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塔里木大学毕业论文（设计）任务书学院机械电气化工程学院班级学生姓名学号课题名称小型果树移栽机起止时间2011年12月 1日 2012 年 5 月 29 日（共14 周）指导教师安静职称讲师课题内容本装置用于枣树果苗的移栽，体积小，行动方便。能够完成果树幼苗的挖掘，运送，栽培，覆土等工作。拟定工作进度（以周为单位）第1周第2周 通过查找文献资料，了解国内外现状。第2周第5周 设计总体方案。第6周第9周 结构进行具体设计。第10周第12周 撰写设计说明书，对部分问题修改、调整。第13周第14周 整理资料准备答辩。主要参考文献1武科，陈永成.几种典型的移栽机J.新疆农机化,2009:12-14.2熊耐新,全蜡珍.我国棉花移栽机的现状与发展趋势J.湖南农机,2010(10):1-3.任务下达人（签字） 年 月 日任务接受人意见任务接受人签名 年 月 日小型枣树移栽机铲斗组件的仿真分析（塔里木大学机械电气化工程学院，新疆 阿拉尔 843300）摘要: 本设计的小型枣树移栽机，用于挖掘直径在2-6cm的较小树木，挖掘土球直径为50cm，土球高度为60cm。关键词：小型枣树移栽机；铲斗组件；安全系数；仿真；等量应力变化中图分类号： 文献标识码：ASmall jujube tree transplanting machines bucket assembly simulation analysisChangYinPeng(Mechanical Electrical Engineering College of Tarim University, Xinjiang Alar 843300)Abstract : The design of small jujube transplanting machine, used for mining2-6cm in diameter, smaller trees, digging soil ball diameter is 50cm, height 60cm soil ball.Keywords: Small jujube tree transplanting machines Blade assembly Bucket assembly Blade wall Hydraulic cylinderCLC: Document Code: A1.引言随着经济和科学技术的发展，加强科学技术的投入和技术创新。加大宣传力度，提高农民的积极性。同时要使栽植的稳定性和栽植速度大大提高，降低生产成本和劳动强度。我国在移栽机研制过程中，农机与农艺明显脱节，需要进一步完善与育苗设施及相应的配套技术。在引进基础上要克服不足，尽量设计出适合经济作物的移栽机，加强自动喂苗栽植器1的研究，增加检测与传感装置，适时地控制栽植过程。力求达到预期的栽植效果。同时还要加强自动提苗机构的设计，应将通用移栽机2与专用移栽机相结合，增强移栽机的环境适应性，提高其通用性。枣树在栽植过程中都是沿用传统的人工栽植的方法，传统栽植法劳动力大、强度大，机器的机动性、适应性低，能耗高、效率较低等问题。要实现由传统栽植技术向现代栽植技术的转变。需因地制宜，大力发展枣树栽植机械化3。为了充分利用资源减少自然灾害，争取高产，机械化移栽是有效途径。这样可以解决人工栽植过程中的栽植劳动强度大，所需劳动力较多，产品粗大笨重，成本高、效率低，质量难以保证的问题。现代设计方法不仅要考虑机械静强度，而且还要考虑机械的动态性，这样才能提高机械设备的性能和效率。随着移栽技术的作用日益突出，降低了农民的劳动强度、提高工作效率，机械移栽的行距、株距和深度保持一致，质量稳定可靠，为枣树种植的规模化提高了前提，为生态作业打下了良好的基础。生态果业机械化发展已经步入新的历史起点4，生态果业机械化作为发展现代化农业的主要内和主要标志，适合地区生产需要的栽植机植种类较少、单一，科技含量不高，不能满足果业生产发展的要求。人工移栽劳动强度大，需劳动力多，效率低，严重影响了经济作物的发展，不能较快地推进种植果林业的发展。新型的栽植机的改造和设计提高了机具的性能和效率5，并为其他的林业与木工机械动态设计开辟新的道路，使得我国的机械赶得上时代并达到世界的水平，这对于提高我国植树造林机械化的进程有巨大的推动作用，同时对于我国林业的经济效益和生态效益具有重大意义。也对枣果业的发展具有重要的现实意义。2.结构原理和工作过程本实用新型涉及一种液压小型枣树移栽机，属于园林机械技术领域。此小型树木移栽机由提升架滑道、 提升架液压缸、提升架、铲斗组件滑道、铲斗组件和铲斗滑块等部件组成 ，挖树的动作是由各组件配合完成，铲斗组件用来铲断树木的侧根并使根球与周围土壤分离机架刚性固定在配套拖拉机或其他动力机械上；提升架由1个提升油缸来驱动，铲斗组件由两铲斗液压缸驱动铲斗组件的开合由开合盖板驱动大致工作作流程如下：驾驶林木移栽机靠近要移栽的树木，在快接近的时候停下，驾驶枣树移栽机使被移栽树木木处于铲斗组什中间位置，合上开合盖板，使铲斗组件闭合包围枣树，铲斗组件在铲斗组件液压缸作用下压下切断树木的根部，打开提升油缸把所挖树木提升上来，完成枣树的挖掘工作。本设计结构简单、操作简便、机动灵活、作业效率高，适用于苗圃、林场、园林等场所的树坑挖掘、小型树木带土起挖移栽、短距离树木运输。其总体结构示意图如下图所示：1铲斗 2架子一侧 3六角厚螺母 4特大垫圈 5闭合盖板 6六角厚螺母 7拉杆垫圈 8机架滑轨 9提升架曲柄 10提升架液压刚 11机架 12摇杆 13拉杆14提升架 15铲斗液压缸桶套 16六角头螺栓图1 小型枣树移栽机总体结构示意图枣树移栽机的挖掘主要靠铲斗组件，铲斗组件的作用是在挖掘工作时切断树木的根部，保证挖掘的顺利进行。从受力分析的角度看铲斗组件受到的载荷也较大，而且铲斗组件的空间位置随时间不断变化。所以铲斗组件的性能直接影响枣树移栽机的寿命和作业性能，必须合理的设计铲斗组件的结构，提高刚度，使应力分布合理，尽量达到结构的最优化。随着有限元技术和通用有限元软件的发展，利用CAE技术对零件的结构进行工程数值模拟，结构优化仿真等有限元分析逐渐成为结构设计的有效工具。3.铲斗组件有限元模型的建立3.1铲斗组件的受力分析铲斗组件安装在架子一侧的滑块外生杆上并与铲斗液压缸活塞杆刚性的焊接在一起，由于移栽机铲斗液压缸活塞杆在工作过程中启动瞬间是匀速运动的，所以所受内力与外力是相互平衡的，可以用静力学代替动力学分析。铲斗组件所受的驱动力只有铲斗组件液压缸对它的正压力，同时受到土壤对铲斗顶部的作用力，土壤对铲斗组件的腹部压力及铲斗组件与土壤的摩擦力，在分析时我们可以抓主忽次，可以忽略土壤的摩擦力的作用。3.2铲斗组件的有限元建模首先，用solidworks2010进行铲斗组件的三维实体造型，然后用Solidworks SimulationXpress6模块对铲斗组件进行网格划分，图3为划分网格后，施加力和约束的有限元模型，在solidworks中对实体模型进行网络划分后共有15884个节点，7736个单元数。图3 铲斗组件网络划分4.铲斗组件仿真方案与结果分析4.1方案汇总方案一假设原始建模铲斗组件上的每个面都受到铲斗液压缸的最大理论推力20100N，土壤对铲斗的压强为 2 0000N/方案二假设原始建模铲斗组件上的每个面都受到均布载荷，即三个面分别收到的力均为20100/3=6700N,土壤对铲斗的压强为20000N /方案三对铲斗模型进行改变，改变铲斗模型的支撑厚度，在每个面上添加铲斗液压缸的最大理论推力，土壤对铲斗的压强为 20000N/方案四在案例三的模型上对铲斗组件上的每个面施加均布载荷，即三个面分别收到的力均为20100/3=6700N,土壤对铲斗的压强为20000N /方案五综合分析案例一至案例四，对模型再次更改，对原始模型在支撑部位增加厚度同时对支撑边缘添加圆角。4.2结果分析方案一结果分析：针对方案一假设每个施加力的面都是施加最大理论力值可以得出如下结果： （1）Stress（-vonMises-）等量应力变化情况虽然大部分应力变化比较小，但是铲斗组件连接点附近的等量应力变化较大，存在不稳定因素；（2）铲斗组件的底部的Displacement变化幅度太大，其中部至上不过度的安全颜色趋于零，处于危险状态；（3）Deformation中部位移变化较大，没有达到理想的变形要求；（4）Factor of Safety安全系数大部分呈现蓝色，符合要求，但是支撑部位出现红色的安全警告因此极易断裂，因此还需要对此进行改进。 方案二结果分析：在方案一的基础上建立方案二，假设每个施加力的面都是施加最大理论力值的平均值可以得出如下结果：（1）Stress（-vonMises-）等量应力变化情况虽然大部分应力变化比方案一要低，但是仍然存在不稳定因素；（2）铲斗组件的上部边缘的Displacement变化幅度太大趋于红色最大值；（3）Deformation中部位移变化较大，没有达到理想的变形要求；（4）Factor of Safety安全系数全部呈现蓝色，符合要求。因此还需要对此方案进行改进，对模型进行改进。方案三结果分析：方案三是在方案二的基础上对铲斗模型进行改变，改变铲斗模型的支撑厚度，然后在每个面上施加最大理论力值可以得出如下结果：（1）Stress（-vonMises-）等量应力变化情况明显比方案一小的多，但比方案二要稍大；（2）铲斗组件的底部的Displacement变化幅度太大，其中部至上不过度的安全颜色趋于零，处于危险状态；（3）Deformation中部位移变化较小，近乎达到理想的变形要求；（4）Factor of Safety安全系数大部分呈现蓝色，符合要求，但是支撑部位出现红色的安全警告因此极易断裂所以还需要改进。方案四结果分析：在方案三的基础上建立方案四，每个施加力的面都是施加最大理论力值的平均值可以得出如下结果： （1） Stress（-vonMises-）等量应力变化情况明显的比前三个方案变化程度小，因此方案四的等量应力变化情况是趋于合理的；（2）铲斗组件的上部的Displacement变化幅度稍有些大，其中部至上部过度的安全颜色逐渐增加，危险状态明显减少；（3）Deformation中部位移变化较大，没有达到理想的变形要求；（4）Factor of Safety安全系数全部呈现蓝色，符合要求。接着在分别分析方案一至方案四的和位移及位移变化情况，可以得出以下结论，在方案一中铲斗组件顶部位移变化很大；在方案二中铲斗组件顶部位移变化达到要求，但是侧部位移存在隐患；在方案三中铲斗组件顶部位移达到要求，但支撑处部分位移存在潜在隐患；在方案四中铲斗组件顶部位移和侧部位移均达到要求。然后再分别分析方案一至方案四的安全系数变化情况，在方案一中安全系数大部分是合格的，支撑部位附近的安全因数是小于1的，因此支撑部位是不合格的；在方案二中安全系数均是大于等于1的，因此是合格的；在方案三中安全系数大部分是合格的，支撑部位附近的安全因数是小于1的，因此支撑部位是不合格的；在方案四中安全系数均是大于等于1的，因此安全系数变化符合要求的。综合比较可知方案四的Stress（-vonMises-）等量应力变化情况、合位移、位移、及安全系数的变化相对于前三个方案是最优的，但是其Stress（-vonMises-）等量应力变化情况任然存在不稳定因素，因此还需要对方案四进行优化。 方案五结果分析：再对铲斗组件进行建模，对原始模型在支撑部位增加厚度同时对支撑边缘添加圆角后再次进行分析，最后得出其Stress（-vonMises-）等量应力完全达到要求，其合位移、位移、及安全系数的变化也相当合理，因此方案五是最优的。