,and as expected,the nonlinear damper generally tends to dissipate more energy compared to its linear counterpart.Good compatibility was achieved between the experimentally measured damper force-velocity curves and those estimated from CFD analyses.Using a thermography camera,a rise in temperature of the dampers was measured during the tests.It was found that output force of the manufactured devices was virtually independent of temperature even during long duration loadings.Accordingly,temperature dependence can be ignored in CFD models,because a reliable temperature compensator mechanism was used(or intended to be used)by the damper manufacturer.

A simplified approach to modelling blasts in computational fluid dynamics (CFD)

This paper presents a time-efficient numerical approach to modelling high explosive(HE)blastwave propagation using Computational Fluid Dynamics(CFD).One of the main issues of using conventional CFD modelling in high explosive simulations is the ability to accurately define the initial blastwave properties that arise from the ignition and consequent explosion.Specialised codes often employ Jones-Wilkins-Lee(JWL)or similar equation of state(EOS)to simulate blasts.However,most available CFD codes are limited in terms of EOS modelling.They are restrictive to the Ideal Gas Law(IGL)for compressible flows,which is generally unsuitable for blast simulations.To this end,this paper presents a numerical approach to simulate blastwave propagation for any generic CFD code using the IGL EOS.A new method known as the Input Cavity Method(ICM)is defined where input conditions of the high explosives are given in the form of pressure,velocity and temperature time-history curves.These time history curves are input at a certain distance from the centre of the charge.It is shown that the ICM numerical method can accurately predict over-pressure and impulse time history at measured locations for the incident,reflective and complex multiple reflection scenarios with high numerical accuracy compared to experimental measurements.The ICM is compared to the Pressure Bubble Method(PBM),a common approach to replicating initial conditions for a high explosive in Finite Volume modelling.It is shown that the ICM outperforms the PBM on multiple fronts,such as peak values and overall overpressure curve shape.Finally,the paper also presents the importance of choosing an appropriate solver between the Pressure Based Solver(PBS)and Density-Based Solver(DBS)and provides the advantages and disadvantages of either choice.In general,it is shown that the PBS can resolve and capture the interactions of blastwaves to a higher degree of resolution than the DBS.This is achieved at a much higher computational cost,showing that the DBS is much preferred for quick turnarounds.

CFD技术在地板辐射采暖复合机械送风下人体热舒适性的应用

采用计算流体力学数值模拟的方法,探究地板辐射采暖复合机械送风形式的2种送风气流组织变化对人体热舒适的影响。根据模拟得到工作区平面的平均温度、湿度、风速及其分布情况探究2种工况下人体舒适度。并通过对比2种气流组织下头足温差、垂直温差以及热舒适性指标预计平均舒适度V_(PM)、预计不满意率P_(PD)对人体热舒适度进行定量评价。结果表明:在送风风速、温度相同的条件下,下送风与上送风工作面平均温度基本相同,风速提升0.02 m·s^(-1),湿度下降0.6%。上送风的空气温度分层更明显,2者的头足温差分别是0.09℃、0.02℃,皆不会令人感到不舒适。上送风和下送风2种气流组织的V_(PM)、P_(PD)值均为-0.18、6%,均符合GB/T 33658—2017《室内人体热舒适环境要求与评价方法》的热舒适要求。综合考虑室内温度分布以及头足温差等指标后,表明在地板辐射采暖复合机械送风中下送风气流组织的效果更好。

CFD simulation of hydrodynamics and mixing performance in dual shaft eccentric mixers

This work aims to systematically study hydrodynamics and mixing characteristics of non-Newtonian fluid(carboxyl methyl cellulose,CMC)in dual shaft eccentric mixer.Fluid rheology was described by the power law rheological model.Computational fluid dynamics was employed to simulate the velocity field and shear rate inside the stirred tank.The influence mechanism of the rotational modes,height difference between impellers,impeller eccentricities,and impeller types on the flow field have been well investigated.We studied the performance of different dual-shaft eccentric mixers at the constant power input with its fluid velocity profiles,average shear strain rate,mixing time and mixing energy.The counter-rotation mode shows better mixing performance than co-rotation mode,and greater eccentricity can shorten mixing time on the basis of same stirred condition.To intensify the hydrodynamic interaction between impellers and enhance the overall mixing performance of the dual shaft eccentric mixers,it is critical to have a reasonable combination of impellers and an appropriate spatial position of impellers.

