Full Dynamic Analysis Research Articles

Numerical Development of a Coupled One-Dimensional/Three-Dimensional Computational Fluid Dynamics Method for Thermal Analysis With Flow Maldistribution

Abstract This work describes the development of a methodology that couples one-dimensional (1D) network elements with three-dimensional spatial computational fluid dynamic (CFD) elements to analyze shell-and-tube heat exchangers with dense tube bundles. The 1D elements represent the tube flow while the spatial elements represent the external auxiliary flow. This reduces the computational expense significantly as compared to full computational fluid dynamics analysis of the same system, while a detailed transient temperature distribution can still be obtained. The methodology uses a unique combination of relaxation algorithms, a polynomial regression mapping procedure, and discretisation methods to create a coherent numerical methodology. Simulations are performed on a TEMA-FU-type shell-and-tube heat exchanger. The methodology was validated against full CFD and indicates errors between the calculated logarithmic mean temperature differences (LMTD) of less than 2% over a range of turbulent flow conditions. Various combinations of media for primary and auxiliary fluids are considered, to test the applicability and robustness of the methodology. Finally, a transient simulation of timed step inputs for the flowrate and temperature of both primary and auxiliary fluids also corresponds with a full CFD analysis. It is concluded that the proposed 1D-CFD method is effective for simplifying the analysis of flow-through tube bundles.

Simplified Full Dynamic Analysis of a Railway Tunnel in Ethiopia

This paper presents an effective means of analyzing the safety of a tunnel under dynamic loading in areas with seismic records. A particular case of the railway tunnel in the earthquake-prone regions of the escarpment seismic zone of Ethiopia was the specific focus area of the research. Probabilistic seismic hazard analysis (PSHA) and deaggregation have been conducted to determine the design earthquake required as an input for the dynamic analysis. The PSHA performed by considering the operating design earthquake with conservative assumptions of the local geological features resulted in a peak ground acceleration of 0.36. Two pairs of design earthquake have been obtained from the deaggregation process, which were used to filter acceleration time histories for the selected design earthquake from the ground motion database of Pacific Earthquake Engineering Research Center. Finally, full dynamic analyses of the tunnel have been performed by applying the scaled acceleration time histories corresponding to the structure in the specific site. It was demonstrated how to prove the stability of the tunnel located in difficult ground conditions by performing plane strain analyses with the possible minimum computational efforts.

A simplified method for probabilistic seismic risk evaluation of nuclear containment structure

Damage performance and annual frequency of exceedance are the focus of probabilistic safety assessment for nuclear power plant structures. However, conventional displacement-based global damage index and classical method for calculating the annual frequency of exceedance of the nuclear containment structure suffers from some limitations and deficiencies. Based on seismic energy balance concept, an innovative energy-based global damage index is proposed in this study. Based on truncated incremental dynamic analysis (TIDA) technique, a simplified method for calculating the annual frequency of exceedance of the nuclear containment structure is developed. To verify the effectiveness of the proposed global damage index and the proposed simplified method for calculating the annual frequency of exceedance, the proposed energy-based global damage index is compared to roof displacement based damage index. The annual frequency of exceedance calculated by the simplified method is compared to a more accurate but computationally demanding approach (full incremental dynamic analysis technique based approach). Finally, statistics of the annual frequency of exceedance are estimated by the parametric bootstrap method. Results indicated that energy-based global damage index proposed in this study can well reflect the global deformation characteristics of the nuclear containment structure. The variability of the proposed global damage index is smaller than that of roof displacement based global damage index, which indicates the superiority of the proposed global damage index. In general, the proposed simplified method for calculating the annual frequency of exceedance can provide good estimation of the annual frequency of exceedance of the nuclear containment structure corresponding to different damage levels. With regard to the statistics of the annual frequency of exceedance, the mean value of the annual frequency of exceedance is not sensitive to the number of bootstrap samples, while the coefficient of variation of the annual frequency of exceedance is sensitive to the number of bootstrap samples. When the number of bootstrap samples is larger than 300, the statistics of the annual frequency of exceedance tend to be stable.

