Influences of Rifle Weight, Weight Distribution and Layout on Aiming Comfort

A rifle in a soldier''s system is often equipped with a grenade launcher, aiming device, etc., which increases the weight of the rifle and changes its center of gravity. This study explores how the rifle weight, weight distribution and layout (e.g. stock length, position of grip and forestock) affect aiming comfort. In the paper, the upper extremity muscle activity was used to characterize the aiming comfort. A human-rifle musculoskeletal model was developed, which was validated by the surface electromyography (EMG) data. The results showed that the design parameters of rifle (weight, distance of gravity center to body and layout) had a significant influence on aiming comfort. The greater the weight was, the stronger the muscle activity was. With the distance increasing, first the muscle activity decreased, and then increased when the distance is exceeding a certain value. In addition, the combined influences of weight and distance illustrated that there was an optimal distance to make the slightest muscle movements for certain weight. For designing a rifle''s layout, more muscular exertions were required to maintain the holding posture with the stock length increasing, which was suggested to be in the range of 0.18.m to 0.27.m. Results can be used to optimize the ergonomics design of rifle, improving the comfort of the rifle aiming process and the shooting accuracy.     

A new type of leak-floor flip bucket

Flip buckets are commonly used to discharge flow away from a hydraulic structure into the downstream to dissipate energy.A new leak-floor flip bucket is presented,making the ski-jump water jet a typical long-narrow nappe.Based on the model experiments and numerical simulation,the flow pattern,formation process and mechanism of the leak-floor flip bucket are studied.The results show that cross section flow shape develops from the"Y-type"to"|-type",and this is because the natural pressure difference is generated when water flows through the leak-floor area and moves transversely from both sides to the center.Different from the slit-type flip bucket with sidewall contraction,the leak-floor flit bucket makes the water jet narrow and long without high pressure on the side walls of the flip bucket.Under the same jet length condition,the maximum sidewall pressure of the slit-type is 4.67 times that of the leak-floor flip bucket.The effects of flow discharge on the jet length are less significant for the leak-floor bucket than for the slit-type bucket.     

车用LPG燃料喷雾过程的研究

利用光学纹影方法和高速CCD摄影建立了LPG燃料喷雾实验装置,并使用计算机图像处理技术得到了单孔LPG液态自由喷雾的瞬态喷雾特性,包括喷雾贯穿距离、喷雾角度、喷雾面积等。结果表明:在t<1 ms的喷雾初始阶段,液态LPG喷雾贯穿距离呈二次曲线增长,喷雾面积呈线性增长,喷雾角度快速增长;在t>1 ms的喷雾充分发展阶段,喷雾贯穿距离呈线性增长,喷雾面积则在经历了短暂的缓慢增长之后又迅速呈直线增长,喷雾角度则逐渐减小。     

淤质与粉质互层土中管桩沉桩过程的土压力

为了研究预应力空心开口管桩沉桩过程中周围土体中的土压力分析,选取杭州郊区某建筑工地进行现场试验.本次试验在试验场地内和防挤沟两侧共埋设了6组振弦式孔隙水压力计和土压力盒,并且在管桩桩端安装了一个土压力盒测试管桩沉桩过程中桩端土压力的变化情况.试验结果表明：在沉桩过程中,周围土体中的径向土压力呈先增大后减少趋势,随着深度的增加,径向土压力的影响越来越大;桩端阻力的变化与静力触探锥尖阻力的变化曲线较为相似,锥尖阻力的变化曲线相比桩端阻力表现出更为明显的波动.该试验结果能够为相关研究和设计提供参考和依据.     

金刚石和CBN超高速冲击磨削Q235A实验研究

为研究Q2 35A钢在超高速磨削条件下的磨屑形成机理,使用真实的人造金刚石和CBN颗粒作为磨料,将其粘接在7.6 2mm的子弹头部,利用81式步枪作为加速、加载装置,对Q2 35A钢进行了72 0m/s的超高速冲击磨削实验研究。对实验结果进行了深入、细致的检测和分析。实验结果表明,Q2 35A在超高速冲击作用下,弹着点会产生瞬间高温,达到或超过Q2 35A的熔点,从而在子弹与钢板相接触区域的材料形成流动相,流动物质在磨粒和冲击波的作用下离开基体而形成磨屑。验证了冲击成屑理论的正确性。     

复合受力蛇形槽保险机构性能分析

目的研究扭力矩对机构运动性能的影响．方法从理论和试验结果两方面对惯性筒加扭矩后的结果进行了分析和讨论．结果推证了复和受力蛇形槽保险机构下降运动和上升运动动力学模型．结论从提高机构远距离解除保险性能的角度出发,提出了一种新的组合受力曲折槽保险机构结构设想．     

