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245MI - Architettura NavaleA.A. 2020/21
Ship Model Testing
Docente: Prof. Mitja MorgutUniversità degli Studi di TriesteDipartimento di Ingegneria e ArchitetturaVia A. Valerio 10, 34127 TriesteEdificio C5 - Stanza C5_2.44mail: [email protected]
Towing tank Models Turbulence generation
Towing tanks
Architettura Navale, A.A. 2020/21
Example of a schematic view of a towing tank
Towing tank Models Turbulence generation
Towing tanks
Architettura Navale, A.A. 2020/21
Ï Are filled with fresh water
Ï Range in length from 30 m to more than 1300 m,with widths between 4 m and 18 m,and water depths between 1.5 m and 8 m
Ï Typically at one end of the basin there is the trim tank, whichprovides easy access to a floating model.Before the run a model is lowered into the trim tank for ballasting.
Ï Most towing tanks have a wave maker at the end opposite to thetrim tank.
Ï A beach at the trim tank end of the basin employed to damp thewaves generated by the wave maker.
Towing tank Models Turbulence generation
Towing tanks
Architettura Navale, A.A. 2020/21
Ï Are filled with fresh water
Ï Range in length from 30 m to more than 1300 m,with widths between 4 m and 18 m,and water depths between 1.5 m and 8 m
Ï Typically at one end of the basin there is the trim tank, whichprovides easy access to a floating model.Before the run a model is lowered into the trim tank for ballasting.
Ï Most towing tanks have a wave maker at the end opposite to thetrim tank.
Ï A beach at the trim tank end of the basin employed to damp thewaves generated by the wave maker.
Towing tank Models Turbulence generation
Towing tanks
Architettura Navale, A.A. 2020/21
Ï Are filled with fresh water
Ï Range in length from 30 m to more than 1300 m,with widths between 4 m and 18 m,and water depths between 1.5 m and 8 m
Ï Typically at one end of the basin there is the trim tank, whichprovides easy access to a floating model.Before the run a model is lowered into the trim tank for ballasting.
Ï Most towing tanks have a wave maker at the end opposite to thetrim tank.
Ï A beach at the trim tank end of the basin employed to damp thewaves generated by the wave maker.
Towing tank Models Turbulence generation
Towing tanks
Architettura Navale, A.A. 2020/21
Ï Are filled with fresh water
Ï Range in length from 30 m to more than 1300 m,with widths between 4 m and 18 m,and water depths between 1.5 m and 8 m
Ï Typically at one end of the basin there is the trim tank, whichprovides easy access to a floating model.Before the run a model is lowered into the trim tank for ballasting.
Ï Most towing tanks have a wave maker at the end opposite to thetrim tank.
Ï A beach at the trim tank end of the basin employed to damp thewaves generated by the wave maker.
Towing tank Models Turbulence generation
Towing tanks
Architettura Navale, A.A. 2020/21
Ï Are filled with fresh water
Ï Range in length from 30 m to more than 1300 m,with widths between 4 m and 18 m,and water depths between 1.5 m and 8 m
Ï Typically at one end of the basin there is the trim tank, whichprovides easy access to a floating model.Before the run a model is lowered into the trim tank for ballasting.
Ï Most towing tanks have a wave maker at the end opposite to thetrim tank.
Ï A beach at the trim tank end of the basin employed to damp thewaves generated by the wave maker.
Towing tank Models Turbulence generation
Towing tanks
Architettura Navale, A.A. 2020/21
Ï A pair of rails for the towing carriage is mounted on top of the sidewalls.
The rails have to be parallel to each other
The rails have to be parallel to the water surface and thus they mustfollow the Earth’s curvature. They form an arc when viewed from theside.
s = R−√
R2 − L2
4
For instance, for the towing tank at HSVA, having the length L=300m, the rails have a sagitta of s=1.8mm.
Towing tank Models Turbulence generation
Towing tanks
Architettura Navale, A.A. 2020/21
Ï A pair of rails for the towing carriage is mounted on top of the sidewalls.
