Letteratura scientifica selezionata sul tema "Wall impulse response"

To identify the damage within retaining wall structures, the Hilbert–Huang Transforms of the impulse response function and virtual impulse response function were performed. The Hilbert marginal energy ratio spectrums of the impulse response function and virtual impulse response function were acquired. To reflect damage information effectively, those bands with stronger damage sensitivity were extracted via the threshold value ε0. Then, the Hilbert feature bands, which were more sensitive to damage within retaining walls, were selected by considering the contribution of the residual band to the damage identification. Based on the feature bands, the Hilbert damage feature vector, which reflects the variations of Hilbert marginal energy ratio caused by damage, was created. Based on the damage feature vector, two damage identification indexes (the energy ration standard deviation and Energy Ration Standard Deviation), which were based on the impulse response function and virtual impulse response function, respectively, were proposed to identify damage within retaining walls. To investigate the validity of the damage indexes, vibration tests on a pile plate retaining wall were done. The test results show that the damage feature vector is a zero vector or the value of damage index is zero when the wall is undamaged. The damage feature vector is a nonzero vector or the value of the damage index is more than zero when the wall is damaged. Thus, the damage state of the wall can be detected sensitively via the damage feature vector or damage indexes. Partial damage causes greater fluctuation of trend surface of the damage index. The location of partial damage can be diagnosed validly via the coordinate of peak value in the trend surface. The quantitative relationship formula between the damage index and damage intensity is established. The damage intensity of the wall can be calculated reversely, when the damage index is available. Either the energy ration standard deviation or Energy Ration Standard Deviation can be used to detect the damage state, diagnose the damage location, and identify the damage intensity. In comparison with the energy ration standard deviation, the stability and damage sensitivity of the Energy Ration Standard Deviation is much better.

We study the evolution of velocity fluctuations due to an isolated spatio-temporal impulse using the linearized Navier–Stokes equations. The impulse is introduced as an external body force in incompressible channel flow at $Re_{\unicode[STIX]{x1D70F}}=10\,000$. Velocity fluctuations are defined about the turbulent mean velocity profile. A turbulent eddy viscosity is added to the equations to fix the mean velocity as an exact solution, which also serves to model the dissipative effects of the background turbulence on large-scale fluctuations. An impulsive body force produces flow fields that evolve into coherent structures containing long streamwise velocity streaks that are flanked by quasi-streamwise vortices; some of these impulses produce hairpin vortices. As these vortex–streak structures evolve, they grow in size to be nominally self-similar geometrically with an aspect ratio (streamwise to wall-normal) of approximately 10, while their kinetic energy density decays monotonically. The topology of the vortex–streak structures is not sensitive to the location of the impulse, but is dependent on the direction of the impulsive body force. All of these vortex–streak structures are attached to the wall, and their Reynolds stresses collapse when scaled by distance from the wall, consistent with Townsend’s attached-eddy hypothesis.

Impulse ground motions are applied to single story structures with different in-plane wall strength and stiffness, rotational inertia, and out-of-plane wall stiffness to obtain the dynamic response considering torsion. A simple hand method to evaluate the impulse response is developed. It is shown that the median increase in response of the critical component considering torsion from many earthquake records is similar to that from impulse records. Using this information, a simple design methodology is proposed which enables the likely earthquake response of critical elements considering torsion to be obtained from building analyses not considering torsion. A design example is also provided.

Pressure-impulse diagrams have been extensively used for damage assessments of structural components subject to a specified blast loading. In this paper, a numerical method is used to generate pressure-impulse diagrams for unreinforced masonry walls subjected to blast loading. A previously developed plastic damage material model accounting for strain rate effects is used for brick and mortar. Three levels of damage criteria are defined based on maximum deflection of the wall and rotation of the supports. The obtained blast response for unreinforced masonry walls are validated against field test data. It is shown that the obtained pressure-impulse diagrams have an improved ability to evaluate the damage level of masonry walls.

In order to obtain the damage characteristics of a roadway wall caused by a gas explosion, the damage evaluation theory of a roadway wall under the dynamic and static loads of a gas explosion is analyzed in this paper. Meanwhile, an evaluation method (overpressure–impulse criterion) is selected to evaluate the damage of the roadway wall under the impact load of the gas explosion. A mathematical model and a physical analysis model of the roadway wall damage are established by LS-DYNA software. The dynamic response of the roadway wall caused by the dynamic and static loads of the gas explosion is numerically simulated. The overpressure and impulse of gas explosion propagation are measured, while the damage data of the roadway wall under different overpressure and impulse loads are obtained. The P-I curves of the roadway wall under different dynamic and static loads of gas explosion are drawn. The fitting formula of P-I curves of the roadway wall is obtained. The influence of different geostress loads (0–20 MPa) on the P-I curve is analyzed. The shape of the P-I curve is similar under different geostress conditions. The difference is mainly shown in different sizes of P0 and I0. The numerical simulation results show that the P-I curve and the effect of geostress on roadway wall damage could reflect the dynamic response of the roadway wall. The damage degree and damage range of the roadway wall increase with the increase in explosion load energy. Under the action of different geostresses, the overpressure asymptote P0 and the impulse asymptote I0 show linear changes. The above research results could provide a theoretical basis and data support for the evaluation of roadway wall damage caused by gas explosions.

