Optimal design of a light commercial freezer through the analysis of the combined effects of capillary tube diameter and refrigerant charge on the performance

In this work, a discussion on a methodology to optimize the performance of a commercial freezer by using a simulation tool is presented. In order to provide a practical tool for deciding the best combination of refrigerant charge and capillary tube diameter, the results of the numerical studies are shown in the form of two-dimensional maps. The usefulness of this type of representation lies in the possibility of selecting the best operating point of the system, taking into account not only the efficiency or the power consumption but also the technical constrictions imposed by parameters such as the suction line temperature, the condenser subcooling, the evaporator superheat, and the run-time ratio. The discussion leads to the conclusion that the useful performance map is drastically reduced when all the operation requirements must be satisfied. Once the system design had been optimized, an additional numerical study, aimed at identifying the influence of the external conditions on the system behavior, was performed. The results show that the performance reduction can be effectively minimized modifying the refrigerant charge.     

Adverse fetal outcome in road accidents: Injury mechanism study and injury criteria development in a pregnant woman finite element model

This study documents the development of adverse fetal outcome predictors dedicated to the analysis of road accidents involving pregnant women. To do so, a pre-existing whole body finite element model representative of a 50th percentile 26 weeks pregnant woman was used. A total of 8 accident scenarios were simulated with the model positioned on a sled. Each of these scenarios was associated to a risk of adverse fetal outcome based on results from real car crash investigations involving pregnant women from the literature. The use of airbags and accidents involving unbelted occupants were not considered in this study. Several adverse fetal outcome potential predictors were then evaluated with regard to their correlation to this risk of fetal injuries. Three predictors appeared strongly correlated to the risk of adverse fetal outcome: (1) the intra uterine pressure at the placenta fetal side area (r = 0.92), (2) the fetal head acceleration (HIC) (r = 0.99) and (3) area of utero-placental interface over a strain threshold (r = 0.90). Finally, sensitivity analysis against slight variations of the simulation parameters was performed and assess robustness of these criteria.     

Interlaminar fracture of CF/EP composite containing a dual-component microencapsulated self-healant

We present an experimental study of the self-healing ability of carbon fibre/epoxy (CF/EP) composite laminates with microencapsulated epoxy and its hardener (mercaptan) as a healing agent. Epoxy- and hardener-loaded microcapsules (average size large: 123 μm; small: 65 μm) were prepared by in situ polymerisation in an oil-in-water emulsion and were dry-dispersed at the ratio 1:1 on the surface of unidirectional carbon fabric layer. The CF/EP laminates were fabricated using a vacuum-assisted resin infusion (VARI) process. Width-tapered double cantilever beam (WTDCB) specimens were used to measure mode-I interlaminar fracture toughness of the CF/EP composites with a pre-crack in the centre plane where the microcapsules were placed. Incorporation of the dual-component healant stored in the fragile microcapsules provided the laminates with healing capability on delamination damage by recovering as much as 80% of its fracture toughness. It was also observed that the recovery of fracture toughness was directly correlated with the amount of healant covering the fracture plane, with the highest healing efficiency obtained for the laminate with large capsules.     

Are electric self-balancing scooters safe in vehicle crash accidents?

With the pressing demand of environmentally friendly personal transportation vehicles, mobility scooters become more and more popular for the short-distance transportation. Similar to pedestrians and bicyclists, scooter riders are vulnerable road users and are expected to receive severe injuries during traffic accidents. In this research, a MADYMO model of vehicle–scooter crash scenarios is numerically set up. The model of the vehicle with the scenario is validated in pedestrian–vehicle accident investigation with previous literatures in terms of throwing distance and HIC₁₅ value. HIC₁₅ values gained at systematic parametric studies. Injury information from various vehicle crashing speeds (i.e. from 10 m/s to 24 m/s), angles (i.e. from 0 to 360°), scooter's speeds (i.e. from 0 m/s to 4 m/s), contact positions (i.e. left, middle and right bumper positions) are extracted, analyzed and then compared with those from widely studied pedestrian–vehicle and bicycle–vehicle accidents. Results show that the ESS provides better impact protection for the riders. Riding ESS would not increase the risk higher than walking at the same impact conditions in terms of head injury. The responsible reasons should be the smaller friction coefficient between the wheel-road than the heel-road interactions, different body gestures leading to different contact positions, forces and timing. Results may shed lights upon the future research of mobility scooter safety analysis and also the safety design guidance for the scooters.     

