On the generalized eigenvalue problem for the Rossby wave vertical velocity in the presence of mean flow and topography

In a series of papers, Killworth and Blundell have proposed to study the effects of a background mean flow and topography on Rossby wave propagation by means of a generalized eigenvalue problem formulated in terms of the vertical velocity, obtained from a linearization of the primitive equations of motion. However, it has been known for a number of years that this eigenvalue problem contains an error, which Killworth was prevented from correcting himself by his unfortunate passing and whose correction is therefore taken up in this note. Here, the author shows in the context of quasigeostrophic (QG) theory that the error can ulti- mately be traced to the fact that the eigenvalue problem for the vertical velocity is fundamentally a non- linear one (the eigenvalue appears both in the numerator and denominator), unlike that for the pressure. The reason that this nonlinear term is lacking in the Killworth and Blundell theory comes from neglecting the depth dependence of a depth-dependent term. This nonlinear term is shown on idealized examples to alter significantly the Rossby wave dispersion relation in the high-wavenumber regime but is otherwise irrelevant in the long-wave limit, in which case the eigenvalue problems for the vertical velocity and pressure are both linear. In the general dispersive case, however, one should first solve the generalized eigenvalue problem for the pressure vertical structure and, if needed, diagnose the vertical velocity vertical structure from the latter.

Wave spectra assimilation in typhoon wave modeling for the East China Sea

The East China Sea is a hot area for typhoon waves to occur. A wave spectra assimilation model has been developed to predict the typhoon wave more accurately and operationally. This is the first time where wave data from Taiwan have been used to predict typhoon wave along the mainland China coast. The two-dimensional spectra observed in Taiwan northeast coast modify the wave field output by SWAN model through the technology of optimal interpolation (OI) scheme. The wind field correction is not involved as it contributes less than a quarter of the correction achieved by assimilation of waves. The initialization issue for assimilation is discussed. A linear evolution law for noise in the wave field is derived from the SWAN governing equations. A two-dimensional digital low-pass filter is used to obtain the initialized wave fields. The data assimilation model is optimized during the typhoon Sinlaku. During typhoons Krosa and Morakot, data assimilation significantly improves the low frequency wave energy and wave propagation direction in Taiwan coast. For the far-field region, the assimilation model shows an expected ability of improving typhoon wave forecast as well, as data assimilation enhances the low frequency wave energy. The proportion of positive assimilation indexes is over 81% for all the periods of comparison. The paper also finds that the impact of data assimilation on the far-field region depends on the state of the typhoon developing and the swell propagation direction.

A priori error analysis of space–time Trefftz discontinuous Galerkin methods for wave problems

We present and analyse a space–time discontinuous Galerkin method for wave propagation problems. The special feature of the scheme is that it is a Trefftz method, namely that trial and test functions are solution of the partial differential equation to be discretised in each element of the (space–time) mesh. The method considered is a modification of the discontinuous Galerkin schemes of Kretzschmar et al. (2014) and of Monk & Richter (2005). For Maxwell’s equations in one space dimension, we prove stability of the method, quasi-optimality, best approximation estimates for polynomial Trefftz spaces and (fully explicit) error bounds with high order in the meshwidth and in the polynomial degree. The analysis framework also applies to scalar wave problems and Maxwell’s equations in higher space dimensions. Some numerical experiments demonstrate the theoretical results proved and the faster convergence compared to the non-Trefftz version of the scheme.

Interaction between wave and coastal structure: Validation of two lagrangian numerical models with experimental results marine 2011

Numerical modeling of the interaction among waves and coastal structures is a challenge due to the many nonlinear phenomena involved, such as, wave propagation, wave transformation with water depth, interaction among incident and reflected waves, run-up / run-down and wave overtopping. Numerical models based on Lagrangian formulation, like SPH (Smoothed Particle Hydrodynamics), allow simulating complex free surface flows. The validation of these numerical models is essential, but comparing numerical results with experimental data is not an easy task. In the present paper, two SPH numerical models, SPHysics LNEC and SPH UNESP, are validated comparing the numerical results of waves interacting with a vertical breakwater, with data obtained in physical model tests made in one of the LNEC's flume. To achieve this validation, the experimental set-up is determined to be compatible with the Characteristics of the numerical models. Therefore, the flume dimensions are exactly the same for numerical and physical model and incident wave characteristics are identical, which allows determining the accuracy of the numerical models, particularly regarding two complex phenomena: wave-breaking and impact loads on the breakwater. It is shown that partial renormalization, i.e. renormalization applied only for particles near the structure, seems to be a promising compromise and an original method that allows simultaneously propagating waves, without diffusion, and modeling accurately the pressure field near the structure.