Wind-induced dynamic performance of a super-large hyperbolic steel-truss cooling tower

In order to study the wind-induced performance of super-large steel structure cooling towers, a super-large hyperbolic 216.3m-high cooling tower comprising a double-layer steel-truss structure with steel-sheet cladding was taken as a case study. The dynamic characteristics of this cooling tower were analyzed and compared with those of a similar-scale reinforced concrete cooling tower. Then, fluctuating wind loads measured in wind tunnel tests were applied directly to a structural finite-element model based on proper orthogonal decomposition and reconstruction of the wind pressures. The displacement response of the cooling tower was subsequently obtained by full transient dynamic analysis, and then the distribution characteristics of mean response, the mode participation contribution of the fluctuating displacement responses, the wind-induced vibration factors and the influence of structural damping ratio were investigated and compared with those of a concrete cooling tower. The comparison results mainly show that the steel-structure cooling tower has higher natural vibration frequencies, a lower-order number of lateral overturning mode (indicating a higher risk of overturning collapse), simpler resonant modes, smaller variance ratio of resonant component and weaker sensitivity of dynamic response to structural damping. The study results could assist in wind resistance design of similar super-large steel-structure cooling towers.

Effect of contacting bodies’ mechanical properties on the dynamics of a rolling cylinder

This paper investigates the influence of the material properties on the deceleration dynamics of a deformable cylinder rolling with slipping on a half-space of the same material. The interaction of the cylinder and the half-space is described by the 2D quasistatic contact problem of viscoelasticity (Goryacheva: J Appl Math Mech 37(5):877–885, 1973; Contact mechanics in tribology. Kluwer, Dordrecht 1998) which includes as limiting cases the absolutely rigid and elastic materials. Full dynamical analysis of the problem including the phase portrait, the dependence of the deceleration distance on the mechanical properties of the contacting bodies and on the friction coefficient is provided. The qualitative features of deceleration are justified by asymptotic analysis.

Impact of High Energy Mining-Induced Seismic Shocks from Different Mining Activity Regions on a Multiple-Support Road Viaduct

In this paper, the dynamic responses of a large-scale multiple-support road viaduct to mining-induced seismic events registered in two regions of mining activity were compared. The regions differ in geological structure, which results in discrepancies in the dominant frequency content. Spatial variation of ground motion causing the kinematic excitation non-uniformity was accounted for in the dynamic analyses of this large-scale structure. Non-uniform mining-induced kinematic excitation models were proposed, with respect to the specificity of mining origin quakes. The dynamic performance of the viaduct was determined using three different methods of calculation: the time history analysis, the response spectrum analysis, and the multiple support response spectrum analysis. Both the uniform and non-uniform kinematic excitation models were adopted for the dynamic performance assessment. The research revealed that the dynamic response of some members of the structure, determined using the non-uniform excitation model, was significantly greater than that obtained for the uniform one. Hence, in the dynamic analysis of multiple-support structures under mining-induced events, the effect of spatial variation of ground motion should be considered. The study pointed out that the commonly used response spectrum analysis may lead to the underestimation of the dynamic response of large-scale multiple-support structures. Instead, the multiple support response spectrum method, which takes into account the non-uniformity of ground motion, is recommended as a conservative approximation. This method provides a safe upper estimation of the full-dynamic analysis results of large-scale structures under mining-induced tremors. Finally, the research indicated that the dynamic performance of a structure strongly depends on the frequency range attributed to a specific mining region. The dynamic performance of identical engineering structures under tremors of similar maximal amplitudes may differ significantly due to discrepancies in frequency contents of shocks occurring in various mining regions.

A macro-element approach to analyse bridge abutments accounting for the dynamic behaviour of the superstructure

This paper describes an original approach to the study of the seismic behaviour of bridge abutments. The proposed method incorporates a simplified description of the dynamic response of the bridge structure into a finite-element model of the soil–abutment system. Specifically, the dynamic behaviour of the bridge structure is described by a macro-element that simulates the loads transferred to the abutment during the seismic event. The macro-element is identified using a structural model of the bridge as a reference. This approach improves the current analysis methods based on sub-structuring, limiting at the same time the computational demand needed for a complete study of the soil–structure interaction. In the paper, the validity of the procedure is demonstrated comparing the results of the simplified approach with the results obtained from full three-dimensional dynamic analyses of idealised soil–bridge systems, using non-linear advanced constitutive models to describe the soil behaviour. Based on these results, a strategy is devised for the calibration of the bridge macro-element, making use of a limited number of input parameters.

