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Knowledge about wood transportation distances is essential for sustainable forest management and related decision making in forest protection against fire or flood events. In this context, we developed the geoprocessing tool TraDis to allow for the calculation of two-dimensional (2D) and three-dimensional (3D) distance between a forest stand and the nearest forest road (i.e., pre-skidding distance) and the distance between this road and the nearest hauling place (i.e., skidding distance). The first aim of this study is to present the workflow for the calculation of the primary wood transportation distance using the TraDis tool. A detailed description, flowchart, and scheme are provided for these purposes. The second aim is to present the applicability of this workflow through a case study. The study area included 391 ha of forest stands, 58 km of forest roads, and 18 hauling places, and the transportation distances were calculated for various target objects, such as 366 forest stands, 10,341 square cells, 7220 hexagon cells, and 83,120 tree crowns. The results show that, while there is the ability to calculate the 2D distances for six forests, eight cells, and three crowns in one second, the calculation time for 3D distances is 1.6 times longer. Moreover, the pre-skidding distance and skidding distance at the 3D level were 3.6% and 0.9% greater than these distances at the 2D level, respectively.

Scientific research on reduced-impact logging has been addressed to develop effective approaches and methodologies to limit soil disturbance caused by forest operations. In recent years, the development of soil trafficability maps based on soil wetness indices is the approach that has been extensively used in the context of the Boreal forests. In particular, the depth-to-water (DTW) index has been identified as an interesting solution for the identification of areas particularly sensitive to soil disturbance. This study aimed to evaluate the cost-benefit factor of DTW maps for the identification of soil-sensitive areas in the Mediterranean context. In particular, a DTW map was developed for two oak coppice areas located in Italy and harvested over a period of 2–4 years with different mechanisation levels. Soil surveys concerning soil moisture, physico-chemical properties (bulk density, penetration resistance, shear resistance, organic matter), and biological properties (soil microarthropods community measure via soil biological quality (QBS-ar) index) were carried out in these forests, checking for significant differences between the zones at DTW index ≤1 (which should be more sensitive to soil disturbance) and the other areas of the forest soil. The results obtained revealed the efficiency of a DTW index in potential areas at a higher level of soil moisture. On the other hand, the values of soil physico-chemical properties in the areas at a DTW index ≤1 did not differ significantly from the ones in other zones. However, the values of the QBS-ar index in areas with a low DTW index were significantly lower than the ones in zones at the DTW index >1. Therefore, the obtained findings reveal that the DTW index is a reliable tool to identify and predict which areas are more prone to impact soil biological properties. [ABSTRACT FROM AUTHOR]

Rolling-element bearings (REB) can develop severe damage due to skidding (slipping) between the rolling elements and bearing races. Skidding can be described as gross sliding between the bearing surfaces in relative motion and can result in significant surface distress such as smearing, especially at light loads and high rotational speeds. Under these conditions, skidding occurs between the rolling elements and the bearing races, leading to increased wear (higher friction coefficient), elevated bearing temperature, significant power losses, and reduced service life of the bearing. The main objective of this study is to investigate the significance of various sensing technologies (induction, vibration, ultrasound, acoustic, and optical) in detecting skidding in standard series roller bearings as well as custom-made roller bearings for aero-engine applications. The bearings have a bore diameter of 60 mm and 90 mm, respectively. Jet and under-race lubrication techniques have been used to supply oil to the bearings under test. The custom-made aero-engine test bearing features special channels to allow under-race lubrication of the rollers/races contacts as well as the cage land. The effect of radial load, rotational speed, and oil flow on roller skidding have also been investigated and analyzed. Tests have been performed on a dedicated high-speed experimental bearing facility and data was recorded using a commercially available data acquisition system. [ABSTRACT FROM AUTHOR]

Farm tractors have been applied in forest operations to carry out several tasks such as tree/felling/processing, forwarding, loading, skidding and cable yarding. Farm tractors can be equipped with special logging equipment that allows for their safe and efficient work in the harvesting of forest stands. This research is aimed to collect and review available literary sources on the productivity of farm tractors during skidding operations. The study results showed that work productivity of farm tractors for timber skidding has been studied by several researchers around the world. According to the results, the reported work productivity of skidding with farm tractors varied from 1.2 m³/PMH0 to 15.8 m³/PMH0 among international studies. Main variables impacting the work productivity of skidding included skidding distance, load volume, number of pieces per turn, tree diameter, tree length, slope of skid trails and engine power. Proper skid trail planning, applying suitable skidding equipment (e.g. winches, sulkies etc.), considering suitable engine size and proper safety standards can all help improving the work efficiency of the farm tractors during timber extracting. The information provided in this research can help the forest industry users and researchers gain proper knowledge on the work productivity of farm tractors applied for timber skidding. The study results can be also useful for planning and development purposes within small-scale forest operations. [ABSTRACT FROM AUTHOR]

