Papers by Aly Mousaad Aly
Vibration control in wind turbines to achieve desired system-level performance under single and multiple hazard loadings
Structural Control and Health Monitoring
Vibration control of high-rise buildings for wind: a robust passive and active tuned mass damper
Smart Structures and Systems, 2014
ABSTRACT During their lifetimes, high-rise and slender buildings may experience natural frequency... more ABSTRACT During their lifetimes, high-rise and slender buildings may experience natural frequency changes under wind speed, ambient temperatures and relative humidity variations, among other factors, which make the tuned mass damper (TMD) design challenging. In this paper, a proposed approach for the design of robust TMDs is presented and investigated. The approach accounts for structural uncertainties, optimization objectives and input excitation (wind or earthquake). For the use of TMDs in buildings, practical design parameters can be different from the optimum ones. However, predetermined optimal parameters for a primary structure with uncertainties are useful to attain design robustness. To illustrate the applicability of the proposed approach, an example of a very slender building with uncertain natural frequencies is presented. The building represents a case study of an engineered design that is instructive. Basically, due to its geometry, the building behaves differently in one lateral direction (cantilever building) than the other (shear building). The proposed approach showed its robustness and effectiveness in reducing the response of tall buildings under multidirectional wind loads. In addition, LQG and fuzzy logic controllers enhanced the performance of the TMD.
LQR design for the MR damper
Journal of Energy and Power Technology, 2021
During their lifecycle, wind turbines can be subjected to multiple hazard loads, such as highinte... more During their lifecycle, wind turbines can be subjected to multiple hazard loads, such as highintensity wind, earthquake, wave, and mechanical unbalance. Excessive vibrations, due to these loads, can have detrimental effects on energy production, structural lifecycle, and the initial cost of wind turbines. Vibration control by various means, such as passive, active, and semi-active control systems provide crucial solutions to these issues. We developed a novel control theory that enables semi-active controller tuning under the complex structural behavior and inherent system nonlinearity. The proposed theory enables the evaluation of semi-active controllers' performance of multi-degrees-of-freedom systems, without the need for time-consuming simulations. A wide range of controllers can be tested in a fraction of a second, and their parameters can be tuned to achieve system-level performance for different optimization objectives.
EMI Technical Article, Dynamics, American Society of Civil Engineers (ASCE), 2018
In recent years, as a result of significant climate change, stringent windstorms are becoming mor... more In recent years, as a result of significant climate change, stringent windstorms are becoming more frequent than before. Given the threat that windstorms bring to people and property, wind/structural engineering research is imperative to improve the resilience of existing and new infrastructure, for community safety and assets protection. The Windstorm Impact, Science and Engineering (WISE) research program at Louisiana State University (LSU) focuses on creating new knowledge applicable to the mitigation of existing and new infrastructure, to survive and perform optimally under natural hazards (Figure 1). To achieve our research goals, we address two imperious challenges: (i) characterization of realistic wind forces on buildings and other types of structures; and (ii) developing advanced control theory to accelerate the optimal tuning of smart structures, with the aim of developing novel probabilistic analytical methods to address the complex behavior and inherent nonlinearity in semi-active control, for multiple hazards.
Wind and Structures, 2020
This paper focuses on the processes of wind flow in the atmospheric boundary layer, to produce re... more This paper focuses on the processes of wind flow in the atmospheric boundary layer, to produce realistic full-scale pressures for the design of low-rise buildings. CFD with LES turbulence closure is implemented on a scale 1:1 prototype building. A proximity study was executed computationally in CFD with LES that suggests new recommendations on the computational domain size, in front of a building model, apart from common RANS-based guidelines (e.g. COST and AIJ). Our findings suggest a location of the test building, different from existing guidelines, and the inflow boundary proximity influences pressure correlation and reproduction of peak loads. The CFD LES results are compared to corresponding pressures obtained by open jet, full scale, wind tunnel, and the ASCE 7-10 standard for roof Component & Cladding design. The CFD LES shows its capability to produce peak pressures/loads on buildings, in agreement with field pressures, due to its capabilities of reproducing the spectral contents of the inflow at a 1:1 scale.
