Simulated Time Histories Research Articles

Revealing the role of the effector-regulatory t cell loop on autoimmune disease symptoms via nonlinear analysis

In this paper, we investigate the influence of the effector-regulatory (Teff-Treg) T cell interaction on the T-cell-mediated autoimmune disease dynamics. The simple 3-dimensional Teff-Treg model is derived from the two-step model reduction of an established 5-dimensional model. The reduced 4- and 3-dimensional models preserve the dynamical behaviors in the original 5-dimensional model, which represents the chronic and relapse-remitting autoimmune symptoms. Moreover, we find three co-existing limit cycles in the reduced 3-dimensional model, in which two stable periodic solutions enclose an unstable one. The existence of multiple limit cycles provides a new mechanism to explain varying oscillating amplitudes of lesion grade in multiple sclerosis. The complex multiphase symptom could be caused by a noise-driven Teff population traveling between two coexisting stable periodic solutions. The simulated phase portrait and time history of coexisting limit cycles are given correspondingly.

Simulating the near-field pulse-like ground motions of the Imperial Valley, California, earthquake

Long-period pulse-like ground motions in the near-field are likely to induce severe damage to large structures due to resonance at the natural frequencies of engineered construction. To investigate the origin and characteristics of large velocity pulses from the seismic source, this study identifies 14 stations with velocity pulses from 32 strong-motion seismographs located in the near-field of the Imperial Valley MW 6.5 earthquake. The pulse-like ground motions are simulated by a kinematic approach using a fourth-order accurate finite-difference method. The results show that the slip asperity in the northern part of the fault plane contributes more to large velocity pulses than the asperity that originates in the hypocentral zone. The two-sided pulses on the fault-normal component and the one-sided pulses on the fault-parallel component are mainly regulated by the fault rupture and slip directions, respectively. Compared with the pseudo-velocity response spectrum, the displacement response spectrum better captures the resonance effect of long-period pulse-like ground motion on large structures. The location of the maximum ground motion coincides with the surface projection area of the large asperity, and the amplitude and the attenuation rate of each horizontal component vary with increasing distance from the fault. The difference in the ground motion peaks on both sides of the fault implies that the fault-normal component is more sensitive to the fault dip angle than the fault-parallel component. We reproduce the pulse-like ground motions up to 1 Hz by fitting the simulated velocity time histories, response spectrum and ground motions to observed data. Using the pulse records of the Imperial Valley earthquake, the 1994 Northridge MW 6.7 earthquake, and the 1999 Chi-Chi MW 7.6 earthquake, we compare the effects of earthquake magnitude on peak value and distribution of large velocity pulses, in which a reasonable consistency can be observed. Our simulated results of near-field pulse-like ground motions are beneficial to clarify the pulse mechanism.

Post-stall flight dynamics of commercial transport aircraft configuration: A nonlinear bifurcation analysis and validation

Loss-of-control has become the largest fatal accident category for worldwide commercial jet accidents, and any initiative aimed at preventing such events requires an understanding of the fundamental aircraft behavior, especially the flight dynamics at post-stall region at which loss-of-control usually occurred. A series of low-speed static and dynamic wind tunnel tests of the Common Research Model over a large angle of attack/sideslip envelope was conducted and a non-linear aerodynamic model was developed. The bifurcation analysis, complemented by time-history simulation was used to understand the post-stall flight dynamics and the numerical analysis results were preliminary validated by wind tunnel virtual flight test. Several representative post-stall behaviors for the transport aircraft have been identified, including departure, periodic oscillation, post-stall gyration and steep spiral, etc. Furthermore, the predicted periodic oscillation in pitch motion has been perfectly duplicated in wind tunnel virtual flight test. The approach used in this work shows a promising way to uncover the flight dynamics of transport aircraft at extreme and loss-of-control flight conditions, as well as to apply to nonlinear unsteady aerodynamics modeling and validation, flight accident investigation, advanced flight control law design or studying initiative for loss-of-control prevention or mitigation.

