Jonas Čėsna

Rotary plate vacuum pumps have become widely used as a source of vacuum for milking systems. The main features of a plate vacuum pump include design simplicity, high efficiency, low cost and adaptability to climatic conditions. A plate vacuum pump requires the improvement of specific performance indicators. This refers to the indicator of specific productivity and specific energy intensity. It is possible to improve the vacuum pump by optimizing the design parameters and technological models of operation. The known studies allow the establishment of rational geometric parameters, the number of plates, the ratio of the main dimensions and eccentricity. However, the problem of reducing the degree of uneven air pumping from the vacuum system needs a scientific solution. The use of a vacuum cylinder in a vacuum line of an increased diameter partially solves the problem of vacuum pressure fluctuations. But such a decision requires additional material costs. In addition, the power of a vacuum pump increases to compensate for the pressure losses. In this study, the authors proposed the design of a double-action plate vacuum pump. It was proven that the simultaneous operation of combined rotors with plates shifted by 45° decreased the degree of air pumping by 7.8%. The research results indicated that the productivity of the developed vacuum pump increased by 13.6%. The drive power increased by 12%, and the specific energy intensity was 20% lower than that of vacuum pumps with similar geometric parameters. The relationship between rational kinematic and design parameters of a double-action vacuum pump was established.

The research is aimed at creating a methodology for increasing the positioning accuracy of an industrial robot and minimizing the vibration of the robot gripper by applying machine learning based on the developed mathematical model for estimating the positioning error. Two components of positioning accuracy are considered: geometric and kinematic errors and elastic static deformations. The dynamic error in the partial system of motion of the robot manipulator links is analyzed. The equation of partial motions is obtained from Lagrange’s differential equation of motion of the II kind. The system of differential equations for the positioning error was solved analytically by Euler’s method. An example of modeling the position and orientation error of the gripper due to temperature deformations of the third link for the manipulator scheme is given. An example of the modeling of static deformations and errors of the manipulator with elastic pliability of the robot links is given. An example of dynamic error modeling in a partial system of motion of the robot links is given. The proposed method of modeling robot gripper positioning errors makes it possible to increase the positioning accuracy of the industrial robot and minimize the vibration of the gripper. Having a mathematical model of positioning errors, it is possible to compensate for the positioning error by changing the speed of movement of the gripper reference point before determining the direct kinematic task.

One of the most modern technologies for growing row crops is strip-till. Currently, it occupies an intermediate position between conventional tillage and no-till technologies. Special complex and expensive machines are used to implement strip-till technology practically. To avoid this, a combined unit is proposed, including a tractor and two simple machines: a front-disc harrow and a chisel plough mounted behind the tractor. As experimental studies have shown, this unit makes implementing the strip-till one-pass technology possible. In this case, the oscillations process in the soil-loosening depth of strips is low-frequency since at least 95% of this statistical parameter variance is concentrated in the frequency range of 0–16.8 s⁻¹ or 0–2.7 Hz, and its maximum falls at a frequency of 0.4 Hz. The soil-loosening depth in the strips can deviate from the mean value by ±2 cm once per 7.1 m of the combined unit’s path. With a mean speed of its movement of 2.1 m·s⁻¹, the release frequency of the mean value of the soil-loosening depth exceeding ±2 cm is only 0.29 s or 0.05 Hz. Not less than 95% of the loosened strips’ non-straightness oscillations variance is in the frequency range of 0–0.25 m⁻¹, and the value of the variance itself is small and amounts to 1.08 cm². Proceeding from this, the non-straightness of the loosened strips by the combined unit can be considered satisfactory since its indicators meet the requirements for the non-straightness of row crops in terms of variance and frequency oscillations.

During the operation of the cooling system, a large array of temperature and humidity values was obtained inside and outside the cowshed. On the basis of the obtained data set, mathematical models of temperature, humidity and temperature–humidity indices were developed. The modelled values were relevant to the actual values. The mathematical models were built on the basis of regression analysis of the data set. The data set was obtained as a result of the observations of temperature and relative humidity on one of the farms in Lithuania in semi-insulated box-type cowshed for 244 places in the summer. It was established that the efficiency of the air-cooling system is higher at a higher temperature and lower relative humidity of the air entering the cowshed. Lower humidity values contribute to a more intense decrease in the temperature–humidity index during the operation of the cooling system. The presented mathematical models are useful tools for decision making regarding the choice of cooling system operation models, as they allow one to evaluate the cooling efficiency, taking into account the influence of external factors.

