An experimental apparatus and method for viscous gravity flow interaction with a permeable bed

Abstract

The application discloses an experimental device and method for interaction between viscous gravity flow and permeable seabed, and belongs to the technical field of gravity flow physical models. In view of the limitation that the prior art cannot synchronously acquire the flow field and the mechanical response of the permeable seabed, a multi-channel mechanical sensing system and a stereoscopic particle image velocimetry technology are integrated to construct a cross-scale coupling measurement platform. The device comprises a water tank system, a stereoscopic PIV unit, a multi-channel mechanical sensing unit and a central synchronous control system. The multi-channel mechanical sensing unit is conformally integrated with a honeycomb support grid by using a PVDF flexible piezoelectric sensor array, and the transient kinetic energy and spatial orientation of a micro force chain network are quantitatively analyzed by combining a viscous force chain inversion algorithm based on a Hamaker constant. Microsecond-level space-time alignment is realized by FPGA synchronous control, a complete causal chain from coherent vortices in the flow field to the evolution of viscous force chains and then to the mechanical response of the seabed is established, and high-fidelity data support is provided for safety evaluation of seabed engineering structures.

Description

Technical Field

[0001] This invention belongs to the field of physical modeling technology of gravity flow, specifically relating to an experimental apparatus and method for the interaction of viscous gravity flow with a permeable substrate. Background Technology

[0002] Submarine gravity currents, as a geological fluid dynamic phenomenon capable of long-distance material transport, pose a severe challenge to the evolution of deep-sea topography and the structural stability of submarine cross-interface infrastructure. Long-term observations in several regions worldwide where gravity currents are frequent indicate that the seabed topography generally exhibits significant dynamic evolution and permeability characteristics.

[0003] Subsurface permeability, as a product of the cumulative effects of dynamic processes such as submarine earthquake-induced landslides, is primarily determined by the spatially non-uniform distribution of coarse-grained gravel and the porous media structure formed by its vertical accumulation. Subsurface permeability significantly influences the initiation, transport, and deposition processes of gravity flows by altering boundary interaction mechanisms. For viscous gravity flows, cohesive forces such as van der Waals forces between micron-sized particles play a dominant role, leading to easy aggregation, dispersion, and remodeling of particles.

[0004] Subsurface permeability not only alters the frontal propagation velocity and sediment thickness distribution of gravity flow through seepage flux input and output, but also regulates the dynamic balance of interparticle adhesion through unsteady fluctuations in pore water pressure, profoundly influencing the reconstruction of microscopic viscous force chain networks and energy dissipation mechanisms. Compared to smooth boundaries, the evolution of gravity flow motion, the development of interfacial turbulent structures, and sediment transport patterns on permeable substrates all exhibit significant differences.

[0005] However, a systematic understanding of the interfacial instability under the coupling of seepage and particles, and the resulting cross-scale regulation mechanisms of mass exchange and momentum transport processes on the dynamic behavior of viscous gravitational flow, remains lacking. For a long time, empirical research on such physical processes has been constrained by the inherent domain segmentation of existing measurement methodologies. Current non-invasive flow field identification paradigms mainly rely on particle image velocimetry based on light scattering principles. While this technique can provide high-fidelity velocity field data, its measurement scope is limited to the fluid domain, failing to perceive the mechanical evolution and pore flow dynamics response within the permeable substrate.

[0006] Meanwhile, existing acoustic Doppler measurement methods, due to resolution limitations, struggle to resolve the micrometer-scale shear structures at the permeation interface. Point-based pressure or conductivity probes pre-installed on the permeation substrate exhibit severe detection blind spots due to spatial discreteness, failing to reconstruct the continuous stress distribution on the permeation surface. Furthermore, chemical tracer methods, with their significant lag in response mechanism, struggle to capture the transient evolution of viscous force chains during turbulent initiation. This prevents current methods from establishing a complete physical causal chain linking coherent vortices in the flow field, interfacial permeation effects, and the reconstruction of internal viscous force chains. Consequently, the resolved transient turbulent events cannot establish a deterministic causal relationship with the complex spatiotemporal dynamic mechanical feedback induced at the permeation boundary.

[0007] In summary, at the current technological level, a critical technological gap exists between the precise analysis of the transient dynamic characteristics of the flow field and the continuous measurement of the multiphysics response of the permeable substrate. Existing technologies cannot establish a direct causal relationship between the two in the temporal and spatial dimensions, which severely restricts a deeper understanding of the gravity flow erosion mechanism and viscous fluid dynamics under the permeable interface effect. Therefore, based on the aforementioned pressing technical problems, this invention proposes an experimental apparatus and method for studying the interaction between viscous gravity flow and the permeable substrate using multi-channel sensing. Summary of the Invention

[0008] To address the limitations of existing measurement techniques in simultaneously acquiring the flow field of viscous gravity flow and its induced mechanical response in a permeable substrate, this invention provides an experimental apparatus and method for studying the interaction between viscous gravity flow and a permeable substrate. This invention achieves cross-scale coupled analysis of the macroscopic flow field topology of viscous gravity flow and the evolution characteristics of the microscopic viscous force chains at the permeable substrate interface through high-frequency synchronous sampling and microscopic physical model inversion techniques.

[0009] An experimental apparatus for the interaction between viscous gravity flow and a permeable substrate according to the present invention includes:

[0010] A water tank system is used to generate viscous gravity flow, and a composite graded permeable substrate is configured in the main experimental section. The permeable substrate includes a bottom structural base, a middle honeycomb support grid, and a top porous media layer of sediment.

