Detailed Dynamic Response Research Articles

Sloshing of Liquid in a Cylindrical Tank with Multiple Baffles and Considering Soil-Structure Interaction

In this study, the liquid sloshing in a cylindrical tank considering soil–structure interaction and undergoing horizontal excitation is investigated analytically. Multiple rigid annular baffles are positioned on the rigid wall to mitigate the liquid sloshing. Firstly, combined with the subdomain partition method for sloshing, the complex liquid domain is partitioned into simple subdomains with the single condition for boundary. Based on continuity conditions of velocity and pressure as well as the linear sloshing equation for free surface, the exact solution for convective velocity potential is derived with high accuracy. By yielding the similar hydrodynamic shear and moment as those of the original system, a mechanical model is developed to describe continuous sloshing, and parameters of the model are given in detail. Then, by means of the least squares approach, the Chebyshev polynomials are utilized to fit impedances for the circular surface foundation. A lumped parameter model is employed to represent influences of soil on the superstructure. Finally, by using the substructure method, a coupling model of the soil–tank system is developed to simplify the dynamic analysis. Comparison investigations are carried out to verify the effectiveness of the model. Detailed sloshing characteristics and dynamic responses of sloshing are analyzed with regard to different baffle sizes and positions as well as soil parameters, respectively. The novelty of the present study is that an equivalent analytical model for the soil–foundation–tank–liquid system with multiple baffles is firstly obtained and it allows the dynamic behaviors of the coupling system to be investigated with high computation efficiency and acceptable accuracy.

Development of nuclear fuel assembly 3D reduced model and modal analysis

Due to the geometric complexity of fuel assembly (FA), virtually all reactor dynamic analysis models incorporated drastically simplied FA by lumped mass and beam. Considering the rapid advances of computer technology and analysis software, improving reactor dynamic analysis by 3D model is now possible. As a first step toward this goal, this research investigates and attempts to develop a reduced 3D FA dynamic analysis model to assess more accurate and detailed dynamic response of FA. A modal analysis of a 3D FA model was developed and showed the responses of the FA. The model was tuned to the test results up to 4th modes which were the upper value of test results. The model showed 3D response of FA and revealed additional modes of dynamic behaviors such as torsional motion and composite of bending and torsional motion.

Optimizing system operation with nadir considerations via simulations of detailed system dynamic responses

Decarbonization processes around the world are pressing system operation significantly, particularly in terms of ensuring appropriate reliability and stability levels when integrating massive amounts of converter-based generation technologies (CGTs). In this context, this work proposes an optimization-simulation model to optimize system operation with nadir considerations via simulation of detailed system dynamic responses. We propose a Gauss–Seidel iterative method to incorporate the precise governors’ dynamic responses determined by the simulations within the sequential optimization problems. Through several case studies, we demonstrate the benefits of our approach and analyze the impacts of incorporating a detailed representation of units’ dynamic responses. We also compare our frequency nadir-constrained approach against an alternative inertia-constrained approach that ensures minimum amounts of inertia levels. Particularly, we show that ensuring minimum amounts of inertia may lead to inefficient economic outputs in terms of costs and integration of renewable generation without security gains in terms of frequency stability compared with constraining frequency nadir.

Nonlinear Solid–Fluid Coupled Seismic Response Analysis of Layered Liquefiable Deposit

