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A.W. Vredeveldt
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3 records found
1
The under water ventilation of methanol vapour
A numerical investigation
Master thesis
(2023)
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C. De Boom, L. van Biert, A.W. Vredeveldt, Ad van Hoeve, I. Akkerman, A.J. Bottger, Sietse Bolt
In order to meet the shipping industry's emissions reduction goals, it is imperative to explore and adopt alternative marine fuels. Methanol (or methyl alcohol) is expected to play a large role in the future. However, current regulations limit the attractiveness of methanol as marine fuel due to the inability to use the space around a venting point on deck. Hazardous area zones are installed around fuel tank vapour outlets due to the flammability and toxicity of methanol vapour. Consequently, these areas become very impractical. This thesis investigates the ventilation of the fuel tank vapour below the waterline instead on deck in order to be able to limit/eliminate these areas. Therefore, the main research question is:
"What is the concentration of methanol at deck level when methanol is vented below the waterline?"
An Eulerian based CFD model and a simple integral model are used to predict the methanol concentration above the waterline. The integral model predicts the gas concentration above the waterline based on the gas flow rate reaching the surface and the radial inflow rate of air. The CFD model tracks parcels (group of bubbles with the same properties) using the force balance in the discrete phase model. Both of the models are successfully validated against experimental data from the "Rotvoll experiment" wherein methane was released at the bottom of a water basin. The CFD model showed strong superiority over the integral model, o.a. due to the lack of gas dissolution in the integral model.
The numerical models are applied to the case wherein a mixture of methanol and nitrogen is vented due to an overpressure. The overpressure could be caused by for example the failure of the vapour return line when bunkering or a fire. The bunker tanks are protected by a pressure relief valve, which reduces the overpressure by directing the gases in the bunker tank towards the venting location below the waterline. The flow rate characteristic (pressure - flow rate) of the pressure relief valve determines the rate at which the gases are injected in the water. The gas dissolution showed strong dependence on the departure bubble diameter and the venting depth. Different cases with different initial bubble sizes and different venting depths were simulated. The CFD model showed that in the most critical case (lowest venting depth 0.5m and largest initial bubble size 0.08m) the gas dissolution is large enough such that no methanol vapour reaches the deck of the ship and barge. The subsea venting of methanol-nitrogen vapour proved to be a safe alternative compared to the venting above deck. ...
"What is the concentration of methanol at deck level when methanol is vented below the waterline?"
An Eulerian based CFD model and a simple integral model are used to predict the methanol concentration above the waterline. The integral model predicts the gas concentration above the waterline based on the gas flow rate reaching the surface and the radial inflow rate of air. The CFD model tracks parcels (group of bubbles with the same properties) using the force balance in the discrete phase model. Both of the models are successfully validated against experimental data from the "Rotvoll experiment" wherein methane was released at the bottom of a water basin. The CFD model showed strong superiority over the integral model, o.a. due to the lack of gas dissolution in the integral model.
The numerical models are applied to the case wherein a mixture of methanol and nitrogen is vented due to an overpressure. The overpressure could be caused by for example the failure of the vapour return line when bunkering or a fire. The bunker tanks are protected by a pressure relief valve, which reduces the overpressure by directing the gases in the bunker tank towards the venting location below the waterline. The flow rate characteristic (pressure - flow rate) of the pressure relief valve determines the rate at which the gases are injected in the water. The gas dissolution showed strong dependence on the departure bubble diameter and the venting depth. Different cases with different initial bubble sizes and different venting depths were simulated. The CFD model showed that in the most critical case (lowest venting depth 0.5m and largest initial bubble size 0.08m) the gas dissolution is large enough such that no methanol vapour reaches the deck of the ship and barge. The subsea venting of methanol-nitrogen vapour proved to be a safe alternative compared to the venting above deck. ...
In order to meet the shipping industry's emissions reduction goals, it is imperative to explore and adopt alternative marine fuels. Methanol (or methyl alcohol) is expected to play a large role in the future. However, current regulations limit the attractiveness of methanol as marine fuel due to the inability to use the space around a venting point on deck. Hazardous area zones are installed around fuel tank vapour outlets due to the flammability and toxicity of methanol vapour. Consequently, these areas become very impractical. This thesis investigates the ventilation of the fuel tank vapour below the waterline instead on deck in order to be able to limit/eliminate these areas. Therefore, the main research question is:
"What is the concentration of methanol at deck level when methanol is vented below the waterline?"
An Eulerian based CFD model and a simple integral model are used to predict the methanol concentration above the waterline. The integral model predicts the gas concentration above the waterline based on the gas flow rate reaching the surface and the radial inflow rate of air. The CFD model tracks parcels (group of bubbles with the same properties) using the force balance in the discrete phase model. Both of the models are successfully validated against experimental data from the "Rotvoll experiment" wherein methane was released at the bottom of a water basin. The CFD model showed strong superiority over the integral model, o.a. due to the lack of gas dissolution in the integral model.