[0011] The three-dimensional particle image velocimetry unit is used to project a sheet light source into the target measurement volume element and acquire tracer particle images to reconstruct the three-dimensional transient velocity vector field of the viscous gravity flow in the region adjacent to the permeation interface.

[0012] The multi-channel mechanical sensing unit includes a flexible piezoelectric sensor array conformally integrated in the form of a discrete lattice on the surface of the stress-bearing ribs of the honeycomb support grid, and a high-resolution analog-to-digital conversion module coupled to the sensor array through a multi-channel multiplexing architecture. The multi-channel mechanical sensing unit embeds an analytical module based on micro-dynamic physical constraints, which is used to invert the transient kinetic energy and spatial preference orientation of the viscous force chain from the dynamic mechanical response collected by the sensor array.

[0013] The pore water pressure monitoring unit includes a pore water pressure sensor array arranged below the support grid, used to acquire transient superpore water pressure evolution data inside the permeable medium;

[0014] The central synchronization control unit is used to output a unified trigger signal with deterministic time delay compensation to forcibly lock the sampling timing of the three-dimensional particle image velocimetry unit, the multi-channel mechanical sensing unit and the pore water pressure monitoring unit, so as to realize the spatiotemporal co-position measurement of the flow field and the multi-physics field response.

[0015] Furthermore, the water tank system includes a high-density gravity flow energy storage tank, a liftable initial ramp, a low-density environmental fluid tank, and a fast-opening and closing electric gate.

[0016] The high-density gravity flow energy storage tank and the low-density environmental fluid tank are connected by an electric gate, and the liftable initial ramp is set at the outlet of the high-density gravity flow energy storage tank.

[0017] Furthermore, the bottom structural base has a fluid circulation chamber, the grid spacing of the middle honeycomb support grid is optimized to ensure unobstructed flow of fluid across the interface, and the top porous media layer of sediment is laid with sediments of a specific particle size distribution according to experimental requirements.

[0018] Furthermore, the stereo particle image velocimetry unit includes at least two sets of high-speed cameras configured to set solid angles and conforming to the Schumpfler optical criterion, and a high-energy pulsed laser emission group for projecting a high-energy-density sheet light source into the target measurement volume; the sheet light source measurement area is configured directly above the permeation substrate and perpendicular to the axis of the permeation substrate.

[0019] Furthermore, the high-resolution analog-to-digital conversion module is a delta-sigma type analog-to-digital conversion integrated circuit based on the ADS1256 chip, and the multi-channel mechanical sensing unit also includes an integrated wireless sensing and digitization module, which integrates the ADS1256 chip and a low-power wireless radio frequency communication unit.

[0020] Furthermore, the central synchronization control unit includes a PIV control server and a central synchronization main controller. By outputting a unified main trigger signal with deterministic time delay compensation, it forcibly locks the sampling timing of the three-dimensional particle image velocimetry unit, the multi-channel mechanical sensing unit, and the pore water pressure monitoring unit, ensuring that heterogeneous physical field data achieves spatiotemporal alignment within microsecond precision.

[0021] Furthermore, it also includes an automatic scanning high-precision laser bed surface scanner, which is mounted above the main experimental water tank to acquire a three-dimensional digital elevation model of the permeable bed surface in real time during the gravity flow scouring process.

[0022] Furthermore, it also includes an environmental multiphysics monitoring module, which includes at least one of the following: an online rheological monitoring probe for real-time verification of the non-Newtonian flow index of viscous gravity flow, an acoustic Doppler velocimeter for providing single-point high-precision time-resolved velocity vector data, and a non-contact ultrasonic flow meter for quantitative analysis of environmental fluid compensated flow velocity.

[0023] Furthermore, the analysis module processes the high-frequency mechanical pulses obtained by the high-resolution analog-to-digital conversion module and extracted by the flexible piezoelectric sensor array, and combines them with the preset Hamek constant and interface geometric parameters to construct a viscous coupling operator and topological connection weights. It captures the stress transmission coherence through dynamic cross-correlation tensors and synthesizes the topological strength index of the viscous force chain to quantitatively invert the transient kinetic energy and spatial preference orientation of the viscous force chain.

[0024] The present invention provides a method for inverting viscous force chains in the interaction between viscous gravity flow and a permeable substrate, comprising the following steps:

[0025] S1. Construct and calibrate the permeable substrate water tank system, install the permeable substrate integrating a flexible piezoelectric sensor array and a pore water pressure sensor array at the predetermined position, and configure a particle image velocimetry unit to make the laser sheet light plane coincide with the target fluid profile;

[0026] S2. Generate a viscous gravity flow with controllable parameters and allow it to reach its full development state, while simultaneously configuring an environmental fluid with a matching refractive index;

[0027] S3. By outputting a unified trigger signal through the central synchronization control unit, the sampling timing of each measurement unit is synchronously locked to achieve spatiotemporal alignment of heterogeneous physical field data;

[0028] S4. Based on the three-dimensional transient velocity vector field, the interface dynamic thickness scale and vortex core rotation intensity scalar field are extracted to characterize the coherent vortex structure in the macroscopic flow field;

[0029] S5. Based on dynamic mechanical response, combined with the preset Hamek constant and interface geometric parameters, a viscous coupling operator and topological connection weight are constructed. The stress transmission coherence is captured by the dynamic cross-correlation tensor, and the topological strength index of the viscous force chain is synthesized to quantitatively invert the transient kinetic energy and spatial preference orientation of the viscous force chain.