Simulation of strong ground motion for a potential Mw7.3 earthquake in Kopili fault zone, northeast India

In this study, we present the results of strong ground motion simulation carried out for a potential earthquake (Mw7.3) in the Kopili source zone of northeast India using the stochastic finite fault modeling technique. Prior to simulation of the potential event, the technique was validated by simulating a recorded earthquake Mw5.3, which was located close to the Nagaon district of Assam, India. The earthquake records (Mw5.3) of ten stations in the study region were analyzed, and average source parameters, namely corner frequency, seismic moment, stress drop and source radius, estimated to be 0.48 Hz, 1.44E + 24 dyne-cm, 103.4 bar and 2.7 km, respectively. While estimating the source parameters, the path attenuation parameters (Q and ko) also constrained at each seismic station. Using the constrained attenuation parameters, site amplification factors and source parameters, we simulated strong ground motion time histories for Mw5.3 event at individual sites and found them comparable with amplitude and frequency content of the respective observed records satisfactorily. The results, therefore, validated the technique used in the study. Further, the fault parameters, site amplification factors and average of the constrained attenuation parameters were used in simulation of the potential event (Mw7.3) and strong ground motion predicted for the entire northeast region (NER) at a grid interval of 0.5°. We used average values of constrained quality factor (Q) and Kappa parameter (ko) equivalent to 182f 0.95 and 0.038, respectively, in the simulation. It is apparent that the simulated PGA conditionally followed the attenuation curves of the region, and hence, we suggest developing an appropriate attenuation curve for the NER. The study reveals that the sites located up to 250 km distance away from the source zone may experience significant PGA ranging between 160 Gals and 360 Gals. The cities located within this zone, viz., Tezpur, Nagaon, Udalguri, Diphu and Bomdila, may witness strong to very strong ground shaking associated with substantial damage to buildings and other important structures in the region.

Construction of a Viaduct with a Launching Girder in a Cyclonic Region

The construction of the viaduct of the Nouvelle Route du Littoral, connecting Saint-Denis to La Grande Chaloupe in La Réunion, is particularly challenging in terms of the wind environment. In addition to being built in a cyclonic region, the 5.4 km long viaduct is being built in open sea, 100–150 m from the coast. The gust wind speed can reach up to 64 m/s at deck level during a cyclonic event. The height (10 m) and length (270 m) of the double truss launching girder make it particularly sensitive to turbulent wind and induce significant additional wind load on the viaduct and the cantilever under construction during a cyclonic event. The 120 m span and relatively large width (28 m) of the deck also play an important part in the dynamic response of the whole structure. This paper presents how the local wind conditions and the aerodynamic properties of the deck and the launching girder were determined. The methodology used to perform the time history simulations of the viaduct during the construction phase are then described, as well as the main results for the studied configurations.

Shaking table tests on V-shaped RC columns at the weak ground storey of a building

This paper presents experimental and numerical investigations of the seismic behaviour of V-shaped reinforced-concrete (RC) columns at the weak ground storey of a building. Two half-scaled RC columns were tested to failure by a simulated ground acceleration time history using a shaking table. The test setup was designed to simulate the sliding mechanism of the column specimens, termed the double-curvature mechanism, which is expected to occur in a soft-storey building. The seismic responses of the specimens were evaluated and compared with each other in terms of general performance, hysteresis response and failure modes. Thereafter, a fibre-element model, verified by the test data, was used to conduct a parametric study on the effects of axial load ratio and longitudinal reinforcement arrangement on the seismic performance of irregularly shaped columns.

A Generalization of the Stochastic Summation Scheme of Small Earthquakes to Simulate Strong Ground Motions

A generalization of the stochastic summation scheme of small earthquakes following a general form of the source spectrum (ω−n) model is developed to estimate the proper probability density functions for rupture propagation over the fault and to simulate site-specific strong ground motions in two independent stages. The probability density functions for rupture propagation are first developed for a single-corner-frequency source model, and then extended to multiplicative and additive double-corner-frequency source models to partially account for the effects of finite-fault rupture such as fault geometry, rise time, and rupture time on ground motions, and to better match observed Fourier amplitude spectra (FAS). The generalized two-stage stochastic summation scheme developed in this study can be used to simulate realistic strong-ground-motion time histories from small events, represented as empirical Green’s functions (EGFs), by specifying only two source parameters of the seismic moment and stress drop for a given site. The proposed two-stage stochastic summation schemes are tested using numerical examples following the theoretical source models as well as observed ground motions of the 2011 Mw 9.0 Tohoku earthquake in Japan and the 1994 Mw 6.7 Northridge earthquake in California to verify the applicability of the approach. Comparisons between the observed and simulated time histories for these two earthquakes, their response spectra, and FAS show satisfactory performance of the proposed approach for engineering purposes. The results of these comparisons indicate that the proposed stochastic summation of small events as EGFs can adequately replicate observed ground motions and evaluate uncertainties in ground motions with the generation of many time history realizations corresponding to a multitude of possible rupture processes . The proposed approach can also be used to generate multiple realistic acceleration time histories matched on average to the target response spectra for use in earthquake performance design, and to develop ground-motion models for low-seismicity regions, where there is a lack of recording of strong ground motions.

