Test device and test method based on vortex-induced motion towed test

Abstract

The present application relates to a kind of test device and test method based on vortex-induced motion towed test, belong to the technical field of offshore platform test.It includes floating structure model, floating structure model is located on water surface and is arranged multiple one-way force sensors in circumference, one end of single one-way force sensor is fixed on floating structure model, the other end is connected with light steel wire rope;The other end of light steel wire rope is connected spring group after passing through universal pulley, the tail end of light steel wire rope is fixed on the mooring point of support pole after passing through the fixed pulley on truss;Setting tow vehicle system on water surface, floating structure model is matched with tow vehicle system and located below tow vehicle system;Floating structure model is installed with multiple-degree-of-freedom motion measuring instrument.The present application changes truss height to determine the length of steel wire rope and spring group, adjusts the pre-tension of spring system by changing mooring point position or the length of contraction steel wire rope, test process is convenient, vortex-induced motion test test capacity is greatly improved.

Description

Technical Field

[0001] This invention relates to the field of marine platform testing technology, and in particular to a testing device and method based on vortex-induced motion towing test. Background Technology

[0002] Deep-draft column-type offshore platforms, such as SPARs, semi-submersible platforms, and FPSOs, are subjected to the action of ocean waves and currents. Within a certain Reynolds number range, the viscosity of water causes boundary layer separation and generates periodic vortex shedding behind the main structure. The vortex shedding reduces the pressure behind the main structure, generating drag loads that cause the structure to move in the direction of flow. At the same time, since the vortex shedding occurs alternately on both sides of the main structure, it also generates lift with periodic oscillations perpendicular to the flow direction. It is this periodic excitation that leads to the vortex-induced motion of the offshore platform.

[0003] The mooring system of an offshore platform allows for six degrees of freedom of motion: sway, roll, heave, pitch, roll, and yaw. However, only horizontal displacements, namely sway and pitch, are the dominant motions in vortex-induced motion. In vortex-induced motion studies, the platform's sway direction is usually set to be aligned with the incoming flow direction, while the sway direction is the primary direction for generating transverse vortex-induced motion. Within this directional framework, the platform's sway—i.e., motion perpendicular to the flow—and its pitch—i.e., motion downstream are the main issues to focus on in vortex-induced motion studies. In particular, sway motion, generally speaking, the amplitude of motion caused by vortex shedding in the transverse direction is larger than that in the downstream direction, and transverse motion is prone to resonance response under certain conditions. Therefore, transverse motion is a focal point in vortex-induced motion studies. The response amplitude of vortex-induced motion is large and the period is long, which increases the fatigue failure of anchor chains and risers, shortens the overall fatigue life, and increases the total damping of the structure. For the design of mooring systems and risers, the estimation of vortex-induced motion of offshore platforms is particularly important.

[0004] Currently, eddy-induced motion prediction mainly involves two approaches: numerical simulation and tank model testing. Due to the complexity and unique characteristics of eddy-induced motion problems, numerical simulation involves many issues such as grid sensitivity, boundary layer simulation, wall effects, surface roughness, and turbulence models. Therefore, tank testing remains the primary research approach. However, because moored offshore platforms exhibit coupling effects under the influence of waves and currents, model testing faces numerous difficulties and challenges, mainly in the following aspects: (1) Offshore platforms are usually constrained by complex mooring systems. The key to the success of vortex-induced motion tests is to simplify them into horizontal mooring systems that take into account multiple degrees of freedom of motion. (2) The platform exhibits complex spatial motion under the action of waves and flow. The key is to identify and accurately obtain the quantitative motion and load in the main direction of vortex-induced motion.

[0005] Currently, most experimental studies on eddy-induced motion models are small-scale models, implemented in water tanks using simple nylon ropes or single flexible springs. Larger models use fixed-point flow generation to simulate eddy-induced motion. However, the main problem is that the simulated eddy-induced motion has a low Reynolds number, resulting in significant errors in reality. Summary of the Invention

[0006] To address the shortcomings of existing production technologies, the applicant provides a testing device and method based on vortex-induced motion towing tests, thereby enabling the testing of vortex-induced motion of floating structure models in wave currents, significantly improving the testing capability of vortex-induced motion, and promoting the development of hydrodynamics in marine engineering equipment.