5结论1）用有限元分析方法变连续结构为离散结构，代替了传统的理论分析方法，节省了大量的计算时间，并提高了计算的准确性、科学性和可靠性，缩短了设计周期。2）根据有限元应力分析、位移分析、合位移分析及安全系数分析对铲斗组件进行改进设计，使铲斗组件的应力分布更趋于合理符合作业工况的要求。6.参考文献1胡军,封俊,曾爱军.大葱移栽机的发展现状与移栽前景J. 农机化研究,2002（2）:13.2 王君玲,高玉芝,李成华. 挠性圆盘式移栽机移栽裸根苗的埋苗率试验J. 沈阳农业大学学报，2006(10):792794.3张波屏.现代种植机械M.北京：机械工业出版社,1997:14.4汤智辉,贾首星.新疆兵团林果业机械化现状与发展J.农机化研究,2008（11）:58.5王乃康,矛也冰,赵平.现代园林机械M.北京:中国林业出版社,2000:147152.6 陈超祥,叶修梓.零件与装配体教程E.北京：机械工业出版社,2011:152165.小型果树移栽机一、 课题研究的目的和意义枣树在栽植过程中都是沿用传统的人工栽植的方法，传统栽植法劳动力大、强度大，机器的机动性、适应性低，能耗高、效率较低等问题。要实现由传统栽植技术向现代栽植技术的转变。需因地制宜，大力发展枣树栽植机械化。为了充分利用资源减少自然灾害，争取高产，机械化移栽是有效途径。这样可以解决人工栽植过程中的栽植劳动强度大，所需劳动力较多，产品粗大笨重，成本高、效率低，质量难以保证的问题。红枣种植过程机械化程度的提高，大大降低了劳动强度，大量解放劳动生产力向二三产业转移，有助于农村城市化、工业化，对提高农民素质和生活质量，实现农业现代化具有重要的作用。红枣生产中的移栽是枣树抚育机械之一，是实现枣业全程机械化的一个重要一环。因此移栽机研究的目的毋庸置疑。生态果业机械化发展已经步入新的历史起点，生态果业机械化作为发展现代化农业的主要内和主要标志，适合地区生产需要的栽植机植种类较少、单一，科技含量不高，不能满足果业生产发展的要求。因此在此大好的趋势之下发展小型果树移栽机是非常有意义的。二、现状及分析1、国内研究现状及分析国内对农作物的机械化育苗移栽技术的研究早在20世纪50年代未60年代初就已经开始。由于没有突破育苗移栽机械化过程中的技术难题使这一技术搁浅。近年来由于农业生产的发展，新技术、新工艺的出现，为移栽机具的发展提供了很好的发展前景，20世纪80年代以后近年来由于农业生产的发展，移栽机具发展迅速，从不到l 000台上升到将近8 000台。东北等大型农场多采用工厂化营养钵苗和机械化栽植技术，总体水平相对较高。我国长期以来，树苗栽植一直沿用传统的手工劳动方式，劳动强度大，生产效率低。由于枣树种植面积的增加和农村劳动力的转移，移栽技术落后、效率低已成为枣树生产的制约因素，枣树移栽机械化和自动化已成为农民越来越迫切的要求。与小麦、水稻、玉米生产机械化发展速度相比，枣树移栽机械化的发展比较缓慢。这种状况与当前加快实现农业现代化的形式要求不适应。有关资料显示，英国、法国、美国和日本等国在自动栽植机的研制方面均取得了很大的成绩。我国从在20世纪60年代开始研制移栽机，初期主要用来移栽玉米和棉花等作物，我国在这方面的研究起步晚，技术进步缓慢，目前整体技术水平还较低。植树造林方面的机械也是很少，我国于1953年开始引进移栽植树机，在东北地区西部营造防护林。1960年开始设计和制造拖拉机牵引式半自动投苗植树机。为了适应沙区防风固沙植树造林的要求，国家不断投资科研经费来研制植树机，2001年研制成功的深栽造林钻孔机在我国西部、特别在干旱和半干旱地区造林具有广阔和特殊的应用前景。2001年填补我国机械化造林空白的新型液压植树机（JYZ-80）在内蒙古达拉特旗白土梁林场研制成功并投入批量生产。这种植树机由履带式拖拉机牵引，采用液压系统调节耕深，开沟深度随意调节，最大开沟深度为80cm，主要适用于沙区、荒漠地区栽植带根苗、扦插苗、沙柳等。我国的移栽技术刚刚处于起步试验阶段，目前仍以人工移栽为主。人工移栽难以实现大规模种栽植，从而导致生产规模小，生产效益低，不利于移栽技术的推广。从长远来看，机械化移栽可以实现育苗移栽一体化。现阶段我国移栽技术发展极不平衡。我国针对不同的果树及其它作物分别研制了相应的栽植机，由于栽植作业质量与农艺要求还有一定差距，未能大面积推广。随着林果业种植面积和生产规模的扩大，在有人工作业方式使用，已不能满足林果产业化的步伐。我国在引进国外技术的基础上开发自己的产品，以缓解劳动力紧张和提高生产效率。在我国，枣树的栽植具有季节性和区域性特点，机具作业时间短，单一性能机具的年使用率降低，因此在今后的设计中，应尽量考虑一机多用的问题。具体要改进的措施：一是研制适用不同的土壤条件和工作条件的机具，二是设计通用机架，在更换其他工作部件后即可完成其他果树林作业项目，提高其使用率。三是要考虑人机的工程学原理，要让人舒服，健康的工作，提高安全性能。现在我们国家的技术还不够成熟，好多还是借鉴他国的，单一的机械不能通用到其他地区的工作，有待机械多样化，不仅能够适用种植枣树苗还要适用其他的树种，更要发展到植树造林的机械上一样可以通用。种种的原因、地理位置及技术条件证明我们加大力度发展机械化势在必行。2、国外研究现状及分析 世界上移栽技术发展较早的发达国家和地区主要是欧美和日本等国，该技术在早期主要应用于蔬菜和经济作物的移栽，随后逐步用于玉米等粮食作物的移栽。早在上世纪20 年代初期就开展了钵苗移栽的生产工艺研究，研制出结构简单的秧苗移栽机具，在一定程度上减轻了人工移栽劳动强度；到上世纪30 年代出现手工喂苗的移栽机械，移栽技术得到实质性发展，使秧苗送入沟中这一过程实现机械化。上世纪50 年代开始，欧洲国家研制出不同结构形式的半自动移栽机和制钵机；到了上世纪70 年代和80 年代，半自动移栽机在欧美、前苏联等农业较发达的国家和地区得到广泛应用，使制钵、育苗、移栽技术有机结合。目前，国外的移栽技术已基本成熟，栽植后的农作物达到农艺要求，工作可靠性也较高。欧美一些农业较发达的国家，如法国、德国、荷兰、美国等国家，大部分的蔬菜生产和几乎全部的大地花卉生产都采用育苗移栽种植模式和生产工艺。日本在20 世纪80 年代，90的甜菜已实现移栽种植，移栽机自动化程度较高。从移栽机的工作过程看，这些农业机械水平较高的国家多采用钵体苗半自动移栽机械，作业过程中采用人工喂苗，并根据作业对象的不同通过更换或调节栽植器来实现机械移栽，扩大机械移栽的作业范围，提高其通用性。三、任务要求及预期目标的可行性分析任务要求树苗移栽的工艺过程主要包括开沟、送苗入沟、植苗和覆土压实等工序。为了提高树苗栽植后的成活率，树苗移栽应具有以下要求：栽植树苗根系的栽植深度应一致，并保持直散状态，避免前后左右弯曲。栽植树苗的株距应均匀一致，地上茎秆应保持直立状态，前后倾斜不超过45。栽植时开沟的深度、覆土质量及压实程度应满足农艺要求。移栽机各部机构在栽植过程中不应损伤苗木。栽植作业过程中，由于地形，土壤条件以及树苗本身的差异性，树苗的运动存在随机误差，影响栽植作用质量。任务重点对送苗、开沟、覆土、打埂、镇压，及栽植过程中影响株距和秧苗直立状态的主要因素进行研究分析，重点应该在设计的送苗、开沟、覆土、打埂、镇压装置机构的设计上，对影响因素分析不应该是主要的目的吧？。预期目标的可行性分析 我国的移栽机的发展特点是起步晚、发展比较慢；在研制过程中农机和农艺难以有效结合；移栽机功能比较单一、通用性较差；没有形成标准化、系列化、规格化；缺乏完善、科学的对移栽机标准和评价的方法；移栽成本依旧较高；作业稳定性、可靠性等性能距发达农业国家还有一定差距。纵观国内外移栽机的发展和应用情况，加上对各种不同类型移栽机的对比，总结未来移栽机的发展方向和趋势：（1）栽植质量更加优良。设计出的移栽机能够具有更好的工作质量、满足农艺要求、理想的栽植深度、直立度、较低的漏苗率和伤苗率等。（2）栽植速度进一步提高。目前市场上的移栽机多数为半自动化机具，栽植速度受人工限制，劳动强度仍然较大，移栽机在解决好此类问题的同时能更好的适应现代化农业的要求。（3）功能更加完善，机型更加齐全。目前多数移栽机仅具有单一的移栽功能，未来将集铺膜、施肥、除草、铺膜等多种功能于一体，并形成多机型、多系列的标准化产品。在移栽机的通用性方面也将进一步提高，通过局部的更换调整便能方便地实现不同作物及同一作物不同移栽苗的移栽，具有明显的一机多用功能。（4）机具的质量更加可靠。随着设计手段和加工制造技术的不断提高，移栽机的零部件及装配将更加合理，降低机具的损坏率和返修率，保证移栽机的连续作业能力。（5）设计的移栽机将更加合理。随着人性化设计水平的不断提高，在对移栽机进行设计过程中将更加注重移栽工作人员的作业姿势和劳动强度，将人工作业劳动强度将至最低。（6）农机与农艺结合的更加合理。农艺将更适应于农机，农机将更好地为农艺服务，实现农机与农艺的紧密结合。综上所述我认为小型果树移栽机的要达到的预期任务要求（栽植树苗根系的栽植深度应一致，并保持直散状态，避免前后左右弯曲。栽植树苗的株距应均匀一致，地上茎秆应保持直立状态，前后倾斜不超过45。栽植时开沟的深度、覆土质量及压实程度应满足农艺要求。移栽机各部机构在栽植过程中不应损伤苗木）及实现对送苗、开沟、覆土、打埂、镇压应该是切实可行的。其实现过程应该是一个综合的过程，它应该有开沟装置，覆土装置，动力装置以及实现其功能的其他装置。四、本课题需要重点研究的、关键的问题及解决的思路 本课题重点研究枣树果苗的挖掘，移栽，运送，栽培，其关键的问题就是移栽机构的设计及其他辅助机构的设计。具体的解决的思路如下：查找相关资料进行方案的确定，进行机构的构想和可行性分析，最后做出总体设计。五、工作条件及解决方法 （1）万方数据库和图书馆查阅相关资料，了解红枣移栽机机及移栽机行业的发展现状。（2）从了解的信息中确定设计方案。（3）查阅相关资料，了解移栽机构，以确定方案中所需的移栽机构。 (4) 遇到关键性的问题向老师请教（4）画出装配图。利用AutoCAD软件绘制二维装配图和零件图。（5）参考资料中的计算方法及公式等进行计算校核。六、完成本课题的工作方案及进度计划拟定工作进度 第1周第2周 通过查找文献资料，了解国内外现状。第2周第5周 设计总体方案。第6周第9周 结构进行具体设计。第10周第12周 撰写设计说明书，对部分问题修改、调整。第13周第14周 整理资料准备答辩。七、主要参考文献1汤智辉，贾首星.新疆兵团林果业机械化现状与发展J.农机化研究，2008（11）：58.2刘磊，陈永成.兵团移栽技术的应用与发展概况J.农机化研究，2008（9）:240241.3金诚谦.链夹式移栽机栽植作业质量影响因素分析N.农业机械学报，2008（8）：196198.4宋代平.生态植树机动态性能的理论研究.东北林业大学硕士论文C.2004（9）：1105.5于建国，屈锦卫.国内外挖坑机的研究现状及发展趋势J.新疆农机化，2007 (1)：5657.6 何新川，差心玲，邵艳英.多功能果树开沟、打埂、破埂机J.新疆农机化，20071：54.7 李志鑫，陈风，王维新. 国内移栽机具发展现状J.新疆农机化，2004（2）：328卢勇涛，李亚雄，刘洋，李斌，王涛. 国内外移栽机及移栽技术现状分析C. 新疆农机化，2011（4）：19徐金苏，赵匀. 基于ADAMS和ANSYS的辣椒移栽机构的力学仿真与应力分析N. 浙江理工大学学报,2009(9):第26卷10武科，陈永成，毕新胜.