Ramp Length Research Articles

Factors influencing driver behaviour along curved merging interchange terminals

Problem statement. To promote safe and comfortable driving operations, design manuals and policies call for merging terminal ramps to be built along straight roadway sections. However, this prescription may need to be overlooked when there is no alternative to terminals being designed along curves. This study aims to assess the impact of design factors on driver behaviour along curved acceleration terminals with continue or reverse curvature prior to joining the motorway. Methodology. A driving simulation experiment was conducted to observe longitudinal and transversal driver behaviour when certain factors (i.e., radius, ramp length, motorway curve direction, and traffic conditions along the motorway segment) were manipulated. The forty-eight drivers involved were separated into groups based on age and gender. Results. The motorway radius has a significant impact on longitudinal performance, while traffic volume impacts on the merging point where vehicles enter the adjoining motorway lane. Compared to linear terminals, the merging abscissa need to be longer on curved ones so as to compensate for the blind spot and enable drivers to identify and accept gaps between vehicles in the traffic flow. The ramp-terminal connection type influences the speed at the beginning of the terminal, the position of the merging point and transversal driver behaviour. Conclusions. Although some limitations in the study were necessary to limit their impact on the experimental design, the results here may prove useful when considering the adoption of appropriate engineering countermeasures at the design stage of entry terminals along curved motorway segments.

Law of Incipient Separation over Curved Ramps as Inferred by Reynolds-Averaged Navier–Stokes

In this study, numerical simulations of spatially developing incompressible turbulent boundary layers (SDTBLs) with adverse pressure gradient (APG) over two-dimensional smooth curved ramps have been performed by solving the Reynolds-averaged Navier–Stokes (RANS) equations. First, it has been verified that the RANS results converge with respect to domain and grid size, and the effects of different inflow conditions have been assessed. Then, the RANS results have been validated by comparing them with the experiments of Song and Eaton (Experiments in Fluids, Vol. 36, No. 2, 2004, pp. 246–258) for the separated turbulent flow over an arc at a reference Reynolds number based on the momentum thickness of . Furthermore, the effects of the ramp’s slope and curvature on the skin-friction and pressure coefficients for polynomial and half-Gaussian ramps at have been investigated. From this investigation, a numerical criterion has been discovered for the inception of flow separation in SDTBL over smooth curved ramps. The criterion relies only on the geometrical parameters of normalized maximum slope magnitude, , and height-to-length ratio of the ramp, , and on the Reynolds number of the flow based on the ramp length, . Specifically, incipient separation occurs when the magnitude of the normalized maximum slope, , reaches a critical value specified as , where , , and are constants. Accordingly, the flow separates over a smooth curved ramp for which .

Hydraulics of sharp-crested weir culverts with downstream ramps in free-flow, partially, and fully submerged-flow conditions

Laboratory experiments were conducted to investigate the hydraulics and discharge characteristics of sharp-crested weir culverts with downstream ramps for hydraulically smooth wall boundary and for free, partially submerged, and fully submerged-flow conditions. Four weir-culvert models were tested with different weir heights, ramp lengths, and culvert heights. The partially submerged-flow conditions were created when a slight increase in tailwater caused the headwater to rise due to partial submergence of the culvert. In this flow regime, supercritical flow over the ramp interacted with culvert outflow and this flow regime was classified as Supercritical Jet Interaction Regime or SJIR. Once tailwater reached the weir crest, the weir flow regime became submerged indicating fully submerged-flow condition. Based on the variations of water surface profiles, submerged flows were further classified into Surface Jump Regime (SJR), Surface Wave Regime (SWR), and Deeply Submerged Regime (DSR) and the boundaries between each flow regime were defined by regime plots. To predict discharge of weir culverts with downstream ramps, variations of discharge coefficient with weir geometry and flow regimes were studied and empirical formulations were developed. In addition, free and partially submerged flow discharges were predicted by implementing the interaction factor. It was found that the interaction factor was independent of the Froude number in SJR, while it correlated with the Froude number in SJIR. Under submerged-flow conditions, evaluation of the discharge characteristics of the proposed weir-culvert model showed correlations with water surface flow regimes and a three-stage prediction formula was proposed for estimation of submerged flow. The energy losses over weir-culvert models were also calculated and it decreased with submergence.

