Patent Publication Number: US-10315741-B2

Title: Underwater propulsion apparatus and underwater exploration apparatus

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application is the US National Phase of International Patent Application No. PCT/JP2015/078083, filed Oct. 2, 2015, which claims priority to Japanese Application No. 2014-205122, filed Oct. 3, 2014, each of which is incorporated by reference in its entirety. 
     TECHNICAL FIELD 
     The present invention relates to an underwater propulsion apparatus and an underwater exploration apparatus, and particularly to a pump-jet-driven underwater propulsion apparatus and an underwater exploration apparatus using the underwater propulsion apparatus. 
     BACKGROUND ART 
     An underwater exploration apparatus, such as an autonomous underwater vehicle (AUV), has been known as an underwater robot. A variety of microstructure sensors are incorporated in the underwater exploration apparatus. The underwater exploration apparatus is intended to be used, for example, to observe a marine ecosystem, such as the distribution of planktons. 
     CITATION LIST 
     Patent Literature 
     Patent Literature 1: Japanese Patent Laid-Open No. 8-48295 
     Patent Literature 2: Japanese Patent Laid-Open No. 2010-115971 
     Patent Literature 3: Japanese Patent Laid-Open No. 7-179196 
     SUMMARY OF INVENTION 
     Technical Problem 
     The underwater exploration apparatus of related art, however, has the following problems: 
     First of all, in the case of a propeller-driven underwater exploration apparatus, when a propeller attached to the exterior of an apparatus body rotates, the apparatus body undesirably vibrates, and water around the apparatus body is agitated. An observation target, such as planktons, is therefore disturbed. The propeller-driven method is therefore unsuitable for the observation. 
     On the other hand, in the case of a pump-jet-driven underwater exploration apparatus, the problem of vibration described above is relieved. In the case of pump-jet propulsion of related art, however, when the number of revolutions of an impeller decreases, the pressure of the blasted flow decreases, and it is therefore undesirably difficult to produce propulsion force necessary in low-speed operation. 
     Further, an underwater exploration apparatus in water is preferably capable of not only forward movement and pivotal movement but also backward movement, quick pivotal movement, deceleration, and other types of control. It is, however, difficult for the underwater exploration apparatus of related art to perform fine attitude control. 
     The present invention has been made on the basis of the technical problems described above, and an object of the present invention is to provide an underwater propulsion apparatus and an underwater exploration apparatus producing a small amount of vibration and capable of fine attitude control. 
     Another object of the present invention is to provide an underwater propulsion apparatus and an underwater exploration apparatus capable of ensuring propulsion force necessary in low-speed operation. 
     Solution to Problem 
     An underwater propulsion apparatus according to the present invention includes a main body, 
     at least one pump having a channel and an impeller provided in the channel, the channel having an inlet in an outer circumferential surface of the main body and a nozzle on a side downstream of the inlet and in a tail portion of the main body, and 
     a plurality of direction control wings attached to an outer surface of the main body and located in positions downstream of the nozzle and close thereto, each of the plurality of direction control wings having an upstream end pivotally supported by the main body. 
     The underwater propulsion apparatus described above may further include a diffuser attached to the main body so as to surround an outer circumference of the nozzle. 
     In the underwater propulsion apparatus described above, the diffuser may be provided with a first entrained flow introducing channel that passes through the diffuser and introduces water flow flowing along an outer side of the diffuser into a propulsion channel sandwiched between the diffuser and the direction control wings. 
     In the underwater propulsion apparatus described above, an outer surface of a downstream end portion of the diffuser may be provided with a plurality of first entrained flow introducing grooves that extend from an upstream side toward a downstream side and have a depth that increases with distance toward the downstream side. 
     In the underwater propulsion apparatus described above, an edge portion upstream of the nozzle may be provided with a second entrained flow introducing channel that passes through the edge portion and introduces water flow flowing along an outer side of the main body into the channel and in a portion close to the nozzle. 
