Dynamic wind loads acting on structures by definition are statistically correlated both in space and time. However, conventional approaches for the analysis of distributed aerodynamic loads, such as the proper orthogonal decomposition... more
Dynamic wind loads acting on structures by definition are statistically correlated both in space and time. However, conventional approaches for the analysis of distributed aerodynamic loads, such as the proper orthogonal decomposition (POD), can only present relevant spatial pattern that is encapsulated in a set of coherent structures. In this regard, this paper provides an operator-theoretic approach that describes a nonlinear/chaotic dynamical system in a functional space rather than the conventional phase space via the introduction of the Koopman operator. Subsequently, spectral analysis of the Koopman operator provides a spatial-temporal characterization of the time-dependent wind loads. We proposed an augmented dynamic mode decomposition (DMD) method to obtain the spectral decomposition results. Specifically, the proposed DMD algorithm is augmented by means of the delay coordinate embedding, and the identified eigen-tuples (eigenvalues, eigenvectors, and time evolution) can not...
Datasets in engineering applications are often limited and contaminated, mainly due to unavoidable measurement noise and signal distortion. Thus, using conventional data-driven approaches to build a reliable discriminative model, and... more
Datasets in engineering applications are often limited and contaminated, mainly due to unavoidable measurement noise and signal distortion. Thus, using conventional data-driven approaches to build a reliable discriminative model, and further applying this identified surrogate to uncertainty analysis remains to be very challenging. A deep learning approach is presented to provide predictions based on limited and noisy data. To address noise perturbation, the Bayesian learning method that naturally facilitates an automatic updating mechanism is considered to quantify and propagate model uncertainties into predictive quantities. Specifically, hierarchical Bayesian modeling (HBM) is first adopted to describe model uncertainties, which allows the prior assumption to be less subjective, while also makes the proposed surrogate more robust. Next, the Bayesian inference is seamlessly integrated into the DL framework, which in turn supports probabilistic programming by yielding a probability ...
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As many physical processes of interest to Civil Engineers manifest nonlinear and nonstationary features, their complete characterization may not be accomplished via Fourier transforms, necessitating a new analysis framework in the... more
As many physical processes of interest to Civil Engineers manifest nonlinear and nonstationary features, their complete characterization may not be accomplished via Fourier transforms, necessitating a new analysis framework in the time-frequency domain. This paper overviews recent developments in wavelet-based analysis of a number of physical processes of relevance to the Civil Engineering community. It is shown that the dual nature of wavelet transforms, being a simultaneous transform in time and frequency, permits adaptation of a number of traditional system identification and analysis schemes. For example, the extension of wavelet transforms to the estimation of time-varying energy density permits the tracking of evolutionary characteristics in the signal using instantaneous wavelet spectra and the development of measures like wavelet-based coherence to capture intermittent correlated structures in signals. Similarly, system identification methodologies originally referenced in e...
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Wind-related catastrophes (e.g., hurricanes, tornadoes, thunderstorms/downbursts) inflict enormous devastation on the built environment and result in a staggering number of fatalities. To better manage the impact of extreme wind events, a... more
Wind-related catastrophes (e.g., hurricanes, tornadoes, thunderstorms/downbursts) inflict enormous devastation on the built environment and result in a staggering number of fatalities. To better manage the impact of extreme wind events, a new culture of resilience needs to be developed based on innovative design solutions. By harnessing new technologies, quality of life and economic strength can be improved. The concept of shared resources is at the center of any plan and includes the exchanging of databases, computational and experimental resources, and full-scale data, as well as participating in collaborative research. Current examples of networked facilities for hazard reduction are the Network for Earthquake Engineering Simulation (NEES) (Van Den Einde et al., 2007). These facilities have made high-end resources accessible to groups otherwise limited by their personal research tools allowing them to expand the scope of their research to address complex problems. A similar model...