A seismic response analysis of layered, liquefiable sites plays an important role in the seismic design of both aboveground and underground structures. This study presents a detailed dynamic site response analysis procedure with advanced nonlinear soil constitutive models for non-liquefiable and liquefiable soils in the OpenSees computational platform. The stress ratio controlled, bounding surface plasticity constitutive model, PM4Sand, is used to simulate the nonlinear response of the liquefiable soil layers subjected to two seismic ground motions with different characteristics. The nonlinear hysteretic behavior of the non-liquefiable soil under earthquake excitations is captured by the Pressure Independent Multi Yield kinematic plasticity model with a von Mises multi-yield surface. The soil elements are modelled utilizing the solid–fluid fully coupled plane-strain u-p elements. The seismic response of the layered liquefiable site in terms of the development of excess pore water pressure, acceleration, ground surface settlement, and stress–strain and effective stress path time histories under two representative earthquake excitations are investigated in this study. The numerical results indicate that both the characteristics of ground motions and the site profile have a significant influence on the dynamic response of the layered liquefiable site. Under the same intensity of ground motion, the loose sand layer with a 35% relative density is more prone to liquefaction and contractive deformation, which causes irreversible residual deformation and vertical settlement. The saturated soil layer can effectively filter the high-frequency components and amplify the low-frequency components of ground motions. Moreover, the liquified site produces a 40% post-earthquake consolidation settlement after the excess pore pressure dissipation.

Parametric study on the Multangular-Pyramid Concave Friction System (MPCFS) for seismic isolation

A series of comprehensive parametric studies are conducted on a steel-frame structure Finite-Element (FE) model with the Multangular-Pyramid Concave Friction System (MPCFS) installed as isolators. This new introduced MPCFS system has some distinctive features when compared with conventional isolation techniques, such as increased uplift stability, improved self-centering capacity, non-resonance when subjected to near-fault earthquakes, and so on. The FE model of the MPCFS is first established and evaluated by comparison between numerical and theoretical results. The MPCFS FE model is then incorporated in a steel-frame structural model, which is subjected to three chosen earthquakes, to verify its seismic isolation. Further, parametric study with varying controlling parameters, such as isolation foundation, inclination angle, friction coefficient, and earthquake input, is carried out to extract more detailed dynamic response of the MPCFS structure. Finally, limitations of this study are discussed, and conclusions are made. The simulations testify the significant seismic isolation of the MPCFS. This indicates the MPCFS, viewed as the beneficial complementary of the existing well-established and matured isolation techniques, may be a promising tool for seismic isolation of near-fault earthquake prone zones. This verified MPCFS FE model can be incorporated in future FE analysis. The results in this research can also guide future optimal parameter design of the MPCFS.

Repeated low-velocity impact response and damage mechanism of glass fiber aluminium laminates

Glass fiber aluminium laminate (GLARE) is a kind of fiber metal laminates widely applied in aircraft structures, frequently subjected to low-velocity impact incidents. The purpose of this paper is to investigate the dynamic response and damage mechanism characterization of GLARE under single and repeated low-velocity impacts. Firstly, a progressive degradation finite element (FE) model was developed and validated. Three different failure criteria were compared to analyze the damage behavior of composites of GLARE in terms of accuracy and efficiency, wherein a user defined material subroutine VUMAT was introduced. Then, the validated model was used to study the influence of the impact angle. Four different impact angles including 30°, 45°, 60° and 90° were analyzed in terms of plastic deformation, impact contact force, energy absorption and internal damage. Finally, the simulation of GLARE subjected to repeated impacts was carried out, in which the cumulative damage effects were considered. The detailed dynamic response and damage evolution of aluminium layers and composite layers as well as their interfaces with the number of impacts increasing were revealed.

Forward design of a complex enzyme cascade reaction.

Enzymatic reaction networks are unique in that one can operate a large number of reactions under the same set of conditions concomitantly in one pot, but the nonlinear kinetics of the enzymes and the resulting system complexity have so far defeated rational design processes for the construction of such complex cascade reactions. Here we demonstrate the forward design of an in vitro 10-membered system using enzymes from highly regulated biological processes such as glycolysis. For this, we adapt the characterization of the biochemical system to the needs of classical engineering systems theory: we combine online mass spectrometry and continuous system operation to apply standard system theory input functions and to use the detailed dynamic system responses to parameterize a model of sufficient quality for forward design. This allows the facile optimization of a 10-enzyme cascade reaction for fine chemical production purposes.