To eliminate the influence of excitation on the wavelet packet frequency band energy spectrum (ES), ES is acquired via wavelet packet decomposition of a virtual impulse response function. Based on ES, a character frequency band vector spectrum and damage eigenvector spectrum (DES) are created. Additionally, two damage identification indexes, the energy ratio standard deviation and energy ratio variation coefficient, are proposed. Based on the damage index, an updated damage identification method for retaining wall structures is advanced. The damage state of a retaining wall can be diagnosed through DES, the damage location can be detected through the damage index trend surface, and the damage intensity can be identified by establishing a quantitative relationship between the damage intensity and damage index. To verify the feasibility and validity of this damage identification method, a vibration test on a pile plate retaining wall is performed. Test results demonstrate that it can distinguish whether the retaining wall is damaged, and the location of partial damage within the retaining wall can be easily detected; in addition, the damage intensity of the wall can also be identified validly. Consequently, this damage identification theory and method may be used to identify damage within retaining wall structures.

Based on the finite element software ABAQUS, this paper deals with numerical simulation to dynamic response of reinforced concrete wall under blast loading. Study shows that the explosion resistance performance of the wall with four edges fixed or with two opposite edges fixed are better than that of the wall one edge fixed and another opposite edge simply supported. The greater the explosion impulse, the bigger the maximum displacement of the wall. When reinforcement ratio of the wall increases, the explosion resistance performance of the wall will be improved. At the same time, reasonable reinforcement and external conditions should be made sure. Keywords: Blast Loading, Numerical Simulation, Shear Wall, Dynamic Response

P-wave and S-wave displacements occur at high angles of incidence in vertical seismic profiles (VSPs). Therefore, the coupling of a geophone sonde to the borehole wall must be rigid in all directions. A sonde that is well coupled should have no resonant frequency within the seismic band and should provide geophone outputs that accurately represent the earth’s ground motion. An in‐situ coupling response experiment conducted under normal VSP field conditions provides a measure of the sonde‐to‐borehole wall coupling. The sonde is locked in the borehole and a surface source is excited at different offsets and azimuths. An analysis of the P-wave direct arrivals enhances damped oscillations that represent an estimate of the coupling impulse response. This response is characterized by the viscoelastic behavior of a Kelvin model related to the complex compliance [Formula: see text], where κ is the elastic spring constant, η is the damping constant, and ω is the angular frequency. The complex modulus κ−iωη is proportional to the contact width of the sonde with the borehole wall. Increasing the width by a factor of 4.5 causes a similar increase in κ−iωη where the resonant frequency and initial amplitude of the coupling impulse response increase by a factor of two. Also, the initial amplitude of the coupling impulse response appears to be inversely proportional to the locking force of the sonde. For a constant contact width, increasing the locking force by a factor of 1.37 decreases the amplitude of the response by 3.5 dB.

1. The electrical responses of nociceptive (N) lateral and N medial neurons of the leech segmental ganglion to mechanical, chemical, and thermal stimulation of the skin were studied in a superfused ganglion-body wall preparation. 2. Mechanical indentation of the skin > 10 mN evoked in both types of cells a sustained discharge of impulses; afterdischarge was often observed with suprathreshold stimulations. 3. Application to the cutaneous receptive area of 10-100 mM acetic acid or of NaCI crystals and solutions also elicited a firing response in N medial and N lateral cells. In contrast, capsaicin applied to the skin (3.3 x 10(-5) to 3.3 x 10(-2) M) excited N lateral but not N medial neurons. Likewise, impulse discharges were obtained when capsaicin was applied to the cell bodies of N lateral but not of N medial neurons. 4. In both types of N neurons, heating of the skin above 39 degrees C evoked a discharge of impulses whose frequency was roughly proportional to temperature values. 5. Application of repeated suprathreshold heating cycles at 10-min intervals enhanced the impulse frequency of the response (sensitization). Shorter time intervals between heating cycles depressed the response to heat. Sensitization could not be obtained by equivalent soma depolarizations obtained by intracellular current injection. 6. Impulse discharges evoked by irritant agents were also augmented by previous application of noxious heat. 7. N lateral neurons fired in response to low-pH solutions and capsaicin directly applied onto the ganglion. N medial neurons responded inconsistently to acid and were insensitive to capsaicin. Action potentials evoked in N lateral cells by capsaicin had a slow rise, a prominent hump, and a prolonged afterhyperpolarization. 8. It is concluded that N neurons of the leech segmental ganglion respond to different modalities of noxious stimuli applied to their peripheral receptive fields and develop sensitization after repeated noxious stimulation. These properties are typical of mammalian polymodal nociceptors; thus N neurons may be a simple model for analysis of membrane mechanisms associated with polymodality of nociceptive neurons.