Interaction of Urban Underground Twin Metro Tunnels Under Static and Earthquake Loading

New Delhi is a city affected by near/far-field earthquakes, where underground metro construction activities have been undertaken since the early 2000s. Due to the seismic effects, these structures are designed by conventional force/displacement methods. The present study validates the efficacy of these methods, numerically. For this, varying geotechnical conditions in static and seismic cases were quantified with the expected ground motion. Bored tunnels at different cover depths were modeled in 2D and 3D, to ascertain the static response of these structures, followed by a true dynamic analysis. It was found that conventional design procedures using force methods gave conservative estimates for increments on the tunnel liner. Also, the importance of a full dynamic analysis could not be ignored because (i) higher surface spectral responses were found at the tunnel pillar location and (ii) the cumulative strains on the tunnel liner were found to exceed permissible limits.

Validation of a numerical model based on dynamic centrifuge tests and studies on the earthquake damage mechanism of underground frame structures

A series of dynamic centrifuge tests were performed to analyse the seismic response and failure mechanism of the underground frame structures. In the model test, the model structure experienced complete collapse, which has rarely been reported in previous studies. This study aimed to obtain an effective numerical model based on physical tests that could properly simulate large deformations or even the collapse of soil-structure systems under earthquake loads. The tests were numerically analysed via a full dynamic time history analysis considering the non-linear properties of the material and contact. The process of establishing numerical model and the method of determining material parameters were elaborated. The numerical results were compared to experimental data to validate the effectiveness of the numerical model. Finally, the calibrated numerical model was used to carry out further research on the seismic damage response and failure mechanism (i.e., collapse damage) of underground structures. Some of most important insights based on the model test and numerical results are as follows. The top and bottom of the column of underground frame structure were determined to be the weakest positions under earthquake loading conditions and were vulnerable to bending-shearing failure. The vertical earthquake load could significantly increase the axial forces on the columns and then reduce their horizontal deformation capacity. The columns subjected to high axial compression were prone to complete brittle failure under a relatively strong horizontal earthquake load and caused the overall collapse of the underground frame structure. Therefore, the underground frame structure could avoid complete collapse under a strong earthquake load as long as the column was free from damage and provided sufficient vertical support.

Vibration Serviceability of Footbridges: Classical vs. Innovative Material Solutions for Deck Slabs.

In this study, the human-induced dynamic performance of modern footbridges equipped with either classical reinforced concrete (RC) or innovative glass fiber-reinforced polymer (GFRP) composite deck slabs were investigated and compared. The numerical studies were carried out for two bridges: a three-span cable-stayed footbridge and a three-span continuous beam structure. Two variants of both bridges were taken into consideration: the footbridges equipped with traditional RC slabs and the structures benefitted with GFRP slabs. The risk of resonance as well as the vibration serviceability and the comfort criteria assessment of the footbridges with different slab materials were assessed. The investigation revealed that the footbridges, both cable-stayed and beam, benefitted with the GFRP slabs had higher fundamental frequency than those with the traditional RC slabs. The footbridges with the GFRP slabs were less exposed to the resonance risk, having fundamental frequencies above the limit of the high risk of resonance. The effect of shifting up the natural frequencies by introducing GFRP slabs was more remarkable for the lightweight beam structure than for the cable-stayed footbridge and resulted in a more significant reduction of the resonance risk. The calculated maximum human-induced accelerations of the footbridges benefitted with the GFRP slabs were meaningfully higher than those obtained for the footbridges with the RC slabs. The study proved that, with the same GFRP slab, meeting vibration serviceability and comfort criteria limits in the case of very lightweight beam structures may be more problematic than for cable-stayed footbridges with more massive structural systems. In the research, particular attention was paid to examining the impact of higher harmonics of the moving pedestrian force on the structures benefitted with the GFRP composite slabs. It occurred that in the case of footbridges, both cable-stayed and beam, equipped with the RC slabs higher harmonics of human force did not play any role in the dynamic performance of structures. However, in the case of the footbridges benefitted with the GFRP slabs, the impact of higher harmonics of the pedestrian force on the dynamic behavior of structures was clearly visible. Higher harmonics excited accelerations comparable to those executed by the first harmonic component. This conclusion is of great importance for footbridges equipped with GFRP slabs. The fundamental frequency may place a footbridge in the low or even negligible risk resonance range and the higher frequencies corresponding to vertical modes may be located above the limit of 5 Hz that ensures avoiding resonance. Nevertheless, the fact that fundamental modes are so responsive to higher harmonics significantly increases the risk of resonance. The amplification of the dynamic response may occur due to frequencies related to second or third harmonics (i.e., being half or a third of the natural frequencies). In such cases, full dynamic analysis of a footbridge at the design stage seems to be of crucial importance.

