Tong Ge

Experimental Research on Trenching in Stiff Clay by Submerged Vertical Traveling Jets

ABSTRACT Zhang, S.; Zhao, M.; Ge, T., and Wang, C., 2016. Experimental research on trenching in stiff clay by submerged vertical traveling jets. This study investigated trenching by submerged circular traveling jets in stiff clay using an experimental method. The testing clay was prepared as mixtures of natural clay and cement with shear strength ranging from 60 kPa to 90 kPa. The jet pressure, the nozzle translational velocity, and the diameter of the nozzle all varied in the test. A cohesive sediment scouring theory was employed to reveal the mechanism of the jet trenching. It showed that the boundary layer shear force on the jet-soil interface might be the predominant mobilizing force for jet trenching. The trench depth was found to increase with the jet pressure, erodibility coefficient, and the diameter of the nozzle and decrease with the translational velocity of the nozzle and the threshold stress of the clay. The essence of the traveling jet trenching could be considered as jet erosion. The efficiency of jet trenching was found be higher when the jet worked with low pressure and large diameter. The trench depth of a large nozzle could be obtained by testing a small one.

Practicability Research and Design of the Underwater Plane

When traditional underwater vehicles (TUV), including AUVs, ROVs, submarines and underwater gliders, cruise, they are neutral in buoyancy normally and their buoyancy are produced by buoyancy materials or big ballast tanks, thus these components take up the major part of the vehicles’ volumes. Differently, an underwater plane (UP) cruises in the condition of negative buoyancy. Its wings bear the residual gravity, which makes its resistance and volume decreased drastically at the same speed and with the same payload. To prove the practicability of the UP, we find the advantages of the UP in the velocity or resistance and volume compared with the TUV on the same premise through theoretical arithmetic. So far, a model, we designed in the similar way of designing an airplane, has been manufactured to make sure that the UP could work in water. In a model trial in the tank, the model completed regular motions well and shown good maneuverability and stability. So, the concept of the UP is not only practicable but valuable.Copyright

Kane’s Approach to Modeling Underwater Snake-Like Robot

The paper presents a detailed methodology for dynamic modeling of underwater snake-like robot using Kane’s dynamic equations. This methodology allows construction of the dynamic model simply and incrementally. The generalized active forces and the generalized inertia forces were deduced. The forces which contribute to dynamics were determined by Kane’s approach. The model developed in this paper includes gravity, control torques and three major hydrodynamic forces: added mass, profile drag and buoyancy. The equations of hydrodynamic forces were deduced. The methodology provides a direct method for incorporating external environmental forces into the model. The resulting model is obtained in closed form. It is computationally efficient and provides physical insight as to what forces really influence the system dynamics. The dynamic model provides a framework for modern model-based control schemes.

Experiments on high-performance maneuvers control for a work-class 3000-m remote operated vehicle

The challenge of high-performance maneuvers for a deep-ocean underwater vehicle is to design proper controllers and ensure the high accuracy of vehicle state measurements. Current underwater vehicle control solutions are considered to be a unique controller designed to reject the disturbance and noise. However, the controller is based on a precise hydrodynamic model. It requires multiple underwater experiments and complex theoretical analysis. In this article, a hybrid control strategy is presented for the work-class remote operated vehicle. It tries to compose several proportion–integral–differential controllers into one intelligent sequence in terms of task requirements. The proposed approach employs the iterative learning method to improve the performance of the depth holding and the way-point tracking. A remote operated vehicle system weighted about 1.5 tons is provided as a physical platform for scientific investigations using acoustic Doppler current profiler, inertial navigation system, depth sensor, and an altimeter. Results from the simulation and the experiment in the basin show that the proposed approach provides high accuracy at both conditions: tracking way-points with or without ocean currents and disturbances, which show the effectiveness of the proposed approach. In addition, the thrust vector defined for a propeller facilitates the control of underwater vehicle as the thruster configuration changes.

The prediction of traveling jet trenching in stiff clay based on the erosion failure mechanism

ABSTRACT The performance of traveling jet trenching in stiff clay was tested. All the key parameters varied in the experiment, including the jet velocity, the shear strength of clay, the diameter of the nozzle, and the translational velocity of the nozzle. The jet–soil interface was found to be an arc. An equation was given to describe the interface. On the basis of the erosion failure mechanism, a new method is presented for predicting jet trenching depth. We first calculated the trajectory of the jet–soil interface and then predicted the distribution of the boundary layer shear stress along the jet–soil interface. The point where the wall shear stress was equal to the critical shear strength of clay was the ultimate trenching depth. The predictive results were found to fit the experimental results well.

Numerical study of sand scour with a modified Eulerian model based on incipient motion theory

ABSTRACT Application of the standard Eulerian model to simulations of sand scour results in unrealistic phenomena. Therefore, the present work develops a modified Eulerian model based on sand incipient motion theory. The modified model is applied for simulating a two-dimensional single vertical jet and a moving planar jet. The simulation results generally demonstrate fairly good agreement with published results of scour profiles and the velocity contours of the water and sand phases. In addition, equations to describe self-similar scour profiles for the moving planar jet cases are given. The results demonstrate that the modified model efficiently and accurately simulates the two-dimensional sand scour produced by jets, particularly for the moving jet cases.

The scour prediction of non-contact trencher with numerical method

Numerical method was used to predict scour in order to obtain steady profile of seabed when Non-contact trencher is working. Single-phase model was carried out to simulate the flow field. Combining the empirical formulae, the hydrodynamic forcing on the wall of predesigned trench could evaluate the ability of deposition and erosion. Then a multiphase model, Eulerian model, was adopted to simulate the fix-point jetting of trencher, which can predict the ability of trenching. Furthermore, this model was also used to calculate the flow field with trencher’s working. The numerical method can predict the scour ability of trencher and the scour depth is in agreement with engineering requirement.

Output Feedback Control for an Active Heave Compensation System

To reduce the adverse effect of the unexpected vessel heave motion on the response of underwater payloads, a control strategy is presented for an active heave compensation system using an electro-hydraulic system driven by a double-rod actuator. An adaptive observer is designed to estimate the unmeasured system states and the unmodeled forces. An observer is also proposed to asymptotically reconstruct the vessel motion. By using these observers, the Lyapunov’s direct method and backstepping technique, an output feedback controller is proposed to force the heave compensation error to converge to a small bounded area around the origin. Simulations illustrate the effectiveness of the proposed control scheme.