仓储粮堆机械通风时压力场的模拟研究

以仓储粮堆机械通风试验为基础,以实仓试验相关数据为依据,建立了仓储粮堆机械通风过程中内部压力场分布的计算流体动力学(CFD)模型,并进行了不同通风风量条件下开环流熏蒸口和开人孔时的数值模拟计算。最后通过实仓试验数据和模拟结果进行验证。结果表明,仓储粮堆机械通风过程CFD模型能够真实反映机械通风过程中粮堆内部压力场的分布情况,将计算流体力学模拟技术应用于仓储粮堆压力场的预测分析是可行的。     

储粮压力对玉米粮堆温度场影响的实验与模拟研究

粮堆温度场的分布受储粮压力变化的影响较大。利用自制粮堆实验装置进行了三种不同储粮压力下玉米粮堆静态储藏实验。通过在两壁面提供恒定的温度梯度,竖向方向施加不同压力构建出粮仓内多因子实验环境。根据测点数据拟合出了不同时刻温度分布云图,以及不同储粮压力下温度场变化趋势,得出储粮压力对玉米粮堆温度场的影响规律。并采用COMSOL软件对不同工况下温度场的分布进行数值模拟,模拟结果验证了随着储粮压力增大,粮堆内热量传递也变缓慢,达到稳态时的温度也越低。     

准静态仓粮堆内部流场CFD模拟研究

利用计算流体动力学方法对通风期间粮堆内部流场(温度场、速度场、压力场)进行计算模拟。对不同通风条件和边界条件的粮堆内部流场进行模拟仿真,发现在不同的通风速率、不同的通风时间下,其粮堆温度场、速度场和压力场的变化不仅表现在不同粮层之间,在同粮层的不同位置也存在变化。通过对通风风速为7 m/s的粮堆降温过程的试验结果和CFD模拟结果对比分析可知:试验采集点的温度数值和CFD模拟结果数值平均误差小于1.0℃,其模拟结果和试验结果得出粮堆温度的变化过程基本一致。     

密闭粮堆中水分和温度变化的模拟研究

通过数值模拟的方法对考虑呼吸作用的密闭粮仓内温度和水分随时间的变化进行了探究。在数值模拟过程中,对真实粮仓进行适当的简化,建立数学模型,利用有限元法,对不同初始温度的粮堆进行数值模拟分析,研究粮堆内部温度和水分变化与呼吸作用的关系,当粮堆的初始温度较高时,呼吸作用对粮堆温度和水分的影响非常显著。利用研究结果可以为粮堆进行合理的"人工干预"提供理论依据。     

高大平房仓粮堆插管机械通风数值仿真研究

对平房仓粮食通风中空气流速分布问题进行CFD数值模拟。考虑粮仓压力的分布,针对通风笼式通风中所采用的通风笼进行独立建模分析,获得其阻力和风速关系数据。并将其应用于粮仓整体数值模型中,提升了模拟的真实性。基于某粮库所采用的粮堆"插管"技术进行粮堆插管模拟,并对插管效果进行评估。结果表明:通过粮堆插管的合理布置,可使粮食内部空气流动速度得到有效改善。通过对插管附近流场、压力场的观察,给出了插管提升通风效果的原理和插管优化设计的方向。     

高大平房仓双侧吸出式斜流通风数值模拟和实验的比较研究

本研究基于数值模拟方法,对高大平房仓双侧吸出式斜流降温保水通风实验工况进行了数值模拟仿真,分析了在双侧吸出式斜流通风过程中粮堆温度和水分的变化规律,对实验数据与计算机模拟结果进行了对比分析。同时,探究了斜流通风与横向通风相结合时的降温保水效果。研究发现,采用双侧吸出式揭膜斜流通风,在通风空气温度和湿度合适的情况下,可以实现高大平房粮堆上部的快速降温保水效果。在进行斜流通风后,再适当地进行一段时间的横向通风,就可以有效地降低粮堆底部的粮温,而且粮堆水分基本不变。斜流与横向相结合的通风方式可以实现储粮快速降温保水效果。     