The rails have to be parallel to each other
The rails have to be parallel to the water surface and thus they mustfollow the Earth’s curvature. They form an arc when viewed from theside.
s = R−√
R2 − L2
4
For instance, for the towing tank at HSVA, having the length L=300m, the rails have a sagitta of s=1.8mm.
Towing tank Models Turbulence generation
Towing tanks
Architettura Navale, A.A. 2020/21
Ï A pair of rails for the towing carriage is mounted on top of the sidewalls.
The rails have to be parallel to each other
The rails have to be parallel to the water surface and thus they mustfollow the Earth’s curvature. They form an arc when viewed from theside.
s = R−√
R2 − L2
4
For instance, for the towing tank at HSVA, having the length L=300m, the rails have a sagitta of s=1.8mm.
Towing tank Models Turbulence generation
Towing tanks
Architettura Navale, A.A. 2020/21
Ï A pair of rails for the towing carriage is mounted on top of the sidewalls.
The rails have to be parallel to each other
The rails have to be parallel to the water surface and thus they mustfollow the Earth’s curvature. They form an arc when viewed from theside.
s = R−√
R2 − L2
4
For instance, for the towing tank at HSVA, having the length L=300m, the rails have a sagitta of s=1.8mm.
Towing tank Models Turbulence generation
Towing tanks
Architettura Navale, A.A. 2020/21
Ï A pair of rails for the towing carriage is mounted on top of the sidewalls.
The rails have to be parallel to each other
The rails have to be parallel to the water surface and thus they mustfollow the Earth’s curvature. They form an arc when viewed from theside.
s = R−√
R2 − L2
4
For instance, for the towing tank at HSVA, having the length L=300m, the rails have a sagitta of s=1.8mm.
Towing tank Models Turbulence generation
Towing tanks
Architettura Navale, A.A. 2020/21
Ï A pair of rails for the towing carriage is mounted on top of the sidewalls.
The rails have to be parallel to each other
The rails have to be parallel to the water surface and thus they mustfollow the Earth’s curvature. They form an arc when viewed from theside.
s = R−√
R2 − L2
4
For instance, for the towing tank at HSVA, having the length L=300m, the rails have a sagitta of s=1.8mm.
Towing tank Models Turbulence generation
Towing tanks
Architettura Navale, A.A. 2020/21
The towing carriage:
Ï is a moving laboratory
Ï carries power supplies and electronics to process data from sensors
Ï have to be free of vibrations that could be transferred to theresistance measurement system.This places great demands on the speed control of the carriagemotors, roundness of wheels, alignment of rails, stiffness of thecarriage structure.
Towing tank Models Turbulence generation
Towing tanks
Architettura Navale, A.A. 2020/21
The towing carriage:
Ï is a moving laboratory
Ï carries power supplies and electronics to process data from sensors
Ï have to be free of vibrations that could be transferred to theresistance measurement system.This places great demands on the speed control of the carriagemotors, roundness of wheels, alignment of rails, stiffness of thecarriage structure.
Towing tank Models Turbulence generation
Towing tanks
Architettura Navale, A.A. 2020/21
The towing carriage:
Ï is a moving laboratory
Ï carries power supplies and electronics to process data from sensors
Ï have to be free of vibrations that could be transferred to theresistance measurement system.This places great demands on the speed control of the carriagemotors, roundness of wheels, alignment of rails, stiffness of thecarriage structure.
Towing tank Models Turbulence generation
Towing tanks
Architettura Navale, A.A. 2020/21
The towing carriage:
Ï is a moving laboratory
Ï carries power supplies and electronics to process data from sensors
Ï have to be free of vibrations that could be transferred to theresistance measurement system.This places great demands on the speed control of the carriagemotors, roundness of wheels, alignment of rails, stiffness of thecarriage structure.
