Impedance Function Research Articles

A novel road traffic flow prediction model using hybrid Particle Swarm Optimization (PSO) and Radial Basis Function Neural Network (RBFNN)

<p>Traffic congestion is a major problem in urban areas, leading to increased travel time, air pollution, and fuel consumption. Road impedance function, which describes the relationship between traffic status and travel time, plays an important role in predicting travel time and managing traffic flow. Traditional methods for estimating road impedance function rely on manual calibration and may have limitations in reflecting the complexity of traffic patterns. To address these challenges, researchers have proposed various machine learning models for predicting travel time and road impedance function. In this paper, a hybrid particle swarm optimization—radial basis function neural network model is proposed for improving the accuracy of the road impedance function. The model takes into consideration various vehicle types and is validated using travel time data collected from a road section in Huai’an City, China. The effectiveness of the proposed model is compared with the traditional road impedance function calibrated by nonlinear regression. The experimental results indicate that the Mean Relative Error (MRE) of PSORBFNN is increased by 3.89% and 6.28% respectively when compared with DPNR training samples and validation samples. When compared with DPPSO training and validation samples, the MRE of PSORBFNN is increased by 2.87% and 3.3% respectively. These findings suggest that the proposed model could guide and assist traffic engineers and practitioners in predicting travel time on road sections with improved accuracy.</p>

Approach for a floating pile embedded in poroelasitc soil under horizontal dynamic load

The deformation mechanism in the horizontal direction of a floating pile under dynamic load should be paid extensive attention. The closed-form solution of dynamic characteristics of a floating pile in poroelasitc soil subject to horizontal dynamic load is obtained by a newly developed framework in this paper. Firstly, based on the three-dimensional continuum model and Biot’s poroelastic theory, the governing equations of the pile surrounding soil and pile end soil are respectively established. Secondly, the pile shaft reaction is calculated by use of the conventional method used in many existing literatures, and the pile base resistance is obtained with the aid of the Hankel transform technique and mixed boundary-value conditions that came from the contact interaction between a rigid massless disk with its beneath soil layer of finite thickness. Thirdly, the Timoshenko beam theory is applied to depict the pile vibration considering its shear deformation, and thus the dynamic impedance functions at pile head are derived. Subsequently, the correctness of the proposed solution is verified through comparisons with the existing results from other scholars. Finally, a parameter analysis about the thickness of the pile end soil, pile slenderness ratio and soil permeability are performed. Results suggest that the soil layer thickness and pile slenderness ratio have a pronounced effect on the pile dynamic behavior, and considering the soil permeability is more realistic to pile vibration response. The obtained results can exert great significance to the serviceability of floating pile for engineering practice.

Effect of Soil–Structure Interaction on Inelastic Displacement Ratios of Bridge Structures Subjected to Pulse-Like Ground Motions

This study aimed to investigate the effect of soil–structure interaction (SSI) on the inelastic displacement ratio of bridge structures subjected to near-fault pulse-like earthquake ground motions. SSI was modeled using a discrete-time recursive filter approach and frequency-dependent foundation–soil impedance functions. A total of 105 near-fault earthquake ground motion records were used for the analysis. The study also compared the soil–foundation–superstructure (SFS) system with a fixed-base system to explore the effects of spectral period normalization, strength reduction factor, earthquake magnitude, site-to-source distance, and peak ground velocity on the inelastic displacement ratio. The findings indicate that both the SFS and fixed-base systems have significant inelastic displacement demand under near-fault earthquakes, with values that can be 2–3 times higher than those predicted by ASCE-41-13, particularly in the short period range. Furthermore, as the structural period approaches the earthquake pulse period, the SFS system generally shows larger inelastic displacement ratios compared to the fixed-base system. The analytical results provide insight into the factors affecting the inelastic displacement ratio for near-fault pulse-like earthquakes.

Frequency- and intensity-dependent impedance functions of laterally loaded pile groups in cohesionless soil

The frequency-dependent horizontal impedance functions of a model floating 2 × 2 pile group, embedded in cohesionless sand under a 1g condition, were investigated experimentally. The tests were conducted using large amplitude loads inducing soil yielding. The soil-pile system was housed in a laminar shear box fastened to the top of a unidirectional shaking table. Quasi-static and dynamic loads were applied in a lateral direction under the fixed pile-head condition to evaluate the force–displacement relationship and the horizontal impedance functions, respectively. The results of the quasi-static loading exhibited rate-dependent behavior for the lateral load-bearing capacity of the piles. Notably, the analysis of the soil surface near the piles, using a stereo-PIV calibration, demonstrated a consistent failure pattern despite the significant variation in velocity. Furthermore, an important observation was the convergence of the horizontal dynamic impedance functions towards the secant static stiffness as the amplitude of dynamic loading increased.