计算流体力学技术在粮食储藏中的研究进展

粮堆湿热模型可以全面构造粮堆内部温度场,可以用数学的方法进行粮堆内部温度场的模拟,用现有数据来构造整个粮堆内部的温度场。主要介绍了CFD数值模拟的理论基础,根据粮食的多孔介质传热传质特性,提出了粮堆中用CFD方法进行数值模拟的可行性;分析了国内外在粮堆热传递方面已做出的研究成果以及此软件的应用发展现状。     

基于COMSOL静态储粮玉米粮堆温度场研究

以初始温度为26℃,边长为1 m并设有冷、热壁面的方形玉米粮堆仓为研究对象，利用数值模拟软件COMSOL,对仓内粮堆温度场进行数值模拟分析，并基于验证的模型研究粮堆内外存在温差时，其内部温度随时间的变化规律。结果表明：靠近冷、热壁面的粮堆温度变化较快；仓内粮堆温度在冷热壁面间形成梯度，出现分层现象；不同初始粮温条件下，壁面与粮堆温差影响仓内粮堆温度分布，储藏96 h后，初始粮温为22℃的粮堆温度变化幅度最大，为24.9℃;粮堆与壁面温差较大的条件下，热量传递较快，仓内粮堆温度逐渐趋于稳定；初始粮温一致，不同种类粮食条件下，在储藏192 h后，大豆、小麦、玉米、稻谷和油菜籽仓内粮堆最终温升分别为2.21、2.18、2.17、2.64和2.40℃;密度和孔隙率差异共同影响仓内粮堆温度的分布，孔隙率较大的玉米粮堆，温度更加均匀。     

基于DEM-CFD的粮堆气流阻力与传热特性模拟研究

谷物固定床干燥是测定通风过程中谷物温湿度变化、气流阻力规律的常用方法,在固定颗粒床中孔隙分布对粮堆气流阻力与传热特性影响明显。本研究采用离散单元法(DEM)模拟了大豆颗粒随机堆积的孔隙结构,并对堆积颗粒间的接触进行处理,利用DEM-CFD方法模拟了大豆固定床中的气流阻力与传热特性。结果表明：粮堆压力降与入口速度近似呈二次函数关系,与考虑壁面效应的Reichelt方程计算结果一致。固定床层内部速度与温度场分布不均匀,受床层孔隙率分布、入口风速影响较大,近壁面区域气流速度与降温速度均高于床层中心区域。     

基于Workbench的青核桃力学特性分析

根据青核桃去皮过程中的受力特点,分析青核桃静力学特性,建立青核桃的几何模型;通过对青核桃进行不同加载方式下的压力试验,运用Workbench对青核桃在不同加载方式下的力学特性进行仿真模拟。通过比较压力试验和模拟仿真值,发现二者的结果一致,说明仿真的可行性,所建的力学模型可以分析核桃青皮在去皮过程的破损机理,可为研制新型青核桃去皮机械提供参考依据。压力试验与有限元模拟结果表明,施加相同压力条件下,方向并不是去青皮的决定性因素。     

基于GWO-BP神经网络及粮食压缩实验对粮食孔隙率的预测

孔隙率是影响粮堆内热湿传递的关键参数,为探究粮仓中散装粮堆孔隙率的分布规律,通过开展粮食压缩实验来获取不同的粮食种类在不同水分含量和竖向压力条件下的孔隙率。提出了一种基于灰狼算法优化BP(GWO-BP)神经网络的粮食单元体孔隙率预测模型,并将该模型与BP神经网络模型、随机森林模型的孔隙率预测结果进行对比,最后利用粮食单元箱实验对该模型的泛化能力进行验证。结果表明,GWO-BP神经网络模型的孔隙率预测性能最佳,该模型的评价指标R2为0.960 5、RMSE为0.013 7及MAE为0.0131,均在允许的范围内。本研究为粮食孔隙率的确定提供了一种神经网络预测的方法,为深入开展粮堆多场耦合分析提供了重要基础,为安全储粮提供了理论支持。     

