MAGNETOHYDRODYNAMICS Vol. 56 (2020), No. 1, pp. 51–65
DOI: 10.22364/mhd.56.1.5

DESIGN OF MARINE VEHICLE POWEREDBY MAGNETOHYDRODYNAMIC THRUSTER
Cherng-Shyong Chan 1,2 , Jia-Hong Cheng 2 , Cing-Hui Zeng 3 ,Jen-Rung Huang 4 , Yu-Hsuan Chen 2 , Yen-Ju Chen 3 ,Thi Trang Pham 5 , Wei-Hsiang Chao 6 , Jen-Tzong Jeng 5 ,Tsung-Long Liu 2,4 , Kuan-Cheng Pan 2,4 ,Yan-Hom Li 2,3 , Ching-Yao Chen 2
1

Department of Mechanical Engineering, National Yunlin Universityof Science and Technology, Taiwan, R.O.C.
2
Department of Mechanical Engineering, National Chiao Tung University, Taiwan, R.O.C.
3
Department of Mechanical and Aerospace Engineering, Chung Cheng Instituteof Technology, National Defense University, Taiwan R.O.C.
4
Department of Power Vehicle and Systems Engineering, Chung Cheng Instituteof Technology, National Defense University, Taiwan R.O.C.
5
Department of Mechanical Engineering, National Kaohsiung Universityof Science and Technology, Taiwan, R.O.C.
6
Materials and Electro-Optics Research Division, National Chung-Shan Instituteof Science and Technology, Taiwan R.O.C.
e-Mail: pankc@url.com.tw, yanhom@ndu.edu.tw, chingyao@mail.nctu.edu.tw
The present study outlines the design of a magnetohydrodynamic (MHD) thruster system whichis capable to power a 3-meter ship model cruising at a speed of V = 0.5 m/s using the Lorentz
force generated by the electric field and magnetic field in conducting seawater. Based on thecomputational fluid dynamics (CFD) simulation of a modified Delft 372 catamaran model, thethrust needed to achieve the targeted cruising speed is first estimated. To achieve the estimated magnitude of the thrust, dimensions of thruster modules are designed based on numericalsimulations of magnetic field, for better distributions of the strength and uniformity of the magnetic field. Additional CFD simulations of the flows through the thruster module, coupled withmagnetic and electric fields, are conducted to realize the hydrodynamics. Consequently, several
configurations of thruster modules are manufactured and experimented. A particular configuration of a shielded two-unit module is chosen to power the ship model. Finally, a complete
system of MHD-1 marine vehicle, including a ship model, multiple MHD thruster modules andpower suppliers, is assembled and tested. The system is shown capable to cruise closely to thetargeted speed.

Introduction. Magnetohydrodynamics (MHD) is a unique branch of fluid dynamics concerned with the dynamics and behavior of conducting fluids affected by magnetic
and electric fields. The typical conducting magnetofluids include plasma, liquid metals,
salt water and electrolytes. By using the Lorentz force generated by the perpendicularly imposed magnetic field and electric current, the applications of MHD have beenof interest to engineers since its initiation in the 1940’s [1], e.g., propulsion systems [2–12], pumps [13, 15–17], motor [18], heat transfer devices [19], metal processes [20] andgenerators [21]. Among them, MHD propulsion applied to marine vehicles has been along and active field, since first proposed in [2] in the 1960’s because of the conductive
property of seawater to achieve a propellerless power system. In the following developments, superconductors were applied to generate MHD propulsion [3, 4] as an extremely
strong magnetic field is required to achieve a better electrical efficiency, e.g., about 40%
efficiency at 5 Tesla [6]. However, the heavy weight as well as the complexity of the su51