Wind and Structures, 2013
With the sustainability movement, vegetated building envelopes are gaining more popularity. This ... more With the sustainability movement, vegetated building envelopes are gaining more popularity. This requires special wind effect investigations, both from sustainability and resiliency perspectives. The current paper focuses on wind load estimation on small-and full-scale trees used as part of green roofs and balconies. Small-scale wind load assessment was carried out using wind tunnel testing in a globaleffect study to understand the interference effects from surrounding structures. Full-scale trees were investigated at a large open-jet facility in a local-effect study to investigate the wind-tree interaction. The effect of Reynolds number combined with shape change on the overall loads measured at the base of the trees (near the roots) has been investigated by testing at different model scales and wind speeds. In addition, high-speed tests were conducted to examine the security of the trees in soil and to assess the effectiveness of a proposed structural mitigation system. Results of current research show that small-scale testing may overestimate wind loading on actual trees when the tests do not account fully for tree-wind interaction. On the other hand, the full-scale testing shows that at higher wind speeds the load coefficients tend to be reduced, limiting the wind loads on trees. No resonance or vortex shedding was visually observed.
6th American Association for Wind Engineering Workshop (online) Clemson University, Clemson, SC, USA, 2021
Large-eddy simulation (LES) has proven to offer superior accuracy in regards to predicting surfac... more Large-eddy simulation (LES) has proven to offer superior accuracy in regards to predicting surface pressures compared to the Reynolds-averaged Navier Stokes (RANS) models. However, the primary impediment is the high computational cost associated with LES. The authors attempt to investigate the computational cost and accuracy by employing different sub-grid scale (SGS) models in LES and hybrid RANS-LES models. One of the prerequisites of accurate pressure estimations is to ensure a horizontally homogeneous empty computational domain. This study aims to compare the computational competence qualitatively and quantitatively using an empty domain in regards to the ability to maintain horizontal homogeneity. The Wall-adapting eddy viscosity (WALE) SGS model in LES exhibits a significant reduction in computational time. Moreover, the application of detached eddy simulation (DES) and its modified versions manifest encouraging results in reducing computational time and retaining accuracy.
6th American Association for Wind Engineering Workshop (online) Clemson University, Clemson, SC, USA, 2021
Wind flow over low-rise buildings in the atmospheric boundary layer (ABL) is accompanied by some ... more Wind flow over low-rise buildings in the atmospheric boundary layer (ABL) is accompanied by some complex flow physics such as flow separation and generation of vortices in the shear layer. The uncertainties associated with such complex flow mechanisms make the case-by-case experimental or numerical investigation of buildings' aerodynamic behavior fundamental. Engineers have aspired to replicate the full-scale real wind behavior in wind-tunnels to create more resilient infrastructures. Traditional wind-tunnel experiments struggle to accurately predict surface pressures despite being widely embraced by the structural engineering community. This limitation is attributed to the lack of large-scale turbulence and low Reynolds numbers in wind-tunnels. Such drawbacks prompted the consideration of aerodynamic testing by the open-jet concept. Open-jet experiments of building models with higher Reynolds numbers reveal the generation of higher mean and peak pressure coefficients, compared to those obtained from wind-tunnels; the findings reinforce the initial hypothesis.
6th American Association for Wind Engineering Workshop (online) Clemson University, Clemson, SC, USA, 2021
In this paper, experimental investigations of a large-scale (1:50) high-rise building model are p... more In this paper, experimental investigations of a large-scale (1:50) high-rise building model are performed at a high Reynolds number (~21 million), to evaluate the wind loads and the corresponding structural responses. A total of 256 pressure taps are mapped on all sides of the building model, to determine dimensionless pressure coefficients on the surfaces. Wind loads at each floor are evaluated using the pressure integration technique. The dynamic properties of the full-scale building are obtained from a finite element model in ANSYS. The wind-induced responses are calculated by applying wind loads on an equivalent lumped mass model of the building derived from the finite element model. Excessive vibration occurred in the crosswind direction that exceeds the serviceability requirements. To attenuate these vibrations, a pendulum pounding tuned mass damper (PTMD) based on Hertz contact law is proposed.
