Simulation method and device for wave load centrifugal test of large-diameter thin-walled cylindrical structure

Abstract

The application provides a simulation method and device for wave load centrifugal test of large-diameter thin-wall cylindrical structure, which comprises the following steps: preparing a scale model of large-diameter thin-wall cylindrical structure and fixing the scale model in a simulated foundation in a model box; the scale model divides the internal space of the model box into two mutually isolated spaces, which are respectively used as the sea side and the land side of the scale model; water is injected into the sea side and the land side of the scale model and the water levels of the two sides are consistent; the centrifuge is operated to make the model box in a supergravity environment; water is slowly injected into the land side of the scale model in the model box until the design height, then the water injection is stopped and the centrifuge is closed, and the total rotational moment and the total sliding force generated by the height difference of the water levels of the sea side and the land side are used to simulate the wave load and the corresponding load value generated by the static water level difference on the structure. The application adjusts the height difference of the water levels of the sea side and the land side of the structure to simulate the original wave load size and the torque effect of the wave load on the structure, and is especially suitable for curved surface structures with small thickness and low rigidity.

Description

Technical Field

[0001] This invention belongs to the field of soil mechanics testing technology, specifically relating to a method and apparatus for simulating wave load centrifugal tests on large-diameter thin-walled cylindrical structures. Background Technology

[0002] Large-diameter thin-walled cylindrical structures have been widely used in projects such as wharves, breakwaters, revetments, and cofferdams due to their advantages such as good overall performance, small amount of work required for installation on water, short construction time, strong seismic performance, and relatively low cost.

[0003] Large-diameter thin-walled cylindrical structures primarily bear lateral wave loads, which can be characterized by wave pressure and wave suction at wave crests or troughs under various most unfavorable conditions. Currently, centrifugal model tests typically employ two wave load simulation methods: one uses a cyclic reciprocating actuation device for equivalent simulation, suitable for waves with low heights, as the wave pressure and suction loads acting on the structure are relatively small, making the test easy to implement; however, for waves with very high heights, the wave pressure and suction loads acting on the structure are enormous, requiring significant investment and effort to develop more powerful cyclic reciprocating actuation devices, making this method time-consuming and labor-intensive. The second method uses concentrated force loading to simulate wave loads, but this method is only suitable for vertical structures with large wall thickness and high stiffness. Large-diameter thin-walled cylindrical structures are characterized by small thickness, low stiffness, and curved, bottomless surfaces, making the above wave load simulation methods infeasible. To address these issues, this invention proposes a centrifugal wave load simulation method suitable for large-diameter thin-walled cylindrical structures. Summary of the Invention

[0004] The purpose of this invention is to address the shortcomings of the prior art by providing a method and apparatus for simulating wave load centrifugal tests on large-diameter thin-walled cylindrical structures. This method and apparatus are particularly suitable for curved structures with small thickness and low stiffness.

[0005] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0006] A method for simulating wave load centrifugal tests on large-diameter thin-walled cylindrical structures includes:

[0007] A scaled-down model of a large-diameter thin-walled cylindrical structure was prepared and fixed in a simulated foundation inside a model box. The scaled-down model divided the internal space of the model box into two isolated spaces, which served as the sea side and land side of the scaled-down model, respectively.

[0008] Water is injected into the seaside and landside of the scaled-down model to make the water levels on both sides equal;

[0009] Run the centrifuge to subject the model box to a hypergravity environment;

[0010] Slowly fill the land side of the scaled-down model inside the model box with water until the design height is reached, then stop filling the water and turn off the centrifuge. Utilize the total rotational torque and total sliding force generated by the water level difference between the land and sea sides to generate equivalent wave loads and static water level differences to the corresponding load values ​​generated on the structure.

[0011] As a preferred embodiment, the water injection rate is such that the water level rise rate is less than 2 mm / min. Slow water injection allows for full observation of the structural internal forces and overall displacement changes during the water injection process (i.e., the load application process). If the water is added too quickly, excess water may not have enough time to drain, causing the structure to be subjected to a load exceeding the design value and affecting structural stability.

[0012] In a preferred embodiment, the simulated foundation is prepared by layering soil samples from the engineering site. Specifically, soil samples are collected from the engineering site, transported to the laboratory, impurities are removed, and the soil is prepared in layers in a special test model box. Once the soil strength reaches the design value, the pre-processed large-diameter thin-walled cylindrical scaled-down model is placed in the designated position.

[0013] Another object of the present invention is to provide a wave load centrifugal test simulation device for a large-diameter thin-walled cylindrical structure used in the above method, including a model box, a simulated foundation, a scaled-down model, a land-side overflow pipe, a sea-side overflow pipe, and a pore pressure sensor;

[0014] The simulated foundation is prepared in layers according to soil control indicators and is located at the bottom of the model box. The scaled model is fixed in the simulated foundation inside the model box, and the internal space of the model box is divided into two mutually isolated spaces, which serve as the sea side and land side of the scaled model, respectively.