Fragility analysis of an ageing monopile offshore wind turbine subjected to simultaneous wind and seismic load

The loads induced as a result of seismic activities may jeopardize the serviceability of offshore wind turbines or may even lead the structure to reach the ultimate strength. The maximum load-carrying capacity of a support structure can be estimated by performing a structural assessment which accounts for the nonlinear effects arising from the material and geometry. The present work aims to analyze the fragility of a 5 MW monopile offshore wind turbine structure subjected to seismic activities accounting for soil interactions and time-variant structural degradation. The offshore wind turbine structure is subjected to different ground motions with different intensity. The nonlinear full transient dynamic structural analysis is carried out based on the finite element method, and the nonlinear monopile structural response during the different seismic activities is discussed. Finally, the fragility curves associated with the serviceability limit state design and the ultimate strength limit state are developed.

A static equilibrium condition for the steady-state analysis of variable-stroke swash plate mechanism

Variable-stoke swash plate mechanisms are widely used for compressors in automotive air-conditioning systems, but the dynamics of the system has not been investigated sufficiently. In the present study, we derived a dynamic equation based on the Lagrangian mechanics for the mechanism and solved it numerically. The solutions were compared with the ones obtained from the commercial multibody dynamics software, DAFUL. We proposed a static function that can be conveniently used to predict the steady-state behavior of the system without conducting a full dynamic analysis of the variable-stoke swash mechanism. Using the static function, for example, we showed why the stroke of the variable-stoke swash tends to increase with the driving speed and showed a simple way to reverse the tendency. Especially, we observed that the system can have multiple steady-state solutions depending on initial conditions. Based on this observation, we theoretically showed that a hysteresis phenomenon can occur in the variable-stoke swash mechanism so that the behavior of the system can depend on the operation history of the system.

Advanced Seismic Assessment of Four Masonry Bell Towers in Italy after Operational Modal Analysis (OMA) Identification

ABSTRACT The paper presents an advanced seismic assessment of four masonry bell towers located in Northern Italy based on detailed 3D FE models on which elastic parameters were previously identified by operational modal analysis. The numerical assessment includes a preliminary identification of the elastic moduli of the different volumes of each tower made by means of a fast-micro-GA approach. After proper identification of the main four eigenfrequencies, non-linear static (pushover) and full non-linear dynamic analyses are performed adopting a material model for masonry which is characterized by softening and two distinct damage parameters in both tension and compression. The results obtained with non-linear static and non-linear dynamic analyses in all the simulations performed exhibit a satisfactory match, suggesting similar conclusions in terms of general dynamic response and seismic vulnerability of the towers.