     In the underwater propulsion apparatus described above, an outer surface of an edge portion upstream of the nozzle may be provided with a plurality of second entrained flow introducing grooves that extend from an upstream side toward a downstream side and have a depth that increases with distance toward the downstream side. 
     In the underwater propulsion apparatus described above, the tail portion of the main body may have a conical shape with a head portion truncated. 
     An underwater exploration apparatus according to the present invention includes 
     a hull having a stern, 
     at least one pump having a channel and an impeller provided in the channel, the channel having an inlet in an outer circumferential surface of the hull and a nozzle on a side downstream of the inlet and in the stern, and 
     a plurality of direction control wings attached to an outer surface of the hull and located in positions downstream of the nozzle and close thereto, each of the plurality of direction control wings having an upstream end pivotally supported by the hull. 
     The underwater exploration apparatus described above may further include a diffuser attached to the hull so as to surround an outer circumference of the nozzle. 
     In the underwater exploration apparatus described above, the diffuser may be provided with a first entrained flow introducing channel that passes through the diffuser and introduces water flow flowing along an outer side of the diffuser into a propulsion channel sandwiched between the diffuser and the direction control wings. 
     In the underwater exploration apparatus described above, an outer surface of a downstream end portion of the diffuser may be provided with a plurality of first entrained flow introducing grooves that extend from an upstream side toward a downstream side and have a depth that increases with distance toward the downstream side. 
     In the underwater exploration apparatus described above, an edge portion upstream of the nozzle may be provided with a second entrained flow introducing channel that passes through the edge portion and introduces water flow flowing along an outer side of the hull into the channel. 
     In the underwater exploration apparatus described above, an outer surface of an edge portion upstream of the nozzle may be provided with a plurality of second entrained flow introducing grooves that extend from an upstream side toward a downstream side and have a depth that increases with distance toward the downstream side. 
     In the underwater exploration apparatus described above, the stern of the hull may have a conical shape with a head portion truncated. 
     Advantageous Effects of Invention 
     The present invention can provide an underwater propulsion apparatus and an underwater exploration apparatus producing a small amount of vibration and capable of ensuring propulsion force necessary in low-speed operation and performing fine attitude control. 
     The present invention can further provide an underwater propulsion apparatus and an underwater exploration apparatus capable of ensuring propulsion force necessary in low-speed operation. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1( a )  is a side view of an underwater propulsion apparatus  1  according to an embodiment, and  FIG. 1( b )  is a rear view of the underwater propulsion apparatus  1 . 
         FIG. 2  is a partially enlarged cross-sectional view of the underwater propulsion apparatus  1 . 
         FIG. 3( a )  is a side view of a diffuser  8  through which entrained flow introducing channels  10  are provided, and  FIG. 3( b )  is a side view of the diffuser  8  in which entrained flow introducing grooves  11  are provided. 
         FIG. 4( a )  shows the diffuser  8 , direction control wings  9 , and the pass of water flow in forward movement of the underwater propulsion apparatus  1 , and  FIG. 4( b )  shows the diffuser  8 , the direction control wings  9 , and the pass of the water flow in pivotal movement of the underwater propulsion apparatus  1 . 
         FIG. 5  is an enlarged view showing the diffuser  8 , the direction control wing  9 , and the path of the water flow in the forward movement. 
         FIG. 6  is an enlarged view showing the diffuser  8 , the direction control wing  9  on one side, and the path of the water flow in the pivotal movement. 
         FIG. 7  is an enlarged view showing the diffuser  8 , the direction control wing  9  on the other side, and the path of the water flow in the pivotal movement. 
         FIG. 8( a )  shows the diffuser  8 , the direction control wings  9 , and the path of the water flow in quick pivotal movement, and  FIG. 8( b )  shows the diffuser  8 , the direction control wings  9 , and the path of the water flow in backward movement. 