Experimental and numerical study of a printed circuit heat exchanger

Printed circuit heat exchangers (PCHEs) are promising to be employed in very-high-temperature gas-cooled reactors (VHTRs) due to their high robustness for high-temperature, high-pressure applications and high compactness. PCHEs typically serve as intermediate heat exchangers (IHXs) that isolate the secondary loop from the reactor’s primary system and hence must be sufficiently robust to maintain the system integrity during normal and off-normal conditions. In addition, the performance of the PCHE-type IHX could considerably affect the nuclear power plant overall operation since any transients on the secondary side would be propagated back to the reactor’s primary coolant system via the IHX. It is therefore imperative to understand how the PCHE would dynamically respond to a variety of transients. In the current study, experiments were first conducted to examine the steady-state thermal performance of a reduced-scale straight-channel PCHE. A dynamic model benchmarked in a previous study was then used to predict the steady-state and transient behavior of the PCHE. The steady-state temperature profiles of the working fluids on both the hot and cold sides and in the solid plates of the heat exchanger were obtained, which served as the initial condition for the transient simulations. The detailed dynamic response of the straight-channel PCHE, subject to inlet temperature variations, helium mass flow variations, and combinations of the two, was simulated and analyzed. In addition, two sets of transient tests, one for helium inlet temperature increase and the other for helium inlet temperature decrease, were experimentally carried out to assess the applicability of the dynamic model. Comparisons of the numerical results with the experimental data show that the dynamic model is successful in predicting the experimental transient scenarios. Although difference was observed between the numerical results and experimental data, the comparisons suggest that the numerical solutions are sufficiently accurate and conservative and that the applicability of the dynamic model proposed for predicting the steady-state and transient performance of the straight-channel PCHE has been confirmed. Furthermore, both the numerical and experimental studies provide insights into the dynamic performance of the PCHE.

Seismic response and stability of underground rock caverns: a case study of Baihetan underground cavern complex

The seismic stability of the underground cavern complex, which houses the Baihetan hydropower plant in Yunnan Province, China, currently the world’s 2nd largest underground rock cavern group, is studied in this article. A preliminary performance-based seismic assessment approach specified for underground rock caverns is firstly proposed. The seismic performance objectives are classified. Reference earthquake motions are specified with the determination of the seismic variables. Detailed dynamic response analyses (Method 2B) are conducted based on the parameters given by the cyclic dynamic loading tests with medium strain rate. The seismic response of acceleration, stress, displacement and failure zones are studied. In addition, the seismic spectrum characteristics are analysed with a newly introduced wavelet packet technique. The mechanism of the support measures for seismic stability is also discussed. The assessment for seismic performance of the underground cavern complex is obtained by integrating these results. Serviceability objective of the underground cavern complex under operating basis earthquake may be satisfied, and the safety objective be feasible but with the presence of the proposed reinforcement system. The seismic isolation design is preferred, yet not necessary. And if any seismic isolation design is to be adopted, the frequency absorption range of the isolation material is expected to be 1–4 Hz.

Experimental and numerical dynamic investigation of an energy efficient liquid cooled chiller-less data center test facility

Data centers cooling systems constitute a large portion of the total data center energy consumption, therefore, many new cooling technologies have been developed to improve the energy efficiency. A data center cooling facility proposed by IBM is constructed to reduce cooling energy use to less than 5% of the total Information Technology energy use through a combination of warm water cooling servers and liquid-side economization. In this work, several experimental tests are conducted on this cooling test facility and the results are reported and analyzed. The detailed dynamic responses of each component used in the cooling infrastructure design are investigated using the test results combined with simulation results. The experimental tests designed and the corresponding analyses present a brief understanding of the dynamic performance of this data center test facility, including both inside and outside of the computer room. A transient effectiveness method is introduced and used to analyze the heat exchangers performance. The work presented provides an analyzing method which can be used to investigate and characterize the transient performance of heat exchangers which are working in the cooling and heating systems with multiple coupled heat transfer loops, in which multiple heat exchanger units are used.