Modelo de propagação para redes sem fio fixas na banda de 5,8 GHZ em cidades típicas da região amazônica

O estudo da perda de propagação, nas cidades da região amazônica, envolve ambiente caracterizado pelo clima tropical e, suburbano densamente arborizado. Levando consideração à importância da faixa ISM 5,8 GHz, esta dissertação apresenta um modelo propagação para a faixa de frequência em questão, agregando as características da atenuação experimentada pela onda de rádio quando se propaga em ambientes de cidades típicas região amazônica. Para tanto, medidas de potência recebida foram coletadas em 335 clientes fixos, distribuídos em 12 cidades na região norte do Brasil, sendo estes atendidos pelo programa de inclusão digital do estado do Pará, Navega Pará. Também foram realizadas medidas com mobilidade no campus da Universidade Federal do Pará (UFPA). Apresenta ainda o desempenho do modelo proposto sobre outros modelos (Modelo SUI e COST231-Hata) descritos na literatura, para redes sem fio fixas e com mobilidade. As métricas desempenho utilizadas foram o erro RMS e o desvio padrão com relação aos dados medidos. O ajuste dos parâmetros do modelo proposto é realizado através do método de mínimos quadrados lineares, aplicado em duas etapas para diminuir a incerteza sobre os parâmetros ajustados. O modelo proposto alcançou um erro RMS de 3,8 dB e desvio padrão de 2,3 dB, superando os demais modelos que obtiveram erros RMS acima de 10 dB e desvios padrão acima de 5 dB. Os resultados obtidos mostram a sua eficiência sobre outros modelos para predição de perdas na faixa de 5,8 GHz em sistemas fixos e móveis.

Hypersonic phonon propagation in mesoscopic systems by Brillouin spectroscopy

Phononic crystals, capable to block or direct the propagation of elastic/acoustic waves, have attracted increasing interdisciplinary interest across condensed matter physics and materials science. As of today, no generalized full description of elastic wave propagation in phononic structures is available, mainly due to the large number of variables determining the band diagram. Therefore, this thesis aims for a deeper understanding of the fundamental concepts governing wave propagation in mesoscopic structures by investigation of appropriate model systems. The phononic dispersion relation at hypersonic frequencies is directly investigated by the non-destructive technique of high-resolution spontaneous Brillouin light scattering (BLS) combined with computational methods. Due to the vector nature of the elastic wave propagation, we first studied the hypersonic band structure of hybrid superlattices. These 1D phononic crystals composed of alternating layers of hard and soft materials feature large Bragg gaps. BLS spectra are sensitive probes of the moduli, photo-elastic constants and structural parameters of the constituent components. Engineering of the band structure can be realized by introduction of defects. Here, cavity layers are employed to launch additional modes that modify the dispersion of the undisturbed superlattice, with extraordinary implications to the band gap region. Density of states calculations in conjunction with the associated deformation allow for unambiguous identication of surface and cavity modes, as well as their interaction with adjacent defects. Next, the role of local resonances in phononic systems is explored in 3D structures based on colloidal particles. In turbid media BLS records the particle vibration spectrum comprising resonant modes due to the spatial confinement of elastic energy. Here, the frequency and lineshapes of the particle eigenmodes are discussed as function of increased interaction and departure from spherical symmetry. The latter is realized by uniaxial stretching of polystyrene spheres, that can be aligned in an alternating electric field. The resulting spheroidal crystals clearly exhibit anisotropic phononic properties. Establishing reliable predictions of acoustic wave propagation, necessary to advance, e.g., optomechanics and phononic devices is the ultimate aim of this thesis.

Theoretical Simulation of the A5 VEB Structure Pyrotechnique Shock Propagation

This paper presents some of the modelling criteria that have been used for the study of pyrotechnic shock propagation in the A5 VEB Structure, as well as the main conclusions from a mathematical model of the axymmetric effects in it. The separation of the lower stage of the ARIANE 5 Vehicle Equipment Bay (VEB)Structure is to be done using a pyrotechnic device. The wave propagation effects produced by the explosion have been analyzed with a computer program using as shape functions the analytical solution to the frequency response of a Timoshenko-Rayleigh beams and shells in that way the discretization can have elements as large as possible, depending on the material properties and boundary conditions. Moreover an enormous amount of possibilities in the treatment of concentrated masses, springs and dashpots, either with respect to a fixed reference or between nodes, is open for translational as well as rotational degrees of freedom.