几种典型的移栽机C. 新疆农机化，2009（3）：12学生签名 年 月 日指导教师审阅意见指导教师签名 年 月 日河北建筑工程学院毕业设计（论文）外文资料翻译 系别： 机械工程系 专业： 机械设计制造及其自动化 班级： 机094 姓名： 杨东胜 学号： 2009307413 外文出处： /locate/jterra （用外文写）附 件：1、外文原文；2、外文资料翻译译文。指导教师评语：签字： 年 月 日1、 外文原文（复印件）2、外文资料翻译译文译文标题（3号黑体，居中） （小4号宋体，1.5倍行距）。（要求不少于3000汉字）The numerical modelling of excavator bucket filling using DEMC.J. Coetzee*, D.N.J. ElsDepartment of Mechanical and Mechatronic Engineering, University of Stellenbosch, Private Bag X1, Matieland 7602, South AfricaReceived 15 February 2007; received in revised form 25 February 2009; accepted 28 May 2009Available online 25 June 2009AbstractThe filling of an excavator bucket is a complex granular flow problem. In order to optimize the filling process, it is important to under-stand the different mechanisms involved. The discrete element method (DEM) is a promising approach to model soil-implement inter-actions and it was used in this study to model the filling process of an excavator bucket. Model validation was based on the accuracy withwhich the model predicted the bucket drag force and the development of the different flow regions. Compared to experimental measure-ments, DEM predicted lower bucket drag forces, but the general trend was accurately modelled. At the end of the filling process the errorin predicted drag force was 20%. Qualitatively, there was a good agreement between the observed and the modelled flow regions in termsof position and transition from one stage to the other. During all stages of filling, DEM was able to predict the volume of material insidethe bucket accurately to within 6%.? 2009 ISTVS. Published by Elsevier Ltd. All rights reserved.1. IntroductionEarthmoving equipment plays an important role in theagricultural, earthmoving and mining industries. Theequipment is highly diverse in shape and function, but mostof the soil cutting machines can be categorised into one ofthree principal classes, namely blades, rippers and buckets(shovels). This paper focuses on the numerical modelling ofexcavator bucket filling using the discrete element method(DEM).Buckets are found on a number of earthmoving machin-ery. Draglines are used to remove blasted overburden fromopen cut mines. Its removal exposes the coal depositsbeneath for mining. A dragline is a crane-like structurewith a huge bucket of up to 100 m3in volume suspendedby steel ropes. Draglines are an expensive and essential partof mine operations and play an important role in the com-petitiveness of South African mines. In the coal miningindustry it is generally accepted that a 1% improvementin the efficiency of a dragline will result in an R1 millionincrease in annual production per dragline 1. Bucketsare also found on hydraulic excavators, loaders and shovelexcavators.The filling of a bucket is a complex granular flow prob-lem. Instrumentation of field equipment for measuringbucket filling is difficult and expensive. It is possible touse small-scale (usually 1/10th scale) experimental rigs toevaluate bucket designs 1,2 but they are expensive andthere are questions regarding the validity of scaling 3,4.To scale-up results from model experiments is problematicsince there are no general scaling laws for granular flows asthere are for fluid dynamics 5.According to Cleary 5 the filling of buckets, in theabsence of very large rocks, is observed to be relativelytwo-dimensional with little motion in the transverse direc-tion. The flow pattern along a cross-section of the bucket inthe drag direction is the most important aspect of fillingand can be analysed satisfactorily using two-dimensionalmodels. Rowlands 2 made similar observations based ondragline bucket filling experiments.According to Maciejewski et al. 6, in practical caseswhen the motion of a bucket or bulldozer blade is dis-cussed, plane strain conditions apply only in some defor-mation regions. The plane strain solution for such toolscan be assumed only with limited accuracy. Maciejewski0022-4898/$36.00 ? 2009 ISTVS. Published by Elsevier Ltd. All rights reserved.doi:10.1016/j.jterra.2009.05.003*Corresponding author. Tel.: +27 21 808 4239; fax: +27 21 808 4958.E-mail address: ccoetzeesun.ac.za (C.J. Coetzee)./locate/jterraAvailable online at Journal of Terramechanics 46 (2009) 217227JournalofTerramechanicset al. 6 also investigated the assumption of plane strainconditions in soil bins where the soil and tool motion isconstrained between two transparent walls. For measure-ments in such a bin, the force acting on the tool due tothe friction between the soil and the sidewalls has to be esti-mated or neglected. They have shown that for a high num-ber of teeth on the bucket, the teeth do not act as separatethree-dimensional objects but as one wide tool built upfrom several modules. The deformation pattern in frontof such an assembly of teeth was found to be plane straindeformation. The authors, however, concluded