Nonlinear Dynamic Interactions Research Articles

On the measurement of the nonlinear dynamics of sandwich sector plate surrounded by the auxetic concrete foundation: Introducing a machine learning algorithm for nonlinear problems

The measurement of the nonlinear dynamics of sandwich rotary sector plates is crucial for measurement engineers as it enables the precise analysis and understanding of the behavior of advanced composite structures under dynamic conditions. These measurements help in identifying and mitigating potential issues related to vibration, stability, and fatigue, which are critical in industries like aerospace, automotive, and civil engineering. Accurate data on nonlinear dynamics aids in the optimization of design, enhancing performance, durability, and safety. Furthermore, it supports the development of predictive maintenance strategies, reducing downtime and operational costs, and contributing to the advancement of engineering materials and techniques. So, in the current work, for the first time, nonlinear dynamics of sandwich rotary sector plate via a mathematical modeling and machine learning algorithm is presented. First, due to a lack of information on the nonlinear dynamics of sandwich rotary sector plates, a dataset for training, testing, and validating the machine learning algorithm is presented. For this purpose, using Hamilton’s principle, Von-Karman nonlinearity, and first-order shear deformation theory (FSDT), the nonlinear governing equations are obtained. Also, due to increasing stiffness and stability, an auxetic concrete foundation covers the sandwich structure. After that using the two-dimensional generalized differential quadrature method (GDQM) and Newmark’s time integration method (NTIM), the nonlinear equations are solved. This research provides valuable insights for engineers in designing advanced composite structures with improved dynamic properties. The results also contribute to the broader understanding of nonlinear dynamic interactions in complex material systems, paving the way for innovative applications in various engineering fields.

Seismic performance of underground subway station structure near the strike-slip fault by the developed hybrid IBE-FEM method

To investigate the influence of strike-slip faults on the seismic responses of underground structures, based on the single-layer potential theory of the boundary element concept and the fault-site-underground structure coupling mechanisms, we proposed a hybrid indirect boundary element-finite element numerical method (IBE-FEM) to simulate efficiently the seismic response of the entire process from the near seismogenic-fault to the underground structure. Initially, based on the kinematic finite-fault model, the seismic wavefield of an overlying soft-soil sedimentary-layer site subjected to strike-slip faults with source parameters, such as rupture velocity, dip-angle, and upper-boundary burial depth, was solved using the indirect boundary element method (IBE). Subsequently, the accuracy of the IBE-FEM in predicting the site seismic wavefield was verified. On this basis, the influence laws of the source parameters and the fault-site coupling effects on the seismic performance of the structure were preliminarily investigated by establishing a numerical model of the nonlinear dynamic interaction system of a soil-underground structure. The results showed that the seismic responses of the underground structure located in the footwall far-fault region were more strongly affected by variations in the rupture velocity. The lateral deformation of the structure under the rupture velocity condition of bedrock shear-wave velocity (vs) was dramatically increased compared to sub-vs, and the lowest amplification is 59 %. Furthermore, the hanging wall and seismic damage concentration effects significantly impacted the structure located in a strike-slip fault site with a shallow-burial. This study provides a reliable and efficient analytical method for the seismic design of underground structures in complex near-fault regions.

Seismic response of tripod suction bucket foundation for offshore wind turbine considering multidirectional earthquake loads

Tripod suction buckets offer several advantages as offshore wind turbine (OWT) foundations, including cost-effective installation, high stability, and resistance to overturning. In seismically active regions, OWTs experience horizontal and vertical directions seismic excitations. This study employed an advanced three-dimensional nonlinear finite element analysis to investigate the influence of vertical seismic motions on the dynamic behavior of tripod bucket foundations installed in nonhomogeneous clay deposits. By adopting a simple kinematic hardening model to capture the foundation-soil nonlinear dynamic interaction, parametric analyses were conducted to study the effect of vertical seismic motions, considering several earthquake types and undrained shear strengths of the clay deposit. The results show that the influence of the vertical seismic motion on the dynamic response and deformation of the nacelle depends on the dominant frequency of the vertical seismic motion and the overturning resistance capacity of the OWT in different horizontal directions. The deformation mechanisms of an OWT vary with the strengths of the clay deposits. Based on these analyses, this study offers insights into the influence of vertical seismic motions on the dynamic response of tripod suction bucket foundations.