Public demands for forest products and services have been increasing gradually in many countries all over the world. Among the forest products, mostly round woods are produced in Turkey due to high economic value. On the other hand, there is a significant increase in demand for industrial woods in the domestic market in recent years. The reason behind this increase is the need of domestic companies in the wood-based panel industry for a large amount of wood raw material. . Farm tractors are the most widely used forest machinery in the extraction of industrial wood in Turkey. Farm tractors can be effectively used in mechanized harvesting operations after receiving some modifications and additional attachments. The modified farm tractors are affordable machinery for small logging contractors since their initial purchasing costs and hourly operating costs are quite low comparing with the forest harvesting equipment (i.e. skidder, forwarder, cable yarder). In this study, productivity of a modified farm tractor was analyzed during forwarding of industrial wood products. The study was implemented in Pinus nigra stand located in (?) the city of Afyonkarahisar in Turkey. In the study, the effects of forwarding distance on productivity were evaluated using statistical analysis. The results indicated that the most time-consuming work stage was unloading the truck and piling the wood products at the landing area, followed by ( in terms of time-consumption) collecting woods and loading the tractor at the stump. The average productivity of the forwarding operation was 6.06 stere/h (stere is the amount of wood pile with the height, width, and depth of one meter). It was also found that the productivity of the forwarding was significantly affected by the forwarding distance.

Beech (Fagus spp.) is one of the most common tree species in Europe and Western Asia. The implementation of sustainable forest Operations (SFOs) in beech forests is therefore crucial in terms of sustainable forest management. This review summarises the state of the art concerning time-motion studies carried out in beech forests, defining the work productivity and the related costs of different harvesting systems applied in these stands. The main focus in recent years on felling and processing operations has been the introduction of fully mechanised systems in beech forests, obtaining satisfactory results in terms of work productivity. However, the working performance is still lower than in coniferous stands. Skidding and forwarding resulted in suitable techniques for ground-based extraction, both showing a clear inclination towards increasing working performance when applying higher levels of mechanisation. Aerial extraction by cable yarders is particularly important in beech forests, considering that these are often located in steep terrains. Further efforts should be dedicated to enhancing the training for operators to extend the application of aerial extraction systems, which ensures good levels of work productivity and limited soil disturbances. In summary, this review aimed to give a clear insight into forest operations in beech forests which could be useful for forest managers, forest engineers and researchers in the sector of sustainable forest operations.

Copyright of Bearing is the property of Bearing Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Skidding is one of the commonly used technical options to extract wood from felling to landing. As such, several studies have been carried out to evaluate its effectiveness in terms of economics, environmental impact, and ergonomics. Most ergonomic studies have addressed the exposure to noise and vibration, and less effort has been devoted towards the evaluation of the skidder operators' working environment. To our knowledge, the exposure to variability in temperature and humidity has not yet been studied for skidding operations. This study aimed at evaluating the variability of such microclimate parameters and at comparing them to their counterparts recorded in the forest environment. Based on comparative datasets collected in November 2020, our results indicate that skidder operators might endure a significant variation in temperature and relative humidity during operations, which in turn may affect their health. Compared to the forest environment, the differences in temperature and relative humidity were evident, contrasting and occurred in short periods of time, as an effect of the skidding operations and mobility on increased distances and of a considerable altitudinal range. It is likely for such variability to also come from the work behavior of different operators. Given the results and the season in which the data was collected, as well as other constraints of the study, further studies should be carried out to separate the operation time from the rest and meal breaks, to evaluate the variability in microclimate throughout all seasons, to control the state of the cabin doors, and to solve the problem of control data mobility so as to accurately reflect the outdoor conditions for each location a skidder may work on during skidding operations. [ABSTRACT FROM AUTHOR]

Small tree size represents the main challenge when designing a cost-effective harvesting system for European short-rotation plantations. This challenge is further complicated by the need to obtain 4-m logs for high-end products, which rules out the possibility to deploy whole-tree chipping. Both challenges can be met through mass handling, which must begin at the time of felling and continue uninterrupted along the whole supply chain. The authors designed and tested a simple system based on an excavator-based feller buncher, two farm tractors converted into grapple skidders and an excavator-based grapple saw adapted to operate as an impromptu slasher. This system proved capable of containing harvesting cost below 17 € per green ton, while matching the necessary work quality requirements, in terms of value recovery and log quality specifications. Furthermore, the whole system can be acquired with a limited capital investment, estimated at ca. 400,000 €. Being based on general purpose equipment, the system is also versatile enough for deployment in a number of alternative jobs, when the coppicing season is over. [ABSTRACT FROM AUTHOR]