         FIG. 9  is an enlarged view showing the diffuser  8 , the direction control wings  9 , and the path of the water flow in the quick pivotal movement or the backward movement. 
         FIG. 10  is a side view of an underwater exploration apparatus  30  according to an embodiment. 
     
    
    
     DESCRIPTION OF EMBODIMENT 
     An embodiment according to the present invention will be described below with reference to the drawings. In the drawings, components having the function have the same reference character and no detailed description of the components having the same reference character will be repeated. 
     (Underwater Propulsion Apparatus) 
     The configuration of an underwater propulsion apparatus  1  according to an embodiment of the present invention will be described with reference to  FIGS. 1 to 3 .  FIG. 1( a )  is a side view of the underwater propulsion apparatus  1 , and  FIG. 1( b )  is a rear view of the underwater propulsion apparatus  1 .  FIG. 2  is a partially enlarged cross-sectional view of the underwater propulsion apparatus  1  including a diffuser  8  and direction control wings  9 .  FIG. 3( a )  is a side view of the diffuser  8 , through which entrained flow introducing channels  10  are provided, and  FIG. 3( b )  is a side view of the diffuser  8 , in which entrained flow introducing grooves  11  are provided. 
     The underwater propulsion apparatus  1  includes a main body  2 , at least one pump  3 , the diffuser  8 , and a plurality of direction control wings  9 , as shown in  FIGS. 1( a ), 1( b ) , and  2 . The underwater propulsion apparatus  1  is, for example, attached to an underwater robot that acts in water and used to move the underwater robot and control the attitude thereof. 
     Each of the components of the underwater propulsion apparatus  1  will next be described in detail. 
     The main body  2  is so configured that at least a tail portion thereof has a conical shape, as shown in  FIGS. 1( a ) and 1( b ) . The tail portion of the main body  2  preferably has a conical shape with a head portion thereof truncated, as shown in  FIG. 1( a ) . It is noted that the main body  2  does not necessarily have a conical shape and may, for example, have a cylindrical shape, a box-like shape, a prismatic shape, or a pyramidal shape. 
     Channels  4 , through which sucked water flows, are provided in the main body  2  so as to pass therethrough, as shown in  FIG. 2 . Each of the channels  4  has an inlet  6  at one end thereof and a nozzle  7  at the other end thereof. The inlet  6  is provided in the outer circumferential surface of the main body. The nozzle  7  is provided on the side downstream of the inlet  6  and in the tail portion of the main body  2 . For example, in the case where the tail portion of the main body  2  has a conical shape, the nozzles  7  each have an arcuate opening formed along the circumferential direction of the tail portion, and in the case where the tail portion of the main body  2  has a box-like shape, the nozzles  7  each has a rectangular opening and are formed along the circumferential direction in the four side surfaces of the tail portion. The nozzles  7  do not necessarily have an arcuate or rectangular shape and may, for example, have an elliptical shape or any other arbitrarily curved shape. The thus configured channels  4  each have the inlet  6  in the outer circumferential surface of the main body  2  and the nozzle  7  on the side downstream of the inlet  6  and in the tail portion of the main body. 
     Each of the pumps  3  has the channel  4  and an impeller  5  provided in the channel  4 , as shown in  FIG. 2 . When the impeller  5  rotates at high speed, water is sucked via the inlet  6 , and jet flow is discharged (blasted) via the nozzle  7 . Employing the pump-jet-driven method using the pump  3  allows suppression of vibration of the main body  2  (vibration at low frequency ranging from 1 to 50 Hz, in particular) as compared with the propeller-driven method. 
     The pumps  3  are provided at a plurality of locations in the main body  2  in correspondence with the direction control wings  9 . In this case, the inlets  6  and the nozzles  7  are provided at a plurality of locations on the outer circumferential surface of the main body  2  in correspondence with the number of pumps. 
     It is noted that only one pump  3  may instead be provided in the main body  2 . In this case, one channel  4  branches off in a portion downstream of the impeller  5  toward the nozzles  7  provided in correspondence with the direction control wings  9 . 