МЕТОД ВИЗНАЧЕННЯ ОСНОВНИХ ПАРАМЕТРІВ ВАНТАЖНОГО ЛЮКА В ХВОСТОВІЙ ЧАСТИНІ ФЮЗЕЛЯЖУ ЛІТАКІВ ТРАНСПОРТНОЇ КАТЕГОРІЇ

A method has been developed for determining principal parameters for aft cargo door of transport aircraft. A list of input data is given and a technique for finding them is described. An example based on an existing transport aircraft is considered. The following has been used as source data: basic cargo nomenclature to be transported by the designed aircraft, cargo overall dimensions and weight, methods of loading and mooring, loading facilities. More over the design, operational and regulatory parameters are needed, such as landing gear configuration, its bottoming system, extension of rails of the upper equipment for loading/unloading, cargo trajectories during loading and airdropping, codes of the international regulatory bodies such as FAR, CS, AP. Based on the source data, the principle of determining the dimensions of the cargo compartment, cargo floor and the loading sites in the form of a ramp with a pressure bridge, and air stairs is given. The relation between the ramp length and the cargo floor length is described taking into account the loading, unloading and air dropping operations. Correct calculation of these parameters is the most important task, because performance of the future transport aircraft directly depends on the solution. The technique of determining the cargo door opening, development of the load-bearing structure of the transport aircraft fuselage aft section, its main strong elements – the cargo door beam, the ramp, the attachment units, the ramp locks – is given. The interconnection of the ramp load-bearing structure with the load-bearing structure of the fuselage aft part, the options for transferring loads perceived by the ramp to the frame are described. Examples of two types – flat and volumetric – of the cargo door beams, as well as the method of their assignment are considered. Trajectories of the extreme points of the in-gauge load are determined using graphical method for loading, unloading, and airdropping operations. Taking into account the positions of these trajectories makes it possible to select the desired cutout in the fuselage aft section. While designing the aft cargo doors the main features are highlighted. These features when considered make it possible to determine the most optimal parameters of the cutout, the cargo door type and its components.

Sub-maximally Activated Rat Soleus Fibers Exhibit Stretch Activation

Stretch activation occurs when a muscle develops force after an imposed stretch. The effect is large in some types of insect flight muscle and is also thought to contribute to cardiac function. The potential role of stretch activation in mammalian skeletal muscle is less clear. We activated chemically permeabilized rat soleus fibers in solutions with pCa values (=log10[Ca2+]) ranging from 9.0 to 4.5 and imposed ramp and hold length changes of different sizes (0.002 to 0.07 muscle lengths) and different stretch velocities (0.07 to 1.40 muscle lengths per second). All experiments were performed at 22C. When fibers were stretched in pCa 9.0 solution, force increased linearly during the stretch and decayed during the hold portion of the trial. This is consistent with the behavior of a simple visco-elastic system. Fibers immersed in solutions with pCa values between 6.6 and 6.0 exhibited more complex properties. During the stretch, the force response was biphasic due to the muscle's short-range stiffness. Immediately after the stretch, force dropped transiently, and then rose to a peak value of up to 130% of the pre-stretch isometric force. This is stretch activation. The peak stretch activated force increased with the magnitude of the stretch but was not markedly changed by stretch velocity. Fibers immersed in solutions with pCa values less than 6.0 exhibited a short-range stiffness but force declined during the hold portion of the trial and did not exhibit a delayed activation. Our measurements demonstrate that mammalian skeletal muscle can exhibit prominent stretch activation in solutions with sub-maximal calcium concentrations. To investigate the mechanisms responsible for stretch activation, we ran preliminary simulations using the MyoSim model of dynamically coupled myofilaments. These calculations suggest that force-dependent recruitment from the myosin OFF state may contribute to stretch activation.

Research on deceleration lane length of special ramp for freight cars on passenger-freight separation expressway

In order to obtain the truck-specific ramp deceleration lane length index for passenger and cargo separation, the UMRR chain Kepler radar speedometer is used to collect the vehicle speed data under the free-flow state of the ramp feature points (starting point, diversion point and small nose point of the transition section). The KS normal distribution test is carried out on the sample data. On the basis of satisfying the test requirements, the speed and acceleration characteristics of the deceleration lane vehicle are analysed, and then the parameters in the secondary deceleration theory are re-determined. Based on this, the deceleration lane length value of the truck-specific ramp is calculated.