Background and Purpose: Optimisation of skid road network is very important in forest utilisation because transport is considered to be the most expensive part of timber production. Designing forest traffic infrastructure means positioning its location in the forest area using traditional or modern methods. Many factors influence the skidding costs, and winching distance is one of them. The use of modern techniques gives an opportunity to forest practitioners that simulate different network variants and choose the most appropriate ones. Materials and Methods: The research object is Compartment 27, which belongs to Forest Administration Unit "Prijedor", with the area of 46.72 ha. Investigation is divided into the phase of field work and the phase of designing secondary forest road network variants in the office. Field work includes the traditional and Global Positioning System (GPS) marking of trees for cutting and the creating of Geographic Information System (GIS) database. In relation to spatial distribution of trees for cutting, skid roads and skid trail networks are laid by using the GPS. The new scondary road network is laid in the field and compared with three simulated variants of secondary road network that are laid by ArcGIS 10.3. Secondary road network is planned by using Network Analyst tools and Shortest path method that is based on Dijkstra’s algorithm. These variants are simulated based on different average winching distances of 10, 20 and 30 m. Results: The area of the compartment is divided into two transportation zones. Total length of the secondary road network designed in the traditional way is 4816 m, thus achieving the secondary openness of 103 m·ha-1. In simulated Variant I, with winch pulling distances of 20 m, the total length of secondary roads is 5590 m with costs of 14352.62 €, in Variant II with winching distance of up to 40 m length of secondary roads it is 3228 m with costs of 7426.78 €, and in Variant III with winch rope length of up to 60 m, the length of roads is 2219 m, with costs of 4400.89 €. The achieved mean skidding distances are relatively similar in all variants. When taking into account the average length of the winch rope, considering all three new-design variants, it can be said that there is almost no difference in productivity and skidding costs. Conclusions: Mean winching distance has influence on skidding costs, but only in variants where mean skidding distance is decreasing. Smaller winching distance is justified only from the aspect of work humanization. Small differences in skidding costs between variants have no practical significance except for large quantities of wood assortments.

Poplar plantations have been widely practiced in the coastal area of the Caspian Sea in northern Iran. In this research, soil compaction following logging operations carried out by wheeled cable skidder was investigated in two poplar plantations with different characteristics including moist soil and dry soil. The soil gravimetric moisture content (MC) in the dry site ranged from 13% to 14.4%, while in the moist site it ranged from 30.5% to 34.6%. The mineral soil samples were collected from the skid trails in both sites. The impact of skidding operations on soil layers (soil depth, SD) was examined by measuring rut depth (RD), penetration resistance (PR), bulk density (BD), and total porosity (TP) at five traffic intensities (TI). Results indicated that MC and TI had a significant effect on RD, PR, BD, and TP; however, SD had a significant effect on PR and BD. The values of BD were significantly higher in the moist site than in the dry site, while the values of PR and TP were significantly higher in the dry site than in the moist site. The RD in the moist site (11.7 cm) was 1.65 times more than RD in the dry site (7.1 cm) after one pass where a pass was defined as one empty and one loaded trip over a spot. The differences between BD after 10 and 15 passes were not significant on the dry site, but significant in the moist site. We concluded that skidding operations should be conducted when soil conditions are dry. [ABSTRACT FROM AUTHOR]

Scientific research on reduced-impact logging has been addressed to develop effective approaches and methodologies to limit soil disturbance caused by forest operations. In recent years, the development of soil trafficability maps based on soil wetness indices is the approach that has been extensively used in the context of the Boreal forests. In particular, the depth-to-water (DTW) index has been identified as an interesting solution for the identification of areas particularly sensitive to soil disturbance. This study aimed to evaluate the cost-benefit factor of DTW maps for the identification of soil-sensitive areas in the Mediterranean context. In particular, a DTW map was developed for two oak coppice areas located in Italy and harvested over a period of 2–4 years with different mechanisation levels. Soil surveys concerning soil moisture, physico-chemical properties (bulk density, penetration resistance, shear resistance, organic matter), and biological properties (soil microarthropods community measure via soil biological quality (QBS-ar) index) were carried out in these forests, checking for significant differences between the zones at DTW index ≤1 (which should be more sensitive to soil disturbance) and the other areas of the forest soil. The results obtained revealed the efficiency of a DTW index in potential areas at a higher level of soil moisture. On the other hand, the values of soil physico-chemical properties in the areas at a DTW index ≤1 did not differ significantly from the ones in other zones. However, the values of the QBS-ar index in areas with a low DTW index were significantly lower than the ones in zones at the DTW index >1. Therefore, the obtained findings reveal that the DTW index is a reliable tool to identify and predict which areas are more prone to impact soil biological properties.