Reconciling the efficacy and effectiveness of masking on epidemic outcomes.

During the COVID-19 pandemic, mask wearing in public settings has been a key control measure. However, the reported effectiveness of masking has been much lower than laboratory measures of efficacy, leading to doubts on the utility of masking. Here, we develop an agent-based model that comprehensively accounts for individual masking behaviours and infectious disease dynamics, and test the impact of masking on epidemic outcomes. Using realistic inputs of mask efficacy and contact data at the individual level, the model reproduces the lower effectiveness as reported in randomized controlled trials. Model results demonstrate that transmission within households, where masks are rarely used, can substantially lower effectiveness, and reveal the interaction of nonlinear epidemic dynamics, control measures and potential measurement biases. Overall, model results show that, at the individual level, consistent masking can reduce the risk of first infection and, over time, reduce the frequency of repeated infection. At the population level, masking can provide direct protection to mask wearers, as well as indirect protection to non-wearers, collectively reducing epidemic intensity. These findings suggest it is prudent for individuals to use masks during an epidemic, and for policymakers to recognize the less-than-ideal effectiveness of masking when devising public health interventions.

Generating synthetic population for simulating the spatiotemporal dynamics of epidemics.

Agent-based models have gained traction in exploring the intricate processes governing the spread of infectious diseases, particularly due to their proficiency in capturing nonlinear interaction dynamics. The fidelity of agent-based models in replicating real-world epidemic scenarios hinges on the accurate portrayal of both population-wide and individual-level interactions. In situations where comprehensive population data are lacking, synthetic populations serve as a vital input to agent-based models, approximating real-world demographic structures. While some current population synthesizers consider the structural relationships among agents from the same household, there remains room for refinement in this domain, which could potentially introduce biases in subsequent disease transmission simulations. In response, this study unveils a novel methodology for generating synthetic populations tailored for infectious disease transmission simulations. By integrating insights from microsample-derived household structures, we employ a heuristic combinatorial optimizer to recalibrate these structures, subsequently yielding synthetic populations that faithfully represent agent structural relationships. Implementing this technique, we successfully generated a spatially-explicit synthetic population encompassing over 17 million agents for Shenzhen, China. The findings affirm the method's efficacy in delineating the inherent statistical structural relationship patterns, aligning well with demographic benchmarks at both city and subzone tiers. Moreover, when assessed against a stochastic agent-based Susceptible-Exposed-Infectious-Recovered model, our results pinpointed that variations in population synthesizers can notably alter epidemic projections, influencing both the peak incidence rate and its onset.

Seismic fragility analysis of subway station structure subjected to sequence-type ground motions

As a critical urban infrastructure, the subway station damaged in an earthquake not only leads to interruption of underground transportation, but may also result in serious casualties and economic losses. The current seismic design of underground structures only considers the mainshock effects but ignores the potential hazards of aftershocks. However, most mainshocks are often followed by aftershocks in a short period of time. In the past earthquakes, it was reported that the mainshock-damaged engineering structures suffered more serious structural damage and even complete collapse when subjected to aftershocks before restoration. This paper proposes a framework for the development of seismic fragility curves of underground structures subjected to sequence-type ground motions. Finite element models of a two-story, three-span subway station considering nonlinear dynamic soil-structure interaction (SSI) was established in this study. A comprehensive assessment of the seismic performance of the subway station structure under the sequence-type ground motions was conducted on the SSI model. Both the mainshock-aftershock fragility analysis of the intact structure and the aftershock fragility analysis of the mainshock-damaged structures were performed by combining the traditional seismic probability demand model and the back-to-back mainshock-aftershock probability demand model. The numerical results indicated that the impact of aftershocks on the seismic performance of subway station structures cannot be ignored. The aftershock fragility of the structure is highly dependent on the mainshock-damaged state. The failure probability of a severely mainshock-damaged subway station structure is much higher in the aftershocks than structures in other damage states. Besides, the probability of the mainshock-damaged structure transferring to a more severe level of damage state increases with the increase of the intensity of aftershock motions. For the subway station under sequence-type ground motions, the transition probability of one severer level of damage state is greater than 40 % for the 1.0 g peak ground acceleration of aftershocks and the transition probability of more than two severer level of damage state is less than 10 %.