     The diffuser  8  is attached to the main body  2  so as to surround the outer circumference of the nozzles  7 , as shown in  FIGS. 1( a ), 1( b ) , and  2 . The diffuser  8  is provided in accordance with the outer circumferential shape of the tail portion of the main body  2 . For example, in the case where the tail portion of the main body  2  has a conical shape, the diffuser  8  has a cylindrical shape, and in the case where the tail portion of the main body  2  has a box-like shape, the diffuser  8  has the shape of a rectangular tube. The diffuser  8  is fixed to the main body  2  via a plurality of columnar connectors (not shown) that link the main body  2  to the diffuser  8 . 
     When the diffuser  8  is provided, the channel of water flow (peripheral flow) flowing around the underwater propulsion apparatus  1  narrows, resulting in an increase in the speed of the peripheral flow. Since the peripheral flow that flows at the higher speed is likely to be drawn by the jet flow blasted via the nozzles  7 , the propulsion force can be increased. 
     The direction control wings  9  are provided at a plurality of locations, as shown in  FIGS. 1( a ) and 1( b ) . In the present embodiment, four direction control wings  9  are provided, as shown in  FIG. 1( b ) . In the present invention, the number of direction control wings  9  is not limited to four, and two, three, or five or more direction control wings  9  may be provided. 
     Each of the direction control wings  9  is attached to the outer surface of the main body  2  and located in a position downstream of the nozzles  7  and close thereto in such a way that the direction control wing  9  follows the shape of the tail portion of the main body  2 , as shown in  FIGS. 1( a ), 1( b ) , and  2 . For example, in the case where the tail portion of the main body  2  has a conical shape, the direction control wings  9  are attached in an annular shape. In the case where the tail portion of the main body  2  has a box-like shape, the direction control wings  9  are attached to the four sides of the tail portion. 
     Each of the direction control wings  9  has an upstream end pivotally supported by the main body  2 . In more detail, each of the direction control wings  9  is attached to the main body  2  so as to pivot around an axis of rotation L extending in the direction of a tangent to the outer circumference of the main body  2 , as shown in  FIG. 2 . The direction control wings  9  are pivotable independently of one another. 
     When each of the direction control wings  9  pivot around the axis of rotation L, the flow direction of the jet flow and the peripheral flow (entrained flow) drawn by the jet flow can be controlled, as will be described later in detail. 
     Entrained flow introducing channels  10  are provided so as to pass through a lower end portion of the diffuser  8 , as shown in  FIG. 2 .  FIG. 3( a )  is a side view of the diffuser  8  provided with the entrained flow introducing channels  10 . Each of the entrained flow introducing channels  10  has an opening  10   a  provided in an outer surface  8   a  of the diffuser  8  and an opening  10   b  provided in an inner surface  8   b  of the diffuser  8 . The opening  10   b  in the inner surface  8   b  is provided in a position downstream of the opening  10   a  in the outer surface  8   a , as shown in  FIGS. 2 and 3 ( a ). 
     The entrained flow introducing channels  10  introduce the water flow flowing along the outer side of the diffuser  8  into propulsion channels C sandwiched between the diffuser  8  and the direction control wings  9 . The propulsion force can therefore be further increased. The entrained flow introducing channels  10  also work when the underwater propulsion apparatus  1  quickly pivots or moves backward, as will be described later in detail. 
     The entrained flow introducing channels  10  are not necessarily provided in the lower end portion of the diffuser  8  and may be provided in another portion. 
     The diffuser  8  may instead be provided with a plurality of entrained flow introducing grooves  11 , as shown in  FIG. 3( b ) . In more detail, the plurality of entrained flow introducing grooves  11  may be provided in the outer surface  8   a  of a downstream end portion of the diffuser  8 . The entrained flow introducing grooves  11  are so formed that they extend from the upstream side toward the downstream side and the depth of the grooves increases with distance toward the downstream side. The entrained flow introducing grooves  11  allow the water flow flowing along the outer side of the diffuser  8  to be introduced into the propulsion channels C so that the propulsion force increases, as in the case of the entrained flow introducing channels  10 . 
