Arthur Mynett | UNESCO-IHE Institute for Water Education (original) (raw)
Papers by Arthur Mynett
Flood losses used to be assessed statistically, based on the risk analysis approach (CUR, 1990; V... more Flood losses used to be assessed statistically, based on the risk analysis approach (CUR, 1990; Vrijling, 2001). With the development of remote sense technology and driven by the
Wave loading and the dynamics of ships in ocean waves are important factors for structural design... more Wave loading and the dynamics of ships in ocean waves are important factors for structural design and optimal routing. Although computer programs are available to determine the wave forces and ship motion response, information on the input wave conditions is essential for the assessment of the computational results. With the advent of directional wave buoys, mathematical wave prediction models and oceanographic satellites this type of information is becoming available. The multi-national LEWEX measurement campaign was set up to assess various prediction and measurement procedures. Results of the Dutch oceanic research vessel HM1MS Tydeman are presented together with laboratory experiments and numerical computations. Implications for on-board analysis procedures are outlined.
Extreme wave conditions are important factors in the design of offshore structures. Large scale, ... more Extreme wave conditions are important factors in the design of offshore structures. Large scale, long term wave conditions in the region of interest can be obtained from numerical hindcast computations and satellite observations. Also, ocean wave buoys are available on an operational basis to monitor local wave conditions and evaluate the small scale, short term wave parameters at a particular site. For the statistical description of wave heights in random seas the Rayleigh distribution is widely used. Although theoretically only valid for Gaussian surface elevation and narrow band spectra, the applicability of the Rayleigh distribution is supported by considerable experimental evidence in both oceanography and ocean engineering science. However, in case of extreme wave heights during severe storm conditions, non-linear effects may be of importance, implying the Rayleigh distribution to be modified. Carefully designed measurements or experiments are required to verify these modifica...
The Ribb River is one of the components of the Blue Nile River system located in the North West... more The Ribb River is one of the components of the Blue Nile River system located in the North Western part of Ethiopia. It drains to Lake Tana, the source of the Blue Nile River. The Ribb has a length of 130 km, with a catchment area of 1,812 km2. The average yearly rainfall of the catchment is 1300 mm, with 80 % occurring between the months of June and September. The average and daily maximum discharge of the river are 15 m3/s and 220 m3/s, respectively. A large dam and a diversion weir 30 km downstream of the dam are under construction to irrigate 15,000 ha of Fogera flood plain (WWDSE and TAHAL, 2007). Downstream of the dam location, the Ribb is a meandering river with slope ranging from 0.18% to 0.03%. The river bed material is dominated by sand with a gravel component in its upper reaches. Intensive agriculture without any natural resources conservation, deforestation, dike construction, pump irrigation and sand mining are the most impactful activities in the...
The international journal hydropower & dams, 2012
In this study, a two-dimensional plane strain finite element model is used for the prediction of ... more In this study, a two-dimensional plane strain finite element model is used for the prediction of mechanical and hydraulic behaviour of pre-stressed concrete-lined pressure tunnels. Results obtained from numerical models are presented and compared with the one calculated using analytival solutions.
rock mass where the in situ state of stress is uniform. The rock mass was assumed to behave elast... more rock mass where the in situ state of stress is uniform. The rock mass was assumed to behave elastically and two cases were examined: whether the rock mass has an isotropic elastic property or not. A two-dimensional plain strain elastic-plastic Jointed Rock model was used to study the response of the rock mass to excavation. The elastic behaviour of the rock mass was assured in the model by simply providing adequate cohesion. The study reveals that the distribution of excavation-inducedstresses and deformations in the space surrounding rock mass having anisotropic properties differs from that obtained under the assumption of isotropic properties. The neglect of the effect of elastic anisotropy can result in a significant underestimation of stresses and displacements in rock and thus also in the design of support measures and the final pressure tunnel linings. Additionally, when the tunnel geometry is circular and the rock mass contains one joint set where the plane of elastic anisotr...