Cherng-Shyong Chan, et al.
perconductor prevented the practical uses of MHD propulsion. Nevertheless, the studyof MHD propulsion was continued for several decades. In 1988, the capability of MHD
propulsion in a ship was successfully demonstrated [5], and large-scale vehicles were able
to be powered by MHD thrusters, for instance, the MHD-propelled Yamato 1 [9] andHEMS-1 [10] built in the 1990’s. It has been widely reported that the progresses indeveloping MHD-propelled submarines are ongoing in recent years, e.g., news reported
in [22]. Taking the advantages of the advancement of key technologies of magnetism anddesign tools, such as permanent magnets of neodymium iron boron, lithium batteries
and powerful numerical software, we intend to develop a small scale marine unmanned
surface vehicle (USV) using permanent magnets. In addition, the designed marine MHD
USV possesses the potential ability of thrust vector control (TVC) by installing multiple
thruster units. The MHD USV is expected to perform special tasks, of which stealthand maneuverability are crucial, even the electric efficiency might be extremely low. The
details of the design procedures and tested results are reported in the present paper.
At the first stage of design, the major concern of the marine MHD USV is mainly
the net propulsion, which involves the MHD thrust and hydrodynamic drag, so that
understanding of the magnetic, electric and flow fields is crucial. The governing equationsof hydrodynamics with the incorporated Lorentz force in an incompressible Newtonian
fluid are expressed as the augmented Navier–Stokes equations [18]∇·u∂u
+ (u · ∇)u
ρ
∂t


=

0,

(1)

=

−∇p + µ∇2 u + FL .

(2)

Here, t, u, p, µ and ρ denote, respectively, the time, velocity vector, pressure, viscosityand density of the conducting fluid. FL represents the force density of the Lorentz force
and takes the form of
FL = (J × B),(3)

where J and B are the current density and the magnetic field, respectively and arederived by the Maxwell equation and Ohm’s law given as
∇·B

=

J =

0,

(4)

σ[−∇ψ + (u × B)].

(5)

Here σ and ψ are the electric conductivity and the electric potential, respectively. For asufficiently conducting medium, the electric charge is conserved, i.e. ∇ · J = 0, so thatthe electric potential equation is governed by∇2 ψ = ∇ · (u × B).

(6)

These equations will be solved numerically to provide guidelines for better design.
1. Results and discussion.
1.1. Design of the ship model.
The present study aims to power a scaled-down
ship model by the MHD thrusters with a cruising speed of V = 0.5 m/s. The dimensionsof the ship model, named MHD-1 modified from the Delft 372 catamaran model [23], isshown in Fig. 1. It has been well concluded that the resistance on the surface ship is
induced both by the viscous skin friction and by the gravitational surface waves. To estimate the needed thrust, i.e. the total induced drag of the sailing ship model, a numerical52

Design of marine vehicle powered by magnetohydrodynamic thruster
0.80 m0.30 m0.50 m0.33 m3.20 mFig. 1. Geometry and dimension of the modified Delft 372 catamaran model designed in thepresent study.

(e)
(a)

35

(b)

(c)

Drag Force, [N]

28

21

14

7

(d)
0

10

20

30

40

50

60

70

Time, [s]Fig. 2.

Flow field (a),(c) and wave height (b),(d) at t = 1 and 6 s; (e) temporal evolutionof the total drag obtained by numerical simulation of the ship model with a cruising speed of
V = 0.5 m/s.

simulation was carried out to solve the full 3D unsteady Reynolds–Averaged–Navier–Stokes (RANS) equations. The computational domain (30 m × 6 m × 2.5 m) includes theseawater (or the air) beneath (or above) the surface. The viscosity and density of theseawater and air are taken as µwater = 9.7 × 10−4 kg/m·s, ρwater = 1.023 × 103 kg/m3 andµair = 1.789 × 10−5 kg/m ·s, ρair = 1.225 kg/m3 , respectively. The turbulent effects aredealt with the k-ǫ model. The ship model is designed to have a draught of 0.33 m beneath the seawater surface with a displacement of 525 kg and encounter a free stream
velocity of V = 0.5 m/s. The Volume of Fluid (VOF) method is applied to capture thewaving surface of seawater. The set of equations is numerically solved by ANSYS Fluent [24], and the results are shown in Fig. 2.
Figs. 2a,c and b,d show the velocity distribution in the middle cross-section fromthe side and the wave height on the surface from top, respectively, at t = 1 s and 6 s.
When the ship model just starts to move from rest at t = 1 s, strong induced wakes
associated with the significant heights of the wave at the bow and stern of the ship areclearly observed. The presence of the strong wake and high wave results in significant
resistance, as shown at very early time in Fig. 2e. As time proceeds, the wake and thewave on the surface continuously get weaker, e.g., t = 6 s shown in Figs. 2c,d. This strong53Cherng-Shyong Chan, et al.
z
y

x

(a)

(b)

(c)

(d)

B

l
Unit: mmFig. 3.

