Vertical Contact Forces Research Articles

Dynamic responses of the high-speed train with polygonal wheels considering gear transmissions

To examine the influence of polygonal wheels on the dynamic responses of high-speed train, a vehicle-track dynamics model was developed. This model incorporated gear transmissions using multibody dynamics methodology and gear dynamics theory. The effect of gear transmissions on the dynamic responses of the high-speed train was evaluated by comparing the results of the developed model with those of a non-geared traditional model. The dynamic responses of the train were studied by examining the combined effects of wheel polygonal excitation and time-varying mesh stiffness excitation. The results indicated that the vertical wheel-rail contact force and vibration amplitude of the model with polygonal wheels were larger than those of the normal model. Similarly, the geared transmission model exhibited greater contact force and vibration amplitude compared to the non-geared transmission model, attributed to the increased excitation. The evolution of the wheel polygon’s order and wear depth could significantly increase the vertical wheel-rail contact force and the wheel load reduction rate. The safety limits for wheel polygon order and wear depth were established. The model with gear transmissions is more closely aligned with the actual situation and exhibits higher safety performance, providing valuable reference for wheel turning.

Experimental and numerical study on mechanical properties of sand-contaminated ballast aggregates in confined condition

This study investigates the impact of sand contamination on the mechanical properties of railway ballasted tracks in confined condition. A combination of experimental confined uniaxial compression tests and discrete element method (DEM) simulations was employed. The experiments assessed the bulk density and elastic modulus of ballast aggregates, while the DEM simulations focused on sand movement, coordination numbers, and contact forces to elucidate the mesoscopic behavior. Findings from both experiments and simulations consistently demonstrate that sand contamination linearly increases the bulk density and causes a non-linear increase in the elastic modulus of ballast aggregates. With increasing degrees of sand contamination under vertical loading, both coordination numbers and contact forces are reduced. Sand intrusion initially leads to an uneven distribution of sand grains, primarily in the lower layer of the ballast aggregate; however, this distribution becomes more uniform when contamination exceeds 62.5%. The presence of sand particles diminishes the contact forces between ballast particles, thereby escalating the challenges associated with maintenance and repair.

Numerical study on the influence of cemented components on the mechanical properties of Xiyu Conglomerate

Xiyu Conglomerate is a common type of weakly cemented gravel stone formation found in northwestern China. This material is mainly composed of mud, mud–calcium, and calcium cement, possessing mechanical properties that are superior to those of soils but significantly weaker than those of rocks. Assessing these properties is crucial in ensuring the successful implementation of hydraulic engineering projects involving this material. This work establishes a microscale contact bonding model with a mud–calcium transition by surveying Xiyu Conglomerate’s material composition in a typical engineering area. The particle flow code method is used to investigate the influence of cemented materials on the mechanical properties of the conglomerate. After appropriate model calibration, numerical results show that the difference between the vertical and lateral contact forces becomes increasingly significant as the proportion of mud cement decreases and the content of calcium cement increases. The bond breakage process within the cemented material can be divided into three stages: no bond breakage, rapid bond breakage, and differential bond breakage development. When the mud cement content exceeds 50 %, the characteristics tend toward a soil-like behavior, while it resembles a soft rock behavior if the calcium cement content exceeds 50 %. Mud cement connects particles internally, whereas calcium cement strengthens the structure, both contributing to the randomness, heterogeneity, and discontinuity of Xiyu Conglomerate. The results can serve as a reference for future construction and engineering practices in the region.