调谐液柱阻尼器-结构系统风致振动响应的CFD/CSD耦合分析方法

针对调谐液柱阻尼器(tuned liquid column damper, TLCD)难以建立其精确的非线性理论分析模型,且其力学性能试验成本高和耗时长等问题,首先采用计算流体动力学(CFD)数值模拟方法,对TLCD系统的力学性能和动力特征进行仿真模拟,在此基础上进一步提出了基于计算流体动力学/计算结构动力学(CFD/CSD)耦合分析方法,求解带TLCD系统的高层建筑结构的风致动力响应。通过开展某一TLCD系统在特定底部激励下的力学性能和动力特性试验,得到其内液体晃荡的自由液面波高和晃动力时程,验证了CFD数值模拟方法可以准确地分析TLCD水箱内液体的非线性晃动特征。随后对风工程领域广泛采用的76层建筑结构振动控制Benchmark模型,假设其顶部设置TLCD系统时主体结构在三种风速重现期(10、50和100年)风速对应的横风向动力风荷载激励下的风致控制效率,采用提出的CFD/CSD耦合分析方法,进行了数值仿真模拟分析。耦合分析结果表明,TLCD系统对Benchmark模型的风致加速度、速度和位移响应均有一定的控制效果,对加速度响应的控制效果要优于对位移响应的控制效果。该研究方法可为复杂TLCD系统对高层建筑的风振控制分析提供有效的参考。

A Computational Fluid Dynamics (CFD) Analysis of an Undulatory Mechanical Fin Driven by Shape Memory Alloy

Many fishes use undulatory fin to propel themselves in the underwater environment. These locomotor mechanisms have a popular interest to many researchers. In the present study, we perform a three-dimensional unsteady computation of an undulatory mechanical fin that is driven by Shape Memory Alloy （SMA）. The objective of the computation is to investigate the fluid dynamics of force production associated with the undulatory mechanical fin. An unstructured, grid-based, unsteady Navier-Stokes solver with automatic adaptive remeshing is used to compute the unsteady flow around the fin through five complete cycles. The pressure distribution on fin surface is computed and integrated to provide fin forces which are decomposed into lift and thrust. The velocity field is also computed throughout the swimming cycle. Finally, a comparison is conducted to reveal the dynamics of force generation according to the kinematic parameters of the undulatory fin （amplitude, frequency and wavelength）.

COMPUTATIONAL FLUID DYNAMICS(CFD) SIMULATIONS OF DRAG REDUCTION WITH PERIODIC MICRO-STRUCTURED WALL

Computational fluid dynamics（CFD） simulations are adopted to investigate rectangular microchannel flows with various periodic micro-structured wall by introducing velocity slip boundary condition at low Reynolds number. The purpose of the current study is to numerically find out the effects of periodic micro-structured wall on the flow resistance in rectangular microchannel with the different spacings between microridges ranging from 15 to 60 pm. The simulative results indicate that pressure drop with different spacing between microridges increases linearly with flow velocity and decreases monotonically with slip velocity; Pressure drop reduction also increases with the spacing between microridges at the same condition of slip velocity and flow velocity. The results of numerical simulation are compared with theoretical predictions and experimental results in the literatures. It is found that there is qualitative agreement between them.