A street-point method to measure the spatiotemporal relationship between walkability and pedestrian flow

Walkability indicators are a pivotal method to evaluate the role of the built environment in peoples' decisions regarding active mobility, supporting the application of public measures that contribute to more sustainable and resilient regions. Currently, data used to evaluate associations between walkability indicators and travel behavior is obtained via traditional methods of data collection, like questionnaires, that are costly and hard to scale in large urban environments. Moreover, the spatial resolution of most indicators may not be sufficient to support granular local public interventions. To face these issues, we propose a novel walkability indicator that provides a score of walkability for every one-meter street point, based on street conditions and accessibility to points of interest calculated with a Cumulative-Gaussian impedance function. Resorting to Linear and Geospatial Weighted Regressions, we evaluate the associations between walkability features and pedestrian flow data retrieved from mobile phone communication signals for a week in March 2022. The relationship between walkability features and pedestrian flow is stronger during workdays, in which accessibility to education, food amenities and government services are the most important predictors. On the weekend, the features with more explanatory power are accessibility to crosswalks and leisure amenities. Accessibility to public transport, sidewalk width and slope seem to impact pedestrian decisions independently of the day type, although the impact is stronger on weekends. This study provides policy makers and urban planners with a practical tool to effectively support the evaluation of current street conditions and access areas that are underserved, as well as plan and gauge new local interventions, while objectively understanding their impacts on pedestrian mobility.

An efficient numerical algorithm for solving the dynamic impedance function of arbitrary-shaped foundations in layered soil

In soil–structure interaction analysis, the dynamic impedance solution can be obtained using Green's function based on frequency dependence. To satisfy the mixed boundary conditions of the ground–ground interface, the interface should be frequently divided into several evenly spaced sub-elements instead of finite elements. Generally, the accuracy increases and the computational efficiency decreases with an increase in the number of sub-elements. To obtain reliable solutions and improve efficiency, a numerical algorithm for solving the dynamic impedance function of arbitrary-shaped foundations in layered soil was investigated. Based on the wave propagation equation of a horizontally layered half space, the relationship between the number and radius of sub-disk elements and their dynamic impedance matrix was derived using the high-precision method of solving Green's function for the individual sub-disk elements. The derived equation provides an efficient and accurate method to calculate the dynamic impedance of rigid layered foundations and was verified based on numerical examples. The numerical examples revealed that the proposed method reproduced the results in the literature. With the given accuracy, this method reduces the calculation time and improves the calculation efficiency. This proposed high-precision method for solving the foundation dynamic response is well suited to practical engineering applications.

Semi-analytical study of defective pile-beam systems under transient excitation: Implications for low-strain testing

This paper establishes a theoretical model of defective pile-beam system. The soil around the pile is modeled as a continuous three-dimensional model. The pile is modeled as a Rayleigh-Love rod model that considers its transversal inertia effect. The defect of the pile is simulated by a pile segment with a different radius from the normal pile segment. The impedance function recursion method, along with RSPT and AIFTM, is utilized to derive the impedance of the pile top. The beam is modeled as a Timoshenko beam and the transient excitation is applied at the connection between the pile and the beam. Analytical solution for the dynamic response of the system in the frequency domain is derived, and the discrete Fourier transform is used to obtain a semi-analytical solution for the time-domain response. The velocity at the connection between the pile and beam and the pile body can be measured to assess defects. The semi-analytical solution presented in this paper was validated through comparison with FEM results. Reflection from necked segment is more pronounced at pile-beam connection than at pile body. Both velocity curves at these two points should be measured when beam cross-section height is large to determine pile integrity. The peak value and arrival time of characteristic waves are influenced by burial depth, necking section parameters, beam cross-section height, cantilever length, and soil parameters. These findings can provide guidance for the application of low strain integrity testing in pile-beam systems.

Vertical impedance functions of pile groups under low-to-high loading amplitudes: numerical simulations and experimental validation

Vertical impedance functions of pile groups under low-to-high loading amplitudes: numerical simulations and experimental validation

An Analytical Approach to Locate Short Circuit Fault in a Cable Using Sweep Frequency Response Analysis

In this paper, analytical methods are proposed for the location of a short circuit fault in a power cable using sweep frequency response analysis (SFRA). The impedance spectroscopy is estimated using classical transmission line (TL) theory whereas the driving point impedance function (DPIF) of the cable is proposed to be constructed either by using experimental SFRA data or analytically from the knowledge of the frequency-dependent parameters, material properties, and dimensions of the cable. Finally, an analytical formula is proposed for the estimation of the location of a short-circuit fault using the location of poles and zeros of the impedance function before and after the fault. The formulae are validated using FEM software simulations as well as experimentally on a test cable.