Research on the traction characteristic evaluation of urban rail vehicles based on entropy weight TOPSIS

This paper aims to investigate the influence of different speed at the end of the constant power section of the traction characteristic curve (TCC) on the vehicle dynamic performance and evaluate the TCC. A dynamics co-simulation model is developed in SIMPACK and MATLAB for dynamic analysis of the urban rail vehicle (URV) under different traction characteristics. Then it is used to investigate how acceleration distance and vehicle dynamic performance varies with the speed at the end of the constant power section of the TCC under different starting torques. Moreover, the entropy weight TOPSIS method which is widely used to solve the multi-objective decision-making problem is chosen to evaluate the traction characteristics based on various dynamic performance indexes over 25 test sections and acceleration distance. The results show that under traction conditions, the starting torque has effects on the lateral and vertical accelerations of car body, lateral and vertical wheel-rail contact forces, derailment coefficient and wheel unloading factor. The higher the torque, the greater the value of each index, that means the poorer the vehicle ride characteristics and running safety. For a given starting torque, the dynamic performance indexes increase with the increase of the speed at the end of the constant power section from 50 km/h to 80 km/h during the vehicle speed-up process. The maximum growth rate of the lateral and vertical accelerations of car body, lateral and vertical wheel-rail contact forces are 17%, 8%, 8% and 2%, respectively, when the speed at the end of the constant power section increases from 50 km/h to 80 km/h. Last, the comprehensive evaluation of traction characteristics using entropy-weight TOPSIS method reveals when the starting torque is 800 [Formula: see text], 1000 [Formula: see text], 1200 [Formula: see text] and 1400 [Formula: see text], the corresponding optimal speed at the end of the constant power section is 80 km/h, 80 km/h, 70 km/h and 50 km/h, respectively. The result of the study can provide theoretical support for traction characteristic design and traction control for URVs.

Railway Bridge Runability Safety Analysis in a Vessel Collision Event

Bridges connecting islands close to the coast and crossing the sea have been attracting the attention of several researchers working in the field of train–bridge interactions. A runability analysis of a bridge during the event of a ship impact with a pier is one of the most interesting and challenging scenarios to simulate. The objective of the present paper is to study the impact on the running safety of a train crossing a sea bridge as a function of different operational factors, such as the train travelling speed, the type of impacting ship, and the impact force magnitude. Considering train–bridge interactions, a focus is also placed on wheel–rail geometrical contact profiles, considering new and worn wheel–rail profiles. This work is developed considering a representative continuous deck bridge with pier foundations located on the sea bed composed of six spans of 80 m. Time-domain simulations of trains running on the bridge during ship impact events were carried out to quantify the effect of different operating parameters on the train running safety. For this purpose, derailment and unloading coefficients, according to railway standards, were calculated from wheel–rail vertical and lateral contact forces. Maps of the safety coefficients were finally built to assess the combined effect of the impact force magnitude and train speed. The present investigation also showed that new wheel–rail contact geometrical profiles represent the most critical case compared to moderately worn wheel–rail profiles.

A frequency-domain simulation method for the evolution of rail corrugation in curves

Rail corrugation remains a major problem in many railways and metros, leading to high noise and vibration levels as well as potential damage to the track and vehicle. A frequency domain simulation method is proposed for the evolution of the rail surface roughness, which can simulate the formation and development of rail corrugation in curves. A coupled vehicle-track dynamic model is established in the frequency domain to calculate the dynamic vertical and lateral wheel-rail contact forces and the associated vibration. The wheel-rail contact state is determined by using a multi-body dynamics model. The frictional-work wear model is used to calculate the roughness change caused by wheel-rail dynamic interaction. The method is verified by comparing the results with those of on-site testing on a 300 m radius curve of a metro line. It is shown that the main causes of rail corrugation are associated with the peaks in the vertical wheel-rail forces in the frequency domain, generated by the interaction between the wheel and rail. At short wavelengths the corrugation is associated with the wave reflections in the rail between adjacent axles. The phase relationship between the vertical wheel-rail force and the initial roughness has a strong influence on the roughness growth trend, leading to preferential growth in certain wavelength bands. The wheel-rail contact state and friction parameters affect the rate of development of the corrugation. Finally, a corrugation index is proposed to allow quick evaluation of the wavelength and growth rate of corrugation.