基于CFD的FPSO风载荷规范计算适用性研究

[目的]目前,设计人员多使用针对大型油轮的OCIMF规范和针对海上平台的API规范对FPSO风载荷进行计算,但因FPSO船舶上层建筑更为复杂,需进一步研究这2种规范对于FPSO风载荷计算的适用性。[方法]建立具有通用型上部模块的某30万吨级大型FPSO数值模型,对恶劣海况下不同风向角、横倾角下的FPSO所受风载荷进行数值模拟,分析其中存在的遮蔽效应;与规范计算结果进行对比分析,讨论在风载荷作用下FPSO受到的横倾力矩。[结果]结果显示,船舶正浮状态受到的最大风载荷和横倾力矩出现在270°风向角;船舶横倾状态下受到的风载荷和横倾力矩比正浮状态更大,最大横倾力矩出现在10.5°横倾角280°风向角;采用API规范和OCIMF规范得到的FPSO风载荷计算结果与CFD计算结果相差较大,二者在270°风向角的结果与CFD分别相差13.6%和24.5%。[结论]数值仿真给出的流场细节有利于分析上部模块间的遮蔽效应,能够较为准确地预报船舶所受到的风载荷,可以为考虑遮蔽效应的FPSO稳性设计提供参考。

铁皮石斛复合凝胶CFD数值模拟与个性化3D打印性能预测

铁皮石斛粉富含多糖,具有特殊流变学特性,可用于开发3D打印食品材料。本文探讨铁皮石斛粉对淀粉基凝胶3D打印适应性的影响。通过流变学、质构学、扫描电子显微镜、X-射线衍射(XRD)、傅里叶红外光谱(FT-IR)等检测手段,结合计算流体动力学(CFD)模拟,分析铁皮石斛粉对淀粉基凝胶3D打印材料结构及打印特性的影响。结果表明,添加石斛粉对淀粉基凝胶的微观结构、流变及质构特性有显著的影响。随着石斛添加量由0 g(SG)增到1.00 g(SG-1.00D),淀粉基凝胶的硬度由(59.81±1.39)g增到(105.67±2.05)g,黏附性由(43.40±2.07)g·s增到(78.59±0.23)g·s。石斛添加量为0.15 g可以优化凝胶体系的网络结构。添加石斛可引起FT-IR特征峰的迁移,增强17°附近XRD衍射特征标记峰的强度,说明生成了更强的氢键,然而未生成新的物质。SG-0.15D凝胶体系的打印速度可达6.13×10-21/s,打印效果最优。研究结果为石斛在3D打印食品材料中的应用提供了参考,为实际生产石斛3D打印材料提供了技术支持。

基于CFD/CSD耦合的翼面抖振响应数值模拟研究

发展一种考虑气动弹性效应的CFD/CSD耦合计算方法,对翼面抖振响应进行了数值模拟研究。针对抖振的发生往往伴随着较大尺度分离流动,采用脱体涡模拟方法提高湍流模拟的保真度。针对抖振响应模拟时间历程长、计算量大的特点,基于自主发展的动态网格自动化生成方法以及非定常流动和气动弹性高效求解技术,从而提高响应计算效率。分别对大迎角三角翼和超临界机翼进行了抖振响应模拟研究,通过与文献或试验结果的比较以及时频特性分析,验证了所发展方法在大迎角抖振和跨声速抖振响应预测中的可靠性和精确性。