(Left) Geometry and dimension of a single MHD thruster unit. Four configurationsof thruster modules are considered: (a) single-unit module, (b) shielded single-unit module, (c)two-unit module, and (d) shielded two-unit module.

transit phenomenon leads to a significant fluctuation of the total resistance till t ≈ 40 s,
as also shown in Fig. 2e, and eventually evolves to a nearly constant value about 7 N
after t > 40. This nearly steady resistance of 7 N serves as a reference value to design
the MHD thrusters, whose total thrust should be capable to overcome the resistance andto power the ship model for steady cruise.
1.2. Design of MHD thruster module.
The thrust by the Lorentz force (TL )depends on the external magnetic field, so that the strength and distribution of the magnetic field are important for a better design of the thruster module. After considering
the weight of the iron shell and available magnets, the dimension of a single thruster
unit is proposed and shown in Fig. 3. A pair of permanent magnets of neodymium ironboron (NdFeB, N40) are placed at the bottom and top of the soft-iron shell. Note thatdifferent thicknesses of the shell have been tested, and the thicker shell always results inhigher magnetic strength inside the thruster, as expected. Nevertheless, considering theweight constraint, a 2-mm iron shell was chosen to optimize the field-to-weight ratio of
the MHD thruster. Four configurations of the thruster modules were considered, as also
shown in Fig. 3, such as (a) a single-unit module, (b) a single-unit module with additionalshielding by a NiFe alloy, (c) a two-unit module, and (d) a two-unit module with additional shielding. Detailed distributions of magnetic fields for these four configurations
are simulated by ANASYS Maxwell, and the results are illustrated in Figs. 4, 5 and 6.
Fig. 4a shows the magnetic lines and strength distribution of the plain single-unit
module by a 2D simulation. The non-uniformity of the magnetic field can be clearly observed, in which a weaker strength locates at the central region (z = 0), in particular, atthe edges (|x| > 25 mm). The full 3D simulation shown in Figs. 4b,c also confirms the observation. The field distribution in the cross-section at the central region, e.g., y = 0 mm,
as shown in Fig. 4b, is between B = 0.1 ∼ 0.27 T, with an average of Bavg = 0.194 T. The
field strength and uniformity deteriorate at the outer position of the thruster module(|y| > 0). Shown in Fig. 4c, the field strength is at the cross-section of y = ±25 mm,
where are the positions of 1/4 and 3/4 length of the thruster unit (total 100 mm, as
shown in Fig. 3). The variation of the field strength is enhanced with a weaker average
54Design of marine vehicle powered by magnetohydrodynamic thruster
B, 1.00
[T]

(a)

0.95
0.90
0.85
0.80
0.75
0.70
0.65
0.60
0.55
0.50
0.45
0.40
0.35
0.30
0.25
0.20
0.95
0.10
0.05

(b) y = 0 mm, Bavg = 0.194 T(c) y = 25 mm, Bavg = 0.181 T
B, [T])
0.35-0.40
0.35

0.35
0.30-0.35
0.25

0.25-0.30

0.25

0.15

0.20-0.25

0.15

0.15-0.20
0.05

0.05
40

0.10-0.15

40

20

20

z,

m]

-20
-40

-40

20
0.00-0.05

x , [m

-20

0

m]

-20

]
m

0

z,

-20

0

x , [m

[m

20

40

m

0

[m

]

0.05-0.10
40-40 -40

Fig. 4.