Dynamics of the hysteretic voltage-induced torsional strain in tantalum trisulfide

We have studied how the hysteretic voltage-induced torsional strain, associated withcharge-density-wave (CDW) depinning, in orthorhombic tantalum trisulfide depends onsquare-wave and triangle-wave voltages of different frequencies and amplitudes. Thestrains are measured by placing the sample, with a wire glued to the center as atransducer, in a radio frequency cavity and measuring the modulated response of thecavity. From the triangle waves, we map out the time dependence of the hysteresisloops, and find that the hysteresis loops broaden for waves with periods less than30 s. The square-wave response shows that the dynamic responses to positive andnegative voltages can be quite different. The overall frequency dependence isrelaxational, but with multiple relaxation times which typically decrease withincreasing voltage. The detailed dynamic response is very sample dependent,suggesting that it depends in detail on interactions of the CDW with sampledefects.

A study on dynamic response of cable-seabed interaction

A numerical method is developed to investigate the dynamic response of cable-seabed interaction in this paper. The motion of cable is described by the Lumped Parameter Method, while the seabed, unlike the prevailing simplified model of elastic foundation, is modeled as an irregular continuous rigid surface with rebound and friction existing, and the forces exerted by the seabed consist of normal counterforce and isotropic tangential Coulomb friction resistance. To describe the detailed dynamic response, two coefficients are introduced by analogy with the theory of rigid body collision with friction. The cable-seabed kinematic and dynamic contact conditions are formulated subsequently, and are used to incorporate the seabed effect into the cable dynamics to produce a set of ordinary differential governing equations. In this paper, we employ 4th order Runge-Kutta method to solve these equations. Several simulation cases are presented to illustrate the seabed effect. The results show that friction and impact have a prominent influence on the statics and dynamics of the cable.

3차원 축류압축기 블레이드의 유체유발진동 해석

In this study, flow-induced vibration(FIV) analyses have been conducted for a 3D compressor blade model. Advanced computational analysis system based on computational fluid dynamics(CFD) and computational structural dynamics(CSD) has been developed in order to investigate detailed dynamic responses of designed compressor blades. Fluid domains are modeled using the computational grid system with local grid deforming and remeshing techniques. Reynolds-averaged Navier-Stokes equations with <TEX>$\kappa-\epsilon$</TEX> turbulence model are solved for unsteady flow problems of the rotating compressor model. A fully implicit time marching scheme based on the Newmark direct integration method is used for computing the coupled aeroelastic governing equations of the 3D compressor blade for fluid-structure interaction(FSI) problems. Detailed dynamic responses and instantaneous pressure contours on the blade surfaces considering flow-separation effects are presented to show the multi-physical phenomenon of the rotating compressor blade.

Dynamic response of bridges to moving trains: A study on effects of random track irregularities and bridge skewness

This paper describes research undertaken to consider the dynamic responses of an existing railway bridge subjected to moving trains. The study investigated dynamic effects produced by different service trains, as well as the influence of random track irregularities and bridge skewness. This research was carried out using the dynamic bridge–train interaction (DBTI) model developed and previously verified by the authors. Generally, dynamic amplification of displacements was found to be moderate and compared favourably with recommendations of current design codes. The use of complex numerical models for bridge–train dynamics produced detailed dynamic responses; such results may be quite beneficial to bridge owners in the assessment of existing bridges which exhibit excessive dynamic responses. Random track irregularities were found to have minor effects on the dynamic amplification factors and bridge accelerations; however, lateral responses of the bridge were considerably affected by irregularities. Effects of irregularities were more pronounced in train responses; generally, the train responses increased with decreasing track profile quality. Bridge skewness was found to increase fundamental natural frequency of the bridge; this leads to a shift in the dynamic amplification factor towards higher speeds and alterations of its magnitude. Three-dimensional models were found necessary for accurate predicting of this response.