Inelastic static and dynamic seismic response assessment of frames with stochastic properties

The article studies the inelastic seismic response assessment of structures with spatially varying material properties via the stochastic finite element method. This is a problem with a complex response function due to stochastic variability and material nonlinearity. Existing formulations either assume linear-elastic behaviour, or use dense models in order to capture both stochasticity and inelasticity. This results to models that require excessive computational resources. The article shows that for material nonlinear problems, the stochastic variability can be taken into consideration using flexibility-based models which allow performing repeated time-history simulations within a reasonable computational time, without loss of accuracy. The interpolation can be adjusted through a user-defined parameter, thus avoiding the need for a dense FE mesh. Contrary to past research, the modelling proposed has many applications in structural engineering, since it allows nonlinear, static or dynamic, simulations of real-scale frame structures with stochastic properties. The proposed method is demonstrated in the framework of the spectral representation method combined with Monte Carlo simulations, but it can be combined with any other method for the description of the stochastic field. A generic single-storey steel frame and a six-storey reinforced concrete frame are considered in order to demonstrate the efficiency of the proposed modelling.

Derivation of analytical fragility curves using SDOF models of masonry structures in Erzincan (Turkey)

Seismic loss estimation studies require fragility curves which are usually derived using ground motion datasets. Ground motion records can be either in the form of recorded or simulated time histories compatible with regional seismicity. The main purpose of this study is to investigate the use of alternative ground motion datasets (simulated and real) on the fragility curves. Simulated dataset is prepared considering regional seismicity parameters corresponding to Erzincan using the stochastic finite-fault technique. In addition, regionally compatible records are chosen from the NGA-West2 ground motion database to form the real dataset. The paper additionally studies the effects of hazard variability and two different fragility curve derivation approaches on the generated fragility curves. As the final step for verification purposes, damage states estimated for the fragility curves derived using alternative approaches are compared with the observed damage levels from the 1992 Erzincan (Turkey) earthquake (Mw=6.6). In order to accomplish all these steps, a set of representative masonry buildings from Erzincan region are analyzed using simplified structural models. The results reveal that regionally simulated ground motions can be used alternatively in fragility analyses and damage estimation studies.

Simulation of wind velocity time histories on long span structures modeled as non-Gaussian stochastic waves

A methodology is proposed for efficient and accurate modeling and simulation of correlated non-Gaussian wind velocity time histories along long-span structures at an arbitrarily large number of points. Currently, the most common approach is to model wind velocities as discrete components of a stochastic vector process, characterized by a Cross-Spectral Density Matrix (CSDM). To generate sample functions of the vector process, the Spectral Representation Method is one of the most commonly used, involving a Cholesky decomposition of the CSDM. However, it is a well-documented problem that as the length of the structure – and consequently the size of the vector process – increases, this Cholesky decomposition breaks down numerically. This paper extends a methodology introduced by the second and fourth authors to model wind velocities as a Gaussian stochastic wave (continuous in both space and time) by considering the stochastic wave to be non-Gaussian. The non-Gaussian wave is characterized by its frequency–wavenumber (FK) spectrum and marginal probability density function (PDF). This allows the non-Gaussian wind velocities to be modeled at a virtually infinite number of points along the length of the structure. The compatibility of the FK spectrum and marginal PDF according to translation process theory is secured using an extension of the Iterative Translation Approximation Method introduced by the second and third authors, where the underlying Gaussian FK spectrum is upgraded iteratively using the directly computed (through translation process theory) non-Gaussian FK spectrum. After a small number of computationally extremely efficient iterations, the underlying Gaussian FK spectrum is established and generation of non-Gaussian sample functions of the stochastic wave is straightforward without the need of iterations. Numerical examples are provided demonstrating that the simulated non-Gaussian wave samples exhibit the desired spectral and marginal PDF characteristics.