(a) Magnetic lines and strength distribution of a plain single-unit module obtained by
2D simulation. The flux lines are not shown in the iron shell, where magnetization saturation
occurs. The strength distribution was obtained by 3D simulation at the cross-section at (b)y = 0 mm and (c) y = ±25 mm.

of Bavg = 0.181 T. Also observed in Fig. 4a is the significant leakage of the magnetic flux
outside the shell because of the magnetization saturation in the iron shells. These results
lead to two major drawbacks: (1) the dramatic decrease of the magnetic strength awayfrom the magnets, and (2) the significant leakage of the magnetic flux.
Based on the results shown in Fig. 4, a shielded two-unit module is considered, i.e.
the configuration shown in Fig. 3d. By connecting the two units in series, the region witha dramatic drop of the strength at the edges may be minimized. In addition, the magnetic
leakage could also be improved with outer NiFe alloy shielding. The simulation resultsof the shielded two-unit module are displayed in Fig. 5. The average field strengths in
the cross-sections at the center (y = 0 mm) and at 1/4 (or 3/4) length (y = ±50 mm) are
increased to Bavg = 0.21 T and 0.205 T, respectively, which are improved significantly.
The sample modules of these four configurations were manufactured, and their corresponding field strengths along the central axis (x = 0 and z = 0) were measured by aGauss meter, as shown in Fig. 6. In general, the measured strengths are in good agreement with the simulations. As suggested by the simulations, the strength is stronger with55

Cherng-Shyong Chan, et al.
B, [T]
1.00
0.95
0.90
0.85
0.80
0.75
0.70
0.65
0.60
0.55
0.50
0.45
0.40
0.35
0.30
0.25
0.20
0.95
0.10
0.05

(a)

(b) y = 0 mm, Bavg = 0.21 T(c) y = 50 mm, Bavg = 0.205 T
B, [T]
0.35-0.40
0.35

0.30-0.35

0.35

0.25

0.25-0.30

0.25

0.15

0.20-0.25

0.15

0.15-0.20
0.05

0.05
0.10-0.15

40

20

20

-20

z,

m]

-40 -400.00-0.05]
020

x , [m 0
m]

-20
-20

[m

-20

0

x , [m

[m

20

40

m

0

z,

]

0.05-0.10
40

m

40

-40 -40

Fig. 5. (a) Magnetic lines and strength distribution of a shielded two-unit module obtained by
2D simulation. The flux lines are not shown in the iron shell, where magnetization saturation
occurs. The strength distribution was obtained by 3D simulation at the cross-section at (b)y = 0 mm and (c) y = ±50 mm.
shielding. In addition, the two-unit modules can elongate the region of nearly uniform
strength, so that the weaker edging effect decreases. As a result, the shielded two-unit
module is expected to better power the ship model.
Simulations of the current density J were also carried out to verify the better performance of the two-unit module. The design of the thruster unit is shown in Fig. 7a. To
ensure a good electrical insulation, the surfaces of the NdFeB magnets and iron shell were
all coated with varnish. The electrodes, which are arranged at the lateral sides of theseawater channel, were also electrically insulated with varnish at the input and output
ends. The spaces between the electrodes and the lateral sides of the iron shell were filledwith polyvinyl chloride (PVC) foam to further improve the electrical insulation. The
electrodes are made from flat aluminum sheets with the input-and-output current leads
extended outside the seawater channel. We have found that at the current as high as
120 A, only a negligible amount of the aluminum anode is dissolved at the electrolysis ofsalt water within an hour.
The difference in electric potential applied to these two electrodes is ψ E = 64 V inthe simulations concerned with the electrolytic conductivity of seawater σ = 5 S/m. For
56

Design of marine vehicle powered by magnetohydrodynamic thruster
Bz , [T]





VKLHOGHGïXQLWPRGXOH
ïXQLWPRGXOHVKLHOGHGVLQJOHïXQLWPRGXOHVLQJOHïXQLWPRGXOHïXQLWPRGXOH VLP
VKLHOGHGïXQLWPRGXOH VLP


ï

ï

ï

ï

ï













y, [cm]Fig. 6.

Measured field strength along the y-axis at the central cross-section (x = 0 and z = 0).
Simulated results are also shown by solid lines.

