Patent Grant
8496410
Embedding rigid objects into underwater substrates is of interest in a wide range of applications. Currently available technologies (e.g., suction caisson, concrete blocks, propellant anchor, helical anchor, drag anchor, vibratory anchor, and pile) are relatively heavy and hard to transport and/or require considerable amount of energy and power for penetration of substrate and/or extraction of the penetration device. Specifically, suction caissons require large structures of orders of tens of meters and are designed to pump water out of the vessel and needs to be extracted by pressurizing the inside cavity. Similarly, Concrete blocks rely heavily on weight for anchoring force and as such are very difficult to transport. Concrete blocks are also difficult to extract once sunken into a substrate. Propellant anchors require high levels of energy to penetrate substrates and are not easily extracted. The propellant anchors also require a secondary device for insertion. Helical anchors require a counteraction torque against substrate to insert and require a torque for extraction as well. Helical anchors also require a secondary device to set in place. Drag anchors require dragging and a secondary device (e.g., ship) to set and also require a vertical pulling force for extraction. Vibratory anchors require a vibrating mass above the substrate surface and preferably above the water surface to avoid damping. The vibratory anchor also requires a pulling force for extraction. Piles require a secondary hammer system to drive into a substrate and also large vertical forces for extraction.
Fluidizing a substrate reduces burrowing resistance and facilitates penetration of a rigid body. Most existing methods in the literature rely on pumping water into substrates in order to fluidize substrates and facilitate penetration. However, pumping water into substrates is expensive and requires significant amount of energy. Therefore, it would be desirable to fluidize substrates without insertion of water.
A method or corresponding apparatus in an example embodiment of the present invention relates to penetrating a particulate substrate with a man-made or artificial vessel. In one preferred embodiment, the apparatus includes at least one vessel and a displacement module coupled with the vessel. The actuation of the displacement module fluidizes the particulate substrate proximate to the vessel and thereby reduces resistance of the particulate substrate to movement of the vessel and causes further penetration of the apparatus through the particulate substrate. The actuation of the displacement module fluidizes the particulate substrate by drawing water in or above the particulate substrate towards the vessel.
The displacement module may fluidize the particulate substrate proximate to the vessel by contracting from a first position to a second position and expanding back to the first position. The displacement module may fluidize the particulate substrate proximate to the vessel by radial or spherical expansion and contraction of the vessel. In one embodiment, the displacement module contracts and expands between the first and the second positions at predetermined time intervals and includes a predetermined time lapse between successive expansions of the vessel.
The displacement module may actuate in a horizontal direction, a vertical direction, or combination thereof, and may include a piezoelectric actuator such that actuations of the piezoelectric actuator fluidizes the particulate substrate proximate to the vessel.
Another example embodiment of the present invention relates to a method for penetrating a particulate substrate that fluidizes the particulate substrate proximate to a lower portion of an artificial vessel and fluidizes particulate substrate proximate to a side portion of the vessel. In this embodiment, the vessel will move into space occupied by the fluidized substrate at the lower portion of displacing fluidized substrate from the lower portion to a space proximate the side portion thereby penetrating the particulate substrate.
The fluidization of the particulate substrate proximate to the lower portion of the artificial vessel may be induced prior to fluidization at the side portion of the vessel. The fluidization of the particulate substrate proximate to the lower portion of the artificial vessel may be induced simultaneously with fluidization at the side portion of the vessel.
Yet another example embodiment of the present invention relates to another method and a corresponding apparatus for penetrating a particulate substrate. In one preferred embodiment, the apparatus includes a rod and an end-effector rigidly linked to the rod. The end-effector is moveable by retraction of the rod from a first position to a second position and includes at least one arm and a displacement module at the arm that is coupled with the arm. The actuation of the displacement module fluidizes the particulate substrate proximate to the arm. Specifically, retraction of the end-effector from the first position to the second position fluidizes the particulate substrate in a path of penetration and subsequent actuation of the displacement module fluidizes the particulate substrate adjacent the path of penetration. Fluidizing the particulate substrate adjacent the path of penetration reduces the resistance of the particulate substrate to movement of the end-effector and causes penetration of the apparatus through the particulate substrate.
The end-effector may include a plurality of arms that move in relation to each other in a direction normal to the path of movement of the end-effector from the first position to the second position. The end-effector may include a wedge between the arms, whereby movement of the wedge parallel to the path of movement from the first to the second position causes movement of the arms relative to each other in a direction normal to the path of the movement of the end-effector from the first position to the second position. The wedge may be linked to the rod.
Yet another embodiment may include a second end-effector such that the end-effectors are linked by the rod, and at least one of the end-effectors causes movement of the rod to thereby cause movement of the lower of the end-effectors between the first and second positions. The first and second positions may be distinct relative distances between the end-effectors.