Recent events including deliberate terrorist attacks and accidental explosions have highlighted the need for comprehensive research in the area of structural response to blast loading. Research in this area has recently received significant attention by the civil engineering community. Reinforced Concrete (RC) water reservoir tanks are an integral part of the critical infrastructure network of urban centers and are vulnerable to blast loading. However, there is a lack of research and knowledge on the performance of RC reservoir walls under blast loading. The objective of this research study is to experimentally investigate the performance of reinforced concrete reservoir walls subjected to blast loading and to analyze the structural response. This study provides experimental test data on the performance of reinforced concrete reservoir walls under blast loading and complementary analytical predictions using the Singe-Degree-Of-Freedom (SDOF) analysis method. The reservoir walls in this study were designed according to the water volume capacity using the Portland Cement Association (PCA 1993) methodology. The design was validated using software SAP 2000. The experimental program involved the construction and simulated blast testing of two RC reservoir wall specimens with different support conditions: (1) two opposite lateral edges fixed, bottom edge pinned and top edge free; and (2) two opposite lateral edges fixed, and bottom and top edges free. The first boundary condition was intended to promote two-way bending action, while the second was dominated by one-way bending. The two specimens were each subjected to a total of six consecutive incrementally increasing blast tests. The experimental program was conducted in the shock tube testing facility that is housed in the University of Ottawa. Wall displacements, reinforcement strains, and reflected pressures and impulses were measured during testing. Analytical calculations were conducted using the equivalent SDOF method to simulate the dynamic response of the RC reservoir wall specimens under different blast loadings. Published tables, charts and coefficients contained in Biggs (1964) and UFC 3-340-02 (2008) were adopted in the equivalent SDOF calculations. The analytical results were compared against the ii experimental data. The SDOF method predicted smaller displacements than those recorded during testing. The approximate nature of the parameters and tables used in the equivalent SDOF calculations contributed to the discrepancy between the analytical and experimental results. Furthermore, assumptions regarding the support conditions and neglecting residual damage from previous blast tests contributed to the underestimation of the displacements.

L'objectif de cette thèse est de contribuer à améliorer significativement le diagnostic acoustique de salles in situ en développant des nouvelles approches à la croisée de l'apprentissage automatique, de l'optimisation, du traitement du signal audio et de la physique acoustique. Les travaux présentés dans ce manuscrit portent sur l'estimation des propriétés d'absorption acoustique de chacune des parois d'une salle à partir de plusieurs réponses impulsionnelles de salle acquises pour des positions libres de sources et de microphones, ainsi que de mesures des paramètres géométriques et des réponses des appareils associés. Plusieurs méthodes sont proposées pour la résolution de ce problème inverse complexe en visant progressivement une description plus fine des propriétés d'absorption des parois, une application à des données simulées plus réalistes et une plus grande simplicité de mise en oeuvre. Ces travaux aboutissent à la présentation d’une approche d’estimation des réponses impulsionnelles des parois d’une salle par optimisation dans le domaine temporel. Celle-ci est fondée sur une nouvelle extension du modèle de réponse impulsionnelle de salle issu de la méthode des sources-images permettant de rendre compte des erreurs sur la mesure des paramètres géométriques, en plus de la dépendance spatio-fréquentielle des réponses des sources et des microphones
The aim of this thesis is to contribute to significantly improve in situ acoustic diagnosis of rooms by developing new approaches at the crossroads of machine learning, optimization, audio signal processing and acoustics. The work presented in this manuscript focuses on estimating the acoustic absorption properties of each wall in a room from multiple room impulse responses acquired for free positions of sources and microphones, along with measurements of geometric parameters and responses of the associated devices. Several methods are proposed to solve this complex inverse problem, progressively aiming for a more detailed description of the absorption properties of the walls, application to more realistic simulated data, and greater ease of implementation. This work culminates in the presentation of an approach for estimating the wall’s impulse responses by optimization in the time domain. This approach is based on a new extension of the room impulse response model derived from the image source method, which accounts for errors in the measurement of the geometric parameters, in addition to the spatial frequency dependence of the source and microphone responses

This paper analyzes empirically the effect of crude oil price change on the economic growth of Indian-Subcontinent (India, Pakistan and Bangladesh). We use a multivariate Vector Autoregressive analysis followed by Wald Granger causality test and Impulse Response Function (IRF). Wald Granger causality test results show that only India’s economic growth is significantly affected when crude oil price decreases. Impact of crude oil price increase is insignificantly negative for all three countries during first year. In second year, impact is negative but smaller than first year for India, negative but larger for Bangladesh and positive for Pakistan.