This paper proposes a dynamic model to investigate the vibration response of a cylindrical roller bearing considering skidding. This model considers the frictional forces and the contact forces between rolling elements and races simultaneously. The interactions between the frictional forces and the dynamic responses of rolling bearing when skidding happens are also included in the model. It improves previous quasi-dynamic models in which the contact forces and frictional forces between races and rolling elements were determined by a separate load distribution model via the static force and moment equilibrium equations for races. The variations of the friction forces in a rotational period are elaborated, and the generating mechanism is also explained. It is found that the existence of skidding may lead to fluctuations and a significant increase of the friction force. The effect of skidding on the bearing vibration is studied by comparing the simulated results with those predicted by previous models under the pure rolling assumption. The results show that the friction forces will increase the vibration level and introduce impact components into the vibration response. It is necessary to consider the influence of skidding on the bearing vibration response using the proposed model, especially for high-speed bearings. [ABSTRACT FROM AUTHOR]

The effectivity of timber skidding process evaluated through the time consumption is mostly affected by the technology, ergonomic demands and environmental factors connected with the technology used. There is still an inadequate research eff ort aimed to time consumption and work effectivity of forest skidders in Slovakia, which is one of the causes of insufficient payments for their work. The paper compares time consumptions for particular work operations of the forest skidders calculated from the data from field measurements compared with standardized forest skidders time consumptions published in the Collection of performance standards (MLVH 1992) of the Ministry of Agriculture of the Slovak Republic. Measuring the time consumption of skidders was carried out using the methods of continual time study, i.e. by connecting the work day snapshot with the fluent chronometry. The results confirmed statistically significant differences in time consumption for particular work operations such as winching and work on the forest landing between cable and cable-grapple skidder. Generalized linear models confirmed that particular work operations (winching, skidding and works on the forest landing) in both technologies are affected by the same production factors. We found significant differences of the basic standardized times for the particular work operations (Calculated standardized times on based measured time versus actual standards of the Slovak Ministry) only in the case of the HSM 805 HD skidder. [ABSTRACT FROM AUTHOR]

Copyright of Artvin Çoruh Üniversitesi Orman Fakültesi Dergisi is the property of Artvin Coruh University and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Two most common systems of forest biomass supply chains in Serbia are evaluated by using the Life Cycle Assessment (LCA) approach: 'cut-to-length' system with penduculate oak (CLO) on flat terrains with a tractor equipage, and 'tree-length' system with moesian beech (TLB) on more steep terrains, with a skidder. The main focus is put on the fuel consumption and its environmental impact on various stages of wood chips supply chain. Results indicate chipping as a most environmentally burdensome due to the low process productivity and high diesel combustion in outdated machines. CLO system exhibits lower environmental burden due to the 2%–35% lower impact in six out of eleven analysed impact categories compared to the TLB. The main reason is the skidding performed on a more steep terrain with a more powerful machine consuming more diesel than the tractor equipage. The higher impact of the felling operation in CLO system is caused by additional time for processing short oak assortments. The evaluated environmental impacts are consequence of the machinery old age used in Serbian forests. The application of a modern, energy efficient, combined machines such as harvesters and forwarders is recommended though it could have a lot of drawbacks. • Life cycle assessment of cut to length (CLO) and tree length (TLB) wood processing method is performed. • 13%–30% lower impacts are obtained in TLB compared to CLO. • Highest environmental impacts are caused by wood chipping. • Extraction with a tractor equipage - less environmental friendly than skidding. [ABSTRACT FROM AUTHOR]

The purpose of this work was to develop a model of the interaction process between the wheeled forwarder and the soil of the cutting area, which allows evaluating the influence of soil conditions, the parameters of the wheeled forwarder, as well as load and number of cycles of its application, on the indicators of resistance and adhesion of the forwarder to the traction surface. Modeling results for 3- and 4-axle forest machines with different load levels showed that for different soil categories, types of bodies, and tire sizes. The results of the approximation analysis enabled the derive of calculation formulas for estimating the propulsive coefficient and rut depth after the first passage depending on the values of load-bearing capacity, body load coefficient, wheel width, and soil deformation module. The proposed model can be used at laying down the skidding roads and its optimization not only in economic terms but also with respect to the environment as intensive harvesting operations lead to extensive soil destructions. The practical application of the results is expressed in increased performance capacities of wood skidding operations and minimization of costs for restoring the productivity of forest area. [ABSTRACT FROM AUTHOR]

Copyright of Bearing is the property of Bearing Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