Avoiding heat stress in cows is an important condition for animal productivity and the maintaining of animal health. For this, it is necessary to provide an optimal microclimate in cowsheds using systems of air cooling. The paper analyzes one of these systems—an air humidification–cooling system. The research was carried out in a semi-insulated box-type cowshed containing 244 places. The changes in temperature, relative humidity, and temperature humidity index (THI) were studied for the air coming from outside and for the air inside the cowshed. Considering the fact that the cows were in the cowshed most of the time (51.5%) under heat stress, the use of a cooling system is appropriate. It was established that a cooling system is capable of compensating for heat released by animals. It was determined that with an increase in air temperature the relative efficiency of a cooling system increases. An intensive constant air exchange provided using fan operation avoids an excessive growth of relative humidity in a cowshed. To reduce the consumption of electricity and water, the paper suggests regulation of both the power of the fans of the system and the water supply to the nozzles not using temperature but using THI. Theoretically, when THI is used to regulate the operation of the cooling system, the consumption of electrical energy is reduced by 17.8%, and the consumption of water is reduced by 43.2% when compared to the option when the temperature is used to regulate the operation of a cooling system.

In this work, a study was performed on the influence of the ratio of height to the diameter of the reduction zone of a small-size downdraft gasifier as well as of the fuel fraction sizes on the gas quality (the quality was evaluated for CO content). The ratio of a full side area to the volume of a fuel fraction (SVR) was used as a fuel parameter. The maximum CO concentration was observed when using a small fuel fraction with SVR—0.7–0.72 mm⁻¹ and when adhering to the ratio of height to the diameter of the reduction zone H/D—0.5–0.6. The maximum electric power for gasoline generators (nominal power equaled 4 kW) when using the gas received from the fast-growing hybrid willow biomass equaled 2.4 kW. This power is 37.5% lower than when using gasoline and 7.0% lower than when using the gas received from the hardwood biomass. The emissions of harmful gases into the atmosphere by the gasoline generator engine equaled 0.12–0.14% CO and 24–27 mln⁻¹ C_xH_y. The emissions were 64.8 times less for CO and 8.5 times less for C_xH_y when compared with using gasoline.

This paper offers an algorithm to account for potential actions on the efficient production of renewable energy. The algorithm consists of a substantiated choice of a certain type of renewable energy, the evaluation of its potential, and the regulation of the processes of obtaining that renewable energy. Also, potential resources for agricultural biofuel production have been analyzed and it has been determined that there is real biomass potential in Lithuania. It will thus be beneficial to make appropriate managerial decisions on the methods of biofuel processing and consumption, as well as on means of receiving the economic, energy and environmental effects. The total potential of by-product biomass of crop production was determined, and the thermal and electric potential of the crop by-products were calculated. Additionally, the potential for production of gas-like types of fuel (biomethane, biohydrogen, and syngas) from crop by-products was determined. The potential for the production of diesel biofuel from oil crop waste (bran) was also found, and the potential for livestock by-products for receiving gas-like types of fuel (biomethane, biohydrogen) was established. The corresponding thermal and electric equivalents of the potential were found and the potential volumes of the biomethane and biohydrogen production were calculated. The total energy equivalent equals, on average, 30.017 × 10⁶ GJ of the thermal energy and 9.224 × 10⁶ GJ of the electric energy in Lithuania. The total potential of biomethane production (taking into account crop production and animal husbandry wastes) on average equals 285.6 × 10⁶ m³. The total potential of biohydrogen production on average equals 251.9 × 10⁶ m³. The cost equivalents of the energy potential of agrarian biomass have been calculated. The average cost equivalent of the thermal energy could equal EUR 8.9 billion, electric energy—EUR 15.9 billion, biomethane—EUR 3.3 billion and biohydrogen—EUR 14.1 billion. The evaluation of the agricultural biomass potential as a source of renewable energy confirmed that Lithuania has a large biomass potential and satisfies the needs for the production of renewable energy. Thus, it is possible to move to the second step, that of making a decision concerning biomass conversion.