A System Dynamics Approach to Technological Learning Impact for the Cost Estimation of Solar Photovoltaics

Technological learning curve models have been continuously used to estimate the cost development of solar photovoltaics (PV) for climate mitigation targets over time. They can integrate several technical sources that influence the learning process. Yet, the accurate and realistic learning curve that reflects the cost estimations of PV development is still challenging to determine. To address this question, we develop four hypothetical-alternative learning curve models by proposing different combinations of technological learning sources, including both local and global technological experience and knowledge stock. We specifically adopt the system dynamics approach to focus on the non-linear relationship and dynamic interaction between the cost development and technological learning source. By applying this approach to Chinese PV systems, the results reveal that the suitability and accuracy of learning curve models for cost estimation are dependent on the development stages of PV systems. At each stage, different models exhibit different levels of closure in cost estimation. Furthermore, our analysis underscores the critical role of incorporating global technical sources into learning curve models.

Computational evaluation of flight performance of flapping-wing nano air vehicles using hierarchical coupling of nonlinear dynamic and fluid-structure interaction analyses

This study endeavours to introduce an inventive hierarchical coupling methodology for evaluating the flight capabilities of polymer micromachined flapping-wing nano air vehicles (FWNAVs) using advanced computational tools. Furthermore, our objective is to provide a practical demonstration of FWNAVs in both tethered and airborne scenarios. These dual objectives represent the distinctive and pioneering aspects of this research. Such FWNAVs, which are insect-inspired robots, have a 2.5-dimensional structure. An FWNAV comprises a micro piezoelectric drive system and a pair of micro thin flexible wings. The drive system includes a micro transmission and a piezoelectric bimorph actuator. The flight performance of the designed FWNAV is evaluated using a hierarchical coupling approach, where the whole system is decomposed into a micro wing and a micro piezoelectric drive system. The coupling between these parts is modelled as one-way coupling and that between the micro wings and the surrounding air is modelled as strong coupling. In the one-way coupling analysis, nonlinear structural dynamic analysis is conducted for the micro piezoelectric drive system, where the dynamic response is transmitted to the micro wings via the Dirichlet boundary condition. In the strong coupling analysis, strongly coupled fluid-structure interaction analysis is conducted for the micro wings and the surrounding air to consider their strong coupling. The optimisation of flight performance is conducted using fluid-structure interaction analysis to achieve sufficient lift force to support the weight of an FWNAV. The design of a tethered and flyable FWNAV with a size of 10 mm or smaller is demonstrated. This FWNAV can be easily fabricated using polymer micromachining.

