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electrode pair, and seawater passage. overall efficiency appears to be low, mechanisms such as load factor, chanSince each thruster has only one sea- this value has long been expected foran nel aspect ratio, and end effect were water inlet and one outlet, flow divi. experimental ship of this size. The presented. It is reported that in sion to and combination from the six Japanese are already considering the November 1991, ANL had run their MHD channels are configured inter- MHD ship of the next phase, seawater MHD loop achieving flows of nally. Each thruster produces 8,000 N YAMATO-2. Proposing to use super- several meters per second and load of Lorentz force at a combined 4-T conducting magnets of more than 8T, factors on the order of 4. However, this magnetic field and 4,000-A total elec- YAMATO-2 would be much more information must be confirmed in future trode current. The six magnets in the energy efficient.

scientific reports. The Naval Underthruster share the same cryogenics dewar

water Systems Center (NUSC) has been and cryostat. The effective length of Propulsion

working on the Superconducting Electhe active Lorentz force region is

tromagnetic Thruster (SCEMT) proj3 meters. Each dipole magnet was wound YAMATO-1 produces 8,000 N of ect for several years. They reported with double layers of 1.82- by 10.86-mm Lorentz force at each thruster. As the that, in their 3.3-T system, pressure NbTi superconducting cables. efficiency of converting the Lorentz increases in the MHD channel with

The operation of YAMATO-1 will force into thrust is estimated to be electrode voltage and magnetic field. begin with the energization of the 50%, the propelling thrust of each They also provided a comparison superconducting magnets on the dock. thruster is about 4,000 N. Hence, each between the theoretical prediction and Once energized, the superconducting of the six MHD channels in a thruster experimental result. The overall efficoils are maintained persistently and contributes 667 N. The inside diameter ciency was generally less than 4%. Two no more current charging by the power of the seawater duct of each MHD U.S. industrial firms, Newport News supply is required. Nevertheless, elec- channel is 0.24 meter, and the inside Ship Building and Textron Defense tricity remains necessary for the elec- diameter of the superconducting coil is Systems, presented their conceptual trodes to pass current through the 0.36 meter. The gross ship tonnage is designs of MHD-propelled submarines seawater. Two diesel generator units 280 tons, while each thruster weighs and the associated naval stealth charare placed onboard to provide the needed 18 tons. The electrode currents are acteristics. Since 1987, Textron has been electricity for the source panels of elec- produced by two 2,000-KW MTU Bentz developing an MHD propulsion systrodes. The speed of the ship is con- diesel engines and two 2,105-KVA ac tem for generic attack class submarines. trolled by regulating the electrode generators. The ac current must be They presented their optimization study, current, while the maneuverability of rectified and filtered into dc current. performance assessment, and the prothe ship is controlled by distributing Many of these performance character- pulsion system/submarine integration differential currents to the individual istics have been confirmed in the dock. study. Their conceptual design study thrusters or by controlling the conven- However, the sea trials of YAMATO-1 has shown that the conventional protional rudder at the back of the ship in the spring of 1992 will verify all the pulsion system can be removed and the The control panel in the maneuvering performance characteristics while at MHD propulsion system added to the room provides all these functions. Since sea cruising.

submarine without any overall adverse diesel engines are used for electric power Several noticeable research and mass or performance impact. generation, which includes the power development efforts in superconduct- Other international contributions for liquid helium refrigeration, venti- ing MHD ship propulsion were pre- included the former U.S.S.R.'s theolation and silencing of the exhaust gas sented by various organizations in the retical and experimental investigations from the diesel engines are important United States. They were all laboratory of helical superconducting MHD proconsiderations for safety and comfort. scale studies, and few plans for experi- pulsion, in which the simplicity of using

YAMATO-1 is designed to have a mentalshipor sea trials were made. An a solenoid coil design of the magnet cruising speed of about 8 knots and can experimental investigation of a large was appreciated. The United Kingdom accommodate 10 persons. Its overall scale MHD thruster is currently under contributed in the area of superconenergy conversion efficiency is about way at Argonne National Laboratory ducting homopolar machinery. China, 4%. Power losses are generally due to (ANL). A 6-T dipole magnet with a France, Germany, and Yugoslavia disthe load factor (or counter electromag- 1-meter bore diameter is being used for cussed the theoretical aspects of MHD netic force), hydrodynamic friction in electromagnetic pumping of seawater ship propulsion, ranging from thruster the MHD channels, Joule heating while in a closed system. Although no exper- optimization, efficiency improvement, current is passed through seawater, and imental results were given at MHDS'91, seawater electrochemistry, to analytithe skin drags of the ship. Although 4% theoretical studies addressing loss cal magnetohydrodynamics, etc.