     Cutouts  12  may further be formed in the downstream end portion of the diffuser  8  in accordance with the entrained flow introducing grooves  11 , as shown in  FIG. 3( b ) . The water flow in the propulsion channels C can therefore be discharged out of the diffuser  8  via the cutouts  12  with the direction control wings  9  being in contact with the downstream end portion of the diffuser  8  (see  FIG. 9 ) when the underwater propulsion apparatus  1  quickly pivots or moves backward. 
     Entrained flow introducing channels  13  having the same shape as that of the entrained flow introducing channels  10  in the diffuser  8  may be provided in an edge portion upstream of the nozzles  7 , as shown in  FIG. 2 . In more detail, entrained flow introducing channels  13 , which introduce the water flow flowing along the outer side of the main body  2  into the channels  4  and in portions close to the nozzles  7 , may be provided in the edge portion upstream of the nozzles  7  so as to pass through the edge portion. 
     Entrained flow introducing grooves having the same shape as that of the entrained flow introducing grooves  11  in the diffuser  8  shown in  FIG. 3( b )  may be provided. In more detail, a plurality of entrained flow introducing grooves that extend from the upstream side toward the downstream side and having a depth that increases with distance toward the downstream side may be provided in the exterior surfaces of edge portions upstream of the nozzles  7 . 
     Providing the entrained flow introducing channels having the same shape as that of the entrained flow introducing channels  10  and the entrained flow introducing grooves having the same shape as that of the entrained flow introducing grooves  11  in the edge portions upstream of the nozzles  7  as described above allows the jet water flow blasted via the nozzles  7  to readily draw, in the vicinity of the nozzles  7 , the water flow flowing along the outer side of the main body  2 , whereby the propulsion force produced by the jet flow F can be increased. 
     The principle of the propulsion of the underwater propulsion apparatus  1  will now be described with reference to  FIG. 5 . The jet flow F blasted via the nozzles  7  flows along the surfaces of the direction control wings  9  in accordance with a Coanda effect (effect that allows jet flow to flow along wall surface), as shown in  FIG. 5 . The jet flow F, which is high-speed flow, draws the peripheral flow flowing around the underwater propulsion apparatus  1  so that the drawn peripheral flow becomes entrained flow. In the present embodiment, since the diffuser  8  is provided, the peripheral flow flowing around the underwater propulsion apparatus  1  passes through the narrow propulsion channels C. The speed of the peripheral flow therefore increases, so that the peripheral flow is more likely to be drawn by the jet flow F, whereby the propulsion force increases. 
     Entrained flow G 1  shown in  FIG. 5  is peripheral flow flowing via the upstream end of the diffuser  8  into the propulsion channel C. Entrained flow G 2  is peripheral flow passing along the outer side of the diffuser  8 , passing through the entrained flow introducing channel  10 , and flowing into the propulsion channel C. Water flow that is the sum of the jet flow F, the entrained flow G 1 , and the entrained flow G 2  (hereinafter simply referred to as “summed flow”) propels the underwater propulsion apparatus  1 . 
     The summed flow flows along the surface of the direction control wing  9  and then flows along the surface of the head-truncated conical-shape tail portion of the main body  2 . The summed flow having flowed along the tail portion forms backwater having a streamlined tail shape (that is, shape corresponding to head portion of cone) behind the main body  2 . The backwater becomes an imaginary body of the main body  2  (rear end portion of main body  2 ). The tail portion of the main body  2  is therefore allowed to have the head-truncated conical shape, as shown in  FIG. 1( a ) . The main body  2  can therefore be shortened by the length corresponding to the head of the cone. The length of the hull of an underwater exploration apparatus (hull  31 , which will be described later) using the underwater propulsion apparatus  1  can therefore be increased, whereby the volume of the hull can be increased. 
