Numerical Simulation of Wave Field near Submerged Bars by PLIC-VOF Model

Investigating the wave field near structures in coastal and offshore engineering is of increasing significance. In the present study, simulation is done of the wave profile and flow field for waves propagating over submerged bars, using PLIC-VOF （Pieeewise Linear Interface Construction） to trace the free surface of wave and finite difference method to solve vertical 2D Navier-Stokes （N-S） equations. A comparison of the numerical results for two kinds of submerged bars with the experimental ones shows that the PLIC-VOF model used in this study is effective and can compute the wave field precisely.

Numerical study on the characteristics of flow field and wave propagation near submerged breakwater on slope

In this study, characteristics of flow field and wave propagation near submerged breakwater on a sloping bed are investigated with numerical model. The governing equations of the vertical two-dimensional model are Reynolds Averaged Navier Stokes equations. The Reynolds stress terms are closed by a nonlinear k - ε turbulence transportation model. The free surface is traced through the PILC-VOF method. The proposed numerical model is verified with experimental results. The numerical result shows that the wave profile may become more asymmetrical when wave propagates over breakwater. When wave crest propagates over breakwater, the anticlockwise vortex may generate. On the contrary, when wave hollow propagates over breakwater, the clockwise vortex may generate. Meanwhile, the influenced zone of vortex created by wave crest is larger than that created by wave hollow. All the maximum values of the turbulent kinetic energy, turbulent dissipation and eddy viscosity occur on the top of breakwater. Both the turbulent dissipation and eddy viscosity increase as the turbulent kinetic energy increases. Wave energy may rapidly decrease near the breakwater because turbulent dissipation increases and energy in lower harmonics is transferred into higher harmonics.

Numerical Investigation of the Multiphase Flow Originating from the Muzzle of Submerged Parallel Guns

A two-dimensional model,employing a dynamic mesh technology,is used to simulate numerically the transient multiphaseflowfield produced by two submerged parallel guns.After a grid refinement study ensuring grid inde-pendence,five different conditions are considered to assess the evolution of cavitation occurring in proximity to the gun muzzle.The simulation results show thatflow interference is enabled when the distance between the par-allel barrels is relatively small;accordingly,the generation and evolution of the vapor cavity becomes more com-plex.By means of the Q criterion for vorticity detection,it is shown that cavitation causes the generation of vorticity and the evolution of the vapor cavity can result in an asymmetric distribution of vorticity for a certain distance of the barrels.In particular,the evolution of the vapor cavity can hinder the expansion of the gas and force it toflow outward,while an asymmetric distribution of vorticity can lead to a gas jetflowing outward and rotating simultaneously.

Effect of electromagnetic stirring on flow field in mold under submerged entry nozzle clogging

A physical model with mercury as analog was developed to investigate the influences of electromagnetic stirring（EMS） on flow field in slab continuous casting when the submerged entry nozzle（SEN） was clogged with different clogging rates（0,10% ,25% ,and 50% ）. The flow field in mold under different EMS currents（0, 40 A, and 60 A） was measured by an ultrasonic Doppler velocimeter. The results proved that the flow field in the mold was a typical double roll structure under non-clogging SEN. As the SEN clogging rate increased, the flow field structure was transformed from a double roll to asymmetry flow. When the clogging rate reached 50%, the up circulation disappeared on the clogged side. The zone under the meniscus near the narrow face was a non-flowing area. EMS could correct bias flow caused by SEN clogging and improve the symmetry of the flow field during SEN clogging.

