This paper proposes a new dynamic driving risk potential field model under the connected and automated vehicles environment that fully considers the dynamic effect of the vehicle's acceleration and ...steering angle. The statistical analysis of the model's parameter reveals that acceleration and steering angle will directly affect the distribution of the driving risk potential field and that this strong correlation should not be ignored if one is interested in the vehicle's microscopic motion behavior. We further develop a driving risk potential field-based car-following model (DRPFM) to remedy the failure of acceleration consideration under the conventional environment, whose parameters are calibrated by filtered I-80 NGSIM data with frequent traf?c oscillations. Simulation results indicate that our proposed DRPFM model is proved to be a good description of car-following behavior and outperforms two classical car-following models (Optimal Velocity Model and Intelligent Driver Model) in frequent oscillation phases due to our consideration of potential acceleration data acquisition in real-time under the CAVs environment. In addition, this DRPFM model is applied to deduce the safety conditions for vehicle lane-changing. The analysis results prove that this model can reasonably explain the influencing factors between driver types and lane-changing safety conditions in practice.
AbstractOutput-only modal identification plays an important role in the structural health monitoring of large-scale structures. In recent years, blind source separation (BSS) has achieved great ...success in structural modal identification. Sparse component analysis (SCA), which is one of the most popular methods of BSS, has the capability to handle nonstationary excitation and underdetermined problems. In the process of SCA, clustering number, which is equal to the number of active modes, plays an important role in the estimation of modal matrix, in which the hierarchical clustering algorithm is used. However, the clustering number is always unknown in the clustering step, which makes application inconvenient. To fill this gap, an improved SCA method, equipped with a process of estimating the clustering number, is proposed in this paper. After transforming the signals into time-frequency (TF) domain, the single-source-points (SSPs) detection process is applied to pick out the TF points at which only one mode makes a contribution to the responses. The clustering technique is preceded by a preprocessing step to determine the clustering number. The key idea is that the clustering number is equal to the number of columns in the modal matrix, which is reflected in the number of lines in the scatter plot of two observations. A normalization method is proposed to distinguish the clusters clearly. The number of clusters is acquired through statistical analysis of the normalized vectors. After obtaining the modal matrix, the smoothed zero-norm algorithm is used to recover the modal responses in order to extract natural frequencies and damping ratios. An experimental cantilever beam and a three degree-of-freedom (DOF) numerical system with closely spaced modes were used to verify the effectiveness of the proposed method. The results showed that the improved SCA could detect the number of active modes for the beam and the numerical system. Full-scale data measured from the Green Building located at the Massachusetts Institute of Technology (MIT) campus and the Tianjin Yonghe Bridge were analyzed to verify the effectiveness of the proposed method in practical applications.
Summary
Mode identification in civil engineering uses ambient excitation response, where the excitation is assumed to be stationary white noise. However, practical engineering conditions cannot ...satisfy this assumption of ideal excitation. This paper proposes an innovative method based on eigensystem realization algorithm and a proposed virtual frequency response function. The formulation of the virtual frequency response function is derived from the ratio of the cross‐power and autopower spectral density functions of the measurement signals. The impulse responses are calculated by inverse Fourier transform of the product of the virtual frequency response function and the frequency response function of the reference point. After obtaining impulse responses, eigensystem realization algorithm is then performed to identify structural modes. The proposed virtual frequency response function and eigensystem realization algorithm are validated by a numerical example. The results show that the virtual frequency response function and eigensystem realization algorithm can give much a better impulse response than natural excitation technique and identify more precise mode parameters. Finally, the proposed method is applied to a practical engineering bridge, where the results by the virtual frequency response function and eigensystem realization algorithm can also give better results than those given by natural excitation technique and eigensystem realization algorithm.