     Control of the attitude of the underwater propulsion apparatus  1  having the configuration described above (forward movement, pivotal movement, quick pivotal movement, and backward movement) will next be described in detail. 
     &lt;Forward Movement&gt; 
     In the forward movement (rectilinear movement) of the underwater propulsion apparatus  1 , the direction control wings  9  are positioned so as to have the same angle with respect to a center axis M of the main body  2 , as shown in  FIG. 4( a ) . Since the summed flow having passed along the direction control wings  9  flows symmetrically with respect to the center axis M toward the rear side of the main body, the underwater propulsion apparatus  1  rectilinearly moves. 
     Further, changing the angle of the direction control wings  9  allows change in the forward movement speed with the number of revolutions of each of the impellers  5  maintained at a fixed value. 
     &lt;Pivotal Movement&gt; 
     In pivotal movement (right-handed pivotal movement) of the underwater propulsion apparatus  1 , the direction control wing  9  on one side (left in  FIG. 4( b ) ) pivots around the axis of rotation L in such a way that the downstream end of the direction control wing  9  moves away from the diffuser  8  (that is, approaches main body  2 ), as shown in  FIGS. 4( b )  and  6 . Negative moment of rotation is thus produced. 
     On the other hand, the direction control wing  9  on the other side (right in  FIG. 4( b ) ) pivots around the axis of rotation L in such a way that the downstream end of the direction control wing  9  approaches the diffuser  8  (that is, moves away from main body  2 ), as shown in  FIGS. 4( b )  and  7 . Positive moment of rotation is thus produced. 
     Since the summed flow (jet flow F, entrained flow G 1 , and entrained flow G 2 ) having passed along the direction control wings  9  on both sides flows obliquely rearward and rightward with respect to the main body  2 , as shown in  FIG. 4( b ) , the underwater propulsion apparatus  1  pivots right-handed. 
     &lt;Quick Pivotal Movement&gt; 
     In quick pivotal movement (right-handed quick pivotal movement) of the underwater propulsion apparatus  1 , the direction control wing  9  on one side (left in  FIG. 8( a ) ) pivots around the axis of rotation L in such a way that the downstream end of the direction control wing  9  moves away from the diffuser  8  (that is, approaches main body  2 ), as shown in  FIGS. 8( a )  and  6 . Negative moment of rotation is thus produced. 
     On the other hand, the direction control wing  9  on the other side (right in  FIG. 8( a ) ) pivots around the axis of rotation L in such a way that the downstream end of the direction control wing  9  comes into contact with a downstream end portion of the diffuser  8 , as shown in  FIGS. 8( a )  and  9 . The exit (blast port) of the propulsion channel C is therefore closed, and the jet flow F and the entrained flow G 1  pass through the entrained flow introducing channel  10  (or cutout  12  of entrained flow introducing groove  11 ) and exits out of the diffuser  8 . Since the opening  10   b  of the entrained flow introducing channel  10  is provided downstream of the opening  10   a , the jet flow F and the entrained flow G 1  flow backward, as shown in  FIG. 9 . A braking effect is thus provided. Therefore, when the backward blasted flow is produced on one side of the main body  2 , the underwater propulsion apparatus  1  can make quick pivotal movement having a small radius of rotation, as shown in  FIG. 8( a ) . 
     &lt;Backward Movement&gt; 
     In backward movement of the underwater propulsion apparatus  1 , the direction control wings  9  pivot around the axis of rotation L in such a way that the downstream ends of the direction control wings  9  come into contact with the downstream end portion of the diffuser  8 , as shown in  FIGS. 8( b )  and  9 . Since each of the propulsion channels C is therefore closed, and the jet flow F and the entrained flow G 1  pass through the entrained flow introducing channels  10  and flow backward, as shown in  FIG. 9 , the underwater propulsion apparatus  1  moves backward. 
