Abstract:
A ship has an electromagnetic thrust generator including a cylindrical magnet in which there is arranged a helical duct for conducting sea water. The magnet includes a coil housing in which a superconducting coil is disposed. The duct includes an outer wall disposed opposite the internal surface of the coil housing. Electrode members are mounted on inner and outer walls of the duct to create an electrical field across the duct.

Description:
TECHNICAL FIELD 
     The present invention relates to a thrust generator which is suitable for a superconducting Electro Magnetic Thruster (hereinafter referred as EMT) of ship propulsion devices, a Dynamic Positioning Systems for ocean platforms and an Electro-Magnetic pumps acting upon an electrically conductive fluid, for example, sea water and a MHD generator and pumps and generators of pumping-up power systems. 
     BACKGROUND OF THE INVENTION 
     It is known to use dipole, quadralpol, saddle and racetrack type superconducting magnets for EMTs. The conventional EMTs may however be too big and too heavy to gain enough thrust for full-scale ships because of a low magnetic field of such magnets and it being difficult to construct the magnets. The magnetic field must be so strong, e.g., 10 to 20 Teslas, to obtain enough propulsive efficiency for EMT ships. The EMT having such a strong magnetic field may be a huge one while an on-board EMT propulsion device is limited in size and weight because of restricted hull space. Now, EMT propulsion units are unsatisfactory with respect to size, weight, thrust force and high magnetic field. In view of this, there is an important technological desire to develop EMTs for practical use. 
     DISCLOSURE OF INVENTION 
     The present invention is intended to provide light weight and compact thrust generators having high thrust and high magnetic field superconducting magnets. According to the present invention, the superconducting EMT generator comprises a super conducting solenoid magnet and a helical thrust duct with a pair of electrodes inserted in the hollow interior of the superconducting solenoid magnet. The inlet and the outlet of the spiral duct are spaced axially apart with respect to the longitudinal center axis of the solenoid magnet. In the case of sea water as a conductive fluid flowing in the thrust duct, an anode or a positive electrode is arranged continuously on the inner side wall of the duct, and a cathode or a negative electrode is disposed on the outer side wall of the duct because of a decreasing effective electrochemical reaction area of electrode by producing hydrogen bubbles at the cathode. 
     It is possible to generate the maximum thrust in case of a ratio of 3.5 of outer radius to inner radius of the duct. 
     The thrust duct with rectangular cross section is suitable for avoiding waste of the thrust volume. 
     A pair of superconducting solenoid magnets can be arranged in a row. Also, magnets arranged in parallel can form a closed loop magnetic flux line, resulting in the magnetic flux density generated by a pair of superconducting magnets being so much stronger than a single superconducting magnet. 
     The higher magnetic flux density generates a higher thrust and a higher propulsive efficiency. 
     It is possible that the magnetic field can be perfectly shielded by mounting superconducting material films or coils at the end of EMT units. 
    
    
     BRIEF DESCRIPTION OF DRAWINGS 
     FIG. 1 shows a simplified cut-away perspective view of a device adopting the present invention. 
     FIG. 2 shows an enlarged detailed longitudinal section taken through a portion of FIG. 1. 
     FIG. 3 shows a general layout illustration of the EMT, shown in FIG. 1, for use as a ship propulsion system. 
     FIG. 4 shows a front view of FIG. 3. 
     FIG. 5 shows a cross section of a foil as shown in FIG. 4. 
     FIG. 6 shows a vector schematic of the Lorentz&#39;s forces acting on the foil of FIG. 4. 
     FIG. 7 shows a general layout illustration of EMTs mounted in the hull of a ship. 
     FIG. 8 shows a front view of FIG. 7. 
     FIG. 9 shows a plan view of the arrangement of EMTs which provides a closed flux path. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Preferred embodiments of the present invention will now be described hereinafter referring to the accompanying drawings. The thrust generator of the present invention provides a superconducting solenoid magnet 1 and a spiral thrust duct 2. The duct 2 includes inner and outer walls 2a, 2b, interconnected by intermediate walls 2c. The superconducting magnet 1 includes a housing 1A containing coils 3 of wound superconducting wires insulated in a highly efficient thermal container of cryostat. The superconducting solenoid magnet generates a strong magnetic field in the hollow interior 4 of the magnet defined by a circular cylindrical inner surface of the housing (the direction of magnetic field being shown by arrow B). The superconducting solenoid magnet 3 is operating in the persistent current mode. The winding concept of superconducting solenoid magnet 3 may be a pancake type or a layered type. 
     The thrust duct 2 is hollow, has a rectangular cross section, and forms a helix. The helical portion of the thrust duct 2 is inserted in the hollow interior of the superconducting solenoid magnet 1. Both an inlet 5 and an outlet 6 of the duct 2, each having an opening 7, 8, extend longitudinally with respect to the longitudinal center axis 1a of the superconducting solenoid magnet 1. There is however no restriction concerning the cross sectional form of the thrust duct 2 in the present invention. 
     Electrodes 9a, 9b are fixed at respective side walls of the thrust duct 2. In the illustration of FIG. 1, an anode 9a is arranged on the inner side wall of the thrust duct 2, and a cathode 9b is arranged on the outer side wall of the thrust duct 2 because of a decreasing effective electrochemical reaction area of the cathode 9b caused by hydrogen bubble production during operation. The present invention is not restricted with respect to the arrangements of electrodes. 
     In FIG. 1, the reaction between the magnetic field B generated by the fixed superconducting magnet 1 in the ship and the electric current J passing through the sea water from anode 9a to cathode 9b generates a Lorentz&#39;s force f (each direction is shown by an arrow). Sea water acting as a conductive fluid 10 flows into the helical portion 2 of the thrust duct 2 from the opening 7 of the inlet 5 of the thrust duct 2. In the helical portion 2 of the thrust duct 2, the sea water 10 is pressed by Lorentz&#39;s force f. The thrust of the ship is obtained by jetting sea water from the opening 8 of the outlet 6. 
     Moreover, the maximum thrust is obtained when the ratio between the outer radius ro and the inner radius ri of the thrust duct is, ro≅3.5 ri. 
     Now, upon introducing the electrode electric current Jso, and the electrode voltage Vso, the input electric power Peo is calculated by the following equations, 
     