CE 3415 Structural Analysis I (Spring 2014)
On the evaluation of wind loads on solar panels: The scale issue
Solar power can improve the quality of life and reduce dependency on traditional energies that ar... more Solar power can improve the quality of life and reduce dependency on traditional energies that are a significant source of pollution and global warming. Solar panels are common devices used for collecting solar energy. To balance between sustainability and resilience, it is essential to provide an accurate estimate of the design wind loads for the solar panels. Traditionally design wind loads for buildings and other structures are obtained using building codes and standards. The solar panels represent a relatively recent technology and indeed there is no complete guidance ready for codification of wind loads on these types of structures. Available wind tunnel data show discrepancies in wind loads on solar panels, owing to inconsistent model scales and test flows, among other factors. To eliminate such discrepancies in the test results and to allow for accurate wind load estimation, the current paper investigates the geometric scale and the inflow turbulence characteristics as potential causes of high uncertainties. Computational fluid dynamics (CFD) simulations are employed and results are compared with available wind tunnel data, as a complementary tool with a potential to simulate wind loads at full-scale. The results show that the geometric scale is a primary reason for the discrepancies in peak wind loads, which can be avoided by adapting the inflow turbulence and using a proper testing protocol. The results show an evidence of the correctness of a hypothesis that the lack of large-scale turbulence can dramatically affect peak wind loads on test objects. Consequently, recommendations are articulated regarding the best usage of the available wind load estimation tools. This is expected to lead to consistent and accurate results from wind tunnel testing and CFD simulations, a crucial step toward codification of wind loads on solar panels.
Internal pressure in a low-rise building with existing envelope openings and sudden breaching
Wind and Structures, An International Journal, 2013
ABSTRACT Abstract. This paper presents a boundary-layer wind tunnel (BLWT) study on the effect of... more ABSTRACT Abstract. This paper presents a boundary-layer wind tunnel (BLWT) study on the effect of variable dominant openings on steady and transient responses of wind-induced internal pressure in a low-rise building. The paper presents a parametric study focusing on differences and similarities between transient and steady-state responses, the effects of size and locations of dominant openings and vent openings, and the effects of wind direction angle. In addition, the necessity of internal volume correction during sudden breaching was considered, i.e., a transient response experiment was investigated. A comparison of the BLWT data with ASCE 7-2010, as well as with limited large-scale data obtained at a ‘Wall of Wind’ facility, is presented.
Wind and Structures, Feb 16, 2011
Abstract. Wind loads on low-rise buildings in general and residential homes in particular can dif... more Abstract. Wind loads on low-rise buildings in general and residential homes in particular can differ significantly depending upon the laboratory in which they were measured. The differences are due in large part to inadequate simulations of the low-frequency content of atmospheric velocity fluctuations in the laboratory and to the small scale of the models used for the measurements. The imperfect spatial coherence of the low frequency velocity fluctuations results in reductions of the overall wind effects with respect to the case of ...
Simplified wind flow and aerodynamic response of residential homes: laboratory and computational fluid dynamics simulations
unina.stidue.net, Oct 3, 2011
ABSTRACT: The reliable measurement of pressures on low-rise buildings in the atmospheric boundary... more ABSTRACT: The reliable measurement of pressures on low-rise buildings in the atmospheric boundary layer (ABL) flow remains a challenge, as has been shown by the large discrepancies among results obtained in different wind tunnel facilities or even in the ...
Control of wind-induced motion in high-rise buildings with hybrid TM/MR dampers
In recent years, high-rise buildings received a renewed interest as a means by which technical an... more In recent years, high-rise buildings received a renewed interest as a means by which technical and economic advantages can be achieved, especially in areas of high population density. Taller and taller buildings are being built worldwide. These types of buildings present an asset and typically are built not to fail under wind loadings. The increase in a building\'s height results in increased flexibility, which can lead to significant vibrations, especially at top floors. Such oscillations can magnify the overall loads and can be annoying to the top floors\' occupants. This paper shows that increased stiffness in high-rise buildings may not be a feasible solution and may not be used for the design for comfort and serviceability. High-rise buildings are unique, and a vibration control system for a certain building may not be suitable for another. Even for the same building, its behavior in the two lateral directions can be different. For this reason, the current study addresses the application of hybrid tuned mass and magneto-rheological (TM/MR) dampers that can work for such types of buildings. The proposed control scheme shows its effectiveness in reducing floors\' accelerations for both comfort and serviceability concerns. Also, a dissipative analysis carried out shows that the MR dampers are working within the possible range of optimum performance. In addition, the design loads are dramatically reduced, creating more resilient and sustainable buildings. The purpose of this paper is to stimulate, shape, and communicate ideas for emerging control technologies that are essential for solving wind related problems in high-rise buildings, with the objective to build the more resilient and sustainable infrastructure and to optimally retrofit existing structures.
