A higher order coupled frequency characteristics study of smartmagneto-electro-elastic composite plates with cut-outs using finite element methods

This article deals with investigating the effect of cut-outs on the natural frequencies of magneto-electro-elastic (MEE) plates incorporating finite element methods based on higher order shear deformation theory (HSDT). In order to consider the influence of cut-out, the energy of the cut-out domain is sub-tracted from the total energy of the entire plate. The governing equations of motions are derived through incorporating Hamilton's principle and the solution is obtained using condensation technique. The proposed numerical formulation is verified with the results of previously published literature as well as the numerical software. In addition, this research focuses on evaluating the effect of geometrical skewness and boundary conditions on the frequency response. The influence of cut-outs on the degree of coupling between magnetic, electric and elasticfields is also investigated.     

基于ANSYS火炮身管传热仿真

火炮连续发射过程中身管内壁温度持续升高会加快身管的烧蚀磨损,为此分析研究影响身管温度变化的射速、环境温度等主要因素.利用ANSYS软件建立火炮身管有限元模型,对身管内外壁的对流传热和身管壁内的热传导进行仿真,计算求解得到了不同射击模式及不同环境温度下身管内外壁温度的变化规律,结果表明射速增大、环境温度越离,身管温度上升越快.研究成果为依据身管内外壁温度控制火炮发射强度来延长身管寿命提供一定的理论依据.     

运送有毒物泄漏造成水体污染的扩散模型及求解方法研究

运送有毒物发生交通事故,导致有毒物泄漏引发水体污染,会造成严重影响。在分析污染事故的特点、危害的基础上,根据水力学及污染物的迁移转化规律,建立了有毒物泄漏水体后的转移弥散模型,即将控制水流的圣维南方程和描述有毒物迁移的对流弥散方程进行耦合。运用低数值耗散的半离散中心迎风格式求解方程,其结果可以预测污染河段长度和延续时间。最后,通过实例进行了模拟计算。     

Physical and damping properties of kenaf fibre filled natural rubber/thermoplastic polyurethane composites

The paper presents the investigation of the effect of alkaline treatment of sodium hydroxide (NaOH) on physical and dynamic mechanical analysis (DMA) viscoelastic properties of kenaf fibre filled natural rubber (NR)/thermoplastic polyurethane (TPU) composites. The treated kenaf fiber, NR and TPU were weighed and proportioned according to the required compositions and were blended using hot mixed Brabender machine. The polymer composites were then fabricated using the hot press to form a sample board. The sample was cut and prepared and water absorption, density, thickness swelling and DMA tests were performed. As far as physical properties are concerned, composites with the highest NR amount of shows the best results, which indicates good fiber bonding adhesion. The polymer composites with the highest amount of TPU shows the highest damping properties at high temperature.     

Military Expenditures and Natural Resources: Evidence from Rentier States in the Middle East and North Africa

It has been argued that the discovery of a new natural resource greatly increases the risk of conflict. This research aims to study the effect of natural resources on military spending, using the data from rentier states in the Middle East and North Africa (MENA) countries from 1987 to 2012. In considering the ‘resource curse,’ the types of natural resources matter. Our empirical results demonstrate that the ‘resource curse’ arising from the abundance of certain natural resources, particularly oil and forest resources, leads to increases in military spending. In contrast, the rent from coal and natural gas has a negative impact on military spending, while the rent from minerals has no impact on military spending, controlling for GDP growth and per capita income.     

A new experimental way for the monitoring of the real/equivalent in-service-time of double base rocket propellant by coupling VST and PCA

The assessment of the real in-service-time(RIST)and the equivalent in-service-time(EIST)of double base rocket propellants(DBRPs)is of utmost importance for the safe storage and use of weapon systems as well as the efficiency of the accelerated aging plans.In this work,four DBRPs with similar chemical composition and different natural aging have been artificially aged at T = 338.65 K for 4 months with sampling every 30 days.The unaged and artificially aged samples have been investigated by vacuum stability test(VST)at five isothermal temperatures(T = 333.15 K,343.15 K,353.15 K,363.15 K,and 373.15 K).The volume of the evolved gases in VST was found to decrease with natural/artificial aging.Furthermore,the VST data were treated and subjected to principal component analysis(PCA).The results showed excellent discrimination of the DBRP samples according to their stability thermal properties.Most of the variance was described by the first principal component(PC1)whose scores were linearly correlated with the natural aging durations when PCA is applied on VST data obtained at T = 363.15 K.In light of the obtained results,a new experimental way for the estimation of the real/equivalent IST was proposed,which takes into account the impact of the natural aging of the sample.The approach predicts successfully the RIST of two similar DBRPs with a relative deviation of less than 2％.At the specific heating temperature T = 338.65 K,the developed model provides more conceivable EIST values,with asymptotic behavior against artificial aging duration evolution,thus overcoming some shortcomings of the common generalized van't Hoff formula(GvH).     

Dynamics in pastoral resource management and conflict in the Borana rangelands of southern Ethiopia

Based on primary and secondary data, this paper provides a qualitative account of current changes in the pattern of natural resource management as a result of resource degradation and conflict in the Borana rangelands of southern Ethiopia. Population pressure, recurrent drought and the depleted carrying capacity of pastoral resources, as well as the encroachment of neighbouring ethnic groups, present the Borana community with a significant challenge. The diminishing resilience of traditional politico-judicial institutions under the famous Gada system often result in the rise of new forms of land use such as farming and private enclosures, which compete with the traditional communal tenure system. The gradual collapse of traditional norms and value systems and the apparent inefficiency in the formal administrative structures have exacerbated the problems of resource degradation and conflict between multiple resource-users.     

潜艇耐压壳体深潜安全性监测技术初探

从设备状态监测诊断技术的一般内容出发,论述了丧失稳定是潜艇耐压壳体在深潜时的主要破坏模式,振动固有频率是表征其安全性储备的特征量。据此提出了安全性监测装置的组成,实艇应用前景及有待研究的问题。     

ENERGY FOR SECURITY:

Though North Korea agreed to partial denuclearization in February 2007, achieving that goal is at best a long way off. A natural gas pipeline linking all of Northeast Asia and promising energy and economic help could help convince the isolated nation to step away from its nuclear programs entirely; it could also provide the nonproliferation and energy security benefits that have eluded the region for so long. These economic benefits could motivate the other nations involved in the six-party talks to deal with North Korea more than if only nuclear reactors were offered.     

临近空间飞艇内部自然对流的流场特征仿真研究

针对临近空间飞艇,对其内部氦气的自然对流特征进行了数值模拟。首先采用计算流体力学方法,并利用自编的用户自定义函数将外部的温度边界条件导入壁面网格。进而,在不同的稳态条件下,通过对内部氦气压力、温度、速度的分布等流场特征参数的研究,分析了临近空间飞艇内部气体自然对流的运动特性及其影响规律,并对自然对流非稳态变化过程进行了初步的探索。仿真结果表明,在临近空间环境下,飞艇内部氦气的自然对流,对于内部氦气自身的热交换具有一定程度的促进作用,而对蒙皮受力和结构安全性影响很小。