Search

The basic terrain-following (BTF) coordinate simplifies the lower boundary conditions of a numerical model but leads to numerical error and instability on steep terrain. Hybrid terrain-following (HTF) coordinates with smooth slopes of vertical layers (slopeVL) generally overcome this difficulty. Therefore, the HTF coordinate becomes very desirable for atmospheric and oceanic numerical models. However, improper vertical layering in HTF coordinates may also increase the incidence of error. Except for the slopeVL of an HTF coordinate, this study further optimizes the HTF coordinate focusing on the thickness of vertical layers (thickVL). Four HTF coordinates (HTF1–HTF4) with similar slopeVL but different vertical transition methods of thickVL are designed, and the relationship between thickVL and numerical errors in each coordinate is compared in the classic idealized thermal convection [two-dimensional (2D) rising bubble] experiment over steep terrain. The errors of potential temperature θ and vertical velocity w are reduced most, by approximately 70% and 40%, respectively, in the HTF1 coordinate, with a monotonic increase in thickVL according to the increasing height; however, the errors of θ increased in all the other HTF coordinates, with nonmonotonic thickVLs. Furthermore, analyses of the errors of vertical pressure gradient force (VPGF) show that due to the interpolation errors of thickVL, the inflection points in the vertical transition of thickVL induce the initial VPGF errors; therefore, the HTF1 coordinate with a monotonic increase in thickVL has the smallest errors among all the coordinates. More importantly, the temporal evolution of VPGF errors manifests top-type VPGF errors that propagate upward gradually during the time integration. Only the HTF1 and HTF4 coordinates with a monotonic increase in thickVL near the top of the terrain can suppress this propagation. This optimized HTF coordinate (i.e., HTF1) can be a reference for designing a vertical thickVL in a numerical model. [ABSTRACT FROM AUTHOR]

One of the basic requirements for sustainable forest management in mixed broadleaved stands is to provide suitable conditions for natural regeneration of trees. These conditions include, but are not limited to, the frequency, quality and the composition of seedling species. Compacted soil layers caused by forest machinery traffic are the most common problem affecting seedling establishment and growth after skidding operations. In this study, we evaluated the frequency, quality, diversity of seedling species and physicochemical properties of soil on 10-, 20- and 30-year-old abandoned skid trails. Further comparison to the values of the mentioned above parameters in control areas allowed for the evaluation in terms of natural recovery processes, under varying traffic intensity and the longitudinal slope of the skid trails in a mixed broadleaved forest. Results showed that there is a significant positive trend of recovery for soil physicochemical properties and ecological characteristics (density and quality) of seedling growing on the skid trails. The time required to recover soil properties and ecological attributes of seedlings increased with increasing traffic intensity and slope of the skid trail. Our results showed that it takes 20 and 30 years to fully recover the chemical and physical properties of the soil, respectively. On the 30-year-old skid trails, density and species diversity indices were fully recovered, but the quality of the seedlings was not restored to the control conditions. The results suggest the importance of a proper planning of the skid trail network, avoiding in particular skid trails with a slope gradient higher than 20%. [ABSTRACT FROM AUTHOR]

The growing interest in accessing steep terrain is pushing the expansion of the operating range of ground-based machines through winch-assist technology. However, cable tensile forces remain a major concern in the advancement of this technology. In this study, cable tensile forces in a winch-assist harvesting operation based on an anchor machine configuration were investigated. A harvesting machine tethered on ground slopes of up to 103% (45.9°) was observed over four days. Cable tensile forces were recorded at both the harvesting and anchor machines, at a frequency of 100 and 10 Hz, respectively. Cameras and GNSS devices enabled the execution of a time and motion study and the recording of machine positions. At the harvesting machine, peak tensile forces of up to 400 kN were recorded. Downhill movements of the harvesting machine were the cause of the highest peaks which, however, never exceeded the endurance limit of the cable. Numerous local variations in cable tensile forces exceeded 50 kN for just a few hundredths of a second, with a maximum variation of 300 kN in less than a second. Movements of the harvesting machine were the main cause of the major local variations. Depending on work element and harvesting machine movements, cable tensile forces were higher at either the harvesting or anchor machines; however, the highest peak tensile forces per work element and the related working loads were always recorded at the harvesting machine. Some implementation steps for improving the safety of winch-assist harvesting operations using anchor machines are also discussed. [ABSTRACT FROM AUTHOR]