Implications of Design Assumptions on Capacity Estimates and Demand Predictions of Multispan Curved Bridges

The paper presents a detailed seismic performance assessment of a complex bridge designed as a reference application of modern codes for the Federal Highway Administration. The assessment utilizes state-of-the-art assessment tools and response metrics. The impact of design assumptions on the capacity estimates and demand predictions of the multispan curved bridge is investigated. The level of attention to detail is significantly higher than can be achieved in a mass parametric study of a population of bridges. The objective of in-depth assessment is achieved through investigation of the bridge using two models. The first represents the bridge as designed (including features assumed in the design process) while the second represents the bridge as built (actual expected characteristics). Three-dimensional detailed dynamic response simulations of the investigated bridge, including soil-structure interaction, are undertaken. The behavior of the as-designed bridge is investigated using two different analytical platforms for elastic and inelastic analysis, for the purposes of verification. A third idealization is adopted to investigate the as-built bridge’s behavior by realistically modeling bridge bearings, structural gaps, and materials. A comprehensive list of local and global, action and deformation performance indicators, including bearing slippage and inter-segment collision, are selected to monitor the response to earthquake ground motion. The comparative study has indicated that the lateral capacity and dynamic characteristics of the as-designed bridge are significantly different from the as-built bridge’s behavior. The potential of pushover analysis in identifying structural deficiencies, estimating capacities, and providing insight into the pertinent limit state criteria is demonstrated. Comparison of seismic demand with available capacity shows that seemingly conservative design assumptions, such as ignoring friction at the bearings, may lead to an erroneous and potentially nonconservative response expectation. The recommendations assist be given to design engineers seeking to achieve realistic predictions of seismic behavior and thus contribute to uncertainty reduction in the ensuing design.

Dynamic compression of highly compressible porous media with application to snow compaction

A new experimental and theoretical approach is presented to examine the dynamic lift forces that are generated in the compression of both fresh powder snow and wind-packed snow. At typical skiing velocities of 10 to 30ms the duration of contact of a ski or snowboard with the snow will vary from 0.05 to 0.2s depending on the length of the planing surface and its speed. No one, to our knowledge, has previously measured the dynamic behaviour of snow on such a short time scale and, thus, there are no existing measurements of the excess pore pressure that can build-up in snow on this time scale. Using a novel porous cylinder–piston apparatus, we have measured the excess pore pressure that would build-up beneath the piston surface and have also measured its subsequent decay due to the venting of the air from the snow at the porous wall of the cylinder. In further experiments, in which the air is slowly and deliberately drained to avoid a build-up in pore pressure, we have been able to separate out the force exerted by the ice crystal phase as a function of its instantaneous deformation. A theoretical model for the pore pressure relaxation in the porous cylinder is then developed using consolidation theory. Dramatically different dynamic behaviour is observed for two different snow types, one (wind-packed) giving a steady continuous relaxation of the excess pore pressure and the other (fresh powder) leading to a piston rebound with negative pore pressure. A feature of the rebound is the apparent debonding of sintered ice crystals after maximum compression. This behaviour is described well by introducing a debonding coefficient where the debonding force is proportional to the expansion velocity of the medium. The experimental and theoretical approach presented herein and the previous generalized lubrication theory for compressible porous media, have laid the foundation for understanding the detailed dynamic response of soft porous layers to rapid deformation.

Nonlinear Aeroelastic Simulation of a Full-Span Aircraft with Oscillating Control Surfaces

In this paper, the transonic and low-supersonic aeroelastic behavior of the generic fighter model was investigated in the time domain. The simulation of flutter flight test using forced harmonic motion of control surfaces including inertial coupling effects was conducted at the various conditions. The detailed dynamic aeroelastic responses are computed using a coupled time-marching method based on the effective computational structural dynamic and computational fluid dynamics techniques. The nonlinear aerodynamic effects due to an existing shock wave on the lifting surfaces were considered using a transonic small disturbance equation. A modal model obtained by a free vibration analysis was used for the structural model. The relations between the computed flutter boundary and the simulation results of the responses using the harmonic motions of control surfaces at various conditions were investigated.