Simulation of the stress regime during grain filling in bamboo reinforced concrete silo

Design and development of low-cost farm silos call for a strong understanding of its structural performance and loads. Limited studies address the effect of stored grains on silos. A farm level bamboo reinforced concrete (BRC) silo with a flat bottom has been designed for the storage of rough rice. A full-scale 3D finite element (FE) model of the BRC silo has been developed and the grain filling in progressive layers simulated in the ANSYS^® software. The stored grain and silo body interactions have been modeled considering the characteristic properties of both rough rice as well as the BRC, with minimal simplifications. The numerical results have been compared with the outcomes of classical theories (Jannsen’s and Reimbert’s) and design code (IS 4995-1974). While a significant difference was observed between the lateral stress magnitudes predicted by the numerical and analytical methods, the axial wall stresses from FEM approach deviated from the IS code values by 16%. Contrary to the analytical approaches, FEM predicted non-uniform stress distribution due to the bulk grain at the silo bottom. The numerical approach could also identify the localized peak pressures and stress distribution patterns within the grain layers, which is usually beyond the scope of analytical techniques. Possible reasons for fluctuations in stress patterns are discussed in detail. The study unveiled the intricacies involved in the FEM and the analytical outcomes while predicting the stresses in small and medium scale silos intended for use on farms.     

Study on clothing pressure distribution of calf based on finite element method

This study examines the clothing pressure distribution on the calf using pressure bandages with different levels of tightness. A dynamic clothing pressure test device was fabricated to obtain numerical values for the clothing pressure on key points of the calf, which were used to construct and verify a finite element model of the clothing pressure distribution. A 3D multilayer calf model was established with a simple and rapid method. After point cloud data of the calf outline were obtained by a 3D body scanner; a multilayer calf model comprising skin, muscle, and bone was fitted by reverse engineering software. The results of this model were consistent with the test values of the clothing pressure at key points. These results cannot only be a practical guide for the scientific and rational design and manufacture of tight-fitting clothing but also provide a quantitative basis for the development of clothing pressure standards.     

筒仓粮堆内部竖向压力计算方法

考虑到筒仓粮堆内部同一水平面上竖向压力的不均匀分布现象,提出储料对仓壁的摩擦及粮堆内部储料间摩擦的共同作用是造成粮堆内部竖向压力不均匀分布的主要因素。根据有限元结果与实验数据,提出了筒仓仓壁处和筒仓内部有效摩擦系数分布规律的数学表达式。基于该表达式,推导出粮堆空间任意一点竖向压力的理论计算方法和简化公式。公式结果与有限元和实验数据有较好的一致性。     

仓储粮堆通风干燥湿热传递模型的研究进展

从古到今,治国理政的首要之务是粮食安全。粮食仓储安全尤为重要,关系到一个国家的国家安全。由于粮食干燥储存方法原始、干燥技术落后等原因,我国每年收获后会损失大量粮食。粮食中湿热分布不均不仅会降低粮食的品质,而且会因霉变、虫害等问题严重影响食品安全。因此,如何快速、均匀而又低能耗地降低粮堆含水率或者温度,保证粮食品质,同时节约能源,是粮食干燥储藏研究的一个重要方向,具有重要的理论及现实意义。通风干燥是保证储粮中湿热均匀分布的重要措施,建立干燥模型预测粮堆的湿热分布是研究粮堆干燥过程中湿热传递的重要手段。该研究综述了粮堆湿热传递的经验模型、连续模型和离散模型,其中经验模型容易获得,但是应用较少;连续模型应用较多,但不能反映粮堆的孔隙结构;离散模型可以很好的反应粮堆的孔隙结构,但其计算量大,并且难以理解和构建。最后该研究指出可以根据不同的湿热传递过程,结合先进的计算方法和处理技术,建立相应的模型,以满足不同的模拟要求,并对粮堆通风干燥湿热传递模型未来的研究方向进行了展望。     