Reliability of super-slope bridge-rack system on rack railway

ABSTRACT During the operation of rack railway on super-slope bridges (especially under temperature load), structural deformation of bridge-end is much larger than that of rack due to the difference of structural continuity between bridge and rack, which greatly increases local stress in rack, damages rack and fastener, and seriously threatens the operation reliability. To investigate the reliability of rack caused by temperature load and nonlinear dynamic interaction between super-slope bridge and rack, a detailed vehicle-rack(rail)-bridge coupled dynamic model is established with consideration of nonlinear dynamic meshing behaviour of gear-rack system and nonlinear dynamic contact behaviour of wheel-rail system. Then a field test is performed to obtain the basis dynamic behaviour of rack railway and validate the established numerical model. On this basis, the effects of temperature load, gear-rack meshing behaviour and wheel-rail contact behaviour on deformation and internal stress of rack-bridge system are investigated. Finally, the method to guarantee the structural reliability of rack railway on super-slope bridge is proposed. Results show that rack deformation nearby bridge gap is highly inconsistent with bridge deformation subject to different loads, and the internal stresses in rack and bolt exceed limit values written in relevant code, which seriously threatens the reliability of the rack structure. The maximum rack stress is 898 MPa, which exceeds the tensile strength of rack. The maximum shear stresses of bolts between fastener and rack and between fastener and sleeper are 1510 MPa and 656 MPa respectively, which exceed the shear strength of bolts. According to the calculation results in this paper, elastic fastener is suggested to be used to connect rack and sleeper, which can effectively reduce stress in rack and bolt, and improve the reliability of the rack structure.

Three-step staircase-like pulses generation in a butterfly-shaped mode-locked fiber laser

We experimentally observed three-step staircase-like pulses (TSSLP) delivered from a butterfly-shaped mode-locked fiber laser An integrated twin nonlinear amplifying loop mirrors (NALM) incorporating highly nonlinear fibers (HNLF 65, 52 m) acts as a homogeneous hybrid-like artificial saturable absorber (HH-SA). With the most available pump power, the obtained sub-stairs in TSSLP with 10.06, 9.61, 12.59 ns durations and 0.33, 3.46 and 5.38 W peak intensities at 1.23 MHz, respectively. The second-peak can be tuned from 0.1 to 3.46 W while the third-duration ranging from 9.86 to 14.12 ns. The achievements reveal that the proposed HH-SA scheme creates effective intensity discrimination while enjoying more consistent properties. It provides more flexible transfer curve and pulse-shaping mechanism, with novel features to meet the requirements of various engineering customizations. The versatility and stability of the HH-SA device, make it highly attractive as a stable platform for studying new pulses together with nonlinear interaction dynamics in fundamental physics.

The Effect of Soil Liquefaction and Lateral Spreading to the Seismic Vulnerability of RC Frame Buildings Considering SSI

ABSTRACT Evidence of past earthquakes highlighted the seismic vulnerability to buildings due to soil liquefaction and lateral spreading phenomena. Damage to buildings on a liquefiable site, especially on a gently sloping site, can be severe. The liquefied soil can undergo permanent lateral ground displacements as large as several meters in some cases, which can be severely disastrous to buildings. Recent physical tests and effective stress analyses of nonlinear dynamic soil-structure interaction (SSI) proved that simplified empirical processes are often improper for evaluating liquefaction-induced building settlements. A better understanding of the SSI effects is also essential in cases where the underlying soil is susceptible to liquefaction. In this respect, the interaction of the earthquake excitation and ground failure (i.e. soil liquefaction and lateral spreading) for buildings considering SSI is investigated herein. Typical low-code reinforced concrete (RC) frame buildings of different heights with shallow spread footings on liquefiable level-ground or sloping soils subjected to ground shaking are considered. The direct SSI approach is implemented. Predictive relationships are established between the maximum normalized differential displacements (horizontal or settlement) and the permanent ground displacement (PGD) vector at the level of foundation for low-code RC frame buildings with shallow spread footings on soils with high liquefaction potential subjected to ground shaking. Finally, vulnerability is expressed in terms of fragility and vulnerability curves as well as in terms of fragility surfaces as a function of two intensity measures.

