Experimental Study On Rheological Properties Of Marine Mud Flow

The 21st century is the century of the ocean.The ocean economy has once again become a new growth point of the world economy,and the national strategic position of the ocean has been unprecedentedly improved.In the report of the 19th National Congress of the Communist Party of China,General Secretary Xi put forward the strategic concept of "adhering to the overall planning of land and sea and building a strong maritime country".In recent years,under the support of the strategy of accelerating the construction of a "marine power",the development of marine oil and gas energy and the exploration of marine mineral resources have developed rapidly;the deployment of marine underwater monitoring systems and the construction of marine artificial facilities have entered a stage of rapid growth.However,the seabed environment is complex,mainly composed of clay and silt sand with very poor engineering properties.These soils have the characteristics of high liquid limit,high compressibility and low strength,which inevitably triggers the instability of the seabed and leads to the occurrence of seabed.Various marine geological disasters such as bed collapse,submarine landslide,marine mud flow and turbidity current.The occurrence of marine geological disasters has caused damage to the safety and stability of underwater drilling platforms,submarine communication optical cables,monitoring equipment laid on the seabed,seabed test platforms,submarine waterways,and reclaimed islands and reefs.So far,marine disaster research has become an urgent task.As an important marine geological disaster,marine mud flow research on the rheological characteristics of marine mud flow movement can effectively analyze and predict the damage of the submarine slope,provide a scientific basis for the construction and protection of marine engineering,and promote marine science and technology.development is of great significance.In this paper,the rheological characteristics of marine mud flow are studied on the basis of soil mechanics and rheology,with laboratory experiments and numerical simulation as the main research methods.Referring to the instruments designed by Zhang Lei and Liu Wenyuan of China University of Geosciences,and based on the related principles of Anton Paar viscometer and cross-plate shearing instrument,a soil rotational rheometer was made.The marine mud flow samples were prepared artificially,and the influence of different clay components and cementing substances on the rheological properties of marine mud flow was studied.The ANSYS FLUENT numerical simulation software was used to carry out numerical simulation on the data obtained from the rheological test to analyze the movement of marine mud flow.speed and pressure variation.The main conclusions of this paper are as follows:1.Under different rotational speed conditions,the torque value of marine mud flow increases with the increase of rotational speed,and changes nonlinearly.The Herschel-Bulkley rheological model fitting was performed on the measured rotational speed and torque values,and it was found that the marine mud flow has the characteristics of non-Newtonian fluid and shear dilution.2.The torque value of marine mud flow increases with the increase of clay minerals under different clay mineral contents;under a certain clay mineral content,with the increase of shear rate,the apparent viscosity of mud flow decreases rapidly until the downward trend Smooth;when the shear rate is constant,the apparent viscosity of mud flow increases with the increase of clay content.3.When the shear rate is constant,the shear stress of the mud flow increases with the increase of shear time.After reaching the peak value,the shear stress gradually decreases with the increase of shear time until it tends to a certain constant value;In addition,the peak shear stress of mud flow increases with the increase of shear rate,and the yield time decreases with the increase of shear rate.4.Salt crystal cementation enhances the overall strength of marine mud flow.It is mainly reflected in the change of microstructure and macroscopic surface characteristics.On the one hand,the water in the soil and the pores are full of salt solutes,and the salt in the soil undergoes a chemical reaction,filling the gaps and cementing it into a structural part of the soil,making the soil Structural enhancement.On the other hand,due to the different solubility of salt solutions in different soil pores,salts with low solubility will precipitate,crystallize,and adhere to the surface of soil particles to form a shell,which increases the strength of soil particles.5.The variation curve of mud flow shear stress with shear rate with different salt crystal cementation content follows the rheological law.From the fitting results of the Herschel-Bulkley model,the mud flow shear strength after salt crystal cementation increases,and the yield stress and The apparent viscosity is significantly increased;When the content of salt crystal cement is more than 30%,the change of shear rate does not play a dominant role in the rheological properties and rheological parameters of marine mud flow,but is gradually dominated by salt crystal cement.6.The comparative study of the numerical simulation of water and marine mud flow with 20% clay minerals shows that the mud flow will experience the process of changing from laminar motion to turbulent motion.In the state of laminar flow,shear circles will be formed one by one,which are arranged outward in turn,with certain layering characteristics;in the state of turbulent flow,they are no longer regular and regular shear circles,but Mix and perturb each other,forming small eddies.The whole process of water motion follows the state of turbulent motion and is free and loose.7.The pressure field of the mud flow shows a symmetrical characteristic distribution,which is stably distributed in the area of shear damage.Although the pressure field of water also exhibits a symmetric shape,it is less constrained by its expansion due to its smaller viscosity,so it can relatively freely spread for a longer distance.The comparative study of the two shows that the velocity field distributions of mud flow and water are partially similar,but the pressure field distribution is quite different,and the pressure of mud flow is much larger than that of water during the movement.