[0030] S6. Based on the three-dimensional transient velocity vector field and the dynamic mechanical response, couple and analyze the cross-interface mass permeability and unsteady momentum flux;

[0031] S7. Based on transient excess pore water pressure evolution data and interface normal load, analyze the effective stress evolution of the permeable substrate and identify the critical liquefaction state;

[0032] S8. Based on the spatiotemporal matching relationship between the topological strength index of the viscous force chain and the scalar field of the vortex core rotation strength, establish a physical causal chain from the flow field dynamic events to the mechanical response of the permeable substrate.

[0033] The beneficial effects of this invention are reflected in:

[0034] 1. This invention innovatively integrates two advanced measurement technologies, the ADS1256 multi-channel mechanical sensing system and particle image velocimetry, to construct a new experimental platform capable of synchronous and spatiotemporally co-located measurement of the velocity field and dynamic stress-strain field during the interaction between viscous gravity flow and a permeable substrate. This enables dynamic analysis and quantitative characterization of the evolution process of the viscous force chain of gravity flow, solving the measurement problems of existing technologies.

[0035] 2. This invention can quantitatively invert the transient kinetic energy evolution law and spatial preference orientation of the viscous force chain network inside viscous gravity flow, and verify it by quantitative comparison with CFD numerical simulation data, thereby providing a high-fidelity, cross-scale dynamic characteristic dataset for revealing the microscopic physical mechanism of viscous gravity flow under the permeation interface effect.

[0036] 3. This invention establishes a physical causal chain from flow field dynamic events to viscous force chain evolution and then to the mechanical response of the permeable substrate. It can accurately analyze the instantaneous impact and force chain transmission effect of specific vortices on the permeable substrate, thereby improving the fidelity and reliability of the data required for the safety assessment of subsea engineering structures. Attached Figure Description

[0037] Figure 1 This is a schematic diagram of the overall architecture and key component layout of an experimental device for the interaction between viscous gravity flow and permeable substrate proposed in this invention.

[0038] Figure 2 This is a detailed diagram of the steps of the invention method. Detailed Implementation

[0039] The present invention will now be described in further detail with reference to the accompanying drawings.

[0040] To make the technical solution, structural features, and achieved technical effects of the present invention clearer and more complete, the present invention will be described in detail below with reference to preferred embodiments. It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other.

[0041] like Figure 1 As shown in the figure, this embodiment provides an experimental apparatus for the interaction of viscous gravity flow with a permeable substrate, including a water tank system, a three-dimensional particle image velocimetry unit, a multi-channel mechanical sensing unit, a central synchronous control system, and an auxiliary monitoring module.

[0042] The water tank system is used to generate viscous gravity flow with specific rheological characteristics, and a composite-graded permeable substrate is configured in the main experimental section. The system includes:

[0043] Homogenization and supply tank 1: used to prepare high-density gravity fluid, the fluid inside of which is quantitatively transported to high-density gravity flow energy storage tank 3 by precision volumetric pump 2;

[0044] High-density gravity flow energy storage tank 3: used to establish a hydrostatic pressure gradient and potential energy storage before the experiment begins;

[0045] The adjustable initial ramp 4 is located at the outlet of the energy storage tank to precisely control the initial release dynamics of the gravity flow.

[0046] Environmental fluid preparation and circulation tank 5: used for preparing background fluid;

[0047] Low-density environmental fluid tank 6: Serves as the main experimental water tank, and the internal water volume is maintained stable by circulating pump 7;

[0048] The rapidly opening and closing electric gate 10 controls the occurrence of the experiment. Its instantaneous opening can minimize the disturbance to the fluid and ensure that the high potential energy fluid rapidly evolves into a gravity flow head front with clear demarcation characteristics and a stable structure at the moment of release.

[0049] In one example, the stereo particle image velocimetry unit comprises: a laser emitter for projecting a high-energy-density sheet light source within the target measurement volume; at least two sets of high-speed cameras 13 and 14 configured with a specific solid angle of 60°–90° between cameras and an off-axis angle of 30°–45° per camera, conforming to the Shempfler optical criterion; and tracer particles uniformly distributed in the fluid as kinematic characterization carriers. This unit works collaboratively to reconstruct the three-dimensional, three-component transient velocity vector field of the gravitational flow in the region adjacent to the permeation interface through stereo matching and 3D reconstruction algorithms, providing data support for analyzing the modulation law of the normal jet generated by the permeation effect on the near-wall turbulent structure.

[0050] In one example, the signal quantization and analysis core of the multi-channel mechanical sensing unit relies on the ADS1256, a delta-sigma analog-to-digital converter with ultra-low noise characteristics and 24-bit high resolution. This integrated circuit is coupled to a set of high-sensitivity flexible piezoelectric mechanical sensor arrays 11 through a multi-channel multiplexing architecture.

[0051] The flexible piezoelectric sensor is made of polyvinylidene fluoride (PVDF) copolymer film material, which possesses a high voltage constant and good mechanical compliance. The sensor is conformally integrated into the surface of the stress-bearing ribs of a honeycomb support grid in a discrete lattice configuration. The PVDF film is bonded to the rib surface using a high-performance epoxy resin adhesive (such as 3M DP460). In-plane polarization along the length of the ribs (using d...) is employed. 31 This design utilizes grid ribs as a mechanical transmission medium, ensuring the sensor's sensitivity to in-plane deformation of the ribs. Electrodes are led out from the lower surface of the thin film via flexible printed circuit cables, and are coated with a 15-25μm thick Parylene C film as a waterproof shielding layer. This layout employs grid ribs as a mechanical transmission medium, ensuring the vertical continuity of the internal pore channels of the substrate while sensitively capturing unsteady pressure pulsations and dynamic response characteristics induced by the impact of the upper gravity flow and the reconstruction of internal viscous force chains.