Dynamic response modeling of high-speed planing craft with enforced acceleration

An approach is investigated in this study for structural dynamic analysis of a high-speed planing hull, in which the pointwise acceleration data collected from sea trials are enforced as base excitation. The paper first performed the full boat analysis of an 11-meter high speed craft for a period of one wave impact selected from each of nine seakeeping runs. The sea trial acceleration data collected from 11 accelerometers placed close to the centerline and the keel are enforced as input, while those from 3 accelerometers placed around the pilot cabin are selected for validation. The substructure dynamic analysis of the isolated pilot cabin was then conducted and validated, in which 7 pointwise enforced accelerations are selected from the simulation output of the full boat dynamic analysis. The substructure dynamic analysis enables detailed investigation of local stress concentrations where critical equipment and personnel are located. The proposed approach can be extended to rigid-flexible body coupling analysis of a high-speed craft when it is running with large pitching and yawing motion.

Evolution Mechanism of Wind Vibration Coefficient and Stability Performance during the Whole Construction Process for Super Large Cooling Towers

Wind-induced damage during the construction process and the evolution of damage over time are important reasons for the wind-induced destruction of large cooling towers. In fact, wind vibration coefficient and stability performance will evolve with the construction height and material properties over time. However, the existing studies generally ignore the impact of wind load and structural performance during the construction period. In this study, we built the 3D physical model separately for all eight construction stages a super large cooling tower which is being currently constructed and stands 210 m. The dynamic characteristics of the cooling tower were analyzed in each stage. First, the flow field information and 3D time history of aerodynamic forces were obtained for the whole construction process using large eddy simulation (LES). Full transient dynamic finite element analysis was used to calculate the dynamic responses of the tower under the real-time changes of wind loads during the whole construction process. Five calculation methods were used to trace the evolution of wind vibration coefficient during the whole construction process of the super large cooling tower. Then the formula for wind vibration coefficient changing with the construction height was fitted. The differential values of wind vibration coefficient during the whole construction process of the cooling tower were discussed by taking the meridional axial force as the objective function. On this basis, the influence and working mechanism of wind vibration coefficient, concrete age, construction load, geometric nonlinearity, internal suction force on buckling stability, and ultimate bearing capacity of the cooling towers were investigated. This research provides an enhanced understanding on the evolution of wind-induced stability performance in super large cooling towers and a methodology to prevent wind-induced damage during the construction process.

Surface structure and stacking of the commensurate (13×13)R13.9∘ charge density wave phase of 1T−TaS2(0001)

By quantitative low-energy electron diffraction (LEED) we investigate the extensively studied commensurate charge density wave (CDW) phase of trigonal tantalum disulphide (1T-TaS$_2$), which develops at low temperatures with a $\left(\sqrt{13}\times\sqrt{13}\right)$R13.9{\deg} periodicity. A full-dynamical analysis of the energy dependence of diffraction spot intensities reveals the entire crystallographic surface structure, i.e. the detailed atomic positions within the outermost two trilayers consisting of 78 atoms as well as the CDW stacking. The analysis is based on an unusually large data set consisting of spectra for 128 inequivalent beams taken in the energy range 20-250 eV and an excellent fit quality expressed by a bestfit Pendry R-factor of R=0.110. The LEED intensity analysis reveals that the well-accepted model of star-of-David-shaped clusters of Ta atoms for the bulk structure also holds for the outermost two TaS$_2$ trilayers. Specifically, in both layers the clusters of Ta atoms contract laterally by up to 0.25 $\r{A}$ and also slightly rotate within the superstructure cell, causing respective distortions as well as heavy bucklings (up to 0.23 $\r{A}$) in the adjacent sulphur layers. Most importantly, our analysis finds that the CDWs of the 1$^{\text{st}}$ and 2$^{\text{nd}}$ trilayer are vertically aligned, while there is a lateral shift of two units of the basic hexagonal lattice (6.71 $\r{A}$) between the 2$^{\text{nd}}$ and 3$^{\text{rd}}$ trilayer. The results may contribute to a better understanding of the intricate electronic structure of the reference compound 1T-TaS$_2$ and guide the way to the analysis of complex structures in similar quantum materials.