微孔的磨料水射流抛光CFD模拟及试验

为解决飞秒激光微孔难以抛光的问题,结合磨料水射流去除函数稳定、自适应性强等特点,采用磨料水射流抛光方法提高飞秒激光微孔质量。利用Fluent软件对不同工艺参数下的磨料水射流微孔抛光过程进行计算流体力学(computational fluid dynamics,CFD)模拟,分析不同参数下的流场分布、侵蚀速率及壁面剪切力作用规律;然后通过响应面法对射流靶距、射流压力及磨料粒径等3因素进行优化试验,以微孔内壁面剪切力均方差为响应值,建立其响应面方程,获得最佳抛光参数组合并进行试验验证。结果表明:射流压力对微孔内壁面剪切力的影响最大,当射流压力从0.80 MPa增至1.50 MPa时,微孔内壁面剪切力增大2倍以上。射流的不同结构段因性质不同可适用于不同工况。利用响应面法分析得到水射流微孔抛光的最佳工艺参数组合是:射流冲击角,90°;射流靶距,3.5 mm;射流压力,1.10 MPa;磨料粒径,15.0μm。在该条件下抛光微孔内壁面的表面粗糙度R_a降至0.354μm。磨料水射流抛光可显著改善微孔壁面质量,且响应面法预测的数据模型有较高准确性。

Computational fluid dynamics-discrete element method simulation of stirred tank reactor for graphene production

Liquid phase exfoliation(LPE)process for graphene production is usually carried out in stirred tank reactor and the interactions between the solvent and the graphite particles are important as to improve the production efficiency.In this paper,these interactions were revealed by computational fluid dynamics–discrete element method(CFD-DEM)method.Based on simulation results,both liquid phase flow hydrodynamics and particle motion behavior have been analyzed,which gave the general information of the multiphase flow behavior inside the stirred tank reactor as to graphene production.By calculating the threshold at the beginning of graphite exfoliation process,the shear force from the slip velocity was determined as the active force.These results can support the optimization of the graphene production process.

Preliminary Evaluation of Hemodynamic Effects of Fontan Palliation on Renal Artery Using Computational Fluid Dynamics

Background:The assessment of renal function is important to the prognosis of patients needing Fontan palliation due to the reconstructed compromised circulation.To know the relationship between the kidney perfusion and hemodynamic characteristics during surgical design could reduce the risk of acute kidney injury(AKI)and the postoperative complications.However,the issue is still unsolved because the current clinical evaluation methods are unable to predict the hemodynamic changes in renal artery(RA).Methods:We reconstructed a three-dimensional(3D)vascular model of a patient requiring Fontan palliation.The technique of computational fluid dynamics(CFD)was utilized to explore the changes of RA hemodynamics under different possible blood flow rates.The relationship between the kidney perfusion and hemodynamic characteristics was investigated.Results:The calculated results indicated the declined tendency of the pressure and pressure drop as the flow rate decreased.When the flow rate decreased to two-thirds of its baseline,both the pressure of left renal artery(LRA)and the pressure of right renal artery(RRA)dipped below 50%,and the pressure of RRA fell more quickly than that of LRA.Uneven distribution of WSS was observed on the trunk of RA,and the lowest WSS was found at the distal of RA.The average WSS in RA dropped to around 50%as the flow rate reached one-third of its baseline.Conclusions:As a promising approach,CFD can be utilized to quantitatively evaluate the hemodynamic characteristics of RA and contribute to offsetting the drawbacks of clinical assessments of renal function,to help realize better prognosis for the patients with Fontan palliation.

Computational fluid dynamics(CFD) simulation of effect of baffles on separation in mixer settler

The main ideas in the development of the solvent extraction mixer settler focused on achieving clean phase separation,minimizing the loss of the reagents and decreasing the surface area of the settlers.The role of baffles in a mechanically agitated vessel is to ensure even distribution,reduce settler turbulence,promote the stability of power drawn by the impeller and to prevent swirling and vortexing of liquid,thus,greatly improving the mixing of liquid.The insertion of the appropriate number of baffles clearly improves the extent of liquid mixing.However,excessive baffling would interrupt liquid mixing and lengthen the mixing time.Computational fluid dynamics(CFD) provides a tool for determining detailed information on fluid flow(hydrodynamics) which is necessary for modeling subprocesses in mixer settler.A total of 54 final CFD runs were carried out representing different combinations of variables like number of baffles,density and impeller speed.CFD data shows that amount of separation increases with increasing baffles number and decreasing impeller speed.