De vloeistofbeweging pond een horizontaal, harmonisch translerend schip op ondiep water kan als e... more De vloeistofbeweging pond een horizontaal, harmonisch translerend schip op ondiep water kan als een potentiaalprobleem worden beschouwd. Voor een twee-dimensionaal model wordt een benaderde oplossing voor de snelheidspotentiaal verkregen door toepassing van de eindige elementen methode volgens het Galerkin-principe. De resultaten worden zowel vergeleken met een analytische oplossing als - herleid tot hydrodynamische coefficienten van toegevoegde massa en demp - met meetgegevens.
In the design of single point mooring systems, wave loading is a dominant factor. Usually a disti... more In the design of single point mooring systems, wave loading is a dominant factor. Usually a distinction is made between wave frequency and low frequency excitation. In the wave frequency regime, a Rayleigh distribution is often employed to obtain the extreme values required for the design. In the low frequency range, extreme values are usually derived from an exponential distribution. Although the justification is based on theoretical considerations and experimental investigations in laboratory conditions, the lack of reliable full-scale data to verify the underlying assumptions is often mentioned. In this paper the results obtained from large-scale, long- duration in-situ measurements are presented. The probability distributions derived for the surge forces in both the wave frequency and the low frequency regime, confirm the theoretical considerations, provided crest-to-trough values are used. In the experiments a consistent difference was observed between crest-amplitudes and trou...
Rock Mechanics and Rock Engineering, 2016
Abstract This paper presents the mechanical and hydraulic behaviour of passively prestressed conc... more Abstract This paper presents the mechanical and hydraulic behaviour of passively prestressed concrete-lined pressure tunnels embedded in elastic transversely isotropic rocks subjected to non-uniform in situ stresses. Two cases are distinguished based on whether the in situ vertical stress in the rock mass is higher, or lower than the in situ horizontal stress. A two-dimensional finite element model was used to study the influence of dip angle, α, and horizontal-to-vertical stress ratio, k, on the bearing capacity of prestressed concrete-lined pressure tunnels. The study reveals that the in situ stress ratio and the orientation of stratifications in the rock mass significantly affect the load sharing between the rock mass and the lining. The distribution of stresses and deformations as a result of tunnel construction processes exhibits a symmetrical pattern for tunnels embedded in a rock mass with either horizontal or vertical stratification planes, whereas it demonstrates an unsymmetrical pattern for tunnels embedded in a rock mass with inclined stratification planes. The results obtained for a specific value α with coefficient k are identical to that for α + 90° with coefficient 1/k by rotating the tunnel axis by 90°. The maximum internal water pressure was determined by offsetting the prestress-induced hoop strains at the final lining intrados against the seepage-induced hoop strains. As well as assessing the internal water pressure, this approach is capable of identifying potential locations where longitudinal cracks may occur in the final lining.
Shallow Flows, 2004
A few decades ago computational fluid dynamics (CFD) was in its infancy. Limitations on memory an... more A few decades ago computational fluid dynamics (CFD) was in its infancy. Limitations on memory and computation speed compelled CFD programmers to use single precision values, which was adequate at that time. Through time the computation speed grew exponentially, and prices of memory banks dropped. So, almost naturally the size and complexity of problems in CFD have increased, but the computation precision has not. It appears that for large simulations, up to 100.000 grid points or more, the acquired accuracy is questionable. If in the (near) future increased computation speed would allow even larger simulations, measures should be taken to ensure sufficiently accurate results. Increasing the machine precision would achieve this aim. Furthermore, numerical adaptations might also increase the accuracy. Row-scaling will for instance improve the results of the continuity equation at hardly any expense. Stricter and/or different stopping criteria for iterative processes will surely increase the accuracy in several cases. Several processes, like the turbulence model and the flooding and drying criteria, cause a certain loss of accuracy, which is not always compensated by accuracy improvements. Much could be gained if they were to be improved. An addition to the complexity of CFD in the course of years is the transition from twodimensional to three-dimensional models. Unconditional stability of the scheme for the discretised two-dimensional shallow-water equations seems to have become conditional in the threedimensional case. The numerical stability has become very much dependent on boundary conditions.