[0052] To address the non-uniform loads generated by interparticle viscous force chains within viscous gravity flows, the multi-channel mechanical sensing unit incorporates an analytical module based on microscopic dynamic physical constraints. This module, running on a host computer, processes high-frequency mechanical pulses acquired by the ADS1256 and extracted from the flexible sensor array on the grid surface in real time via a USB interface. Combining this with preset Hamek constants and interface geometric parameters, it achieves quantitative inversion of the transient kinetic energy and spatial preference orientation of the viscous force chains, ultimately forming a closed-loop identification chain from the coherent structure of the flow field to the microscopic stress evolution of the permeable substrate.

[0053] In one example, the central synchronization control system, acting as the nerve center of the device, consists of a PIV control server 21 and a central synchronization main controller 22. Through a multi-channel programmable delay chip controlled by an FPGA, it independently compensates for the time delay of each trigger signal, outputs a unified main trigger signal, and forcibly locks the sampling frequencies of the electric gate, laser pulse, camera exposure, and wireless telemetry module 12, ensuring that heterogeneous physical field data achieves spatiotemporal alignment and causal correlation analysis within microsecond-level precision.

[0054] The key to this system is that the sheet light source measurement area of ​​the particle image velocimetry unit is precisely positioned directly above the permeation substrate and perpendicular to the axis of the permeation substrate, thereby ensuring the spatial co-location of flow field measurement and strain measurement.

[0055] In one example, the auxiliary monitoring module is used to supplement fluid physical property characteristics and terrain evolution data, including:

[0056] Online rheological monitoring probe 18: integrated into the outlet end of precision volumetric pump 2, used for real-time verification of the non-Newtonian flow index of viscous gravity flow;

[0057] Acoustic Doppler current meter 19: Deployed downstream of the measurement area to provide single-point, high-precision, time-resolved velocity vector data;

[0058] Non-contact ultrasonic flow meter 20: installed on the inner wall of the water tank for quantitative analysis of the compensated flow velocity of environmental fluids;

[0059] Automatic scanning high-precision laser bed surface scanner 17: Erected above a low-density environmental fluid tank, it is used to acquire a three-dimensional digital elevation model of the permeable bed surface in real time during gravity flow scouring.

[0060] In this embodiment, the permeable substrate 8 is physically composed of three layers:

[0061] The bottom layer is a structural base with fluid circulation function, and has a built-in fluid circulation chamber;

[0062] The middle layer is a high-permeability honeycomb support grid with optimized grid spacing to ensure unobstructed fluid flow across the interface. This layer is the core layer for mechanical sensing, and the aforementioned high-sensitivity flexible piezoelectric sensor array 11 is conformally integrated on the surface of its stress-bearing ribs.

[0063] The top layer is a porous media layer of sediment with a specific particle size distribution laid out according to experimental requirements.

[0064] This configuration is designed to simulate the complex dynamic evolution of viscous gravity flow at the permeable boundary, which involves pore water pressure feedback and momentum exchange. To monitor the dynamic feedback inside the permeable medium, a micro-pore water pressure sensor array 9 is embedded in the structural base below the support grid to acquire transient superpore water pressure evolution data induced by the upper gravity flow.

[0065] Based on the above experimental setup, this embodiment also provides a method for inverting viscous force chains during the interaction between viscous gravity flow and a permeable substrate, based on ADS1256 multi-channel mechanical sensing and particle image velocimetry, including the following steps:

[0066] Step S1: Model building, layout, and spatial calibration of the infiltration substrate water tank system

[0067] The permeable substrate, integrated with a high-sensitivity flexible piezoelectric sensor array, was installed at a predetermined position in the main experimental water tank, and its three-dimensional spatial coordinates were precisely calibrated. A particle image velocimetry unit was configured, and the solid angle pose of high-speed cameras 13 and 14 and the sheet light planes of laser emission groups 15 and 16 were adjusted to ensure that the laser sheet light planes coincided with the target fluid profile directly above the substrate, and that the measurement area covered the axis of the permeable substrate and its upstream development section.

[0068] Step S2: Dynamic excitation and rheological initial state construction of viscous gravitational flow

[0069] A controllable gravity flow is generated in the experimental water tank gate chamber and allowed to reach full development in the measurement area.

[0070] First, a high-density gravity flow is configured in the homogenization and supply tank 1. A low-density environmental fluid with the same refractive index is configured in the environmental fluid preparation and circulation tank 5. After being stirred, the fluid is pumped into the high-density gravity flow energy storage tank 3 and the low-density environmental fluid tank 6 by the precision volumetric pump 2 and the circulation pump 7, respectively.

[0071] To eliminate particle image distortion and measurement errors introduced by light refraction at the density interface, this embodiment precisely prepares the components of the high-density fluid and the ambient fluid to achieve refractive index matching between the two-phase fluid systems. This step involves an iteratively optimized measurement and preparation process consisting of a refractometer and a high-precision density meter: the concentrations of the light fluid (glycerol-aqueous solution) and the heavy fluid (potassium dihydrogen phosphate-aqueous solution) are alternately titrated and fine-tuned until the refractive index difference between the two working fluids is controlled to be less than 5 × 10⁻⁶. -4 Within an extremely small threshold. During the mixing process, the density difference is monitored in real time by a densitometer and serves as the primary constraint condition, while the refractive index difference is approximated using a pre-established linear relationship between refractive index and density, ensuring that the final operating conditions simultaneously meet the density difference required for rheological stratification and the refractive index matching requirements required for optical measurement.