基于空间矩的圆标记中心亚像素定位算法

针对圆标记中心的高定位精度要求,提出一种新的基于空间矩的亚像素定位算法。建立了基于空间矩的圆曲线亚像素边缘检测算法,并用最小二乘边缘拟合算法来获取圆标记中心的亚像素位置,克服了基于传统的Lyvers空间矩算法进行圆标记中心定位存在的误差大的缺点。仿真对比实验表明该算法相对于其他算法具有更高的精度。     

盾构开挖对桩基内力和变形的影响

为研究盾构开挖对建筑物的影响,以某6层框架结构为研究对象,考虑上部结构-桩基-土体的共同作用。采用有限元软件ABAQUS6.14-1建立了盾构隧道、土体、桩基、上部框架的整体三维有限元模型,计算分析盾构下穿框架结构对桩基础变形和内力的影响。有限元计算结果表明:桩距盾构轴线的距离不同对桩底水平位移的影响比桩顶大,不同位置的桩的轴力受盾构开挖的影响各有不同,当开挖面推进到桩轴线并前进4倍洞径以内时桩的水平位移、弯矩和轴力的变化最为显著,桩上部所受弯矩较大且距地面0.2倍桩长处弯矩最大,应用采桩基础托换的方法减小该位置处的桩身弯矩。     

DYNAMIC STRESS-CONCENTRATION EFFECT ON STRESS WAVES IN COMPOSITE MODELS WITH DIFFERENT FIBER-END GEOMETRIES (Abstract)

The stress-concentration effect of fiber-end geometries on the propagating stress waves in composite models was investigated by the dynamic photoelastic method. Aluminum fibers with rectangular, semicircular, V-and wedge-shape ends simulating such materials as reinforced concrete and fiber-bundle-reinforced composites were cast in epoxy resin to form the models. Impact was applide by the bullet of a rifle. The effects of the reinforced rod or fiber-bundle ends on the dynamic birefringent patterns were analyzed by comparing the fringe patterns at the same locations in a plain model of identical Contour under the same loading conditions.     

防热复合材料高温体积烧蚀模型

分析了防热复合材料在高温烧蚀过程中所发生的物理－化学变化;根据能量和质量守恒定律,建立了防热复合材料的体积烧蚀模型,并对某碳／酸醛复合材料的烧蚀过程进行了数值模拟。结果表明,材料的烧蚀不仅与温度而且与升温速率相关;升温速率越大,达到相同烧蚀温度时的烧蚀量减小,烧蚀过程中温度的渗透速度减慢,温度梯度减小。材料内部孔隙中气体的压力影响区域较温度的影响区域小,最大压力点随时间增加逐渐内移,最大压力相应增大。     

内隔墙长度对抽水引发基坑围挡侧移的影响

结合实际工程地质条件,开展三维数值分析,研究内隔墙对限制开挖前抽水引发基坑围挡变形的有效性,探究在不同抽水深度与不同围挡嵌固比条件下,内隔墙长度对基坑围挡变形控制效果的影响. 结果表明：随内隔墙长度增大,内隔墙对基坑围挡变形的控制效果增强. 在不同抽水深度条件下,内隔墙对基坑围挡变形的控制效率不同,当抽水深度大于20 m时,内隔墙长度须大于基坑宽度的0.75倍或者采用全贯通式内隔墙,以取得较好的变形控制效果;当抽水深度小于10 m时,可将内隔墙长度设置为基坑宽度的0.25~0.50倍,预期也可取得较可观的变形控制效果. 在不同围挡嵌固深度条件下,内隔墙对变形的控制效率不同,延长基坑围挡嵌固深度能增强内隔墙在抽水深度范围内的变形控制效果.     

硬质合金刀具的脱焊及其控制方法

通过工艺分析及实验研究,揭示了钎料选择不当,钎剂没有进行脱水处理,钎焊工艺选择不当,钎焊法中电压参数不稳定及钎焊过程中刀槽发生了较大的塑性变形是引起硬质金刀具焊的主要原因,进而提出相应的控制措施。     

A sink moving scheme based on local residual energy of nodes in wireless sensor networks

In the application of periodic data-gathering in sensor networks, sensor nodes located near the sink have to forward the data received from all other nodes to the sink, which depletes their energy very quickly. A moving scheme for the sink based on local residual energy was proposed. In the scheme, the sink periodically moves to a new location with the highest stay-value defined by the average residual energy and the number of neighbors. The scheme can balance energy consumption and prevent nodes around sink from draining their energy very quickly in the networks. The simulation results show that the scheme can prolong the network lifetime by 26%–65% compared with the earlier schemes where the sink is static or moves randomly. Foundation item: Project(60673164) supported by the National Natural Science Foundation of China; Project(20060533057) supported by the Specialized Research Foundation for the Doctoral Program of Higher Education of China     