Numerical Methods in Geotechnical Engineering, 2014
Tunnelling and Underground Space Technology, 2014
The bearing capacity of prestressed concrete-lined pressure tunnels is governed by the in situ st... more The bearing capacity of prestressed concrete-lined pressure tunnels is governed by the in situ stress of rock mass, which generally has different magnitudes in the vertical and horizontal direction. Two cases were distinguished, based on whether the vertical stress is greater than the horizontal stress or not. By means of a finite element model (FEM), the resulting distribution of stresses, strains and deformations due to tunnelling processes was revealed. The bearing capacity of pressure tunnels was determined based on the superposition principle. The results obtained demonstrate the significance of horizontal-tovertical stress coefficients in the bearing capacity of pressure tunnels prestressed by grouting. Favourite locations where crack openings in the final lining may occur are identified, which is useful for taking measures regarding the tunnel tightness and stability.
![Research paper thumbnail of The Quest for a Three-Dimensional Theory of Ship-Wave Interactions [and Discussion]](https://attachments.academia-assets.com/109764451/thumbnails/1.jpg)
](Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences, 1991
The radiation and diffraction of water waves by ships can be analysed in classical terms from pot... more The radiation and diffraction of water waves by ships can be analysed in classical terms from potential theory. The linearized formulation is well studied, but robust numerical implementations have been achieved only in cases where the vessel is stationary or oscillating about a fixed mean position. Slender-body approximations have been used to rationalize and extend the strip theory of ship motions, providing analytic solutions and guidance in the development of more general numerical methods. The governing equations are reviewed, with emphasis on the interactions between the steady-state velocity field due to the ship’s forward translation and the perturbations due to its unsteady motions in waves. Recent computations based on the boundary-integral-equation method are described, and encouraging results are noted. There is growing evidence that the influence of the steady-state velocity field is important, and the degree of completeness required to account for the steady field depe...
Journal of Hydraulic Research, 1994
Hydroinformatics represents a technological challenge for a research and consultancy organisation... more Hydroinformatics represents a technological challenge for a research and consultancy organisation such as DELFT HYDRAULICS. Building problem-solving systems by combining numerical models with computer technologies such as databases, geographical information systems (GIS), visualization systems, artificial intelligence and intelligent user interfaces, is only part of the work. The other part is quality control: ensuring that the results obtained with hydroinformatics systems
Journal of Hydraulic Research, 1992
... chapter 1) gives basic features of hydraulic jump which is the transition from supercritical ... more ... chapter 1) gives basic features of hydraulic jump which is the transition from supercritical ... The form of a stilling basin depends on existing hydraulic conditions, geology, and topography ... 9. Two subsequent chapters (10 and 11) describe stilling basins in expanding channels and ...
Ecological Modelling, 2006
A model for simulating freshwater mussel population dynamics is presented. The model is a hydroin... more A model for simulating freshwater mussel population dynamics is presented. The model is a hydroinformatics tool that integrates principles from ecology, river hydraulics, fluid mechanics and sediment transport, and applies the individual-based modelling approach for simulating population dynamics. The general model layout, data requirements, and steps of the simulation process are discussed. As an illustration, simulation results from an application
The international journal hydropower & dams, 2013
Pressure tunnels are in operation subjected to internal water pressure. When the hoop tensile str... more Pressure tunnels are in operation subjected to internal water pressure. When the hoop tensile stress acting at the lining intrados exceeds the tensile strength of concrete, longitudinal cracks occur in the concrete lining. As a consequence of crack openings, the internal water pressure will act at the lining extrados and cause high local water losses. If left untreated, these losses will induce the washing out of joint fillings and increase the risk of hydro-jacking of the surrounding rock mass. When pressure tunnels are situated close to valley slopes, excessive water losses can endanger the stability of the rock mass and provoke landslide. Whether or not the internal water pressure is fully effective at the lining extrados, it depends predominantly on the number of cracks and the width of crack openings. The width of cracks can be estimated based on the total circumferential deformation of the rock mass, which is governed not only by mechanical boundary pressures, but also by seep...