• The ATDSA method for bearing spall size estimation with skidding is presented. • Skidding rate is estimated based on time delay coefficients of impulse segments. • Skidding removal processing clears the spectral sidebands with BCF interval. • ATDSA method deliver consistent averaged waveform with different skidding rates. The size of the bearing spall fault can be estimated by the time interval between the roller's entry and exit points in the bearing vibration signal. However, the entry vibration response is typically low amplitude and masked in environmental noise. The time-domain average (TDA) method is effective for periodic impulse enhancement. However, bearing skidding is unavoidable during its running, and the cage's speed fluctuations caused by skidding will lead to non-periodicity of the impulses. The performance of TDA seriously deteriorated with such skidding because of the time-varying period. This paper presents the adaptive time-domain sliding average (ATDSA) method to address the bearing skidding problem. The similarity feature between each impulse segment is utilized, and a time delay matrix is constructed to estimate the skidding rate and mitigate the skidding effect. The frequency spectrum of the reconstructed signal shows clear sidebands with BCF interval. And the obtained averaged waveform has high resolution in both the low-frequency entry and high-frequency exit events. Simulation and experiment results show that it can effectively suppress the skidding effect and estimate the spall size correctly under different speeds. [ABSTRACT FROM AUTHOR]

Careful planning of skid trails as wood extraction routes in forests is an ongoing task and necessary for minimizing the environmental damage. The main objective of this study is to find skid trails to extract marked trees from stand sites to landing sites using a GIS-based decision support system (DSS) and network analysis techniques, where environmental information is incorporated into the objective. The techniques were applied in a stand where single trees are felled in near-to-nature conditions. This system is called a single tree selection cutting method. Parameters considered for mapping the terrain stability include slope, soil and stream network. The analytical hierarchy process was used to estimate the weights of these parameters. Routing between marked trees and log landing was done using a GPS-tracking survey and then the analysis was done using new route and service area tools in GIS. The service area tool shows accessibility of marked trees by skid trails. Results showed that on average the length of the route decreased by 6.65 and 19.22% with the use of a new route tool in compartments 29 and 4, respectively. In conclusion, DSS techniques increased accessibility of marked trees and decreased the length of the route.

One of the main problems in close-to-nature management of high forests is linked to the ecological and economic aspects of salvage logging. This research involved analysing soil disturbance from salvage logging in four mountain forests, managed with close-to-nature silviculture: the Hyrcanian forest (three forest compartments in Iran), using extraction by skidder, and the Camaldoli forest (one parcel in Italy), using extraction by tractor. The point transect method was used for assessing soil disturbance and also included further measurements of ruts' size and selected physical soil parameters on skid trails after operation. After a windstorm, more than 94% and 17% of the area were undisturbed in the Hyrcanian and Camaldoli forests, respectively. Bulk density, penetration resistance, and pH did not show any significant differences with their average values specifically between disturbed and undisturbed soil after a windstorm. Related only to the effect of salvage logging, more than 80% of the area was undisturbed. The results were significantly lower in terms of the average values of soil variables such as bulk density, penetration resistance, and total porosity in disturbed soil than in undisturbed soil. For all the sites that were studied, bulk density and penetration resistance increased with the increasing number of machines that passes, while total porosity decreased. The results showed significant positive correlations between bulk density and penetration resistance, bulk density and pH value, and total porosity and pH value and significant negative correlations between bulk density and total porosity and penetration resistance and total porosity. The results indicated that the point transect method of assessing soil disturbance provides a rapid assessment of soil conditions for monitoring soil disturbance after salvage logging. Our results also indicated that to reduce impacts to soil during salvage logging, if the volume of windthrow timber is low, salvage logging is not always necessary because of the broad ecological importance as well as the economic aspects of dead wood in forest ecosystems. [ABSTRACT FROM AUTHOR]

In order to synthesize controllers for wheeled mobile robots (WMRs), some design techniques are usually based on the assumption that the set of kinematic constraints are fully satisfied. Nevertheless, when a WMR moves on a trajectory, phenomena such as slipping, skidding and deformability (also related to flexibility) can cause violation of kinematic constraints as well as system instability. Previous research has shown that to make the tracking error converge toward a small neighborhood containing the origin, in WMRs that moving at different speeds, it can be used an outer closed-loop scheme based on an auxiliary control law with aid of estimations of the slipping and skidding variations. But, although these previous works use slipping/skidding variations, the flexibility parameter is not taken into account to compute the auxiliary control law, making the outer closed-loop less robust for different flexibility values in the dynamic. The work reported here proposes a control scheme fully influenced by the flexibility parameter and whose robustness will be based on an auxiliary control law that uses a nonlinear function in terms of flexibility and slipping/skidding variations. The results obtained from experimental and simulations tests will show that the flexible auxiliary control law not only ensures that the error converges to a small neighborhood close to origin but also it is more insensitive to the speed increasing of the WMR. • Wheeled mobile robots become unstable with slipping, skidding, and flexibility. • Tracking error converges toward a neighborhood of the origin when an auxiliary control law is used. • Better robustness is guaranteed when the flexibility is included in the auxiliary control law. • Dynamic confined space of velocities can be used to synthesize a flexible version of the auxiliary control law. • The flexible auxiliary control law is more insensitive to the speed increasing. [ABSTRACT FROM AUTHOR]