Replacement of tibialis cranialis tendon with polyester, silicone-coated artificial tendon preserves biomechanical function in rabbits compared to tendon excision only

BackgroundArtificial tendons may be an effective alternative to autologous and allogenic tendon grafts for repairing critically sized tendon defects. The goal of this study was to quantify the in vivo hindlimb biomechanics (ground contact pressure and sagittal-plane motion) during hopping gait of rabbits having a critically sized tendon defect of the tibialis cranialis and either with or without repair using an artificial tendon.MethodsIn five rabbits, the tibialis cranialis tendon of the left hindlimb was surgically replaced with a polyester, silicone-coated artificial tendon (PET-SI); five operated control rabbits underwent complete surgical excision of the biological tibialis cranialis tendon in the left hindlimb with no replacement (TE).ResultsAt 8 weeks post-surgery, peak vertical ground contact force in the left hindlimb was statistically significantly less compared to baseline for the TE group (p = 0.0215). Statistical parametric mapping (SPM) analysis showed that, compared to baseline, the knee was significantly more extended during stance at 2 weeks post-surgery and during the swing phase of stride at 2 and 8 weeks post-surgery for the TE group (p < 0.05). Also, the ankle was significantly more plantarflexed during swing at 2 and 8 weeks postoperative for the TE group (p < 0.05). In contrast, there were no significant differences in the SPM analysis among timepoints in the PET-SI group for the knee or ankle.ConclusionsOur findings suggest that the artificial tibialis cranialis tendon effectively replaced the biomechanical function of the native tendon. Future studies should investigate (1) effects of artificial tendons on other (e.g., neuromuscular) tissues and systems and (2) biomechanical outcomes when there is a delay between tendon injury and artificial tendon implantation.

Vertical contact forces affect vibration perception in human hairy skin.

Skin is the largest organ of the human body and fulfills many important functions, like detecting mechanical stimuli. Skin can be divided into glabrous (non-hairy) and hairy skin. These two skin types differ with regard to their mechanical properties and in the distribution of mechanoreceptors. Although many investigations focus on glabrous skin, hairy skin still plays a fundamental role in various activities, e.g., with regard to the perception of pleasantness or for developing wearable vibrotactile devices for pattern recognition in persons with disabilities. Unfortunately, investigations on influencing factors, like vertical contactor force, are scarce for hairy skin. Similarly, it would also be interesting to investigate whether regional vibratory sensitivity differences are present across the human torso. Hence, this study investigated the effects of vertical contactor forces and different anatomical locations on vibration perception. Four anatomical torso regions were studied. Based on findings in glabrous skin, we generally hypothesized improved vibration perception with increasing contactor forces and regional sensitivity differences between the anatomical locations. Forty young and healthy individuals participated (23.0 ± 2.0 yrs), and vibration perception thresholds (VPTs) were determined at 30 Hz for three vertical force levels (0.6, 2.4, and 4.8 N) at four torso locations (sternum, deltoid/shoulder, lower back, middle lateral torso side). Higher contactor forces resulted in lower VPTs corresponding to improved vibration perception, regardless of anatomical location. In addition, the sternum region was more sensitive than the remaining three regions, regardless of force level. The reasons for these findings may be a varying number and activation pattern of afferents activated under the different conditions. The findings of this study complement the understanding of vibrotactile sensitivity in hairy skin and may offer implications when developing vibrotactile devices or clothing/textiles, for example.

Influence of shortwave irregularity on increasing the vehicle running speed on bi-block ballastless track lines