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The lack of systematic validation for the design process supporting tall buildings motivated the authors’ research groups and their collaborators to found the Chicago Full-Scale Monitoring Program over a decade ago. This project has... more
The lack of systematic validation for the design process supporting tall buildings motivated the authors’ research groups and their collaborators to found the Chicago Full-Scale Monitoring Program over a decade ago. This project has allowed the sustained in-situ observation of a collection of tall buildings now spanning worldwide. This paper overviews this program and the lessons learned in the process, ranging from appropriate technologies for response measurements to the factors influencing accurate prediction of dynamic properties all the way to how these properties then influence the prediction of response using wind tunnel testing and whether this response does indeed correlate with in-situ observations. Through this paper, these wide ranging subjects are addressed in a manner that demonstrates the importance of continued promotion and expansion of fullscale monitoring efforts and the ways in which these programs can provide true value-added to building owners and managers.
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This paper presents a probabilistic performance-based topology optimization framework for the conceptual design of uncertain building systems in seismic zones. The stochastic nature of the ground motions is rigorously considered in a... more
This paper presents a probabilistic performance-based topology optimization framework for the conceptual design of uncertain building systems in seismic zones. The stochastic nature of the ground motions is rigorously considered in a simulation-based probabilistic performance assessment framework that allows for the definition of a novel decoupling technique that efficiently separates the probabilistic analysis from the optimization loop. In particular, the methodology is based on the construction of a series of approximate sub-problems with simplified governing equations, which conveniently allows their evaluation using established techniques for static, deterministic topology optimization problems. The applicability and efficiency of the method is demonstrated on a case study.
Thunderstorm generated gust fronts are responsible for structural damage in many areas of the world. However, the resulting impact of gust front winds is not understood to the level that flow kinematics, dynamics and its impact on... more
Thunderstorm generated gust fronts are responsible for structural damage in many areas of the world. However, the resulting impact of gust front winds is not understood to the level that flow kinematics, dynamics and its impact on structures can be quantified. Gust front winds are highly transient and have a flow profile that differs significantly from a typical boundary layer flow field. This study focuses on investigating the effects of flow profile and its transient nature on the aerodynamics of bluff, prismatic bodies. A gust front flow field is modeled using a multiple fan wind tunnel and the resulting surface pressures are captured on a suite of prismatic models, which vary in size in relationship to the oncoming wind profile. The temporal variations in surface pressures are analyzed using traditional time, frequency and time-frequency domain approaches. Results indicate the changing nature of the surface pressure field in time, highlighting differences between local and areaa...
... Fluctuating Wind Loads on Buildings. by Ahsan Kareem , M.ASCE , (Asst. Prof., Dept. of Civ. Engrg., Univ. of Houston, Houston, Tex.) Journal of the Engineering Mechanics Division , Vol. 108 , No. 6 , November/December 1982 , pp. ...
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205 patients were examined and evaluated regarding gastrointestinal symptoms return of intestinal sounds return of bowel motion and length of hospital stay following cesarean section. They were classified into two groups. The first is the... more
205 patients were examined and evaluated regarding gastrointestinal symptoms return of intestinal sounds return of bowel motion and length of hospital stay following cesarean section. They were classified into two groups. The first is the study group which consisted of 95 patients who were fed immediately after cesarean section. The second group is the control group which consisted of 110 patients in whom delayed feeding according to the authors hospital protocol was done. There were no significant difference between the control and the study group regarding gastrointestinal symptoms return of bowel motion or hospital stay. There was a significant number of patients in the study group in whom earlier detection of intestinal sounds was found. The present study reached a conclusion that routine early feeding of patients undergoing cesarean section can be implemented without an increase in gastrointestinal symptoms or length of hospital stay. (authors)
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A wind tunnel study of a square cross-section building model immersed in thick turbulent boundary layers simulating two typical neutral atmospheric flow conditions was undertaken in order to determine the fluctuating crosswind force and... more
A wind tunnel study of a square cross-section building model immersed in thick turbulent boundary layers simulating two typical neutral atmospheric flow conditions was undertaken in order to determine the fluctuating crosswind force and the effects of incident flow properties on the fluctuating pressure field acting on the model. The procedure developed permits the crosswind acceleration levels of square cross-section tall buildings to be estimated at the preliminary design stages. Measurements were conducted to investigate the causes and effects of interaction due to upstream and surrounding buildings. The pertinent problem parameters of human biodynamic sensitivity to building motion were identified. An analysis for the design of a passive energy dissipative device (tuned mass damper) was carried out.