Measurement and Numerical Simulation of Ground and Subgrade Vibrations of Beijing Urban Rail Line 13

Urban rail transit is an effective way to deal with the problem of traffic congestion in major cities. Trains travel through dense residential and commercial areas, providing convenient transportation while also result in vibration problems in the surrounding environment. Long‐lasting vibrations result in disturbance to people’s sleep, malfunction of sensitive equipment, and even damage to heritage buildings. Compared with elevated and tunnel sections, ground surface urban railway generates vibrations and propagates to the surroundings via a more direct path in the form of surface waves, which makes the environmental problem more prominent. Due to the complexity of the train‐track‐ground system, the characteristics of the vibration propagation and attenuation are yet to be revealed. In this paper, we investigate the vibration of the ground and the subgrade next to the Beijing Urban Rail Line 13 by a field measurement combined with a mathematical model. The duration of ground vibration is divided into two parts: the train passing time and the Doppler effect‐related tailing part. Through a regression analysis of the duration, the train passing time is identified and the train traveling speed is estimated. The attenuation relationship of ground vibration intensity is expressed by a piecewise function. In the subgrade, the vibration intensity of particle decays with increasing depth and the stress decay rate is faster than that of the acceleration. The dynamic wheel/rail interaction behaves stationary and periodic, and the magnitude fluctuates up and down with the quasi‐static axle weight. The intensity attenuation relationship fitted in this paper provides a basis for designing new lines and renewing old lines and can be used as a reference for the development of vibration‐reduction technology. The simulated time history of the wheel‐rail force provides an excitation sample for further model experiments and numerical simulation. The proposed train speed identification method may be useful for parameter identification of moving sources such as ships, automobiles, and airplanes.

Analysis of platform motions effect on the fatigue loads and aerodynamic unsteadiness in floating offshore wind turbines

Floating platform motions introduce an additional level of complexity to the analysis models for floating offshore wind turbines. A series of simulations of the NREL 5MW wind turbine on a semi-submersible platform, in constrained (fixed) and free-to-move configurations, were done in OpenFAST software. Simulated time histories show that the platform motions increase the force and bending moment at the blade root by 3% and 7.4% respectively, while increase the same quantities at the tower base by 61.3% and 59.4%. The rainflow counting method was used to calculate the cyclic load and fatigue at the blade root and the tower base. The results show that the platform motions result in higher fatigue on the tower base in both design load cases, power production and parked. Platform motions show a lesser effect on the fatigue at blades root while the wind turbine is operational and negligible effect while idling. Understanding the relation between platform motions and the differences in loads and consequently the fatigue can provide better tools for wind turbine design.

Aerodynamic Modeling of ATTAS Aircraft using Mamdani Fuzzy Inference Network

This article presents aerodynamic modeling of the fixed-wing aircraft using the Mamdani fuzzy inference network (MFIN). A Mamdani fuzzy inference system with a Gaussian membership function has been used as a nonlinear regression functional node to create a multilayer network, called MFIN. The multilayered MFIN incorporates the nonlinear function approximation capability of the multilayered neural network in addition to robustness against uncertainties and measurement noises. The limited-memory Broyden–Fletcher–Goldfarb–Shanno optimization technique has been used to optimize network parameters to learn the nonlinear yawing moment dynamics of the Advanced Technology Testing Aircraft System (ATTAS) aircraft. Since every node in the network learns the nonlinearity of the dynamics, the proposed MFIN becomes capable of learning highly nonlinear dynamics. The adequacy of the proposed network is validated using the recorded flight data from the ATTAS aircraft of the DLR German Aerospace Centre in two cases: 1) trimmed low-angle-of-attack flight condition and 2) quasi-steady stall high-angle-of-attack (highly nonlinear complex) flight condition. The simulated time history tracking performance, mean square error, $R^2$ score, and explained variance score of the proposed network are compared with state-of-the-art methods. Also, the robustness of the proposed approach is demonstrated by evaluating its performance against test data corrupted with additive white Gaussian noise.