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Figure 1. The YAMATO-1 experimental ship (courtesy of the Japan Ship & Ocean Foundation).

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8,000N (abt. BOOkg)/ thruster (Current of electrode : abt. 4,000A/thruster)



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Figure 2. The YAMATO-1's MHD thruster (courtesy of the Japan Ship & Ocean Foundation). Superconducting Magnet High-T superconducting ceramic suggested the need to investigate the

materials, in multilayer form, have been two-phase turbulence of seawater under Superconducting magnets are the suggested as the shielding material for the influence of a strong magnetic field. critical elements of MHD ship propul- magnetic fields. Low-cost, lightweight, Electrochemical reactions on the sion technology. Multi-tesla magnets and castable polymer concrete was also electrode surfaces can result in elecare normally required for MHD ship suggested as another candidate for trode erosion. This poses a serious propulsion. In YAMATO-1, each indi- magnetic shielding. The wall of the problem for the day-to-day operation vidual magnet was designed for 3.5 Tat cryostat can be designed to serve both of an MHD ship. The anode appeared the center of the dipole. Because of the thermal insulation and shielding pur- to be more vulnerable to attack by circular arrangement of the six mag- poses. In this case, it is a double-layered, chlorine than the cathode by hydrogen. nets with alternating polarities for fiber-reinforced plastic (FRP) mate- Systematic electrode material evaluaadjacent magnets, a compound mag- rial with one layer of amorphous Ni-Fe tions were carried out by Japanese and netic field of 4T could be achieved. alloy and another layer of superinsula- American researchers. To date, it is the The YAMATO-1 magnets would tion sandwiched in-between. Based on consensus that the dimensional stable require an operating current of 3,288 A, the Japanese experience in the shield- anode (DSA) performs most satisfacan inductance of 0.55 H, and a stored ing of the magnetic levitation railroad, torily. DSA is normallya titanium elecenergy of 3.83 MJ. The cryogenics sys- laminated superconducting board was trode coated with a rare-earth (Ru or tem of the magnets will be discussed in suggested as an effective shielding Ir) oxide. For the purpose ofenhancing the next session.

mechanism using the Meissner effect. oxygen and suppressing chlorine proIt has been generally suggested that,

duction, the Japanese have investigated for a practical MHD ship to achieve Electrolysis and Electrode the Mno, coating of titanium. Its inireasonable energy conversion efficiency,

tial results were encouraging. With the superconducting magnets of 8 T or The electrochemical reactions on suppression of chlorine generation one higher magnetic field are required. the electrode surfaces in an MHD would be able to reduce the ocean Considering the even higher field in channel are very complex. Hydrogen environmental pollution of chlorine the coil winding, it would appear that bubbles are generated on the cathode discharged by the MHD thrusters. It Nb Sn will become the choice super- and chlorine and/or oxygen bubbles are was also suggested that nonmetal elecconducting material. However, it must produced on the anode. Depending on trodes could possibly be more corrobe remembered that Nb Sn is a much the anode material, the amount of oxygen sion resistant. Therefore, further invesmore expensive material!

production could vary. The flow in an tigation is necessary for glassified

MHD channel of an MHD ship can be graphite and silicon. For short mission Refrigeration and Shielding characterized to be multiphase and marine vehicles, such as torpedoes, the

multicomponent. The two-phase pres- problem of electrode erosion is pracIn YAMATO-1's normal operation sure drop strongly impacts the perfor- tically nonexistent. mode, helium boil-off due to the heat mance of the MHD thruster. The proleak into the cryostat must be recov- duction of bubbles is linearly depen- DISCUSSION AND ered and recondensed into useful dent on the electrode current. The CONCLUSION cryogen. The amount of heat leak is propagation of bubbles is affected by about 8 W for each thruster. There- the turbulence intensity of the flow and The electromagnetic (or MHD) fore, two 10-W-capacity helium refrig- the solubilities of different gases in the propulsion of marine vehicles was erators were designed, built, and placed flow. The presence of gas bubbles dis- conceptualized as early as 1961 (Rice) onboard YAMATO-1. They recycle the places the conductive seawater and, in United States. A small model ship helium in closed systems to avoid the hence, decreases the local conductance. was built and the working principle was loss of expensive helium. Particularly, To remedy such a problem, the flow demonstrated in 1967 (Way). However, low-vibration, low-noise micro-turbines rate in the MHD channel must be it remained a technical speculation due for helium compression were devel- maintained high enough to flush away to the weight penalty and low magnetic oped. The refrigerator consists of a the bubbles. Conductivity enhancement field of electromagnets until the recent screw compressor, a heat exchanger, a by introducing strong electrolytes into great advances in superconducting Joule-Thompson valve, and a cold the flow was also suggested. All these magnet technology. The Japanese are box housing the above-mentioned phenomena were discussed in the to be complimented on making signifcomponents.