Compared with slab ballastless track, bi-block ballastless track has the advantages of simpler constructed components and better economy, and has been used in high-speed railways for nearly 20,000 km in China. During the construction, the position deviation between sleepers and the disturbance of sleeper position caused by track bed concrete pouring can easily lead to shortwave irregularity with wavelength of 1 ∼ 2 m of bi-block ballastless track. Massive detection data on several high-speed railway lines showed that the standard deviation of vertical wheel-rail contact forces on bi-block ballastless track was about 58% higher than that on slab ballastless track. In this paper, a vehicle-track coupled dynamic analysis model was established, which can consider 1 ∼ 2 m shortwave irregularities of the track. Under the current construction and operation control standards, the dynamic responses of vehicles and tracks under different running speeds were studied. The results showed that vertical shortwave irregularity mainly affected the dynamic response of the wheel and rail, and rarely affected the dynamic response in other components. Compared with no shortwave irregularity, when the track had shortwave irregularity with σv = 0.8 mm, the peak value of the vertical acceleration of wheelset increased by 4.1 times, the standard deviation of wheel-rail contact force increased by 3.9 times, the vertical acceleration of frame increased by 1.7 times, and the vertical acceleration of track bed increased by 1.8 times, while the vibration acceleration of car body had almost no effect. When the track had shortwave irregularity with σh = 0.8 mm, the lateral acceleration of wheelset increased by 2.3 times. When the track had shortwave irregularity with σv = 0.8 mm and the vehicle speed increased to 450 km·h−1, the wheel load reduction rate reached 0.85, which exceeded the safety limit. Consider the results of this study, following suggestions can be obtained:(1) the shortwave irregularity with wavelength of 1 ∼ 2 m can be measured indirectly by the standard deviation of wheel-rail vertical contact force or wheelset vibration acceleration. (2) To control the wheel load reduction rate within 0.6, the standard deviation of random vertical irregularity should be controlled within 0.6 mm when running speed is 350 km/h, and within 0.4 mm when running speed is 400 km/h or above.

Failure analysis of the pure carbon strip affected by dynamic contact force during current-carrying sliding

The pure carbon strip is widely used in high-speed Electro Mechanical Units (EMUs) transit. Dynamic contact between the pantograph and the catenary produces internal cracks in the pure carbon strip, which results in the break of the pantograph and interruption of power transmission. The tribological properties and failure mechanism of the pure carbon strip is studied in this paper. The current-carrying tribology experiments were carried out on a flexible loading test rig. It is found that the dynamic contact in pantograph/catenary system produces regular influence on arc discharge and current transmission. The cracks and arc erosion are the most important failure mechanisms subjected to the periodic vertical contact force. The carbon fibers in the strip became orderly arranged honeycomb-structures after oxidation and sublimation. These honeycomb-structures distributed nearby the pores and induced the initiation and propagation of cracks. Therefore, preparing high-strength carbon fibers and eliminating the combination gap between the carbon fibers and the carbon matrix are recommended to prevent the failure of pure carbon strip. Results in this paper are expected to provide data support for the failure analysis and manufacturing technology to the pure carbon strip, as well as providing theoretical supports to the locomotives in service.

Investigating Glenohumeral Joint Contact Forces and Kinematics in Different Keyboard and Monitor Setups using Opensim.

The musculoskeletal complaints of the shoulder are prevalent in people who work with computers for a long time. This study aimed to investigate the glenohumeral joint contact forces and kinematics in different keyboards and monitor setups using OpenSim. Twelve randomly selected healthy males participated in an experimental study. A 3×3 factorial design was used in which three angles were considered for the monitor and three horizontal distances for the keyboard while performing standard tasks. The workstation was adjusted based on ANSI/HFES-100-2007 standard to maintain a comfortable ergonomic posture for controlling confounding variables. Qualisys motion capture system and OpenSim were used. The maximum mean range of motion (ROM) of both shoulders' flexion and adduction was observed when the keyboard was 15 cm from the edge of the desk, and the monitor angle was 30°. The maximum mean ROM of both shoulders' internal rotation was recorded for the keyboard at the edge of the desk. Peak forces for most right shoulder complex muscles were obtained in two setups. 3D shoulder joint moments were significantly different among nine setups (P-value<0.05). The peak anteroposterior and mediolateral joint contact forces were recorded for the keyboard at 15 cm and the monitor at zero angles (0.751 and 0.780 N/BW, respectively). The peak vertical joint contact force was observed for the keyboard at 15 cm and the monitor at 15° (0.310 N/BW). The glenohumeral joint contact forces are minimum for the keyboard at 8 cm and the monitor at zero angles.