         J.sub.30 =j.sub.c (2πr.sub.c ·b)n=j.sub.c (2πr.sub.c)1 
    
     
         V.sub.30 =[(r.sub.c ·j.sub.c)/σ]·1n(r.sub.e /r.sub.c)                                                 (1) 
    
     
         P.sub.60 =[j.sub.c.sup.2 ·(r.sub.c ·j.sub.c)/σ]·1n(r.sub.e /r.sub.i) 
    
     where; 
     jc:Electric current density at the reference radius rc (A/m 2 ) 
     rc:Reference radius (m 2 )=(ro+ri)/2 
     b:Cell length of the thrust duct 2 (m) 
     n:Number of cells of the thrust duct 2 
     l:Overall length of the thrust duct 2 (m) 
     s:Sea water electric conductivity (S/m) 
     The Lorentz&#39;s force F LO  is calculated by, ##EQU1## 
     Substituting Equation (1) into Equation (2), ##EQU2## 
     Squaring equation, ##EQU3## 
     As a result, ##EQU4## where A is defined as follows. 
     
         A=P.sub.e σB.sup.2 π1/2 
    
     The maximum Lorentz&#39; force is obtained when it is satisfied by the following relation. 
     
         δ (F.sub.LO).sup.2 /δ ri=o 
    
     The numerical solutions are shown in TABLE 1 which demonstrates that the maximum Lorentz&#39;s force attained when the thrust duct dimension is satisfied by the relation, ro≅3.5 ri. 
     
                       TABLE 1______________________________________ro (m)   ri (m)         ro/ri  ri/ro______________________________________0.8      0.228          3.509  0.2850.7      0.2            3.5    0.2861.0      0.285          3.508  0.2850.3      0.009          3.333  0.31.2      0.34           3.529  0.2831.5      0.43           3.488  0.28______________________________________ 
    
     FIG. 3 to FIG. 6 shows a semi-submerged catamaran or an extended performance hydrofoil (EPH) in which the EMTs of the present invention are used for the propulsion system. As shown in FIG. 3, each EMT propulsion unit is mounted in a long, slender, submerged body. A fully-submerged foil 22 is mounted between two submerged bodies arranged by EMT propulsion units. Buoyant lift is combined with the dynamic lift of a fully-submerged foil 22 and the submerged body. 
     This foil 22 has a superconducting racetrack magnet 23 in itself and a pair of electrodes 24 are fixed on the upper surface of the foil. FIG. 6 shows the vector schematic of the forces acting upon the upper surface of the foil. The reaction between the magnetic field B (produced by fixing the superconducting racetrack magnet in the foil) and the electric current J from electrodes produces a Lorentz&#39;s force f&#39; along the flow stream longitudinal axis of the foil 22. The sea water on the surface of the foil is accelerated by Lorentz&#39;s force. The flow velocity difference between the upper surface 22a and the under surface generates lifting force L by Bernoulli&#39;s law. The lifting force per unit length L is calculated by the following equation. 
     
         L=ρUΓ=ρU(U.sub.u -U.sub.d)·1 (N/m) 
    
     where; 
     σ: Sea water density (Kg/m 3 ) 
     U: Absolute ship velocity (m/s) 
     Γ: Circulation (Total amount of maelstrom) 
     Uu: Flow velocity upon the foil (m/s) 
     Ud: Flow velocity under the foil (m/s) 
     1: Overall length of the foil (m) 
     For example, TABLE 2 shows the relation between flow velocity difference and lifting force. 
     