that thiswas true for the particular cohesive soil (sandy clay) andmay not apply to other (especially rocky and brittle) mate-rials. In this study the bucket had a full-width lip with noteeth and based on the findings by Maciejewski et al. 6,the assumption of plane strain was made and two-dimen-sional DEM models were used.Analytical methods 711 used to model soiltool inter-action are limited to infinitesimal motion of the tool andthe given geometry of the problem. These methods werenot expected to be valid for the analysis of the subsequentstages of advanced earth digging problems 12. The analyt-ical methods are based on Terzaghis passive earth pressuretheory and assumptions of a preliminary soil failure pattern13. Complicated tool geometry (such as buckets) and largedeformations cannot be modelled using these methods 14.The discrete element method is a promising approach tomodel soil-implement interaction and can be used to over-come some of the difficulties encountered by analyticalmethods 15. In DEM, the failure patterns and materialdeformation are not needed in advance. The tools are mod-elled using a number of flat walls and the complexity of thetool geometry does not complicate the DEM model. Largedeformation in the granular material and the developmentof the granular material free surface are automatically han-dled by the method.Cleary 5 modelled dragline bucket filling using DEM.Trends were shown and qualitative comparisons made, butno experimental results were presented. The process ofhydraulic excavator bucket filling was investigated experi-mentally by Maciejewski and Jarzebowski 12. The aim oftheir research was optimization of the digging process andbucket trajectories. It is shown that the most energy efficientbucket is the one where the pushing effect of the back wall isminimized.Owenetal.21modelled3Ddraglinebucketfill-ing. In there approach, the bucket was modelled with thefinite element method and the soil with DEM. Ellipsoidsand clumped spheres were used to approximate the particleangularity. The bucket followed a prescribed path.Esterhuyse 1 and Rowlands 2 investigated the fillingbehaviour of scaled dragline buckets experimentally withthe focus on rigging configuration, bucket shape and teethspacing. They have shown that the aspect ratio of thebucket (width to depth) plays and important role in thedrag distance needed to fill a bucket. The bucket with theshortest fill distance was found to produce the highest peakdrag force.The main objective of this study was to demonstrate theability of DEM to predict the drag force on the bucket andthe material flow patterns that develop as the bucket fillsup. The DEM results were compared to experiments per-formed in a soil bin.2. The discrete element methodDiscrete element methods are based on the simulation ofthe motion of granular material as separate particles. DEMwas first applied to rock mechanics by Cundall and Strack16. In this study, all the simulations were two-dimensionalandperformedusingcommercialDEMsoftwarePFC2D17.A linear contact model was used with a spring stiffness knin the normal direction and a spring stiffness ksin the sheardirection (Fig. 1). Frictional slip is allowed in the tangentialdirectionwithafrictioncoefficientl.Thedampingforceactson a particle in the opposite direction to the particle velocityand is proportional to the resultant force acting on the par-ticle with a proportionality constant (damping coefficient)C 17. For a detailed description of DEM, the reader isreferred to Cleary and Sawley 18, Cundall and Strack16, Hogue 19 and Zhang and Whiten 20.3. ExperimentalTwo parallel glass panels were fixed 200 mm apart toform the soil bin. The bucket profile was fixed to a trolleywhich was driven by a ball screw and stepper motor. TheFrictionknksFig. 1. DEM contact model.218C.J. Coetzee, D.N.J. Els/Journal of Terramechanics 46 (2009) 217227complete rig could be set at an angle h to the horizontal asshown in Fig. 2a. The first arm was then rotated and fixedsuch that both arms remained vertical. The second armremained free to move in the vertical direction. First, coun-terweights were added at position A (Fig. 2a) to balancethe combined weight of the bucket profile and the secondarm assembly. This resulted in a weightless” bucket.Counterweights were then added at position B to set theeffective” bucket weight. Since arm 2 was always verticaleven for rig angles other then zero, the effective bucketweight always acted vertically downwards (Fig. 2c). Bucketweights of 49.1 N, 93.2 N, 138.3 N and 202.1 N were used.When the bucket was dragged in the direction as indi-cated, it was also free to move in the vertical direction asa result of the effective bucket weight and the force of thegrains acting on it. The bottom edge of the bucket wasalways set to be parallel to the drag direction and the mate-rial free surface. This