Frozen curtain characteristics during excavation of submerged shallow tunnel using Freeze-Sealing Pipe-Roof method

The Freeze-Sealing Pipe-Roof(FSPR)method,which has been applied for the first time in the Gongbei Tunnel of the Hong Kong-Zhuhai-Macao Bridge,is a new approach of tunnel pre-support that allows flexible adjustment of freeze tube arrangement and can be adapted to different environmental conditions.When the FSPR method is used to construct shallow burial submerged tunnels,the frozen wall to hold back groundwater during excavation will be weakened by air and water flows inside and outside the tunnel,and its waterproof performance needs to be further investigated.In this paper,a two-dimensional numerical model of the temperature field considering excavation and moving water boundary is established based on the preliminary design scheme and in-situ conditions and is used to analyze the variation in frozen curtain properties with various active freezing times during excavation.The results show that excavation has a weakening effect on both sides of the frozen wall,with a greater effect on the inner side,and a positive temperature appears in the local area inside the jacked pipe.The concrete fill in the jacked pipe obviously improves the freezing efficiency,and the tunnel excavation after 60 days of active freezing in the interval filling mode can ensure that the frozen soil thickness at the thinnest segment exceeds 2 m,i.e.,the design requirement.In practice,the active freezing time can be extended appropriately to reduce the influence of river water flow above the tunnel.The study serves as a technical reference for the design and implementation of similar projects.

Research Progress on Anti-clogging Technology of Submerged Entry Nozzles for Continuous Casting

The causes, the formation process, and the prevention of submerged entry nozzle(SEN) clogging were introduced. The influence of electric field on the SEN clogging was focused on, including the basic theory and measurement of SEN charging,the preliminary research on SEN charging, the influence of molten steel on the wetting behavior of refractory materials in electric field, and the influence of electric field on the oxide inclusions in molten steel. Based on the influence of the hydrodynamics, chemistry and other factors on refractory materials, structure, inclusion particle transfer and adhesion, many anti-clogging researches have been carried out, such as optimizing process conditions, compositing anti-clogging inner lining materials, innovating SEN structure and applying physical fields, which solve the problem of SEN clogging to a certain extent.However, the problems of weak adaptability and superficial study on clogging mechanism are still prominent. The electric field control is a new technology to prevent clogging. Although it has achieved certain results in on-site continuous casting trials,some problems such as the method of applying electric field, the electric field parameters and the equipment still need to be gradually improved, and the surface characteristics of inclusions and SEN materials at high temperatures need to be further studied. It was pointed out that the combination of materials and applied electric field will become an important direction for SEN anti-clogging technology.

镍铁矿热炉熔炼过程中的多物理场耦合

建立了一个三维多物理场耦合模型,揭示矿热炉运行过程中电磁、温度、化学反应间的相互作用机理该模型不仅将电磁理论、多相流动、传热、还原反应整合到统一的计算框架中,还通过用户自定义函数(UDFs)将电弧热、焦耳热和化学反应热加入到能量方程源项中研究了不同电极插入深度下的熔池温度分布,并分析了熔池不同位置处的还原反应量结果表明:随着电极插入深度的增加,熔池温度不断升高在磁场作用下,熔池底部温度分布均匀熔池区内氧化镍比铁氧化物还原更彻底,而坩埚区内镍铁氧化物均被彻底还原当电极插入深度为21m和22m时,有助于提高炉料温度,适用于升温阶段当电极插入深度为20m时,炉料温度和铁氧化物的还原量更为均衡,适用于稳定熔炼阶段。

固体发动机水下点火尾流场计算

为研究固体发动机水下点火初期喷管内燃气泡的流动和发展过程及流场结构,利用CFD方法通过fluent分析软件对固体火箭发动机水下点火过程气液两相流场进行数值模拟计算,得到了发动机尾流场燃气马赫数、压力、温度等瞬态阶段演变情况。结果表明,发动机水下点火时,燃气与水之间产生强烈地相互作用,射流通道沿轴向存在周期性胀缩,一个周期内相继出现膨胀—液体回压—回流—颈缩—继续膨胀现象,随着流场发展涨缩强度逐渐减弱,颈缩位置向下游移动;燃气射流初期,轴向压力最高点在燃气泡头部位置;点火初始时刻喷管出口出现压力峰值;全计算域内温度在一定范围内振荡,沿轴向远离出口区域有剧烈的传热和明显的气液混合。

