The effect of compressibility,loading position and probe shape on the rupture probability of tomato fruits

In this study, factors affecting the rupture probability of tomato fruits were investigated. The experiments were carried out at five compressibility levels (4%, 8%, 12%, 16% and 20%), four loading positions and two probe shapes. The fruit size, shape and mass did not have a significant effect on the rupture probability. The compressibility was the most important independent variable affecting the rupture probability of tomato fruits in the model. The rupture probability of quadrilocular tomato fruit loaded from the cross-wall tissue was the highest, and the odds of being ruptured was 14.5 times higher for quadrilocular tomato fruit loaded from the cross-wall tissue compared to the locular tissue. The curved probe was much more sensitive than the plate probe for rupturing of tomato fruits during the compression tests. It is clear that these investigated factors need to be considered carefully in design and control of tomato harvesting equipment.     

交错障碍物对瓦斯爆炸影响的实验研究

为了研究交错障碍物对瓦斯爆炸火焰形状、火焰速度及爆炸压力的影响,设计并搭建了150mm×150mm×500mm半封闭透明腔体的瓦斯爆炸实验台,采用化学当量比浓度的甲烷-空气预混气体,并与平行障碍物工况进行了比较.实验结果表明:与平行障碍物相比,交错障碍物明显增强了火焰形变,提高了火焰速度和爆炸压力,其中火焰速度和爆炸压力的提升率最高分别达到78.0%和198%.因此,在实际巷道中,应尽量避免障碍物的交错放置.     

Rheological and diffusion behaviours of Zr41Ti14Cu12.5Ni10Be22.5 bulk metallic glass around glass transition

1 Introduction Since the Au-Si metallic glass were firstly prepared by rapid cooling technique in 1960 by DUWEZ et al[1], the study of structure and property of metallic glass has received much attention. The atom transportation behaviors (rheological an…     

Numerical study and multi-objective optimization of flexible screening process of flip-flow screen: A DEM-FEM approach

Vibrating flip-flow screens are widely used in deep screening processes. However, in-depth studies on flexible screening processes and the optimization of their operating parameters are limited. This study combines the discrete element method (DEM) and finite element method (FEM) to establish a coupled DEM–FEM model for simulating flexible screening processes. The reliability of the model was experimentally verified. Single-factor and central composite experiments were conducted to analyze the effects of y-direction amplitude, relative amplitude, installation angle, and frequency on particle speed, screening efficiency, and sieve plate stress. Finally, multi-objective optimization was implemented. The results revealed the dynamic response of the amplitude and stress on the flexible screen surface under the impact of materials. Moreover, a mathematical fitting model was derived to describe the relationship between the evaluation index and vibration parameters. Accordingly, a foundation for effectively improving the performance and reliability of flexible screening was established.     

Experimental study on explosion characteristics of syngas with different ignition positions and hydrogen fraction

The influence of different ignition positions and hydrogen volume fractions on the explosion characteristics of syngas is studied in a rectangular half-open tube. Three ignition positions were set at the axis of the tube, which are 0 mm, 600 mm and 1100 mm away from the closed end, respectively. A range of hydrogen volume fraction (φ) from 10% to 90% were concerned. Experimental results show that different ignition positions and hydrogen volume fraction have important influence on flame propagation structure. When ignited at 600 mm from the closed end on the tube axis, distorted tulip flame forms when flame propagates to the closed end. The formations of the tulip flame and the distorted tulip flame are accompanied by a change in the direction of the flame front propagation. The flame propagation structure and pressure are largely affected by the ignition position and the hydrogen volume fraction. At the same ignition position, flame propagation speed increases with the growing of hydrogen volume fraction. And the pressure oscillates more severe as the ignition location is closer to the open end. And pressure oscillations bring two different forms. The first form is that the pressure has a periodic oscillation. The amplitude of the pressure oscillation gradually increases. It takes several cycles from the start of the oscillation to the peak. For the second form, the pressure reaches the peak of the oscillation in the first cycle of the start to the oscillation.     