四光幕交汇立靶测试系统及纸靶校准方法

介绍了一种新的测试方法：将四个矩形光幕以特定的角度分别放置在六面体的两个面和两个对角面上，当弹丸从光幕穿过，用测时仪记录弹丸穿过四个光幕的时刻，依据四个时刻值计算出弹丸穿过光幕的位置坐标．文中分析了四光幕交汇立靶测试测试系统的原理．提出一种用纸靶测量坐标值对测试系统的测量结果进行校准的方法，推导了校准公式．根据纸靶弹孔位置坐标，对原始公式进行修正，修正后的结果，减少了与纸靶比对的误差．     

铝胺双重封堵钻井液在成3井二开长裸眼井段的应用

成3井是为探索侏罗系油藏而在准噶尔盆地中央坳陷部署的一口预探井,完钻井深4 821 m。二开裸眼段长3 200 m,井壁稳定难度大;西山窑组至八道湾组煤层发育,井壁失稳严重。通过使用铝胺抑制防塌钻井液,施工中采用合理密度支撑–多元协同抑制–双重封堵防塌措施,辅助相应的维护处理工艺,解决了长裸眼段和煤层段的井壁失稳难题,而且机械钻速得到显著提高。全井机械钻速7.68 m/h,创造该区块钻速新纪录。     

振荡翼捕获能量系统的流体动力性能

采用Fluent求解绕二维振荡翼层流流场的非定常、不可压缩Navier-Stokes方程,将域动网格策略用在滑移交界面内流体域,使之与翼一起运动,该方法可保证核心区域网格质量。研究了Re=1100、θ0=76.33°、y0=5、k=0.88时,俯仰轴位置对NACA0015振荡翼气动特性和能量捕获性能的影响,以及升沉--俯仰相位差和俯仰轴位置对系统的耦合影响。结果表明,俯仰轴位置会影响振荡翼的升力特性、俯仰力矩特性及能量捕获性能,当系统因俯仰轴位置偏离平均压力中心而造成能量捕获性能下降时,改变升沉--俯仰相位差可改善系统的能量捕获性能。     

Savonius式水轮机水动力学性能

为了研究S式水轮机水动力学性能,利用流体动力学软件建立S式水轮机的网格模型,分析流场特性,对S式水轮机在不同叶尖速比与重叠比的水动力学及能量提取性能进行研究.结果表明：S式水轮机在运动过程中存在负力矩情况,这是造成功率系数较低的主要原因.S式水轮机适合在低叶尖速比下工作,且力矩系数随着叶尖速比的增大而减小,存在一个最优叶尖速比使水轮机的功率系数达到最大,重叠比能减少甚至消除负力矩情况,改善水轮机的水动力学性能.在研究参数范围内,重叠比在0.15附近时,S式水轮机综合性能最优,功率系数可以达到最大值0.256.     

一类非线性波方程解的爆破

依据势井理论,通过构造不稳定集,结合凸性分析,证明了一类非线性波动方程解的爆破性.     

缩短自由电子激光放大器饱和长度的研究

缩短自由电子激光器中的束-波互作用饱和长度,能够有效地降低加速器、摇摆器以及整体器件的成本。为探索缩短束-波互作用饱和长度的途径,本文作者采用非线性数值模拟方法,研究自由电子激光放大器中关键参数对束-波互作用饱和长度的影响。以一种红外自由电子激光放大器为例,对摇摆器磁场振幅在3 000 Ga做±10%较大调整,对应的饱和长度5.92 m,仅缩短0.11 m(减少不足2%); 通过对摇摆器周期、电子束能量、激光波长的搭配进行优化,当摇摆器周期为3.8 cm、电子束能量为105 MeV、激光波长为853 nm时达到最优,使饱和长度缩短到4.35 m(减少26.5%)。结果表明:摇摆器振幅对饱和长度的影响不大,但电子束能量、摇摆器周期、激光波长三者之间的恰当匹配至关重要,可明显缩短对应的束-波互作用饱和长度。       

非均匀压缩药芯焊丝电弧窄间隙焊接

研究了药芯焊丝电弧焊（ＦＣＡＷ）工艺方法在窄间隙焊接领域中的工程应用可行性．采用非均匀压缩药芯焊丝电弧技术实现了居中单丝无电弧摆动条件下的低线能量高质量焊接，解决了窄间隙焊接中两侧壁难以均匀熔合的技术关键．