scholarly journals Numerical Study of the Seismic Efficiency of Buckling-Restrained Braces for Near and Far-Fault Inputs

2015 ◽  
Vol 9 (1) ◽  
pp. 281-294
Author(s):  
G.L. Palazzo ◽  
P. Martín ◽  
F. Calderón ◽  
V. Roldán ◽  
F. López-Almansa
Keyword(s):  
Dynamic Response ◽  
Numerical Study ◽  
Experimental Studies ◽  
Time Interval ◽  
Short Time Interval ◽  
Far Field ◽  
Near Fault ◽  
Buckling Restrained Braces ◽  
Seismic Records ◽  
Far Fault

Buckling-restrained braces are commonly installed in building structures as concentric diagonal or chevron braces to protect the main construction from seismic actions. These elements have shown repeatedly their usefulness for reducing the seismic response, both from theoretical and experimental studies; and a number of practical applications have been reported. However, seismic records with near-fault effects possess special characteristics that might impair the performance of these devices, similarly as what occurs in base isolation; about energy issues, in such records (containing strong velocity pulses) the energy is delivered in a short time interval, thus being difficult to be absorbed. This work presents a numerical study regarding the performance of buckling-restrained braces under three types of seismic records: cortical far-field, subductive far-field and near-field (i.e. containing velocity pulses). The study is carried out on a symmetric 4-story steel moment-resisting unbraced frame that was tested at the E-defense laboratory, Japan; the dynamic response of such unbraced bare frame is numerically simulated, obtaining a satisfactory agreement. The same numerical model is used to describe the 2-D dynamic behavior of the steel frame equipped with buckling-restrained braces. The inputs are three series of ten ground motion records; each of these series belongs to one of the three aforementioned types. The average responses for each of the three types of inputs are compared; the obtained results show that the buckling-restrained braces are able to reduce the dynamic response of the frame and that no significant differences can be observed among the efficiency for far-fault and near- fault records.

scholarly journals Effects of Nanosecond Repetitively Pulsed Discharges Timing for Aeroengines Ignition at Low Temperature Conditions by Needle-Ring Plasma Actuator

Energies ◽  
2021 ◽  
Vol 14 (18) ◽  
pp. 5814
Author(s):  
Ghazanfar Mehdi ◽  
Sara Bonuso ◽  
Maria Grazia De Giorgi
Keyword(s):  
Combustion Process ◽  
Experimental Studies ◽  
Plasma Actuator ◽  
Inlet Temperature ◽  
Time Interval ◽  
Short Time Interval ◽  
Air Plasma ◽  
Plasma Discharges ◽  
Plasma Actuation

These days, various national and international research organizations are working on the development of low NOx combustors. The present work describes the experimental and numerical characterization of flow dynamics and combustion characteristics in a rectangular burner. A ring-needle type plasma actuator was developed and driven by a high voltage nanosecond pulsed generator under atmospheric conditions. Smoke flow visualizations and Proper Orthogonal Decomposition (POD) were carried out to identify the relevant flow structures. Electrical characterization of the non-reactive flow was carried out to predict the electrical power and the optimum value of the reduced electric field (EN), which is useful for the implementation of a numerical model for the study of plasma-assisted ignition. A detailed plasma kinetic mechanism integrated with all excited species was considered and validated with experimental studies. Numerical modeling of plasma ignition has been performed by coupling ZDPlasKin with CHEMKIN. Energy and power consumption for methane/air plasma actuation is higher than the air plasma actuation. This could be due to the excitation and ionization of methane that required more energy deposition and power. The mole fraction of O atoms and ozone was higher in the air than the methane/air actuation. However, O atoms were produced in a very short time interval of 10−7 to 10−6 s; in contrast, the concentration of ozone was gradually increased with the time interval and the peak was observed around 10−1 s. Plasma discharges on the methane/air mixture also produced radicals that played a key role to enhance the combustion process. It was noticed that the concentration of H species was high among all radicals with a concentration of nearly 10−1. The concentration peak of CH3 and OH was almost the same in the order of 10−2. Finally, the mixture ignition characteristics under different low inlet temperatures were analyzed for both air and methane/air plasma actuation in the presence of different plasma discharges pulses numbers. Results showed that it is possible to reach flame ignition at inlet temperature lower than the minimum required in the absence of plasma actuation, which means ignition is possible in cold flow, which could be essential to address the re-ignition problems of aeroengines at high altitudes. At Ti = 700 K, the ignition was reached only with plasma discharges; ignition time was in the order of 0.01 s for plasma discharges on methane/air, lower than in case of plasma in air, which permitted ignition at 0.018 s. Besides this, in the methane/air case, 12 pulses were required to achieve successful ignition; however, in air, 19 pulses were needed to ignite.