[0007] The technical solution adopted in this invention is as follows: A testing device based on vortex-induced motion towing test includes a floating structure model. The floating structure model is located on the water surface and multiple unidirectional force sensors are arranged circumferentially. One end of each unidirectional force sensor is fixed to the floating structure model, and the other end of the unidirectional force sensor is connected to a lightweight steel wire rope. The other end of the lightweight steel wire rope is connected to a spring assembly after passing through a universal pulley. The tail end of the lightweight steel wire rope passes through a fixed pulley on the truss and is fixed to the mooring point of the support rod. A trailer system is set on the water surface, and the floating structure model is matched with the trailer system and located below the trailer system. A multi-degree-of-freedom motion measuring instrument is also installed on the floating structure model.

[0008] As a further improvement to the above technical solution: Preferably, the unidirectional force sensors are divided into four groups on the outer periphery of the floating structure model and are respectively set in a 45° oblique direction.

[0009] Preferably, the omnidirectional pulley is mounted on a support rod, and the support rod is fixed to the side wall of the trailer system.

[0010] Preferably, the truss is mounted on top of the trailer system.

[0011] Preferably, the trailer system includes a towing system for simulating flow and a wave-generating system for simulating wave environmental conditions.

[0012] A test method for a test device based on a vortex-induced motion towing test includes the following steps: Step 1: Determine the stiffness of the spring assembly that meets the requirements accurately to obtain the equivalent mooring system that satisfies the overall horizontal stiffness coefficient; Step 2: Simulate flow and wave environmental conditions using a trailer system to subject the floating structure model to wave and current effects; Step 3: The floating structure model generates six degrees of freedom motion and multiple sets of mooring forces along the arrangement direction; Step 4: Based on the data measured in Step 3, derive the resultant force in the horizontal direction of the floating structure model. The resultant force in the horizontal direction consists of longitudinal force and lateral force.

[0013] Preferably, the process of determining the stiffness of the spring assembly that meets the requirements in step one is as follows: Step 1: Based on the drainage mass of the floating structure model m Additional mass m a Natural period of sway in a mooring system for a floating structure model T To determine the overall horizontal stiffness coefficient of vortex-induced motion K The relationship is represented as:

[0014] Step 2: When the entire system is in equilibrium, it is symmetrical in all directions. Based on the overall horizontal stiffness coefficient obtained in Step 1... K And the radius of the floating structure model R Length of cable between the floating structure model and the omnidirectional pulley L 0. Vertical distance y 0 and pretension F 0 for the angle between the cable and the horizontal at the equilibrium position i The relationship between 0 is:

[0015] Step 3: Floating structure model (4) Longitudinal displacement Δx At that time, the lengths of the cables on the lightweight steel wire ropes were respectively L 1 and L 2. The tension on the cable is F 1 and F 2. At this time, the resultant force in the horizontal direction ΔFx It can be represented as:

[0016] in:

[0017] Step 4: Solve for the stiffness of each spring group based on the relationship in Step 3. K 0, and obtain the overall horizontal stiffness coefficient. K The equivalent mooring system.

[0018] Preferably, the derivation process of the horizontal resultant force of the floating structure model in step four is as follows: Step 1: Define the center of gravity of the floating structure model as the origin of the moving coordinate system o-xyz, and the trailer system as the fixed coordinate system O-XYZ; Step 2: Set the initial zero position of the floating structure model in still water as the equilibrium position, and assume that the floating structure model is symmetrical in all directions. Six-degree-of-freedom motion of the center of gravity of a floating structure model: G[x 0 ，y 0 ，z 0 ,the 0 ,f 0 ，β 0 ]； The initial tension on the cable is F 0, initial cable length is L 0, with an angle of 0 to the horizontal. f 0; Step 3: After the wave-current takes effect, Real-time six-degree-of-freedom motion of the center of gravity of a floating structure model: G'[x i ，y i ，z i ,the i ,f i ，β i ] ; The real-time tension on the cable is: F 1i ，F 2i ，F 3i ，F 4i ; The real-time angle with the horizontal is: f 1i ,f 2i ,f 3i ,f 4i ; Step 4: Define the mooring points on the floating structure model, including: Point A ( x 1 ，y 1 ，z 1) Point B ( x 2 ，y 2 ，z 2) Point C ( x 3 ，y 3 ，z 3) Point D ( x 4 ，y 4 ，z 4) After being affected by the wave current, the position A' of the mooring point in the fixed coordinate system can be obtained in real time using the transformation matrix J between the fixed coordinate system and the moving coordinate system.x 1i ，y 1i ，z 1i Point B' x 2i ，y 2i ，z 2i Point C' x 3i ，y 3i ，z 3i ) and point D' ( x 4i ，y 4i ，z 4i ); Step 5: Based on the real-time mooring point positions A, B, C, and D, and combined with the real-time tension obtained from the unidirectional force sensors at each mooring point, F 1i ，F 2i ，F 3i ，F 4i Ignoring the motion in the Z direction and based on the laws of ship motion, the longitudinal force in the horizontal direction is calculated. F x and lateral force F y .