type of motion resembles that of adragline bucket which is dragged in the drag direction bya set of ropes, but with freedom of motion in all otherdirections 2.Spring loaded Teflon wipers were used to seal the smallopening between the bucket profile and the glass panels. Aforce transducer was designed and built to measure the dragforce on the bucket. A set of strain gauges was bonded to asteel beam of which the position is shown in Fig. 2a. Theset of four strain gauges was used to measure the force inthe drag direction. Other force components were notmeasured. The force transducer was calibrated and thecalibration checked regularly to avoid drift in the measure-ments. For rig angles other than zero, the force transducerwas zeroed before the drag commenced. This compensatedforthecomponentofthebucketweightthatactedinthedragdirection. The vertical displacement of the bucket was mea-sured with a linear variable differential transformer (LVDT)andusedasinputtotheDEMsimulation. Inboththeexper-imentsandtheDEMsimulationsthebucketwasgivenadragvelocity of 10 mm s?1. The dimensions of the bucket profileare shown in Fig. 2b.In this study corn grains were used. Although the corngrains are not real soil, Rowlands 2 observed that seedgrains are suitable for experimental testing and closelyresemble natural soil flow into dragline buckets.4. DEM parameters and numerical modelFig. 3 shows the range of measured grain dimensionsand the equivalent DEM grain. A normal distributionwithin the range of dimensions given was used to createthe clumped particles. Clumps can be formed by addingtwo or more particles (discs in 2D and spheres in 3D)together to form one rigid particle, i.e. particles includedin the clump remain at a fixed distance from each other17. Particles within a clump can overlap to any extentand contact forces are not generated between these parti-cles. Clumps cannot break up during simulations regardlessof the forces acting upon them. In the model 20,00030,000clumped particles were used.A calibration process, presented in another paper, wasdeveloped for cohesionless material. The particle size, shapeand density were determined from physical measurements.The laboratory shear tests and compressions tests were usedto determine the material internalfriction angleandstiffnessrespectively. These tests were repeated numerically usingDEM models with different sets of particle friction coeffi-cientsandparticle stiffness values.Thecombinationofsheartestandcompressiontestresultscouldbeusedtodetermineaunique set of particle friction and particle stiffness values,Table 1.ADirection of drag Direction of vertical motion 2nd Arm1st ArmBForce transducer 100 mm200 mm150 mm Max volume 35 mm45WbcosWbCounter weights abcFig. 2. Experimental setup.5 - 98 - 125 - 64 - 53 - 6R 2.5 - 4.5 R 1.5 - 3.0 3.0 - 5.0 abFig. 3. (a) Physical grain dimensions and (b) DEM grain model.Dimensions in (mm).C.J. Coetzee, D.N.J. Els/Journal of Terramechanics 46 (2009) 217227219In the software used, PFC2D, so-called walls are used tobuild structures. The test rig and the bucket, with the samedimensions as in the experiment, were built from walls. Thewalls are rigid and move according to prescribed transla-tional and rotational velocities. The forces and momentsacting on the walls do not influence the motion of the wall.During the experiments a constant drag velocity of10 mm s?1was applied while the vertical displacementwas measured. The vertical displacement was influencedby both the rig angle and the effective bucket weight. A typ-ical result is shown in Fig. 4. Except for the initial transi-tion, the vertical velocity was nearly constant, for a givensetup, and increased with an increase in bucket weight. Inthe DEM model, the drag velocity was set to 10 mm s?1and the measured vertical displacement was read from adata file and applied to the bucket.Standard functions build into PFC2Dwere used toobtain the forces and moments acting on individual wallsand on the bucket as a whole. For rig angles other thanzero, the rig was kept horizontal but the gravity compo-nents were set accordingly.5. Results and discussionIt is difficult to make quantitative comparisons regard-ing flow patterns. When comparing the material freesurface, some comparisons could however be made. Figs.5 and 6 show how the material flowed into the bucket forrig angles of h = 0? and h = 20?, respectively. When com-paring the shape of the material free surface, the simula-tions were able to predict the general shape during theinitial stages of filling. The simulations however failed toaccurately predict the material free surface during the finalstages of filling.Curves were fitted to the experimental free surface andoverlaid on the numerical results in Figs. 5 and 6. The max-imum difference between the two free surfaces (heapheight) was measured along the direction perpendicularto