NUMERICAL STUDY OF THE STATE OF SOIL DAMS AS A RESULT OF IMPACT OF SHOCK WAVES AND UNSTEADY LOADS

2021 ◽  
pp. 55-62
Author(s):  
E. V. ANDREEV ◽  
Keyword(s):  
Shock Waves ◽  
Numerical Study ◽  
Pressure Head ◽  
Operational Reliability ◽  
Hydraulic Structures ◽  
Time Interval ◽  
Short Time Interval ◽  
Urgent Task ◽  
Temperature Dependences ◽  
The Impact

At the stage of the life cycle, ensuring the operational reliability and safety of pressure head hydraulic structures is an urgent task. One of the serious threats at the present stage is the destruction of hydraulic structures by the impact of non-stationary loads, by directed explosions in the immediate vicinity of the structures or on their surface. Shock waves pose a serious threat to hydraulic structures. Impulse short-term impact on the solid surfaces of hydraulic structures or on the aquatic environment characterizes the specifi cs of the problem under consideration, as the nonstationary of the process of motion of continuous media into which, in a short time interval, a volume of energy can be released that can deform or completely destroy them. Scenarios of this kind can occur either in the immediate vicinity of a hydraulic structure or as a result of the collision of solid bodies on its surface. Water upstream of the hydro technical structure and its body is a complex liquid because many of its characteristics differ significantly in size from similar characteristics of other liquids or have so-called anomalies on pressure and temperature dependences.

An experimental and numerical study for investigating the promising stratified reinforced concrete slabs

2021 ◽  
pp. 136943322110122
Author(s):  
Sameh Yehia ◽  
Tarek Aly ◽  
Osama Hassan
Keyword(s):  
Numerical Study ◽  
High Strength ◽  
Flexural Behavior ◽  
Experimental Program ◽  
Time Interval ◽  
Slab Thickness ◽  
Short Time Interval ◽  
Strength Concrete ◽  
Reinforced Concrete Slabs ◽  
Short Time

It is well known that through the structural design, the safety and economic considerations of the project represent major factors, which must be always in mind. From this point of view, the concept and idea of “Stratified Concrete” were developed. Stratified Concrete consists of two or more types of concrete; in particular, composite materials consisting of High Strength Concrete (HSC) and Normal Strength Concrete (NSC). This study showed the flexural behavior for stratified sections (HSC-NSC) by taking a short time lap (1 h) between the two mixes to get a good bond between them. An experimental program was conducted to investigate the flexural behavior of NSC (25 MPa), HSC (60 MPa), and three HSC-NSC with the effect of changing the thickness of the HSC layer of slabs (20, 40, 75 mm) that had subjected to double static loads. As well, these slabs’ experimental results were numerically verified. The most important achievement is the success of the idea of casting different strengths of concrete layers using a short time interval to improve the bending behavior of the slabs, and reach the superior thickness of the HSC layer, which represents almost a quarter of the slab thickness.

scholarly journals Effects of Near Fault and Far Fault Ground Motions on Nonlinear Dynamic Response and Seismic Improvement of Bridges

2018 ◽  
Vol 4 (6) ◽  
pp. 1456 ◽  
Author(s):  
Mohammad Hajali ◽  
Abdolrahim Jalali ◽  
Ahmad Maleki
Keyword(s):  
Dynamic Response ◽  
Ground Motion ◽  
Nonlinear Dynamic ◽  
Nonlinear Dynamic Analysis ◽  
Time History ◽  
Relative Displacement ◽  
Near Fault ◽  
Acceleration Rate ◽  
Near Fault Earthquakes ◽  
Far Fault

In this study, the dynamic response of bridges to earthquakes near and far from the fault has been investigated. With respect to available data and showing the effects of key factors and variables, we have examined the bridge’s performance. Modeling a two-span concrete bridge in CSI Bridge software and ability of this bridge under strong ground motion to near and far from fault has been investigated. Nonlinear dynamic analysis of time history includes seven records of past earthquakes on models and it was observed that the amount of displacement in the near faults is much greater than the distances far from faults. Bridges designed by seismic separators provide an acceptable response to a far from fault. This means that in bridges using seismic separators, compared to bridges without seismic separators, Acceleration rate on deck, base shearing  and the relative displacement of the deck are decrease. This issue is not seen in the response of the bridges to the near faults. By investigating earthquakes near faults, it was observed that near-fault earthquakes exhibit more displacements than faults that are far from faults. These conditions can make seismic separators critical, so to prevent this conditions FDGM should be used to correct the response of these bridges. Based on these results, it can be said that the displacement near faults with forward directivity ground motion is greater than far from faults. So that by reducing the distance from the faults, the maximum value of the shearing and displacement of the deck will be greater.

