| 1. |
- Dahlqvist, Peter, et al.
(författare)
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Potential benefits of managed aquifer recharge MAR on the Island of Gotland, Sweden
- 2019
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Ingår i: Water. - : MDPI AG. - 2073-4441. ; 11:10
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Tidskriftsartikel (refereegranskat)abstract
- The Island of Gotland (3000 km2), east of mainland Sweden, suffers from insufficient water availability each summer. Thin soils and lack of coherent reservoirs in the sedimentary bedrock lead to limited reservoir capacity. The feasibility of Managed Aquifer Recharge (MAR) is explored by identifying suitable areas and estimating their possible contribution to an increased water availability. MARis compared to alternative water management measures, e.g., increased groundwater abstraction, in terms of costs and water availability potential. Results from GIS analyses of infiltration areas and groundwater storage, respectively proximity to surface water sources and surface water storage were classified into three categories of MAR suitability. An area of ca 7700 ha (2.5% of Gotland) was found to have good local conditions for MAR and an area of ca 22,700 ha (7.5% of Gotland) was found to have moderate local conditions for MAR. These results reveal the MAR potential on Gotland. The water supply potential of MAR in existing well fields was estimated to be about 35% of the forecasted drinking water supply and 7% of the total water demand gap in year 2045. It is similar in costs and water supply potential to increased surface water extraction. © 2019 by the authors.
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| 2. |
- Gomez, Erik, et al.
(författare)
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Torsional vibrations in heavy-truck powertrains with flywheel attached centrifugal pendulum vibration absorbers
- 2022
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Ingår i: Mechanism and machine theory. - : Elsevier BV. - 0094-114X .- 1873-3999. ; 167
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Tidskriftsartikel (refereegranskat)abstract
- A nonlinear centrifugal pendulum vibration absorber (CPVA) with normal-force dependant friction loss is investigated in a torsional model of a downspeeded powertrain of a heavy-truck. The engine model includes gas-pressure excitation and the existing pendulum model is extended to include a continuous formulation of end-stops at the end of the pendulum-path. Furthermore, the friction loss of the pendulum is experimentally determined. A pendulum-path parameter-study in the complete powertrain model is conducted to consider the effects of the system dynamics on the CPVA. It is shown that the performance of the CPVA is affected by the powertrain system-dynamics and thus important to consider in the design of the CPVA. Downspeeding of the engine by appropriate gearing of the driveline is a measure to decrease the CO2 emissions. However, downspeeding increases the torsional vibration and noise of the powertrain with conventional torsional vibration reduction methods. The CPVA can be used to reduce the torsional vibration and thus facilitate to reach environmental goals.
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| 3. |
- Sjöstrand, Jakob, et al.
(författare)
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Effect of normal load evolution on transient torsional vibrations during clutch engagement
- 2020
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Ingår i: Proceedings of ISMA 2020 - International Conference on Noise and Vibration Engineering and USD 2020 - International Conference on Uncertainty in Structural Dynamics. - : KU Leuven Department Mechanical Engineering Division. ; , s. 1433-1447
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Konferensbidrag (refereegranskat)abstract
- Different models of the evolving normal load in the clutch friction interface and their respective influence on friction induced torsional driveline vibrations, during clutch engagement, are examined. This is done in the context of driveline vibrations of heavy duty vehicles with combustion engines. In prior studies of clutch synchronisation a lot of focus has been devoted to the characteristics of the coefficient of friction. A negative gradient of the coefficient of friction, with respect to slipspeed, can lead to driveline instabilities, sometimes referred to as clutch start-up judder. However, the way in which the normal load evolves, and consequently how the friction torque builds up during synchronization, has been given less attention. This study compares the influence of a linear evolution of the normal load to a quadratic evolution. It is shown that the slope of the normal load at the beginning of synchronization is pivotal to the excitation of driveline vibrations, where a decrease of the slope effectively reduces the self-excited vibrations.
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| 4. |
- Sjöstrand, Jakob, 1987-, et al.
(författare)
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LuGre friction based dry clutch model in a heavy-truck powertrain context
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- A dry friction clutch model which allows for continuous time domain simulation of all working states of theclutch operation cycle is developed. The model uses the push rod position as input and in combination withthe load-deflection relationship of the cushion springs together with a normal force controlled dynamic LuGrefriction model, the transmitted friction torque through the dry clutch system is calculated. The output data from a pre-existing clutch engagement test rig is used to test the validity of the proposed model during afull clutch operation cycle. The test rig consists of a diesel engine, a dry clutch system and a transmission.During the clutch operation cycle the push rod position is recorded together with the rotational velocitiesof the flywheel and transmission input shaft. For the proposed dry clutch model, time domain simulationsshows a clear correlation between push rod position and the torsional response of the test rig model, bothin terms of engagement and disengagement of the clutch. Optimal engine speeds leads to reduced CO2 emissions and requires swift and frequent gear shifts. The proposed dry clutch simulation model can assistthis development.
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| 5. |
- Sjöstrand, Jakob, 1987-
(författare)
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Transient vibrations from dry clutch operation in heavy-duty truck powertrains : Modelling, simulation and validation
- 2021
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- For internal combustion engines used in heavy-duty vehicles, increased engine efficiency and consequently reduced CO2 emissions can be obtained if the engine speed can be kept within an optimal speed range. This requires swift and frequent gear shifts where the dry friction clutch is utilized. Enhanced dry clutch simulation models and a better understanding of the involved phenomena can assist the development towards swifter gear shifts and help reduce CO2 emissions. The work presented in this thesis focuses on the modelling of dry clutch systems for heavy-duty applications and their effect on the torsional response of the driveline during transient events such as clutch engagement and disengagement. During these events it is primarily the first vibration mode of the driveline that is active and consequently it is possible to greatly reduce theof degrees of freedom (DOFs) of the powertrain model and still capture the relevant dynamics of the powertrain. The reduced set of differential equationsdescribe the torsional motion of the powertrain and the equations of motion are solved numerically in the time-domain. From a mathematical point ofview, the equations of motion turn "stiff" when the clutch is locked. This issue is resolved by utilizing numerical solution techniques suitable for stiff differential equations. In the simulations it was observed that no engine torque fluctuations were transferred through the slipping clutch. Consequently the response of the driveline is purely modal during sliding. If the gradient of the coefficient of friction is negative the modal response is possibly unstable with exponentially growing vibration amplitudes as an effect. Moreover, the way in which the clamp load evolves during clutch engagement is found to severely effect the excitation of transient vibrations during clutch synchronization. It can be shown that reducing the gradient of the evolving clamp load at the onset of sliding will reduce the amplitude of the friction induced vibrations. Reducing the torsional vibration amplitudes will help avoid the jerky motion of the vehicle during launch and increase comfort for driver and passengers.
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