(a)

(b)

z
y
x

NdFeB magnet
Iron shell

Iron shell
NdFeB magnet

PVC foamFig. 7. Designs of (a) a single-unit MHD thruster with a pair of aluminum electrodes installed
perpendicularly to the magnets, and (b) a completed two-unit thruster module. The aluminum
plates fully cover the inner sides of the iron shell. The arrows show the input/output of theelectric current I.

an ideal situation, the magnitude of the electric potential would be half the differenceof the applied potential in the central section, i.e. ψ = 32 V at x = 0. Nevertheless, themagnitudes of the electric potential across the central section for the single-unit and twounit modules, respectively shown in Figs. 8a,b, are generally less than 32 V. The electric
potential at the middle region of the two-unit module is closer to the ideal magnitude,
whereas the electric potential of the whole single-unit module is significantly smaller.
The corresponding distributions of the current density are illustrated in Figs. 8c,d, respectively. Note that only the region inside the thruster is shown. Consistent with the57

Cherng-Shyong Chan, et al.
Jx , [A/m2 ]
[V]

(a)

(c)

y
z✛

[V]

✻

(b)

(d)

y
z ✛

✻

Fig. 8. Simulations of MHD thruster modules at the central cross-section (x = 0) for ψ E =64 V: (a) electric potential for the single-unit module; (b) electric potential for the two-unit
module; (c) current density inside the single-unit module; (d) current density inside the twounit module. The two rectangular blocks in (a) and (b) are the side views of permanent magnets.
Note, (c) and (d) share the same colorscale.

distributions of the electric potential, the current density is apparently much stronger inthe middle of the two-unit module. Since the Lorentz force is directly proportional tothe current density, these results contribute to the better design of the two-unit module.
Based on the results obtained in the simulations of magnetic field and electric current
density, the two-unit module has been chosen as the complete design shown in Fig. 7b.
To overcome the strong repulsive force between the magnet modules, the NdFeB magnets
were fastened to the iron shell by fiber-reinforced plastic (FRP) plates and bolts. Then,the two units were bolted together to form a two-unit module, of which the front andback ends of the thruster were covered with the FRP plates to fix the position of themagnets. The input/output current leads were bent to the end surfaces of the thruster.
1.3. Flow simulation of MHD thruster module. Numerical simulations of the flow
field incorporated using the Lorentz force through the thruster module were also carriedout by ANSYS Fluent to determine the performance of the thruster module of different
configurations. Geometries and dimensions similar to the thruster module shown in Fig. 3
and Fig. 7 were used. Furthermore, based on the measured field strength obtained inFig. 6, a uniformed field strength of Bz = 0.2 T was assumed. By simplification, not only
the Ohm’s law was coupled with the Navier–Stokes equations but the Maxwell equation,
too. The potential difference applied to the electrodes was ψ E = 64 V, and it yielded
the average current strength I ≈ 25.9 A and 57.7 A within the thruster chamber for the
single-unit and the two-unit module, respectively. Fig. 9a shows the flow induced by
the Lorentz force to a stationary single-unit thruster, i.e. with no cruising speed V = 0.
58

Design of marine vehicle powered by magnetohydrodynamic thruster
(a)

(c)

(e)

(b)

(d)

(f )

Fig. 9.

Flow simulations of MHD thruster modules at the central cross-section (x = 0): (a)single-unit with V = 0 m/s and Bz = 0.2 T and ψ E = 64 V; (b) two-unit module with V = 0 m/s,
Bz = 0.2 T and ψ E = 64 V; (c) single-unit module with V = 0.5 m/s, Bz = 0 T; (d) two-unit module with V = 0.5 m/s and Bz = 0 T; (e) single-unit module with V = 0.5 m/s, Bz = 0.2 T andψ E = 64 V; (f) two-unit module with V = 0.5 m/s, Bz = 0.2 T and ψ E = 64 V. The two rectangular blocks are the side views of the permanent magnets.