Valutamarknaden är världens största marknad och en nödvändig del av dagens globala samhälle, som gör det möjligt för företag att göra affärer i olika valutor och mellan olika gränser. Marknaden utgör en stor handelsplattform för både små och stora aktörer, för vilka det är viktigt att prognostisera valutakurser med gott resultat. Att modellera finansiella instrument i form av tidsserier är en av de vanligaste investeringsstrategierna och dess användningsområde sträcker sig från valutamarknaden till bland annat aktiemarknaden och råvarumarknaden. I denna uppsats undersöks fyra olika statistiska metoder för att modellera valutakursen Euro-US Dollar givet historisk data, och prognoser görs med de framtagna modellerna. Dessa metoder är slumpvandring, ARIMA, ARIMA-GARCH och VAR. Vidare undersöks för den dynamiska VAR-modellen hur valutamarkanden påverkar, och blir påverkad av, långa och korta räntan. Resultaten visar att ARIMA(3,1,2) förklarar valutakursen bäst medan VAR(2) med valutakursen och skillnaden mellan långa räntor som ingående variabler ger de bästa prediktionerna.
The foreign exchange market is the world’s largest market and is an essential part of the global society of today. The FX market enables companies to trade with different currencies across country borders. It is also a large trade-platform for both big and small financial actors, who greatly benefit from the advantages of good predictions. Modeling of financial instruments is one of the most commonly used investment strategies and its area of application ranges from the FX market to markets suchas the stock market and the commodity market. In this paper, four different statistical models are used to model the currency pair Euro-US Dollar. These methods are random walk, ARIMA, ARIMA-GARCH and VAR. Besides investigating which method that gives the best forecasts, the method that best describes the training datais also found. Furthermore, for the dynamic VAR model, it is explored how the FX market affects, and is affected by, the long term and short term interest. The results show that ARIMA(3,1,2) is the best at describing the exchange rate while VAR(2) with the exchange rate and the difference between long term interests as variables gives the best predictions.