Towing tank Models Turbulence generation
Towing tanks
Architettura Navale, A.A. 2020/21
Remember that:
Ï a towed model generates a wave pattern dynamically similar to thewave system of the full scale vessel, if the tests are carried out at thesame Froude number.
Ï finite length of a basin, of course, limits the usable observation time,especially in case of high speed vessels.
Towing tank Models Turbulence generation
Towing tanks
Architettura Navale, A.A. 2020/21
Remember that:
Ï a towed model generates a wave pattern dynamically similar to thewave system of the full scale vessel, if the tests are carried out at thesame Froude number.
Ï finite length of a basin, of course, limits the usable observation time,especially in case of high speed vessels.
Towing tank Models Turbulence generation
Towing tanks
Architettura Navale, A.A. 2020/21
Remember that:
Ï a towed model generates a wave pattern dynamically similar to thewave system of the full scale vessel, if the tests are carried out at thesame Froude number.
Ï finite length of a basin, of course, limits the usable observation time,especially in case of high speed vessels.
Towing tank Models Turbulence generation
Towing tanks
Architettura Navale, A.A. 2020/21
Towing tank Models Turbulence generation
Ship models
Architettura Navale, A.A. 2020/21
Ï Ship models are scale replicas of the real vessels’ hull shape.
λ= LS
LM= BS
BM= TS
TM
λ2 = SS
SM
λ3 = ∇S
∇M
Ï Ship models are made as long as possible according to therestrictions of towing tank.
Ï The distribution of ballast is not important for resistance tests aslong as displacement and attitude are correct.
Towing tank Models Turbulence generation
Ship models
Architettura Navale, A.A. 2020/21
Ï Ship models are scale replicas of the real vessels’ hull shape.
λ= LS
LM= BS
BM= TS
TM
λ2 = SS
SM
λ3 = ∇S
∇M
Ï Ship models are made as long as possible according to therestrictions of towing tank.
Ï The distribution of ballast is not important for resistance tests aslong as displacement and attitude are correct.
Towing tank Models Turbulence generation
Ship models
Architettura Navale, A.A. 2020/21
Ï Ship models are scale replicas of the real vessels’ hull shape.
λ= LS
LM= BS
BM= TS
TM
λ2 = SS
SM
λ3 = ∇S
∇M
Ï Ship models are made as long as possible according to therestrictions of towing tank.
Ï The distribution of ballast is not important for resistance tests aslong as displacement and attitude are correct.
Towing tank Models Turbulence generation
Ship models
Architettura Navale, A.A. 2020/21
Ï Ship models are scale replicas of the real vessels’ hull shape.
λ= LS
LM= BS
BM= TS
TM
λ2 = SS
SM
λ3 = ∇S
∇M
Ï Ship models are made as long as possible according to therestrictions of towing tank.
Ï The distribution of ballast is not important for resistance tests aslong as displacement and attitude are correct.
Towing tank Models Turbulence generation
Turbulence generation
Architettura Navale, A.A. 2020/21
Overview
Ï At model scale the Reynolds number is in the order of 100 timessmaller than in full scale
Ï At model scale the boundary layer flow can be partly or evencompletely laminar if no turbulence stimulation device is applied.
Ï At full scale the boundary layer is turbulent over the entire hull,except for a couple of centimeters behind the bow where thetransition from laminar to turbulent takes place.(On model this transition would happened, without a properturbulence stimulation, at a position considerably further aft)
Ï Thus, to obtain/guarantee a reliable extrapolation of model scaleresults to full scale, turbulence generators have to be applied (used)on the model.Enforcing a turbulent boundary layer allows to employ the samefrictional (or model-ship correlation) line in the computation of thefrictional resistance of model and ship.
Towing tank Models Turbulence generation
Turbulence generation
Architettura Navale, A.A. 2020/21
OverviewÏ At model scale the Reynolds number is in the order of 100 times
smaller than in full scale
Ï At model scale the boundary layer flow can be partly or evencompletely laminar if no turbulence stimulation device is applied.