Development of an optimised, standard-compliant procedure to calculate sound transmission loss: numerical measurements

Availability of low-frequency characteristics of sound insulating elements is required in order to achieve efficient control of noise sources and reduced level of annoyance in the low-frequency range. Previous work by the author has addressed the problem of designing an enhanced calculation environment for the estimation of sound Transmission Loss (TL). In this work, numerical prediction of TL of sound insulating structures is performed using a procedure, which is in compliance with the ISO recommendations for acoustic measurements. The room-structure-room finite element representation, employed to solve sound propagation and sound-structure interaction problems, as well as the dynamic coupling of and the sound energy propagation through successive air-structure layers are investigated. Several cases of single-layered plain structures of common sound insulating materials such as steel, glass and aluminium with various thickness values are modelled and the calculated TL is compared with published experimental results. It is shown that although the detailed dynamic response of the structures is not accurately predicted due to uncertain parameters, such as the test-specimens dimension and vaguely known boundary conditions, the octave band averaged TL is sufficiently predicted for the majority of the tested materials. Extension of the method to multi-layered structures is attempted and discrepancies at low frequencies are depicted. Finally, the effect of poor mode distribution of the measurement rooms upon the estimated TL is examined in focus. Comparison is performed between TL values calculated with typical and intensely modified transmission rooms. The low-frequency improvement on measurements, when the second ones are used, is demonstrated.

Angle-of-Attack Effect on Transonic/Supersonic Aeroelasticity of Wing-Box Model

N understanding of the aeroelastic behavior of e ight vehicles in the transonic and low-supersonic regimes is of great importance for e ight safety. The e utter boundary in this regime varies with changes in the initial angle of attack. Aeroelastic analyses and experiments on the effect of initial angle of attack have been performed previously. Early studies of the two-degree-of freedom airfoil system were performed using the HYTRAN2 (Ref. 1) and an Euler code. 2 For a three-dimensional wing at high angles of attack in incompressible e ow, there is the work by Strganac and Mook. 3 In their paper, using the unsteady vortex-lattice method, the equations of motion were integrated, considering the nonlinear effects of the separated vortex. Yates et al. 4 analyzed the effect of angle of attack on a large aspect ratio transport-type wing with a supercritical airfoil, using a modie ed strip analysis employing wind-tunnel steady aerodynamic data. Also, the CAP-TSD code 5 has been applied to the active e exible wing wind-tunnel model to investigate static and dynamic aeroelastic behaviors below Mach 0.95. These studiesprovideagoodfoundationforunderstandinginitialangle-ofattack effects, both theoretically and practically, and motivated by this,wewillexamineindetailtheeffectofbothpositiveandnegative angles of attack on a typical e ghter wing-box model with an asymmetric airfoil in the transonic and low-supersonic e ow regions. The critical effect of a negative angle of attack and unusual frequency changes due to the effect of normal shocks are presented. The computed steady aerodynamic results for rigid and deformed shapes of the model are presented and compared. Also, detailed dynamic aeroelastic responses are computed using a coupled time-marching method based on the effective computational structural dynamic (CSD) and computational e uid dynamic (CFD) techniques, 6 which are similar to those used in Ref. 5. CSD analyses for the wing-box model have beenperformed using MSC/NASTRAN.Thevariations

On the importance of normal vibrations in modeling of stick slip in rock sliding

In this paper, numerical studies of friction‐induced dynamic instabilities, particular, stick‐slip sliding of rocks, are presented. Of special interest is the importance of normal compliance of the interface and associated normal vibrations in the occurrence of dynamic instabilities. To clearly illustrate this importance, the interface is represented by the Oden‐Martins constitutive model which does not exhibit explicit velocity or slip dependence of friction. This friction model is utilized in the context of a rather simple rigid body model to perform numerical studies representative of granite blocks in relative sliding at very slow overall velocities. The model represents a common experimental setting that has been used to study stick slip of sliding rock blocks. To capture the stick‐slip phenomenon the detailed dynamic response of this system is modeled numerically. These studies indicate the importance of the normal compliance of the interface on the stability of sliding. In particular, dynamic coupling of the degrees of freedom contributes to dynamic instability of the system and can cause stick‐slip motion. Both stable and unstable sliding are predicted and examined.