Malcolm Smeaton | University of Otago (original) (raw)
Papers by Malcolm Smeaton
—This paper looks at how channel constriction affects the available power in a channel and the op... more —This paper looks at how channel constriction affects the available power in a channel and the optimal turbine array design that maximises power production. Constricted channels have lower potentials than unconstricted channels but can generate more power from fewer turbines. Turbines placed in the constricted zone can achieve a higher blockage ratio as well as take advantage of the high velocity flow. These turbines must tolerate greater loads compared to turbines placed outside of the constriction. Using the power to load ratio as a crude indicator of array economics, we show that the most constricted part of the channel may also be the most economic place to build a turbine farm. For arrays consisting of multiple rows, constraints such as the minimum spacing between rows and the necessity of leaving a navigable area open, free of turbines, greatly affect the optimal array configuration. Compromises must be made between the average power per turbine and the total row power. The best array design depends on the final number of rows that will be in the array. Turbine power diminishes with the addition of each row and the significance of this effect is correlated to the degree of constriction in the channel.
Tidal channels with narrow constrictions are attractive sites for electricity generation due to e... more Tidal channels with narrow constrictions are attractive sites for electricity generation due to energy dense, high velocity flow through the constricted zones. This work uses a 1D model to systematically examine the effect of constriction on channel potential (theoretical maximum power) and transport in channels connecting two large water bodies (Type I) and channels connecting a large water body to an embayment/lagoon (Type II). Type I channels showed a monotonic decrease in potential and transport with increasing constriction due to enhanced bottom drag from the resultant high velocity zone. The effect of constriction on potential and transport in Type II channels varies depending on the relative geometries of the channel and embayment. Type II channels may be geometrically modified to increase power and in some instances this would simultaneously produce a high velocity zone. The flow reduction required to achieve a channel's potential was invariant to changes in constriction for Type I channels and also Type II channels if a “lagoon geometry factor” is less than about 4. A simple approximation for potential provided in the literature for unconstricted channels is extended for use with constricted channels and an approximation for the drag coefficient required to achieve potential is provided.
Proceedings European Wave and Tidal Energy Conference, Nantes France September 2015, Sep 2015
Constricted tidal channels are potentially lucrative sites for energy development as enhanced vel... more Constricted tidal channels are potentially lucrative sites for energy development as enhanced velocities through the
constricted zones may mean less turbines are required to generate the same amount of power than in an unconstricted channel. This work uses a one dimensional model to examine the effect of both width and depth constriction on channel potential (theoretical maximum power) and flow rate in channels connecting two large water bodies (Type I) and channels connecting a large water body to an embayment/lagoon (Type II). Type I channels showed a
monotonic decrease in potential with an increase in constriction. This is believed to be due to enhanced bottom drag resulting from the high velocities within the constricted zone. Increasing constriction in Type II channels can cause potential to increase or decrease depending on the geometry of the terminal lagoon. For both channel types, a depth constriction resulted in a lower potential than a width constriction of equal magnitude. Flow rate behaved in a similar way to potential for the respective channel types. The flow rate reduction required to achieve potential was invariant to channel geometry for Type I channels and Type II channels if the lagoon geometry factor was less than 4.
Proceedings European Wave and Tidal Energy Conference, Nantes France September 2015, Sep 2015
Aspiring to build GW arrays of turbines is essential if tidal stream energy is to make a signific... more Aspiring to build GW arrays of turbines is essential if tidal stream energy is to make a significant contribution to meeting the demand for renewable power. Many channels have the potential to produce several GW. Realizing one GW of this potential is much more complex than installing 1000 one MW turbines because large scale power extraction reduces tidal currents throughout a channel, changing the resource. This work uses a 1D model to estimate the minimum number of turbines required to produce 1 GW in two example channels loosely based on the Pentland Firth and the Minas Passage. The minimum number of 400 m^2 turbines is 350-800, depending on how they are arranged into rows.
For some arrays adding turbines increases the total output of the array, while simultaneously reducing the output of every turbine within it. For other arrays adding turbines increases both the array output and the output of every turbine within it, despite a reduction in tidal currents. Thus turbines in large arrays perform very differently to isolated turbines. Large arrays have turbines which sweep more than 2-5% of a channel's cross-sectional area, which is only 40 turbines in the Pentland Firth.