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Significant amount of inherent vibration energy present in tall buildings as they oscillate under the action of wind is traditionally dissipated into heat by the building damping or damping devices like Tuned Mass Dampers (TMDs)... more
Significant amount of inherent vibration energy present in tall buildings as they oscillate under the action of wind is traditionally dissipated into heat by the building damping or damping devices like Tuned Mass Dampers (TMDs) introduced to ensure the structural safety and occupants’ comfort. A portion of this large amount of vibration energy can be harvested if we replace the damping devices with appropriate energy harvesters and power electronics. Accordingly, this paper assesses the potential of harvestable energy from various TMD configurations and evaluates their effectiveness in mitigating building motion. The wind is modeled and simulated using an autoregressive model and the responses of the building to the across- and along-wind load are calculated via spectral approach. The classic TMD, parallel multiple TMDs, and series multiple TMDs are designed based on the decentralized H2 control for optimal stiffness constants and damping coefficients. The performances, namely, the building acceleration, energy potential, and strokes of the TMDs, are studied and compared for different wind speeds and an actual recorded wind event. During high wind events, over 85 K W of power can be harvested from a building used in a benchmark study. TMDs in series configuration with significantly smaller mass than the classic single TMD can achieve similar performance level and energy harvesting with enhanced robustness, but they require larger strokes.
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There have been significant advances on various fronts concerning dynamic analysis of structures exposed to wind. This includes: new developments in the dynamics of structures utilizing coupled structural and fluid dynamic equations;... more
There have been significant advances on various fronts concerning dynamic analysis of structures exposed to wind. This includes: new developments in the dynamics of structures utilizing coupled structural and fluid dynamic equations; stochastic simulation of stationary, nonstationary, Gaussian and non-Gaussian random loading environments and attendant responses; time and frequency domain and time-frequency domain analysis frameworks. The impact of non- Gaussianity on the local and global response prediction and modeling has also evolved over the years. The role of nonlinearity in structural response to wind, especially for bridge aerodynamics, where this may manifest itself from structural or aerodynamic origins or both is a current focus of research in some circles. One of the emerging and overarching issues in the wind-induced dynamic analysis of structures concerns the need for coupled analysis. This is particularly important for the new generation of tall buildings and long-span...
Topology optimization is widely recognized as a powerful conceptual design tool due to its versatility and ability to identify novel, efficient designs and has recently been adopted in the field of structural engineering for conceptual... more
Topology optimization is widely recognized as a powerful conceptual design tool due to its versatility and ability to identify novel, efficient designs and has recently been adopted in the field of structural engineering for conceptual building design. The currently available techniques in this area have been framed either in a deterministic setting or in an uncertain and stochastic setting that is incapable of providing a full description of the structural reliability within a framework consistent with structural design requirements. This paper presents an efficient simulation-based framework for the topology optimization of uncertain dynamic systems driven by stochastic wind loads that is capable of efficiently ensuring that the optimal structure meets probabilistic performance-based constraints written in terms of first excursion probabilities. In order to efficiently solve this problem a sequential algorithm is presented that is based on representing the probabilistic constraint...
This paper presents a generalized gust-front factor that offers a comprehensive framework for modeling gust-front winds and their attendant load effects on structures. This is akin to the gust loading factor format used in codes and... more
This paper presents a generalized gust-front factor that offers a comprehensive framework for modeling gust-front winds and their attendant load effects on structures. This is akin to the gust loading factor format used in codes and standards world-wide for the treatment of conventional boundary layer winds. The generalized gust-front factor encapsulates dynamic features of gust-front induced wind effects on structures for estimating design loads associated with gust-fronts originating from a thunderstorm/downburst. A web-based portal for the gust-front factor and associated loads available at http://gff.ce.nd.edu can be utilized to evaluate the generalized gust-front factor. In the case of boundary layer winds, the generalized gust-front factor reduces to the gust loading factor.