[0015] The landside overflow pipe and the seaside overflow pipe are fixed to the corresponding model box walls on the landside and seaside, respectively, to control the water level on the landside and seaside; the overflow outlets of the landside overflow pipe and the seaside overflow pipe are adjusted according to the required water level changes;

[0016] Pore ​​pressure sensors are placed on the simulated foundation surfaces on the sea side and land side to measure the water level on both sides.

[0017] In a preferred embodiment, the heights of the landside overflow pipe and the seaside overflow pipe are determined according to the design water level required by the project. The height of the overflow hole of the seaside overflow pipe is lower than the design water level at sea, while the height of the overflow hole of the landside overflow pipe is higher than the design water level at land.

[0018] In one preferred embodiment, the gaps between the scaled-down model and the two sides of the model box along the length direction are filled with bentonite balls for seepage prevention.

[0019] In a preferred embodiment, aluminum alloy tubes are inserted into both sides of the bentonite ball for guidance.

[0020] In a preferred embodiment, the large-diameter thin-walled cylindrical model, after being scaled down by conversion based on the similarity rate of the centrifugal model test, has a thickness of less than 1 mm and a diameter of less than 300 mm.

[0021] In a preferred embodiment, the model box is rectangular in shape, with a net length of less than 1000 mm, a width of less than 350 mm, and a height of less than 450 mm. These dimensions can effectively reduce the influence of boundary effects in centrifugal model tests.

[0022] As a preferred implementation, the distance between the two sides of the model box and the outermost part of the cylindrical model along the length of the model box is no more than 10mm. If the size is too large, it will not be conducive to the seepage prevention on both sides.

[0023] In one preferred embodiment, bentonite balls are placed in the gaps between the two sides of the model box along the length direction and the cylindrical model for waterproofing. Aluminum alloy tubes are inserted into both sides of the bentonite balls so that the bentonite balls remain upright along the height direction of the cylindrical model after absorbing water and expanding.

[0024] In a preferred embodiment, the bentonite ball has a diameter of less than 3 mm, the aluminum alloy tube has a diameter of less than 15 mm, and the height is less than 200 mm. If the bentonite ball is too large, the gap between the bentonite balls will be too large, which is not conducive to seepage prevention.

[0025] Compared with the prior art, the technical solution of the present invention has the following beneficial effects:

[0026] The wave load centrifugal test simulation method and apparatus for large-diameter thin-walled cylindrical structures provided by this invention can adjust the water level on the sea side and land side of the large cylindrical structure according to the specific test requirements. By slowly injecting water into the model box in a hypergravity environment, an equivalent lateral sliding force and an equivalent rotational torque can be generated, objectively restoring the sliding and rotational effects of the prototype wave load on the structure. It is especially suitable for curved surface structures with small thickness and low stiffness. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of a wave load centrifugal test simulation method for a large-diameter thin-walled cylindrical structure according to an embodiment of the present invention;

[0028] Figure 2 This is a model layout diagram in the method of an embodiment of the present invention;

[0029] In the diagram: 1. Model box, 2. Model foundation, 3. Scale model, 4. Landside overflow pipe, 5. Seaside overflow pipe, 6. Pore pressure sensor. Implementation

[0030] The technical solution of the present invention will be described in detail below.

[0031] This invention provides a method and apparatus for simulating wave load centrifugal tests on large-diameter thin-walled cylindrical structures. The method includes the following steps:

[0032] Step 10) Prepare a scaled-down model 3 of the actual large-diameter thin-walled cylindrical structure in the dedicated model box 1;

[0033] Specifically, it includes:

[0034] Soil samples were collected from the project site, transported to the laboratory, and after impurities were removed, prepared in layers in a dedicated test model box 1. Once the model foundation 2 reached its design strength, the pre-fabricated large-diameter thin-walled cylindrical scaled-down model 3 was placed in the designated position, and medium-coarse sand was backfilled inside the cylinder. When constructing model foundation 2, the compaction of sandy soil was controlled, while the undrained strength index was used for soft clay soil. The soil layer thickness and the wall thickness, diameter, and height of the large-diameter thin-walled cylindrical scaled-down model 3 were constructed based on the similarity law of geotechnical centrifuge model tests. The prepared scaled-down model is shown below. Figure 2 As shown.

[0035] In this preferred embodiment, the scaled-down model 3 used has a thickness of less than 1 mm and a diameter of less than 300 mm, and belongs to a large-diameter thin-walled cylindrical structure.