Driven by the Lorentz force, the apparent flow is generated inside the thruster chamber,where the maximum flow speed is about 3.5 m/s. Note that the negative sign shown inthe colorbar of the figure indicates the fluid flow from left to right. A mass flow rateof Q = 2.4 kg/s is pumped to pass through the thruster in the present condition. The
induced flow is significantly enhanced for the two-unit module, as shown in Fig. 9b, where
the maximum speed is increased to about 5 m/s. As a result, the mass flux is further
raised to Q = 3.4 kg/s for the two-unit module. These results indicate that the present
design is capable to pump a significant amount of seawater through the chamber of thethruster.
The flow field associated with the thruster module cruising at V = 0.5 m/s withoutor with the presence of the magnetic field, i.e. Bz = 0/0.2 T, is illustrated in Figs. 9c–f .
While the mass flow rates of the single-unit and two-unit modules remain nearly unchanged at Q = 4.6 kg/s for Bz = 0, the mass flow rate is increased significantly fromQ = 5.1 kg/s for the single-unit to Q = 6.0 kg/s for the two-unit module in the presence of the magnetic field Bz = 0.2 T. Note the increments of the mass flow rate compared with the corresponding module without the magnetic field, i.e. ∆Q = Q(Bz =0.2 T) − Q(Bz = 0 T) are ∆Q = 0.5 and 1.4 kg/s for the single-unit and for the twounit module, respectively. The more significant increment ∆Q for the two-unit module
confirms its better performance.
1.4. Experiments with MHD thruster module.
After a detailed theoretical analysis and experimental measurements, the MHD thruster modules were assembled andtested. The design of the shielded two-unit module was followed as a sample unit of
the MHD thruster in Fig. 10a. First, to verify the better performance of the two-unit
module compared to the single-unit configuration suggested by the theoretical result,experiments in a water tank were conducted. For a fair assessment, the two-unit module
was directly compared with two single-unit modules. These modules are powered by a
Lithium-Polymer (LiPo) battery. The actual applied current was measured at I = 49.6 A.
The thruster modules, fully submerged in the seawater, were hung on a sliding tract with59

Cherng-Shyong Chan, et al.
(a)

t = 0 [s](b)t = 3.48 [s]t = 0 [s](c)t = 3.48 [s]Fig. 10.
(a) A sample manufactured MHD thruster unit. Experimental tests of the MHD
thruster hanged on a sliding track: (b) a two-unit module, and (c) two single-unit modules.

2.52QHïXQLW0RGXOH

27ZRïXQLW0RGXOH

TL = 0.012I

TL , [N]

1.5

1

0.5

0

20

40

60

80

100

120

140

160

180

200

I, [A]

Fig. 11.

Thrust (TL ) vs. current (I).

a negligible friction. The Lorentz force drives the thruster module moving forward oncethe electric current is applied. Two sensors were installed at sides of the tank to sample
the average speed of the modules. Figs. 10b,c illustrate the tests of the two configurations.
The photos were taken at the times when the modules reached the first sensor (t = 0 s)
near the left side of the tank, and when the modules reached the second sensor at theright side. For both cases, apparent jet flows were generated to drive the module to movetoward the right direction. The slightly faster arrival of the two-unit module supports
60

Design of marine vehicle powered by magnetohydrodynamic thruster
the better performance suggested by the theoretical analysis. Nevertheless, the speed
was just about V ≈ 0.1 m/s, which is much less than the expected cruising speed. This ismainly because of the limitation of the testing length, so that there was no sufficient timeallowed for the module to fully accelerate. The other factor is the much lower current
provided. In the ship model tests, the planned current will be as high as to I = 120 A.
Because of the insufficient time allowed for the tests, the MHD thrust, excluding
the induced drag of a moving thruster module, was measured by a pull dynamometer.
Experiments under different electric current strengths were performed, and the results
are shown in Fig. 11. We would like to point out that the condition with the extremely
high current I = 190.2 A was achieved by adding salt to increase the conductivity. A
nearly linear correlation is followed, such that
TL ≈ 0.012I.