服装压力与人体舒适性之关系

从服装压力与人体舒适性关系、服装压力研究的理论基础与以往的研究基础、学科领域发展中的重大贡献介绍、服装压力的测定等4个方面对目前服装压力与人体舒适性关系的研究进行综述,并讨论了如何用数字化模拟的方法建立三维动态服装压力分布模型。     

Mathematical modelling and numerical simulation of phosphine flow during grain fumigation in leaky cylindrical silos

The phosphine distribution in a cylindrical silo containing grain is predicted. A three-dimensional mathematical model, which accounts for multicomponent gas phase transport and the sorption of phosphine into the grain kernel is developed. In addition, a simple model is presented to describe the death of insects within the grain as a function of their exposure to phosphine gas. The proposed model is solved using the commercially available computational fluid dynamics (CFD) software, FLUENT, together with our own C code to customize the solver in order to incorporate the models for sorption and insect extinction. Two types of fumigation delivery are studied, namely, fan-forced from the base of the silo and tablet from the top of the silo. An analysis of the predicted phosphine distribution shows that during fan forced fumigation, the position of the leaky area is very important to the development of the gas flow field and the phosphine distribution in the silo. If the leak is in the lower section of the silo, insects that exist near the top of the silo may not be eradicated. However, the position of a leak does not affect phosphine distribution during tablet fumigation. For such fumigation in a typical silo configuration, phosphine concentrations remain low near the base of the silo. Furthermore, we find that half-life pressure test readings are not an indicator of phosphine distribution during tablet fumigation.     

平房仓中稻谷密度的时空分布值及堆高沉降特性研究

使用粮食回弹模量仪测定出稻谷堆的压缩密度与最大主应力(竖直压应力)及储藏时间的关系模型。选定修正剑桥模型作为稻谷堆的应力与应变关系本构方程,使用有限元方法计算出装粮后瞬时平房仓中稻谷层的竖直压应力分布值。由平房仓中稻谷堆各层的竖直压应力和稻谷堆的压缩密度与最大主应力(竖直压应力)及储藏时间的关系模型计算出平房仓中稻谷层的密度与粮层深度及储藏时间的关系模型。结果表明：稻谷堆压缩密度随最大主应力的增加而增大,随储藏时间的增加而增大,稻谷堆压缩密度关于储藏时间和最大主应力的关系模型是ρ=562.87+1.605 6ln(T)+(46.07+1.105ln(T))(1-e^{-0.000 001 p3_v+0.000 2 p2_v-0.013 5p_v+0.000 3});平房仓中稻谷层密度随粮层深度的增加而增大,随储藏时间的增加而增大,平房仓中稻谷堆密度关于储藏时间和粮层深度的关系模型是ρ=566.94+1.678 1ln(T)+(11.06+0.129 4ln(T)(1-...     

Contact-free measurements and numerical analyses of the strain distribution in the joint area of steel-to-timber dowel joints

Two different dowel-type joints of differing size were loaded in tension parallel to the grain. The strain distribution in the joint area was studied using a contact-free measurement system. The results were compared with those of numerical analysis. The measurement system was found to be a valuable complement to traditional measurement techniques and also to numerical analyses performed in parametric studies. The measurements obtained were shown to be particularly useful for studying the highly nonlinear behavior of timber that is of special importance in characterizing timber dowel joints. Several observations of considerable interest were made on the basis of numerical results in combination with results of the contact-free measurement system. A non-uniform strain distribution in the joint area was detected, for example, and shear strains and tensile strains, both parallel and perpendicular to the grain were found to be concentrated in the areas most likely to influence the failure mode of the joint. A general observation made was that the larger size joint failed in brittle manner, an observation supported by previous research.