author's presentation. The author also icant contributions in superconducting MHD shipbuilding. YAMATO-1 is visualization of MHD seawater flow vice versa). The entire conference was clearly a result of Japan's well- are apparently important but were not extremely harmonious, which could be coordinated national effort. It began as well addressed at MHDS'91. It is the

dressed at MHDS'91. It is the attributed to the hospitality and openthe Ship and Ocean Foundation's sci- author's belief that improving the minded sharing of technical informaentific research guideline to build an understanding of basic physical pro- tion of the Japanese hosts. The techniMHD experimental ship, while fully cesses can only benefit the practical cal tour of YAMATO-1 was especially aware of the low efficiency and medi- applications in the long run.

informative. ocre speed. Nevertheless, the two indus- The Americans are also to be contrial giants (Mitsubishi and Toshiba) gratulated for taking prudent measures ACKNOWLEDGMENT invested significant amounts of finan- in investigating superconducting MHD cial and human resources. Smaller propulsion at various organizations. The author wishes to acknowledge industrial firms also took part in differ- The Defense Advanced Research Proj- the Office of Naval Research for supent projects using their own expertise, ects Agency (DARPA) is the primary porting his research in the subject matter such as cryogenics, superconductivity, sponsor for several MHD test facilities and his trip to MHDS’91. Dr. Gabriel electrochemistry, etc. One very impor- and conceptual studies in United States. D. Roy is acknowledged to be the scitant link in this complex technology Although the stealthy nature of the entific officer of contract N00014-89. infrastructure is the participation of MHD ship is the main justification for J-1693. universities and academic institutions the research efforts in United States, The typing and proofreading of this in the capacity of scientific and intel- the author regretted not being able to article by Elizabeth G. Fink is greatly lectual guidance. The Japanese achieve- see any in-depth quantitative papers appreciated. ment is not so much on YAMATO-l's on the acoustics of MHD thrusters. speed or efficiency. They should be given The Office of Naval Research (ONR, Thomas F. Lin is currently a senior more credit for the integration of the Code 1132P) has also sponsored vari- research associate at the Applied complex subsystems in MHD propul- ous programs addressing more funda- Research Laboratory and an associate sion and for the timely completion of mental issues of MHD propulsion tech- professor in the Nuclear Engineerthe experimental ship. YAMATO-1 will nology. The author believes that the ing Department, Pennsylvania State undergo sea trials in the spring of 1992. sea trial data of YAMATO-1 will be University. He recived his B.S. degree If it meets the expected performance very important for the American MHD from National Tsing Hua University and specifications, it would seem very propulsion community. It will certainly (Taiwan) in 1976, M.S. degree from justified for Japan to move forward and influence the American research and the University of Wisconsin-Madison build the more efficient and higher speed development policy toward MHD ship in 1978, and Ph.D. degree from YAMATO-2. Regardless, Japan is now propulsion. Thus, we shall pay very Rensselaer Polytechnic Institute in by far the world's leader in MHD ship close attention to the forthcoming 1984, all in nuclear engineering and propulsion. It is, however, the author's events, the YAMATO-1 sea runs. engincering physics. From 1984 to observation that the Japanese programs Finally, the international partici- 1985, Dr. Lin was a visiting accelerator could be strengthened in the funda- pants at MHDS'91 and the Japanese physicist at Stanford Linear mental studies of the physical phenom- hosts are to be complimented on tak- Accelerator Center (SLAC). Since ena associated with seawater MHD ing part in very constructive discus- 1985, Dr. Lin has been with Penn thruster flows. The subjects of multi- sions of the subject matter. Many pre- State working on advanced torpedo phase seawater flow under a strong sentations were very well prepared, propulsion by liquid metal combustion magnetic field, computational magneto- thought provoking, and properly trans- and magnetohydrodynamics. hydrodynamic simulation, and direct lated from Japanese to English (and

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