The support structure is a major component of a cableway system, as it supports the cable and ensures that the ropeway has sufficient headroom. However, most traditional cableways in southern plantations use a living stand as the support structure. The living stand is limited by its growth position. Therefore, guaranteeing an optimal skidding route is difficult. In addition, it does not meet the requirements of modern small-scale wood collection. To solve the problem of finding a suitable living stand for the support of an artificial forest cableway, a movable sectional support fixed by cables was designed in this study. The support mode, segmentation ratio, and fixed position of the cable were optimized based on mechanical and simulation analyses. An optimal pressure resistance was obtained when the segment was located at 0.59L of the rod, which was 1.7 times greater than that without the segmentation. A cable saddle was used, allowing the force of the support to be changed from the bending moment to the pressure, and the stress condition of the support was improved. Simultaneously, the tight cable fixture increased the constraint condition and reduced the flexibility of the support structure.The strength of the cable-fixed support was tripled as compared to the support without cable fixing. The segmented design reduced the weight of individual components, and the maximum single weight was less than 50 kg, thus enabling the support to be easily transferred and installed. The support was made of cost-effective standard galvanized pipe. Following trial and production verification, the movable and assembled forest cableway support was determined to be safe and reliable as well as convenient to transfer and erect. This type of support structure is particularly suitable for selective cutting in hilly and mountainous forest areas as well as for small-scale clear cutting. Promoting small cableway skidding in artificial forest logging work is critical to reducing the impact of logging operations on ecological environments. [ABSTRACT FROM AUTHOR]

• A shortest path algorithm to find terrain transportation cost. • An inverse shortest path optimization model to find forwarder productivity functions. • A test case is solved using the metaheuristic variable neighborhood search. • The result is used to calculate a regional map of variable forwarding cost. This paper presents an optimization model designed to find productivity functions for timber forwarding. Timber forwarding or skidding has for some 25 years been calculated using shortest path formulations on grid networks. Unfortunately, few productivity studies relate to such grids. Here, an inverse shortest path problem is presented, basically panning out costs on the grid based on point cost estimates. The formulation is tested using point cost estimates from the national forest inventories of Norway, together with a terrain model and other public spatial data (e.g. roads, water). The problem is optimized using the metaheuristic variable neighborhood search. The results of the test cases were achieved in reasonable time, and indicate that part of the solution space might be convex. The productivity function found for one of the test cases was used to create a variable forwarding cost map of the case area. [ABSTRACT FROM AUTHOR]

Skidding is a phenomenon that frequently occurs in ball-raceway contact areas of bearings and often leads to their early failure. This paper presents a skidding analysis of angular contact ball bearings (ACBBs) subjected to various boundary conditions. A five degrees-offreedom quasi-static model for ACBBs was employed to investigate skidding with ball and race contact forces and inertial loading by rotational speed. The model provided the internal load distribution of all rolling elements, which was subsequently used for the skidding prediction. Hirano's criterion was used as a theoretical basis for the skidding analysis of ACBBs. Simulations were performed to investigate the influence of external loading, rotational speed, and angular misalignment on the bearing skidding. The effects of the preload method and initial contact angle on the skidding were also considered. As a result, this study provided an in-depth observation of skidding in ACBBs subjected to various operating conditions. [ABSTRACT FROM AUTHOR]

The problem of a two-axle four-wheel vehicle skidding on a horizontal homogeneous plane arising when locking or slipping the wheels of one of its axles is considered. The wheels of the other axis of the vehicle retain or lose their grip with the supporting plane. The cases are discussed when following the recommendation adopted in theory of driving a car to "turn the steering wheel (front wheels) towards the rear axle drift" allows reducing the angular speed of the vehicle rather than when the front wheels are turned or turned the other way) [ABSTRACT FROM AUTHOR]

The growth and quality of natural seedlings are important goals of forest management in uneven-aged high stands. In this study, the recovery process of the physical and chemical properties of soil, as well as growth variables of beech seedlings on the skid trails after skidding operations in three time periods (10, 20, and 30 years) were investigated in the Hyrcanian forests of Iran. Results revealed that the soil chemical properties (organic C, total N, and pH) were fully recovered after 20 years, while soil physical properties (bulk density, porosity, and penetration resistance) were not yet fully recovered even after 30 years. The values of growth characteristics (stem and root system) and the quality index of beech seedlings were not statistically different from those of the control area ones after 20 years. According to our findings, the process of recovering soil characteristics after forest operations is long and takes more than 30 years. Considering the effect that soil compaction can have on seedling establishment and growth, proper planning of the forest operation is needed to limit the negative effects of forest operations, which meets the requirements of sustainable forest management. We suggest designing skid trails with a minimum distance of 140 m from each other and with a longitudinal slope of less than 15%, in compliance with the principles of best management practice (BMP).