Seismic performance and fragility of two-story and three-span underground structures using a random forest model and a new damage description method

This paper proposes a new method for evaluating the seismic performance and fragility of large underground structures. A typical underground subway station consisting of a two-story and three-span structure was used as the research subject. Considering the variation of sites and the uncertainty of input ground motions, we developed a finite element model of a nonlinear dynamic soil-underground structure interaction system. Based on the incremental dynamic analysis method, the nonlinear seismic responses of the subway station structure were calculated for 900 cases. Python (software) was used to accelerate the processing of the large number of numerical simulation data. Based on the seismic damage characteristics of an underground structure, this paper proposes a new concept of average seismic damage value to evaluate the damage condition of the underground structure to overcome the inadequacies induced by an expert’s intuitive judgment. Meanwhile, the random forest prediction model was adopted to predict the seismic performance levels (SPLs) of the underground structure, and a non-parametric test was performed to verify the correlation between the degree of seismic damage and the inter-story drift ratios (IDR) of the large underground structure. This proved that the IDR could describe the seismic damage of shallow-buried underground structures; we advanced a precise quantification system of the SPL for shallow-buried subway station structures with two-story and three-span using probability statistics. The peak ground velocity (PGV) is more suitable than the peak ground acceleration (PGA) for use as the seismic intensity measure (IM) for large underground structures when the stiffness of the soil foundation becomes soft. In addition, the seismic fragility curves of the shallow-buried subway station structure were constructed and analyzed using the developed quantification system for the SPL.

Experimental investigation of gear rattle and nonlinear dynamic interaction in a dual-clutch transmission

Dual-clutch transmissions (DCT) having high efficiency and powershift are widely used in passenger cars thanks to the dual-clutch and preselection strategies. However, the dual-clutch transmission gear rattle behaviour still needs to be fully discovered, especially the influence caused by different preselection strategies. In this regard, the gear rattle sensitivity and dynamic evolution of the geartrain in a DCT were experimentally investigated on a rattle test bench and vehicle powertrain. The rattle response and instantaneous speed of all speed gears potentially contributing to the overall rattle are measured. The measured results from the DCT were compared with a similar structure six-speed manual transmission to depict its characteristics. Moreover, a multi-degree-of-freedom nonlinear torsional model was established to gain the nonlinear dynamic response along with the rising torsional irregularities; the model considers the crucial parameters affecting rattle behaviour. Two qualitative criteria were consequently given based on the numerical results and the law of the gear motion.The experimental results on the rattle test bench show that the DCT rattle behaviour varies with different preselected gears and is quite different from the manual transmission. The rattle sensitivity curves disclose an abrupt jump-up phenomenon when the excitation level reaches a certain level. The nominal input speed, preselection gear and lay-shaft configuration considerably determine the excitation level and amplitude increase of the jump-up on the rattle response. Based on the proposed qualitative criteria, a strongly nonlinear dynamic response is observed in the loaded gear pair under preselection conditions and deteriorates the rattle noise. A considerable dynamic interaction between active and passive sub-gearboxes is found. The appearance of the harmonics of the excitation frequency on the active input shaft that generates the high impact amplitude and density contributes to the jump-up and high vibration response on the rattle sensitivity. Finally, vehicle experiments reproduce the rattle jump-up and dynamic torsional interaction in the DCT powertrain are confirmed.

Response of a high-speed train travelling over a long and high-pier viaduct during moderate earthquakes

This contribution presents the results of numerical simulations in which a high-pier viaduct under lateral and vertical non-stationary spatially variable seismic ground motions is crossed by an articulated high-speed train at several speeds. The spectral representation method is employed to generate the required number of acceleration time-history series at each support location of the railway viaduct studied. Wave passage, local soil conditions and loss of coherency effects have been accounted for in the simulated ground-motion time histories, with several peak ground accelerations. Train and bridge responses have been obtained by means of a non-linear dynamic interaction multibody and finite element model. An analysis of train running safety indices has been carried out. The properties of earthquakes and train speeds which may cause problems to traffic safety are detailed, as is the train derailment probability. The numerical simulation outcomes show that it is not safe for the train to travel over the studied viaduct in earthquakes with peak ground acceleration equal to 0.03 g and for train speeds above 280 km/h.