Surface profile texture characterization of trimmed laminated composite in the stacking sequence direction

The surface texture characterization of laminate composites is complex due to its heterogeneous structure and to the different stratified surface properties. Profile roughness parameters are highly impacted by those different layer properties, and their distributions are relatively spread out. A new filtering technique is proposed to improve the surface roughness parameter efficiency. To present issues from current filtering methods and to highlight this new approach, profile surface roughness taken from trimmed carbon fibre reinforced plastics samples are inspected in the composite stacking sequence using a contact profilometer. For each measurement, several roughness parameters are calculated. The efficiency of different filtering techniques is investigated through the roughness parameters distribution, calculated for up- and down-milling and for different tool wear. The new proposed technique, based on the separate characterization of plateaus and large deep valleys of the composite surface profiles, is found to be particularly efficient on the down-milling face.     

A numerical database for ultrasonic defect characterisation using array data: Robustness and accuracy

Elastodynamic scattering matrices are known to contain geometrical information about a given scatterer, such as its size and shape. Here, the extent to which this scattered information can be retrieved using an ultrasonic array and used to characterise defects for Non-Destructive Evaluation is explored. Experimentally measured defect scattering matrices are compared to a database of possible scatterers and the nearest neighbour used to characterise the defect's geometry in terms of crack length and orientation. As an example, a database of scattering matrices for small (lengths 0.2–2.0 mm) cracks at a range of frequencies (2–20 MHz) is formed. The short range similarity (i.e. that between close neighbours) and the long range similarity (i.e. uniqueness) are used to understand the uncertainties inherent in this approach. In addition, the effect of spatially coherent noise, such as grain scattering in a polycrystalline metal, on the scattered information content is quantified. It is shown that as the noise level or frequency increases, so the information retrievable from a given crack is reduced, setting bounds on the accuracy of characterisation possible from a given ultrasonic dataset.     

Exploring stop-go decision zones at rural high-speed intersections with flashing green signal and insufficient yellow time in China

The objective of this study is to empirically analyze and model the stop-go decision behavior of drivers at rural high-speed intersections in China, where a flashing green signal of 3 s followed by a yellow signal of 3 s is commonly applied to end a green phase. 1, 186 high-resolution vehicle trajectories were collected at four typical high-speed intersection approaches in Shanghai and used for the identification of actual stop-go decision zones and the modeling of stop-go decision behavior. Results indicate that the presence of flashing green significantly changed the theoretical decision zones based on the conventional Dilemma Zone theory. The actual stop-go decision zones at the study intersections were thus formulated and identified based on the empirical data. Binary Logistic model and Fuzzy Logic model were then developed to further explore the impacts of flashing green on the stop-go behavior of drivers. It was found that the Fuzzy Logic model could produce comparably good estimation results as compared to the traditional Binary Logistic models. The findings of this study could contribute the development of effective dilemma zone protection strategies, the improvement of stop-go decision model embedded in the microscopic traffic simulation software and the proper design of signal change and clearance intervals at high-speed intersections in China.     