the drag direction. Two measurements were made, onewhere DEM predicted a higher heap height, and onemeasurement where DEM predicted a lower heap height.The values and the positions where they were measuredare indicated in the figures. Taking the nominal particlesize as 10 mm, DEM predicted the heap height accuratelywithin 1.54.5 particle diameters.Fig. 7 shows typical drag forces obtained from experi-ments and simulations. The large jump in the drag forceat the beginning of the experiment was observed in mostof the runs and could not be explained and needs furtherinvestigation. From this result, it is clear that the DEMmodel captured the general trend in drag force, but it pre-dicted lower values compared to the measured values. Overthe complete drag of 800 mm, the model predicted a forcewhich was 1550 N lower than the measured force. At theend of the drag the error was 20%. The frictional forcebetween the Teflon wipers and the glass panels was mea-sured in a run without grains. This frictional force was sub-tracted from the measured drag force. Frictional forcesbetween the grains and the side panels would also havean influence on the measured results. These frictional forcescould not be measured or included in the 2D DEM modeland might be the reason why the model predicts lower dragforces 6.The drag energy was defined as the area under the dragforcedisplacement curve. Making use of different rigangles h and effective bucket weights Wb, the drag energyE700up to a displacement of 700 mm is compared in Fig. 8.The first observation that could me made was that withan increase in effective bucket weight, for a given rig angleh, there was a linear increase in required drag energy. Acloser investigation showed that with an increase in bucketweight, the bucket was forced deeper into the materialwhich caused a higher drag force when compared to abucket with less weight.The second observation that can be made is that with anincrease in the rig angle, there is a decrease in drag energy.The effective bucket weight Wbalways acted verticallyTable 1Summary of corn properties and DEM parameters used.Macro propertyMeasuredDEMInternal friction angle23?24?Angle of repose25 2?24 1?Bulk density778 kg m?3778 kg m?3Confined bulk modulus1.60 MPa1.52 MPaMaterial-steel friction14?14?Calibrated DEM propertiesParticle stiffness, kn= ks450 kN/mParticle density, qp855 kg/m3Particle friction coefficient, l0.12Other propertiesDamping, C0.2Model width0.2 m0100200300400500Drag displacement mm60070020406080100Vertical displacement mm120Wb= 202.1 N138.3 N93.2 N 49.1 N Fig. 4. Measured vertical displacement of the bucket with h = 10? andfour values of effective bucket weight Wb.220C.J. Coetzee, D.N.J. Els/Journal of Terramechanics 46 (2009) 217227downward (Fig. 2c) so that the normal force pushing thebucket into the material is given by Wb? cos (h). Thus, withan increase in rig angle, there is a decrease in the normalforce pushing the bucket into the material. This caused areduction in the drag force, and hence a reduction in thedrag energy, when compared to results using a lower rigangle. The DEM simulations were able to capture the gen-eral trends, but it predicted drag energies lower than themeasured. The reason for this is that the predicted dragforces were too low due to the exclusion of the frictionforces between the grains and the glass panels. It would,however, still be possible to use the simulation results forqualitative optimization of bucket filling.Using the simulation results it was possible to identifyhow much of the total force was exerted on each of thebucket sections. In Fig. 9 the bucket was divided into sixsections. The graphs show, as a ratio of the total dragforce, the force on each of the sections. From the startup to a displacement of 200 mm (25% of total displace-ment) the total force acted mainly on the lip and the bot-tom section. As material started to flow into the bucket,the other sections came into play, first the inner curveand finally the front section. Less than 5% of the forceacted on the top section. This was far less than the bottomsection (30%). The reason for this is that the material insidethe bucket showed little movement relative to the bucketFig. 