基于移动有限元法的裂纹梁振动分析

采用移动有限元法和局部柔度法对移动质量作用下含裂纹简支梁进行了振动计算分析.计算考虑了裂纹和移动质量的相对位置对梁固有频率的影响,以及移动质量在不同位置、速度情况下对裂纹梁的动力响应的影响.结果分析表明,裂纹与移动质量的存在会使得梁的动态位移有不同程度的增大,且随着移动质量位置和裂纹位置的改变会使得梁的固有频率变小.     

Material characterization of composite laminates using dynamic response and real parameter-coded microgenetic algorithm

An efficient nondestructive evaluation procedure is proposed for inversely determining material constants of composite laminates using dynamic response at one point on the plate surface. Material constants of composite laminates are determined by minimizing the difference between the measured dynamic response of the actual plate and the computed response of the plate with assumed material properties. For robust and efficient function minimization, a real parameter-coded microgenetic algorithm (real-GA) is proposed on the basis of the existing binary coded uniform microgenetic algorithm (uniform GA). Four different crossover operators are constructed for the real-GA. Performances of the present real-GA and the existing uniform GA are studied using several typical benchmark test functions and an order-3 deceptive function. The present real-GA is then implemented as the inverse solver in the minimization process of material characterization. From hundreds of tests conducted on the benchmark functions, the order-3 deceptive function, and the material characterization problems, it is found that the real-GA is two to five times faster in converging to the global optimum compared with the uniform GA. Numerical examples for material characterization of composite laminates have demonstrated the robustness, efficiency, and accuracy of the proposed procedure.     

An innovative eigenvalue problem solver for free vibration of Euler–Bernoulli beam by using the Adomian decomposition method

This paper deals with free vibration problems of Euler–Bernoulli beam under various supporting conditions. The technique we have used is based on applying the Adomian decomposition method (ADM) to our vibration problems. Doing some simple mathematical operations on the method, we can obtain ith natural frequencies and mode shapes one at a time. The computed results agree well with those analytical and numerical results given in the literature. These results indicate that the present analysis is accurate, and provides a unified and systematic procedure which is simple and more straightforward than the other modal analysis.     

Damage localization in irregular shape structures using intelligent FE model updating approach with a new hybrid objective function and social swarm algorithm

Health monitoring of structures and damage diagnosis are important research disciplines under investigation worldwide. Soft computing techniques are usually used to solve the uncertain complex inverse problem of revealing structural damage. In the current research, FE model updating (FEMU) paradigm is embraced for solving the damage tracking problem in three dimensional irregular shape structures. By taking into account the complexity of problem, the pivotal point is to efficiently educe damage through well-evolved objective function. Therefore, a novel objective function merging the modal characteristics of modal strain energy (MSTEN) and mode shape curvature (MSC) is established. Posteriorly, to solve the FEMU problem, a hybrid algorithm combining the particle swarm optimization with a new social version of the sine–cosine optimization algorithm (SPSOSCA) is proposed. The SPSOSCA is considered to take advantage of two enhanced search mechanisms to overcome the overall problem complexity. The proposed paradigm is evaluated using many damage scenarios even under noise conditions and the total outcome reveals outstanding performance with fair computational time.     

基于多重反射法对周期结构的频率响应研究

采用多重反射法对受到外扰的二组元周期梁结构的频率响应进行了研究．施加至Ⅱ周期梁结构上的外部扰动被假定为一入射波，传播波入射到不连续处会产生反射波和透射波，进而在周期结构中会产生多重的反射和透射．首先，基于波的多重反射，考虑施加扰动的组元上的波场；其次，由于波的透射，分别考虑两个传播方向上的其他组元的波场，作为初始波场；最后，可先考虑某个组元右侧的所有组元上的向左传播的波在其上的叠加，作为一次迭代波场；再考虑某个组元左侧的所有组元上的向右传播的波在其上的叠加，作为二次迭代波场．依次类推，基于多重反射法，叠加了入射波引起的多重反射和透射，得到了所有组元的波场．给出了周期梁结构中任一点的波幅与入射波幅之间的函数关系，确定了受外扰的周期梁结构的传播常数及相应的波场的迭代次数．     

