•DKDE is optimal for estimating train bogie frame load distributions.•DKDE avoids boundary bias while maintaining the PDF as a genuine PDF.•Proper extrapolated load spectra of train bogies are ...obtained with DKDE.
The load spectra of a train bogie frame are used for bogie frame design, simulated fatigue testing and reliability evaluation and fatigue life prediction, however, modelling the bogie load spectrum is one of the most challenging tasks in this field. In this paper, diffusion-based kernel density estimation (DKDE) is used to obtain the load spectra distributions of train bogie frames. A full-scale B-type subway motor bogie and a full-scale high-speed EMU trailer bogie are analysed. DKDE, Gaussian kernel density estimation (GKDE) and parametric estimation are used to fit the distributions of the loads. Goodness-of-fit tests suggest that the distributions obtained by DKDE are close to the actual distributions. Fatigue damage are calculated to evaluate the distributions estimated by DKDE and GKDE. From the distributions obtained by DKDE, reasonable maximum load values and reasonable extrapolated load spectra are deduced.
Fluctuating loads on tidal turbines are important for fatigue analysis and there is limited information or simulation available for full-scale conditions. Here, CFD simulations have been performed ...for a geometry-resolved full-scale tidal-stream turbine and compared with experimental data from a 1 MW machine deployed at the EMEC test site. Initially, Reynolds-averaged Navier-Stokes (RANS) and large-eddy simulations (LES) were performed using an inflow mean velocity profile representative of the site but low inflow turbulence. Mean blade pressures were similar for the two types of turbulence closure and yielded mean power coefficients comparable with measurements. Then, to simulate the effect of turbulence on loads, LES with synthetic turbulence prescribed at inlet was employed. For these simulations, inflow profiles of mean velocity, Reynolds stresses and length scales were determined from a precursor channel-flow simulation, with additional factoring of stresses and length scales to match hub-height conditions measured on site. Fluctuations in thrust, power and blade bending moment arise cyclically from onset mean velocity shear and the blocking effect of the support tower and over continuous spectral ranges from blade-generated turbulence, approach-flow turbulence and waves. LES simulations with realistic inflow turbulence satisfactorily reproduced the relative spectral distribution of blade bending moments in low-wave conditions.
•RANS and LES simulations of a geometry-resolved, full-scale tidal turbine.•Comparison of mean and fluctuating load data with a 1 MW turbine deployed at sea.•Synthetic eddy model producing realistic inflow turbulence for LES.•Rapidly-decaying wake from nacelle; slowly-varying, vortex-bounded wake from rotor.•LES with realistic inflow turbulence matches measured spectrum of blade bending moments.
In the present article a method based on Monte Carlo Simulation (MCS) is developed with which any spectrum extrapolation method can be statistically evaluated. Thereby, the duration of service life ...spectrum and the extrapolation factor can be specified arbitrarily. In addition to the evaluation of extrapolation methods, the simulation model allows to calculate statistically based safety factors for load assumption. The use of general, mostly conservative factors can thus be omitted. For the extrapolation of load spectra, a procedure with kernel density estimators using an adaptive bandwidth is developed. The new Kernel Density Estimation (KDE) method contains three parameters for controlling the adaptive bandwidth which are optimized using the simulation model. During optimization, mathematically describable spectra are used, which are completely described by the maximum amplitude of the spectrum, the spectrum range and the spectrum shape parameter.
•Proposed loads partition for fatigue design, based on measurements at the wheels.•Multi-input load case consideration for fatigue design when performing manoeuvres.•Parallel process of loads ...resulting from manoeuvres, and random phenomena.•Stress tensor formulation related to the vehicle structure and its dynamic features.
It is essential for car manufacturers to ensure their vehicle robustness under a daily usage. As no detailed method nor standard prevails, each manufacturer is expected to setup its own methodology for safety parts life-assessment. The early stages of a renewed methodology are proposed in this study. This is based on proving-grounds measurements analysis to quantify the impact of various loads. The method, developed from the load measured at the vehicle wheels, considers the multi-input load case and its variable amplitude content. Measured time-series are analyzed and partitioned into two main categories depending on the time-correlation between the load axes. The driver-induced loads, Driven-Road, (DR) loads, are separated from the effects of random road conditions, Random-Road, (RR) loads. Then, for partition validation, a suitable life quantification method is applied in parallel to the two types of loading. On one hand, an assumption based on strong physical meaning eases the Rainflow Counting method application on the DR load. On the other hand, the use of spectral methods is explored to handle the random loads. This paper details the partition process of the time-series and each of the subsequent validation steps of the method to apply such a partition. Such a validation is performed via a comparison of the pseudo-damage between a referenced signal and the one issued from the partition.
