robot

Abstract

A robot includes a mechanical arm that outputs power for an underwater operation, a first thruster, a second thruster, and a surface portion in which a dimple is formed. A shape of the surface portion is a shape formed in such a manner that a predetermined velocity of a relative water flow in water corresponds to a Reynolds number indicating a supercritical region regarding a change in drag coefficient. The surface portion includes a surface of each of a first frame, each control unit, a cover member, and the mechanical arm.

Description

CROSS-REFERENCE TO RELATED APPLICATION

[0001] Priority is claimed on Japanese Patent Application No. 2024-010184, filed in Japan on Jan. 26, 2024, the entire content of which is incorporated herein by reference.BACKGROUND OF THE INVENTIONField of the Invention

[0002] The present invention relates to a robot.Description of Related Art

[0003] Conventionally, for example, there is known a small or medium-sized underwater robot assumed to move at a low velocity in water, to be stagnant, to operate under a low velocity water flow and the like, in which portability and operability are valued. For such small or medium-sized underwater robot, it is desired to improve, for example, an increase in output of a propulsion machine, a reduction in fluid resistance and the like so as to cope with operation under a high-velocity water flow.

[0004] Conventionally, for example, there is known a structure in which a plurality of ridges and a plurality of depressions are provided on an object surface, thereby maintaining laminarization and reducing flow resistance even in a case where a flow velocity of a fluid flow (surface flow) in contact with the object surface increases (refer to, for example, Patent Document 1 mentioned below).

[0005] [Patent Document 1] Japanese Unexamined Patent Application, First Publication No. 2010-7846SUMMARY OF THE INVENTION

[0006] However, for example, in a case of increasing an output of a propulsion machine, there arises a problem that it is necessary to add the propulsion machine, increase supply power and the like. For example, in a case of downsizing or changing a shape of a machine body in order to reduce the fluid resistance, there arises a problem that effective improvement becomes difficult due to a size of a mounted component and restrictions in structure or function of an exposed portion such as an arm.

[0007] For example, in a case of maintaining the laminarization of the surface flow as in the above-described structure of the conventional technique, there is a problem that boundary layer separation is likely to occur, and the operation under a high-velocity water flow becomes difficult due to an increase in pressure drag.

[0008] An object of an aspect according to the present invention is to provide a robot capable of reducing fluid resistance.

[0009] In order to solve the above problem and achieve the object, the present invention adopts an aspect described below.

[0010] A robot according to an aspect of the present invention includes a power device configured to output power for an underwater operation, and a surface portion in which a dimple is formed.BRIEF DESCRIPTION OF THE DRAWINGS

[0011] FIG. 1 is a perspective view illustrating a constitution of a robot of an embodiment of the present invention;

[0012] FIG. 2 is a perspective view of a cover member forming a surface portion of the robot of the embodiment of the present invention;

[0013] FIG. 3 is a cross-sectional view illustrating a dimple of the surface portion of the robot of the embodiment of the present invention;

[0014] FIG. 4 is a diagram illustrating an example of a correspondence relationship between a fluid resistance coefficient and a Reynolds number in a surface portion of a cylindrical portion according to the robot of the embodiment of the present invention; and

[0015] FIG. 5 is a diagram illustrating an example of a correspondence relationship between a shape of the dimple, the fluid resistance coefficient, and the Reynolds number in the surface portion of the robot of the embodiment of the present invention.DETAILED DESCRIPTION OF THE INVENTION

[0016] Hereinafter, a robot according to an embodiment of the present invention will be described with reference to the accompanying drawings. A robot 10 of the embodiment is, for example, an unmanned undersea vehicle (UUV), an unmanned surface vehicle (USV) or the like, which is an unmanned moving body on and under water. For example, the UUV, which is an unmanned submersible, includes a remotely operated vehicle (ROV), an autonomous underwater vehicle (AUV) and the like. For example, the ROV includes a so-called underwater drone and the like.

[0017] FIG. 1 is a perspective view illustrating a constitution of the robot 10 of the embodiment.

[0018] Hereinafter, axial directions of an X-axis, a Y-axis, and a Z-axis orthogonal to one another in a three-dimensional space are directions parallel to the respective axes. For example, as illustrated in FIG. 1, the X-axis direction is parallel to a front-rear direction of the robot 10, the Y-axis direction is parallel to a left-right direction of the robot 10, and the Z-axis direction is parallel to an up-down direction of the robot 10. For example, a positive direction of the X-axis is a forward direction of the robot 10, a positive direction of the Y-axis is a leftward direction of the robot 10, and a positive direction of the Z-axis is an upward direction of the robot 10.