5. Bucket filling results with rig angle h = 0?.C.J. Coetzee, D.N.J. Els/Journal of Terramechanics 46 (2009) 217227221and the pressure on the top section was only due to theweight of the material inside the bucket. On the bottomsection, the pressure was due to the combined weight ofthe material inside the bucket and the weight of the bucketitself. During the complete filling process, 2030% of thedrag force acted on the lip. This shows that the design ofthe lip and teeth is important. It is well known that thelength of the lip/teeth and the angle of attack are importantfactors influencing bucket filling 2 .Rowlands 2 made use of mixtures of millet, peas andcorn in his 2D test rig. The observation of the filling behav-iour led to the development of a theory that describes theflow characteristics and patterns of material entering thebucket. Rowlands 2 named this concept the Shear ZoneTheory. He observed that definite planes of shear (rupture)formed between distinct moving material regimes. Theseshear planes changed orientation and location dependingon initial setup and during different stages of the filling pro-cess itself. The generalised theory is shown in Fig. 10. Thedifferent flow regions, as named by Rowlands 2, are indi-cated on the figure. The movements of the material relativeto the bucket are indicated by the arrows.The virgin material remains largely undisturbed until thefinal third of the drag during which bulldozing” occurs.The initial laminar layer flows into the bucket during thefirst third of the drag (Fig. 10a). After entering to a certaindistance, this layer fails at the bucket lip and subsequentlybecomes stationary with respect to the bucket for theFig. 6. Bucket filling results with rig angle h = 20?.222C.J. Coetzee, D.N.J. Els/Journal of Terramechanics 46 (2009) 217227remainder of the drag (Fig. 10b and c). At steeper dragangles, the material flows more rapidly towards the rearbecause of the added gravitational assistance. This effectcan be seen by comparing Figs. 5 and 6.With the laminar layer becoming stationary, a new zone,the active flow zone, develops (Fig. 10). In this zone, thematerial displacement is predominantly in the verticaldirection. The active dig zone is located above the teethand bucket lip. This area develops as material starts toenter the bucket and increases in size after failure of the ini-tial laminar layer. In this zone, the virgin material fails andeither flows into the bucket as part of the laminar layerduring the first part of filling or moves into the active flowzone during the latter part of filling.The dead load that has resulted from live” material inthe active flow zone ramps up and over the initial laminarlayer. Some of the material in the initial laminar layer failsand starts to form part of the dead load (Fig. 10c). Duringexperiments and while the material was flowing, a definiterupture or shear line could be observed here. With anincrease in drag angle, the active dig zone and active flowzone tended to join into one continuous band.1002003004005006007008000ExperimentSimulation250200Drag force N 15010050Displacement in drag direction mm Fig. 7. Typical bucket drag forces with rig angle h = 10? and a bucketweight Wb= 138.3 N. = 0 = 10 = 20 Experiment Simulation 40 40220200 180160140120WbN 10080 60 506070 80100 120 110 90E700 J Fig. 8. Bucket drag energy E700as a function of the bucket weight Wbfordifferent rig angles h.010020030040050060070080000.10.20.30.40.5Displacement mm Drag force ratio FrontInner curveTopLip Bottom Outer curve LipTopBottomFrontInner curveOuter curveFig. 9. Bucket drag force distribution with h = 10?.Active dig zone Initial laminar layer Active dig zone Initial laminar layerActive flow zone Virgin material Active dig zone Dead loadActive flow zone Initial laminar layer Shear lineShear line Shear line Dead load shear line Virgin material Virgin material bcaFig. 10. The Shear Zone Theory according to Rowlands 2.C.J. Coetzee, D.N.J. Els/Journal of Terramechanics 46 (2009) 217227223It should be noted that Fig. 10 only shows three stagesof the filling process, but in reality there is a gradual tran-sition from one stage to the next. It should also be notedthat this is a generalised theory and there will be variationsin the results when different materials and bucket geome-tries are used. During experiments two definite shear linescould be observed. The one extended from the tip of thelip up to the free surface. This is named the cutting shearline. The second line is the one between the initial laminarlayer and the dead load, called the dead load shear line.Making use of DEM and investigating the flow regionsfurther, the following procedure was devised. The bucketwas moved through the material and paused” after each100 mm. The displacement vector of each particle was thenset to be zero after which the bucket was given a furtherdisplacement of 1015 mm (13 particle lengths). The par-ticle displacement ratio PDR was defined as the ratio of themagnitude of the particle absolute displacement vector tothe magnitude of the bucket absolute displacement vector.The particles were then coloured according to their individ-ual PDR values. A PDR equal to unity means that the par-ticle is moving with the bucket. The result is shown inFig. 11. This is in effect the average velocity ratio over ashort period.The flow regimes as predicted by the Shear Zone Theoryare indicated on the figure. The three pictures correspondFig. 