Dynamic Traffic Allocation Model Considering the Effects of Vehicle Emission Diffusion

Vehicle exhausts diffuse into roadside crowd breathing zones, thereby jeopardising human health. This study applies dynamic traffic distribution theories to comprehensively consider the impact of vehicle emission diffusion. The results provide a theoretical basis for improving the diffusion of urban traffic pollution to benefit the surrounding environment for roadside crowds. Firstly, a multi-vehicle cellular transport model that is suitable for analysing dynamic traffic distribution is constructed considering the distinct emission factors of various types of vehicles. Secondly, a multi-vehicle emission model is established to consider a range of driving conditions. Then, the concept of roadside crowd exposure risk is introduced, and we describe a method for calculating the total amounts of pollutants emitted by vehicles and inhaled by roadside crowds. The impact of vehicle emission diffusion is comprehensively discussed in terms of vehicle emissions and roadside crowd exposure risk. A generalised impedance function considering the influence of vehicle exhaust emission diffusion is also established based on the weighted average of actual vehicle travel time, multi-model emissions and roadside crowd exposure risk. Finally, this generalised impedance function is integrated into the dynamic optimal user allocation model, and a dynamic traffic allocation model considering the influence of vehicle emission control is developed.

Investigation of the dynamic vertical behaviour of a floating pile embedded in unsaturated poroelastic half-space

This paper proposes an analytical solution for investigating the dynamic vertical behaviour of a floating pile in unsaturated poroelastic half-space by considering the dynamic properties of the soil below the pile base. The pile shaft resistance is derived by applying Hankel integral transformation to the governing equations, and the pile base resistance is derived by introducing the potential function and operator decomposition methods. The dynamic interaction between the soil and the pile is considered by virtue of the impedance function. To account for the mixed boundary conditions of the pile-soil interface, an analytical solution for the vertical dynamic response of a floating pile is derived in the frequency domain. Additionally, by utilizing the inverse Fourier transform and convolution theorem, a quasi-analytical solution for the velocity response of the floating pile is derived in the time domain. Furthermore, the derived solution is verified through comparisons with existing solutions available in the literature. Finally, a parametric study is performed to investigate the influence of saturation and intrinsic permeability on the dynamic flexibility coefficient of porous unsaturated half-space, the influence of saturation on the dynamic impedance of the soil layer, and slenderness ratio on the vertical behaviour of floating pile and end-bearing pile.

Lumped parameter model for vertical vibrations of surface circular foundations on nonhomogeneous soil

PurposeA newly developed frequency-independent lumped parameter model (LPM) is the purpose of the present paper. This new model’s direct outcome ensures high efficiency and a straightforward calculation of foundations’ vertical vibrations. A rigid circular foundation shape resting on a nonhomogeneous half-space subjected to a vertical time-harmonic excitation is considered.Design/methodology/approachA simple model representing the soil–foundation system consists of a single degree of freedom (SDOF) system incorporating a lumped mass linked to a frequency-independent spring and dashpot. Besides that, an additional fictitious mass is incorporated into the SDOF system. Several numerical methods and mathematical techniques are used to identify each SDOF’s parameter: (1) the vertical component of the static and dynamic foundation impedance function is calculated. This dynamic interaction problem is solved by using a formulation combining the boundary element method and the thin layer method, which allows the simulation of any complex nonhomogeneous half-space configuration. After, one determines the static stiffness’s expression of the circular foundation resting on a nonhomogeneous half-space. (2) The system’s parameters (dashpot coefficient and fictitious mass) are calculated at the resonance frequency; and (3) using a curve fitting technique, the general formulas of the frequency-independent dashpot coefficients and additional fictitious mass are established.FindingsComparisons with other results from a rigorous formulation were made to verify the developed model’s accuracy; these are exceptional cases of the more general problems that can be addressed (problems like shallow or embedded foundations of arbitrary shape, other vibration modes, etc.).Originality/valueIn this new LPM, the impedance functions will no longer be needed. The engineer only needs a limited number of input parameters (geometrical and mechanical characteristics of the foundation and the soil). Moreover, a simple calculator is required (i.e. we do not need any sophisticated software).