Doctoral Thesis Civil Engineering
The work presented here was accomplished at the Department of Civil Engineering of University of Minho. This work involves detailed numerical studies intended to better understand the blast response of masonry structures, develops strain dependent constitutive material plasticity model for masonry, and addresses iso-damage curves for typical masonry infill walls in Portugal under blast with different loading conditions, which can be adopted for practical use in the case of enclosures. A bomb explosion near a building, in addition to a great deal of casualties and losses, can cause serious effects on the building itself, such as noticeable damage on internal and external frames, collapsing walls or shutting down of critical life safety systems. Until Oklahoma City bombing in 1995, studies dealing with the blast behavior of structures were a field of limited interest in the civil engineering community. After this terrorist attack, a great deal of effort has been done to better understand the blast response of the structures and devise solutions to reduce destructive damages and casualties due to such devastative loads. Moreover, the studies on the influence of the high strain rate on mechanical characteristics of construction materials such as steel and concrete have been carried out intensively. Unfortunately, despite the high vulnerability of masonry structures against high strain rates, such investigations on masonry structures and material properties are still scarce. In this regard, conducting experiments and validating numerical models with field test data leads to a better understanding of the blast response of masonry walls and the relevance of the different masonry material properties, which, consequently, results in innovation of strengthening techniques and of assessment and design methods. The framework of blast loading and its effect on structures is briefly revised and different expressions for prediction of blast pressure parameters are illustrated. A brief review of the recent characterization of the dynamic masonry properties, which resulted in derivation of dynamic increase factors (DIF) is presented. Performance of masonry walls against blast loading regarding experimental activities are addressed subsequently. Moreover, a series of numerical simulation of masonry structures subjected to blast loads were performed along with parametric studies to evaluate the effectiveness of most relevant parameters on the global blast response of the structures. The prominent parameters involved in parametric studies were distinguished and their effectiveness on the blast response of masonry walls is put forward. Different failure criteria have been proposed to estimate the damage level of masonry walls subjected to blast loading. The damage criteria utilized in both numerical and experimental studies are also introduced in detail. The present study proposes a dynamic 3D interface model that includes non-associated flow rule and high strain rate effects, implemented in the finite element (FE) code ABAQUS as a user subroutine. The model capability is validated with numerical simulation of unreinforced block work masonry walls subjected to low velocity impact. The results obtained are compared with field test data and good agreement is found. Subsequently, a comprehensive parametric analysis is accomplished with different joint tensile strengths and cohesion, and wall thickness to evaluate the effect of the parameter variations on the impact response of masonry walls. Furthermore, a new strain rate dependent anisotropic constitutive material continuum model is developed for impact and blast applications in masonry, with validation using the high strain rate response of masonry walls. The present model, implemented in FE code ABAQUS as a user subroutine, adopted the usual approach of considering different yield criteria in tension and compression, given the different failure mechanisms. These criteria are plasticity based, obey a non-associated flow rule, are numerically stable and inexpensive, and are characterized by a few material input parameters. The analysis of two unreinforced block work masonry parapets and a masonry brick work infill wall subjected to high strain rate loads is carried out to validate the capability of the model. A comparison is done between the numerical predictions and test data, and good agreement is noticed. Next, a parametric study is conducted to evaluate the influence of the most likely dominant parameters along the three orthogonal directions and of the wall thickness on the global behavior of masonry walls. Iso-damage curves are given for tested masonry infill walls according to three different types of typical Portuguese masonry infill walls, also with three different thicknesses. By performing multiple analyses, the pressure-impulse (P-I) diagrams are obtained under different loading conditions, which can be used for design purposes. Finally, the new continuum plasticity model is taken into engineering applications to solve real problems. The full-scale numerical simulation of the blast response of Al-Askari holy shrine is considered to practice and validate the model capability. The numerical results including the failure of the dome, roof, minarets and side facades are well predicted compared with the reference data. Besides the real explosion, two different scenarios are also defined to estimate the most likely high strain rate response of the shrine under different explosions producing different pressure profiles.
O trabalho aqui apresentado foi realizado no Departamento de Engenharia Civil da Universidade do Minho. Este trabalho envolve estudos numéricos detalhados que pretendem entender melhor a resposta às explosões das estruturas de alvenaria, desenvolver modelos constitutivos para a alvenaria no âmbito da teoria da plasticidade, e abordar curvas de iso-dano para paredes típicas de alvenaria de enchimento em Portugal sob explosão com diferentes condições de carga, que possam ser usadas no projeto das ensolventes. A explosão de uma bomba perto de um edifício, além de uma grande quantidade de vítimas e perdas materiais, pode causar efeitos graves sobre o edifício em si, tais como danos visíveis nos pórticos internos e externos, colapso de paredes ou encerramento de sistemas críticos de apoio à vida. Até ao atentado de Oklahoma City, em 1995, os estudos sobre o comportamento á explosão de estruturas eram um tema de interesse limitado na comunidade de engenharia civil. Após este ataque terrorista, um grande esforço tem sido feito para entender melhor a resposta das estruturas a explosões e para criar soluções para reduzir os danos e perdas humanas devido a essas ações devastadoras. Além disso, estudos sobre a influência da velocidade de deformação sobre as características mecânicas dos materiais de construção tais como aço e betão foram levados a cabo com grande desenvolvimento. Infelizmente, apesar da alta vulnerabilidade das estruturas de alvenaria contra as elevadas velocidades de deformação, a investigação sobre as estruturas de alvenaria e as propriedades dos seus materiais são ainda escassos. Neste sentido, a realização de experiências e a validação de modelos numéricos com os resultados de ensaios levam a uma melhor compreensão da resposta de paredes de alvenaria a explosões e premitem identificar a relevância das diferentes propriedades dos materiais de alvenaria, o que, consequentemente, resulta em inovação de técnicas de reforço e de avaliação de segurança e ferramentas de projeto. O estado da arte sobre ações de explosão e o seu efeito sobre as estruturas é brevemente revisto, incluindo diferentes expressões para definição dos parâmetros de pressão de explosão. Uma breve revisão da recente caracterização das propriedades dinâmicas de alvenaria resultou na caracterização do fator de aumento dinâmico (DIF). Em seguida, aborda-se o desempenho de paredes de alvenaria contra ações de explosão de um ponto de vista da atividade experimental. Além disso, foi realizada uma série de simulações numéricad de estruturas de alvenaria sujeitas a ações de explosão, juntamente com estudos paramétricos, para avaliar a eficácia dos principais parâmetros sobre a resposta da explosão global das estruturas. Os parâmetros mais relevantes envolvidos em estudos paramétricos foram distinguidos e o seu efeito na resposta de paredes de alvenaria a explosões é apresentada. Vários critérios de rotura têm sido propostos para estimar o nível de dano de paredes de alvenaria sujeitas a carregamento de explosões. Os critérios utilizados nos estudos de danos, tanto numéricos quanto experimentais, são apresentados em detalhe. O presente estudo propõe um modelo de interface 3D dinâmica que inclui regra de escoamento não-associado e efeitos da velocidade de deformação, implementado no código de elementos finitos (FE) ABAQUS como uma sub-rotina do utilizador. A capacidade do modelo é validado com simulações numéricas de paredes de alvenaria não armada submetidos a impacto a baixa velocidade. Os resultados obtidos são comparados com os dados de ensaios e boa concordância é encontrada. Subsequentemente, uma análise paramétrica abrangente é realizado com diferentes resistências à tração comum e coesão, e espessura da parede, para avaliar o efeito das variações de parâmetros em resposta a impactos nas paredes de alvenaria. Além disso, um modelo constitutiva contínuo do material dependendo da velocidade de deformação é desenvolvido para aplicações de impacto e explosão em alvenaria, com validação usando a resposta de paredes de alvenaria a velocidades elevadas de deformação. No presente modelo, implementado no código FE ABAQUS como uma sub-rotina do utilizador, foi adotado o método habitual de considerar diferentes critérios de rotura em tração e compressão, tendo em conta os diferentes mecanismos de falha. Estes critérios são baseados na teoria da plasticidade, obedecem a uma regra de escoamento não-associado, são numericamente estáveis e de baixo custo, e são caracterizados por pouco parâmetros de entrada do material. A análise de dois parapeitos não armados de alvenaria e uma pareder de enchimento de alvenaria de tijolo submetidos a cargas de alta velocidade de deformação é realizado para validar a capacidade do modelo. A comparação é feita entre as previsões numéricas e ensaios, com bons resultados. Em seguida, é realizado um estudo paramétrico para avaliar a influência dos parâmetros dominantes mais suscetíveis ao longo das três direções ortogonais, e da espessura da parede sobre o comportamento global das paredes de alvenaria. As curvas de iso-danos são obtidas para três tipos típicos de parede de alvenaria de enchimento em Portugal, com três espessuras diferentes. Com recurso a várias análises, os diagramas pressão-impulso (PI) são obtidos para diferentes paredes de enchimentos de alvenaria sob diferentes condições de carga, o que permite o dimensionamento em projeto corrente. Finalmente, o novo modelo de plasticidade contínuo é utilizado em aplicações de engenharia para resolver problemas reais. A simulação numérica em escala real da resposta à explosão do santuário sagrado de Al- Askari é considerado para a prática e validação da capacidade do modelo. Os resultados numéricos, incluindo o colapso da cúpula, telhado, minaretes e fachadas laterais estão a prever bem em comparação com os dados de referência. Para além da explosão real, dois diferentes cenários são também definidos para estimar a resposta mais provável da alta taxa de deformação do santuário sob diferentes explosões, a produzir perfis de pressão diferentes.
Portuguese Foundation of Science and Technology (FCT) - project CH-SECURE

