Cohesive/adhesive failure interaction in ductile adhesive joints Part II: Quasi-static and fatigue analysis of double lap-joint specimens subjected to through-thickness compressive loading

This paper proposes a new methodology for the finite element (FE) modelling of failure in adhesively bonded joints. Cohesive and adhesive failure are treated separately which allows accurate failure predictions for adhesive joints of different thicknesses using a single set of material parameters. In a companion paper (part I), a new smeared-crack model for adhesive joint cohesive failure was proposed and validated. The present contribution gives an in depth investigation into the interaction among plasticity, cohesive failure and adhesive failure, with application to structural joints. Quasi-static FE analyses of double lap-joint specimens with different thicknesses and under different levels of hydrostatic pressure were performed and compared to experimental results. In all the cases studied, the numerical analysis correctly predicts the driving mechanisms and the specimens’ final failure. Accurate fatigue life predictions are made with the addition of a Paris based damage law to the interface elements used to model the adhesive failure.     

Magnetic refrigeration: a promising new technology for energy saving

Magnetic refrigeration is an emerging, environment-friendly technology based on a magnetic solid that acts as a refrigerant by magnetocaloric effect. The reference cycle for magnetic refrigeration is AMR (Active Magnetic Regenerative refrigeration). In this paper, attention is directed towards the near-room-temperature range. We compare the energetic performance of a commercial R134a refrigeration plant to that of a magnetic refrigerator working with an AMR cycle. The comparison is carried out by means of a mathematical model. In these simulations, we consider different solid magnetic refrigerants, namely, Gd, Gd_0.95Dy_0.05, Gd_0.9Tb_0.1,Gd₅Si₂Ge₂, MnAs_0.9Sb_0.1, and MnAs_0.95Sb_0.05. We compared two different geometries of the regenerator: a porous medium and a flat plate. In the former, the Coefficient of Performance (COP) of the AMR cycle is better than that of the vapour compression plant only in the low mass flow-rate range. Whereas in a flat plate regenerator, the COP of the AMR cycle is better than that of the vapour compression plant only in the high mass flow-rate range.     

输电线路故障查找浅析

简述了输电线路故障的类型和原因，并提出了输电线路故障查找工作的实施要点，以供参考。     

A new approach for mitigating blackout risk by blocking minimum critical distance relays

Electric power systems are complex and commonly run near their operational limits. Power systems are basically designed based on the (N − 1) criterion. In these systems, total or partial blackouts are unavoidable. Cascading failures following an initial event is recognized as the main mechanism for power system blackouts. Undesirable activation of zone 3 of distance relays due to their local function has been identified as one of the major causes for propagation of cascading failures. In this paper, in order to mitigate the risk of power system blackouts, a novel approach is proposed for recognizing the critical line outages with the highest contribution in cascading failure and preventing their undesirable outage by blocking zone 3 of their distance relay. In this paper, based on the statistical activation of distance relays, a deterministic–probabilistic approach is developed for identifying the critical lines with the highest contribution in blackouts due to activation of zone 3 of their distance relays. In order to avoid interference of relay blocking with the main protection duty of distance relays, the proposed approach recognizes the minimum critical lines with the highest contribution in cascading failure for blocking zone 3 of their distance relays. The proposed approach is demonstrated on the New England 39-bus system and detailed simulation studies carried out to examine the validity and effectiveness of the proposed approach.     

316L板翅结构钎焊接头力学性能试验

采用高温短时拉伸试验和相应数学模型分析研究了316L T形钎焊接头的力学性能.使用扫描电镜（SEM）和能谱分析（EDS）分析了失效钎焊接头裂纹尖端和焊缝区域的微观组织及性能，进一步探讨了板翅钎焊结构的失效机理.结果表明，基于T形板试样的高温拉伸载荷位移曲线能较好地反映焊缝的起裂和裂纹扩展过程，1~2 mm/min为合理的试验加载速率取值范围；钎焊过程中焊缝区会出现明显的铁元素富集现象，为板翅结构高温失效的主要诱因.     