scholarly journals Unsteady Magnetohydrodynamic Heat Transfer in a Semi-Infinite Porous Medium with Thermal Radiation Flux: Analytical and Numerical Study

2011 ◽  
Vol 2011 ◽  
pp. 1-17 ◽  
Author(s):  
O. Anwar Bég ◽  
J. Zueco ◽  
S. K. Ghosh ◽  
Alireza Heidari
Keyword(s):  
Shear Stress ◽  
Thermal Radiation ◽  
Numerical Study ◽  
Transverse Magnetic ◽  
Convection Flow ◽  
Time Interval ◽  
Short Time Interval ◽  
Plate Surface ◽  
Plate Temperature ◽  
Laplace Transform Technique

The unsteady, buoyancy-induced, hydromagnetic, thermal convection flow in a semi-infinite porous regime adjacent to an infinite hot vertical plate moving with constant velocity, is studied in the presence of significant thermal radiation. The momentum and energy conservation equations are normalized and then solved using both the Laplace transform technique and Network Numerical Simulation. Excellent agreement is obtained between both analytical and numerical methods. An increase in Hartmann number (M2) strongly decelerates the flow and for very high strength magnetic fields (M2=20), the flow is reversed after a short time interval. The classical velocity overshoot is also detected close to the plate surface for low to intermediate values of M2 at both small and large times; however this overshoot vanishes for larger strengths of the transverse magnetic field (M2=10). An increase in radiation-conduction parameter (Kr) significantly increases temperature throughout the porous regime at both small and larger times, adjacent to the plate, but decreases the shear stress magnitudes at the plate. Temperature gradient is reduced at the plate surface for all times, with a rise in radiation-conduction parameter (Kr). Shear stress is reduced considerably with an increase in Darcian drag parameter (Kp).

A procedure for matching the near-fault ground motions based on spectral accelerations and instantaneous power

2021 ◽  
pp. 875529302110145
Author(s):  
Esra Zengin ◽  
Norman A Abrahamson
Keyword(s):  
Time Series ◽  
Response Spectrum ◽  
Ground Motions ◽  
Structural Response ◽  
Rate Of Change ◽  
Time Interval ◽  
Short Time Interval ◽  
Pulse Period ◽  
Near Fault ◽  
Instantaneous Power

Selection of ground motions for use in nonlinear dynamic analysis is one of the most critical steps for both code-based design and probabilistic seismic risk assessment of structures. In practice, time-domain spectrum-matching methods, which add wavelet functions to an initial acceleration time series, have been widely used to obtain a record whose response spectrum closely matches the desired target spectrum. Although the spectral shape is known to be a good predictor of structural response, it does not represent the critical aspects of the velocity pulses, such as pulse amplitude and pulse period for near-fault ground motions. The Instantaneous Power ( IP( T1)), defined as the maximum rate of change of energy of the bandpass-filtered velocity time series over a short time interval given by half of the structural period, has been shown to be an effective alternative parameter to capture effects of the presence of a velocity pulse and the pulse period in near-fault record selection. We introduce an approach to modify time series so as to simultaneously match a target response spectrum and IP spectrum over a specified period interval. We demonstrate that the records modified using the proposed approach produce results comparable to those obtained using unscaled records, and prevent potential bias in structural response, relative to results when matching is performed without consideration of IP.

On Multiple Access of a Large Number of Machine-Type Devices in Cellular Networks

2018 ◽  
pp. 105-114
Author(s):  
O. S. Galinina ◽  
S. D. Andreev ◽  
A. M. Tyurlikov
Keyword(s):  
Success Probability ◽  
Random Access ◽  
Time Interval ◽  
Short Time Interval ◽  
Control Mechanisms ◽  
Network Access ◽  
Smart Meters ◽  
Machine To Machine ◽  
Machine To Machine Communication ◽  
Machine Communication

Introduction: Machine-to-machine communication assumes data transmission from various wireless devices and attracts attention of cellular operators. In this regard, it is crucial to recognize and control overload situations when a large number of such devices access the network over a short time interval.Purpose:Analysis of the radio network overload at the initial network entry stage in a machine-to-machine communication system.Results: A system is considered that features multiple smart meters, which may report alarms and autonomously collect energy consumption information. An analytical approach is proposed to study the operation of a large number of devices in such a system as well as model the settings of the random-access protocol in a cellular network and overload control mechanisms with respect to the access success probability, network access latency, and device power consumption. A comparison between the obtained analytical results and simulation data is also offered. 

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