A modified spectral representation method to simulate non-Gaussian random vector process considering wave-passage effect

Wave-passage effect is always of great importance when performing the dynamic analysis of lager scale structures. This effect can be easily considered in the simulation of Gaussian vector process, but there is not an efficient way to consider it in simulating non-Gaussian vector process. In this paper, a method is proposed to generate stationary non-Gaussian vector process considering wave-passage effect. In the simulation of vector process, wave-passage effect leads to a complex-defined cross spectral density matrix (CSDM). To separate the phase part from the CSDM, an improved form of spectral representation method (SRM) is proposed, in which the phase part representing the wave-passage effect can be directly expressed in an explicit form in the simulation formula. Then the characteristic of phase part representing the wave-passage effect during the nonlinear translation (translating underlying Gaussian vector process to the prescribed non-Gaussian vector process) is investigated. Interestingly, it is found that, the phase part is not changed. Based on this good feature, the modified SRM and the iterative scheme can be combined to simulate non-Gaussian vector process considering wave-passage effect. Two examples, involving the simulation of seismic ground motions and wind velocity time histories, are presented to show the characteristics of the simulated vector process and to verify the capabilities of the proposed method.

Structural Reliability Estimation with Participatory Sensing and Mobile Cyber-Physical Structural Health Monitoring Systems

With the help of community participants, smartphones can become useful wireless sensor network (WSN) components, form a self-governing structural health monitoring (SHM) system, and merge structural mechanics with participatory sensing and server computing. This paper presents a methodology and framework of such a cyber-physical system (CPS) that generates a bridge finite element model (FEM) integrated with vibration measurements from smartphone WSNs and centralized/distributed computational facilities, then assesses structural reliability based on updated FEMs. Structural vibration data obtained from smartphones are processed on a server to identify modal frequencies of an existing bridge. Without design drawings and supportive documentation but field measurements and observations, FEM of the bridge is drafted with uncertainties in the structural mass, stiffness, and boundary conditions (BCs). Then, 2700 FEMs are autonomously generated, and the baseline FEM is updated by minimizing the error between the crowdsourcing-based modal identification results and the FEM analysis. Furthermore, using 151 strong ground motion records from databases, the bridge response time history simulations are conducted to obtain displacement demand distribution. Finally, based on reference performance criteria, structural reliability of the bridge is estimated. Integrating the cyber (FEM analysis) and the physical (the bridge structure and measured vibration characteristics) worlds, this crowdsourcing-based CPS can provide a powerful tool for supporting rapid, remote, autonomous, and objective infrastructure-related decision-making. This study presents a new example of the emerging fourth industrial revolution from structural engineering and SHM perspective.

Loss impact factors for lifetime seismic loss assessment of steel concentrically braced frames designed to EC8

ABSTRACTThis study employs multiple earthquake time-history response simulations, and the FEMA P-58 performance assessment methodology to evaluate the influence of key design parameters on the lifetime seismic repair costs incurred by case study concentrically braced frames (CBFs) designed to Eurocode 8. The parameters considered include structural mass, stiffness (natural period) and ductility (behaviour factor). A new factor termed the Loss Impact Factor (LIF), is used to quantify the influence of each of these parameters on lifetime costs. Under dissipative seismic design principles, bracing members in CBFs may behave inelastically under infrequent, high-intensity earthquakes. Larger values of the design behaviour factor, q, selected by the structural engineer result in higher ductility demands during these earthquakes, but also reduce the design seismic action, leading to smaller, lighter and more flexible structural members. Hence, variations in one parameter necessarily influence the others, as well as initial construction cost. The variation in expected lifetime seismic repair costs with respect to each of these parameters, which is less clear, is the subject of this paper. Costs are shown to reduce with increased structural mass, stiffness and initial cost, with the impact of the latter two parameters generally increasing with both seismic hazard and frame height.