     As described above, in the underwater propulsion apparatus  1  according to the present embodiment, which is provided with the diffuser  8 , the channels of the peripheral flow are narrowed so that the speed thereof increases, and the peripheral flow is drawn to the jet flow. Therefore, according to the present embodiment, the jet flow and the entrained flow drawn by the jet flow can increase the propulsion force. 
     Further, the jet flow and the entrained flow drawn by the jet flow can ensure propulsion force necessary also in low-speed operation in which the each of impellers  5  rotates at a reduced speed. 
     Further, the present embodiment, in which the pump-jet-driven method using the impellers  5  is employed, allows suppression of vibration of the main body  2  (low-frequency vibration, in particular) as compared with a propeller-driven method. 
     Moreover, in the present embodiment, the plurality of direction control wings  9  are attached in an annular shape to the outer surface of the main body  2  and located in positions downstream of the nozzles  7  and close thereto, and the upstream ends of the direction control wings  9  are pivotally supported by the main body  2 . The jet flow and the entrained flow drawn by the jet flow then flow along the outer surfaces of the direction control wings  9  in accordance with the Coanda effect. Pivotal movement of the direction control wings  9  allows efficient control of the direction of the jet flow and the entrained flow. Therefore, according to the present embodiment, fine control of the attitude of the underwater propulsion apparatus  1 , such as forward movement, pivotal movement, quick pivotal movement, and backward movement, can be performed. 
     In the underwater propulsion apparatus  1  described above, the diffuser  8  can be omitted. Also in this case, the jet flow and the entrained flow drawn by the jet flow can propel the underwater propulsion apparatus. Further, pivotal movement of the direction control wings  9  allows change in the direction of the jet flow flowing along the outer surfaces of the direction control wings  9  to control the attitude of the underwater propulsion apparatus. 
     The underwater propulsion apparatus  1  described above may be attached to the stern of a cylindrical hull, as in an embodiment that will be described later, or may be attached to the stern or the bottom of a ship, such as a small boat. 
     (Underwater Exploration Apparatus) 
     An underwater exploration apparatus  30  will next be described with reference to  FIG. 10  as an underwater robot (AUV) using the underwater propulsion apparatus described above.  FIG. 10  is a side view of the underwater exploration apparatus  30  according to an embodiment. 
     The underwater exploration apparatus  30  has a torpedo-like shape, and the underwater propulsion apparatus  1  is attached to the stern of the underwater exploration apparatus  30 , as shown in  FIG. 10 . In other words, the underwater exploration apparatus  30  includes a hull  31 , which has a conical stern, the at least one pump  3 , the diffuser  8 , and the plurality of direction control wings  9 . The hull  31  is, for example, so sized that the overall length is about 4.5 m and the diameter is about 60 cm. 
     The hull  31  does not necessarily have a torpedo-like shape or a cylindrical shape and may, for example, have an egg-like shape, a box-like shape, a prismatic shape, a conical shape, a pyramidal shape, or an arbitrary combination thereof. The stern of the hull  31  does not necessarily have a conical shape and may, for example, have a cylindrical shape, a box-like shape, a prismatic shape, or a pyramidal shape. 
     The hull  31  accommodates not only a variety of sensors and measurement apparatus according to observation purposes and targets but also a controller, a battery, and other components. 
     A Doppler velocity log (DVL)  35 , a gyro compass  36 , and a depth meter (not shown) are provided as the variety of sensors and measuring apparatus. A microstructure sensor  32 , a plankton camera  33  for observing planktons, and a multi-beam sonar  34  may be provided at the bow of the hull  31 . 
     The controller  39  includes an electronic system, such as a computer, and controls the variety of sensors and measuring apparatus. The controller  39  may further control the number of revolutions of the pumps  3  (impellers  5 ) and control the angle of each of the direction control wings  9 . 