[0019] As illustrated in FIG. 1, the robot 10 includes a lower first portion 11 and an upper second portion 13 coupled to each other.

[0020] The first portion 11 includes, for example, a plurality of coupling members 21a and a frame member 21b forming a first frame F1. An outer shape of each of the plurality of coupling members 21a is, for example, a columnar shape extending in the up-down direction and the like. The plurality of coupling members 21a is fixed to, for example, corners and the like of the frame member 21b and coupled to the second portion 13 to be described later. An outer shape of the frame member 21b is, for example, a ladder shape having a rectangular frame shape and the like. The frame member 21b supports, for example, various devices mounted on the first portion 11.

[0021] The first portion 11 includes, for example, two mechanical arms 23, four first thrusters 25a and two second thrusters 25b, a camera system 27a and a sensor 27b, and one front side control unit 29a and two rear side control units 29b.

[0022] Proximal ends of the two mechanical arms 23 are fixed to left and right corners of a front portion of the frame member 21b. Each mechanical arm 23 is, for example, a manipulator, and includes a hinge (joint) driven by an actuator and a plurality of beams (links) connected by the hinge (joint). Each mechanical arm 23 includes, for example, an end effector (hand) 23a that is provided at a distal end thereof and performs various works such as gripping and moving of an object. Each mechanical arm 23 includes a power device 23b that outputs power for operation at the proximal end thereof. Each mechanical arm 23 is arranged, for example, on an inner side of left and right ends of the frame member 21b when stopping, and allows the distal end thereof to protrude outward (forward and the like) of the robot 10 when operating.

[0023] The four first thrusters 25a are arranged in such a manner that two of them are arranged left and right in each of the front portion and a rear portion of the frame member 21b, for example.

[0024] The two second thrusters 25b are arranged left and right in the center portion in the front-rear direction of the frame member 21b, for example.

[0025] Each first thruster 25a is a so-called azimuth thruster. Each first thruster 25a includes, for example, a support that rotates about a first rotation axis in the up-down direction, and a propeller that is supported by the support and rotates about a second rotation axis orthogonal to the first rotation axis. Each first thruster 25a generates thrust in a direction orthogonal to the up-down direction, for example.

[0026] Each second thruster 25b includes, for example, a propeller that rotates about a rotation axis inclined at an acute angle with respect to the up-down direction. Each second thruster 25b generates thrust in a direction at least including the up-down direction, for example.

[0027] The camera system 27a is arranged in the center portion in the left-right direction in the front portion of the frame member 21b, for example. The camera system 27a includes, for example, a camera that images the outside on the front side of the robot 10 and a plurality of lighting bodies that illuminates the outside on the front side of the robot 10.

[0028] The sensor 27b is arranged in a portion below the camera system 27a in the front portion of the frame member 21b, for example. The sensor 27b is, for example, a Doppler velocity log (DVL) and the like that detects a relative velocity on the basis of sound wave radiation and detection of a reflected wave and a scattered wave.

[0029] The one front side control unit 29a is arranged in a portion behind the camera system 27a in the front portion of the frame member 21b, for example.

[0030] The two rear side control units 29b are arranged left and right in the rear portion of the frame member 21b, for example.

[0031] Each of the control units 29a and 29b includes, for example, a box-shaped housing that seals the inside in a sealed state, and a power supply, an electronic control unit and the like arranged inside the housing. Each of the control units 29a and 29b controls, for example, an operation of each mechanical arm 23, each of the thrusters 25a and 25b, the camera system 27a, the sensor 27b, and a drive unit of the second portion 13 to be described later.

[0032] The second portion 13 includes a cover member 30, a second frame covered with the cover member 30, a buoyancy member, and the drive unit. The second portion 13 generates buoyancy by the buoyancy member arranged inside the cover member 30.

[0033] The cover member 30 has an outer shape in, for example, a rectangular box shape, and includes a surface on which a plurality of through holes for allowing the inside and the outside to communicate with each other is formed. The cover member 30 is fixed to the second frame.

[0034] For example, the second frame is fixed to the plurality of coupling members 21a of the first frame F1 and supports the cover member 30 and the drive unit.