This study analysed the skyline tensile forces in 502 complete work cycles during ordinary cable logging operations on 12 different cable lines in the Italian Alps. The objectives of the research were to quantify the frequency of exceeding the recommended safe working limits and to determine the skyline peak tensile forces and dynamic amplifications, as well as their explanatory variables. Data collection was based on skyline tensile force monitoring synchronized with the video recording of the logging operations and the monitoring of the carriage positions. The load volumes were measured at the landing, and the total loads were estimated for each cycle. The results showed 55% of the work cycles exceeding the safe working load. The highest peak tensile forces were often recorded while starting the load moving during lateral skid. High-peak tensile forces were also recorded during inhaul, where the tensile forces were amplified by the cyclic load behaviour. It appears that some operators underestimate the effects of pretension, payload, and cable line geometry on the magnitude of the skyline tensile force. The complexity in identifying reliable theoretical models inclusive of dynamic amplifications and the inefficacy of the load limiters installed on the machines highlighted the need to improve the best practices within the operators, and to adopt technical solutions for the continuous skyline tensile force monitoring during ordinary cable logging operations. [ABSTRACT FROM AUTHOR]

Turbulent flow fields over a two-dimensional steep ridge and three-dimensional steep hill with rough and smooth surfaces are investigated by using a delayed detached-eddy simulation (DDES) with the specified height as a new control parameter. The applicability of typical turbulence models in previous studies is evaluated by using validation metrics. While all turbulence models simulate the turbulent flow fields over the steep rough terrain well, the k − ε model overestimates the mean wind speed and underestimates the turbulent kinetic energy over steep, smooth terrain. The large-eddy simulation captures the large-scale vortices and improves the mean wind speed, but overestimates the turbulent kinetic energy due to the inaccurate specification of the surface roughness. The detached-eddy simulation considering the surface roughness shows further improvement, but still overestimates the turbulent kinetic energy, since the region using the Reynolds-averaged Navier-Stokes model is too thin. The modified DDES model with a new control parameter is suitable for the prediction of the mean wind speed and turbulence as demonstrated by the visualization of instantaneous flow fields through vortex cores, and a quadrant analysis to examine the organized motion, with strong organized motions identified in the wake region of smooth terrain. Roller vortices are significant on the lee side of the two-dimensional smooth ridge, while horseshoe vortices appear in the wake region of the three-dimensional smooth hill. [ABSTRACT FROM AUTHOR]

Current state-of-the-art atmospheric general circulation models tend to strongly overestimate the amount of precipitation around steep mountains, which constitutes a stubborn systematic error that causes the climate drift and hinders the model performance. In this study, two contrasting model tests are performed to investigate the sensitivity of precipitation around steep slopes. The first model solves a true moisture advection equation, whereas the second solves an artificial advection equation with an additional moisture divergence term. It is shown that the orographic precipitation can be largely impacted by this term. Excessive (insufficient) precipitation amounts at the high (low) parts of the steep slopes decrease (increase) when the moisture divergence term is added. The precipitation changes between the two models are primarily attributed to large-scale precipitation, which is directly associated with water vapor saturation and condensation. Numerical weather prediction experiments using these two models suggest that precipitation differences between the models emerge shortly after the model startup. The implications of the results are also discussed. [ABSTRACT FROM AUTHOR]

Timber extraction is based on two transportation modes-off-road and on-road-that are connected by a set of landing nodes. Forest operations planning that is oriented toward harvesting consists of concurrently locating a truck road network, designating landing/loading sites along that network, and allocating stands to specific harvest technologies (e.g., cable roads). In central Europe, this problem has, until recently, been solved primarily with rules of thumb. By contrast, only a few attempts, designed for plantation systems, have been made to find the mathematical optima. Here, we present a modeling approach to identify a minimal-cost solution for this problem of laying out truck roads and cable roads when the terrain is steep. This technique is based on a Mixed Integer Linear Programming formulation. Our approach is as good as or better than state-of-the-art methods. Here, the overall costs of harvesting and roading were decreased by about 7 % compared with techniques that called for a heuristic solution only. Depending upon parameter choices, we also determined that a computing time ranging from 4 min to 8 hrs was required when assessing a logging area of 4.3 km. [ABSTRACT FROM AUTHOR]

Construction of forest roads can cause short-term and long-term negative effects on forest ecosystems in different ways if they are not well planned and appropriately maintained. In this research, environmental damages caused by an excavator during road construction were examined in steep terrain covered by beech ( Fagus orientalis L.) stands. The study was conducted along a 1.5 km road in western Blacksea Region of Turkey. All of the road construction operations were monitored during a construction period, and measurements of cross sections sizes and stand damages were measured during and after the construction activities. The road construction was evaluated according to the appropriate method and standards. The average widths of roadway, fill slope and construction zone were 4.82, 6.91, and 16.61 m, respectively. Along the 1,500 m road, forested area impacted was 24,915 m while the number of trees cut was 1,495 and rate of the damaged trees below the fill slope was found to be 24.7 %. In the study, based on the appropriate method and standards, less forested area might have been impacted (23 %). As a result of regression analysis, it was found that the rate of damaged trees increased as the values of the proportion of rocks, the width of the road surface and the width of the cut-slope increased. To reduce the negative effects of forest road construction on the environment, new forest road construction by excavators should be performed using appropriate methods within mountainous terrains. [ABSTRACT FROM AUTHOR]