Implementation challenges of application of radio frequency identification (RFID) in warehouse

Warehouse is an essential component in the supply chain, linking the chain partners and providing them with functions of product storage, inbound and outbound operations along with value-added processes. Allocation of warehouse resources should be efficient and effective to achieve optimum productivity and reduce operational costs. Radio frequency identification (RFID) is a technology capable of providing real-time information about supply chain operations. It has been used by warehousing and logistic enterprises to achieve reduced shrinkage, improved material handling and tracking as well as increased accuracy of data collection. However, both academics and practitioners express concerns about challenges to RFID adoption in the supply chain. This paper provides a comprehensive analysis of the problems encountered in RFID implementation at warehouses, discussing the theoretical and practical adoption barriers and causes of not achieving full potential of the technology. Lack of foreseeable return on investment (ROI) and high costs are the most commonly reported obstacles. Variety of standards and radio wave frequencies are identified as source of concern for decision makers. Inaccurate performance of the RFID within the warehouse environment is examined. Description of integration challenges between warehouse management system and RFID technology is given. The paper discusses the existing solutions to technological, investment and performance RFID adoption barriers. Factors to consider when implementing the RFID technology are given to help alleviate implementation problems. By illustrating the challenges of RFID in the warehouse environment and discussing possible solutions the paper aims to help both academics and practitioners to focus on key areas constituting an obstacle to the technology growth. As more studies will address these challenges, the realisation of RFID benefits for warehouses and supply chain will become a reality.

Magnetic resonance imaging of the manipulation of a chemical wave using an inhomogeneous magnetic field

The effects of applied magnetic fields on the traveling wave formed by the reaction of (ethylenediaminetetraacetato)cobalt(II) (Co(II)EDTA2-) and hydrogen peroxide have been studied using magnetic resonance imaging (MRI). It was found that the wave could be manipulated by applying pulsed magnetic field gradients to a sample contained in a vertical cylindrical tube in the 7.0 T magnetic field of the spectrometer. Transverse field gradients decelerated the propagation of the wave down the high-field side of the tube and accelerated it down the low-field side. This control of the wave propagation eventually promoted the formation of a finger on the low-field side of the tube and allowed the wave to be maneuvered within the sample tube. The origin of these effects is rationalized by considering the Maxwell stress arising from the combined homogeneous and inhomogeneous magnetic fields and the magnetic susceptibility gradient across the wave front.

Magnetic resonance imaging of a magnetic field-dependent chemical wave

The magnetic field dependence of the travelling wave formed during the reaction of (ethylenediaminetetraacetato)cobalt (II) (Co(II)EDTA2- ) and hydrogen peroxide was studied using magnetic resonance imaging (MRI). The reaction was investigated in a vertical tube, in which the wave was initiated from above. The wave propagated downwards, initially with a flat wavefront before forming a finger. Magnetic field effects were observed only once the finger had formed. The wave propagation was accelerated by a magnetic field with a negative gradient (i.e., when the field was stronger at the top of the tube than at the bottom) and slightly decelerated by positive field gradients.

Inverse space-dependent force problems for the wave equation

The determination of the displacement and the space-dependent force acting on a vibrating structure from measured final or time-average displacement observation is thoroughly investigated. Several aspects related to the existence and uniqueness of a solution of the linear but ill-posed inverse force problems are highlighted. After that, in order to capture the solution a variational formulation is proposed and the gradient of the least-squares functional that is minimized is rigorously and explicitly derived. Numerical results obtained using the Landweber method and the conjugate gradient method are presented and discussed illustrating the convergence of the iterative procedures for exact input data. Furthermore, for noisy data the semi-convergence phenomenon appears, as expected, and stability is restored by stopping the iterations according to the discrepancy principle criterion once the residual becomes close to the amount of noise. The present investigation will be significant to researchers concerned with wave propagation and control of vibrating structures.