矿热炉电/磁/热多物理场耦合热应力场分析

为了探究交流电矿热炉在稳定工作时炉体热应力分布情况,建立了一种大型矿热炉电/磁/热多物理场耦合多相流传热传质和热应力计算模型,采用Fluent软件用户自定义函数(UDFs),实现炉内电热转化现象(电弧热和电阻热)、矿料熔化传热、电/磁/热多物理场耦合仿真分析,探究交流矿热炉在多物理场耦合工况下矿料/熔渣/合金液/炉衬多相间的传热传质机理,并结合热-结构耦合法,开展大型矿热炉工作状态下炉衬热应力仿真计算,精确预测炉衬变形位置和变形量。结果表明:随着电极插入深度的增加,炉膛内的压力与炉体形变量都会降低。

30mm厚EH420船板钢三丝埋弧焊接温度场数值模拟研究

为了减少焊接时产生的高温对热影响区韧性的影响,分别研究了焊接线能量、焊丝功率分配、焊接电压和焊丝间隔对温度场的影响。基于Visual-Environment有限元软件,利用双椭球热源模型,对30 mm厚EH420船板钢三丝埋弧焊接温度场进行了数值模拟。结果表明:1)当线能量从150.26 kJ/cm降低到104.72 kJ/cm时,粗晶区峰值温度降低了322℃;2)当线能量相同时,前丝功率占比从25.00%上升到41.67%,且中丝功率占比不变的情况下,粗晶区峰值温度降低了56.79℃;3)提高焊接电压后,粗晶区峰值温度、熔深和熔宽变化较小;4)焊丝间隔从20 mm增加到45 mm,熔池长度增大了50 mm,并在焊丝间隔40 mm之后出现由单熔池向双熔池转变的现象,粗晶区峰值温度呈现先增大后减小的趋势,焊丝间隔在35 mm达到最高温度1183.62℃;5)从拟合结果得出,在焊接30 mm厚的EH420船板钢“Y”型坡口时,线能量应采用174.54 kJ/cm,在此线能量下前、中、后丝的功率占比采用15∶11∶7且焊丝间隔为20~30 mm,能够有效避免出现焊接缺陷。研究结果既可以保证焊接质量,又可以大幅提高焊接效率,为企业降本增效提供新方法。

Flow field, heat transfer and inclusion behavior in a round bloom mold under effect of a swirling flow submerged entry nozzle

Flow field,heat transfer and inclusion behavior in a 700 mm round bloom mold under the effect of a swirling flow submerged entry nozzle(SEN)were investigated with the aim to enhance the casting process.The results indicate that the impinging flow phenomenon,which is commonly observed in conventional single-port SEN casting,was completely suppressed by the swirling flow SEN coming from a novel swirling flow generator design in tundish.Steel from the SEN port moved towards the mold wall in 360 direction,leading to a uniform temperature distribution in the mold.Compared to a conventional single-port SEN casting,the steel super-heat was decreased by about 5 K at the mold center,and the temperature was increased by around 3.5 K near the meniscus.In addition,the removal ratio of inclusions to the mold top surface in the swirling flow SEN casting was found to be increased.Specifically,the removal ratio of spherical inclusions with diameters of 1,10,50 and 100μm was increased by 18.2%,18.5%,22.6% and 42.7%,respectively.Furthermore,the ratio was raised by 18.2%,20.8%,21.5% and 44.1%for non-spherical inclusions,respectively.