[0035] The buoyancy member is moved by the drive unit inside the cover member 30 in order to change at least any of the center of buoyancy or the center of gravity of the robot 10 as a whole. The buoyancy member is moved to maintain, change or the like a posture of the robot 10, for example, when the robot 10 moves, when each mechanical arm 23 operates and the like.

[0036] The drive unit includes, for example, a power source and a transmission mechanism that transmits power output from the power source to the buoyancy member.

[0037] The robot 10 includes a surface portion S in which a dimple 41 having a predetermined shape is formed by covering a surface of a predetermined portion with a dimple cover member 40, for example. The predetermined portion is at least a portion in contact with a fluid such as water in water, and is, for example, a main body portion of the robot 10 and an exposed portion exposed from the main body portion. The main body portion of the robot 10 is, for example, a portion that is fixedly or stationarily provided in each of the first portion 11 and the second portion 13 and has a relatively large surface area in contact with the fluid such as water. The main body portion of the robot 10 is, for example, the first frame F1, each of the control units 29a and 29b, the cover member 30 and the like. The exposed portion of the robot 10 is, for example, a portion that is put into a motion state in each of the first portion 11 and the second portion 13 to be exposed outward, and has a relatively large surface area in contact with the fluid such as water. The exposed portion of the robot 10 is, for example, each mechanical arm 23 and the like.

[0038] FIG. 2 is a perspective view of the dimple cover member 40 forming the surface portion S of the robot 10 of the embodiment. FIG. 3 is a cross-sectional view illustrating the dimple 41 of the surface portion S of the robot 10 of the embodiment.

[0039] As illustrated in FIG. 2, an outer shape of the dimple cover member 40 is, for example, a cylindrical shape. The dimple cover member 40 includes, for example, a surface 40A formed by dispersing a plurality of dimples 41. An outer shape of a peripheral edge portion 41a forming each dimple 41 is, for example, a circular shape and the like. As illustrated in FIG. 3, each dimple 41 is formed of, for example, a concave surface 41A curved in a concave spherical shape and the like from the circular peripheral edge portion 41a in a thickness direction.

[0040] A shape of the surface 40A on which the plurality of dimples 41 is formed is, for example, a shape formed in such a manner that a predetermined velocity of a relative water flow in water corresponds to a Reynolds number Re indicating a supercritical region regarding a change in drag coefficient. The relative water flow includes, for example, a water flow due to an ocean current, a tidal current and the like with respect to the robot 10 in a stationary state, and a relative flow of water generated with respect to an appropriate portion by a motion such as movement and turning of the robot 10, an operation of each mechanical arm 23 or the like. FIG. 4 is a diagram illustrating an example of a correspondence relationship between a fluid resistance coefficient Cd and the Reynolds number Re in the surface portion S of the cylindrical portion according to the robot 10 of the embodiment.

[0041] As illustrated in FIG. 4, a critical Reynolds number Rec indicates, for example, a boundary between a critical region where the fluid resistance coefficient Cd that changes in a decreasing tendency with an increase in the velocity of the water flow (that is, an increase in the Reynolds number Re) becomes a substantially constant value and a supercritical region where the fluid resistance coefficient Cd becomes a value drastically decreased from the value in the critical region.

[0042] FIG. 5 is a diagram illustrating an example of a correspondence relationship between the shape of the dimple 41, the fluid resistance coefficient Cd, and the Reynolds number Re in the surface portion S of the robot 10 of the embodiment.

[0043] In the example illustrated in FIGS. 3 and 5, the shape of the dimple 41 is described by, for example, a ratio U (=k / h) between a depth k of the concave spherical surface 41A and a diameter h of the circular peripheral edge portion 41a. As illustrated in FIG. 5, the Reynolds number Re indicating the supercritical region changes according to the shape of the dimple 41. For example, as the ratio U (=k / h) between the depth k and the diameter h decreases, the Reynolds number Re indicating the supercritical region changes in an increasing tendency. For example, a first predetermined value U1 is smaller than a second predetermined value U2, the second predetermined value U2 is smaller than a third predetermined value U3, and the third predetermined value U3 is smaller than a fourth predetermined value U4.

[0044] For example, in a case where the diameter h of the dimple 41 is made constant, the Reynolds number Re indicating the supercritical region changes in an increasing tendency as the depth k of the dimple 41 decreases. As a result, the shape of the dimple 41 is set in such a manner that the predetermined velocity of the relative water flow assumed for the robot 10 corresponds to the Reynolds number Re indicating the supercritical region, whereby the fluid resistance coefficient Cd is effectively reduced.