Ï At full scale the boundary layer is turbulent over the entire hull,except for a couple of centimeters behind the bow where thetransition from laminar to turbulent takes place.(On model this transition would happened, without a properturbulence stimulation, at a position considerably further aft)
Ï Thus, to obtain/guarantee a reliable extrapolation of model scaleresults to full scale, turbulence generators have to be applied (used)on the model.Enforcing a turbulent boundary layer allows to employ the samefrictional (or model-ship correlation) line in the computation of thefrictional resistance of model and ship.
Towing tank Models Turbulence generation
Turbulence generation
Architettura Navale, A.A. 2020/21
OverviewÏ At model scale the Reynolds number is in the order of 100 times
smaller than in full scale
Ï At model scale the boundary layer flow can be partly or evencompletely laminar if no turbulence stimulation device is applied.
Ï At full scale the boundary layer is turbulent over the entire hull,except for a couple of centimeters behind the bow where thetransition from laminar to turbulent takes place.(On model this transition would happened, without a properturbulence stimulation, at a position considerably further aft)
Ï Thus, to obtain/guarantee a reliable extrapolation of model scaleresults to full scale, turbulence generators have to be applied (used)on the model.Enforcing a turbulent boundary layer allows to employ the samefrictional (or model-ship correlation) line in the computation of thefrictional resistance of model and ship.
Towing tank Models Turbulence generation
Turbulence generation
Architettura Navale, A.A. 2020/21
OverviewÏ At model scale the Reynolds number is in the order of 100 times
smaller than in full scale
Ï At model scale the boundary layer flow can be partly or evencompletely laminar if no turbulence stimulation device is applied.
Ï At full scale the boundary layer is turbulent over the entire hull,except for a couple of centimeters behind the bow where thetransition from laminar to turbulent takes place.(On model this transition would happened, without a properturbulence stimulation, at a position considerably further aft)
Ï Thus, to obtain/guarantee a reliable extrapolation of model scaleresults to full scale, turbulence generators have to be applied (used)on the model.Enforcing a turbulent boundary layer allows to employ the samefrictional (or model-ship correlation) line in the computation of thefrictional resistance of model and ship.
Towing tank Models Turbulence generation
Turbulence generation
Architettura Navale, A.A. 2020/21
OverviewÏ At model scale the Reynolds number is in the order of 100 times
smaller than in full scale
Ï At model scale the boundary layer flow can be partly or evencompletely laminar if no turbulence stimulation device is applied.
Ï At full scale the boundary layer is turbulent over the entire hull,except for a couple of centimeters behind the bow where thetransition from laminar to turbulent takes place.(On model this transition would happened, without a properturbulence stimulation, at a position considerably further aft)
Ï Thus, to obtain/guarantee a reliable extrapolation of model scaleresults to full scale, turbulence generators have to be applied (used)on the model.
Enforcing a turbulent boundary layer allows to employ the samefrictional (or model-ship correlation) line in the computation of thefrictional resistance of model and ship.
Towing tank Models Turbulence generation
Turbulence generation
Architettura Navale, A.A. 2020/21
OverviewÏ At model scale the Reynolds number is in the order of 100 times
smaller than in full scale
Ï At model scale the boundary layer flow can be partly or evencompletely laminar if no turbulence stimulation device is applied.
Ï At full scale the boundary layer is turbulent over the entire hull,except for a couple of centimeters behind the bow where thetransition from laminar to turbulent takes place.(On model this transition would happened, without a properturbulence stimulation, at a position considerably further aft)
Ï Thus, to obtain/guarantee a reliable extrapolation of model scaleresults to full scale, turbulence generators have to be applied (used)on the model.Enforcing a turbulent boundary layer allows to employ the samefrictional (or model-ship correlation) line in the computation of thefrictional resistance of model and ship.
Towing tank Models Turbulence generation
Turbulence generation
Architettura Navale, A.A. 2020/21
Ï The presence of laminar flow con usually be recognized from the shape ofthe resistance curve, CT .