[0036] Preferably, in this embodiment, the distance between the two sides of the model box 1 along the length direction and the outermost side of the scaled model 3 is no more than 10mm. Bentonite balls are placed in the gap between the side wall of the model box 1 and the scaled model 3 for waterproofing. The diameter of the bentonite balls is less than 3mm. Aluminum alloy tubes with a diameter of less than 15mm and a height of less than 200mm are inserted into both sides of the bentonite balls. This ensures that the bentonite balls remain upright along the height direction of the model cylinder 3 after absorbing water and expanding, thus preventing the bentonite column from tipping over when the centrifuge is running at high speed.

[0037] Step 20) Adjust the water level height on both sides of the structure according to the similarity law of the centrifugal model and the wave load conditions; the rotational torque and sliding force generated by the newly determined water level difference on both sides of the structure are equivalent to the corresponding load values ​​generated by the original wave load and the static water level difference on the structure.

[0038] Specifically, the design water level is determined according to the project requirements, and the height of the overflow holes on both the sea and land sides of the structure is adjusted based on the design value. The height of the overflow hole on the sea side is lower than the design water level on the sea side, and the height of the overflow hole on the land side is higher than the design water level on the land side.

[0039] Step 30) Centrifuge test on scaled model 3. During the operation of the centrifuge, water is slowly added to the land side of the structure in model box 1 to the design height to complete the wave load simulation.

[0040] Specifically, landside overflow pipe 4 and seaside overflow pipe 5 are respectively installed on the side plate in the width direction of model box 1. The position of the overflow hole on the pipe is adjusted according to the water level on both sides. Before the centrifuge is turned on, water is added to both the landside and seaside sides of the large-diameter cylindrical structure 3. The water level reaches the position of the seaside overflow hole and the water level on both sides is the same. Then, under the designed centrifugal acceleration, water is slowly and evenly injected into the landside of structure 3 in model box 1 until the end of the test. The water addition rate is no more than 2 mm / min. The water level on both sides is obtained through the pore pressure sensor 6. Excess water flows out from the overflow holes on both sides to the outside of model box 1. The equivalent lateral sliding force and equivalent rotational torque generated can objectively restore the sliding and rotational effects of the prototype wave load on the structure.

[0041] The centrifugal simulation method for wave load acting on a large-diameter thin-walled cylindrical structure 3 described in the above embodiments can adjust the water levels on the sea side and land side of the large cylindrical structure according to the specific needs of the experiment. By slowly injecting water into the land side of the scaled model 3 in the model box 1 in a hypergravity environment, an equivalent lateral sliding force and an equivalent rotational torque can be generated, objectively restoring the sliding and rotational effects of the prototype wave load on the structure. It is especially suitable for curved surface structures with small thickness and low stiffness.

[0042] A schematic diagram of the wave load centrifugal test simulation method for a large-diameter thin-walled cylindrical structure according to an embodiment of the present invention is shown below. Figure 1 The model box 1 is subjected to wave loads and a static water level difference on both sides. The wave load is simulated by adjusting the water level on both the land and sea sides of the structure. Specifically, the water level on the land side is increased by a certain amount. The landside force increases from Fl0 to Fl1, and the additional landside force is... At the same time, lower the sea level height, reducing the value by [value missing]. The sea-side force decreases from Fs0 to Fs1, and the additional sea-side force is... =Fs0-Fs1. Assume cylindrical model 3 rotates around [the target area] under load. Figure 1 As shown in the figure, point o rotates, and the lever arms of the additional forces on the land and sea sides corresponding to point o are hs and hl, respectively. The adjusted total additional sliding force and total additional sliding torque are shown in formulas (1) and (2), respectively.

[0043] Total additional sliding force (1)

[0044] Total additional torque (2)

[0045] Furthermore, the total rotational torque and total sliding force generated by the newly determined difference in water level on both sides of the structure must be equivalent to the corresponding load values ​​generated by the original wave load and the static water level difference on the structure, so as to ensure that the method is feasible in principle.

[0046] A specific embodiment is provided below.

[0047] Step 1) Collect soil samples from the site and process them in the laboratory. After removing impurities, reshape the soil samples in model box 1 according to the soil layer control indicators. After the model foundation 2 is prepared, place the large-diameter thin-walled cylindrical scaled-down model 3 in the designated position.

[0048] Step 2) Place bentonite balls in the gap between the two sides of the model box 1 and the cylindrical model 3 along the length direction for waterproofing. Insert aluminum alloy tubes into both sides of the bentonite balls so that the bentonite balls remain upright along the height direction of the cylindrical model 3 after absorbing water and expanding.

[0049] Step 3) Based on the principle of equivalent rotational torque and sliding force, calculate the water level height on both sides of the land and sea. The total rotational torque and total sliding force generated by the newly determined difference in water level height on both sides of the structure are equivalent to the corresponding load values ​​generated by the original wave load and static water level difference on the structure.