Scanning the vertical and radial frequencies of curved bridges by a single-axle vehicle with two orthogonal degrees of freedom

This paper scans for the first time the vertical and radial (lateral) frequencies of a horizontal curved beam from the respective motions of a single-axle test vehicle by a theoretical approach. The vehicle is innovatively treated as a system with two orthogonal degrees of freedom (DOFs), each of a spring-dashpot unit, to capture both the vertical and lateral motions. To start, closed-form solutions are derived for the out-of-plane vibration (under the vertical and torsional contact forces) and in-plane vibration (under the centrifugal force) of the curved beam. Then the vertical and lateral motions of the vehicle are derived. Based on this, a generalized formula is derived for the corresponding contact responses. From the analyses using the generalized contact formula, it was demonstrated that: (1) the contact responses outperform the vehicle responses in that more higher bridge frequencies (out-of-plane and in-plane) can be identified; (2) the radius of curvature affects significantly the radial frequencies of the curved beam; (3) the eccentricity of the scanning vehicle has little effect on frequency identification; and (4) pavement roughness’ effect can be remedied by random traffic, and it does not appear in the radial contact response.

Failure Mode Analysis of Bridge Pier Due to Eccentric Impact Based on Separation of Pier and Beam

By considering the near-field vertical seismic spectrum and calculating the change in vertical contact force between the main beam and the pier, the possible vertical separation contact condition of a bridge is deduced. By calculating the extreme value of the pier–beam vertical contact force and the longitudinal deformation of the pier under the structural separation, the influence of the separation on the failure of the pier is determined. Separation increases the risk of pier failure under compression, bending, and shear, and different separation times lead to different longitudinal responses from the pier, and the first failure mode is different. Therefore, it is of great significance to reasonably design bridges near faults.

Improved estimation of rail–wheel contact forces from instrumented wheel-set data through higher harmonic cancellation and a back-propagation neural network scheme

Instrumented wheelsets, equipped with numbers of strain gauges, are widely used to estimate the rail–wheel contact parameters. The accuracy in estimation of rail–wheel contact parameters from the measured strain signals depends on the layout of the strain gauges and correlation techniques adopted for processing measured signals. Harmonic components estimation is the most widely used conventional correlation technique. However, its accuracy in estimation of rail–wheel contact parameters is limited to the order of 80%–90%. This study proposes a signal modification algorithm, initially utilizing cancellation of next significant higher harmonics than those considered in the existing algorithms and then further, a novel Artificial Neural Network architecture for the same purpose.The signal modification approach is based on the realization that the seventh harmonic has significant contribution on the strain signals. The proposed algorithm is aimed at estimating and cancelling the effects of the seventh harmonic in strain signals. The accuracy thus improves to 91% in vertical contact force estimates, while the accuracy in estimation of lateral contact force and lateral contact position are improved to 97% and 95%, respectively. Due to the highly non-linear nature of the rail–wheel contact parameters, an optimized nonlinear mapping is required for further improvement in the accuracy.The viability of using artificial neural networks in estimation of rail–wheel contact parameters have been explored earlier. The proposed architectures are complicated and require extensive manual optimization of tuning parameters. A simple back-propagation artificial neural network architecture, using Bayesian regularization training function with Levenberg–Marquardt optimization technique is proposed in this study. The proposed neural network consists of 18 measured strain signals as input, three hidden layers with 20, 6 and 3 neurons, respectively, and vertical force, lateral force and lateral contact position as three outputs. Accuracies of the order of 99%, 99% and 96% are achieved in the estimation of vertical contact force, lateral contact force and lateral contact position respectively. The input and training data is generated from the multi-body dynamics and finite element simulations.