Towing tank Models Turbulence generation
Turbulence generation
Architettura Navale, A.A. 2020/21
Ï The presence of laminar flow con usually be recognized from the shape ofthe resistance curve, CT .
Towing tank Models Turbulence generation
Turbulence generation
Architettura Navale, A.A. 2020/21
Ï The presence of laminar flow con usually be recognized from the shape ofthe resistance curve, CT .
Towing tank Models Turbulence generation
Turbulence generation
Architettura Navale, A.A. 2020/21
The stimulating device:
Ï increases the resistance due to its own parasitic drag
Ï if it is placed too close to the stem, there is a danger of the laminarflow reestablishing itself
Ï if it is placed in the usual position it leaves the laminar flowundisturbed over the first part of the length up to stimulatorIn this case, the resistance of this portion of the surface will less thanthe turbulent resistance desiredIt is usual to assume that this defect in the resistance balances theadditional parasitic drag
Towing tank Models Turbulence generation
Turbulence generation
Architettura Navale, A.A. 2020/21
The stimulating device:
Ï increases the resistance due to its own parasitic drag
Ï if it is placed too close to the stem, there is a danger of the laminarflow reestablishing itself
Ï if it is placed in the usual position it leaves the laminar flowundisturbed over the first part of the length up to stimulatorIn this case, the resistance of this portion of the surface will less thanthe turbulent resistance desiredIt is usual to assume that this defect in the resistance balances theadditional parasitic drag
Towing tank Models Turbulence generation
Turbulence generation
Architettura Navale, A.A. 2020/21
The stimulating device:
Ï increases the resistance due to its own parasitic drag
Ï if it is placed too close to the stem, there is a danger of the laminarflow reestablishing itself
Ï if it is placed in the usual position it leaves the laminar flowundisturbed over the first part of the length up to stimulatorIn this case, the resistance of this portion of the surface will less thanthe turbulent resistance desiredIt is usual to assume that this defect in the resistance balances theadditional parasitic drag
Towing tank Models Turbulence generation
Turbulence generation
Architettura Navale, A.A. 2020/21
The stimulating device:
Ï increases the resistance due to its own parasitic drag
Ï if it is placed too close to the stem, there is a danger of the laminarflow reestablishing itself
Ï if it is placed in the usual position it leaves the laminar flowundisturbed over the first part of the length up to stimulator
In this case, the resistance of this portion of the surface will less thanthe turbulent resistance desiredIt is usual to assume that this defect in the resistance balances theadditional parasitic drag
Towing tank Models Turbulence generation
Turbulence generation
Architettura Navale, A.A. 2020/21
The stimulating device:
Ï increases the resistance due to its own parasitic drag
Ï if it is placed too close to the stem, there is a danger of the laminarflow reestablishing itself
Ï if it is placed in the usual position it leaves the laminar flowundisturbed over the first part of the length up to stimulatorIn this case, the resistance of this portion of the surface will less thanthe turbulent resistance desired
It is usual to assume that this defect in the resistance balances theadditional parasitic drag
Towing tank Models Turbulence generation
Turbulence generation
Architettura Navale, A.A. 2020/21
The stimulating device:
Ï increases the resistance due to its own parasitic drag
Ï if it is placed too close to the stem, there is a danger of the laminarflow reestablishing itself
Ï if it is placed in the usual position it leaves the laminar flowundisturbed over the first part of the length up to stimulatorIn this case, the resistance of this portion of the surface will less thanthe turbulent resistance desiredIt is usual to assume that this defect in the resistance balances theadditional parasitic drag
Towing tank Models Turbulence generation
Studs
Architettura Navale, A.A. 2020/21
Towing tank Models Turbulence generation
Studs
Architettura Navale, A.A. 2020/21
Towing tank Models Turbulence generation
Trip wire, Hama strip, Sand strip
Architettura Navale, A.A. 2020/21
Towing tank Models Turbulence generation
Turbulence generation
Architettura Navale, A.A. 2020/21