On the Design of High-Rise Buildings for Multihazard: Fundamental Differences between Wind and Earthquake Demand
In the past few decades, high-rise buildings have received a renewed interest in many city busine... more In the past few decades, high-rise buildings have received a renewed interest in many city business locations, where land is scarce, as per their economics, sustainability, and other benefits. Taller and taller towers are being built everywhere in the world. However, the increased frequency of multihazard disasters makes it challenging to balance between a resilient and sustainable construction. Accordingly, it is essential to understand the behavior of such structures under multihazard loadings, in order to apply such knowledge to design. The results obtained from the dynamic analysis of two different high-rise buildings (54-story and 76-story buildings) investigated in the current study indicate that earthquake loads excite higher modes that produce lower interstory drift, compared to wind loads, but higher accelerations that occur for a shorter time. Wind-induced accelerations may have comfort and serviceability concerns, while excessive interstory drifts can cause security issues. The results also show that high-rise and slender buildings designed for wind may be safe under moderate earthquake loads, regarding the main force resisting system. Nevertheless, nonstructural components may present a significant percentage of loss exposure of buildings to earthquakes due to higher floor acceleration. Consequently, appropriate damping/control techniques for tall buildings are recommended for mitigation under multihazard.
Atmospheric boundary-layer simulation for the built environment: Past, present and future
This paper summarizes the state-of-the-art techniques used to simulate hurricane winds in atmosph... more This paper summarizes the state-of-the-art techniques used to simulate hurricane winds in atmospheric boundary-layer (ABL) for wind engineering testing. The wind tunnel simulation concept is presented along with its potential applications, advantages and challenges. ABL simulation at open-jet simulators is presented along with an application example followed by a discussion on the advantages and challenges of testing at these facilities. Some of the challenges and advantages of using computational fluid dynamics (CFD) are presented with an application example. The paper show that the way the wind can be simulated is complex and matching one parameter at full-scale may lead to a mismatch of other parameters. For instance, while large-scale testing is expected to improve Reynolds number and hence approach the full-scale scenario, it is challenging to generate large-scale turbulence in an artificially created wind. New testing protocols for low-rise structures and small-size architectural features are presented as an answer to challenging questions associated with both wind tunnel and open-jet testing. Results show that it is the testing protocol that can be adapted to enhance the prediction of full-scale physics in nature. Thinking out of the box and accepting non-traditional ABL is necessary to compensate for Reynolds effects and to allow for convenient experimentation. New research directions with focus on wind, rain and waves as well as other types of non-synoptic winds are needed, in addition to a more focus on the flow physics in the lower part of the ABL, where the major part of the infrastructure exists.
Journal of Wind Engineering & Industrial Aerodynamics, 2013
Most boundary-layer wind tunnels (BLWTs) were built for testing models of large civil engineering... more Most boundary-layer wind tunnels (BLWTs) were built for testing models of large civil engineering structures that have geometric scales ranging from 1:500 to 1:100. However, producing aerodynamic models of the solar panels at such scales makes the modules too small, resulting in at least two technical problems. First, the resolution of pressure data on such small models becomes low. Second, the test model may be placed in the lower portion of the boundary-layer that is not a true representative of a real world scenario, due to high uncertainty in wind velocity. To alleviate these problems, development of a standardized testing protocol is very important. Such protocol should account for different time and geometric scales to design appropriate wind tunnel experiments that can allow accurate assessment of wind loads on the solar panels. The current paper systematically investigates the sensitivity of wind loads to testing ground-mounted solar panels, both experimentally (in a BLWT) and numerically (by computational fluid dynamics (CFD)), at different geometric scales. While mean loads are not significantly affected by the model size, peak loads are sensitive to both the geometric scale and the spectral content of the test flow. However, when the objective is to predict 3-s (three seconds) peak loads, large models can be tested in a flow that has reduced high-frequency turbulence.
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Papers by Aly Mousaad Aly