This chapter explores the behaviour and performance of glass curtain wall systems under various dynamic mechanical loads, including seismic, wind and impulsive loads. The classification of glass facade systems, comprising framed and frameless types, is first shortly discussed, along with their core components such as glass panels and frames. The challenges posed by glass material, including its vulnerability to impact, stress peaks and extreme loads, are acknowledged. The study further delves into various design standards and regulations for glass facade systems under dynamic loads, addressing seismic events and wind and impulsive loads and hence outlining parameters for assessment, performance criteria, and design considerations in use of glass curtain walls. Additionally, numerical methods are explored as effective tools for simulating and analysing the mechanical response of glass curtain walls under dynamic loads. The utility of these methods is showcased through a case study involving the Finite Element (FE) modelling of a glass curtain wall system exposed to a lateral in-plane load. The results of FE analysis are then compared with literature experimental results, which indicates its capacity to anticipate structural responses and even complex mechanisms under dynamic loads.

The study aims to find the short-run empirical analyses of the impact of oil price fluctuation on the monetary instrument (Exchange rate, Inflation, Interest rate) in Nigeria. We explored the frequently used Toda–Yamamoto model (TY) model, by adopting the TY Modified Wald (MWALD) test approach to causality, Forecast Error Variance Decomposition (FEVD) and Impulse Response Functions (IRFs).The study covered the period 1995 to 2018 (monthly basis), and our findings from MWALD test indicated that there is a uni-directional causality of the log of oil price (lnoilpr) to log of the exchange rate (lnexchr) at 10% level of significance, also there is a contemporaneous response of log of consumer price index (lncpi) to log of exchange rate (lnexchr) and log of interest rate (lnintr), and jointly (lnoilpr, lncpi and lnintr) granger cause lncpi. Also at 5% level of significance lnintr responded due to positive change in lnoilpr and lnexchr, and jointly causes lnintr at 5% level of significance. This is complimented with our findings in FEVDs, and IRFs. The empirical analyses shows that oil price is a strong determining factor of exchange rate, cost of borrowing and directly influences inflationary or deflationary tendencies in Nigeria..