Improving performance of a nonlinear absorber applied to a variable length pendulum using surrogate optimization

The paper investigates a nonlinear vibration mitigation strategy of a variable length pendulum subjected to a harmonic external excitation. A nonlinear absorber in a form of a tri-pendulum system is used to reduce the response of the primary pendulum. Thus, the paper investigates a non-stationary problem of nonlinear vibration mitigation of the primary pendulum using another nonlinear passive pendulum absorber. Due to genuine interest in capturing the nonlinear dynamic interaction, the paper numerically studies the performance of the primary mass and absorber, first, by constructing 2D maps in the unrestrained parametric space, which demonstrate the qualitative behavior of the system. Then, the surrogate optimization technique is used to tune the absorber’s parameters within a given bounded set of parameters’ values. The optimization is conducted based on a priori known reeling speed or acceleration/deceleration of the primary pendulum, thereby completely removing the need for acquiring a current system states essential for active feedback control. The obtained numerical results validate the proposed strategy and demonstrate high performance of the nonlinear passive absorber when it is properly tuned.

Fully nonlinear numerical investigations on the dynamics of fluid resonance between multiple bodies in close proximity

Two-dimensional wave-induced fluid oscillations in two narrow gaps are numerically investigated in the time domain. The arbitrary-Lagrangian–Eulerian finite element model for free-surface flow problems is implemented based on the fully nonlinear potential flow theory. The aim of this study is to study the dynamic evolutions of gap resonance problems with focusing on both the initial transient and the final quasi-steady states, especially for the piston-mode oscillations of fluid bulk in multiple gaps that generally involve multiple response components and the nonlinear dynamic interactions between them. The transient and quasi-steady responses are examined through amplitude and phase analyses. The radiation damping and the time-dependent period-averaged phase adjustment are demonstrated to play significant roles in establishing the dynamic equilibrium process from the transient state to the quasi-steady state. The characteristics of the intrinsic synchronization modes of the quasi-steady oscillations allow us to derive the simplified formulas to predict the resonant and anti-resonant frequencies of the two-gaps system (two degrees-of-freedom) based on a simplified model of one degree-of-freedom. The predictive formulas provide useful insights into the dependence of resonant/anti-resonant frequencies on the relevant geometries of floating bodies. Significant nonlinear hardening stiffness behaviors of fluid responses between multiple bodies in close proximity are further demonstrated by different incident wave amplitudes. The effects of incident wave amplitudes on the amplitudes of responses and higher order harmonics are found to be highly dependent on the frequency bands. The contributions of the higher-order harmonics on the overall responses are explained utilizing the Fourier transformations analysis.

Cardiorespiratory Coordination in Collegiate Rowing: A Network Approach to Cardiorespiratory Exercise Testing.

Collegiate rowing performance is often assessed by a cardiopulmonary exercise test (CPET). Rowers’ on-water performance involves non-linear dynamic interactions and synergetic reconfigurations of the cardiorespiratory system. Cardiorespiratory coordination (CRC) method measures the co-variation among cardiorespiratory variables. Novice (n = 9) vs. Intermediate (n = 9) rowers’ CRC (H0: Novice CRC = Intermediate CRC; HA: Novice CRC < Intermediate CRC) was evaluated through principal components analysis (PCA). A female NCAA Division II team (N = 18) grouped based on their off-water performance on 6000 m time trial. Rowers completed a customized CPET to exhaustion and a variety of cardiorespiratory values were recorded. The number of principal components (PCs) and respective PC eigenvalues per group were computed on SPSS vs28. Intermediate (77%) and Novice (33%) groups showed one PC1. Novice group formed an added PC2 due to the shift of expired fraction of oxygen or, alternatively, heart rate/ventilation, from the PC1 cluster of examined variables. Intermediate rowers presented a higher degree of CRC, possible due to their increased ability to utilize the bicarbonate buffering system during the CPET. CRC may be an alternative measure to assess aerobic fitness providing insights to the complex cardiorespiratory interactions involved in rowing during a CPET.