(7)

The nearly linear TL -I relation is consistent with the theoretical expression of theLorentz force for a fix area. For the particular case of I = 118.6 A and TL = 1.69 N, which
is close to the planned operating condition for the cruising speed V = 0.5 m/s, the applied
electric potential in salty water with 35.7 ppt of salinity was measured at ψ E = 46.4 V.
The electric efficiency η E of the MHD thruster module was obtained byη E = TL V /Iψ E ≈ 0.000154.
The extremelysmall efficiency is consistent with the prediction in [6].
1.5. Test of ship model.
Based on the designs presented above, an MHD-1 shipmodel was manufactured and multiple MHD thrusters were installed, as shown in Fig. 12.
To successfully power the MHD-1 ship model with the cruising speed V = 0.5 m/s, whose

(a)

(b)

Fig. 12. (a) The modified Delft 372 catamaran model MHD-1, and (b) with 5 MHD thruster
modules installed beneath.
61Cherng-Shyong Chan, et al.

(a)

(b)

(c)

Fig. 13. The cruising MHD-1 ship model powered by MHDthrusters at t = t0 (a), t ≈ t0 + 6 s(b) and t ≈ t0 + 9 s (c).
drag is about 7 N according to the CFD estimation, at least five shielded two-unit modules
were required provided the operating electric current I ≈ 120 A, based on the previous
testing results. To verify the capability of the MHD thrusters, we employed 4 to 6 twounit modules under different operating conditions with different strengths of the electric
current, depending on the capacity of the power sources. Generally, the range of thecruising speed was measured at between V = 0.25 ∼ 0.5 m/s. A representative test isillustrated in Fig. 13, where six MHD modules (red objects beneath the ship model)
are working at I ≈ 110 A. The four modules in the front and middle are powered bybatteries, whereas the electricity for the rear two is supplied by a diesel generator. The
total water displacement is about 450 kg. Strong jet flows are observed in Fig. 13 toprovide the propulsive thrust. The cruising speed is closed to the targeted V ≈ 0.5 m/s,
which contributes to the capability of the present design. Further improvements are in
progress, including the weight reduction and streamlined thrusters. The weight reduction
will be achieved by replacing the heavy generator by more efficient batteries. 3D-printed
cowlings will also be attached to the front sides of the thruster modules to decrease theinduced drag.
2. Concluding remarks. The present study applies MHD propulsion to design apropellerless marine vehicle driven by the Lorentz force generated by the coupling effect ofthe magnetic and electric fields in conducting seawater. The flow field of a cruising Delft
62

Design of marine vehicle powered by magnetohydrodynamic thruster
372 catamaran model is first simulated to obtain the necessary thrust. To acquire thebetter configuration of the MHD thruster module, numerical simulations of the magnetic
field and current density were also carried out for stronger force and more uniform distribution. In addition, simulations of the flow passing through the thruster chamber werealso performed to support the appropriateness of the designated configuration of MHD
thrust modules. Based on the theoretical analysis and experimental measurements, thedesignated thruster modules were manufactured and tested. The sample MHD thruster
module was verified to effectively move forward due to the Lorentz force. The grossthrust (TL ) generated by the present design of the MHD thruster module is nearly proportional to the electric current (I), such that TL ≈ 0.012I. The results suggest the shipmodel can be effectively propel to motion by installing a sufficient number of thruster
modules. At last, the MHD-1 ship model installed with multiple MHD thruster modules
has been manufactured and tested. The testing results confirm that the goal can beclosely achieved by the present design.
To conclude the study, we would like to point out that the presented manuscript
merely shows the feasibility of the MHD vehicle by applying currently available permanent magnets and batteries. Much more optimization can be made for better propulsive
efficiency, such as a better magnet arrangement to enhance the thrust. In addition, thehydrodynamic drag can be decreased by the lighter weight, streamlined thruster module
or by the integration of the thruster module with the ship, etc. These works are in
progresses to improve the performance of the MHD propulsion.
Acknowledgements. Support by the National Chung-Shan Institute of Scienceand Technology, Taiwan R.O.C. (grant no. XV08095P498PE-CS) is gratefully acknowledged.
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