Moving Force-Induced Vibration of a Rotating Beam with Elastic Boundary Conditions

In this paper, an analytical technique, the so-called Fourier Spectral method (FSM), is extended to the vibration analysis of a rotating Rayleigh beam considering the gyroscopic effect. The model presented can have arbitrary boundary conditions specified in terms of elastic constraints in the translations and rotations or even in terms of attached lumped masses and inertias. Each displacement function is universally expressed as a linear combination of a standard Fourier cosine series and several supplementary functions introduced to ensure and accelerate the convergence of the series expansion. Lagrange's equation is established for all the unknown Fourier coefficients viewed as a set of independent generalized coordinates. A numerical model is constructed for the rotating beam. First, a numerical example considering simply supported boundary conditions at both ends is calculated and the results are compared with those of a published paper to show the accuracy and convergence of the proposed model. Then, the method is applied to one real work piece structure with elastically supported boundary conditions updated from the modal experiment results including both the frequencies and mode shapes using the method of least squares. Several numerical examples of the updated model are studied to show the effects of some parameters on the dynamic characteristics of the work piece subjected to moving loads at different constant velocities. </jats:p

How Digital Platforms Enhance Urban Resilience

Throughout human history, natural and man-made disasters have devastated cities in unpredictable ways. Cities must therefore respond faster and better to minimize the risks posed by disasters. Nowadays, with the rapid development of communication technology, digital platforms are increasingly becoming an indispensable part of people’s lives; hence, they could become a new force for urban resilience. However, there are few studies on how digital platforms enhance urban resilience, so this paper attempts to use the method of CiteSpace (V.5.8.R3, 64 bit) scientometrics analysis and literature analysis to study the dimensions and trends of urban resilience, the role of digital platforms in the dimensions of urban resilience, especially focusing on how digital platforms impact on urban resilience during COVID-19. The results showed that there is considerable literature on natural disasters and infrastructure, but few papers discuss urban governance, knowledge systems, and social media. Furthermore, it is also found that digital platforms contributed to the enhancement of urban resilience in China and Singapore during COVID-19. These suggests that enhancing urban resilience through digital platforms can be a viable approach

How Digital Platforms Enhance Urban Resilience

Throughout human history, natural and man-made disasters have devastated cities in unpredictable ways. Cities must therefore respond faster and better to minimize the risks posed by disasters. Nowadays, with the rapid development of communication technology, digital platforms are increasingly becoming an indispensable part of people&rsquo;s lives; hence, they could become a new force for urban resilience. However, there are few studies on how digital platforms enhance urban resilience, so this paper attempts to use the method of CiteSpace (V.5.8.R3, 64 bit) scientometrics analysis and literature analysis to study the dimensions and trends of urban resilience, the role of digital platforms in the dimensions of urban resilience, especially focusing on how digital platforms impact on urban resilience during COVID-19. The results showed that there is considerable literature on natural disasters and infrastructure, but few papers discuss urban governance, knowledge systems, and social media. Furthermore, it is also found that digital platforms contributed to the enhancement of urban resilience in China and Singapore during COVID-19. These suggests that enhancing urban resilience through digital platforms can be a viable approach

Analysis of torsional vibration effect on the diesel engine block vibration

In this paper, the coupling effect between the crankshaft torsional vibration and the low speed diesel engine block vibration is investigated. Using finite element method (FEM), a model of low speed diesel engine is established to study the vibration response. The mode results of FEM agree very well with the test. The additional torques acting on the low-speed diesel engine caused by torsional vibration are discussed in detail. The vibration response of the low-speed diesel engine considering the effect of torsional vibration is studied using FEM simulation. By analyzing the effect of torsional vibration, the results demonstrate that the crankshaft torsional vibrations have important effects on the engine block vibration. The results from this study can provide useful theoretical guidance to predict vibration of low-speed diesel engine

A Hybrid Finite Element-Fourier Spectral Method for Vibration Analysis of Structures with Elastic Boundary Conditions

A novel hybrid method, which simultaneously possesses the efficiency of Fourier spectral method (FSM) and the applicability of the finite element method (FEM), is presented for the vibration analysis of structures with elastic boundary conditions. The FSM, as one type of analytical approaches with excellent convergence and accuracy, is mainly limited to problems with relatively regular geometry. The purpose of the current study is to extend the FSM to problems with irregular geometry via the FEM and attempt to take full advantage of the FSM and the conventional FEM for structural vibration problems. The computational domain of general shape is divided into several subdomains firstly, some of which are represented by the FSM while the rest by the FEM. Then, fictitious springs are introduced for connecting these subdomains. Sufficient details are given to describe the development of such a hybrid method. Numerical examples of a one-dimensional Euler-Bernoulli beam and a two-dimensional rectangular plate show that the present method has good accuracy and efficiency. Further, one irregular-shaped plate which consists of one rectangular plate and one semi-circular plate also demonstrates the capability of the present method applied to irregular structures

Effect of late planting and shading on cellulose synthesis during cotton fiber secondary wall development.

Cotton-rapeseed or cotton-wheat double cropping systems are popular in the Yangtze River Valley and Yellow River Valley of China. Due to the competition of temperature and light resources during the growing season of double cropping system, cotton is generally late-germinating and late-maturing and has to suffer from the coupling of declining temperature and low light especially in the late growth stage. In this study, late planting (LP) and shading were used to fit the coupling stress, and the coupling effect on fiber cellulose synthesis was investigated. Two cotton (Gossypium hirsutum L.) cultivars were grown in the field in 2010 and 2011 at three planting dates (25 April, 25 May and 10 June) each with three shading levels (normal light, declined 20% and 40% PAR). Mean daily minimum temperature was the primary environmental factor affected by LP. The coupling of LP and shading (decreased cellulose content by 7.8%-25.5%) produced more severe impacts on cellulose synthesis than either stress alone, and the effect of LP (decreased cellulose content by 6.7%-20.9%) was greater than shading (decreased cellulose content by 0.7%-5.6%). The coupling of LP and shading hindered the flux from sucrose to cellulose by affecting the activities of related cellulose synthesis enzymes. Fiber cellulose synthase genes expression were delayed under not only LP but shading, and the coupling of LP and shading markedly postponed and even restrained its expression. The decline of sucrose-phosphate synthase activity and its peak delay may cause cellulose synthesis being more sensitive to the coupling stress during the later stage of fiber secondary wall development (38-45 days post-anthesis). The sensitive difference of cellulose synthesis between two cultivars in response to the coupling of LP and shading may be mainly determined by the sensitiveness of invertase, sucrose-phosphate synthase and cellulose synthase

Changes of mean air temperature and mean relative humidity at 30 DPA under the coupling of planting date and shading in 2010 and 2011.

<p>* and ** mean significant difference among three shading treatments at 0.05 and 0.01 probability levels, respectively.</p