Explicit–Implicit Co-Simulation Techniques for Dynamic Responses of a Passenger Car on Arbitrary Road Surfaces

To study the durability of a passenger car, this work investigates numerical simulation techniques. The investigations are based on an explicit–implicit approach in which substructure techniques are used to reduce the simulation time, allowing full vehicle dynamic analyses to be performed on a timescale that is difficult or impossible with the conventional finite element model (FEM). The model used here includes all necessary nonlinearities in order to maintain accuracy. All key components of the car structure are modeled with deformable materials. Tire–road interactions are modeled in the explicit package with contact-impact interfaces with arbitrary frictional and geometric properties. Key parameters of the responses of the car driven on six different kinds of test road surfaces are examined and compared with experimental values. It can be concluded that the explicit–implicit co-simulation techniques used here are efficient and accurate enough for engineering purposes. This paper also discusses the limitations of the proposed method and outlines possible improvements for future work.

Vibration of composite beams with deformable shear connection: Mathematical modelling and numerical solution using general-purpose software for two-point boundary value problems

In this paper, we develop from first principles a linear one-dimensional mathematical model for the dynamic response of planar composite beams with deformable shear connection, in which the inertias associated with the axial motion of the components and with the bending rotations of their cross-sections are consistently taken into account. To the best of our knowledge, the paper by Auclair et al. [J. Sound Vib. 366 (2016) 230–247] is the only work which heretofore considered these two effects. However, we point out and correct a flaw in the derivations of these authors. To solve the eigenproblem defining the natural vibration frequencies of the composite beam and the corresponding vibration modes, we advocate an untried approach – the eigenproblem is converted into a “standard” inhomogeneous boundary value problem, which can be solved using freely available state-of-the-art mathematical software. For benchmarking purposes, the formulation of a conventional displacement-based conforming finite element is also briefly addressed. The effect of rotational and axial inertias on the natural vibration frequencies is found to be marginal and considerably less pronounced than the predictions of Auclair and coworkers. In disagreement with the findings of these authors, it appears legitimate to ignore the above-mentioned effect in a full dynamic analysis of composite beams, at least within the practical range of span-to-depth ratios.

Dynamic column loss analysis of reinforced concrete flat slabs

The sudden column loss idealisation is a useful design tool to assess structures for progressive collapse. As such an event is a dynamic problem, suitable account must be taken of these effects. This can either be achieved by a full dynamic analysis of the structure or a simplified static approach, with correction factors for the dynamic influence. This study aims to investigate the response of Reinforced Concrete (RC) flat slab structures after a column loss using experimentally validated Finite Element (FE) models. The nonlinear dynamic response of a structure after such an event is considered, including the redistribution of loads and displacement profile. These results are then compared to equivalent static cases in order to determine the Dynamic Amplification Factor (DAF). For the range of structures considered, the DAF was calculated as between 1.39 and 1.62 for displacements, with lower factors associated with a higher nonlinear response or slower column removal. Additionally, the shear forces in remaining columns may exceed 200% of their fully supported condition, with a different associated DAF. The effects of increasing the tensile strength of concrete due to high strain rates are also considered. Typical Dynamic Increase Factors (DIFs) based on the strain rates were up to 1.23, however, this only applied for a short time period, and in a limited area. Therefore, such effects do not significantly influence the response.

Seismic Design of Metal Arch Culverts: Design Codes Vs. Full Dynamic Analysis

ABSTRACT Corrugated steel plate (CSP) culverts have been used successfully in diverse applications throughout North America and worldwide. Seismic loading has a considerable effect on the performance of large-span culverts. However, there is a lack of comprehensive studies in the literature concerning the seismic performance of these structures. In this study, full dynamic finite element modelling was used to investigate the seismic performance of large-span CSP culverts. First, the static behavior of a long-span culvert was verified using a field case study. Dynamic analyses were then performed with the aid of seismic records with different levels of seismicity. The finite element analysis results were subsequently compared with commonly used simplified seismic provisions to evaluate their suitability. Furthermore, a parametric study was developed to investigate the seismic behavior of CSP culverts under different subsurface conditions, and to examine the effect of changing the culvert rigidity and configuration. This study clearly shows that the commonly used simplified equations underestimate the internal forces, and consequently, for culverts located in zones of high seismicity, a full dynamic finite element analysis is required.