Flood losses used to be assessed statistically, based on the risk analysis approach (CUR, 1990; V... more Flood losses used to be assessed statistically, based on the risk analysis approach (CUR, 1990; Vrijling, 2001). With the development of remote sense technology and driven by the
Wave loading and the dynamics of ships in ocean waves are important factors for structural design... more Wave loading and the dynamics of ships in ocean waves are important factors for structural design and optimal routing. Although computer programs are available to determine the wave forces and ship motion response, information on the input wave conditions is essential for the assessment of the computational results. With the advent of directional wave buoys, mathematical wave prediction models and oceanographic satellites this type of information is becoming available. The multi-national LEWEX measurement campaign was set up to assess various prediction and measurement procedures. Results of the Dutch oceanic research vessel HM1MS Tydeman are presented together with laboratory experiments and numerical computations. Implications for on-board analysis procedures are outlined.
Extreme wave conditions are important factors in the design of offshore structures. Large scale, ... more Extreme wave conditions are important factors in the design of offshore structures. Large scale, long term wave conditions in the region of interest can be obtained from numerical hindcast computations and satellite observations. Also, ocean wave buoys are available on an operational basis to monitor local wave conditions and evaluate the small scale, short term wave parameters at a particular site. For the statistical description of wave heights in random seas the Rayleigh distribution is widely used. Although theoretically only valid for Gaussian surface elevation and narrow band spectra, the applicability of the Rayleigh distribution is supported by considerable experimental evidence in both oceanography and ocean engineering science. However, in case of extreme wave heights during severe storm conditions, non-linear effects may be of importance, implying the Rayleigh distribution to be modified. Carefully designed measurements or experiments are required to verify these modifica...
The Ribb River is one of the components of the Blue Nile River system located in the North West... more The Ribb River is one of the components of the Blue Nile River system located in the North Western part of Ethiopia. It drains to Lake Tana, the source of the Blue Nile River. The Ribb has a length of 130 km, with a catchment area of 1,812 km2. The average yearly rainfall of the catchment is 1300 mm, with 80 % occurring between the months of June and September. The average and daily maximum discharge of the river are 15 m3/s and 220 m3/s, respectively. A large dam and a diversion weir 30 km downstream of the dam are under construction to irrigate 15,000 ha of Fogera flood plain (WWDSE and TAHAL, 2007). Downstream of the dam location, the Ribb is a meandering river with slope ranging from 0.18% to 0.03%. The river bed material is dominated by sand with a gravel component in its upper reaches. Intensive agriculture without any natural resources conservation, deforestation, dike construction, pump irrigation and sand mining are the most impactful activities in the...
The international journal hydropower & dams, 2012
In this study, a two-dimensional plane strain finite element model is used for the prediction of ... more In this study, a two-dimensional plane strain finite element model is used for the prediction of mechanical and hydraulic behaviour of pre-stressed concrete-lined pressure tunnels. Results obtained from numerical models are presented and compared with the one calculated using analytival solutions.
rock mass where the in situ state of stress is uniform. The rock mass was assumed to behave elast... more rock mass where the in situ state of stress is uniform. The rock mass was assumed to behave elastically and two cases were examined: whether the rock mass has an isotropic elastic property or not. A two-dimensional plain strain elastic-plastic Jointed Rock model was used to study the response of the rock mass to excavation. The elastic behaviour of the rock mass was assured in the model by simply providing adequate cohesion. The study reveals that the distribution of excavation-inducedstresses and deformations in the space surrounding rock mass having anisotropic properties differs from that obtained under the assumption of isotropic properties. The neglect of the effect of elastic anisotropy can result in a significant underestimation of stresses and displacements in rock and thus also in the design of support measures and the final pressure tunnel linings. Additionally, when the tunnel geometry is circular and the rock mass contains one joint set where the plane of elastic anisotr...