[0019] The beneficial effects of this invention are as follows: This invention has a reasonable structure and is easy to operate during the test process. It solves the problem of accurately measuring the motion and force of floating structure models under wave and current environment. Finally, it can accurately obtain the amplitude and force characteristics of the vortex-induced motion of the model. The entire test device of this invention is simple, simplifying the complex space mooring system into a horizontal mooring form consisting of four groups, including spring groups, unidirectional force sensors, and lightweight steel wire ropes, in conjunction with the floating structure model. The length of the steel wire rope and spring group is determined by changing the truss height. The pretension of the spring system can be adjusted by changing the mooring point position or shrinking the length of the steel wire rope, thereby ensuring the maximum spatial displacement of the floating structure model under wave and current, realizing rapid adjustment of mooring stiffness and pretension, and is easy to operate. The present invention also has the following advantages: The eddy-induced motion analysis method of the present invention is simple, takes into account the coordinate deviation of each mooring position in detail, and can easily and accurately obtain each motion and load. Attached Figure Description

[0020] Figure 1This is a top view of the test apparatus of the present invention in a simulated state.

[0021] Figure 2 for Figure 1 Side view.

[0022] Figure 3 This is a diagram of the horizontal stiffness of vortex-induced motion in the vortex-induced motion drag test of the present invention.

[0023] Figure 4 This is a schematic diagram of the vortex-induced motion drag test of the present invention.

[0024] The components include: 1. Trailer system; 2. Multi-degree-of-freedom motion measuring instrument; 3. Unidirectional force sensor; 4. Floating structure model; 5. Lightweight steel wire rope; 6. Universal pulley; 7. Support rod; 8. Mooring point; 9. Spring assembly; 10. Fixed pulley; 11. Truss. Detailed Implementation

[0025] The specific embodiments of the present invention will now be described with reference to the accompanying drawings.

[0026] like Figure 1~Figure 4 As shown, the test device based on vortex-induced motion towing test in this embodiment includes a floating structure model 4, which is located on the water surface and has multiple unidirectional force sensors 3 arranged circumferentially. One end of each unidirectional force sensor 3 is fixed to the floating structure model 4, and the other end of the unidirectional force sensor 3 is connected to a lightweight steel wire rope 5. The other end of the lightweight steel wire rope 5 is connected to a spring assembly 9 through a universal pulley 6, and the tail end of the lightweight steel wire rope 5 passes through a fixed pulley 10 on the truss 11 and is fixed to the mooring point 8 of the support rod 7. A trailer system 1 is set on the water surface, and the floating structure model 4 is matched with the trailer system 1 and located below the trailer system 1. A multi-degree-of-freedom motion measuring instrument 2 is also installed on the floating structure model 4.

[0027] In this embodiment, the unidirectional force sensors 3 are divided into four groups on the outer periphery of the floating structure model 4 and are respectively set in a 45° oblique direction.

[0028] In this embodiment, the universal pulley 6 is mounted on the support rod 7, and the support rod 7 is fixed to the side wall of the trailer system 1.

[0029] In this embodiment, the truss 11 is mounted on top of the trailer system 1.

[0030] In this embodiment, the trailer system 1 includes a towing system for simulating flow and a wave-generating system for simulating wave environmental conditions.

[0031] The test method of the test device based on the vortex-induced motion towing test in this embodiment includes the following steps: Step 1: Determine the stiffness of spring assembly 9 to meet the requirements accurately, and obtain the equivalent mooring system that meets the overall horizontal stiffness coefficient; like Figure 3 As shown, the specific process for determining the stiffness of the accurate spring assembly 9 is as follows: Step 1: Based on the drainage mass of floating structure model 4 m Additional mass m a Natural period of sway in mooring system for floating structure model 4 T To determine the overall horizontal stiffness coefficient of vortex-induced motion K The relationship is represented as:

[0032] Step 2: Assuming the entire system is symmetrical in all directions when in equilibrium, use the overall horizontal stiffness coefficient obtained in Step 1. K And the radius of floating structure model 4 R The cable length between the floating structure model 4 and the omnidirectional pulley 6 L 0. Vertical distance y 0 and pretension F 0 for the angle between the cable and the horizontal at the equilibrium position i The relationship between 0 is:

[0033] Step 3: Longitudinal displacement of the floating structure model 4 Δx At that time, the lengths of the five cables on the lightweight steel wire rope were respectively... L 1 and L 2. The tension on the cable is F 1 and F 2. At this time, the resultant force in the horizontal direction ΔFx It can be represented as:

[0034] in:

[0035] Step 4: Solve for the stiffness of each spring group 9 using the relationship from Step 3. K 0, and obtain the overall horizontal stiffness coefficient. K The equivalent mooring system; Step 2: Simulate flow and wave environment conditions using trailer system 1, subjecting floating structure model 4 to wave and current effects; Step 3: The floating structure model 4 generates six degrees of freedom motion and multiple sets of mooring forces along the arrangement direction; Step 4: Based on the data measured in Step 3, derive the resultant force in the horizontal direction of floating structure model 4. The resultant force in the horizontal direction consists of longitudinal force and lateral force. like Figure 4 As shown, the derivation process of the horizontal resultant force of floating structure model 4 is as follows: Step 1: Define the center of gravity of floating structure model 4 as the origin of the moving coordinate system o-xyz, and the trailer system 1 as the fixed coordinate system O-XYZ; Step 2: Set the initial zero position of the floating structure model 4 in still water as the equilibrium position, and assume that the floating structure model is symmetrical in all directions. Floating structure model 4: Six-DOF motion of center of gravity: G[x 0 ，y 0 ，z 0 ,the 0 ,f 0 ，β 0 ]； The initial tension on the cable is F 0, initial cable length is L 0, with an angle of 0 to the horizontal. f 0; Step 3: After the wave-current action... Real-time six-DOF motion of the center of gravity of a floating structure model: G'[x i ，y i ，z i ,the i ,f i ，β i ] ; The real-time tension on the cable is: F 1i ，F 2i ，F 3i ，F 4i ; The real-time angle with the horizontal is: f 1i ,f 2i ,f 3i ,f 4i ; Step 4: Define the mooring points on floating structure model 4, including point A ( x 1 ，y 1 ，z 1) Point B ( x 2 ，y 2 ，z 2) Point C ( x 3，y 3 ，z 3) Point D ( x 4 ，y 4 ，z 4) After being affected by the wave current, the position A' of the mooring point in the fixed coordinate system can be obtained in real time using the transformation matrix J between the fixed coordinate system and the moving coordinate system. x 1i ，y 1i ，z 1i Point B' x 2i ，y 2i ，z 2i Point C' x 3i ，y 3i ，z 3i ) and point D' ( x 4i ，y 4i ，z 4i ); Step 5: Based on the real-time mooring point positions A, B, C, and D, and combined with the real-time tension obtained from the unidirectional force sensor 3 at each mooring point. F 1i ，F 2i ，F 3i ，F 4i Ignoring the motion in the Z direction and based on the laws of ship motion, the longitudinal force in the horizontal direction is calculated. F x and lateral force F y .

[0036] In this embodiment, as an example, taking point A as an example, its coordinate transformation matrix J is expressed as follows:

[0037]

[0038]

[0039] And in sequence we can obtain f 2i ,f 3i and f 4i ; Therefore, we get: Horizontal longitudinal force F x for:

[0040] lateral force F y for:

[0041] The test device and method based on vortex-induced motion towing test of the present invention solve the problem of accurate measurement of motion and force of floating structure model under wave and current environment. Finally, the amplitude and force characteristics of vortex-induced motion of the model can be accurately obtained. The entire test device of the present invention is simple, simplifying the complex space mooring system into a horizontal mooring form consisting of 4 groups of spring group 9, unidirectional force sensor 3 and lightweight steel wire rope 5 set along the 45° inclined direction. It can realize rapid adjustment of mooring stiffness and pretension and is easy to operate.

[0042] The above description is an explanation of the present invention and not a limitation thereof. The scope of the present invention is defined by the claims. Within the scope of protection of the present invention, any form of modification may be made.