[0045] For example, in a case where the predetermined velocity of the relative water flow assumed for the robot 10 corresponds to a first Reynolds number Re1 illustrated in FIG. 5, the shape of the dimple 41 is set in such a manner that the ratio U (=k / h) between the depth k and the diameter h becomes the first predetermined value U1.

[0046] For example, in a case where the predetermined velocity of the relative water flow assumed for the robot 10 corresponds to a second Reynolds number Re2 illustrated in FIG. 5, the shape of the dimple 41 is set in such a manner that the ratio U (=k / h) between the depth k and the diameter h becomes the second predetermined value U2.

[0047] A correspondence relationship between the predetermined velocity of the relative water flow assumed for the robot 10 and an optimum shape of the dimple 41 in the surface portion S may be obtained by, for example, an appropriate test and the like that reproduces an actual fluid flow field.

[0048] As described above, according to the robot 10 of the embodiment, by including the surface portion S in which the dimple 41 is formed, it becomes easy to generate a turbulent flow boundary layer, and by suppressing occurrence of boundary layer peeling, it is possible to suppress an increase in pressure drag and to facilitate operation under a condition that the velocity of the relative water flow becomes high. The condition that the velocity of the relative water flow becomes high may include, for example, a case where the velocity of the relative flow of water generated with respect to an appropriate portion along with the motion such as the movement and turning by the power of each of the thrusters 25a and 25b, the power device 23b and the like, the operation of each mechanical arm 23 or the like in addition to the water flow due to the ocean current, the tidal current and the like in the stationary state becomes high. For example, it is possible to accurately and appropriately maintain the stationary state or execute the motion such as the movement or turning under a high-velocity water flow, and it is possible to accurately and appropriately execute an operation of a movable member such as the mechanical arm.

[0049] Since the predetermined velocity of the relative water flow assumed for the robot 10 corresponds to the Reynolds number Re indicating the supercritical region, the drag coefficient (for example, the fluid resistance coefficient Cd) can be significantly reduced as compared with, for example, a case where the predetermined velocity corresponds to the critical region and the like.

[0050] The dimples 41 are formed on the surfaces of the portions where the velocity of the relative water flow is likely to increase, for example, the main body portion such as the first frame F1, each of the control units 29a and 29b, and the cover member 30, and the exposed portion such as each mechanical arm 23, whereby an increase in pressure drag can be effectively suppressed.

[0051] It is possible to effectively suppress the increase in pressure drag by forming the dimple 41 on the surface of the mechanical arm 23 on which it is difficult to reduce the pressure drag by a shape change due to a shape restriction in addition to the fact that the velocity of the relative water flow tends to increase because this easily expose outward of the robot 10.

[0052] Since the fluid resistance tends to increase in the second portion 13 where an increase in size is preferable for ease of control of the center of buoyancy and the center of gravity, an increase in pressure drag can be effectively suppressed by forming the dimple 41 on the surface of the second portion 13. By forming the dimple 41 on the surface of the second portion 13, it is possible to improve ease of control of the center of buoyancy and the center of gravity while suppressing an increase in fluid resistance accompanying an increase in size of the second portion 13.Modification

[0053] Hereinafter, a modification of the embodiment will be described. The same parts as those in the above-described embodiment are denoted by the same reference numbers, and the description thereof will be omitted or simplified.

[0054] In the embodiment described above, an outer shape of a dimple cover member 40 is a cylindrical shape, but the shape is not limited thereto. For example, the outer shape of the dimple cover member 40 may be another shape such as a sheet shape covering a surface of a predetermined portion of a robot 10.

[0055] In the embodiment described above, an outer shape of a peripheral edge portion 41a forming a dimple 41 is a circular shape, but the shape is not limited thereto. For example, the outer shape of the peripheral edge portion 41a may be another shape such as an elliptical shape, a rectangular shape, or a polygonal shape.

[0056] In the embodiment described above, an outer shape of a concave surface 41A forming the dimple 41 is a curved surface such as a spherical surface, but the shape is not limited thereto. For example, the outer shape of the concave surface 41A may be a bent surface such as a concave polyhedral surface.

[0057] In the above-described embodiment, a depth k is changed corresponding to a Reynolds number indicating a supercritical region out of the depth k of the concave spherical surface 41A describing the shape of the dimple 41 and a diameter h of the circular peripheral edge portion 41a, but there is no limitation, and the diameter h may be changed.