Waviness is the main shape deviation generated in the processing of rolling bearings. The existence of race waviness directly alters displacement excitation and contact stiffness between the ball and the wavy race simultaneously, which will greatly affect the dynamic performance of rolling bearings. Most of the current work studying bearing dynamics with race waviness ignored the influence of waviness on contact stiffness. In addition, the influence of race waviness on bearing skidding problems was rarely investigated. To fill the research gap, a skidding dynamic model of race waviness bearing coupled with the time-varying displacement excitation and time-varying contact stiffness excitation is established by considering the nonlinear factors including internal nonlinear contact, non-continuous collision contact between ball and cage, lubrication friction, clearance and pocket gap. The validity of the dynamic model is verified by previously published results and analytical results of a static model. The influence of waviness amplitude and order on the contact and skidding characteristics are analyzed. The results indicate that the contact stiffness and contact force between the ball and race increase with the waviness amplitude and order. In addition, the waviness also causes fluctuations in the contact force. The increase in waviness amplitude and order restrains the skidding of the ball in the unloaded area. The waviness amplitude causes significant fluctuations in skidding, and the waviness order increases the number of skidding fluctuations. The results provide a theoretical basis for the surface quality assessment of rolling bearings via dynamic studies. • An original skidding dynamic model of race waviness bearing model is proposed. • Time-varying displacement and contact stiffness excitations are established. • Comparisons with the static analytical model are performed. • Influences of waviness amplitude and order on skidding are investigated. [ABSTRACT FROM AUTHOR]

Forest stand decomposition of the Silesian Beskids which is followed by the tree cutting has been observed since the beginning of the 21st century. Changes in forest management due to the introduction of heavy machines for forest work mainly for skidding have been observed in the Silesian Beskids for the last decade. The paper presents results of a three-year investigation of erosion gullies forming in mountain forest after the skidding performed with use of heavy equipment. In the Wilczy Potok catchment comprising an area of above 100 ha 40 gullies were identified. The measurement of the length and depth of gullies showed that the total volume of soil and rock material removed from the catchment area due to erosion accelerated by skidding exceeded 9 000 m3. The year erosion rate for deep gullies was found to be 10%. The presented results show that necessary protective actions and preventive measures should be taken to mitigate the soil degradation processes.

European short-rotation poplar plantations are harvested at 5–8 year rotations and produce relatively small stems (0.05–0.10 m3), which represent a major challenge when designing a cost-effective harvesting chain. Until now, the challenge has been met through whole-tree chipping, which allows mass-handling all through the harvesting chain. However, the production of higher value logs for the panel industry requires devising different solutions. This study presents a fully mechanized low-investment system using an excavator-based feller-buncher shear, a grapple skidder obtained from the conversion of a common farm tractor and an excavator-mounted grapple saw adapted to work as a makeshift slasher. The system was tested in Northwestern Italy, achieving high productivity (between 14 and 20 t fresh weight per scheduled machine hour) and low harvesting cost (between 9 and 14 € t−1 fresh weight). However, crosscutting quality needs further improvement, because almost 50% of the logs did not meet factory specifications. Solutions to solve this issue are proposed. The tested system is suitable for local small-scale operators because it can be acquired with a reasonable capital investment (400,000 €) and it is versatile enough for use in a number of alternative jobs, when the coppice harvesting season is over.

Skidding, which frequently occurs in high-speed rolling bearings, has a significant effect on the thermal distribution and service reliability of the bearings. An improved theoretical model of friction power loss distribution in high-speed and light-load rolling bearings (HSLLRBs) considering skidding is established, and the effects of various operating parameters on the friction power loss are investigated. The results show that the friction power loss of the inner ring and outer ring as well as the total friction power loss of the bearing increase as the slip ratio increases, but that the friction power loss of the cage guide surface and roller oil churning show a reverse trend. In addition, the increase in inner ring speed and kinematic viscosity leads to an increase in bearing friction power loss. The steady and transient temperature field distribution of HSLLRBs is obtained by the finite element method (FEM), and the results show that the inner ring raceway has the highest temperature, whereas the cage has the lowest. The temperature distribution test rig of a full-size roller bearing is constructed, and the influence mechanism of the slip ratio, rotation speed, load, lubrication, and surface topography on the bearing temperature distribution are obtained. The experimental results are consistent with the theoretical results, which also validates the theoretical method. [ABSTRACT FROM AUTHOR]