Residual strength models are widely used to predict the fatigue life of composite laminates under highly variable loads. However, they often require considerable experimental effort to accurately ...determine model parameters. This paper introduces a new approach for predicting the residual strength of composite materials with less experimental data. The method is based on two common strength-based wearout models, the Sendeckyj model and Schaff and Davidson model. The Sendeckyj model consists of an equation with two model parameters, which describes the shape of the S-N curve by fitting fatigue test data. The Schaff and Davidson model is a single-parameter function which calculates the residual strength based on the number of fatigue cycles. Using a novel mathematical algorithm, the residual strength model parameter in the Schaff and Davidson model is estimated directly from the S–N curve without running any residual strength tests. Five data sets from the literature are used to validate the new methodology. The results show that the residual strength model parameter is dependent on both the stress level and the number of loading cycles experienced at this stress level, both of which are considered in the new strategy. In addition, if the fatigue data are well distributed, the residual strength model parameter estimated by the new strategy is close to the experimental data.
Most metallic components and structures are subjected, in service, to random or variable amplitude loadings. There are many examples: vehicles subjected to loadings and vibrations caused by road ...irregularity and engine, structures exposed to wind, off-shore platforms undergoing wave-loadings, and so on. Just like constant amplitude loadings, random and variable amplitude loadings can make fatigue cracks initiate and propagate, even up to catastrophic failures. Engineers faced with the problem of estimating the structural integrity and the fatigue strength of metallic structures, or their propensity to fracture, usually make use of theoretical, numerical, or experimental approaches. This reprint collects a series of recent scientific contributions aimed at providing an up-to-date overview of approaches and case studies—theoretical, numerical or experimental—on several topics in the field of fracture, fatigue strength, and the structural integrity of metallic components subjected to random or variable amplitude loadings.
Sustainment issues associated with military helicopters have drawn attention to the growth of small cracks under a helicopter flight load spectrum. One particular issue is how to simplify (reduce) a ...measured spectrum to reduce the time and complexity of full-scale helicopter fatigue tests. Given the costs and the time scales associated with performing tests, a means of computationally assessing the effect of a reduced spectrum is desirable. Unfortunately, whilst there have been a number of studies into how to perform a damage tolerant assessment of helicopter structural parts there is currently no equivalent study into how to perform the durability analysis needed to determine the economic life of a helicopter component. To this end, the present paper describes a computational study into small crack growth in AA7075-T7351 under several (reduced) helicopter flight load spectra. This study reveals that the Hartman-Schijve (HS) variant of the NASGRO crack growth equation can reasonably accurately compute the growth of small naturally occurring cracks in AA7075-T7351 under several simplified variants of a measured Black Hawk flight load spectra.
•AADTT, VCD, ALS, and number of axles per truck are the main traffic inputs affected by the traffic monitoring duration.•Traffic monitoring data collected over all days of the week are more ...representative than partial week traffic data for pavement design.•Roadways with lower truck traffic generally show higher variability in traffic data; hence, a longer traffic monitoring period is required for such locations in order to obtain reliable traffic inputs for use in pavement design.
The mechanistic-empirical pavement design approach requires defining detailed axle load spectra for each truck class and axle group that can be obtained from continuous site-specific weigh-in-motion (WIM) data. However, it is challenging to collect reliable WIM data over an extended period of time as these systems may experience technical or equipment problems leading to incomplete WIM data. As a result, there may be a need to rely on WIM data collected over shorter traffic monitoring periods to generate the required traffic inputs for use in mechanistic-empirical pavement design. This study examined the effect of the traffic monitoring period on the resulting traffic inputs and the associated pavement performance as predicted using the mechanistic-empirical pavement design approach. The analysis results revealed higher variability in traffic inputs and predicted performance when using shorter traffic monitoring periods. This was more obvious for WIM sites with lower truck traffic. This study also presented a framework for selecting the minimum required traffic monitoring period to achieve a target accuracy level in predicting the pavement service life. The results of this study are expected to assist highway transportation agencies in understanding the impact of the traffic data collection effort on mechanistic-empirical pavement design.
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•A general framework to build simplified loads for fatigue design.•The equivalent signal is insensitive to some amount of uncertainty on the structure.•The case of a multi-channel ...input is developed and illustrated with road load data.
Industrial structures undergo complex loading, often unsuitable for the design and validation phases of their development. Engineers seek simplified signals to replace them, yet equivalent in terms of fatigue. A general framework for the construction of equivalent fatigue loads is presented, intended to take into account some uncertainty on the structure of interest. The guiding idea is to describe this uncertainty through parameters of the structure model, and then to assure the equivalence of damage or failure behavior over the whole range of expected parameters. The approach is applied in the case of structures undergoing multiple channels of concentrated forces.
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