[0072] Subsequently, through the initial ramp 4 and the gate control and main synchronization unit, the electric gate 10 located between the high-density gravity flow energy storage tank 3 and the low-density environmental fluid tank 6 is opened instantaneously. This operation efficiently converts the potential energy stored in the static high-gravity fluid in the energy storage tank into the kinetic energy of the fluid motion, thereby initializing a gravity flow with a clear frontal structure and stable initial dynamic characteristics in the main experimental tank.

[0073] After initialization by the aforementioned steps, the high-density gravity flow propagates forward along the permeable bed 8, engaging in complex multi-physics coupled dynamic interactions with pre-deployed instrumentation structures. This process manifests in space and time as multiple parallel evolving physical phenomena: the fluid front develops into a stable head and body on the acceleration slope; the fluid body induces complex, unsteady vortex shedding and vortex interference phenomena due to boundary layer separation and shear layer instability; at the macroscopic interface between the gravity flow and the overlying environment fluid, intense velocity shear continuously triggers Kelvin-Helmholtz instability, evolving into macroscopic interface vortex structures; in the continuous interaction with the permeable bed 8, high-energy turbulent structures induce sediment initiation and transport, leading to significant bed erosion. This erosion process not only reconstructs the local bed topography, forming dynamic boundaries such as scour pits and sand waves, but also alters the fluid properties of the gravity flow itself through sediment resuspension, thus establishing a complex two-way feedback mechanism.

[0074] To systematically investigate the motion mechanism of viscous gravity flow on a permeable substrate, this embodiment systematically traverses and evaluates a series of controllable dimensionless parameters. This process involves adjusting the inlet fluid density, viscosity, and ramp angle to change the inlet Reynolds number and Frod number; and adjusting the permeability of the permeable substrate to evaluate the modulation law of different conditions on the flow field topology and mechanical response.

[0075] Step S3: Timing locking and high-frequency synchronous sampling of physical field data

[0076] The central synchronization control unit sends a main trigger signal, which is distributed in parallel to each subsystem through the signal transmission link, thereby forcibly locking the opening time of the exposure window of the high-speed camera array and the data acquisition start point of the wireless data telemetry module 12, so as to achieve strict synchronization of heterogeneous measurement modes on the time reference.

[0077] The wireless data telemetry module 12 is an integrated wireless sensing and digitization module. It integrates a delta-sigma analog-to-digital converter circuit based on the ADS1256 chip and a low-power wireless radio frequency communication unit. It is responsible for converting the captured microscopic viscous force chain reconstruction pulses into digital sequences and uploading them to the host computer parsing module in real time.

[0078] Step S4: Macroscopic flow field characterization and kinematic reconstruction of coherent vortex structure

[0079] Within a unified spatiotemporal coordinate framework, specific turbulent events in the flow field are spatiotemporally matched and quantitatively correlated with the topological response of the viscous force chain at the structural boundary.

[0080] To extract key physical information directly related to the motion mechanism from the high-dimensional raw velocity vector field data V(x,z,t) obtained from the particle image velocimetry unit, this embodiment reconstructs the raw velocity field data into an interface dynamics thickness scale and a vortex core rotation intensity scalar field that is completely corresponding in space and time by performing the following mathematical transformation, thus establishing an analytical framework between the observations obtained by the two measurement techniques with very different physical properties.

[0081] Definition of interface dynamics thickness scale:

[0082] Let u(z) be the normal velocity profile function at position x and time t in the flow direction. Define the velocity extrema of the high-gravity fluid layer and the surrounding fluid layer as follows: and The interface dynamics thickness scale at this location Defined as:

[0083]

[0084] in, This refers to the instantaneous shear layer thickness, representing the gradient of the velocity field u. Unit vector normal to the wall The projection onto the vertical velocity gradient. ;max|| represents taking the maximum absolute value of the vertical velocity gradient in the profile; sup{} and inf{} represent taking the supremum and infimum, respectively. Indicates a gravitational fluid layer. This indicates an environmental fluid layer.

[0085] Scalar field of vortex core rotation intensity based on Rortex criterion

[0086] To achieve objective, high-fidelity analysis and quantification of the turbulent coherent structure driving instantaneous extreme stress events within the shear layer and near-wall region, this embodiment employs the Rortex vortex identification criterion based on the velocity gradient tensor invariant. This criterion, through mathematical decomposition of the velocity gradient tensor, precisely decouples the motion of fluid micro-elements into pure rotational components and non-rotational tensile and shear components, thereby eliminating pseudo-vortex contamination caused by shear effects.

[0087] First, define the velocity gradient tensor G, its symmetric strain rate tensor S, and its antisymmetric vorticity tensor Ω:

[0088]

[0089]

[0090]

[0091] Introduce two identification scalars based on the definition of velocity gradient tensor invariants. and :

[0092]

[0093]

[0094] in, Represents strain intensity. The Frobenius norm represents the strain rate tensor S; Represents in-plane rotational intensity. It is the vorticity component in the y-direction.

[0095] The rotational dominance criterion ΔQ = Qr² - Qs² > 0 is used to identify regions in the flow field where pure rotation is dominant. Within these regions, the vortex core rotation intensity scalar is calculated. :

[0096]

[0097] By establishing a co-correlation function between the vorticity field of the permeable substrate flow field and the stress fluctuation of the structural surface, the direct causal relationship between the transient dynamic events of gravity flow and the dynamic response of the permeable substrate is revealed.