The numerical models are applied to the case wherein a mixture of methanol and nitrogen is vented due to an overpressure. The overpressure could be caused by for example the failure of the vapour return line when bunkering or a fire. The bunker tanks are protected by a pressure relief valve, which reduces the overpressure by directing the gases in the bunker tank towards the venting location below the waterline. The flow rate characteristic (pressure - flow rate) of the pressure relief valve determines the rate at which the gases are injected in the water. The gas dissolution showed strong dependence on the departure bubble diameter and the venting depth. Different cases with different initial bubble sizes and different venting depths were simulated. The CFD model showed that in the most critical case (lowest venting depth 0.5m and largest initial bubble size 0.08m) the gas dissolution is large enough such that no methanol vapour reaches the deck of the ship and barge. The subsea venting of methanol-nitrogen vapour proved to be a safe alternative compared to the venting above deck.
"What is the concentration of methanol at deck level when methanol is vented below the waterline?"
An Eulerian based CFD model and a simple integral model are used to predict the methanol concentration above the waterline. The integral model predicts the gas concentration above the waterline based on the gas flow rate reaching the surface and the radial inflow rate of air. The CFD model tracks parcels (group of bubbles with the same properties) using the force balance in the discrete phase model. Both of the models are successfully validated against experimental data from the "Rotvoll experiment" wherein methane was released at the bottom of a water basin. The CFD model showed strong superiority over the integral model, o.a. due to the lack of gas dissolution in the integral model.
The numerical models are applied to the case wherein a mixture of methanol and nitrogen is vented due to an overpressure. The overpressure could be caused by for example the failure of the vapour return line when bunkering or a fire. The bunker tanks are protected by a pressure relief valve, which reduces the overpressure by directing the gases in the bunker tank towards the venting location below the waterline. The flow rate characteristic (pressure - flow rate) of the pressure relief valve determines the rate at which the gases are injected in the water. The gas dissolution showed strong dependence on the departure bubble diameter and the venting depth. Different cases with different initial bubble sizes and different venting depths were simulated. The CFD model showed that in the most critical case (lowest venting depth 0.5m and largest initial bubble size 0.08m) the gas dissolution is large enough such that no methanol vapour reaches the deck of the ship and barge. The subsea venting of methanol-nitrogen vapour proved to be a safe alternative compared to the venting above deck.
Preventing Injuries of High Speed Marine Craft Operators
Incorporating Spinal Injury Models in the Analyses of Various Seat Suspension Principles
Master thesis
(2020)
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Niek van den Nieuwenhuijzen, R.P. Notenboom, A.W. Vredeveldt, C.L. Walters, J.H. den Besten, O.K. Bergsma, H.C. Seyffert
On board of High Speed marine Craft (HSC), the crew and the passengers are exposed to high levels of Whole Body Vibrations (WBV) and large magnitude Repeated mechanical Shocks (RS) caused by the motions of the craft. The HSCs are typically 10 meters long, capable of reaching a maximum speed up to 50 knots and widely used by various maritime organizations. However, the operators and crew suffer from fatigue and injuries, leading to a reduced effectiveness and operational capacity of the marine craft. In an attempt to reduce the physical loads, passive Shock Mitigating Seats (SMS) can be installed. Numerous research has shown that an improperly designed SMS may amplify the wave impacts forces through phenomena such as bottoming out and dynamic amplification. Therefore, it is necessary to ensure that a suspension design works properly by testing the performance during wave impact events, before the seat is manufactured and installed onboard the craft. The problem is that it is difficult to determine the performance of the seats in both the design and off-design conditions with either sea trials or laboratory tests. This research focuses on the prevention of injuries and adverse health effects due to repetitive wave impacts by incorporating an injury model in the analyses of various suspension principles in the design of SMS. In the current analyses of SMS either simplistic or specific models are used which restrict the application of these models to other suspension designs. Therefore, a computer program based on the finite element method is developed that allows realistic input accelerations in the surge, heave and pitch direction. The program incorporates highly non-linear elements, including the effect of bottoming. Additionally, the validity of the half-sine approximation for the wave impact excitation pulse was reviewed and concluded to be inappropriate for design purposes as it underestimates the probability of bottoming. Furthermore, the modified evaluation methods of ISO 2631 Part 5 using an optimized age-dependent coefficient based on gender in combination with a Weibull injury risk model were implemented to evaluate the resulting seat level accelerations. A case study was conducted on a Fast Raiding Interception and Special forces Craft (FRISC) of the Royal Netherlands Navy (RNLN). A design based on a parallelogram of pinned truss elements in combination with a coil spring element was altered by replacing the coil spring with a gas-spring element. The design was analysed with dynamic simulations of full-scale measurements of wave impacts on a lifeboat of the Royal Sea Rescue Institution (KNRM). For the most severe wave impact of the acceleration record, the seat level acceleration was reduced from 17.7 [g] to 2.8 [g]. An operator of the age of 24 years who is exposed to the accelerations for half an hour a day, 30 days a year for two consecutive years was assumed. The probability of spinal injury was reduced for a male operator from 99.5% to 16.3% and for a female operator from 100.0% to 42.0%. These results illustrate the high risk of injury to which the HSC operators are exposed. By incorporating highly non-linear elements and spinal injury models, the program and evaluation methods are capable of modelling various SMS suspension designs and analyse the performance. This can assist the seat designer, engineer or researcher with investigating suitable suspension designs before sea trials, experimental tests and prototype iterations. Therefore, the method offers the possibility to save time and reduce costs. Furthermore, the method can assist in defining new regulations in order to limit the exposure of the operators to physical loads and reduce the risk of spinal injury to an acceptable level.