高职模具类人才培养新模式的研究与实践

为了解决传统教学无法全面培养人才的问题,采用"课程融合+时空耦合+过程结合"的方式开展人才培养研究。以注射模设计与制造生产过程为导向,构建大项目牵引下的跨越课程、跨越学期的课程融合新模式,利用信息通信技术及互联网平台,将互联网与传统教学进行深度融合,创造新的教学生态,构建多元多维互动的时空耦合教学新关系,以全方位评价为引导,构建课程多元多维的评价新机制。以3个班级为对象开展不同模式下的教学,对试验班级成绩进行分析,研究结果表明:课程融合+时空耦合+过程结合新模式培养的学生更好地完成了综合项目,获得了较好的教学效果。     

Study on the influence of joint spacing on rock fragmentation under TBM cutter by linear cutting test

Joint spacing is one of the most important geological factors influencing rock fragmentation by TBM cutters and TBM performance. In order to study the influence of joint spacing, full-scale linear cutting tests have been conducted for the Beishan granite samples with different joint spacing (i.e. one intact sample, two jointed samples with joint spacing of 100 mm and 400 mm). For different joint spacing, the influence of penetration depth on rock fragmentation was also explored by varying the penetration depth with an interval of 0.5 mm. During the test process, the three directional forces acting on the TBM cutter were recorded, and the rock chips formed by each cutting pass were weighed, respectively. By analysing the cutting force, crack initiation/propagation and rock chips, the influences of joint spacing on rock fragmentation process by TBM cutter were investigated. The test results showed that the increase of penetration depth cannot improve the TBM breakage efficiency after reaching a certain value for the intact rock sample, and the normal force for intruding the intact rock is larger than that for intruding the rock jointed samples. It is also found that the sample part below the joint plane is intact, thus joint can restrain the crack propagating cross the joint plane and facilitates the chips formation on the cutting surface. For the rock sample with joint spacing of 100 mm, two rock fragmentation modes were found during the cutting process. One mode is that the cracks initiate from the crushed zone under TBM cutter, and the cracks propagate to the joint plane, consequently form large rock chips. The other one is that the cracks initiate from the joint plane and then propagate to the rock cutting surface, and the cracks initiate before the formation of the crushed zone under the cutter. For the rock sample with joint spacing of 400 mm, there are two rock fragmentation stages, i.e., the normal rock fragmentation stage and the joint-controlled rock fragmentation stage. There is a transitional process between these two stages, and also the median crack can be promoted to propagate vertically to joint plane due to the joint existence. This study can provide useful guidance for operation optimization and performance prediction for TBM operating in jointed rock masses.     

Challenges and opportunities of Rankine cycle for waste heat recovery from internal combustion engine

Internal combustion engines (ICEs) are the major consumers of crude oil, and thus improvements in the fuel consumption performance of ICEs would be significant for global energy conservation and emission reduction. Owing to the constraints in the engine structure and combustion efficiency, more than half of the fuel combustion heat in ICEs is wasted. Therefore, ICE waste heat recovery (ICE-WHR) shows huge potential. Rankine cycle (organic or inorganic) provides a promising solution for ICE-WHR, which could balance efficiency and practicality. In this review, recent advances in Rankine cycles for ICE-WHR are summarized and discussed. To evaluate results from various existing studies, a uniform evaluation standard, thermodynamic perfection, was proposed based on the benchmark of the heat source based ideal thermodynamic cycle(H-iCycle), which is determined by achieving ideal thermal matching to external boundary conditions. Based on this, the effects of three major factors (cycle configuration, working fluid, and key components) on the performance of Rankine cycle can be investigated. In addition, a discussion of several application concerns, including backpressure, weight, power output type, off-design performance dynamic response, and control, enables us to gain a comprehensive understanding and assessment of Rankine cycles in ICE-WHR. With respect to working fluids, C_xH_yO_z and siloxanes with high critical temperature (such as cyclohexane, benzene, toluene, and MM) have a satisfactory thermal matching with waste heat sources. Basic Rankine cycles using these working fluids could yield a high thermodynamic perfection of up to 54.1%. With respect to the cycle configuration, cascade Rankine cycles and dual-pressure Rankine cycles are expected to achieve the highest thermodynamic perfection of 62.3%. Finally, major challenges and perspectives for the future development of Rankine cycles in ICE-WHR are discussed. Four promising research directions suggested in this review include the active design of desirable working fluids, advanced cycle configuration design based on “energy utilization according to quality,” integrated scheme research at three levels (component, system, and energy management), and advanced coordinative control.