[0098] Step S5: Analysis and Inversion of Microscopic Viscous Force Chain Network

[0099] This embodiment utilizes the high-frequency sampling characteristics of the ADS1256 to extract transient excitation measures at local measurement points. This metric is considered as microscopic viscous force. Energy mapping on the structural surface; subsequently, a dynamic cross-correlation tensor is introduced. This is used to capture the coherence of stress transmission between different nodes, corresponding to the cooperative evolution characteristics of viscous force chain networks, where microscopic viscous forces... Defined as:

[0100]

[0101] parameter It is the Hamek constant, which is related to particle size and fluid properties. For surface roughness and For the range of viscous force, parameters The effective particle size of the sediment particles; vector The direction of action is a unit vector, when the interparticle spacing is... At this time, viscous force chains are formed.

[0102] To ensure the physical consistency of the model, the algorithm synthesizes the final intensity index. At that time, a response operator consisting of the Hamek constant and particle geometry parameters was explicitly introduced. And combined with the effective radius of action of viscous force Defined spatial weight kernel function When detected When a nonlinear step occurs, the development morphology of viscous force chains on the surface of the permeable substrate and their asymmetric impact on the structure can be quantitatively identified.

[0103] Energy activation mapping of local dynamic features:

[0104] Utilizing the high-frequency synchronous sampling characteristics of the integrated circuit ADS1256, the transient excitation measure of each flexible piezoelectric sensor node i is extracted. :

[0105]

[0106] In the formula, A characteristic timescale that matches the typical vortex scale of gravity flow; This is the original voltage signal; This is a bandpass filter operator used to lock high-frequency mechanical pulses induced by the breakage or recombination of viscous force chains. This step achieves the initial transformation from voltage fluctuations in the Euler reference frame to local measurement point energy density.

[0107] Physically constrained viscous coupling operators:

[0108] To introduce the physical nature of interparticle interactions within a gravitational flow, this embodiment defines a local viscous response operator based on a microscopic viscous force model. Topology connection weights .

[0109] The response operator Integrating Hamek's constant Effective particle size and micro roughness Physical constraints:

[0110]

[0111] Among them, Hamek constant The value range is 10 -21 Up to 10 -19 J; For surface roughness; This refers to the range of action of the viscous force.

[0112] The topology connection weight Used to determine whether there is a physically significant mechanical transmission channel between any two sensing nodes i and j:

[0113]

[0114] In the formula, The average coherence length of the particle clusters within the viscous turbidity flow; It is a physical domain indicator function, only if the particle spacing obtained from signal inversion is... Within the effective radius of viscous force When the weight is within a certain range, it is activated.

[0115] Analysis of topological coherence of stress propagation:

[0116] Utilizing the time synchronization characteristics of multi-channel signals, the dynamic cross-correlation tensor between signals from different nodes within a spatial neighborhood is calculated:

[0117]

[0118] This study aims to capture the time delay characteristics and signal fidelity of stress disturbances propagating on the surface of the permeable substrate, thereby identifying strong stress paths with high spatiotemporal coherence.

[0119] Synthesis of Topological Strength Index of Viscous Force Chain

[0120] Finally, by performing a nonlinear superposition operation on the sensing spatial domain, a viscous force chain topological strength index characterizing the global viscous force chain development degree is synthesized:

[0121]

[0122] The physical meaning of this index is: when When a nonlinear step increase occurs, it reflects that the clay clumps and skeleton particles inside the viscous gravity flow have entered a blocked state, forming a structured force network that can apply extreme asymmetric loads to the permeable substrate.

[0123] Step S6: Coupling analysis of cross-interfacial mass permeability and unsteady momentum flux

[0124] This step aims to quantitatively characterize the amount of fluid loss occurring at the permeable boundary of viscous gravity flow and its feedback effect on the main flow field through mathematical modeling.

[0125] Reconstruction of unsteady cross-interface penetration flux:

[0126] The system utilizes the instantaneous liquid surface evolution scalar captured by the 3D particle image velocimetry unit and the interfacial dynamic pressure gradient obtained by the multi-channel mechanical sensing unit to establish a dynamic permeation mapping model. To characterize the instantaneous rate of fluid penetration through the porous medium boundary, a dynamic permeation rate operator is defined:

[0127]

[0128] in, The effective permeability tensor of the interface characterizes the pore structure features of the permeable substrate. The instantaneous hydrostatic pressure potential energy is obtained by integrating the velocity and concentration distribution across the entire field. The unsteady impact pressure component is captured in real time by a multi-channel mechanical sensing unit; and These represent the environmental fluid dynamic viscosity and the characteristic thickness of the permeable layer, respectively.

[0129] This operator couples macroscopic flow field height fluctuations with interfacial microscopic pressure pulsations, thereby accurately reversing the cross-interfacial mass exchange flux caused by the "fluid trapping" effect.

[0130] Analysis of the modulation of boundary layer shear stress by momentum loss:

[0131] The system further quantifies the normal momentum flux induced by osmosis. Feedback on mainstream dynamics. By establishing a modified term for the boundary layer momentum integral equation, the algorithm can analyze how substrate permeability modulates the evolution frequency and energy level string characteristics of macroscopic coherent vortices (such as Kelvin-Helmholtz vortices) by changing the velocity gradient distribution in the near-wall region, thus revealing the essential physical laws of energy dissipation in gravity flow under the permeability interface effect.

[0132] Step S7: Analysis of Effective Stress Stratification Evolution and Liquefaction Critical State Identification in Permeable Subsidiary

[0133] This step aims to delve into the interior of the penetration boundary, analyze how external dynamic loads are transformed into internal pore pressure, and ultimately regulate the structural integrity of the substrate.

[0134] Dynamic calibration of unsteady excess pore water pressure response

[0135] An array of miniature pore water pressure sensors deployed beneath the support grid is used to acquire real-time data on the evolution of the pressure gradient within the permeable medium. This embodiment constructs the substrate pressure load index by performing a dimensionless transformation.