Effect of N2 and CO2 on explosion behavior of syngas/air mixtures in a closed duct

The explosion behavior of syngas/air mixtures under the effect of N₂ and CO₂ addition is experimentally investigated in three cases of N₂ and CO₂ volume fractions (0, 20% and 40%). Tests are performed for syngas/air mixtures with varying equivalent ratios (from 0.8 to 2.5) and hydrogen fractions (from 25% to 75%). The effects of N₂ and CO₂ addition on flame structure evolution, flame speed and overpressure histories are analyzed. The results showed that the tulip shaped flames appear in all cases regardless of whether N₂ and CO₂ are added. After flame inversion, the appearance of tulip shaped flame distortion can be observed in syngas/air without N₂ and CO₂ addition and meanwhile the oscillations are seen in the flame front position and speed trajectories. The flame distortion becomes less pronounced with N₂ and CO₂ addition, and the oscillation amplitude of the flame front position and speed reduce accordingly. Both addition of N₂ or CO₂ decrease the flame speed and the maximum overpressure. Therefore, it increases the time required for flame arriving to the discharge vent. Whereas CO₂ has evidently better inhibition performance for syngas/air explosion.     

Wave Propagation in Functionally Graded Piezoelectric-piezomagnetic Rectangular Rings

The ring ultrasonic transducers are widely used in the ocean engineering and medical fields. This paper proposes a double orthogonal polynomial series approach to solve the wave propagation problem in a functionally graded piezoelectric-piezomagnetic (FGPP) ring with a rectangular cross-section. Through numerical comparison with the available reference results for a pure elastic homogeneous rectangular bar, the validity of the proposed approach is illustrated. The dispersion curves and displacement distributions of various FGPP rectangular bars are calculated to reveal their wave characteristics. The results can be used for the design and optimization of the ring FGPP transducers.     

喷头布置方式对细水雾除尘效率的影响

为了研究湿式除尘中喷头布置方式对细水雾除尘效率的影响,设计了由粉尘产生系统、喷雾系统、测试系统组成的细水雾除尘实验平台。对不同喷头布置方式下细水雾除尘效率进行了实验研究,得到了喷雾压力和喷头布置方式对细水雾除尘效率的影响：细水雾除尘效率随喷雾压力的增加而提高,但当喷雾压力超过1.6 MPa后提高速率变缓;各个喷雾压力下,双喷头的除尘效果均优于单喷头;喷头距离尘源越远,全部粉尘的除尘效果越好,而呼吸性粉尘的除尘效果越差。     

7075铝合金二维超声挤压加工表面质量影响因素及其交互作用研究

进行二维超声挤压加工正交试验,研究静压力、挤压速度和进给量等工艺参数及其交互作用对7075铝合金表面质量的影响,并寻求最优工艺参数。通过极差分析和方差分析,确定工艺参数及其交互作用对表面粗糙度和表层硬度的影响主次顺序和影响显著性;基于数据驱动,采用回归分析方法构建表面粗糙度和表层硬度预测模型;基于响应曲面法,分析交互作用对表面粗糙度和表层硬度的影响;利用有约束多目标规划模型,确定最优工艺参数。研究发现：经过二维超声挤压加工后,7075铝合金试件表面粗糙度值明显降低,而表层硬度大幅度提高;表面粗糙度主要取决于挤压速度和进给量的交互作用,而表层硬度主要取决于静压力、挤压速度,以及挤压速度和进给量、静压力和挤压速度的交互作用。基于预测模型获得的表面粗糙度和表层硬度与实测结果基本吻合;基于最小表面粗糙度值和最高表层硬度值目标下的最优工艺参数也与试验结果较为吻合。研究结果表明,工艺参数之间的交互作用对表面质量的影响是不可忽略的,所构建的表面粗糙度模型和表层硬度模型是有效的。     

正交各向异性空心圆柱体的周向SH波

基于线性三维弹性理论,得到了正交各向异性管道中位移表示的周向波控制方程.波动方程中的轴向位移独立于其它两个方向.即波的传播可以分解为SH波和类Lamb波.通过贝塞尔函数求得了这个周向SH波频散方程.方程中决定周向SH波特性的弹性常数有两个,一个决定了波的频率,另一个决定了波速.最后分别讨论了两个弹性常数和波数变化对周向SH波位移模式的影响.