非淹没双空化射流流场及冲击特性数值模拟

空化射流具有比同等条件下普通水射流更强的冲击力,被广泛应用于各种领域。为进一步提高空化射流的工作效率,提出了新型的非淹没双空化射流。基于多相流Mixture模型和RNG k-ε输运方程,研究了双空化喷嘴中内外喷嘴径向间距D 0与出口轴向间距L,以及外喷嘴来流压力P 1对射流轴线速度、压力、含气率与比能的影响,并分析了最优D 0,L,P 1组合下射流冲击平板的壁面压力分布特征。研究结果表明,当D 0=1.5 mm,且L=2 mm时射流的流场特性最优,在此结构下的最优靶距为20~25 mm。对该非淹没双空化射流冲击特性分析发现,相比于传统中心体空化喷嘴,其可产生体积更大的空化云和更好的冲击效果。研究结果可为空化射流的高效应用提供理论基础。

喷管对水下爆轰燃气射流过程影响的数值模拟

为了探究不同喷管构型对水下爆轰燃气射流形态与激波传播过程的影响,基于VOF多相流模型,通过求解二维非稳态雷诺时均Navier-Stokes方程分别对无喷管、加装扩张喷管、收敛喷管的爆轰管水下爆轰过程的内外流场进行二维轴对称数值模拟。研究了喷管构型对水下爆轰过程中形成的透射与反射激波的传播特性、爆轰燃气射流形态演化规律等流场特性的影响。计算结果表明:扩张喷管可以加强向下游传播的透射激波沿轴线方向的指向性,而收敛喷管会减弱透射激波的强度,增强向上游传播的反射激波强度。爆轰燃气泡初期轴向和径向发展速度均随着时间逐渐衰减,喷管对燃气泡的轴向尺度影响较小,但收敛喷管能够显著抑制燃气泡的径向尺度。研究结果可为后续水下爆轰推进的工程化应用提供技术支撑。

淹没堆积体附近水流特性研究

堆积体的存在对其附近水流结构产生明显影响,在通过水槽试验数据验证数值模拟结果良好的基础上,开展淹没堆积体附近流场数值模拟研究。结果表明:堆积体在处于淹没状态时,对堆积体顶部以下的水流仍然起到有效调节作用。在近床面流层,高紊动区是主流扩散所导致的,随着流层上升,高紊动区的分布范围和强度主要受到回流区的控制。涡量较大的区域产生于堆积体表面流场、回流区与主流区的交界范围内,由于这两个区域的涡量较大,因此可能更有利于堆积体颗粒的起动及泥沙输移。

锰硅合金矿热炉电极参数寻优方法研究

电极是锰硅合金交流矿热炉重要组成部分,对炉内炉料的冶炼效率影响至关重要。为了探究锰硅合金交流矿热炉最佳电极参数,建立炉料升温和稳定熔炼阶段三维有限元模型,探究不同电极直径、极心圆直径和电极插入深度对两个阶段温度场的影响。结果表明:矿热炉内电极端部熔池区域温度最高,随着冶炼时间增加,熔池区域增加。在升温阶段,电极直径、极心圆直径和电极插入炉料深度的选取不同炉内平均温度也不一样。电极直径1600 mm、极心圆直径4400mm和电极插入深度2800mm时,炉内平均温度最高。在稳定熔炼阶段,随着电极插入深度改变,炉内熔池区域体积也发生改变,插入深度2800 mm时,熔池反应区体积最大,占整个炉膛体积的44.35%。电极参数不同使炉内平均温度发生改变,影响冶炼质量及效率。

冷凝矿热炉多物理场耦合数值模拟研究

为探究冷凝矿热炉的熔炼过程,通过建立三维冷凝矿热炉电-磁-热-力耦合仿真模型,数值模拟了冷凝矿热炉内部多物理场间耦合机制,研究了不同电极插入深度对炉体温度和应力、应变的影响.结果表明:炉膛内电流沿四条路径流入和流出;电弧周围磁感应强度较大,最大值分布在电弧边缘;焦耳热最大值分布在电弧区周围;随着电极插入深度由1.8 m增至2.2 m,炉底镁砖温度逐渐升高,炉体的应力、应变也随之增大;炉壳外表面受到的环向拉应力大于轴向拉应力.

