Single-Track Bike Trails in the Moravian Karst as Part of Forest Recreation

Recently, cycling has become a popular recreation activity, and mountain biking provides an experience that is sought by an increasing number of people. Bike trails constructed for mountain bikers in access areas lead mostly through the forest and provide not only an extraordinary riding experience but the opportunity to admire the surrounding nature. The reason for constructing such trails from a landowner’s point of view is to help keep bikers’ movements within a defined access area and to ensure adjacent areas are left free for other forest functions. It also helps distribute groups of visitors with other interests to other parts of the forest. This is what we call “controlled recreation”. In this example, it means that if cyclists come to the locality to use the bike trails, they should ride only along the designated trails; however, they may leave these trails and ride on the surrounding land. This article studied the movements of bikers in an accessible area of the Moravian Karst and the regulation of their movements by controlled recreation. Attendance in the area was measured using automatic counters. These were placed at the entry points to the accessible area and just behind the routes where the trails branch off. The results showed that bikers mostly stayed on the formal routes and that the trails were effective, i.e., there was no uncontrolled movement of bikers into the surrounding forest stands. We also noted the time of day that cyclists were active. These results can be used to better plan work in the forest, for example, harvesting and logging. To further the suitable development of accessible areas of the forest, we also compared the usual size of trail areas in two other European countries and the increasing width of bike trails due to the transverse slope of the terrain.

Marineda Footbridge in A Coruña (Spain)

<p>Designed with smooth and slender forms, Marineda footbridge in A Coruña (Spain) is a composite structure for pedestrians and cyclists that solves the access to one of the largest shopping centers in Spain, flying above a high-traffic highway.</p><p>The maximum deck height and the geometry in plan were established by the necessary vertical clearance over the highway and the situation of the starting and end points. In this way, and with the idea of avoiding structural elements over the deck to minimize visual impact, a three-span curved slender beam was designed. The main span is 85.8 meters long and comprises a composite airtight box-girder deck with variable depth from 1.75 meters near piers to 1.00 meter in midspan section. The two lateral spans, one on each side, are formed by a post-tensioned voided slab rigidly connected to pier and abutment, and with a strut element underground forming a rigid frame. In these spans the maximum deck height is 1.90 meters and the minimum is 1.00 meter. The deck width is 4.00 meters to accommodate both cyclists and pedestrians and has a transverse slope of 1.5% from the centerline to each side.</p><p>The curved geometry in plan, with a radius of 55 meters, and the stiffness of the lateral spans allow for an integral structure design without joints, that, along with the slenderness of the main span, give an unique appearance to the footbridge.</p>

ASSESSING THE IMPACT OF THE SLOPES ON RUNWAY DRAINAGE CAPACITY BASED ON WHEEL/PATH SURFACE ADHESION CONDITIONS

Aircraft braking distance is dependent on the friction between the main gear tires and runway pavement surface.Pavement texture, which is divided into macrotexture and micro-texture, has a noticeable effect upon friction, especially when the surface is wet. A risk analysis framework is developed to study the effects of longitudinal and transverse slopes on the aircraft braking distance in wet runway conditions and their influences on the probability of landing overrun accidents.This framework is operating under various water-film thicknesses, Maximum Landing Weights (MLW), and touchdown speed probability distributions for an acceptable range of longitudinal/transverse slopes and pavement texture depths.A simulator code is developed that initially computes the existing water-film thickness, as the result of intense precipitation,under aircraft main gear (depend on aircraft category) and then applies this variable as one of the main inputs to the aircraft braking distance computation. According to the obtained results, longitudinal gradient does not have a significant effect on the existing water depth on the surface although it affects the flow path length. Furthermore, 1% to 1.5% transverse slope causes rapid drainage of water from the runway surface and considerably decreases the probability of runway excursion accidents.

Change in Transverse Slope of Water Surface at River Bend: A Numerical Study

Generation of secondary current in a meandering river flow due to the centrifugal force acting on the bend is three dimensional (3D) in nature. But in case of practical problems like alluvial geomorphic processes, 3D models are not proved to be efficient. Hence, two dimensional (2D) models are generally adopted for such problems. This study offers a presentation of numerical simulation results for turbulent flows around bends of a meandering channel for different meander angles. 2D models were built by the use of iRIC Nays2DH solver for flow simulation of 45˚, 90˚, 135˚, 180˚ meandering bends with varying widths of 0.15m, 0.25m, 0.75m, 1.00m, 1.25m and 1.50m considering constant Froude number with constant meandering length (ML/W) and constant radius of curvature (R/W). Zero equation model was used as turbulence closure with finite differential advections as upwind scheme. The flow behavior has been studied at the apex and cross over portions of bends. From the simulation, the velocity at outer bank was found to be lower than that of the inner bank while the water surface elevation was found to be higher than that of the inner bank. Increase in transverse slope of water surface at bend was observed for increasing meander angles, Froude numbers and decreasing channel widths. Journal of Engineering Science 12(2), 2021, 93-101