                       TABLE 2______________________________________Velocity difference       0.5      1         1.5    2ΔUlifting force L       2 × 10.sup.3                4 × 10.sup.3                          6 × 10.sup.3                                 8 × 10.sup.3______________________________________ 
    
     The basic principle of the hydrofoil concept is simply to lift a ship&#39;s hull out of the water and dynamically support it on wing-like hydrofoils in order to reduce the power required to attain modestly high speeds. As ship speed is increased, the lifting force generated by the water flow over the submerged portion of the foils increases causing the ship to rise and the submerged area of the foils to decrease. For a given speed the ship will rise until the lifting force equals the weight carried by the foils. The lifting force is dependent on ship speed. Prior art hydrofoils, in order to rise from water, require large output propulsion units. In hydrofoils powered by EMTs of the present invention, lifting force is controlled not only by ship speed but also by an electromagnetic force resulting in high thrust, reduction of hull weight and high ship speed. 
     FIG. 7 and FIG. 8 show two EMT propulsion units 20 mounted in parallel in the ship hull 21 to which a pair of EMT foils 25, 25 is connected. 
     The EMT foils system by the present invention is useful for the maneuver control of submarines. 
     In EMT hydrofoils, fundamental characteristics have been calculated as follows: 
     
         ______________________________________(1)  Specifications1.    Ship displacement                  200 metric tons2.    Sailing speed    45 knots3.    EMT propulsion unit                  Spiral type × 2(2)  Weights1.    Hull             80 tons2.    Superconducting magnet                  3O × 2 = 60 tons3.    Cryogenic systems                  5 tons4.    Power generator  25 tons5.    Power supply systems                  15 tons6.    The others       15 tons(3) Characteristics of elemental    equipment1.     Superconducting magnets Type             solenoid type Magnetic field   10-12 Teslas Length           6 m Diameter         1.6 m2.    Lifting devices  EMT foils shown in FIG. 43.    Power generator  Fuel Cell or Gas turbine4.    Electrodes       DSA5.    Hull form        Semi-submerged Catamaran6.    Power supply systems                  Superconducting power                  electric circuit by conven-                  tional and high Tc super-                  conducting materials7.    Cryogenic systems                  on board Helium refrigerator______________________________________ 
    
     The calculated results based on the data are shown in TABLE 3. TABLE 3 shows the characteristics of a Boeing 922 Jetfoil that is the only commercial hydrofoil in the world. The EMT foil exhibited about two times the propulsive efficiency as a Boeing Jetfoil. 
     
                       TABLE 3______________________________________                  EMT foil by the    Boeing 922 Jetfoil                  present invention______________________________________Length (m) 27.43           25Breadth (m)      8.53            10Depth (m)  2.59            4Gross (ton)      162             280Displacement      119             200(ton)Power generator      Gas turbine     Gas turbineOutput of power      5000 × 2  5000 × 2generator (KW)Propulsion system      waterjet propulsor × 2                      waterjet EMT × 2Thrust     104             162Propulsive 0.23            0.41efficiencyShip speed (Knot)      45              45______________________________________ 
    
     The calculated results for large full-scale vessel shows the following. 
     
         ______________________________________(1)  Characteristics1.    Ship displacement                  5000 metric tons2.    Sailing speed    50 Knots3.    EMT propulsion unit                  Spiral type × 12(2)  Weights1.    Hull             2,000 tons2.    Superconducting magnet                  100 × 12 = 1200 tons3.    Cryogenic systems                  200 tons4.    Power generator  200 tons5.    Power supply systems                  400 tons6.    The others       600 tons(3) Characteristics of elemental    equipment1.     Superconducting magnet Type             Solenoid Magnetic field   10-12 Teslas Length           15 m Diameter         5 m2.    Lifting devices  EMT foils shown in FIG. 43.    Power generator  Fuel Cell or Gas turbine4.    Electrodes       DSA5.    Hull form        Semi-submerged Catamaran6.    Power supply systems                  superconducting power                  electric circuit by conven-                  tional and high TC super-                  conducting materials7.    Cryogenic systems                  on board Helium refrigerator______________________________________ 
    
     Superconducting EMT propulsion units 30 can be arranged in four rows as shown in FIG. 9, wherein each pair of rows contains three pairs of ETM propulsion units 30. Superconducting shielding material devices 31 are mounted at both ends of each pair of rows of EMT propulsion units, forming a closed loop for the magnetic flux. As a result, the leakage of the magnetic field is negligible. The superconducting shielding device is made by plates, thin films and coils of high Tc superconducting material or conventional superconducting material. 
     INDUSTRIAL APPLICABILITY 
     The present invention is suitable for the ship propulsion system by generating thrust in the horizontal direction. Also, it is useful for DP Systems to produce the thrust in the horizontal and vertical directions. It is possible to be used as large sea water pumps, flowing sea water into fixed EMTs and discharging from the duct. Using the reverse principle of EMTs, it is possible to use ocean currents (MHD) for power generators.