玉米秸秆散粒体颗粒Burgers接触模型参数的确定方法
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摘要
为建立玉米秸秆散粒体成型离散元模型,以不同压缩参数进行成型试验,利用离散元仿真软件基于内置Burgers模型对压缩过程建立仿真模型,并利用控制变量法针对模型参数设计了5组对照试验,分析颗粒模型微观参数对模型宏观力学行为影响规律。仿真试验结果表明:Maxwell体弹性系数增大时,加载至目标载荷所需位移增加,仿真结束时残余应力增加;Maxwell体黏性系数增大时,加载结束后残余应力增加。Kelvin体弹性系数增大时加载至目标载荷所需的位移减小,仿真结束时残余应力减少。Kelvin体黏性系数增大时加载结束时应力突降值增大,但仿真结束时残余应力减小。摩擦系数主要影响加载至目标载荷所需位移,摩擦系数越大,加载至目标载荷位移越小。依此规律,通过调试微观参数,确定适用于描述样品玉米秸秆散粒体物料的仿真模型参数:Maxwell体弹性系数Em为1.75×105N·m-1,黏性系数ηm为2.6×107N·s·m-1;Kelvin体弹性系数Ek为1.8×104N·m-1,黏性系数ηk为0.7×104N·s·m-1,摩擦系数f为0.5。该参数下仿真模型压缩过程力学曲线与实验室物料压缩试验所得力学曲线吻合;物料填充阶段,力链强度受物料自重影响,载荷开始施加后,强力链主要集中于加载面附近,当施加应力达到0.92MPa时,强力链在成型腔内趋于均匀分布。压缩结束后力链分布特征与实验室物料压缩样品特征吻合,证明了所建立的仿真模型的合理性及模型参数确定方法的可行性,为后续生物质物料成型研究提供了参考。
To generate the Discrete Element Method numerical model of corn stalk pellets, Burgers rheological model based on the discrete element method was introduced to simulate the densification of corn stem pellets in f in this study. Also controlling variable method was applied to measure the relation between rheological parameters and macroscopical mechanical behaviors in five groups of experiment. During the experiments, the displacement and residual stress increased with the augment of the linear spring stiffness in Maxwell part and the residual stress also increased with the increase of dashpot viscosity in this part of the model, while the displacement and residual stress decreased with the linear spring stiffness of Kelvin part. The residual stress decreased with the increase of dashpot viscosity in this part of the model while the sudden drop of stress rose with the increase.The friction coefficient influenced the displacement and increased with its augment. According to above conclusion, parameters of rheological model were adjusted to make the rheological properties of the numerical model fully coincident with corn stalk material. The result showed the coincidence of numerical model and corn stalk material in terms of the mechanical properties and the force chain distribution. In the filling stage, the force chain is affected by the weight of material. When the load is applied, the force chain mainly concentrates near the loading plane, the force chain tends to distribute uniformly in the forming chamber while the applied stress reaches 0.92 MPa. The study provides an approach to analyze the densification of biomass.
To generate the Discrete Element Method numerical model of corn stalk pellets, Burgers rheological model based on the discrete element method was introduced to simulate the densification of corn stem pellets in f in this study. Also controlling variable method was applied to measure the relation between rheological parameters and macroscopical mechanical behaviors in five groups of experiment. During the experiments, the displacement and residual stress increased with the augment of the linear spring stiffness in Maxwell part and the residual stress also increased with the increase of dashpot viscosity in this part of the model, while the displacement and residual stress decreased with the linear spring stiffness of Kelvin part. The residual stress decreased with the increase of dashpot viscosity in this part of the model while the sudden drop of stress rose with the increase.The friction coefficient influenced the displacement and increased with its augment. According to above conclusion, parameters of rheological model were adjusted to make the rheological properties of the numerical model fully coincident with corn stalk material. The result showed the coincidence of numerical model and corn stalk material in terms of the mechanical properties and the force chain distribution. In the filling stage, the force chain is affected by the weight of material. When the load is applied, the force chain mainly concentrates near the loading plane, the force chain tends to distribute uniformly in the forming chamber while the applied stress reaches 0.92 MPa. The study provides an approach to analyze the densification of biomass.
引文
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[3] ZHOU Y G,ZHANG Z X,ZHANG Y X,et al.A comprehensive review on densified solid biofuel industry in China[J].Renewable and Sustainable Energy Reviews,2016,54:1412-1428.
[4]朱金陵,王志伟,师新广,等.玉米秸秆成型燃料生命周期评价[J].农业工程学报,2010,26(6):262-266.
[5]薛志平,白雪卫,张博,等.基于离散元法的螺旋进料器物料流动特性分析[J].沈阳农业大学学报,2017,48(1):63-69.
[6] KAZUYA TAKABATAKE,YUKI MORI,JOHANNES G KHINAST,et al.Numerical modeling of solid biomass combustion:difficulties in initiating the fixed bed combustion[J].Energy Procedia,2017,110:390-395.
[7] KAI FENGA, MONTOYABBM, EVANSTM. Discrete element method simulations of bio-cemented sands[J]. Computers and Geotechnics,2017,85:139-150.
[8] BEHZAD MAJIDI PHILIP ROLFE,MARIO FAFARD,DONALDP ZIEGLER,et al.Numerical modeling of compaction and flow of coke/pitch mixtures using discrete element method[J].Construction and Building Materials,2018,169:315-324.
[9] TOM LEBLICQ,BART SMEETS,HERMAN RAMON,et al.A discrete element approach for modeling the compression of crop stems[J].Computers and Electronics in Agriculture,2016,123:80-88.
[10]李永奎,孙月铢,白雪卫.玉米秸秆粉料单模孔致密成型过程离散元模拟[J].农业工程学报,2015,31(20):212-217.
[11]王成军,刘琼,马履中,等.棉籽颗粒在三自由度混联振动筛面上的运动规律[J].农业工程学报,2015,31(6):49-56.
[12]杨明韶.农业物料流变学[M].北京:中国农业出版社,2010.
[13]霍丽丽,赵立欣,田宜水,等.生物质颗粒燃料成型的黏弹性本构模型[J].农业工程学报,2013,29(9):200-206.
[14]李汝莘,耿爱军,赵何,等.碎玉米秸秆卷压过程的流变行为试验[J].农业工程学报,2012,28(18):30-35.
[15]袁全春,徐丽明,邢洁洁,等.机施有机肥散体颗粒离散元模型参数标定[J].农业工程学报,2018,34(18):21-27.
[16]张涛,刘飞,赵满全,等.玉米秸秆接触物理参数测定与离散元仿真标定[J].中国农业大学学报,2018,23(4):120-127.
[17]杨振伟,金爱兵,周喻,等.伯格斯模型参数调试与岩石蠕变特性颗粒流分析[J].岩土力学,2015,36(1):240-248.
[18]卓家寿,黄丹.工程材料的本构演绎[M].北京:科学出版社,2009.
[19] ITASCA CONSULTING GROUP.PFC3D(Particle flow code in 3 dimensions)theory and background[R].Minneapolis,USA:Itasca Consulting Group,2008:33-39.
[20]孙其诚,王光谦.颗粒物质力学导论[M].北京:科学出版社,2009.