Vibration fatigue dynamic stress simulation under multi-load input condition: Application to metro lifeguard

The formula for calculating the time history of structure dynamic stress under multi-load input condition was deduced based on structural dynamics theory, and fatigue life prediction of weld toe was performed by notch stress approach. In the dynamic stress time history simulation method, firstly, we calculate the frequency response function (FRF) of each external load at concerned point, which including the phase information. Then, the method was based on fast Fourier transform (FFT) to get the frequency domain with real and imaginary part of each external load rather than power spectrum density (PSD) calculation, avoiding loss of the phase information by PSD method. Finally, the dynamic stress frequency domain data could be calculated by FFT results and FRFs, based on above, the dynamic stress time history could be acquired by Inverse FFT (IFFT) of frequency domain data. Compared with the conventional stress PSD calculation method, the method in this paper can retain the phase information of the each external load, and the formula for calculating the dynamic stress under multi-load input condition was verified effective by a metro lifeguard line test data. The line test stress results show that the damage error between the numerical stress and the experimental stress is 4.1%, which is acceptable in project. At last, the method was used to guide the lifeguard structure optimization.

Vibration Reduction of Eccentric Steel 3D Framed Building Considering Soil Flexibility

Seismic demand can be reduced by modifying the structural response of the system. Viscous dampers are an effective passive control device for reducing vibrations in building structures. The present study investigates the performance of linear viscous dampers in vibration control of multi-storey building structures under seismic excitation considering the effect of soil flexibility. Six-storey steel 3D framed buildings with three different building plans, namely symmetric, T and L shapes, are modeled using SAP 2000. Soil type I (hard) and type II (medium) are considered as per IS 1893:2002 to incorporate the effect of soil flexibility by using springs at supports for medium type soil and fixed supports for hard soil. The spring constants are obtained from Gazetas’ equations. To measure the control performance, inter-storey drift and maximum top displacement are considered as objective functions. Linear time history simulation is performed using white noise (ensuring wider frequency content) to quantify the objective functions. After performing the analysis and comparing with the uncontrolled case for both hard and medium soil, it is observed that maximum reduction in inter-storey drift and average top displacement can be obtained. Eccentric plans have larger uncontrolled values than the symmetric plans, thus additional design criteria to be followed when opting for eccentric plans. The study reveals that application of supplemental viscous dampers results in greater control of vibrations in such plans. Vibration control of viscous damper is comparatively better in hard soil than in medium type soil.

Seismic performance of a damage avoidance self-centring brace with collapse prevention mechanism

The Resilient Slip Friction Joint (RSFJ) has recently been developed and introduced to the construction industry. This joint is a friction-based energy dissipation device that owing to its special configuration can provide energy absorption and self-centring behaviour in one package. This device is most applicable when the designers consider a damage avoidance philosophy of design. One of the applications of this device is the RSFJ brace. In this bracing system, the required seismic performance is provided by the RSFJ and the rest of the brace components are aimed to stay elastic. This paper introduces the RSFJ bracing system including the collapse-prevention fuse. This built-in fuse works in a way that when the applied force exceeds the design load, the secondary fuse is activated and the RSFJ brace is still able to provide self-centring up to twice the target deformation with an axial force of up to 1.25 times of the target design force. The performance of this fuse is investigated by experimental tests on the component level and the results are presented. Moreover, a numerical model for a five story steel structure with RSFJ braces is developed and was subjected to non-linear static pushover and nonlinear dynamic time-history simulations in order to investigate the seismic performance of the proposed system. The findings of this research shows that the RSFJ brace system can offer substantial performance benefits and has the merit to be considered as an efficient alternative for the current bracing systems.

An Artificial Seismic Wave Suitable for Suspended Converter Valve in the UHVDC Transmission Project

The finite element model of suspended converter valve in an UHVDC transmission project with characteristics of flexible is constructed, and its vibration characteristics are simulated and analyzed firstly. The results show that this kind of suspended converter valve has obvious long-period character. Secondly, the long period phase of standard response spectrum in Code for Seismic Design of Buildings (GB50011-2010) is modified, and then the artificial seismic wave is synthesized employing the triangular series method. The result shows that this artificial seismic wave has long-period character. Finally, the time-history seismic dynamic simulation of the converter valve is done, and the seismic responses of the converter valve excited by three kinds of seismic wave with different period characters are compared and analyzed. The results show that the swing and stress of the suspended converter valve are larger under the long-period seismic wave synthesized in this paper. The quasi-resonance damage caused by long-period seismic wave should be concerned specially in the actual UHVDC transmission project.