Study on startup characteristics of heat pipe cooled and AMTEC conversion space reactor system

Future exploration of deep space requires space power with high power density, light weight, low cost and high reliability. Space reactor is an excellent candidate with its unique characteristics of high specific power, low cost, strong environment adaptability and so on. Among all types of space reactors, heat pipe cooled space reactor, which adopts the passive heat pipe as core cooling component, is considered as one of the most promising choice and is widely studied all over the world. Startup characteristics of this type space reactor are an active topic.Previous studies mainly focused on the startup from high temperature rather than environmental temperature. In order to simulate the transient startup process from frozen state, a transient analysis code (TAPIRS) for heat pipe cooled space reactor power system (HPS) has been developed and applied to investigate the system transient performance during a startup from zero cold power to full power. The code integrates separately validated point reactor kinetics model, lumped parameter core heat transfer model, combined heat pipe (HP) model (self-diffusion model, flat-front startup model and network model), energy conversion model of alkali metal thermal-to-electric conversion units (AMTEC), and HP radiator model. By comparing the simulation results of the models and steady state with those in the references, the rationality of the models and the solution method is validated. It is found that by adjusting the control drum's rotational speed, the reactor can startup from subcritical state to full power state while the heat pipe and AMTEC from solid state to normal operational state. HPS can startup entirely depending on the nuclear power, and the maximum temperature of the heat pipe does not exceed 1250 K in the whole startup process. The maximum errors of the parameters between the simulation results of this paper and those in the literature at the full power condition are less than 5%. Under the accident of control drum failure with largest reactivity insertion, the fuel temperature can be controlled within the safety limits. These show that the reactor system has characteristics of no single-point failures, the self-stabilization capability under accident conditions.     

两种针对小信号的脉压优化算法及实现

结合某雷达项目,针对项目LFM和Taylor编码两种小时宽带宽积(TB)信号脉冲压缩效果不理想的问题,通过对两种不同小TB信号的实际回波波形和特性进行了分析,针对性地使用了倒推法和循环迭代法,获得了优化的脉压系数。试验得出结论,较之传统的匹配滤波脉冲压缩系数,采用优化脉压系数的LFM和Taylor编码小TB信号脉冲压缩主副瓣比均能提高十几dB。     

A combined M5P tree and hazard-based duration model for predicting urban freeway traffic accident durations

The duration of freeway traffic accidents duration is an important factor, which affects traffic congestion, environmental pollution, and secondary accidents. Among previous studies, the M5P algorithm has been shown to be an effective tool for predicting incident duration. M5P builds a tree-based model, like the traditional classification and regression tree (CART) method, but with multiple linear regression models as its leaves. The problem with M5P for accident duration prediction, however, is that whereas linear regression assumes that the conditional distribution of accident durations is normally distributed, the distribution for a “time-to-an-event” is almost certainly nonsymmetrical. A hazard-based duration model (HBDM) is a better choice for this kind of a “time-to-event” modeling scenario, and given this, HBDMs have been previously applied to analyze and predict traffic accidents duration. Previous research, however, has not yet applied HBDMs for accident duration prediction, in association with clustering or classification of the dataset to minimize data heterogeneity. The current paper proposes a novel approach for accident duration prediction, which improves on the original M5P tree algorithm through the construction of a M5P-HBDM model, in which the leaves of the M5P tree model are HBDMs instead of linear regression models. Such a model offers the advantage of minimizing data heterogeneity through dataset classification, and avoids the need for the incorrect assumption of normality for traffic accident durations. The proposed model was then tested on two freeway accident datasets. For each dataset, the first 500 records were used to train the following three models: (1) an M5P tree; (2) a HBDM; and (3) the proposed M5P-HBDM, and the remainder of data were used for testing. The results show that the proposed M5P-HBDM managed to identify more significant and meaningful variables than either M5P or HBDMs. Moreover, the M5P-HBDM had the lowest overall mean absolute percentage error (MAPE).     

浅谈汽车机械故障原因及防范措施

伴随现代信息科技水平的不断发展,人们开始追求高质量的物质生活水平,交通运输方式也变得更为多样化,汽车作为快捷的交通方式开始普及发展,然而,伴随汽车销售市场的不断扩大,汽车的使用问题也逐渐暴露出来。因此,本文针对汽车经常发生的机械故障问题进行分析,同时提出有效的防范措施,保障汽车可以适当延长使用期限。     

Housing policy in remote Indigenous communities: how politics obstructs good policy

Abstract

When it comes to issues of housing policy, remote Indigenous housing often presents the extreme case. The failures of housing policy are most acute in remote Indigenous Australia, but despite the need to learn from the policy mistakes of the past, there has been little detailed analysis of the policy history. Through documentary and empirical analysis, we show that policies have either failed to be adapted to cultural and geographic contexts or, when they have been culturally responsive, they have lacked attention to the complexities of service delivery. Despite differences in policy settings, the long view is one of the normalization of Indigenous communities, although research points to the need for culturally appropriate arrangements. We argue that rather than politically motivated short-termism, governments need to develop a medium- to long-term approach that approaches policy solutions incrementally, builds capacity within the state and Indigenous communities, and is based on the evidence.