Claims

1. A test method for a test device based on a vortex-induced motion towing test, characterized in that: Includes a floating structure model (4), which is located on the water surface and has multiple unidirectional force sensors (3) arranged in the circumferential direction. One end of each unidirectional force sensor (3) is fixed on the floating structure model (4), and the other end of the unidirectional force sensor (3) is connected to a lightweight steel wire rope (5). The other end of the lightweight steel wire rope (5) is connected to the spring assembly (9) via the universal pulley (6), and the tail end of the lightweight steel wire rope (5) is fixed to the mooring point (8) of the support rod (7) after passing through the fixed pulley (10) on the truss (11). A trailer system (1) is set on the water surface, and a floating structure model (4) is matched with the trailer system (1) and located below the trailer system (1); The floating structure model (4) is also equipped with a multi-degree-of-freedom motion measuring instrument (2); Includes the following steps: Step 1: Determine the stiffness of the spring assembly (9) that meets the requirements accurately to obtain the equivalent mooring system that meets the overall horizontal stiffness coefficient; Step 2: Simulate flow and wave environment conditions through the trailer system (1) to subject the floating structure model (4) to wave and current effects; Step 3: The floating structure model (4) generates six degrees of freedom motion and multiple sets of mooring forces along the arrangement direction; Step 4: Based on the data measured in Step 3, derive the horizontal resultant force of the floating structure model (4), which is the longitudinal force and the transverse force; The process of determining the stiffness of the spring assembly (9) that meets the requirements in step one is as follows: Step 1: Based on the drainage mass of the floating structure model (4) m Additional mass m a The natural period of sway in a mooring system for a floating structure model (4) T To determine the overall horizontal stiffness coefficient of vortex-induced motion K The relationship is represented as: Step 2: When the entire system is in equilibrium, it is symmetrical in all directions. Based on the overall horizontal stiffness coefficient obtained in Step 1... K and the radius of the floating structure model (4) R The cable length between the floating structure model (4) and the universal pulley (6) L 0. Vertical distance y 0 and pretension F 0 for the angle between the cable and the horizontal at the equilibrium position θ The relationship between 0 is: Step 3: Floating structure model (4) Longitudinal displacement Δx At that time, the lengths of the lightweight steel wire rope (5) were respectively L 1 and L 2. The tension on the cable is F 1 and F 2. At this time, the resultant force in the horizontal direction ΔFx It can be represented as: in: Step 4: Solve for the stiffness of each spring group (9) based on the relationship in Step 3. K 0, and obtain the overall horizontal stiffness coefficient. K The equivalent mooring system.

2. The test method of the test device based on the vortex-induced motion towing test as described in claim 1, characterized in that: The unidirectional force sensor (3) is divided into four groups on the outer periphery of the floating structure model (4) and is set at an angle of 45°.

3. The test method of the test device based on the vortex-induced motion towing test as described in claim 1, characterized in that: The universal pulley (6) is mounted on the support rod (7), which is fixed to the side wall of the trailer system (1).

4. The test method of the test device based on the vortex-induced motion towing test as described in claim 1, characterized in that: The truss (11) is mounted on top of the trailer system (1).

5. The test method of the test device based on vortex-induced motion towing test as described in claim 3 or 4, characterized in that: The trailer system (1) includes a towing system for simulating flow and a wave-generating system for simulating wave environmental conditions.

6. The test method of the test device based on the vortex-induced motion towing test as described in claim 1, characterized in that: The derivation process of the horizontal resultant force of the floating structure model (4) in step four is as follows: Step 1: Define the center of gravity of the floating structure model (4) as the origin of the moving coordinate system o-xyz, and the trailer system (1) as the fixed coordinate system O-XYZ; Step 2: Set the initial zero position of the floating structure model (4) in still water as the equilibrium position, and assume that the floating structure model is symmetrical in the upper, lower and left and right. Floating structure model (4) Six-degree-of-freedom motion of the center of gravity: G[x 0 ，y 0 ，z 0 θ 0 φ 0 ，β 0 ]； The initial tension on the cable is F 0, initial cable length is L 0, with an angle of 0 to the horizontal. φ 0; Step 3: After the wave-current takes effect, Real-time six-degree-of-freedom motion of the center of gravity of the floating structure model (4): G'[x i ，y i ，z i θ i φ i ，β i ] ; The real-time tension on the cable is: F 1i ，F 2i ，F 3i ，F 4i ; The real-time angle with the horizontal is: φ 1i φ 2i φ 3i φ 4i ; Step 4: Define the mooring points on the floating structure model (4), including point A ( x 1 ，y 1 ，z 1) Point B ( x 2 ，y 2 ，z 2) Point C ( x 3 ，y 3 ，z 3) Point D ( x 4 ，y 4 ，z 4) After being affected by the wave current, the position A' of the mooring point in the fixed coordinate system can be obtained in real time using the transformation matrix J between the fixed coordinate system and the moving coordinate system. x 1i ，y 1i ，z 1i Point B' x 2i ，y 2i ，z 2i Point C' x 3i ，y 3i ，z 3i ) and point D' ( x 4i ，y 4i ，z 4i ); Step 5: Based on the real-time mooring point positions A, B, C, and D, and combined with the tension obtained in real-time from the unidirectional force sensor (3) at the mooring point, F 1i ，F 2i ，F 3i ，F 4i Ignoring the motion in the Z direction and based on the laws of ship motion, the longitudinal force in the horizontal direction is calculated. F x and lateral force F y .

Images