Controlling species densities in structurally perturbed intransitive cycles with higher-order interactions.

The persistence of biodiversity of species is a challenging proposition in ecological communities in the face of Darwinian selection. The present article investigates beyond the pairwise competitive interactions and provides a novel perspective for understanding the influence of higher-order interactions on the evolution of social phenotypes. Our simple model yields a prosperous outlook to demonstrate the impact of perturbations on intransitive competitive higher-order interactions. Using a mathematical technique, we show how alone the perturbed interaction network can quickly determine the coexistence equilibrium of competing species instead of solving a large system of ordinary differential equations. It is possible to split the system into multiple feasible cluster states depending on the number of perturbations. Our analysis also reveals that the ratio between the unperturbed and perturbed species is inversely proportional to the amount of employed perturbation. Our results suggest that nonlinear dynamical systems and interaction topologies can be interplayed to comprehend species' coexistence under adverse conditions. Particularly, our findings signify that less competition between two species increases their abundance and outperforms others.

Cardiorespiratory Coordination Among Intermediate And Novice Female Collegiate Rowers

Elite rowers present high levels of cardiorespiratory performance. Rowers’ on-water performance can be predicted by a cardiopulmonary exercise test (CPET) and related measured parameters such as maximum oxygen uptake test (VO2max), ventilation (VE), heart rate (HR), expired fraction of oxygen (FeO2) and carbon dioxide (FeCO2). However, such testing provides little information about the non-linear dynamic interactions during rowing and the qualitative synergetic reconfigurations between cardiovascular and respiratory systems to adjust to the individual rowing performance. Cardiorespiratory coordination (CRC) has been proposed as a method to measure the co-variation among cardiorespiratory variables during a CPET. PURPOSE: To measure and compare the CRC through principal components analysis (PCA) between intermediate (9) and novice (9) rowers. METHODS: Eighteen females, members of NCAA Division II team, participated based on their off-water performance on 6000 m time trial and training status (i.e., Intermediate vs, Novice) in a discontinuous incremental rowing ergometer test to exhaustion. A variety of cardiorespiratory values were recorded. VE, HR, FeO2, and FeCO2 values during the last two stages before volitional fatigue between intermediate and novice rowers were analyzed by PCA on SPSS vs28. The number of principal components (PCs) and the first PC eigenvalues were computed for each group. RESULTS: While 67% of participants in the intermediate group showed one PC, only 22% of the novice group displayed 1 single PC. The formation of an additional PC in N rowers was the result of the shift of FeCO2 from the PC1 cluster of variables. CONCLUSIONS: Intermediate rowers showed a trend towards lower number of PCs compared to novice rowers, reflecting a higher degree of CRC. These findings point toward a higher efficiency of cardiorespiratory function in intermediate rowers, potentially as a result of improved bicarbonate buffering efficiency during high-intensity exercise. Intermediate rowers presented better gas exchange and relied less on ventilation for a given oxygen consumption. CRC appears as a complementary measure to assess aerobic fitness as well as cardiorespiratory interactions and their response to exercise in rowing may be useful to coaches, athletes and other stakeholders.

Reduced T-shaped soil domain for nonlinear dynamic soil-bridge interaction analysis

The one-directional three-component wave propagation in a T-shaped soil domain (1DT-3C) is a numerical modeling technique, in a finite element scheme, to investigate dynamic soil-structure interaction (SSI) coupled with seismic site effects, under the assumption of vertical propagation of three-component seismic motion along a horizontal multilayered soil. A three-dimensional elasto-plastic model is adopted for soils, characterized using their shear modulus reduction curve.In this research, the 1DT-3C wave propagation modeling technique is proposed as an efficient tool for bridge design to take into account directly the spatial variability of seismic loading. This approach, in the preliminary phase of bridge study and design, allows the reduction of the soil domain and the easier definition of boundary conditions, using geotechnical parameters obtained with only one borehole investigation for each pier. This leads to a gain in modeling and computational time.