Effect of fluctuations in the down ramp plasma source profile on the emittance and current profile of the self-injected beam in a plasma wakefield accelerator

With its extreme beam parameters, the FACET II facility enables the test of the down ramp injection scheme in the laboratory for the beam-driven plasma wakefield accelerator approach. In addition to the ideal cases studied in previous theoretical work, we investigate the effect of fluctuations in the down ramp plasma source profile on the emittance and current profile of the self-injected beam using 2D and 3D particle-in-cell simulations. We show that down ramps with a length of $\ensuremath{\sim}10\text{ }\text{ }c/{\ensuremath{\omega}}_{p}$ can be reproducibly created by generating a shock in a supersonic flow. Simulations show that the emittance of the injected beam using such down ramps is $\ensuremath{\sim}0.1\text{ }\text{ }\ensuremath{\mu}\mathrm{m}$. A gentler ramp can further reduce the slice emittance of the beam to $\ensuremath{\sim}0.03\text{ }\text{ }\ensuremath{\mu}\mathrm{m}$. The emittance of the injected beam depends on the ramp length but is insensitive to the shape of the ramp. However, the current profile of the injected beam can be manipulated by changing the ramp shape. A simulation shows that, when a noncylindrical driver is used, the emittance of the injected beam differs in the two orthogonal transverse planes and is a few times larger than that of the cylindrical driver case. A full-scale simulation where we use a realistic density profile that includes the up ramp, the injecting down ramp, and the exiting down ramp is presented to show that the beam emittance is preserved during the acceleration and extraction of the beam.

Beam emittance preservation using Gaussian density ramps in a beam-driven plasma wakefield accelerator.

A current challenge that is facing the plasma wakefield accelerator (PWFA) community is transverse beam emittance preservation. This can be achieved by balancing the natural divergence of the beam against the strong focusing force provided by the PWFA plasma source in a scheme referred to as beam matching. One method to accomplish beam matching is through the gradual focusing of a beam with a plasma density ramp leading into the bulk plasma. Here, the beam dynamics in a Gaussian plasma density ramp are considered, and an empirical formula is identified that gives the ramp length and beam vacuum waist location needed to achieve near-perfect matching. The method uses only the beam vacuum waist beta function as an input. Numerical studies show that the Gaussian ramp focusing formula is robust for beta function demagnification factors spanning more than an order of magnitude with experimentally favourable tolerances for future PWFA research facilities.This article is part of the Theo Murphy meeting issue ‘Directions in particle beam-driven plasma wakefield acceleration’.

Analysis of Crash Rates at Freeway Diverge Areas using Bayesian Tobit Modeling Framework

The goal of this study is to evaluate the impact of various risk factors on crash rates at freeway diverge areas. Crash rates data for a three-year period from 367 freeway diverge areas were used for analysis. Four candidate Tobit models were developed and compared under the Bayesian framework: a traditional Tobit model; a random parameters Tobit (RP-Tobit) model; a grouped random parameters Tobit (GRP-Tobit) model; and a random intercept Tobit (RI-Tobit). The results showed that the RP-Tobit model performs best with highest value of Rd2 as well as lowest Mean Absolute Deviance (MAD) and Deviance Information Criteria (DIC), indicating the importance of accounting for unobserved heterogeneity to improve the model fit. Both the GRP-Tobit and the RI-Tobit models provide better performance than the traditional Tobit model. The model results showed that crash rates at freeway diverge areas were positively associated with mainline annual average daily traffic (AADT) and negatively associated with ramp AADT, indicating the different mechanisms of the impact of traffic volume on crash rates at freeway diverge areas. Lane-balanced design and high speed limits at freeway diverge areas have a negative effect on crash rates. The number of lanes on mainline and ramp length have significant heterogeneous effects on crash rates across observations. The RP-Tobit model provides a more comprehensive understanding of the heterogeneous effects of risk factors on crash rates across observations.

