时间序列的变化点检测和趋势分析

趋势分析和变化点检测是时间序列分析中常用的工具. 变化点检测是识别过程行为的自然或人为的突然的变化,而趋势可以定义为对逐渐偏离过去的规范的估计. 本文使用了Cox-Stuart方法和变化点算法分析时间序列数据趋势的存在,并以澳大利亚的近地表风速时间序列为例. 澳大利亚的近地表风速趋势是根据研究出的新开发的风速数据集,通过使用局部表面粗糙度信息,以及不同高度收集的混合观测数据构建. 10 m处的风的速度趋势通常会增加,而2 m处则趋于减小. 假设检验测试,变化点分析和人工检查记录表明有几个因素可能是导致差异的原因,例如伴随仪器变化的系统性偏差,随机数据错误(例如累积日错误)和数据采样问题. 均质化以及基于变化点检测的技术和多期趋势分析阐明了风速趋势不一致的根源.     

基于LMS自适应时延估计和FPGA的超声波测风系统研究

利用超声波传感器进行风速测量时,温度对超声波传播有很大影响,时延估计对超声波测风系统的精度起到很大的作用。本超声波测风系统为避免温度对风速测量中的影响,采用了基于时差法的测量原理,为了提高时延估计值的精度,提出了基于最小均方(LMS)自适应时延估计的测量方法,研制了以单片机Atmega128和现场可编程门阵列(FPGA)为核心的硬件系统。仿真和实际测试的结果表明,该超声波测风系统的时延估计值精确度较高,具有很高的应用价值。     

Simulation of Correlated Non-Gaussian Pressure Fields

Abstract. Among a host of techniques developed for the analysis and prediction of nonlinear structural response, simulation methods are gaining popularity as computational efficiency increases. Implementation of time domain methods require simulated load time histories with case-specific statistical and spectral characteristics. When the assumption of Gaussian wind loading is inappropriate, techniques for simulating non-Gaussian loading must be sought. Over a larger expanse of building surface, simulation of correlated loads at several spatially separated locations is required. This work introduces a multi-variate non-Gaussian simulation method capable of producing realizations with a wide range of spectral and probabilistic characteristics. The correlation between multiple locations is accurately simulated simultaneously, while retaining the appropriate spectral and probabilistic content at each location.Sommario. Tra la varie tecniche per l'analisi e la previsione della risposta structurale non lineare, stanno acquistando grande popolarità i metodi di simulazione poiché incrementano l'efficienza computazionale. L'implementazione dei metodi nel domino del tempo richiede la simulazione di storie temporali di carico con specifiche caratteristiche statistiche e spettrali. Quando l'ipotesi di gaussianità dell'azione del vento non risulta adeguata puòessere necessario ricorrere a techniche di simulazione di carichi non gaussiani. Per superfici di edifici più estese è richiesta la simulazione di carichi correlati in diverse posizioni separate spazialmente. La presente memoria introduce un metodo di simulazione multivariata non-gaussiana capace di riprodurre realizzazioni con un ampio campo di caratteristiche spettrali e probabilistiche. La correlazione tra le molteplici posizioni viene simulata simultaneamente in modo accurato mantenendo in ciascuna posizione caratteristiche spettrali e probabilistiche appropriate.     

Surface flaws using a modified AC magnetic bridge

Scanning patterns of a modified AC magnetic bridge are established through the use of finite-width flaws. From these patterns, the widths and depths of surface flaws can be determined. The technique was also applied fatigue cracks.     

Interferometer with holographic optics

An interferometer with holographic optics, which has a large visualization field, is described. Correction for aberration of the interferometer is obtained, and non-aberration interferograms of the heat flows are made. The interferometer with a 100 mm visualization field can be used for the study of transparent media.     

Saturation mechanism in clarinet-like instruments, the effect of the localised non-linear losses

The question of what limits the amplitude of the oscillations of clarinet-like instruments is investigated. The study is based on numerical simulations in which two kind of losses are taken into account: linear losses and non-linear losses localised at the open end of the tube. The influence of the amount of losses on the saturation process and on the playing range of clarinet-like instruments is shown. Results are confirmed by experiments using an artificial mouth in which the non-linear losses are varied using several terminations with different geometries.     

Atmospheric stability of surface boundary layer in coastal region of the Wol–Ryong site

In order to provide statistically reliable information of a wind energy site, accurate analysis on the atmospheric stability and climate characteristics in a certain area is a prerequisite. Two 2-D ultrasonic anemometers and one cup anemometer, located perpendicular to the prevailing wind direction, were used to measure the atmospheric wind environment at a height of 4.5 m in coastal region of the Wol–Ryong, Jeju, South Korea. The study is aiming to understand the atmospheric stability about a coastal region, and the effect of roughness length. We calculate the Monin–Obukhov length for division of atmospheric stability about unstable regime, neutral regime and stable regime. The distribution of diurnal Monin–Obukhov length is highly sporadic in the coastal region due to the effect of radiant heat from the surface or other environmental effects. In order to calculate the roughness length in coastal region, three different methods are applied in terms of the surface roughness, flow fluctuation and gust wind, which are called logarithmic profile, standard deviation and gust factor methods. In the study, the atmospheric stability was insignificant when applying these three methods. In the results, three different roughness length scales sufficiently showed the effect of obstacle and surface conditions around the measurement position. On the basis of an overall analysis of the short-term data measured in the Wol–Ryong area, Jeju Island, it is concluded that for the development of future wind energy resources, the Wol–Ryong site could be a good candidate for a future wind energy site.     

Postcritical Behavior of Cables Undergoing Two Simultaneous Galloping Modes

Abstract. A nonlinear two degree-of-freedom model, describing a flexible elastic suspended cable undergoing galloping oscillations, is analyzed. By using a perturbative approach, the critical conditions occuring for different values of the aerodynamic coefficients are described. Two different type of critical conditions, corresponding to simple or double Hopf bifurcations are found. The nonlinear postcritical behavior of single taut strings in 1:1 primary internal resonance is studied through the multiple scale perturbation method. In the double Hopf bifurcation case the influence of the detuning between the critical eigenvalues on the postcritical behavior is illustrated. It is found that quasi-periodic motions, which are likely to occur in the linear field when the two critical frequencies are incommensurable, are really unstable in the nonlinear range. Therefore, the postcritical behavior of the string consists of stable periodic motions for any detuning values.Sommario. Viene analizzato un modello non lineare a due gradi di libertrappresentativo di un cavo elastico flessibile sospeso alle estremite soggetto ad oscillazioni galoppanti. Utilizzando un approccio perturbativo, vengono descritte le condizioni critiche per differenti valori dei coefficienti aerodinamici. Sono presenti due diversi tipi di condizioni critiche, corrispondenti a biforcazioni di Hopf semplici e doppie. Attraverso il metodo perturbativo delle scale multiple viene studiato il comportamento post-critico non lineare di singole stringhe tese in risonanza interna primaria 1:1. Nel caso di biforcazione doppia di Hopf viene illustrata l'influenza del detuning tra gli autovalori critici sul comportamento post-critico. Si trova che i moti quasi-periodici, presenti in campo lineare quando le due frequenze critiche sono incommensurabili, sono in realtinstabili in campo non lineare. Quindi, il comportamento post-critico della stringa risulta composto da moti periodici stabili per un qualsiasi valore del detuning.