[0058] In the embodiment described above, the shape of the dimple 41 may be described by, for example, a size of the peripheral edge portion 41a of various shapes forming the dimple 41, a depth of the concave surface 41A of various shapes forming the dimple 41 and the like. For example, at least any one of the size of the peripheral edge portion 41a or the depth of the surface 41A may be set according to magnitude of a predetermined velocity (that is, a predetermined velocity of a relative water flow assumed for a robot 10) corresponding to a Reynolds number Re indicating the supercritical region. For example, as the predetermined velocity (that is, the predetermined velocity of the relative water flow assumed for the robot 10) corresponding to the Reynolds number Re indicating the supercritical region increases, at least any one of a change in an increasing tendency of the size of the peripheral edge portion 41a or a change in a decreasing tendency of the depth of the surface 41A may be set. This makes it possible to easily suppress an increase in pressure drag.

[0059] In the above-described embodiment, a shape of a surface portion S is a shape formed by dispersing a plurality of dimples 41, but the shape is not limited thereto. The shape of the surface portion S is only required to be at least a shape that suppresses an increase in pressure drag or fluid resistance. For example, in a case of the cylindrical dimple cover member 40 illustrated in FIG. 2, at least one annular groove shape or the like formed in a circumferential direction may be made a dimple.

[0060] In the above-described embodiment, the shape of the surface portion S is a shape formed by forming a plurality of dimples 41 of the same shape on the surface, but the shape is not limited thereto. For example, the dimples 41 having different shapes may be formed on a downstream side and an upstream side of the relative water flow. For example, the shape on the downstream side of the relative water flow out of the shape of the surface portion S may be a shape formed in such a manner that the predetermined velocity (that is, the predetermined velocity of the relative water flow assumed for the robot 10) that is relatively smaller corresponds to the Reynolds number Re indicating the supercritical region as compared with the shape on the upstream side.

[0061] In this case, since the velocity of the relative water flow with respect to the robot 10 tends to decrease on the downstream side of the relative water flow as compared with the upstream side, the increase in the pressure drag can be effectively suppressed by setting the shape of the surface portion S so that the smaller predetermined velocity corresponds to the Reynolds number Re indicating the supercritical region.

[0062] According to the above-described embodiment, the following configurations and advantageous effects can be achieved.

[0063] (1): The robot 10 includes a power device (e.g. the power device 23b, the first thruster 25a, the second thruster 25b) configured to output power for an underwater operation, and the surface portion S in which the dimple 41 is formed.

[0064] According to the configuration (1) described above, by including the surface portion S in which the dimple 41 is formed, it becomes easy to generate a turbulent flow boundary layer, and by changing a peeling occurrence point when a laminar flow peels, it is possible to suppress an increase in pressure drag and to facilitate operation under a condition that the velocity of the relative water flow becomes high. The condition that the velocity of the relative water flow becomes high may include, for example, a case where the velocity of the relative flow of water generated with respect to an appropriate portion along with motion such as movement and turning by the power of each of the thrusters 25a and 25b, the power device 23b and the like, an operation of each mechanical arm 23 or the like in addition to the water flow due to an ocean current, a tidal current and the like in a stationary state becomes high. For example, it is possible to accurately and appropriately maintain the stationary state or execute the motion such as the movement or turning under a high-velocity water flow, and it is possible to accurately and appropriately execute an operation of a movable member such as the mechanical arm 23.

[0065] (2): In the configuration (1) described above, a shape of the surface portion S may be a shape formed in such a manner that a predetermined velocity of a relative water flow in water corresponds to the Reynolds number Re indicating a supercritical region regarding a change in the fluid resistance coefficient Cd.

[0066] In a case of the configuration (2) described above, since the predetermined velocity of the relative water flow assumed for the robot 10 corresponds to the Reynolds number Re indicating the supercritical region, the fluid resistance coefficient Cd can be significantly reduced as compared with, for example, a case where the predetermined velocity corresponds to the critical region and the like.

[0067] (3): In the configuration (1) described above, a main body portion (e.g. the first frame F1, each of the control units 29a and 29b, the cover member 30), and an exposed portion (e.g. the mechanical arm 23) exposed from the main body portion are included, in which the surface portion may include a surface of each of the main body portion and the exposed portion.