[0136]

[0137] in, This represents the measured transient pore pressure. This is the integral of the total normal load acting on the interface element; This is the geometric correction factor for the subgrade slope.

[0138] By utilizing the high-frequency sampling redundancy of the ADS1256, a nonlinear transfer function can be established between the explosive ultrapore water pressure pulsation induced by the impact of the gravity flow head front and the instantaneous vortex intensity scalar field captured by PIV, thus realizing the direct physical correlation between "vortex-induced pore response".

[0139] Analysis of Subsoil Liquefaction Criteria Based on Effective Stress Principle

[0140] Incorporating the mechanical equilibrium criteria of porous media, a transient effective stress operator is introduced. The algorithm utilizes a flexible piezoelectric sensor array to obtain the total interface normal load. Simultaneously measured pore water pressure The following difference operation is performed in real time:

[0141]

[0142] When detected Approaching the critical stability threshold ( ≤ 0.05 kPa, meaning the effective stress has basically disappeared), quantitatively determined as an event of "local liquefaction of the substrate and collapse of the force chain network induced by osmotic instability".

[0143] Spatial inversion of the direction of the mechanical instability vector:

[0144] By utilizing the spatial gradients of shear force and pressure captured by arrayed sensors, the instability preference characteristics of the substrate particle skeleton under the reverse impact of infiltration jets are automatically calculated. This step aims to reveal whether the initiation of sediment particle instability under infiltration substrate conditions is dominated by the Reynolds stress of the external flow field or by the upward surging infiltration kinetic pressure within the substrate, thereby constructing a complete causal chain encompassing hydrodynamics, interfacial permeability, and microscopic force chains.

[0145] Through the precisely constructed mathematical model described above, this embodiment can reconstruct fragmented pressure monitoring data into a stress structure skeleton in real time. This not only quantifies the load amplitude but also, by introducing orientation bias correction, inverts the spatial preference orientation of viscous force chains at the permeable substrate interface, thereby revealing the underlying mechanism by which microscopic viscous interactions of gravity flow regulate the dynamic response of the permeable boundary at a physical level. Combined with the transient velocity gradient characteristics obtained by the 3D particle image velocimetry unit, this invention achieves high-fidelity, cross-scale identification of the entire evolution process of viscous gravity flow on the permeable substrate.

[0146] This embodiment can accurately assess the modulation law of key dimensionless parameters such as inlet Reynolds number, Frod number, and substrate permeability on the dynamic response of complex viscous gravity flow propagation phenomena; it constructs an analytical model of eddy intensity field and a topological identification model of viscous force chain based on velocity gradient tensor invariants, realizing the objective quantification of turbulent coherent structures and microscopic viscous force chain networks; through an unsteady fluid-structure interaction identification method, it successfully decouples the unsteady load contribution between cross-interface seepage and viscous force chain reconstruction; and it introduces a multi-physics causal correlation framework to establish the spatiotemporal correspondence between transient topological evolution of the flow field and the distributed mechanical response of the seepage boundary. This invention has high integration, complete measurement dimensions, and strong engineering practicality.

[0147] In the process of describing this invention, it should be clearly understood that any terms involving orientational or positional relationships based on the accompanying drawings, such as "upstream," "downstream," and "near the bed," are intended only to provide a clear illustration of the invention and are not intended to indicate or limit the device or element to have a specific spatial orientation or to be constructed and operated according to a specific spatial orientation. Therefore, they should not be construed as limiting the invention.

[0148] In this invention, unless otherwise explicitly stated and specifically defined, terms such as "integration," "coupling," and "electrical connection" shall be given their broadest reasonable interpretation. They may encompass fixed, detachable, or integrated physical structures; mechanical or electrical functional associations; direct physical contact or indirect interaction through an intermediate medium; and even the synergistic relationship between two independent components within a unified control system. For those skilled in the art, the precise meaning of these terms in this invention can be reasonably interpreted according to the specific technical context.

[0149] The above description is merely a few preferred embodiments of the present invention, intended to illustrate the core technology of the invention, and not to limit the scope of protection of the invention to this. Any equivalent modifications, substitutions, or combinations of structures, methods, or processes made to the technical solutions of the present invention within the spirit and principles of the invention, or any direct or indirect application thereto to other related technical fields, shall be deemed to fall within the scope of patent protection claimed by the present invention.

Claims

1. An experimental apparatus for the interaction of viscous gravity flow with a permeable substrate, characterized in that, include: A water tank system is used to generate viscous gravity flow, and a composite graded permeable substrate is configured in the main experimental section. The permeable substrate includes a bottom structural base, a middle honeycomb support grid, and a top porous media layer of sediment. The three-dimensional particle image velocimetry unit is used to project a sheet light source into the target measurement volume element and acquire tracer particle images to reconstruct the three-dimensional transient velocity vector field of the viscous gravity flow in the region adjacent to the permeation interface. The multi-channel mechanical sensing unit includes a flexible piezoelectric sensor array conformally integrated in the form of a discrete lattice on the surface of the stress-bearing ribs of the honeycomb support grid, and a high-resolution analog-to-digital conversion module coupled to the sensor array through a multi-channel multiplexing architecture. The multi-channel mechanical sensing unit embeds an analytical module based on micro-dynamic physical constraints, which is used to invert the transient kinetic energy and spatial preference orientation of the viscous force chain from the dynamic mechanical response collected by the sensor array. The pore water pressure monitoring unit includes a pore water pressure sensor array arranged below the support grid, used to acquire transient excess pore water pressure evolution data inside the permeable medium; The central synchronization control unit is used to output a unified trigger signal with deterministic time delay compensation to forcibly lock the sampling timing of the stereo particle image velocimetry unit, the multi-channel mechanical sensing unit and the pore water pressure monitoring unit, so as to realize the spatiotemporal co-position measurement of the flow field and the multi-physics field response. The analysis module processes the high-frequency mechanical pulses obtained by the high-resolution analog-to-digital conversion module and extracted by the flexible piezoelectric sensor array. It combines the preset Hamek constant and interface geometric parameters to construct a viscous coupling operator and topological connection weights. By capturing the stress transmission coherence through dynamic cross-correlation tensors, it synthesizes the topological strength index of the viscous force chain to quantitatively invert the transient kinetic energy and spatial preference orientation of the viscous force chain.