AbstractIn the dynamic characteristic analysis of high-speed railway bridges, free-vibration responses after a train passes are valuable for modal identification. However, distinguishing between ...free- and forced-vibration segments requires user intervention, which hinders the reliable and continuous identification of modal parameters, thereby impeding the vibration-based structural state assessment. This paper proposes a free-vibration detection technique whose basis is that the envelope function of each modal component decomposed from the free-vibration data decays exponentially. To extract the modal component adaptively, iterative variational mode decomposition is proposed where the signal is iteratively decomposed into two components until a single-degree-of-freedom component is obtained. Subsequently, the estimated free-vibration data are adopted to identify the modal parameters by the eigensystem realization algorithm with data correlation. A numerical simulation illustrates that the proposed method can provide the optimal free-vibration data for modal analysis. To verify the effectiveness of the proposed method in practice, the accelerations of the railway bridge during the passage of a train are analyzed. The modes can be identified from the estimated free-vibration data but not from the combination of forced- and free-vibration data, which indicates that the separation of forced and free vibration is necessary and can be achieved by the proposed method.
To tackle performance issues stemming from assembly errors in practical fuel cell applications, a criss-crossed matching design for anode and cathode bipolar plates (BPP) is proposed. The ...effectiveness of the proposed design is assessed by joint simulations of finite element analysis (FEA) and computational fluid dynamics (CFD). Concurrently, the orthogonal experimental method is utilized to investigate the performance of the criss-crossed matching design at various operating conditions. The results show that the GDL deformation rate of the criss-crossed matching design with error in practical assembly is merely 4.8%, significantly lower than the 19.9% observed in the aligned matching design. Furthermore, the criss-crossed design performance could be improved by 5.9% compared to the aligned matching design in practical assembly with error. The criss-crossed matching design consistently outperforms the aligned matching design at various operating conditions. Notably, the highest performance growth rate, observed in high stoichiometric ratio and high humidity, reaches 12.38%.
•A criss-crossed matching design of the bipolar plate is proposed.•Criss-crossed design performance is seldomly impacted by assembly errors.•Criss-crossed matching design increases performance by 5.9% over aligned design.•Criss-crossed matching design works well in various conditions.
Background: Combined therapy with tyrosine kinase inhibitors (TKIs) and anti-PD-1 antibodies has shown high tumor response rates for patients with unresectable hepatocellular carcinoma (HCC). ...However, using this treatment strategy to convert initially unresectable HCC to resectable HCC was not reported. Methods: Consecutive patients with unresectable HCC who received first-line therapy with combined TKI/anti-PD-1 antibodies were analyzed. Tumor response and resectability were evaluated via imaging every 2 months (±2 weeks) using RECIST v1.1. Resectability criteria were (1) R0 resection could be achieved with sufficient remnant liver volume and function; (2) intrahepatic lesions were evaluated as partial responses or stable disease for at least 2 months; (3) no severe or persistent adverse effects occurred; and (4) hepatectomy was not contraindicated. Results: Sixty-three consecutive patients were enrolled. Of them, 10 (15.9%) underwent R0 resection in 3.2 months (range: 2.4–8.3 months) after the initiation of combination therapy. At baseline, these 10 patients had a median largest tumor diameter of 9.3 cm, 7 had Barcelona Clinic Liver Cancer stage C (vascular invasion) disease, 2 had stage B, and 1 had stage A. Before surgery, 6 patients were evaluated as a partial response, 3 stable disease, and 1 partial response in the intrahepatic lesion but a new metastatic lesion in the right adrenal gland. Six patients (60%) achieved a pathological complete response. One patient died from immune-related adverse effects 2.4 months after hepatectomy. After a median follow-up of 11.2 months (range: 7.8–15.9 months) for other 9 patients, 8 survived without disease recurrence, and 1 experienced tumor recurrence. Conclusions: Combination of TKI/anti-PD-1 antibodies is a feasible conversion therapy for patients with unresectable HCC to become resectable. This study represents the largest patient cohort on downstaging role of combinational systemic therapy on TKI and PD-1 antibody for HCC.