直流锰硅合金矿热炉电极特性多物理场耦合分析

为了给电极控制系统提供可靠的数据,进一步探究自焙电极特性对电极温度分布、烧结带位置变化和熔池温度分布的影响。建立自焙电极与炉内熔池耦合的多物理场三维模型,研究直流单电极锰硅合金矿热炉整体的电流密度分布、电势分布和温度分布,并探究了不同外加电压、筋片数量、电极糊电导率三个特性时,X=0截面A(0,0,-1.8)到B(0,0,7.2)段温度分布,并判断烧结带位置。研究表明:电压由150 V增大到250 V,电极烧结提前,熔池内最高温度上升112.6%;当电极糊导电率增加,电极烧结延缓,电极电压降减小,熔池温度升高;当筋片数量增加,电极烧结延缓,熔池温度略有升高。该方法可用于控制电极参数提高熔炼效率,防止电极焙烧不良发生电极事故。

窄间隙埋弧焊热-力耦合有限元建模及残余应力分析

窄间隙埋弧焊是厚板焊接的常用方法,分析窄间隙埋弧焊焊接过程中工艺参数对温度与残余应力的分布与演变规律对于指导实际生产具有重要意义。本文通过建立窄间隙埋弧焊热—力耦合有限元模型,分析了焊接速度对焊件温度场和残余应力场的影响规律。

淹没条件下分散射流对浓密板结料浆的扰动试验研究

为研究浓密机喷嘴射流对浓密料浆的影响效应,基于室内试验(喷嘴变径、压力、喷口分布、高能量低衰减)和工业试验(射流时间、扰动范围、料浆浓度)的方法,考察喷嘴射流对料浆的扰动性能,通过计算扰动区域、渗透性能及料浆影响因素确定射流与浓度的匹配关系,构建了流场作用下的CFD数值模型,将取得的成果应用到实际中。表明:1)锥体安装射流系达到剥离板结料浆的目的,为获得稳定的底流浓度提供了方法;2)浓密机在满载状态下工作16 h后启动射流系统是最佳时间,论证了料浆底流浓度与扰动系统之间的时空响应关系:分层纵向上扰动时长为20、15和9 min;3)研究了喷嘴“梅花”型布置射流扫描完全覆盖板结区域,推导了相邻喷口流场最大体积量,验证了喷嘴每层数量20、14、9、6时易形成弧形相切面,利于全区域内料浆的剥离;4)以屈服应力和黏度评价指标考察剪切破坏及压密脱水性能,利于实现浓密机底流浓度稳定。

沉水植物分布格局对湖泊水环境N、P因子影响

利用实地调查数据模拟保安湖沉水植物分布及水环境生态因子场。应用GIS空间分析功能 ,分别空间选取四种优势沉水植物 (金鱼藻CeratophyllumdemersumL .,穗状狐尾藻MyriophyllumspicatumL .,微齿眼子菜PotamogetonmaackianusA .Benn .,及苦草VallisneriaspiralisL .)的分布水域及无沉水植物分布水域的局部生态因子场。根据得到的局部因子场特征 ,比较分析不同水生植物分布格局对水环境中N、P因子的影响。结果显示四种沉水植物的分布对水环境中N、P因子均有显著影响 ,但效果和强度有所差异。四种植物各自分布水域内的N、P因子的平均浓度分别为 ,总氮 (TN) :穗状狐尾藻 (0 .774mg·L- 1 ) >苦草 (0 .71 4mg·L- 1 ) >金鱼藻 (0 .70 1mg·L- 1 ) >微齿眼子菜(0 .695mg·L- 1 ) ;总磷 (TP)平均含量 :穗状狐尾藻 (0 .1 2 3mg·L- 1 ) >微齿眼子菜 (0 .1 1 8mg·L- 1 ) >金鱼藻 (0 .1 0 7mg·L- 1 ) >苦草 (0 .0 79mg·L- 1 )。结果同时表明金鱼藻、微齿眼子菜和苦草对水中TN含量无显著影响 ,而穗状狐尾藻则明显可以提高水中TN水平。四种沉水植物均能有效吸收水中的P ,从而降低水中的TP含量。综合比较发现 。