Propagacão das ondas de rossby nos invernos de máxima freqüência de ocorrência de geadas na pampa úmida

Neste trabalho estudou-se a influência dos padrões de onda extratropicais, que favorecem o desenvolvimento de eventos extremos frios no sudeste Sul-Americano, e em particular na região conhecida como Pampa Úmida. O aquecimento anômalo observado na região do oceano Pacífico tropical ocidental a nordeste da Austrália, durante os invernos de máxima freqüência de ocorrência de Geadas Generalizadas (GG) no centro-leste da Argentina, (região conhecida como Pampa Úmida - PU), atua como disparador de ondas de Rossby, as quais se propagam até o continente, favorecendo assim a ocorrência daqueles eventos. O padrão de propagação obtido nas simulações numéricas com um modelo baroclínico global, mostra o predomínio de um número de onda 3. Adicionalmente, foram analisadas as correlações do vento meridional em altos e baixos níveis observados para os eventos de GG, selecionados dentro dos invernos de máxima freqüência de ocorrência desses eventos. O vento meridional global em 250hPa apresenta regiões com correlação estatisticamente significativa com o vento meridional médio na PU. A configuração obtida no caso do vento meridional global em 250hPa, correlacionado com o vento meridional na PU, pode estar associada ao padrão de propagação das ondas simuladas numericamente a partir da forçante tropical. Igualmente importantes e significativos são os valores de correlação do vento sul nos baixos níveis, em particular para toda região da PU. O padrão de ondas simulado está bem representado pelas significativas correlações entre o vento meridional hemisférico em altos níveis e a temperatura no dia de evento de GG.

The role of the observed tropical convection in the generation of frost events in the southern cone of South America

Based on previous results obtained from observations and linear wave theory analysis, the hypothesis that large-scale patterns can generate extreme cold events in southeast South America through the propagation of remotely excited Rossby waves was already suggested. This work will confirm these findings and extend their analysis through a series of numerical experiments using a primitive equation model where waves are excited by a thermal forcing situated in positions chosen according to observed convection anomalies over the equatorial region. The basic state used for these experiments is a composite of austral winters with maximum and minimum frequency of occurrence of generalized frosts that can affect a large area known as the Wet Pampas located in the central and eastern part of Argentina. The results suggest that stationary Rossby waves may be one important mechanism linking anomalous tropical convection with the extreme cold events in the Wet Pampas. The combination of tropical convection and a specific basic state can generate the right environment to guide the Rossby waves trigged by the tropical forcing towards South America. Depending on the phase of the waves entering the South American continent, they can favour the advection of anomalous wind at low levels from the south carrying cold and dry air over the whole southern extreme of the continent, producing a generalized frost in the Wet Pampa region. On the other hand, when a basic state based on the composites of minimum frosts is used, an anomalous anticyclone over the southern part of the continent generates a circulation with a south-southeast wind which brings maritime air and therefore humidity over the Wet Pampas region, creating negative temperature anomalies only over the northeastern part of the region. Under these conditions even if frosts occur they would not be generalized, as observed for the other basic state with maximum frequency of occurrence of generalized frosts.

Determination of in situ uniaxial compressive strength of coal seams based on geophysical data

The central issue for pillar design in underground coal mining is the in situ uniaxial compressive strength (sigma (cm)). The paper proposes a new method for estimating in situ uniaxial compressive strength in coal seams based on laboratory strength and P wave propagation velocity. It describes the collection of samples in the Bonito coal seam, Fontanella Mine, southern Brazil, the techniques used for the structural mapping of the coal seam and determination of seismic wave propagation velocity as well as the laboratory procedures used to determine the strength and ultrasonic wave velocity. The results obtained using the new methodology are compared with those from seven other techniques for estimating in situ rock mass uniaxial compressive strength.

Ultrasound, eddy current and magnetic Barkhausen noise as tools for sigma phase detection on a UNS S31803 duplex stainless steel

Sigma phase is a deleterious one which can be formed in duplex stainless steels during heat treatment or welding. Aiming to accompany this transformation, ferrite and sigma percentage and hardness were measured on samples of a UNS S31803 duplex stainless steel submitted to heat treatment. These results were compared to measurements obtained from ultrasound and eddy current techniques, i.e., velocity and impedance, respectively. Additionally, backscattered signals produced by wave propagation were acquired during ultrasonic inspection as well as magnetic Barkhausen noise during magnetic inspection. Both signal types were processed via a combination of detrended-fluctuation analysis (DFA) and principal component analysis (PCA). The techniques used were proven to be sensitive to changes in samples related to sigma phase formation due to heat treatment. Furthermore, there is an advantage using these methods since they are nondestructive. (C) 2010 Elsevier B.V. All rights reserved.