Innovative aerodynamic grain separation system for plant harvesting in sloped areas: problems, research and optimization of parameters

This article presents the main problems associated with cereal harvesting in sloping areas. The presented innovative aerodynamic system supporting the separating unit of combine harvester can be one of the ways to counteract the negative effects of harvesting machines work on slopes. The Monte Carlo numerical method, presented in this article, was applied in the optimization of an aerodynamic sieve separation process on an inclined terrain. The given variables are the transverse slope of separator α (of the sieve), longitudinal slope β and the output of the main and side fans. The Monte Carlo method makes it possible to determine an optimized set of parameters (α = 10°, β = 2.8°, δ = 9°), the output of the main fan (0.67 m3 s−1) and the output of the side fan (1.86 m3 s−1), allowing to obtain the best indicator values of 2.1% grain loss and 97.5% grain purity.

A Novel Comprehensive Evaluation Method for Estimating the Bank Profile Shape and Dimensions of Stable Channels Using the Maximum Entropy Principle

This paper presents an extensive and practical study of the estimation of stable channel bank shape and dimensions using the maximum entropy principle. The transverse slope (St) distribution of threshold channel bank cross-sections satisfies the properties of the probability space. The entropy of St is subject to two constraint conditions, and the principle of maximum entropy must be applied to find the least biased probability distribution. Accordingly, the Lagrange multiplier (λ) as a critical parameter in the entropy equation is calculated numerically based on the maximum entropy principle. The main goal of the present paper is the investigation of the hydraulic parameters influence governing the mean transverse slope (St¯) value comprehensively using a Gene Expression Programming (GEP) by knowing the initial information (discharge (Q) and mean sediment size (d50)) related to the intended problem. An explicit and simple equation of the St¯ of banks and the geometric and hydraulic parameters of flow is introduced based on the GEP in combination with the previous shape profile equation related to previous researchers. Therefore, a reliable numerical hybrid model is designed, namely Entropy-based Design Model of Threshold Channels (EDMTC) based on entropy theory combined with the evolutionary algorithm of the GEP model, for estimating the bank profile shape and also dimensions of threshold channels. A wide range of laboratory and field data are utilized to verify the proposed EDMTC. The results demonstrate that the used Shannon entropy model is accurate with a lower average value of Mean Absolute Relative Error (MARE) equal to 0.317 than a previous model proposed by Cao and Knight (1997) (MARE = 0.98) in estimating the bank profile shape of threshold channels based on entropy for the first time. Furthermore, the EDMTC proposed in this paper has acceptable accuracy in predicting the shape profile and consequently, the dimensions of threshold channel banks with a wide range of laboratory and field data when only the channel hydraulic characteristics (e.g., Q and d50) are known. Thus, EDMTC can be used in threshold channel design and implementation applications in cases when the channel characteristics are unknown. Furthermore, the uncertainty analysis of the EDMTC supports the model’s high reliability with a Width of Uncertainty Bound (WUB) of ±0.03 and standard deviation (Sd) of 0.24.

ANALYSIS BANDWIDTH DRAIN ON CITY ROAD

Drainage of surface water from the pavement structure is an important parameter for preserving the designed period and safety during the operation of the pavement structure. The paper presents research on the relationship between the efficiency of drains depending on the cross slope. When the correct selection of transverse slopes and the collection of rain runoff from the catchment area of the road, the safety of the operating conditions itself increases. By changing the transverse slope, the parameters in terms of water runoff speed and drain efficiency also change. During the analysis, this paper also took into account the hydrological parameters for the site where the section in question is located. The analysis in this paper aims to show how the correct selection of cross slopes of pavement structures can be of key importance for the efficiency of the drain, and thus the efficient drainage of surface water from the pavement structure.

Study on Spatial Variation of Shear Mechanical Properties of Soil-rock Mixture

The soil-rock mixture (SRM) is a kind of special engineering geological material, which has been exposed to the field for a long time and is affected by rainwater seepage, geological force, slope sliding force and human activities, resulting in the spatial variability of its mechanical properties. Taking the SRM distributed on a slope of the Three Gorges Reservoir area as the research object, four test locations were selected along and transverse the slope. First, in-situ large-scale direct shear test was carried out, and then the laboratory large-scale direct shear test, particle sieving test, and water content test were carried out in the undisturbed sample to study the variation of shear mechanical properties of SRM distributed in different spatial locations. The results show that: (1) Under the same normal stress, the peak strength of the SRM decreases at a similar rate along the slope direction and the transverse slope direction. (2) The cohesion of the SRM is continuously strengthened, and the friction angle is continuously deteriorated along the slope from high to low, the cohesion and friction angle are almost no variability along the transverse slope. (3) The mechanism of the above-mentioned variation in the shear mechanics parameters of SRM is that the lower the elevation along the slope, the more fragmented the rock, the lower the rock content. (4) Spatial variability models of cohesion and friction angle of SRM were established, which can provide references for related engineering applications.