De vloeistofbeweging pond een horizontaal, harmonisch translerend schip op ondiep water kan als e... more De vloeistofbeweging pond een horizontaal, harmonisch translerend schip op ondiep water kan als een potentiaalprobleem worden beschouwd. Voor een twee-dimensionaal model wordt een benaderde oplossing voor de snelheidspotentiaal verkregen door toepassing van de eindige elementen methode volgens het Galerkin-principe. De resultaten worden zowel vergeleken met een analytische oplossing als - herleid tot hydrodynamische coefficienten van toegevoegde massa en demp - met meetgegevens.
In the design of single point mooring systems, wave loading is a dominant factor. Usually a disti... more In the design of single point mooring systems, wave loading is a dominant factor. Usually a distinction is made between wave frequency and low frequency excitation. In the wave frequency regime, a Rayleigh distribution is often employed to obtain the extreme values required for the design. In the low frequency range, extreme values are usually derived from an exponential distribution. Although the justification is based on theoretical considerations and experimental investigations in laboratory conditions, the lack of reliable full-scale data to verify the underlying assumptions is often mentioned. In this paper the results obtained from large-scale, long- duration in-situ measurements are presented. The probability distributions derived for the surge forces in both the wave frequency and the low frequency regime, confirm the theoretical considerations, provided crest-to-trough values are used. In the experiments a consistent difference was observed between crest-amplitudes and trou...
Rock Mechanics and Rock Engineering, 2016
Abstract This paper presents the mechanical and hydraulic behaviour of passively prestressed conc... more Abstract This paper presents the mechanical and hydraulic behaviour of passively prestressed concrete-lined pressure tunnels embedded in elastic transversely isotropic rocks subjected to non-uniform in situ stresses. Two cases are distinguished based on whether the in situ vertical stress in the rock mass is higher, or lower than the in situ horizontal stress. A two-dimensional finite element model was used to study the influence of dip angle, α, and horizontal-to-vertical stress ratio, k, on the bearing capacity of prestressed concrete-lined pressure tunnels. The study reveals that the in situ stress ratio and the orientation of stratifications in the rock mass significantly affect the load sharing between the rock mass and the lining. The distribution of stresses and deformations as a result of tunnel construction processes exhibits a symmetrical pattern for tunnels embedded in a rock mass with either horizontal or vertical stratification planes, whereas it demonstrates an unsymmetrical pattern for tunnels embedded in a rock mass with inclined stratification planes. The results obtained for a specific value α with coefficient k are identical to that for α + 90° with coefficient 1/k by rotating the tunnel axis by 90°. The maximum internal water pressure was determined by offsetting the prestress-induced hoop strains at the final lining intrados against the seepage-induced hoop strains. As well as assessing the internal water pressure, this approach is capable of identifying potential locations where longitudinal cracks may occur in the final lining.
Shallow Flows, 2004
A few decades ago computational fluid dynamics (CFD) was in its infancy. Limitations on memory an... more A few decades ago computational fluid dynamics (CFD) was in its infancy. Limitations on memory and computation speed compelled CFD programmers to use single precision values, which was adequate at that time. Through time the computation speed grew exponentially, and prices of memory banks dropped. So, almost naturally the size and complexity of problems in CFD have increased, but the computation precision has not. It appears that for large simulations, up to 100.000 grid points or more, the acquired accuracy is questionable. If in the (near) future increased computation speed would allow even larger simulations, measures should be taken to ensure sufficiently accurate results. Increasing the machine precision would achieve this aim. Furthermore, numerical adaptations might also increase the accuracy. Row-scaling will for instance improve the results of the continuity equation at hardly any expense. Stricter and/or different stopping criteria for iterative processes will surely increase the accuracy in several cases. Several processes, like the turbulence model and the flooding and drying criteria, cause a certain loss of accuracy, which is not always compensated by accuracy improvements. Much could be gained if they were to be improved. An addition to the complexity of CFD in the course of years is the transition from twodimensional to three-dimensional models. Unconditional stability of the scheme for the discretised two-dimensional shallow-water equations seems to have become conditional in the threedimensional case. The numerical stability has become very much dependent on boundary conditions.