Modal identification is based on modal superposition theory. For structures with proportional damping, the structural responses are recognized as real modal shapes multiplied by real modal ...coordinates. However, it is not true because the actual modal shapes should be complex even though they can be normalized to real ones. If the modal shapes are recognized as real ones, the modal superposition theory cannot reflect the actual modal parameters. This paper proposes an innovative method to identify complex frequencies for a structure with proportional damping using the identified real modal shapes, where the complex modal shapes are considered. The proportional damping is ideal but always assumed in practical engineering. The characteristic of the proposed method is that the complex property of frequencies is considered along with modal identification process. First, the reason why the complex modal shapes are hidden is revealed. When the real modal shapes are obtained, the Hilbert transform of analytical responses is used to estimate complex coordinates. Then, formulas to identify the complex frequencies are derived. The k‐means clustering method is employed. Finally, the proposed method is used in a numerical example and a practical bridge example. The results show that the proposed method can estimate the complex frequencies effectively, and can be used in practical engineering.
AbstractThe frequency domain decomposition method (FDD) is a commonly used method to identify structural modal parameters and analyze the structural dynamic performance. Although FDD has a high ...identification accuracy in natural frequencies and mode shapes, damping ratios cannot be identified accurately. The logarithmic decay method to identify the damping ratio in FDD needs the transformation from a narrow frequency band to the time domain, which leads to the loss of the corresponding mode outside the narrow band and add other modes in the narrow band. In this paper, an iterative frequency domain decomposition method (iFDD) is proposed to identify the structural damping ratio in frequency domain. Firstly, the natural frequencies and mode shapes are obtained by the FDD method, and the damping ratios during this identification process are assumed to be unknowns. Then, the natural frequencies, mode shapes, and unknowns are substituted into the output power spectrum formula to construct nonlinear equations. The damping ratios are obtained by solving the equations using iterative optimization methods. Finally, a numerical example and benchmark model are employed to validate the effectiveness of the proposed method. The results showed that the proposed iFDD method can identify the damping ratio precisely in the frequency domain, which is better than the traditional FDD performance.
A collaborative design method for multi-types of graphite end plates geometric parameters, membrane electrolyte assembly physical parameters, and operating parameters, was novelly developed to break ...bounds of parameter types for design stage and operational stage matching in fuel cells. A multi-step design method, assisted by a surrogate-assisted hierarchical particle swarm optimization algorithm, was used for the optimal design of multi-type parameters. During this multi-step design process, the initial experiments are implemented following the design of experiments, and further experiments are adaptively carried out under the guidance of the layered optimization method. Experimental evidence of cell performance response to the coupled effects of multi-parameters was firstly provided and discussed in details. The collaborative design of multi-type parameters realized using the proposed multi-step design method was proven to improve the energy conversion efficiency by 10.9%. Different performance requirements, from single to multiple objectives in various types of fuel cells, were also shown to be fulfilled using this collaborative design method.
•Collaborative design of multi-type parameters in fuel cell systems is realized.•A multi-step design method is proposed to break bounds of parameter types.•Design and operational stage matching contributes to energy conversion efficiency improvement.•The design of multi-type parameters can be flexible and adapt to different performance requirements and fuel cells.
•Non-uniform cross-sectional designs are systematically investigated.•Converging design enhances both in- and through-plane methanol transportations.•Converging design is numerically proven to ...enhance power generation to 12%.•Efficacy of non-uniform design is clarified at various experimental conditions.•Optimal application conditions of converging design have also been determined.
Non-uniform cross-sectional designs of serpentine channel in direct methanol fuel cells are systematically studied in the present work. A parametric design is proposed to describe and classify channel geometries whose effects on cell performance are numerically and experimentally analyzed. Numerical results show that the non-uniform converging designs are beneficial for both in- and through-plane methanol transportations, and thus to enhance the peak power generation performance as much as 12% at high-current-density operations. Effectiveness of non-uniform designs for power generation enhancements is also validated by experimental studies which consider various operating conditions, and significant enhancement of power generation (18.4%) is noticed by the usage of non-uniform converging design. Optimal application conditions for the non-uniform converging designs are determined to be the high-current-density operations with high temperatures.
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