Topology optimization has recently been explored as a tool for the conceptual design of efficient structures during the initial building design stage. Although these techniques were originally developed in a deterministic setting, most... more
Topology optimization has recently been explored as a tool for the conceptual design of efficient structures during the initial building design stage. Although these techniques were originally developed in a deterministic setting, most practical applications are subject to inherent uncertainties in the design problem (e.g. stochastic loads, model idealization) and thus there has recently been an effort to incorporate the effect of these uncertainties into the topology optimization procedure. Within this context, the authors have developed an approach that is able to efficiently account for the uncertainties in the problem at hand using concepts from Performance-Based Design. This paper presents a general overview of this method and illustrates its applicability for the topology design of structures under wind and seismic hazards. Read More: http://ascelibrary.org/doi/abs/10.1061/9780784479117.192
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The high frequency force balance (HFFB) technique provides convenient measurements of integrated forces on rigid building models in terms of base bending moments and torque and/or base shear forces. These base moments or forces are then... more
The high frequency force balance (HFFB) technique provides convenient measurements of integrated forces on rigid building models in terms of base bending moments and torque and/or base shear forces. These base moments or forces are then used to approximately estimate the generalized forces of building fundamental modes with mode shape corrections. This paper presents an analysis framework for coupled dynamic response of tall buildings with HFFB technique. The empirical mode shape corrections for generalized forces with coupled mode shapes are validated using measurements of synchronous pressures on a square building surface from a wind tunnel. An alternative approach for estimating the mean and background response components directly using HFFB measurements without mode shape corrections is introduced with a discussion on higher mode contributions. The uncertainty in the mode shape corrections and its influence on predicted responses of buildings with both uncoupled and coupled moda...
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This study presents a new Data-Enabled Design Model for high-rise buildings driven by pressure datasets, DEDM-HRP, which seamlessly combines synchronous pressure measurement databases with a rigorous computational framework to offer... more
This study presents a new Data-Enabled Design Model for high-rise buildings driven by pressure datasets, DEDM-HRP, which seamlessly combines synchronous pressure measurement databases with a rigorous computational framework to offer convenient estimation of wind load effects on high-rise buildings for their preliminary design. To respond to the need for practical applications, DEDM-HRP employs a web-based on-the-fly framework designed with user-friendly/intuitive web interfaces for the assessment of wind-induced responses as well as equivalent static wind loads in the three principal response directions, for any incident wind angle of interest, with minimum added complications or requirements of knowledge of comprehensive background theories for its use.
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In the area of wind engineering, advanced modeling and simulation tools are becoming increasingly important in order to handle non-stationarity and nonlinearity inherent in wind. Previous assumptions, while convenient, have proven to... more
In the area of wind engineering, advanced modeling and simulation tools are becoming increasingly important in order to handle non-stationarity and nonlinearity inherent in wind. Previous assumptions, while convenient, have proven to over-simplify the complexity of the problems associated with dynamic effects. This paper introduces a suite of tools that can be used to model and simulate complex events involving dynamic wind effects on structures.
This study presents a new structural health monitoring (SHM) framework for tall buildings, "SmartSync", utilizing building's existing networks to offer much of the flexibility of the wireless system, and addressing data... more
This study presents a new structural health monitoring (SHM) framework for tall buildings, "SmartSync", utilizing building's existing networks to offer much of the flexibility of the wireless system, and addressing data process/mining for long-term SHM. A centralized server performs basic data acquisition, event triggering and database management, while also providing data visualization that can be securely accessed via a web browser. Additional on-demand modules using web-based on-line approach provide data analysis, database access for current/past data statistics, dissemination and system identification on demand in order to mitigate huge efforts to data process/mining. The SmartSync framework has been deployed in the world-tallest building, Burj Khalifa, and confirmed its efficacy in practical application.
ABSTRACT Performance-based design is fast becoming the benchmark approach for achieving designs that rationally meet society’s need for a truly safe built environment. While the principles of performance-based design have been vigorously... more
ABSTRACT Performance-based design is fast becoming the benchmark approach for achieving designs that rationally meet society’s need for a truly safe built environment. While the principles of performance-based design have been vigorously adopted in the field of seismic engineering, the same cannot be said for wind engineering. There therefore exists the need to define appropriate frameworks that allow the principles of performance-based design to be fully embraced during the design of building systems to resist severe wind events. Obviously the ultimate goal of any project is not to simply meet the performance objectives, but to do so in an economically optimum fashion. This can only truly be achieved through the development of appropriate optimization strategies that rigorously embrace the inevitably uncertain and aleatory nature of both system and environment. This paper focuses on the development of a framework for the probabilistic performance-based assessment of large scale uncertain linear systems driven by experimentally estimated stochastic wind loads. In particular, a simulation-based method is proposed that centers on the concept of decoupling the inherently nested reliability/probabilistic analysis from the optimization loop through the definition of a series of high quality approximate subproblems. The way in which the decoupling is achieved allows practical problems characterized by hundreds of component-wise reliability constraints and high-dimensional discrete design variable vectors to be efficiently and rigorously solved. Examples are presented illustrating the practicality of the proposed approach.
