Browse

Recent Submissions

Now showing 1 - 5 of 5
• Item
Numerical Determination of the Accuracy of Gravity Center Coordinates and Stability of a Model Concept of Harvester with the Rigid Frame
(MDPI, 2022-04-09) Mergl, Václav; Kašpárek, Jaroslav
The paper deals with the verification of the stability of a new design concept of a hybrid harvester intended for thinning and with the determination of deviation between two methods of measuring the machine's center of gravity, i.e., between the methods of determining the center of gravity using the SolidWorks software made by Dassault Systems and using portable vehicle scales with the function of gravity center calculation. The machine was measured in five different positions from going up or down the slope or driving along the contour line. The new prototype of a harvester with a non-conventional rigid frame and both axles steered was found to be unstable at the maximum reach of hydraulic boom if it is situated at a right angle (+/- 90 degrees) to the machine longitudinal axis. A comparison of the two methods of determining the center of gravity resulted in a total deviation of 8.41%, with the deviation for x being on average 14.36% and for y only 3.08%.
• Item
Verifying the Lifting and Slewing Dynamics of a Harvester Crane with Possible Levelling When Operating on Sloping Grounds
(MDPI, 2022-02-20) Mergl, Václav; Kašpárek, Jaroslav
This paper focuses on the force and torque load of a harvester hydraulic crane employed on sloping grounds, both levelled and not levelled. Field research was conducted for this purpose and the results were compared with a dynamic analysis of the crane in MSC Adams. It was found that levelling the slewing platform of the crane is necessary for use on sloping grounds, primar-ily because the effect on the force and lifting torques is reduced. The research showed that when the slope of the slewing gear is up to 12°, the lifting torque reaches a higher maximum lifting force than when the slewing gear is in a horizontal position (0°). As part of the theoretical veri-fication by a dynamic analysis of the crane and the AH6 machine, a different pressure was de-tected in the lifting cylinder of the crane compared to the field research. The total deviation be-tween the simulation and the field research was 9.82%. The slewing torque of the hydraulic crane without the slewing bearing being levelled can be characterized 97.38% by a parabola whose vertex is located in front of the front part of the machine and falls as the crane moves left or right. Overall, it can be determined that when the crane rotates up a slope, whether it is from left or right, the slewing torque reaches the lowest values, and its value increases as the crane gets closer to the front of the machine (along the longitudinal axis of the machine). This change in the slewing torque is then characterized by a parabola. Furthermore, an effect was observed of the slewing gear slope on the lifting torque, which reached higher values in a tilted position than on a flat surface.
• Item
Application of Isothermal and Isoperibolic Calorimetry to Assess the Effect of Zinc on Hydration of Cement Blended with Slag.
(MDPI, 2019-09-10) Šiler, Pavel; Kolářová, Iva; Novotný, Radoslav; Másilko, Jiří; Bednárek, Jan; Janča, Martin; Koplík, Jan; Hajzler, Jan; Matějka, Lukáš; Marko, Michal; Pokorný, Přemysl; Opravil, Tomáš; Šoukal, František
This work deals with the influence of zinc on cement hydration. The amount of zinc in cement has increased over recent years. This is mainly due to the utilization of solid waste and tires, which are widely used as a fuel in a rotary kiln. Zinc can also be introduced to cement through such secondary raw materials as slag, due to increased recycling of galvanized materials. The aim of this work was to determine the effect of zinc on the hydration of Portland cement, blended with ground blast furnace slag (GBFS). This effect was studied by isothermal and isoperibolic calorimetry. Both calorimetry methods are suitable for measurements during the first days of hydration. Isoperibolic calorimetry monitors the hydration process in real-life conditions, while isothermal calorimetry does so at a defined chosen temperature. Zinc was added to the cement in the form of two soluble salts, namely Zn(NO3)(2), ZnCl2, and a poorly soluble compound, ZnO. The concentration of added zinc was chosen to be 0.05, 0.1, 0.5, and 1mass percent. The amount of GBFS replacement was 15% of cement dosage. The newly formed hydration products were identified by X-ray diffraction method (XRD).
• Item
Difference in the magnitude of power saw vibrations affecting the operator during forest felling
(Sciendo, 2023-03-01) Staněk, Luboš; Neruda, Jindřich; Mergl, Václav
This study deals with a question whether the magnitude of vibrations affecting the power saw operator during the tree felling is still the same or not. For this purpose, the tree felling was broken down into several partial operations (pruning of lower tree part; cutting of buttresses; felling; delimbing) at which the values of vibrations were recorded and mutually compared. The vibrations were measured during the felling of 121 trees with the activity being made by one feller with one type of power saw and one type of power saw chain, and the felled trees included both live and dead standing trees. The vibrations were measured on the front and rear handles of the power saw in compliance with standards EN ISO 22867, EN ISO 5349-1 and EN ISO 5349-2. As to the mutual comparison, research results demonstrated a difference in 69.23% of cases. A maximum increase of vibrations during the experiment (17.0 m s(-2)) was recorded on the rear handle during the partial activity of Delimbing live trees, the lowest increase of vibrations (0.320 m s(-2)) being localized in the same partial activity, only on the front handle.
• Item
Analysis of the Heart Rate of Operators of Forwarding Machines during Work Activities
(MDPI, 2023-06-30) Sláma, David; Mergl, Václav; Abramuszkinová Pavlíková, Eva
The aim of this work was to determine the dependence of the heart rate of operators of forwarding machines on the activities performed during the working day within the framework of timber forwarding and to compare individual activities in terms of the level of physical workload. For this purpose, the work shift of operators carrying out timber forwarding was divided into individual activities: driving, maintenance, forwarding, and break. During these work activities, the heart rate of each operator was taken for subsequent evaluation. A portable device, a Garmin smartwatch, was used to measure their heart rate. The results show that the highest pulse rates of the operators occurred during the maintenance of the entrusted machine, while the highest pulse fluctuations were recorded during forwarding. During this activity, the highest heart rate of the entire measurement process was recorded (132.0000 bpm), but also the lowest (42.0000 bpm). Furthermore, it was proven that both the operator and the activity he performs affect the pulse rate. The activities themselves did not differ from each other in only one of the six cases of comparison, specifically, between driving and forwarding.