11. Flow regions using the particlebucket displacement ratio.224C.J. Coetzee, D.N.J. Els/Journal of Terramechanics 46 (2009) 217227to the three pictures given in Fig. 10. After a displacementof 100 mm, the active dig zone is clearly visible with0.40 6 PDR 0.65. The initial laminar layer moves intothe bucket with 0.10 6 PDR 0.25. This corresponds wellto the flow zones shown in Fig. 10a.After 500 mm, the characteristic V” shape of the activeflow zone can be seen with 0.10 6 PDR 0.25. Althoughthe PDR is relatively low, the displacement is predomi-nantly in the vertical direction. The active dig zone is stillpresent and in the back of the bucket, the initial laminarlayer starts to become stationary relative to the bucket.This is visible by the PDR values that increase towardsthe back of the bucket. This corresponds well to the flowzones shown in Fig. 10b.After 800 mm the existence of the dead load shear line isclearly visible. When compared to Fig. 10c, the active flowzone and active dig zone cannot be distinguished from thedead load. The reason for this is that at a bucket displace-ment of 800 mm, the bulldozing effect is large and over-shadows the other flow zones.Dragline bucket optimization is very important in termsof force and energy requirements and cycle time. In someapplications it would be advantageous to fill the bucketusing the minimum amount of energy. In other applica-tions, it would be advantageous to fill the bucket as quicklyas possible to decrease cycle time 1. To investigate fillrates, images from the experiment were taken at differentstages of filling, the outline of the material digitized, andthe volume of material inside the bucket calculated andexpressed as a percentage of the maximum bucket volume.The maximum bucket volume of 0.0146 m3is defined inFig. 2b. Using the DEM results, the same procedure wasfollowed and the results compared.Fig. 12 shows the experimental results using three differ-ent rig angles. The bucket fill percentage is plotted againstbucket displacement in terms of bucket-lengths. In thedragline industry, the target is to get the bucket completelyfilled in 23 bucket-lengths. With an increase of the rigangle from 0? to 10?, there is a slight increase in fill percent-age towards the latter stages of filling. This is due to thefact that when material is disturbed, it flows more easilyinto the bucket. When the rig angle is further increasedto 20? there is, however, a decrease in fill percentage. A fur-ther investigation showed that with an increase in rig angle,the bucket displacement into the material is less. It hasbeen shown that the force perpendicular to the materialsurface is given by Wb? cos (h). Hence, with an increasein the rig angle, the force component forcing the bucketto dig in, decreases. When this force component decreases,the penetration depth of the bucket into the material isreduced and the bucket scoops up less material. Whenthe bucket scoops up less material, there is a decrease in fillpercentage.The comparison between experimental and DEM fillpercentages is summarised in Fig. 13. Using three rigangles h = 0?, 10? and 30? and two effective bucketweights Wb= 49.1 N and 138.3 N, the fill percentagewas calculated at displacements of 100, 200, 300, 400,500, 600 and 700 mm. The 42 data points were plottedand the two lines indicate that in all cases, except fortwo, the DEM results were within 6% of the experi-mental results.In practice, the bucket is rotated to prevent the majorityof the material to fall out when the bucket is disengaged.This principle is depicted in Fig. 14 where, at the end ofits displacement, the bucket was lifted out of the materialand kept at the rig angle. The effect of bucket orientationis clear on the amount of material that the bucket couldhold. Again, the experimental free surface outline is shownon the DEM results with good agreement for h = 0?. Forh = 20?, the DEM model predicts additional material inthe back of the bucket which can be explained by the differ-ence in the final fill state as seen in Fig. 6 at a displacementof 800 mm.0.511.522.50102030405060708090100Displacement bucket lengthBucket fill % = 0 = 10 = 20 Fig. 12. Bucket fill percentage as a function of bucket displacement fordifferent rig angles. = 0, Wb = 49.1 N = 10, Wb = 49.1 N = 20, Wb = 49.1 N = 0, Wb = 138.3 N = 10, Wb = 138.3 N = 20, Wb = 138.3 N102030Experimental %405060010203040Simulation %5060- 6% + 6% Fig. 13. Comparison between experimental and DEM fill percentages.C.J. Coetzee, D.N.J. Els/Journal of Terramechanics 46 (2009) 2172272256. ConclusionsThe main objective of this paper was to demonstratehow accurately the discrete element method can predictthe process of excavator bucket filling. The flow patternsof material entering the bucket, drag force acting on bucketdue to material interaction, energy requirements and thebucket fill rates were compared to experimental observa-tions and measure