—This paper looks at how channel constriction affects the available power in a channel and the op... more —This paper looks at how channel constriction affects the available power in a channel and the optimal turbine array design that maximises power production. Constricted channels have lower potentials than unconstricted channels but can generate more power from fewer turbines. Turbines placed in the constricted zone can achieve a higher blockage ratio as well as take advantage of the high velocity flow. These turbines must tolerate greater loads compared to turbines placed outside of the constriction. Using the power to load ratio as a crude indicator of array economics, we show that the most constricted part of the channel may also be the most economic place to build a turbine farm. For arrays consisting of multiple rows, constraints such as the minimum spacing between rows and the necessity of leaving a navigable area open, free of turbines, greatly affect the optimal array configuration. Compromises must be made between the average power per turbine and the total row power. The best array design depends on the final number of rows that will be in the array. Turbine power diminishes with the addition of each row and the significance of this effect is correlated to the degree of constriction in the channel.
Tidal channels with narrow constrictions are attractive sites for electricity generation due to e... more Tidal channels with narrow constrictions are attractive sites for electricity generation due to energy dense, high velocity flow through the constricted zones. This work uses a 1D model to systematically examine the effect of constriction on channel potential (theoretical maximum power) and transport in channels connecting two large water bodies (Type I) and channels connecting a large water body to an embayment/lagoon (Type II). Type I channels showed a monotonic decrease in potential and transport with increasing constriction due to enhanced bottom drag from the resultant high velocity zone. The effect of constriction on potential and transport in Type II channels varies depending on the relative geometries of the channel and embayment. Type II channels may be geometrically modified to increase power and in some instances this would simultaneously produce a high velocity zone. The flow reduction required to achieve a channel's potential was invariant to changes in constriction for Type I channels and also Type II channels if a “lagoon geometry factor” is less than about 4. A simple approximation for potential provided in the literature for unconstricted channels is extended for use with constricted channels and an approximation for the drag coefficient required to achieve potential is provided.
Proceedings European Wave and Tidal Energy Conference, Nantes France September 2015, Sep 2015
Constricted tidal channels are potentially lucrative sites for energy development as enhanced vel... more Constricted tidal channels are potentially lucrative sites for energy development as enhanced velocities through the
constricted zones may mean less turbines are required to generate the same amount of power than in an unconstricted channel. This work uses a one dimensional model to examine the effect of both width and depth constriction on channel potential (theoretical maximum power) and flow rate in channels connecting two large water bodies (Type I) and channels connecting a large water body to an embayment/lagoon (Type II). Type I channels showed a
monotonic decrease in potential with an increase in constriction. This is believed to be due to enhanced bottom drag resulting from the high velocities within the constricted zone. Increasing constriction in Type II channels can cause potential to increase or decrease depending on the geometry of the terminal lagoon. For both channel types, a depth constriction resulted in a lower potential than a width constriction of equal magnitude. Flow rate behaved in a similar way to potential for the respective channel types. The flow rate reduction required to achieve potential was invariant to channel geometry for Type I channels and Type II channels if the lagoon geometry factor was less than 4.
Proceedings European Wave and Tidal Energy Conference, Nantes France September 2015, Sep 2015
Aspiring to build GW arrays of turbines is essential if tidal stream energy is to make a signific... more Aspiring to build GW arrays of turbines is essential if tidal stream energy is to make a significant contribution to meeting the demand for renewable power. Many channels have the potential to produce several GW. Realizing one GW of this potential is much more complex than installing 1000 one MW turbines because large scale power extraction reduces tidal currents throughout a channel, changing the resource. This work uses a 1D model to estimate the minimum number of turbines required to produce 1 GW in two example channels loosely based on the Pentland Firth and the Minas Passage. The minimum number of 400 m^2 turbines is 350-800, depending on how they are arranged into rows.
For some arrays adding turbines increases the total output of the array, while simultaneously reducing the output of every turbine within it. For other arrays adding turbines increases both the array output and the output of every turbine within it, despite a reduction in tidal currents. Thus turbines in large arrays perform very differently to isolated turbines. Large arrays have turbines which sweep more than 2-5% of a channel's cross-sectional area, which is only 40 turbines in the Pentland Firth.