[0068] In a case of the configuration (3) described above, the dimples 41 are formed on the surfaces of the main body portion (e.g. the first frame F1, each of the control units 29a and 29b, the cover member 30) and the exposed portion (e.g. each mechanical arm 23) where the velocity of the relative water flow is likely to increase, so that the increase in the pressure drag can be effectively suppressed.

[0069] (4): In the configuration (3) described above, the exposed portion may be the mechanical arm 23.

[0070] In a case of the configuration (4) described above, it is possible to effectively suppress the increase in pressure drag by forming the dimple 41 on the surface of the mechanical arm 23 on which it is difficult to reduce the pressure drag by a shape change due to a shape restriction in addition to the fact that the velocity of the relative water flow tends to increase because this easily expose outward of the robot 10.

[0071] (5): In the configuration (2) described above, a shape on a downstream side of a relative water flow out of the shape of the surface portion S may be a shape formed in such a manner that the predetermined velocity that is relatively smaller corresponds to the Reynolds number Re indicating the supercritical region as compared with a shape on an upstream side.

[0072] In a case of the configuration (5) described above, since the velocity of the relative water flow with respect to the robot 10 tends to decrease on the downstream side of the relative water flow as compared with the upstream side, the increase in the pressure drag can be effectively suppressed by setting the shape of the surface portion S so that the smaller predetermined velocity corresponds to the Reynolds number Re indicating the supercritical region.

[0073] (6): In the configuration (2) described above, at least any one of the diameter h of the peripheral edge portion 41a forming the dimple 41 or the depth k of the surface 41A forming the dimple 41 may be set according to a magnitude of the predetermined velocity, and at least any one of a change in the diameter h of the peripheral edge portion 41a in an increasing tendency or a change in the depth k in a decreasing tendency may be set as the predetermined velocity corresponding to the Reynolds number Re indicating the supercritical region increases.

[0074] In a case of the configuration (6) described above, at least any one of the diameter h of the peripheral edge portion 41a or the depth k of the concave surface 41A regarding the shape of the dimple 41 is set according to a predetermined velocity of the relative water flow assumed for the robot 10, so that the increase in the pressure drag can be easily suppressed.

[0075] (7): In any one of the configurations (1) to (5) described above, the second portion 13 that generates buoyancy may be provided, and the surface portion S may include a surface of the second portion 13.

[0076] In a case of the configuration (7) described above, since the fluid resistance tends to increase in the second portion 13 where an increase in size is preferable for ease of control of the center of buoyancy and the center of gravity, an increase in pressure drag can be effectively suppressed by forming the dimple 41 on the surface of the second portion 13. By forming the dimple 41 on the surface of the second portion 13, it is possible to improve ease of control of the center of buoyancy and the center of gravity while suppressing an increase in fluid resistance accompanying an increase in size of the second portion 13.

[0077] The embodiment of the present invention has been presented by way of example, and there is no intention of limiting the scope of the invention. These embodiments can be implemented in various other forms, and various omissions, substitutions, and changes can be made without departing from the gist of the invention. These embodiments and modifications are included in the scope and gist of the invention, and are also included in the invention described in claims and the equivalent scope thereof.

Claims

1. A robot comprising:a power device configured to output power for an underwater operation; anda surface portion in which a dimple is formed.

2. The robot according to claim 1,wherein a shape of the surface portion is a shape formed in such a manner that a predetermined velocity of a relative water flow in water corresponds to a Reynolds number indicating a supercritical region regarding a change in drag coefficient.

3. The robot according to claim 1, comprising a main body portion, and an exposed portion exposed from the main body portion,wherein the surface portion includes a surface of each of the main body portion and the exposed portion.

4. The robot according to claim 3,wherein the exposed portion is a mechanical arm.

5. The robot according to claim 2,wherein a shape on a downstream side of a relative water flow out of the shape of the surface portion is a shape formed in such a manner that the predetermined velocity that is relatively smaller corresponds to the Reynolds number indicating the supercritical region as compared with a shape on an upstream side.

6. The robot according to claim 2, whereinat least any one of a size of a peripheral edge portion forming the dimple or a depth of a surface forming the dimple is set according to a magnitude of the predetermined velocity, andat least any one of a change in the size of the peripheral edge portion in an increasing tendency or a change in the depth in a decreasing tendency is set as the predetermined velocity corresponding to the Reynolds number indicating the supercritical region increases.

7. The robot according to claim 1, comprising a buoyancy portion that generates buoyancy,wherein the surface portion includes a surface of the buoyancy portion.

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