Vessels subjected to internal impulsive loadings, such as those used for controlled-detonation chambers, can be designed for a single impulsive load application or for multiple impulsive loads. Design of a single-use vessel may take advantage of the capability of the vessel material to absorb energy through elastic-plastic behavior, provided that the public health and safety is protected, even though the owner’s investment in the vessel may be compromised because of severe distortion and potential loss of containment functionality. However, when the vessel is designed to contain multiple internal impulse loads, the usual design practice is to require completely elastic response or, at most, very localized elastic-plastic behavior. A recently-approved ASME Boiler & Pressure Vessel Code, Section VIII, Division 3 action (Code Case 2564-2) provides limits for the accumulated plastic strains in such vessels, including a limit on the accumulated plastic strain averaged across the wall thickness of the vessel, that are sufficiently conservative to permit the design of vessels for both single-impulse and for multiple-impulse applications. Analytical or experimental demonstration to meet the Code Case 2564-2 strain limits is straightforward for the single-impulse vessel design, and is relatively straightforward for multiple-impulse vessel designs when the vessel response to any of the individual impulsive loads is nearly elastic. However, when the design-basis impulsive loading for a multiple-impulse vessel design leads to significant plastic straining, the demonstration of design adequacy becomes extremely complex, raising issues of impulsive loading sequences (since elastic-plastic response is load-path dependent, what is the temporal order of the impulse loadings?) and demonstration of shakedown to elastic or near-elastic behavior. In such cases, an analytical demonstration of design adequacy may be impractical, while an experimental demonstration may be both practical and illuminating, especially if the demonstration is carried out at a scale that is both economical and convincing. Here, a one-seventh-scale model of a controlled detonation vessel is used as the basis for demonstrating the effect of shakedown to essentially elastic behavior, with no further accumulation of plastic straining, along with the satisfaction of ASME Code Section VIII, Division 3, local ductility exhaustion requirements. The experiments on a scale model vessel have proved that the phenomenon of shakedown can be demonstrated experimentally, for internal detonation loadings that initially led to plastic strains up to 0.7%.

Many accidents that occur on offshore structures, especially explosions, are extremely hazardous. Violent explosions can have serious consequences for health, safety, and the marine environment. The topsides of offshore platforms are the most likely areas to be exposed to hazards such as hydrocarbon explosions. Therefore, profiled barriers are being increasingly used as blast walls in offshore topsides modules to provide a safety barrier for personnel and critical equipment. The aim of this study is to develop a practical procedure for the nonlinear structural response analysis of corrugated blast walls under explosion. Within the framework of quantified risk assessment and management of offshore installations, more refined computations are required to assess the consequences or hazardous action effects of explosions. In addition, appropriate guidance will be presented on the use of the finite element numerical tool for the above purpose. The structural response has been computed using commercial nonlinear finite element analysis (NLFEA) code and the results compared with the single degree of freedom (SDOF) method. The relationships between blast pressure and the impulse of corrugated blast walls are developed. This study’s insights into modeling techniques and procedures will be applicable to the explosion risk assessment of offshore structures.

The influence of thermal boundary condition at the combustor wall and combustor confinement on the dynamic flame response of a perfectly premixed axial swirl burner is investigated. Large Eddy Simulations are carried out using the Dynamically Thickened Flame combustion model. Then, system identification methods are used to determine the flame transfer function (FTF) from the computed time series data. Two configurations are compared against a reference case with 90 mm × 90 mm combustor cross section and nonadiabatic walls: 1) combustor cross section similar to the reference case with adiabatic combustor walls, and 2) different confinement (160 mm × 160 mm) with nonadiabatic walls. It is found that combustor confinement and thermal boundary conditions have a noticeable influence on the flame response due to differences in flame shape and flow field. In particular the FTF computed with adiabatic wall boundary condition, which produces a flame with significant heat release in both shear layers, differs significantly from the FTF with nonadiabatic walls, where the flame stabilizes only in the inner shear layer. The observed differences in flow field and flame shape are discussed in relation to the unit impulse response of the flame. The impact of the differences in FTF on stability limits is analyzed with a low-order thermoacoustic model.

Abstract Numerical simulations were performed to study the feasibility of erosion detection in hydraulic tubes and hoses using fluid dynamic pressure response analysis. Reflected pressure signals caused by wall thinning were studied to locate and quantify pipe defects. Simulations were conducted for steel pipes as well as hoses. Results showed that for a steel pipe, since the stiffness of the fluid is much less than the pipe material’s, a very big change of wall thickness is needed to have a meaningful change in wave propagation speed and therefore the dynamic pressure response. For hoses, the wall stiffness is much less than steel pipes, hence it is more feasible to detect changes in stiffness. A dataset of 10 000 dynamic pressure impulse responses from samples with randomly generated eroded geometries was calculated to train a gated recurrent unit (GRU) neural network. Results showed that under perfect conditions (no noise), we are able to detect an eroded section’s location, length, and change in wave propagation speed with relative errors of 2.69%, 4.88%, and 3.79%, respectively. The changes in the wave propagation speed was also categorized into three classes of low, mild, and severe erosion with the accuracy of 97.3%. Under more practical conditions including sensor noise, the accuracy of erosion detection is degraded, especially in the case of steel tubing. By retraining the model with noisy data, the drop in the accuracy is compensated to about 96%.