...
On board of High Speed marine Craft (HSC), the crew and the passengers are exposed to high levels of Whole Body Vibrations (WBV) and large magnitude Repeated mechanical Shocks (RS) caused by the motions of the craft. The HSCs are typically 10 meters long, capable of reaching a maximum speed up to 50 knots and widely used by various maritime organizations. However, the operators and crew suffer from fatigue and injuries, leading to a reduced effectiveness and operational capacity of the marine craft. In an attempt to reduce the physical loads, passive Shock Mitigating Seats (SMS) can be installed. Numerous research has shown that an improperly designed SMS may amplify the wave impacts forces through phenomena such as bottoming out and dynamic amplification. Therefore, it is necessary to ensure that a suspension design works properly by testing the performance during wave impact events, before the seat is manufactured and installed onboard the craft. The problem is that it is difficult to determine the performance of the seats in both the design and off-design conditions with either sea trials or laboratory tests. This research focuses on the prevention of injuries and adverse health effects due to repetitive wave impacts by incorporating an injury model in the analyses of various suspension principles in the design of SMS. In the current analyses of SMS either simplistic or specific models are used which restrict the application of these models to other suspension designs. Therefore, a computer program based on the finite element method is developed that allows realistic input accelerations in the surge, heave and pitch direction. The program incorporates highly non-linear elements, including the effect of bottoming. Additionally, the validity of the half-sine approximation for the wave impact excitation pulse was reviewed and concluded to be inappropriate for design purposes as it underestimates the probability of bottoming. Furthermore, the modified evaluation methods of ISO 2631 Part 5 using an optimized age-dependent coefficient based on gender in combination with a Weibull injury risk model were implemented to evaluate the resulting seat level accelerations. A case study was conducted on a Fast Raiding Interception and Special forces Craft (FRISC) of the Royal Netherlands Navy (RNLN). A design based on a parallelogram of pinned truss elements in combination with a coil spring element was altered by replacing the coil spring with a gas-spring element. The design was analysed with dynamic simulations of full-scale measurements of wave impacts on a lifeboat of the Royal Sea Rescue Institution (KNRM). For the most severe wave impact of the acceleration record, the seat level acceleration was reduced from 17.7 [g] to 2.8 [g]. An operator of the age of 24 years who is exposed to the accelerations for half an hour a day, 30 days a year for two consecutive years was assumed. The probability of spinal injury was reduced for a male operator from 99.5% to 16.3% and for a female operator from 100.0% to 42.0%. These results illustrate the high risk of injury to which the HSC operators are exposed. By incorporating highly non-linear elements and spinal injury models, the program and evaluation methods are capable of modelling various SMS suspension designs and analyse the performance. This can assist the seat designer, engineer or researcher with investigating suitable suspension designs before sea trials, experimental tests and prototype iterations. Therefore, the method offers the possibility to save time and reduce costs. Furthermore, the method can assist in defining new regulations in order to limit the exposure of the operators to physical loads and reduce the risk of spinal injury to an acceptable level.
Redesigning the Jockey Seat for fast planing crafts
Integration of composite resilient mounting
In this thesis persistent problems with the shock isolating behaviour of the Jockey Seat are identified and analysed. These Jockey Seat are used on fast planning crafts like the FRISC which is in service with the Royal Netherlands Navy. Past research and existing technology were presented along with two redesign directions. Furthermore, several tools to further analyse the problem in both a static and dynamic setting have been developed.
...
In this thesis persistent problems with the shock isolating behaviour of the Jockey Seat are identified and analysed. These Jockey Seat are used on fast planning crafts like the FRISC which is in service with the Royal Netherlands Navy. Past research and existing technology were presented along with two redesign directions. Furthermore, several tools to further analyse the problem in both a static and dynamic setting have been developed.