基于圆木带锯切速度控制的优化设计

根据切割效率最大化的基本要求,推导出去除率与进给速度、时间的方程式,解决了切割机设计中长期存在的效率问题;并建立了当去除率为恒定时,剪切速度与时间的关系曲线。运用该方法进行圆木切割机设计,可以提高设计的科学性和准确性,具有较高的应用价值。     

Imbibitions, energy test and accelerated ageing in primed and non-primed seeds of Peltophorum dubium

Peltophorum dubium seeds were set to imbibe with four treatments, soaked with solution Captan 0.2% under 10and 27℃,PEG 6000 -1.0 MPa under 10 and 27℃. For each treatment there were four replicates with 40 seeds incubated in 9-cm Petri dishes with double filter paper moistened with testing solution. The imbibition curves showed that the final weight increase were from 70% to 150% in the treatments when imbibition entered a lag phase. Seeds were tested for effects on germination of five treatments: control group (nonprimed), primed with PEG6000 -1.0 MPa at 10 and 27℃, primed with Captan 0.2% at 10 and 27℃. For each treatment, there were three sub-treatments: seeds were soaked in distilled water for 12, 24 and 36h before the energy test. Germination percentages of nonprimed seeds and primed in PEG 27℃ soaked in distilled water during 12 h were the highest, reaching 100%. The lowest germination percentage occurred primed seeds with PEG6000 27℃ and soaked in distilled water during 36 h, which was only 52%. Germination mean time of primed seeds in PEG at 10℃, soaked 24 h was 1.08 days, mean time of primed seeds in PEG at 27℃ soaked 12 h was 2.42 days. Accelerated ageing results showed low or no germination after ageing 72 h. Control group had a higher germination percentage and seeds were more resistant to deterioration than those in primed groups, both in Petri dish (27℃) and vermiculate (room temperature).     

交通流三段式模型理论研究

车流密度、行车速度和交通流量是反映交通流特征的三个基本参数,三者关系的确定和模型的建立是交通工程理论研究的基础。这里在总结前人研究成果的基础上,从交通流的本质特征入手对车流密度与行车速度的关系进行了深入研究,建立了三段式密度-速度理论关系模型,并由此进一步讨论了交通流量与行车速度、交通流量与车流密度之间的理论关系,建立了相关模型,各关系模型图示形状与实测结果的曲线有较好的吻合。这里明确指出了格林希尔茨模型缺陷的本质所在,对交通流三段模式的产生机理进行了探讨。     

大断面球铁件石墨漂浮浅析

对石墨漂浮的形成机理进行了探讨,认为石墨漂浮就其本质来说是取决于石墨球的大小,漂浮的石墨只能是自由生长的石墨和共晶奥氏体图形成前的共晶石墨.提供了石墨漂浮的临界尺寸概念,并指出在实际生产中控制碳当量和加快冷却速度是解决石墨漂浮最有效的办法.     

高速公路建设中PPP投融资模式研究

针对我国目前高速公路建设的投融资现状,分析了高速公路建设运用PPP融资的优势、必要性及可行性。探讨了承担责任、分担风险和分享收益等方面在PPP融资模式中,政府部门与民营企业或个人的职能及优势。     

THE OPTIMUM CUTTING SPEED OF CIRCULAR SAW

Whenthepwticlebortswerecutbyuseoftllllgstencarbidetippedcircularsaw(Fig.l),th9whcientcuttingspeedfortheminimumcostandmaximumproductionwasdiscussedforafewyears.Ingeneral,thehigherthecuttingspeed,thehigherthecuttingheatproducedandtheshorterthelifeofthetoolresulted.Althoughthehighercuttingspeedcouldmalletheproductivityhigher,theamountofwearoftoothwasincreasedandthenthetimesofchangingsawswereincreased.There-foretherewasanoptimumrangeofcuttingspeedswhentheparticleboardswerecutbycircularsawbasedonan…     

低温化学镀镍-磷合金工艺的研究

通过对比低温环境下几个配方工艺,提出了一个在镀速、耐蚀性等方面均表现较好的工艺配方,同时发现了一种有优越作用的复合配合剂。     

空气引射提高风力灭火机风速的分析与试验

为提高小型便携式风力灭火机的灭火射程和风量,提出了通过空气引射增大其出口空气流量,减缓风速衰减的方法。以其接收室收敛角θ,混合室直径Dm以及喷嘴位置S为变量,建立了240个不同尺寸参数组合的计算流体动力学(CFD)模型并进行了模拟和计算,基于其计算结果,用响应曲面法详细分析并揭示了各结构尺寸对亚音速空气引射性能的影响规律。研究了不同尺寸参数下混合室内部压力场的变化,从机理上探讨了各参数对距离风机中心2.5 m处风速和引射系数交互作用及影响的原因。结果表明:Dm与θ对距离风机中心2.5 m处风速影响很大,Dm与θ两者之间的交互作用很强;而S对距离风机中心2.5 m处风速影响较小,且与其他参数的交互性很弱。确定最佳参数组合即当θ为36.25°,Dm为144 mm,S为90 mm时,距离风机中心2.5 m处风速可达最优值,经试验测定该最优值为36.4 m/s。     

Speed Feedback Without Tachometer Generators In DC Speed-governing Systems

In this paper, some methods for realiaing speed feedback are analnd . A new idea to realizespeed feedback without without tachometer generators is proposed and its feasibility is verified by studying anexperimental provision.     

基于液力驱动的播种机综合试验台的研制

研制了一种基于液压驱动的多功能播种机试验台。选用变量叶片泵与调速阀组成容积节流调速回路，实现台车行走和排种器轴转动的无级调速，调速范围分别为3～12km／h和8～100r／min。采用的丝杠螺母升降机构适应不同投种高度的排种器试验要求。试验台装有预加速装置，可最大限度地增加试验空间。为保证试验台车高速行驶时能及时制动，采用缓冲油路和机械两套制动系统。此试验台可满足各种形式排种器的试验要求。