     A battery system  40  includes a battery, such as a secondary cell (lithium ion cell, for example) or a fuel cell, and a battery management unit (BNU). The variety of sensors and measuring apparatus, a communication apparatus, the controller, and other components operate with electricity supplied from the battery. 
     An acoustic communication transducer  37  and a wireless communication antenna  38  may be provided as the communication apparatus in the hull  31 . The wireless communication antenna  38  can also receive a GPS signal. 
     A nose hoist point  41 , which is used to lift the underwater exploration apparatus  30 , may be provided at the bow of the hull  31 , a top-middle hoist point  42  may be provided on an upper central portion of the hull  31 , and a towing eye  43 , which is used to tow sensors and other components may be provided at the stern of the hull  31 . 
     In the underwater exploration apparatus  30  according to the present embodiment, providing the diffuser  8  allows the propulsion force to be increased and propulsion force necessary in low-speed operation to be ensured, as mentioned in the description of the underwater propulsion apparatus  1 . 
     Since the water-jet-driven method using the impellers  5  is employed, the vibration of the hull  31  (low-frequency vibration, in particular) can be suppressed. Since the low-frequency vibration of the hull  31  can be suppressed, a sensor highly sensitive to low-frequency vibration (such as sensor for measuring agitation) can be used. Further, since no helical water flow is produced behind the hull  31  because no propeller is used, a sensor can be towed via the towing eye  43 . Moreover, since no fins for stabilizing the attitude of the hull need to be provided at the tail portion of the hull, a situation in which the hull  31  is caught, for example, by underwater algae can be avoided. 
     Further, causing the plurality of direction control wings  9  to pivot allows fine control of the attitude of the hull  31 , such as forward movement, backward movement, pivotal movement, and quick pivotal movement, to be performed, as mentioned in the description of the underwater propulsion apparatus  1 . 
     In the present embodiment, one underwater propulsion apparatus is attached to the hull, but not necessarily in the present invention, and a plurality of underwater propulsion apparatus may be attached to the hull. For example, two underwater propulsion apparatus  1  may be provided on the right and left sides of a waist portion of the hull. 
     In the underwater exploration apparatus  30  described above, the diffuser  8  can be omitted. Also in this case, the jet flow and the entrained flow drawn by the jet flow can propel the underwater exploration apparatus. Further, the attitude of the underwater exploration apparatus can be controlled by causing the direction control wings  9  to pivot so that the direction of the jet flow flowing along the outer surfaces of the direction control wings  9  is changed. 
     A person skilled in the art may conceive of additional effects of the present invention and a variety of variations thereof on the basis of the above description. Aspects of the present invention are not limited to the embodiments described above. A variety of additions, changes, and partial omissions are possible to the extent that they do not depart from the conceptual idea and sprit of the present invention derived from the contents set forth in the claims and equivalents of the contents. 
     REFERENCE SIGNS LIST 
     
         
         
           
               1  Underwater propulsion apparatus 
               2  Main body 
               3  Pump 
               4  Channel 
               5  Impeller 
               6  Inlet 
               7  Nozzle 
               8  Diffuser 
               8   a  Outer surface 
               8   b  Inner surface 
               9  Direction control wing 
               10  Entrained flow introducing channel 
               10   a ,  10   b  Opening 
               11  Entrained flow introducing groove 
               12  Cutout 
               13  Entrained flow introducing channel 
               30  Underwater exploration apparatus 
               31  Hull 
               32  Microstructure sensor 
               33  Plankton camera 
               34  Multi-beam sonar 
               35  Doppler Velocity Log (Velocity sensor) 
               36  Gyro compass 
               37  Acoustic communication transducer 
               38  Wireless communication antenna 
               39  Controller 
               40  Battery system 
               41 ,  42  Hoist point 
               43  Towing eye 
             C Propulsion channel 
             F Jet flow 
             G 1 , G 2  Entrained flow 
             L Axis of rotation (of direction control wing  9 ) 
             M Center axis (of main body  2 )