基于CFD模拟与数学规划法的熔融聚合物流动管道设计优化

在满足产能和合理的管道压降范围下,如何降低熔融聚合物在熔体管道中黏度降问题是熔体流动管道设计的关键因素。本研究基于计算流体力学(CFD)的方法,对熔体流经管道发生热降解过程进行数值模拟,并在此基础上提出了混合整数非线性规划(MINLP)模型和非连续性非线性规划(DNLP)模型,分别对熔体管道进行设计与布局优化。分析实际算例的数值模拟结果发现,优化后的管道相较于原管道黏度降减小3.48%,同时出口的压降分布范围减小了60.47%,出口的压降分布更加均匀。结果表明,综合利用模拟方法与数学规划模型可实现熔融聚合物流动管道的自动化设计及优化。

证据理论框架下主动学习代理模型驱动的CFD模拟不确定性量化方法

计算流体力学(CFD)模拟中存在模型参数、数值离散和边界条件等诸多形式各异的不确定因素。鉴于证据理论具有灵活的建模框架,且能同时量化CFD模拟中的随机和认知不确定性,基于其提出了一种证据理论框架下主动学习代理模型驱动的CFD模拟不确定性量化方法,以较少的CFD仿真模型调用次数实现对CFD模拟结果的不确定性量化。该方法采用最优最大最小距离策略生成空间分布良好的候选样本点,通过动态熵权-TOPSIS主动学习策略平衡了代理模型的全局探索、局部开发和鲁棒性。此外,提出基于Hartley测度和Jousselme距离的复合收敛准则以判断终止代理模型训练的时间并量化输出响应的不确定性。最后,以采用NASA SC(2)0410翼型剖面的超临界机翼流场CFD模拟为例,分析来流参数和湍流模型参数的不确定性对机翼输出响应升阻比的不确定性量化结果。

基于CFD变形网格法的螺旋桨水中附加转动惯量研究

为了在螺旋桨设计中较为准确地估算螺旋桨在水中的附加转动惯量,为轴系设计提供更为准确的设计输入,并进一步探究螺旋桨设计参数对于附加转动惯量的影响规律,以通用计算流体力学(CFD)软件STAR-CCM+为平台,运用内置的变形网格技术,以某油船螺旋桨为研究对象,进行基于RANS方程全粘流的附加转动惯量数值计算研究。在此基础上,通过参数变换获取两组弦长和螺距等比例变化的螺旋桨模型,计算其附加转动惯量并分析和设计参数之间的关系。结果表明:对于同一弦长分布的桨,附加转动惯量占比(水中附加转动惯量除以自身转动惯量)随螺距的增加而增加;对于同样螺距分布的桨,附加转动惯量占比随弦长的增加而减小。通过回归分析,建立螺旋桨水中附加转动惯量与弦长及螺距的回归模型,实现了设计中的快速预报。

基于CFD方法的FPSO的波浪荷载和运动响应研究

针对浮式生产储油船(Floating production storage and offloading, FPSO)在深水作业时面临的恶劣海况问题,为保证其服役期间的安全性及作业效率,需要准确计算非线性波浪荷载和运动响应。本文应用基于计算流体动力学(Computational fluid dynamics, CFD)的软件STAR-CCM+建立了针对实尺度FPSO模型的数值水池,基于Richardson外推法,针对时间步长和网格尺寸,分析了二者的收敛性和数值不确定度。使用该数值水池模拟了不同波浪工况作用下FPSO的运动响应,计算其受到的二阶波浪力,并与势流结果进行对比。结果发现,随着波陡增大,平均波浪力的CFD结果逐渐大于势流结果,且呈现差异化增大。而波陡大于1/15时,纵摇的CFD结果明显大于势流结果。说明大波陡条件下,黏性效应对平均波浪力和纵摇影响明显,为恶劣海况下预报及修正FPSO的二阶波浪力和运动提供了参考。