A Simple Approach for the Dynamic Analysis of a Circular Tapered Pile under Axial Harmonic Vibration

The tapered pile offers sustainable use of construction materials due to its higher axial and lateral capacity and better performance owing to its geometry. This paper develops a semi-analytical solution of the vertical dynamic impedance of the tapered pile based on the dynamic Winkler theory and transfer matrix method. The accuracy and reliability of the proposed approach are verified by comparing the impedance functions of cylindrical and tapered piles obtained from the analytical solution and finite element analysis. A parametric study is performed to investigate the influence of the taper angle on the vertical dynamic impedance and resonant frequency. The results reveal that the taper angle has a significant influence on the vertical dynamic impedance, while it does not affect the oscillation period of the dynamic impedance and the resonant frequency. Besides, the vibration performance of the tapered pile is better than that of a cylindrical pile with the same volume. For a fixed-volume tapered pile, varying the pile length while keeping the pile tip diameter constant yields a better dynamic impedance than varying the pile tip diameter while keeping the pile length constant. Finally, the vertical displacement amplitude of the tapered pile decreases as the taper angle increases, especially for high-frequency excitation.

Reconstitution and Mutagenesis of Avian Infectious Laryngotracheitis Virus from Cosmid and Yeast Centromeric Plasmid Clones.

The genomes of numerous herpesviruses have been cloned as infectious bacterial artificial chromosomes. However, attempts to clone the complete genome of infectious laryngotracheitis virus (ILTV), formally known as Gallid alphaherpesvirus-1, have been met with limited success. In this study, we report the development of a cosmid/yeast centromeric plasmid (YCp) genetic system to reconstitute ILTV. Overlapping cosmid clones were generated that encompassed 90% of the 151-Kb ILTV genome. Viable virus was produced by cotransfecting leghorn male hepatoma (LMH) cells with these cosmids and a YCp recombinant containing the missing genomic sequences - spanning the TRS/UL junction. An expression cassette for green fluorescent protein (GFP) was inserted within the redundant inverted packaging site (ipac2), and the cosmid/YCp-based system was used to generate recombinant replication-competent ILTV. Viable virus was also reconstituted with a YCp clone containing a BamHI linker within the deleted ipac2 site, further demonstrating the nonessential nature of this site. Recombinants deleted in the ipac2 site formed plaques undistinguished from those viruses containing intact ipac2. The 3 reconstituted viruses replicated in chicken kidney cells with growth kinetics and titers similar to the USDA ILTV reference strain. Specific pathogen-free chickens inoculated with the reconstituted ILTV recombinants succumbed to levels of clinical disease similar to that observed in birds inoculated with wildtype viruses, demonstrating the reconstituted viruses were virulent. IMPORTANCE Infectious laryngotracheitis virus (ILTV) is an important pathogen of chicken with morbidity of 100% and mortality rates as high as 70%. Factoring in decreased production, mortality, vaccination, and medication, a single outbreak can cost producers over a million dollars. Current attenuated and vectored vaccines lack safety and efficacy, leaving a need for better vaccines. In addition, the lack of an infectious clone has also impeded understanding viral gene function. Since infectious bacterial artificial chromosome (BAC) clones of ILTV with intact replication origins are not feasible, we reconstituted ILTV from a collection of yeast centromeric plasmids and bacterial cosmids, and identified a nonessential insertion site within a redundant packaging site. These constructs and the methodology necessary to manipulate them will facilitate the development of improved live virus vaccines by modifying genes encoding virulence factors and establishing ILTV-based viral vectors for expressing immunogens of other avian pathogens.

Modeling impedance boundary conditions and acoustic barriers using the immersed boundary method: The one-dimensional case

Immersed boundary methods are heavily used in computational fluid dynamics, as an alternative to volumetric meshing, when a problem contains irregular geometric features. In wave-based architectural and room acoustics, the dynamics are simplified, but boundary conditions and acoustic barriers are usually described in terms of frequency-dependent impedance and transmittance functions. In this article, a formulation of the immersed boundary method is developed in the informative special case of one-dimensional linear acoustics. It relies on dual driving terms applied to the conservation of mass and momentum equations separately and is directly tunable against boundary impedances and barrier transmittances. It is shown how the driving terms may be combined to model either an impermeable frequency-dependent boundary condition or a barrier with a given transmittance. An explicit time-domain numerical method of finite-difference time-domain type is presented, and it is shown how the immersed boundary condition may be included, at minimal additional computational cost. Special attention is paid to the discrete approximation of the Dirac delta function, necessary in immersed boundary methods, as well as the discretisation strategy for frequency-dependent boundary and barrier conditions. Numerical results are presented. A complete derivation of numerical stability conditions for this immersed boundary method appears in an appendix.

