Tibor Pentek

Ecoefficient Timber Forwarding on Lowland Soft Soils

Environmental acceptability is one of the criteria for assessing work efficiency of sustainable forest management. Environmentally acceptable timber harvesting is determined by procedures involving different machines and tools and adequate ways of timber processing, after which the damage to habitat (soil, water) and stand (standing trees, seedlings) are as low as possible. Due to an increasing influence of the public opinion on the current forest environment, the aesthetic appearance of the ongoing forest work site should also be taken into account as well as its appearance after the works have been completed.

Tyre friction behaviour under abrupt wheel torque transients on slippery road surfaces: experimental analysis and modelling

The paper shows that, during abrupt wheel torque transients for ice surface and low vehicle speeds, the tyre can develop significantly larger longitudinal force than the peak value of the tyre static curve. This so-called dynamic tyre friction potential (DTFP) effect has many influencing factors such as the rate of change of the wheel torque, the vehicle speed, and the tyre dwell time. The paper presents a detailed analysis of the DTFP behaviour based on the experimental data collected by using an in-wheel motor-based tyre test vehicle. The analysis results and an insight into the brush structure of a tyre model lead to the hypothesis that the different influencing factors may be predominantly explained by the bristle dwell time (BDT) effect. Following this hypothesis, the LuGre model of the tyre friction dynamics is extended with a physical BDT sub-model. The experimental validation results show that the proposed model can accurately capture the low-speed tyre–ice friction behaviour during abrupt wheel torque transients.

Forest Transportation Systems as a Key Factor in Quality Management of Forest Ecosystems

The planned values of primary road density in 2010 and 2020 on the level of various relief categories of the Republic of Croatia, besides being the guidelines for strategic planning in the Republic of Croatia, may also be used as landmarks in primary forest road planning on a strategic level in countries of similar orographic, site and stand conditions, as well as the ways of forest management. The existing primary road density should certainly be taken into consideration, and in accordance with the financial, professional and infrastructural resources of a certain country and its forestry, the deadlines for achieving the planned values of primary road density, annual intensity and construction priorities should be defined. The more developed countries and countries with a long forestry tradition, which could have invested significant financial means permanently and systematically into the primary openness of their forests during the last few decades, are expected to have a better primary road density than the Republic of Croatia (which could have started with a more systematic and more intensive forest opening only after being proclaimed independent in the 1990s), and therefore, less need for primary classical openness in the future (with the purpose of achieving planned primary road density) and probably less differences in the existing primary road density of equal or similar (comparable) forest areas, that is, they have a uniform existing primary road density of the same relief categories. A multiple use of truck forest roads, by first of all users outside forestry (e.g. tourism), contributes to greater density and better quality of truck forest roads. Operative planning, as the lowest and the most accurate level of forest road planning, requires a purposeful analysis of the terrain, connecting the possibility of applying potential and suitable timber harvesting systems with terrain factor analysis. At this planning level, timber harvesting systems have a significant influence on the shape and density of the truck forest roads, but even more on the on the shape and density (and existence, in general) of the secondary forest road network. The application of certain timber harvesting systems is, besides the terrain factors, conditioned by the degree of technological growth (technological awareness), resulting in utilization (the possibility of using) the most up-to-date means of timber extraction, and connected with that, the procedures and methods of timber processing. The selection of a timber extraction system is often under the influence of traditional forestry values of a certain country. This paper describes and applies the methodology, but it can serve as a starting point for making a case study in any European and non-European country. Individual differences (specific qualities) of a certain country should be recognized and integrated into the modified methodology in a proper way to make the research results achieve an expected high level. The data about the primary road density does not say much about the quality of spatial distribution of primary forest transportation system components. For better understanding of the real value of primary road density, it is always necessary to present primary classical openness coupled with the average timber extraction distance, or the mean distance of access to the endangered forest area, in the case of forest fire-prevention roads in the karst area. A clear insight into the real, quantitative (amount of primary forest roads) and qualitative (spatial coverage with primary forest roads) parameters of primary forest transportation system may only be achieved by a parallel consideration of primary road density and mean timber extraction distance.