[0050] Step 4) Install the landside overflow pipe 4 and the seaside overflow pipe 5 on the two side plates of the model box 1 in the width direction, respectively. The position of the overflow hole on the pipe body is determined according to the calculated water level height on both sides.

[0051] Step 5) Place pore pressure sensors 6 on both the land and sea sides to obtain the water level height on both sides in real time during the operation of the centrifuge.

[0052] Step 6) Add water to both the land and sea sides of the large-diameter cylindrical structure until the water level reaches the overflow hole on the sea side, and the water level on both sides is the same.

[0053] Step 7) Weigh the overall model, hoist it onto the geotechnical centrifuge, and adjust the counterweight of the centrifuge.

[0054] Step 8) Start the centrifuge to the designed centrifugal acceleration.

[0055] Step 9) Slowly and evenly inject water into the land side of structure 3 in model box 1 under the designed centrifugal acceleration until the end of the test. The water injection rate is no more than 2 mm / min. The water level height on both sides is obtained by the pore pressure sensor 6. Excess water flows out of the overflow holes on both sides to the outside of model box 1.

[0056] Step 10) After the experiment is completed, stop adding water first, and then stop the centrifuge.

[0057] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the specific embodiments described above. The specific embodiments and descriptions in the specification are merely for further illustrating the principles of the present invention. Various changes and modifications can be made to the present invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed.

Claims

1. A method for simulating wave load centrifugal tests on a large-diameter thin-walled cylindrical structure, characterized in that, include: A scaled-down model of a large-diameter thin-walled cylindrical structure was prepared and fixed in a simulated foundation inside a model box. The scaled-down model divided the internal space of the model box into two isolated spaces, which served as the sea side and land side of the scaled-down model, respectively. Water is injected into the seaside and landside of the scaled-down model to make the water levels on both sides equal; Run the centrifuge to place the model box in a hypergravity environment; Slowly fill the land side of the scaled-down model inside the model box with water until the design height is reached, then stop filling the water and turn off the centrifuge. Utilize the total rotational torque and total sliding force generated by the water level difference between the land and sea sides to generate equivalent wave loads and static water level differences to the corresponding load values ​​generated on the structure.

2. The method according to claim 1, characterized in that, The water injection rate is such that the water level rise rate is less than 2 mm / min.

3. The method according to claim 1, characterized in that, The simulated foundation was prepared by layering soil samples from the site where the project was located.

4. The wave load centrifugal test simulation device with a large-diameter thin-walled cylindrical structure used in the method according to any one of claims 1 to 3, characterized in that, Includes a model box (1), a simulated foundation (2), a scaled-down model (3), a landside overflow pipe (4), a seaside overflow pipe (5), and a pore pressure sensor (6); The simulated foundation (2) is prepared in layers according to the soil layer control index and is located at the bottom of the model box. The scaled model (3) is fixed in the simulated foundation (2) inside the model box (1) and the internal space of the model box (1) is divided into two mutually isolated spaces, which serve as the sea side and land side of the scaled model (3) respectively. The landside overflow pipe (4) and the seaside overflow pipe (5) are fixed to the corresponding model box walls on the landside and seaside respectively, and are used to control the water level on the landside and seaside; the overflow outlets of the landside overflow pipe (4) and the seaside overflow pipe (5) are adjusted according to the required water level changes; Pore ​​pressure sensors (6) are placed on the simulated foundation (2) surfaces on the sea side and land side respectively to measure the water level on both sides.

5. The apparatus according to claim 4, characterized in that, The heights of the landside overflow pipe (4) and the seaside overflow pipe (5) are determined according to the design water level required by the project. The height of the overflow hole of the seaside overflow pipe (5) is lower than the design water level of the sea, while the height of the overflow hole of the landside overflow pipe (4) is higher than the design water level of the landside.

6. The apparatus according to claim 4, characterized in that, The gaps between the scaled-down model (3) and the two sides of the model box (1) along the length direction are filled with bentonite balls.

7. The apparatus according to claim 6, characterized in that, Aluminum alloy tubes are inserted into both sides of the bentonite ball for guidance.

8. The apparatus according to claim 4, characterized in that, The large-diameter thin-walled cylindrical model has a thickness of less than 1 mm and a diameter of less than 300 mm.

9. The apparatus according to claim 4, characterized in that, The model box is rectangular in shape, with net dimensions of less than 1000 mm in length, less than 350 mm in width, and less than 450 mm in height; the distance between the two sides of the model box and the outermost part of the cylindrical model along the length direction is no more than 10 mm.

10. The apparatus according to claim 7, characterized in that, The bentonite ball has a diameter of less than 3 mm; the aluminum alloy tube has a diameter of less than 15 mm and a height of less than 200 mm.

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