Still another example embodiment of the present invention relates to a method for penetrating a particulate substrate that pulls a body from a first position in a particulate substrate to a second position and thereby fluidizes a portion of the particulate substrate proximate to a lower portion of the body. In this embodiment particulate substrate is fluidized proximate to a side portion of the vessel and thereby generates a volume into which fluidized particulate can be directed. Movement of the body into the space occupied by the fluidized particulate substrate proximate to the lower portion of the body directs the fluidized particulate substrate to the side portion of the vessel, thereby penetrating the particulate substrate.
The fluidization of the particulate substrate proximate to the side of the body may be caused by mechanical action. The mechanical action may be a change in diameter of the body in a direction normal to the path of flow of penetration of the particulate substrate.
The example embodiment may push the body into the space occupied by the fluidized particulate proximate the lower portion of the body to thereby displace the fluidized particulate substrate and penetrate the particulate substrate.
The present invention has many advantages. The method and apparatus of the invention can be more efficient than other methods of penetrating particulate substrates and has many applications, such as prospecting for natural resources, environmental remediation and clean up, military applications such as landmine detection, creation of low power anchors for submerged or floating systems, reversible and dynamic anchors for applications such from underwater robot tethering and oil rig mooring, tool transport in oil wells, and design of neutralizations systems for underwater mines.
The present invention can yield a power-law relationship between digging energy and depth that approximates ideal. As such, the apparatus provides exponentially higher energy efficiency than other conventional burrowing methods and nearly depth-independent drag resistance.
The foregoing will be apparent from the following more particular description of example embodiments of the invention, as illustrated in the accompanying drawings in which like reference characters refer to the same parts throughout the different views. The drawings are not necessarily to scale, emphasis instead being placed upon illustrating embodiments of the present invention.
a illustrates the relationship between optimized soil deformation energy and depth for the three digging methods.
b demonstrates the power law relationship for up, in, down, and out burrowing according to an example embodiment of the present invention.
c and 3d demonstrate the power law relationship for vertical and horizontal burrowing respectively.
A description of example embodiments of the invention follows.
One example embodiment of the present invention relates to a low-power, lightweight device for burrowing through underwater particulate substrates. The example embodiment utilizes volume contraction and localized fluidization to efficiently move through particulate substrates. The example embodiment may be used to generate compact, lightweight, low-energy, reversible, and dynamic burrowing and anchoring systems for use in under water applications.
The apparatus 100 includes a power source (not shown) compatible with marine environments and as such it avoids wall effects caused by a container and captures the peculiarities of real soil with heterogeneous composition and the presence of organic matter.
In the present example embodiment, the apparatus 100 includes an 80 cubic foot scuba tank (not shown). The scuba tank contains about one-quarter the energy of a standard 12 volt 35 Ah lead acid car battery and functions as the main power source for the apparatus.
The Apparatus 100 employs an end-effector with a leading tip 170 and at least one arm 105a, 105b to dig into soil. In some embodiments, the end-effector may include a plurality of arms that move in relation to each other in a direction normal to the path of movement of the end-effector from the first position to the second position. In the present embodiment, the end-effector includes two arms 105a, 105b. In the present embodiment, the arms 105a, 105b of end-effector are 9.97 centimeters long and 1.52 centimeters wide. The motion of the end-effector also includes two degrees of freedom, namely vertical and horizontal motions.
The horizontal motions of the end-effector, in one embodiment, occur at predetermined time intervals and for predetermined distances. In one example embodiment, the horizontal motions of the end-effector displace the arm(s) of the end-effector about 6.4 millimeters.
The horizontal motion of the arm(s) of the end-effector are accomplished using a displacement module 160. For example, in the example embodiment shown in
The apparatus also includes an inner rod 110 that is used to actuate horizontal movements. The inner rod 110 is housed within an outer rod 120 that is used to move the end-effector vertically, providing a compact coupling to the actuation and measurement systems of the apparatus. In some embodiments, the end-effector is surrounded by a neoprene boot 150 to prevent soil particles from entering the mechanism.
In some embodiments, the end-effector may be made from alloy 932 (SAE 660) bearing bronze and 440C stainless steel. These materials are saltwater compatible and have a low coefficient of sliding friction when lubricated. The dynamic coefficient of friction within one embodiment of the mechanism is about 0.173 with about 0.013 standard deviation under horizontal loads ranging from about 13.34 to about 83.74. Silicon oil may be used as a lubricant since it does not get absorbed by the neoprene boot.
In one embodiment, the wedge angle is about 7.13 degrees. This geometry yields a relatively high transmission ratio of about 1.55, with a maximum of about 1.83 and minimum of about 1.33 corresponding to friction measurements. The corresponding efficiency is about 39% with a minimum of about 33% and a maximum of about 46%. This level of efficiency is tolerable: packaging size, jam-free operation, and the ability to deterministically calculate lost energy outweigh the need for high efficiency. A maximum of about 60% can be achieved using a similar wedge design with the same materials and a wedge angle of about 29°.