Day-to-Day Dynamic Traffic Flow Assignment Model under Mixed Travel Modes Considering Customized Buses

In recent years, customized buses (CBs), a new form of public travel mode between bus and car, has sprung up in China. Its characteristics include flexible routes, each person having a seat and point-to-point travel have attracted travelers who seek high-quality travel, especially car travelers, alleviating traffic congestion at peak periods and leading to a change in urban travel modes. In addition to providing new travel modes, an exclusive bus lane (EBL) is also an effective means to alleviate traffic congestion. Therefore, this paper establishes link impedance functions under mixed travel modes considering the EBL, including customized buses on different kinds of links, and then presents a day-to-day dynamic traffic flow assignment model based on stochastic user equilibrium (SUE). Some conclusions were summarized by numerical case studies. First, the parameter of travelers’ sensitivity to route travel time affects the speed of traffic flow evolution. When it increases to positive infinity, the final state of the traffic network moves from SUE to deterministic user equilibrium (DUE). Second, the parameter on the degree of dependence of travelers on previous experience can not only influence the value size of actual travel time, but also influence the direction of actual travel time evolution. Third, conventional buses and customized buses have higher transportation efficiency than cars, but if the proportion of conventional bus travelers is too large, the total travel time of all travelers in the traffic network may increase. Fourth, when travel demands increase, the proportion of travelers who choose public transit is required to increase to achieve minimum total travel time. Lastly, from the perspective of the whole traffic network in any case, the EBL is not always beneficial. It is recommended to set EBLs when conventional buses and customized bus flows are heavy, which can be judged based on the model established in this paper.

Testing the absorption coefficient of 3D printed perforated panels

Sound absorption is common in most studios, but most residential spaces are not designed for good acoustics. While these rooms are non-ideal, they are sometimes used to record sounds and need to absorb unwanted frequencies. Perforated 3D printed panels have the potential to make inexpensive and modular home treatments. In order to determine if these panels would be effective, the absorptive properties need to be evaluated. There are several ways to test sound absorption, including the in situ subtraction method and the impedance tube transfer function method. Reference materials were used to test the effectiveness of both measurement methods. 3D printed perforated panels were then designed and the absorption was tested. Each surface was tested with the subtraction method, and many different setups for the equipment were tested to find the ideal setup for the most accurate absorption coefficient. The results show varying success. The 3D printed panels were then tested with the transfer function method. An impedance tube was made using PVC pipes and was used to test the transfer function method. This method showed varying results for the absorption coefficient tested, and results will be presented.

Towards Unique Circuit Synthesis of Power Transformer Winding Using Gradient and Population Based Methods

The aim of the paper is to synthesize a nearly unique, physically realizable and mutually coupled ladder circuit representation of a two-winding transformer by identifying the most accurate and reliable optimization technique such that prior knowledge in selecting the initial guess and search space is avoided. To this end, magnitude and phase of the driving-point impedance function are captured by performing sweep frequency response analysis (SFRA). Then, two widely used population-based algorithms namely, particle swarm optimization (PSO) and artificial bee colony (ABC) and one gradient-based sequential quadratic programming (SQP) algorithm are implemented. Two case studies are considered namely, i) 15 MVA, 66/11.55 kV transformer and, ii) 111 kVA, 7.33/1.22 kV transformer. The performance of the aforementioned algorithms is compared using three evaluation parameters namely, repeatability, accuracy and reliability

Model Tests on Determining the Effect of Various Geometrical Aspects on Horizontal Impedance Function of Surface Footings

Model Tests on Determining the Effect of Various Geometrical Aspects on Horizontal Impedance Function of Surface Footings

Evaluation of Conducted Electromagnetic Interference Behavior of Copper Vapor Laser

High power and high repetition rate electrically excited copper vapor laser (CVL) is a strong source of radiated and conducted electromagnetic interference (EMI). The thermal energy required to raise the temperature (∼1600°C) to generate copper vapor and the required voltage pulse for population inversion is provided by the pulse generating unit (PGU). The PGU generates a voltage pulse of the order of ∼13 kV with a rise time of less than 100 ns and a current pulse in the range of ∼500 A with a similar rise time. The high voltage and current generated by PGU along with the high voltage pulse discharge in the laser tube serves as a prominent source of EMI and affects the performance of nearby electronic devices. This article presents a comprehensive study of conducted EMI from a high-power and high voltage discharge inside the CVL system and its impact on laser performance. The conducted noise from the laser is a function of laser impedance and is proportional to the magnitude of load mismatch. A simple and robust technique is presented to reduce the conducted noise from CVL. The correlation between the laser electrode pin configurations and the conducted noise is also presented.