郓城南湖公园水体环境改善与提升方案研究

城市景观水体环境质量的保护与提升是城市生态文明建设的重要内容。结合区域水环境保护和景观功能需求,针对山东省菏泽市郓城南湖景观水体的封闭缓流、受雨水径流污染严重、自净能力差等问题,基于试验观测、模型模拟等手段,定量计算了入湖污染负荷量和净化水质所需的水生植物种植面积,提出利用水力旋流器进行水体污染源截控、构建湖区水体的自循环系统以及采用动植物进行生态综合净化等多种方法相结合的水环境改善与提升方案。采用MIKE21模型对方案实施效果进行模拟。结果表明,污染截控和流场优化可以使得湖区氨氮、COD和TP达到IV类水目标,加上湖区水生生物的净化作用,水环境改善与提升方案基本能保障南湖公园水环境质量保持长期良好状态,实现水生态系统的良性循环。

南通城区文峰水系水环境治理工程的策略与创新

以南通城区文峰水系水环境治理工程为案例,介绍了从整体水系考虑的水体流动性提升策略,并创新采用了拓扑导流墙技术实现水系内部断头河的原位连通,最终达到"濠河—文峰水系—八窑河"的有序流动。监测数据表明,自2019年4月工程投入使用以来,河道水质已稳定提升至Ⅲ类水质标准,河道流速从原先的滞留状态达到现在的6 cm/s以上,市民与河道的互动从零恢复到了正常水平。

三峡水库滞温现象及原因分析

三峡水库蓄水运行后改变了长江的水文节律,根据近30年来的水文、气象、水文监测资料研究发现,三峡库区未出现大范围内稳定的温度分层结构,但在局部时段、局部区域存在一定范围的水温弱分层现象;库区表层水温及下泄水温存在水温滞温现象,即春夏季滞冷、秋冬季滞暖,升温期(3—5月)沿程水温滞冷,平均温差达到3.5℃,延迟时间2~4旬;降温期(10月—次年1月)沿程水温滞暖,平均温差达到3.4℃,延迟时间2~5旬,对坝下游水生生物产生一定影响。文章采用对比分析、趋势分析、回归分析等方法,分析水库滞温现象主要与成库后水体流动性变弱、水体停留时间延长密切相关。

A CFD Based Investigation of the Unsteady Hydrodynamic Coefficients of 3-D Fins in Viscous Flow

The motion of the fins and control surfaces of underwater vehicles in a fluid is an interesting and challenging research subject.Typically the effect of fin oscillations on the fluid flow around such a body is highly unsteady, generating vortices and requiring detailed analysis of fluid-structure interactions.An understanding of the complexities of such flows is of interest to engineers developing vehicles capable of high dynamic performance in their propulsion and maneuvering.In the present study, a CFD based RANS simulation of a 3-D fin body moving in a viscous fluid was developed.It investigated hydrodynamic performance by evaluating the hydrodynamic coefficients (lift, drag and moment) at two different oscillating frequencies.A parametric analysis of the factors that affect the hydrodynamic performance of the fin body was done, along with a comparison of results from experiments.The results of the simulation were found in close agreement with experimental results and this validated the simulation as an effective tool for evaluation of the unsteady hydrodynamic coefficients of 3-D fins.This work can be further be used for analysis of the stability and maneuverability of fin actuated underwater vehicles.

Hydrodynamic Behavior in a Rotating Zigzag Bed

As a high gravity(HIGEE)unit,the rotating packed bed(RPB)uses centrifugal force to intensify mass transfer.Zigzag rotating bed(RZB)is a new type of HIGEE unit.The rotor of RZB consists of stationary discs and rotating discs,forming zigzag channels for liquid-gas flow and mass transfer.As in RPBs,some hydrodynamic behavior in RZB is interesting but no satisfactory explanation.In this study,the experiments were carried on in a RZB unit with a rotor of 600 mm in diameter using air-water system.The gas pressure drop and power consumption were measured with two types of rotating baffle for RZB rotors,one with perforations and another with shutter openings. The circumferential velocities of gas were measured with a five-hole Pitot probe.The pressure drop decreased rapidly when the liquid was introduced to the rotor,because the circumferential velocity of the liquid droplets was lower than that of the gas,reducing the circumferential velocity of gas and the centrifugal pressure drop.The power consumption decreased first when the gas entered the RZB rotor,because the gas with higher circumferential velocity facilitates the rotation of baffles.

Effect of attack angle change on hydrodynamic character of supercavitating bodies

A series of experiments has been done in a moderate-velocity cavitation tunnel to investigate the effects of attack angle change on hydrodynamic characters of supercavitation. Hydrodynamic characters of the aft section at various attack angles were compared. The investigation shows that hydrodynamic forces of the aft section are dependent of supercavity shapes at different attack angles,and the magnitude of hydrodynamic forces of the aft section varies with the change of attack angle. When the aft section is in the fully wetted case,the drag coefficient changes little. Lift and moment coefficients both increase with the increased attack angle,and the increase magnitude is not large. When the aft body planing is on the cavity boundary,the drag coefficient of nonzero attack angle is larger than that of zero attack angle,and the maximal lift and moment coefficients both vary obviously with the increased attack angle. In the case that the body is fully enveloped by cavity,the drag coefficient,lift coefficient and moment coefficient are nearly constant with the change of attack angles.