Simplification of earthquake induced vehicle bridge interaction contact simulation for urban viaducts

AbstractThe possibility of motor vehicles parking on or slowly driving on the urban viaducts during earthquakes has been largely increased to a non‐negligible level due to the traffic jams in most of modern cities. As a fact of the earthquake disaster investigation, detachment and collision between motor vehicles and the bridge deck endangered the safety of both drivers and the bridge structure itself. In recent studies, Hertz model was therefore proposed to simulate this nonlinear contact and collision behavior with the complexity and inefficient in solving the kinetic equilibrium equations of earthquake induced vehicle bridge interaction (VBI) system, and hence hindered the comprehensive numerical analysis. In this paper, two linearized contact models, that is, a piecewise linear tangent model derived by Taylor series expansion of the Hertz model and a piecewise secant model derived by least square method of error minimization of the Hertz model, are both proposed to simplify the simulation of the vehicle bridge contact behavior for earthquake induced VBI system. A total of 3*2041VBI parametric systems considering different vehicle masses, frequencies and ground motions, are calculated and statistically analyzed to compare the accuracy of each model with nonlinear Hertz model. Statistical analysis result shows that the vertical contact force calculated by two simplified models are acceptable in earthquake induced VBI analysis with less than 10% error in more than 99% analysis cases. However, the piecewise tangent model is more accurate than the piecewise secant model when the vehicle and bridge stay attached. If detachment occurs, the secant model would have higher accuracy in predicting the initial peak ground acceleration (PGA) of vehicle detachment from the bridge. Based on this result, a formula using the piecewise secant model for predicting the initial detachment PGA of vehicles from the bridge deck is proposed to simplify the increment dynamic analysis (IDA) method in further earthquake induced VBI analysis.

DYNAMIC FINITE ELEMENT SIMULATION OF WHEEL–RAIL CONTACT RESPONSE FOR THE CURVED TRACK CASE

The wheel–rail interaction will be intensified on account of the complexity of the wheel–rail contact geometry on a curved track. It also may become more complicated and/or have significant difference as the train speed increases, since the dynamic effects cannot be ignored then. In this study, based on explicit Finite Element (FE) software LS-DYNA 971, a Three-Dimensional (3D) elastic-plastic FE model was built to simulate the dynamic wheel–rail contact behaviour of curve negotiating, where the superelevation and roll angle as well as the strain rate effect were considered. The evolution of contact patch and pressure, wheel–rail contact force, the stress/strain state and the acceleration of the axle were employed to examine the wheel–rail transient dynamic response. Furthermore, the influences of axle load, curve radius and strain rate effect were also discussed. It is found that the maximum vertical contact force, contact pressure, stress and strain on the curved track increase with the decreasing curve radius, and they increase with the increasing axle load except for lateral contact force. The wheel–rail dynamic responses on the curved track are significantly enhanced compared to the straight track. Moreover, the strain rate effect can enhance von-Mises stress and contact pressure, suppress the plastic deformation of the rail and wheel, but it has little effect on the vertical and lateral contact forces and stable acceleration of axle. The Rate-Sensitive Factors (RSF) of the wheel and rail on the curved track are weaker than those on the straight track. These findings will be very helpful to study the competitive relationship between the rolling contact fatigue and wear, as well as the crack initiation and propagation problem.

Dynamic response of vehicle-track interaction at the bolted rail joint in the presence of the polygonal wheel

Rail joints are the weakest link in the railway track structure due to the presence of discontinuities in the track stiffness and wheel-rail contact geometry. This paper presents the dynamic response of vehicle-track interaction at the bolted rail joint (BRJ) in the presence of polygonal wheel wear. A three-dimensional coupled vehicle-track dynamic model was established using the finite element method (FEM) and the multi-body system (MBS) approach, in which the flexibilities of the wheelset and track are taken into account. The proposed dynamic model is validated by the comparisons of field measurement and calculated vertical axle-box acceleration in time and frequency domains. The effects of the flexible wheelset in the presence of polygonal wear on the vehicle-track dynamic interaction at the BRJs are illustrated through comparisons with those obtained using without polygonal wheel model. The results show that the polygonal wheel wear and the rail joint irregularities can induce high-magnitude vertical wheel-rail contact force, and exacerbate the vibration responses of the axle box, the wheelset, and the rails. The simulation results also indicate that the wheelset bending modes, the P2 resonance due to rail joint excitation, and the track vibration modes have significant effects on the vertical vehicle-track dynamic interaction at the supported and suspended BRJs.