Passage Performance of Potamodromous Cyprinids over an Experimental Low-Head Ramped Weir: The Effect of Ramp Length and Slope

Low-head ramped weirs are a common instream obstacle to fish movements. Fish passability of these structures, where water passes over but does not generate a waterfall, is primarily related to ramp length and slope, but their relative contribution has seldom been considered. This study aims to assess the passage performance of a potamodromous cyprinid, the Iberian barbel (Luciobarbus bocagei), negotiating an experimental ramped weir with varying ramp length (L) and slope (S). Four configurations were tested, with a constant discharge of 110 L∙s−1. Results suggest that both factors influenced passage performance of fish. Attraction efficiency (AE) increased with increasing L and S, whereas the number of successes (N) and passage efficiency (PE) decreased upon increasing L. For S, it was found that both N and PE peaked at the intermediate level (20%). These results suggest that configurations with the lowest slopes may not necessarily be the best option because they may be less attractive for the fish and their demand for space is higher. Higher slopes (but not excessive) could be more attractive to fish, less space-demanding, and therefore, more cost-effective. Future studies should investigate how discharge and boulder placement influence fish passage across ramped weirs, to improve habitat connectivity.

Quality No-tillage System: The Importance of the Use of Cover Species in Reducing Compaction and Soil and Water Losses Due to Erosion

Water and soil losses due to surface runoff depend on rainfall intensity and periods, vegetation cover, slope, and ramp length, in addition to conservation practices. The implementation of a quality planting system for the effective control of erosion while avoiding the disintegration of the soil structure by the direct impact of dropping is of paramount importance. Nevertheless, the current no-tillage system has led to the emergence of compacted layers in the soil, which reduce water infiltration, favoring surface runoff. Thus, it is necessary to optimize the use of soil cover species, aiming at reducing compaction and, subsequently, losses of water and soil that flow superficially. The purpose of this study is to highlight the importance of using a quality management system to reduce soil and water losses due to erosion caused by compaction. Furthermore, it is hoped that the study may contribute to the guidance of the best use and management of the soil for farmers.

Stochastic Process and Simulation of Traction Load for High Speed Railways

The traction load of a high-speed railway (HSR) may cause significant voltage fluctuations in the traction power supply system and the utility grid. To evaluate power quality, modeling traction load is an urgent need as well as a fundamental work. This paper aims to build a probabilistic model to describe the pattern of traction load changing with time. It is very challenging due to the randomness of train behavior. This paper first investigates the stochastic process of traction load and points out that the size and frequency of load fluctuation, respectively, rely on the slope and length of the rail ramp. Based on this, train power (TP) and headway (TH) are set as two basic components of the probabilistic model, where TP and TH are described by a normal distribution and an exponential distribution, respectively. In addition, a sliding time-window method is developed for generating time-dependent load samples. The proposed method has low complexity, as well as can consider the randomness, giving more realistic simulation results. It can be used to forecast traction load for a planning railway or to establish a measurement-based model for an operating railway. A case study is performed for parameter identification and model verification, and the rapid voltage change (RVC) caused by the HSR loads has been evaluated in different operation scenarios.

Stability analysis of a non-conventional breakwater for wave energy conversion

This paper presents the stability analysis of a non-conventional breakwater cross-section integrating an overtopping wave energy converter, named OBREC. The device consists of a traditional rubble-mound breakwater in which the upper part of the armour layer is replaced by a smooth ramp and a reservoir.The analysis of the structure is carried out by combining model scale experiments and numerical simulations based on the Volume-Averaged Reynolds Averaged Navier-Stokes (VARANS) equations.The numerical analysis is used to complete and extend the results of the physical model test campaign, providing a deeper understanding of the pressure distribution and resultant force behaviour in locations where laboratory measurements were difficult to obtain or not available. Results show that the maximum vertical and horizontal total forces on the device are not simultaneous. At the time instant of the maximum total horizontal force, the vertical force is zero or directed downward, due to the significant positive contribution of the force acting on the sloping ramp. Additional numerical simulations show the influence of the submerged ramp length on the forces acting on the structure using the global and local stability analysis. The presence of the shaft contributes positively to the global stability against the sliding failure mode by reducing the uplift force exerted on the horizontal base. Moreover, the stability analysis shows that the critical conditions for the global failure modes occur at different time instants.