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Citizen Engineering (CE) is a concept that engages a cohort of physically dispersed citizens connected by the Internet to collaboratively solve real-world problems through massive cooperation. With advances in information technology, we... more
Citizen Engineering (CE) is a concept that engages a cohort of physically dispersed citizens connected by the Internet to collaboratively solve real-world problems through massive cooperation. With advances in information technology, we can build transformative cyber-infrastructures to effectively leverage the ''wisdom of crowds''. Regarding the citizen engineers who function as main contributors, there is a wide spectrum of human resources
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In this paper we describe the performance of the Multiplexer/Demultiplexer (MUX/DEMUX) in the Dense Wavelength Division Multiplexer (DWDM) technology based on arrayed waveguide grating (AWG). The accumulated crosstalk in large-scale AWG... more
In this paper we describe the performance of the Multiplexer/Demultiplexer (MUX/DEMUX) in the Dense Wavelength Division Multiplexer (DWDM) technology based on arrayed waveguide grating (AWG). The accumulated crosstalk in large-scale AWG solved by the cascade-connection of small AWGs. We propose two branches of 64 channels each have two stages of AWG cascaded as second and third stages. We introduce an
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Page 1. SPECTRAL WINDOW IN A MEM BASED SPECTRUM ANALYZER Tran Thong and ArifKareem Applied Research Group Tektronix Laboratories Tektronix, Inc. ... Fig. 4 shows the spec-trum of the AM test signal using a Blackman-Harris 4-coefficients... more
Page 1. SPECTRAL WINDOW IN A MEM BASED SPECTRUM ANALYZER Tran Thong and ArifKareem Applied Research Group Tektronix Laboratories Tektronix, Inc. ... Fig. 4 shows the spec-trum of the AM test signal using a Blackman-Harris 4-coefficients window given by ...
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The wave drift forces on tension leg platforms (TLP) are contributed by second-order potential and viscous wave load effects, the fluctuations in wave surface elevation and the influence of platform displaced position on the wave... more
The wave drift forces on tension leg platforms (TLP) are contributed by second-order potential and viscous wave load effects, the fluctuations in wave surface elevation and the influence of platform displaced position on the wave excitation. These forces are expressed in terms of in-phase and out-of-phase drift forces. In this study, computationally efficient time domain and frequency domain based schemes are developed to evaluate the TLP response to drift forces. These schemes retain the statistical relationship that exists among these drift forces and the first-order wave forces which is important for the combined response analysis. A parameter study is conducted to delineate the relative significance of different drift forces for several representative sea-states. I. INTRODUCTION In addition to the wave forces at the typical wave frequencies in a sea-state, a compliant structure experiences slowly varying wave drift forces. These forces originate from various mechanisms involving...
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The recent destruction due to hurricanes and the apparent increase in frequency in the southeastern United States, especially in 2005 season, has prompted many scientists to study possible causes of these changes. Some scientists believe... more
The recent destruction due to hurricanes and the apparent increase in frequency in the southeastern United States, especially in 2005 season, has prompted many scientists to study possible causes of these changes. Some scientists believe that global warming and increased sea surface temperatures are to blame. Warm water holds more energy to fuel hurricanes and may contribute to the conditions needed for the formation of hurricanes. The increased ocean tempera- tures may cause a decrease in wind shear and an increase in evaporation and atmospheric water vapor. These factors all contribute to the conditions conducive to formation of hurricanes. Some scientists, however, simply believe that the recent increases are due to normal multidecadal oscil- lations resulting from currents and Thermohaline Circulation. Whereas others believe that a change in the instrumentation and data collection techniques has led to unreliable data and the creation of trends that do not exist. Although some f...