Double-edged sword: The effect of exergaming on other forms of exercise; a randomized controlled trial using the self-categorization theory

BackgroundNo study has yet adopted the perspective of the self-categorization theory to examine the impact of playing exergames on players' attitudes and intentions towards other forms of exercise.PurposeTo examine the impact of playing exergames on players' attitudes and intentions to engage in other exercise and how such an impact depends on previous exercise frequency.MethodsThis randomized controlled trial recruited 117 college students who were randomly assigned to either an intervention group (n = 55) or a control group (n = 62). Participants in the first group played an exergame for 30 min, three times per week for 12 weeks. This study calculated the changes in the participants' attitudes and intentions before and after the program, and compared the differences between the two groups.ResultsExergaming improved the players' attitudes toward other forms of exercise. Such improvement was significant for frequent exercisers, but not for infrequent exercisers. Surprisingly, playing exergames strengthened the intentions to engage in other forms of exercise for frequent exercisers, but weakened such intentions for infrequent exercisers.ConclusionsExergaming encourages frequent exercisers to engage in other forms of exercise, but does the opposite among infrequent exercisers.OriginalityThis study is the first identifying the contingent effect of exergaming on users' attitudes and intentions toward other forms of exercise.     

Analysis of plant colonization on an arctic moraine since the end of the Little Ice Age using remotely sensed data and a Bayesian approach

Young moraines less than 100 years old are considered as key areas for monitoring the effects of climate change since the end of the Little Ice Age. One way of documenting this change is by recognizing and characterizing the different plant colonization stages and trends that occur on these relatively new environments. Previous studies have shown that remotely sensed data alone are not sufficient to map the vegetation over these types of landscapes because the most significant part of the radiometric information is related to mineral landscape components. Therefore, the authors used an indirect approach which consisted in the following steps.

1.

An optimized sampling procedure was used to collect georeferenced vegetation plot data. A multivariate analysis was then used to define vegetation types that could be related to different colonization stages and environmental contexts.

2.

Color infrared aerial photographs were then used to produce a baseline vegetation map. This map was then integrated into a data base along with other environment factors known to control plant colonization processes, such as climate (wind, temperature), physical landscape components (habitat characteristics) and morphodynamic processes (runoff).

3.

A Bayesian model using conditional probabilities was used to identify the primary environmental habitats corresponding to the different vegetation types.

This protocol was tested on the fore field of the Midre Lovénbreen (Svalbard) glacier where several vegetation belts correspond to well defined stages of deglaciation and corresponding local conditions such as microtopography, microclimate and runoff dynamics.     

A new approach based on a discrete hidden Markov model using the Rocchio algorithm for the diagnosis of heart valve diseases

Abstract: Application of the Doppler ultrasound technique in the diagnosis of heart diseases has been increasing in the last decade since it is non‐invasive, practicable and reliable. In this study, a new approach based on the discrete hidden Markov model (DHMM) is proposed for the diagnosis of heart valve disorders. For the calculation of hidden Markov model (HMM) parameters according to the maximum likelihood approach, HMM parameters belonging to each class are calculated by using training samples that only belong to their own classes. In order to calculate the parameters of DHMMs, not only training samples of the related class but also training samples of other classes are included in the calculation. Therefore HMM parameters that reflect a class's characteristics are more represented than other class parameters. For this aim, the approach was to use a hybrid method by adapting the Rocchio algorithm. The proposed system was used in the classification of the Doppler signals obtained from aortic and mitral heart valves of 215 subjects. The performance of this classification approach was compared with the classification performances in previous studies which used the same data set and the efficiency of the new approach was tested. The total classification accuracy of the proposed approach (95.12%) is higher than the total accuracy rate of standard DHMM (94.31%), continuous HMM (93.5%) and support vector machine (92.67%) classifiers employed in our previous studies and comparable with the performance levels of classifications using artificial neural networks (95.12%) and fuzzy‐C‐means/CHMM (95.12%).