2. The experimental apparatus for the interaction of viscous gravity flow and permeable bed according to claim 1, characterized in that, The water tank system includes a high-density gravity flow energy storage tank, a liftable initial ramp, a low-density environmental fluid tank, and a fast-opening and closing electric gate. The high-density gravity flow energy storage tank and the low-density environmental fluid tank are connected by an electric gate, and the liftable initial ramp is set at the outlet of the high-density gravity flow energy storage tank.

3. The experimental apparatus for the interaction of viscous gravity flow and permeable bed according to claim 1 or 2, characterized in that, The bottom structural base has a fluid circulation chamber, the grid spacing of the middle honeycomb support grid is optimized to ensure unobstructed flow of fluid across the interface, and the top porous media layer of sediment is laid with sediments of a specific particle size distribution according to experimental requirements.

4. The experimental apparatus for the interaction of viscous gravity flow and permeable bed according to claim 1, characterized in that, The stereo particle image velocimetry unit includes at least two sets of high-speed cameras configured with a solid angle and conforming to the Schumpfler optical criterion, and a high-energy pulsed laser emission group for projecting a high-energy-density sheet light source into the target measurement volume; the sheet light source measurement area is configured directly above the permeation substrate and perpendicular to the axis of the permeation substrate.

5. The experimental apparatus for the interaction of viscous gravity flow and permeable bed according to claim 1, characterized in that, The high-resolution analog-to-digital conversion module is a delta-sigma type analog-to-digital conversion integrated circuit based on the ADS1256 chip. The multi-channel mechanical sensing unit also includes an integrated wireless sensing and digitization module, which integrates the ADS1256 chip and a low-power wireless radio frequency communication unit.

6. The experimental apparatus for the interaction of viscous gravity flow and permeable bed according to claim 1, characterized in that, The central synchronization control unit includes a PIV control server and a central synchronization main controller. By outputting a unified main trigger signal with deterministic time delay compensation, it forcibly locks the sampling timing of the three-dimensional particle image velocimetry unit, the multi-channel mechanical sensing unit, and the pore water pressure monitoring unit, ensuring that heterogeneous physical field data achieves spatiotemporal alignment within microsecond precision.

7. An experimental apparatus for the interaction of viscous gravity flow with a permeable substrate according to any one of claims 4 to 6, characterized in that, It also includes an automatic scanning high-precision laser bed surface scanner, which is set up above the main experimental water tank to acquire a three-dimensional digital elevation model of the permeable bed surface in real time during the gravity flow scouring process.

8. An experimental apparatus for the interaction of viscous gravity flow with a permeable substrate according to any one of claims 4 to 6, characterized in that, It also includes an environmental multiphysics monitoring module, which includes at least one of the following: an online rheological monitoring probe for real-time verification of the non-Newtonian flow index of viscous gravity flow, an acoustic Doppler velocimeter for providing single-point high-precision time-resolved velocity vector data, and a non-contact ultrasonic flow meter for quantitative analysis of environmental fluid compensated flow velocity.

9. A method for inverting viscous force chains in the interaction between viscous gravity flow and a permeable substrate based on the experimental apparatus described in any one of claims 1 to 8, characterized in that, Includes the following steps: S1. Construct and calibrate the permeable substrate water tank system, install the permeable substrate integrating a flexible piezoelectric sensor array and a pore water pressure sensor array at the predetermined position, and configure a particle image velocimetry unit to make the laser sheet light plane coincide with the target fluid profile; S2. Generate a viscous gravity flow with controllable parameters and allow it to reach its full development state, while simultaneously configuring an environmental fluid with a matching refractive index; S3. By outputting a unified trigger signal through the central synchronization control unit, the sampling timing of each measurement unit is synchronously locked to achieve spatiotemporal alignment of heterogeneous physical field data; S4. Based on the three-dimensional transient velocity vector field, the interface dynamic thickness scale and vortex core rotation intensity scalar field are extracted to characterize the coherent vortex structure in the macroscopic flow field; S5. Based on dynamic mechanical response, combined with the preset Hamek constant and interface geometric parameters, a viscous coupling operator and topological connection weight are constructed. The stress transmission coherence is captured by the dynamic cross-correlation tensor, and the topological strength index of the viscous force chain is synthesized to quantitatively invert the transient kinetic energy and spatial preference orientation of the viscous force chain. S6. Based on the three-dimensional transient velocity vector field and the dynamic mechanical response, couple analytical cross-interface mass permeability and unsteady momentum flux; S7. Based on transient excess pore water pressure evolution data and interface normal load, analyze the effective stress evolution of the permeable substrate and identify the critical liquefaction state; S8. Based on the spatiotemporal matching relationship between the topological strength index of the viscous force chain and the scalar field of the vortex core rotation strength, establish a physical causal chain from the flow field dynamic events to the mechanical response of the permeable substrate.

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