Numerical Methods in Geotechnical Engineering, 2014
Tunnelling and Underground Space Technology, 2014
The bearing capacity of prestressed concrete-lined pressure tunnels is governed by the in situ st... more The bearing capacity of prestressed concrete-lined pressure tunnels is governed by the in situ stress of rock mass, which generally has different magnitudes in the vertical and horizontal direction. Two cases were distinguished, based on whether the vertical stress is greater than the horizontal stress or not. By means of a finite element model (FEM), the resulting distribution of stresses, strains and deformations due to tunnelling processes was revealed. The bearing capacity of pressure tunnels was determined based on the superposition principle. The results obtained demonstrate the significance of horizontal-tovertical stress coefficients in the bearing capacity of pressure tunnels prestressed by grouting. Favourite locations where crack openings in the final lining may occur are identified, which is useful for taking measures regarding the tunnel tightness and stability.
Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences, 1991
The radiation and diffraction of water waves by ships can be analysed in classical terms from pot... more The radiation and diffraction of water waves by ships can be analysed in classical terms from potential theory. The linearized formulation is well studied, but robust numerical implementations have been achieved only in cases where the vessel is stationary or oscillating about a fixed mean position. Slender-body approximations have been used to rationalize and extend the strip theory of ship motions, providing analytic solutions and guidance in the development of more general numerical methods. The governing equations are reviewed, with emphasis on the interactions between the steady-state velocity field due to the ship’s forward translation and the perturbations due to its unsteady motions in waves. Recent computations based on the boundary-integral-equation method are described, and encouraging results are noted. There is growing evidence that the influence of the steady-state velocity field is important, and the degree of completeness required to account for the steady field depe...
Journal of Hydraulic Research, 1994
Hydroinformatics represents a technological challenge for a research and consultancy organisation... more Hydroinformatics represents a technological challenge for a research and consultancy organisation such as DELFT HYDRAULICS. Building problem-solving systems by combining numerical models with computer technologies such as databases, geographical information systems (GIS), visualization systems, artificial intelligence and intelligent user interfaces, is only part of the work. The other part is quality control: ensuring that the results obtained with hydroinformatics systems
Journal of Hydraulic Research, 1992
... chapter 1) gives basic features of hydraulic jump which is the transition from supercritical ... more ... chapter 1) gives basic features of hydraulic jump which is the transition from supercritical ... The form of a stilling basin depends on existing hydraulic conditions, geology, and topography ... 9. Two subsequent chapters (10 and 11) describe stilling basins in expanding channels and ...
Ecological Modelling, 2006
A model for simulating freshwater mussel population dynamics is presented. The model is a hydroin... more A model for simulating freshwater mussel population dynamics is presented. The model is a hydroinformatics tool that integrates principles from ecology, river hydraulics, fluid mechanics and sediment transport, and applies the individual-based modelling approach for simulating population dynamics. The general model layout, data requirements, and steps of the simulation process are discussed. As an illustration, simulation results from an application
The international journal hydropower & dams, 2013
Pressure tunnels are in operation subjected to internal water pressure. When the hoop tensile str... more Pressure tunnels are in operation subjected to internal water pressure. When the hoop tensile stress acting at the lining intrados exceeds the tensile strength of concrete, longitudinal cracks occur in the concrete lining. As a consequence of crack openings, the internal water pressure will act at the lining extrados and cause high local water losses. If left untreated, these losses will induce the washing out of joint fillings and increase the risk of hydro-jacking of the surrounding rock mass. When pressure tunnels are situated close to valley slopes, excessive water losses can endanger the stability of the rock mass and provoke landslide. Whether or not the internal water pressure is fully effective at the lining extrados, it depends predominantly on the number of cracks and the width of crack openings. The width of cracks can be estimated based on the total circumferential deformation of the rock mass, which is governed not only by mechanical boundary pressures, but also by seep...