Patent Application
20210002847
The present invention relates to a strength test method for an anchor installed underwater for testing whether an anchor for various mooring targets, such as floating photovoltaic power systems, aquaculture cages, floating piers, and water sports facilities, has an intended tensile strength.
A method for inspecting the installation state of an anchor is described in Patent Literature 1.
This inspection method includes lifting a rod of an installed anchor with a hollow hydraulic jack and determining whether a load indicated by a hydraulic gauge reaches an intended resistance against pulling. The hydraulic jack is included in a lifting structure placed at the water bottom under a floating platform.
The method uses large equipment for inspection, including the lifting structure placed at the water bottom, in addition to the floating platform, and further a holder for the hollow hydraulic jack in the lifting structure.
Patent Literature 1: Japanese Patent No. 6252882
One or more aspects of the present invention are directed to a simplified structure for inspecting an anchor.
A strength test method for an anchor installed underwater includes applying, to an anchor installed underwater, a lifting force from above a floating body floating on a water surface to submerge the floating body into water, and setting a volume of submergence by which the floating body is submerged to a value to produce a lifting force corresponding to a predetermined installation strength and determining whether the anchor is immovable.
The volume by which the floating body is submerged to produce the lifting force corresponding to the predetermined installation strength is calculated based on the buoyancy acting on the floating body.
In the structure, the anchor is pulled from above the floating body to submerge a portion of the floating body exposed above the water surface into the water and to apply the lifting force corresponding to the predetermined installation strength to the anchor. When the anchor remains installed, the anchor is determined to have the installation strength. When the anchor fails to remain installed, the anchor is determined to lack the strength. The anchor lacking the strength is pulled up, thus readily moving the floating body and revealing insufficient installation of the anchor.
The method according to the above aspect of the present invention enables the inspection with a simple operation of pulling the installed anchor from above the floating body to submerge the floating body by a predetermined volume into the water. The structure simply includes at least the floating body and a device for determining the volume by which the floating body is submerged.
One embodiment of the present invention will now be described with reference to the drawings.
The test method uses the floating body 13. The floating body 13 floats on the water. More specifically, the floating body 13 has a bottom surface submerged in the water and an upper portion including the upper surface exposed above the water surface. When the predetermined pulling force described above is applied to the anchor 11 from above, the floating body 13 with buoyancy does not entirely become submerged in the water.
The floating body 13 includes gauges 33 to indicate the depth or the volume by which the floating body 13 is submerged in the water. The gauges 33 indicating the depth of submergence can be simpler.
The gauges 33 shown in
Referring now to
The buoyancy acting on the floating body 13 is ρVg (N), where g (m/s2) is a gravitational acceleration, ρ (kg/m3) is the density of water, and V (m3) is the volume of a portion of the floating body 13 submerged below the water surface 12.
The floating body 13 having a mass m (kg) is also under a gravitational force with a magnitude mg (N), which is balanced with the buoyancy (ρVg=mg). Thus, the volume V of the portion submerged in the water is
V=m/ρ,
indicating that the floating body 13 is submerged in the water by m/ρ (m3).
Buoyancy is proportional to the volume of a submerged portion in the water. Thus, a volume V1 (m3) by which the floating body 13 is to be submerged to produce a lifting force corresponding to an intended installation strength is obtained. With this volume of submergence and the dimensions of the floating body 13, a depth H of submergence for the floating body 13 is obtained as, for example, 10 cm for producing a lifting force of 2 t (ton).
For the floating body 13, a machine is used to pull the anchor 11 installed underwater. As indicated by the imaginary lines in
As shown in
The installation strength test for the anchor 11 using the floating body 13 and the construction machine 15 is performed consecutively to the installation of the anchor 11.
More specifically, the construction machine 15 is placed on the floating body 13 used as the working platform 17, and the floating body 13 is towed to a site on the water under which the anchor is to be installed. At the site, the construction machine 15 holds the upper end of the anchor 11 and drives the anchor 11 into a water bottom 18 as shown in
While holding the upper end of the anchor 11, the construction machine 15 subsequently pulls the anchor 11. The anchor 11 driven into the water bottom 18 is not easily pulled out. As indicated by the solid lines in
The volume to be submerged by pulling is set to a value for producing the predetermined lifting force described above. The volume by which the floating body 13 is submerged is determined with the gauges 33 included in the floating body 13.
More specifically, the position of the water surface 12 before the submergence is determined with the scale plates 34 serving as the gauges 33. For example, when a depth of submergence of 10 cm produces a lifting force of 2 t, which corresponds to the intended installation strength, a lifting force is applied to the anchor 11 until the floating body 13 is submerged 10 cm deeper from the yet submerged water surface 12. The scale plates 34 may be checked from above the floating body 13 or may be checked by a diver entering the water for installing the anchor 11.
Although the floating body 13 may be inclined by a lifting force applied to the anchor 11, the scale plates 34, having the scale marks at the four corners indicating the depth of submergence, allow determination of the submergence depth at each corner. This allows easy calculation of the predetermined volume of submergence.
After the depth of submergence reaches a predetermined depth, the floating body 13 retains the state for a predetermined duration. In other words, the floating body 13 retains the state of being submerged by the predetermined volume. The duration is determined as appropriate in accordance with, for example, the use of the anchor 11, an intended installation strength, and an underwater environment. The duration is not excessively long and may be several to ten and several minutes, or more specifically about five minutes, to demonstrate the intended installation strength.
When the anchor 11 remains immovable after being pulled for the duration, the anchor 11 passes the test. When the anchor 11 is lifted, the anchor 11 fails the test and is reinstalled immediately. The anchor 11 installed improperly is lifted, allowing the diver working underwater to notice the movement. The operator operating the construction machine 15 also readily senses the movement, rather than with the digital numbers indicated on the machine.
As described above, the inspection includes the simple operation of pulling the anchor 11 from above the floating body 13 to submerge the floating body 13 in the water by a predetermined volume. The volume by which the floating body 13 is submerged is determined with the gauges 33 included in the floating body 13. The operation includes simply pulling the anchor 11 while checking the gauges 33, and is easy.
The operation uses the floating body 13 including the gauges 33. The anchor 11 is pulled with the construction machine 15 as described above. The floating body 13 eliminates a fixed, dedicated machine (not shown) for pulling the anchor 11. The floating body 13 can thus have a simpler structure, simplifying the entire equipment for the test.
In particular, the floating body 13 also serves as the working platform 17 for installing the anchor 11, further simplifying the entire equipment.
The installation of the anchor 11 and the test on the installation strength are performed consecutively. This increases the operation efficiency, and provides higher reliability in determining the installation strength than in the inspection performed a predetermined time after the installation.
The reliability is further increased by retaining the submerged state of the floating body 13 for a duration in the installation strength test, after simply submerging the floating body 13 by the predetermined volume.
The structure described above is one example for implementing the present invention. The present invention is not limited to the structure described above and may include other structures.
The gauges 33 may include, rather than scale marks for indicating the depth of submergence as described above, other components including a float on the water surface 12 to allow determination of the depth of the actual submergence with a sense rather than with scale marks. The gauges 33 may also include a member that indicates the portion submerged in the water by changing its appearance.
This application is a continuation application of International Patent Application No. PCT/JP2018/016556 filed on Apr. 24, 2018, the entire content of which is incorporated by reference.
| Number | Date | Country | |
|---|---|---|---|
| Parent | PCT/JP2018/016556 | Apr 2018 | US |
| Child | 17024185 | US |