Abstract In wiresaw manufacturing process where thin wire moving at high speed is pushed onto ingot to produce slices of wafer, the wire is constrained by two wafer walls as it slices into the ingot. In this paper, we investigate the vibration of such wire under the constraints of wafer walls. To address this problem, the model for wire vibration with impact to wafer walls is developed. The equation of motion is discretized using the Galerkin’s method. The principle of impulse and momentum is utilized to solve the impact problem. The results of analysis and simulation indicate that the response under a pointwise sinusoidal excitation is neither periodical nor symmetric with respect to the horizontal axis, due to the excitation from the impact. The wire vibration behavior is affected dramatically by the wafer wall constraints.

Thin walled axial members are typically used in vehicles’ side and front chassis to improve crashworthiness. Extensive work has been done in exploring energy absorbing characteristics of thin walled structural members under axial compressive loading. The present study is a continuation of the work presented earlier on evaluating the effects of presence of functionally graded cellular structures in thin walled members. A functionally graded aluminum cellular core in compact form was placed inside a steel square tube. The crushing behavior was modeled using ABAQUS/Explicit module. The variables affecting the energy absorbing characteristics, for example, deformation or collapsing modes, crushing/ reactive force, plateau stress level, and energy curves, were studied. An approximate 35% increase in the energy absorption capacity of steel tube was observed by adding aluminum graded cellular structure to the square tube. The aluminum graded structure crushed systematically in a layered manner and its presence as core supported the steel square tube side walls in transverse direction and postponed the local (tube) wall collapse. This resulted in composite tube undergoing larger localized folds as compared to highly compact localized folds, which appeared in the steel tube without any graded core. The variation in deformation mode resulted in increased stiffness of the composite structure, and therefore, high energy absorption by the structure. Further, a relatively constant crushing force was observed in the composite tube promoting lower impulse. This aspect has a potential to be exploited to improve the crashworthiness of automobile structures.

Abstract In viscoelastic pipes, where the material properties depends on a complex bulk modulus as well as on a complex shear modulus, the sound field within the fluid is affected. Therefore, the dispersion of flexural waves occurs in the pipe, while the speed of flexural waves decreases due to the coupled fluid mass. Coupling between the pipe wall and the fluid as decreases the sound speed in the fluid. Likewise, the speed of sound in fluid is frequency-dependent, just as the group velocity of bending waves depends on the frequency. Wavelet transform of non-stationary sound signal was used to identify the frequency-dependent fluid sound speed. A time-frequency map, constructed by plotting the wavelet coefficient against the translation and scale parameters, shows an alteration in the low frequency waves. The so called “fluid mode” and “pipe mode” resonant frequencies are also clearly evident. Lastly, the impact of different pipe wall material properties is also shown. Wavelet analysis of the measured impulse response of a fluid-filled viscoelastic pipe provides useful tool for investigating its acoustical properties.

Impingement of blast or shock waves on structures is characterized by a substantial transient aerodynamic load that develops over the short time associated with the shock reflection time scale. This mutual interaction between the shock wave and the structure can cause significant deformation of the structure and high strain rates within the material resulting in damage. An experimental investigation was carried out to determine the aeroelastic response of thin flat plates of composite materials during face-on impact with planar shock waves. The experiments were performed in a large-scale shock tube research facility, which had a working section of 12 inches in diameter and a length of 80 ft. Phenolic composite S2-HJ1 plates of 1/8 inch nominal thickness consisting of 12 layers of fibers and epoxy composite S2 plates of 1/8 inch nominal thickness consisting of 10 layers of fibers were tested in the present investigation. Miniature semi-conductor strain-gauges of high frequency response, high speed photography and Digital Image Correlation techniques were employed to measure locally the strain on the exterior side of the plates and high frequency response pressure transducers were used to measure time-dependent wall and total pressure. In order to provide comparison with the response of monolithic material to similar compressive loadings, aluminum and stainless steel plates were also tested under the same conditions. The application of shock loading on the specimen causes significant permanent deformation on the plates which has been measured immediately after the experiment while the specimen is still mounted on the end flange of the shock tube. These experimental data obtained in the present experiments include the measured displacement of the external surface of the plates from their original position in the normal to the plate direction along the radius of the specimen. This displacement is highest at the center of the plate and zero at the location of clamping. The results show that the deformations of the thicker plates are still considerably lower than those obtained in the steel and thinner composite plates although the loading pressure is more than triple in magnitude and the corresponding impulse is about 2.3 times higher. Composite plates were found to suppress several of the modes of the wave patterns while metallic ones demonstrate a rich variety of interacting modes. The frequency content of the strain signals on the surface of composite plates was not always the same with the content of the surface acceleration measured in free vibration experiments.