Rolling element bearing signals are known to exhibit pseudo-cyclostationary properties that limit the efficiency of health monitoring. This paper investigates the restoration of cyclostationarity of train of impulses generated by bearing faults with the definition of a bearing angle-time relationship. Two main contributions structure the present paper. The first part presents a unifying synthesis of the state of art on the issue. The concept of cycle of reference (CoR) for cyclostationarity is presented. The possible causes of the well-used concept of slippage of the rolling-element bearing are explored to highlight the limitations of the cyclostationary theoretical framework. The influence of different types of jitters is presented to show the effect of using shaft cycle of reference on the spectral properties. CoR, on which bearing signals are phase locked so to restore their cyclostationarity, and a method to estimate the appropriate angle-time relationship are introduced. In a second part, original contributions on demodulation parameters and the possible introduction of unwanted artefacts are thoroughly explained along with the definition of a hypothesis test. The superiority of cyclostationarity restoration for monitoring purposes is illustrated on two industrial cases. • The issue of pseudo-cyclostationarity for bearing signal is reminded. • The concept of cycle of reference for cyclostationarity restoration is introduced. • A method for tacholess estimation of bearing-dedicated cycles of reference is presented. • An hypothesis test is defined to ensure the relevance of the method. • Improved health monitoring capacities are demonstrated on numerical and industrial applications. [ABSTRACT FROM AUTHOR]

This study aims at determining the main damage caused by logging in single selection method causing open holes in forests. Little is known about this subject, in spite of extensive studies worldwide. Amount of damages based on the FAO criteria in plots and hectare were assessed according to type, size, intensity and height of damages. Quantitative data of two compartments were compared using t-test. One-way ANOVA and Kruskal-Wallis tests were used to compare multiple groups for quantitative and rating data, respectively. Data were collected by survey of land and one hundred percent measurement in damaged parts. In cutting stage, 79.5% damages were occurred in height >1 m. In skidding stage, 90.4% of damages to wood were observed from a height of 1 meter downward the trunk to the tree root and buttress. The average of the most injuries in the two compartments in cutting and skidding stages were observed in size of 10-50 cm2 (44%) and > 200 cm2, respectively. The intensity of damage in cutting stage is the same (72 percent), but higher in skidding stage, because the slope of cut area in compartment 51 is higher than compartment 121 (95 percent versus 63 percent). The total intensity of damages in compartment 51 was higher than compartment 121 (33 damages versus 19). The rate of injuries to regeneration in compartment 51 in all three stages of vegetation development was higher than compartment 121. The types of damages to stem in compartment 51 were 2 up to nine times, depending on the development stages. The total damages in steep slope were more than gentle slopes (4 times). Ignoring the prescribed cutting direction has a large effect on damage caused.

The first phase of transport of forest products (skidding) in Serbia is usually performed by skid trails with adapted agricultural tractors. The educational base ”Goč - Gvozdac” compartment 21 was the selected object of this research. Data recording was carried out in June 2011. The vehicle driven by the driver was an IMT 565 DV tractor. The organizational form of work was 1T + 1P (tractor driver and assistant). The microphone of a Bruel & Kjaer 4189 noise measuring instrument was mounted on the helmet of the tractor driver in accordance with the ISO 9612: 2012 standard. The recording was performed with a Bruel & Kjaer 2250 instrument. The values of the following parameters with appropriate filters: LAeq (dB(A)), LAIeq (dB(A)), LCpeak (dB(C)), LZeq (dB) were measured. The measured exposure of the workers to noise was the highest in the course of the main productive time (empty or full drive). It was found that the eight-hour exposure to noise of the driver (88 dB (A)) exceeds the limit value of daily exposure according to European legislation. The results show that it is necessary for drivers to use hearing protection equipment when transporting wood with the studied transportation vehicle. [Projekat Ministarstva nauke Republike Srbije, br. TR-31041]

Copyright of Bulletin of the Faculty of Forestry, University of Banja Luka / Glasnik Šumarskog Fakulteta Univerziteta u Banjoj Luci is the property of University of Banja Luka, Faculty of Forestry and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Synthesis of Theoretical & Applied Mechanics / Sinteze de Mecanică Teoretică și Aplicată is the property of Matrix Rom and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The determination of race conformity of ball bearing is mainly based on the classical fatigue life theory; however, besides the fatigue life, skidding may also become the main concern due to high frictional heating in high-speed application; therefore the strategy of race conformity determination should be changed accordingly. This paper investigates the influences of race conformity on the contact characteristics and motion of ball based on the developed dynamic model for angular contact ball bearings. The results show that the race conformity has a significant influence not only on the contact pressure between ball and raceways, but also on skidding of ball on raceway, which implies that the race conformity should be optimally determined according to the different applications. [ABSTRACT FROM AUTHOR]