Hydraulic Characteristics Analysis for Spacer Grid with Flow Openings on Outer Straps

In advanced nuclear fuel design, the outer strap of a spacer grid plays an important role on fuel assembly mechanical and thermal-hydraulic performance, e.g., precluding the risk of hang-up and improvement on the mixing of the coolant. The communication of the outer strap affects the hydraulic force exerted by the spacer grid of the fuel assembly which could induce fuel assembly bow. In present study, in order to understand the influencing factors of hydraulic force exerted by the spacer grid, outer straps with various flow opening design features, different location and size are investigated by a commercially CFD （computational fluid dynamics） code, ANSYS CFX 12.1. Three dimensional rod bundles including the outer strap without and with different openings are modelled for simulation. The analysis results show that the openings on the spacer grid outer strap can reduce the lateral hydraulic loadings perpendicular to the centerline of the fuel rods exerted by the spacer grids obviously because of the pressures inside and outside the spacer grids being balanced. Besides, influences of the opening design features on the hydraulic force, resistance characteristics and lateral flow factor are investigated in details.

Effect of Placements (horizontal with vertical) on Gas-solid Flow and Particle Impact Erosion in Gate Valve

Gate valve has various placements in the practical usages.Due to the effect of gravity,particle trajectories and erosions are distinct between placements.Thus in this study,gas-solid flow properties and erosion in gate valve for horizontal placement and vertical placement are discussed and compared by using Euler-Lagrange simulation method.The structure of a gate valve and a simplified structure are investigated.The simulation procedure is validated in our published paper by comparing with the experiment data of a pipe and an elbow.The results show that for all investigated open degrees and Stokes numbers(St),there are little difference of gas flow properties and flow coefficients between two placements.It is also found that the trajectories of particles for two placements are mostly identical when St << 1,making the erosion independent of placement.With the increase of St,the distinction of trajectories between placements becomes more obvious,leading to an increasing difference of the erosion distributions.Besides,the total erosion ratio of surface T for horizontal placement is two orders of magnitudes larger than that for vertical placement when the particle diameter is 250 μm.

Computation of the Viscous Hydrodynamic Forces on a KVLCC2 Model Moving Obliquely in Shallow Water

The viscous hydrodynamic force and moment on ships moving obliquely in shallow water are important for ship navigation safety.In the paper,the viscous flow field around a KVLCC2 model moving obliquely in shallow water is simulated and the hydrodynamic drag,lateral force and yaw moment acting on the hull are obtained by a general purpose computational fluid dynamics(CFD) package FLUENT with shear-stress transport(SST) k—ωturbulence model.The numerical computation is performed at different drift angels and water depths.The numerical results are compared with experimental results,and a good agreement is demonstrated.

Study on the compatibility of cement-superplasticizer system based on the amount of free solution

The changes of free solution amount, fluidity and the time-depended fluidity loss of cement paste were examined by varying the water-cement ratio and the dosages of superplasticizer. The distribution of solution and flocculation microstructure in flesh cement paste was observed with optical microscope. The change of free solution amount and its effect on the fluidity and bleeding of cement paste was studied. The results show that the adsorbed solution amount has a great influence on the com- patibility of cement-superplasticizer system, including the bleeding degree, the fluidity and the time-depended fluidity loss of cement paste. Superplasticizer increases the fluidity of cement paste by destroying the flocculated cement particle structure and increasing the amount of adsorbed solution. Polycarboxylate superplasticizer shows higher ability of adsorption than naphtha- lene superplasticizer. Over dosage of superplasticizer is not the primary cause of bleeding. The principle reason of bleeding is the high water-cement ratio and the insufficient enhancing ability of water adsorption of superplasticizer.

A survey on fabrication,control,and hydrodynamic function of biomimetic robotic fish

Understanding and replicating the locomotion principles offish are fundamental in the development of artificial fishlike robotic systems,termed robotic fish.This paper has two objectives:(1) to review biological clues on biomechanics and hydrodynamic flow control offish swimming and(2) to summarize design and control methods for efficient and stable swimming in robotic fishes.Our review of state-of-the-art research and future-oriented new directions indicates that fish-inspired biology and engineering interact in mutually beneficial ways.This strong interaction offers an important insight into the design and control of novel fish-inspired robots that addresses the challenge of environmental uncertainty and competing objectives;in addition,it also facilitates refinement of biological knowledge and robotic strategies for effective and efficient swimming.

A Numerical Investigation of Nanocomposite of Copper and Titanium Dioxide in Water Based Fluid Influenced by Instigated Magnetic Region

Presence of external electrical field plays a vital role in heat transfer and fluid flow phenomena. Keeping this in view present article is a numerical investigation of stagnation point flow of water based nanoparticles suspended fluid under the influence of induced magnetic field. A detailed comparative analysis has been performed by considering Copper and Titanium dioxide nanoparticles. Utilization of similarity analysis leads to a simplified system of coupled nonlinear differential equations, which has been tackled numerically by means of shooting technique followed by Runge-Kutta of order 5. The solutions are computed correct up to 6 decimal places. Influence of pertinent parameters is examined for fluid flow, induced magnetic field, and temperature profile. One of the key findings includes that magnetic parameter plays a vital role in directing fluid flow and lowering temperature profile. Moreover, it is concluded that Cu-water based nanofluid high thermal conductivity contributes in enhancing heat transfer efficiently.