Statistical analysis of geometric characteristics and speed reductions for raised pedestrian crosswalks (RPC)

The influence of raised pedestrian crosswalks (RPC) as traffic-calming measures in urban areas is investigated. Speed reduction due to RPCs is statistically modeled based on their geometric characteristics, and considering before- and on-RPC spot speeds. Geometric dimensions of 23 RPCs including street’s width and grade, ramp lengths, top flat crown length and heights, together with 4,672 spot speed observations associated with these RPCs were measured in Qazvin, Iran. To properly model the repeated speed observations on each RPC, the mixed-effects approach is used to estimate the parameters of a linear model. Demonstrating the statistically significant dependence of on-RPC speeds (Vc) on the approaching speeds (Vf) and also the geometric characteristics of the RPC, the proposed model predicts any percentile of Vc as a function of the corresponding percentile of Vf, the RPC’s algebraic difference in ramps’ grades A1 and A2, and the street width. The results of this study help traffic engineers and decision makers implement optimized RPCs in terms of cross-section dimensions and their locations on streets relative to crowded residential area and school zones where speed reduction is needed.

Airport low-level wind shear lidar observation at Beijing Capital International Airport

The low-level wind shear is defined as a sharply change of the wind speed or wind direction within 600 m above the ground level. Due to affecting the airspeed of aircraft during take-off and landing phases, the wind shear can result in the disastrous aircraft accidents. The lidar team at Ocean University of China (OUC) carried out the particular research of the low-level wind shear at Beijing Capital International Airport (BCIA) in 2015 and 2016 by operating a pulse coherent Doppler lidar (PCDL) system. In this field experiment, the radial resolution is 30 m while the angle resolution is 0.1° and the updating rate of observation data is 4 Hz. On account of the high spatial and temporal resolution, the small-scale meteorological phenomenon can be captured. The low-level wind shear is observed by different scanning modes including 5-Doppler beam swing (5-DBS), step-wise plane-position indicator (PPI), multi-elevation PPI, range-height indicator (RHI) and glide path scan. The experiment configuration, the PCDL system, the observation modes and the case study of the wind shear are proposed and experimentally demonstrated. The quick-look algorithms which identifies the wind shear alarm based on the radial velocity data have been developed and tested. A case study of the wind shear shows that the events of low-level wind shear at the southern end of 18R/36L are suspected to be caused by buildings and rows of trees along the glide path under strong northwest wind conditions. Meanwhile, more than 2000 PPI scans have been analyzed to indicate the relationship between wind shear intensity and ramp length. Preliminary validations of the algorithms against wind shear reports from the crew and the terminal control office indicated positive skill. Totally, 14 wind shear cases have been validated by reports from the crew during field observation campaign.

Numerical investigation of over expanded flow behavior in a single expansion ramp nozzle

The single expansion ramp nozzle is severely over-expanded when the vehicle is at low speed, which hinders its ability to provide optimal configurations for combined cycle engines. The over-expansion leads to flow separation as a result of shock wave/boundary-layer interaction. Flow separation, and the presence of shocks themselves, result in a performance loss in the single expansion ramp nozzle, leading to reduced thrust and increased pressure losses. In the present work, the unsteady two dimensional compressible flow in an over expanded single expansion ramp nozzle has been investigated using finite volume code. To achieve this purpose, the Reynolds stress turbulence model and full multigrid initialization, in addition to the Smirnov's method for examining the errors accumulation, have been employed and the results are compared with available experimental data. The results show that the numerical code is capable of predicting the experimental data with high accuracy. Afterward, the effect of discontinuity jump in wall temperature as well as the length of straight ramp on flow behavior have been studied. It is concluded that variations in wall temperature and length of straight ramp change the shock wave boundary layer interaction, shock structure, shock strength as well as the distance between Lambda shocks.