The top nut 130 provides a connection to the outer rod 120 that moves the apparatus 100 in vertical directions. The top nut 130 also prevents the arms 105a, 105b from moving vertically relative to the top nut 130.
Pressure is regulated down from the scuba tank (not shown) to four independent regulators, one for each piston inlet. Air pressure delivered to the pistons 210,220 is measured by a transducer (not shown) at each input port. Displacements of the lower 220 and upper 210 pistons are measured by a string potentiometer (not shown) and an integrated linear potentiometer (not shown), respectively. Sensor excitation, data acquisition, and control of the solenoid valves that send air to the pistons are managed by a Universal Serial Bus (USB) Data Acquisition System (DAQ) device. Power to the data acquisition system is provided by the USB, and power to the solenoid valves is provided by two small onboard lead acid batteries.
The overall energy expended in soil deformation while burrowing is device-dependent and may be calculated by accounting for input energy minus all of the other losses in the system.
For the up and down motion of the apparatus, the energy lost to soil deformation during one stroke is:
ESoil=Ein−EFriction−EPotential.
The energy transferred to the soil during the horizontal motions is:
ESoil=η(Ein−EFriction−EPotential)−EBoot,
where η denotes the efficiency of the apparatus.
The apparatus was tested in a substrate composed of one millimeter soda lime glass beads. Three different kinematics motions were trialed in order to form energetic comparisons between burrowing methods:
1) vertically moving the end-effector;
2) moving the end-effector horizontally and letting it fall under gravity; and
3) carrying out a combination of vertical and horizontal motions.
The minimum energy required to push straight down may be found by measuring the minimum pressure required to fully submerge the end-effector. The minimum energy required for the method involving only horizontal movements may be determined by minimizing the pressure required to open and close the end-effector at full depth. The end-effector was arranged to open and close in 6.4 millimeter strokes.
The minimum energy required to dig using the full up, in, down, and out motions may be optimized by generating a population of parameters (e.g., upward stroke time and downward stroke distance) and selecting a set of parameters that display the best minimum fitness and using the selected set of parameters to approximate the evolution of a biological system. In order to determine the best minimum fitness, a product of the energy expended per unit depth and the exponent of the energy versus depth power law relationship is employed.
a illustrates the relationship between optimized soil deformation energy and depth for the three digging methods. As shown in
up motion: 0.032 seconds
in motion: 6.5 millimeters
down motion: 5 centimeters, and
out motion: 6.5 millimeters.
The mean coefficient of friction in the end effector mechanism was used to generate the curves shown in
b demonstrates the power law relationship for a non-limiting example embodiment of this embodiment of this invention that operates based on up, in, down, and out burrowing.
As shown in
c demonstrates the power law relationship for vertical movement 315c versus the horizontal and vertical motions 310c. The slope for vertical movements only 315c initially was at n=1.47 but increased to n=1.79 over the last 5 centimeters. This is very close to the expected value of n=2. The change in slope may be due to soil surface effects, as displacement of the apparatus was limited to 14 centimeters.
d illustrates that the in/out-only motion 320d provides no energetic benefits over straight vertical movement 315d, with the slope increasing to n=1.70 over the last 5 centimeters.
Thus, by employing horizontal and vertical motions the apparatus achieves considerable drag reduction.
In operation, actuation of the displacement module fluidizes the particulate substrate proximate 402 to the vessel and reduces resistance of the particulate substrate to movement of the vessel and causes further penetration of the vessel 410 through the particulate substrate 402. Specifically, while placed at a position (e.g., Position A 440A) within the particulate substrate 402, the displacement module fluidizes the particulate substrate proximate to the vessel by contracting from a first position 440-A to a second position 440-B, displacing downwards to a new position 440-C within the particulate substrate 402 (e.g., Position C 440-C), and expanding 440-D back to the first position. By repeating its expansions and contraction, the vessel 410 fluidizes the substrate 402 around itself and thereby weakens the particulate substrate 402. Once the particulate substrate 402 is weakened, the vessel is pulled down to a new position in the direction of penetration (e.g., position C 440-C and position D 440-D) under the effect of gravity. In some embodiments, the displacement module includes a piezoelectric actuator, whereby actuation of the piezoelectric actuator fluidizes the particulate substrate 402 proximate to the vessel.
In the example embodiment 600 illustrated in
The teachings of all patents, published applications and references cited herein are incorporated by reference in their entirety.
While this invention has been particularly shown and described with references to example embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the scope of the invention encompassed by the appended claims.
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| Number | Date | Country | |
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| 20100300752 A1 | Dec 2010 | US |