The gasification rate of fuel, biomass gasification in particular, is an important parameter which is worth considering in the process of creating a gasifier with a continuous operation process. The gasification of biomass is a complex thermochemical process. The theoretical and practical studies of the gasification rate of biomass are complicated because of a high thermochemical rate of reactions in the functioning zones of a gasifier. The complexity of the study prevents the achievement of the required accuracy of the analytical model of the gasification rate of biomass. The known theoretical models of the gasification rate only partially describe the dynamics of the gasification rate of biomass. Moreover, most scientific studies are focused on establishing the effects of gasifier parameters and the gasification process on the quality indicators of the received gas but not on the gasification rate of fuel. To build an accurate model of the gasification rate the authors propose a series of experimental studies in a well-defined range of the parameters of a gasifier. The paper suggests a simple mathematical model of the gasification rate of biomass, which is proportional to the amount of plant biomass that remained non-gasified. The coefficients of the gasification rate for straw pellets, wood pellets and wood in pieces have been determined. Under a minimal air supply into an active zone of a gasifier (0.00088 m³/s) a coefficient of gasification rate is nearly the same for the test fuel materials and it differs by 4.7% between wood pellets and straw pellets. When the air supply increases, the gap between the coefficients increases as well and it reaches 9.44 × 10⁻⁵ c⁻¹ for wood pellets, 1.05 × 10⁻⁴ c⁻¹ for straw pellets and 8.64 × 10⁻⁵ c⁻¹ for wood in pieces under air supply into an active zone of a gas generator of 0.01169 m³/s. Straw pellets have the highest gasification rate and wood in pieces has the lowest gasification rate.

Heat stress is becoming an increasingly important problem in Lithuanian cowsheds. Microclimate formation systems were evaluated in the seven most popular cowsheds in Lithuania, with different wall and roof constructions, insulation, ventilation intensity controls, and one cowshed was additionally equipped with an air-cooling system—the air is cooled by spraying water droplets with a high pressure. In cowsheds equipped with fans to intensify the movement of air, the temperature does not fall below the outdoor temperature and the temperature humidity index (THI) is higher than outdoors. During the heat period, the THI rises to 82 and the cows get moderate thermal stress, which adversely affects feed intake and milk yield of dairy cows. In the cowshed, where the air humidification–cooling system is installed, the air temperature during heat is lower than the average in the field of 2.61 ± 0.74 °C. Although the relative humidity in the cowshed is on average 16.29 ± 4.12% wetter during heat than outside, the THI in the barn is lower than outside. The air temperature in this cowshed decreases by 3.17 ± 0.86 °C compared to cowsheds without an air humidification–cooling system. The air humidification–cooling system creates good conditions to reduce the conditions for cows to experience thermal stress. Further research is needed to optimize the amount of water spray and droplet size and increase the efficiency of the cooling system.

Chisel plows with a chisel as a working body, loosen the soil without mixing the layers. The analysis of the conducted research concludes that the most widespread is a cylindrical surface of a chisel working body - a chisel with a constant radius of curvature. It is theoretically established that at the radius of curvature of the bit up to 0.1 m, the soil on the surface of the bit will move chaotically, while the curvature of the bit does not affect the percentage of wrapped plant debris. As the radius of curvature increases, the force of inertia decreases, therefore, the angle of soil rise decreases. For the radius of curvature of the bit bigger than 0.5 m, the force of inertia has almost no effect on the angle of the soil rise. Without the influence of the force of inertia, the soil particles begin to move more orderly, the soil and plant debris begin to move along trajectories corresponding to the shape of the bit, which increases the coefficient of wrapping plant debris. It is established that at the radius of curvature of the bit 0.5 m and at an operating speed of 2 m·s ⁻¹ there is an orderly movement of soil on the surface of the bit, which affects the percentage of wrapping of plant remains. The use of a chisel plow point with a cylindrical surface increases the wrapping of plant remains by an average of 17%.