Quasi‐Steady Evolution of Hillslopes in Layered Landscapes: An Analytic Approach

AbstractLandscapes developed in layered sedimentary or igneous rocks are common on Earth, as well as on other planets. Features such as hogbacks, exposed dikes, escarpments, and mesas exhibit resistant rock layers adjoining more erodible rock in tilted, vertical, or horizontal orientations. Hillslopes developed in the erodible rock are typically characterized by steep, linear‐to‐concave slopes or “ramps” mantled with material derived from the resistant layers, often in the form of large blocks. Previous work on hogbacks has shown that feedbacks between weathering and transport of the blocks and underlying soft rock can create relief over time and lead to the development of concave‐up slope profiles in the absence of rilling processes. Here we employ an analytic approach, informed by numerical modeling and field data, to describe the quasi‐steady state behavior of such rocky hillslopes for the full spectrum of resistant layer dip angles. We begin with a simple geometric analysis that relates structural dip to erosion rates. We then explore the mechanisms by which our numerical model of hogback evolution self‐organizes to meet these geometric expectations, including adjustment of soil depth, erosion rates, and block velocities along the ramp. Analytical solutions relate easily measurable field quantities such as ramp length, slope, block size, and resistant layer dip angle to local incision rate, block velocity, and block weathering rate. These equations provide a framework for exploring the evolution of layered landscapes and pinpoint the processes for which we require a more thorough understanding to predict their evolution over time.

Geometric evaluation of the main operational principle of an overtopping wave energy converter by means of Constructal Design

Abstract Current work aims to study the geometry of an overtopping wave energy converter in real scale using Constructal Design. Problem studied here is submitted to two constraints (areas of wave tank and overtopping ramp) and two degrees of freedom: ratio between the height and length of ramp (H1/L1) (or ramp slope, β) and distance between the bottom of wave tank and the device (S). The effect of H1/L1 and S over dimensionless device available power (Pd) is evaluated for three different ramp area fractions (ϕ) and two different monochromatic waves. Conservation equations of mass, momentum and one equation for the transport of water volume fraction are solved with the finite volume method. To tackle with water-air mixture, multiphase model Volume of Fluid is used. Results showed the applicability of Constructal Design for improvement of device performance. For fixed magnitudes of S, the highest magnitudes of Pd are achieved for the lowest possible ratio of H1/L1. For smaller construction areas of the ramp, intermediate magnitudes of S led to the highest magnitudes of Pd, i.e., the sinking of device does not led necessarily to the best performance. Moreover, optimal shapes are not universal (the same) for the two wave conditions studied.

Neutronic analysis of the fuel loaded irradiation loop device of the RMB Multipurpose Brazilian Reactor

The structuring project of the Brazilian Multipurpose Reactor (RMB) is responsible for meeting the capacity to develop and test materials and nuclear fuel for the Brazilian Nuclear Program. An irradiation test device (Loop) capable of performing fuel test for power reactor rods is being conceived for RMB reflector. In this work neutronic calculations have been carried out in order to determine parameters to the Loop basic design. Safe position determined to be 52.7 cm displaced from the core, where linear heat rate (q’) < 1 W/cm fission power is released in the rig loading fissile sample. Since irradiation rig moves during normal operation of the reactor, displacement of the samples must be investigated in terms of perturbation in the core. Results confirmed efficacy of the 12 cm heavy water layer designed to suppress reactivity effects in the core. Linear heat rate in the fissile sample was calculated in order to estimate predefined power ramps of 50–350 W/cm, information necessary to the project of the displacement device. Ramp lengths of 9.59 cm–13.22 cm were found depending on the peak factor considered for the sample rod and the number of beryllium rows arranged in the reflector.

Prenatal development of rectal patch in large intestine of goats

Prenatal development of rectal patch was studied in 30 goat fetuses ranging from 1.4 cm CRL (24 days of gestation) to 38.0 cm CRI (Crown ramp length). Rectal patch first appeared in goat foetuses by 60 days of gestational age as a continuous band of small to medium–sized lymphocytes in the lamina propria of rectum. During fourth month of gestation, the primordia differentiated into large lymphoid nodules which had an oval basal portion and a pyramidal apical portion, which formed a dome-like structure within the intestinal ridges below the surface epithelium and was surrounded by an irregular capsule. During fifth month, an increase in the number and size of the lymphoid nodules and primordial dome region was noticed. The lymphoid nodules were histologically mature with a prominent germinal center, its corona, a wide dome area and an internodular area with few high endothelial venules. The rectal patch was histologically mature at birth with both primary and secondary nodules in it.