Influence of Pier Size on its Failure Mode under Near-Fault Vertical Earthquake

To calculate the influence of pier size on the pier failure mode, a double-span continuous girder bridge model was selected for analysis. The transient wave function expansion method was used to calculate the excitation conditions required for pier separation and the limit solution of pier longitudinal deformation under pier separation, and the indirect mode superposition method was used to calculate the vertical impact force of the pier-beam. The calculation results show that the higher the pier height, the smaller the section size, the larger the vertical seismic acceleration required to separate the pier-beam, the smaller the vertical contact force of the pier-beam, and the larger the most unfavorable value of the longitudinal deformation of the pier caused by separation. The stress of the bridge pier before and after separation is compared and the influence of separation on the failure of the bridge pier is put forward. The study shows that when pier and beam separation occurs, there may be multiple failure modes superimposed on the pier, and the first failure mode will have variation with the change in pier size.

Numerical coupling strategy using HOS-OpenFOAM-MoorDyn for OC3 Hywind SPAR type platform

The coupled (Potential theory and Navier–Stokes) solver is applied to simulate the interaction of sea waves with substructure of floating offshore wind turbines (FOWT) platform, notably similar to the OC3 Hywind SPAR structure. The intention is to develop a numerical tool that allows the study of the survivability of floating structures in extreme sea states. In this study, the moorings are modeled in two ways. One is by considering the mooring lines as a linear spring with defined spring stiffness, and another is by coupling the solver (foamStar) with a lumped-mass mooring dynamics model (MoorDyn). MoorDyn represents mooring line behavior subject to axial elasticity, hydrodynamic forces, and vertical contact forces with the seabed. The coupled model has been validated against the experiments carried out as part of the SOFTWIND project. The numerical model results of free surface elevation, floating body motions and mooring tensions are compared with the experiments. For wave cases with mild and moderate amplitudes, mooring in the form of a stiffness matrix is sufficient. However, dynamic mooring simulation (MoorDyn) is required for the extreme sea state conditions.

Influence of the turbulence conditions of crosswind on the aerodynamic responses of the train when running at tunnel-bridge-tunnel

High-speed trains (HSTs) often encounter crosswinds with complex pulsating components when running at a tunnel-bridge-tunnel section (TBTS), and their running safety may deteriorate sharply due to the complex terrain conditions in mountainous areas. This study aims to discuss the influence relationship of different turbulent conditions of the crosswind on the aerodynamic response of the HST passing through the TBTS. On the basis of the measured wind field data of a typical TBTS site, the pulsating wind field is numerically reconstructed by large eddy simulation, and the influence of the incoming flow dimension, the turbulence intensity and the average wind speed on the aerodynamic loads of the HST running at the TBTS are analysed. The corresponding influence mechanisms are explained in terms of the pressure distribution and flow field structure of the HST. The influence of the loading dimension of aerodynamic load and incoming turbulence intensity on the dynamic response index of the train body and wheel-rail contact is further discussed by establishing a wind-vehicle-bridge-tunnel coupling dynamic calculation model. The main conclusions are as follows: At the TBTS, the 1D pulsating incoming flow simulation scheme can be used rather than the 3D incoming flow scheme in calculating the aerodynamic response of the HST. The influence of the incoming turbulence intensity on the aerodynamic load of the HST is mainly reflected at the bridge section (BS), The fluctuation extent of the aerodynamic load of the HST increases with the increase in the turbulent intensity of the incoming flow. When the incoming flow turbulence intensity increases from 0 to 0.09, at the BS, the pitching acceleration of the train body and the vertical contact force of the wheel-rail on the leeward side increase by 18% and 16%, respectively. The average wind speed of the incoming flow has an important effect on the aerodynamic load of the HST, especially the head train, running at the TBTS. A linear positive correlation is found between the average wind speed of the incoming flow and the corresponding change amplitude of the aerodynamic load coefficient of the head train. When the HST runs at the TBTS, the five aerodynamic loads should be loaded in the calculation process of the aerodynamic response index of the HST, and the calculated wheel-rail response results are conservative when only two aerodynamic loads are applied to the train body.