Anti-Overturning Fully Symmetrical Triboelectric Nanogenerator Based on an Elliptic Cylindrical Structure for All-Weather Blue Energy Harvesting

Triboelectric nanogenerators(TENGs) have shown promising potential for large-scale blue energy harvesting. However, the lack of reasonable designs has largely hindered TENG from harvesting energy from both rough and tranquil seas. Herein, a fully symmetrical triboelectric nanogenerator based on an elliptical cylindrical structure(EC-TENG) is proposed for all-weather blue energy harvesting. The novel elliptical cylindrical shell provides a unique selfstability, high sensitivity to wave triggering, and most importantly, an anti-overturning capability for the EC-TENG. Moreover, benefiting from its internal symmetrical design, the EC-TENG can produce energy normally, even if it was overturned under a rude oscillation in the rough seas, which distinguishes this work from previous reported TENGs. The working mechanism and output performance are systematically studied. The as-fabricated EC-TENG is capable of lighting 400 light-emitting diodes and driving small electronics. More than that, an automatic monitoring system powered by the EC-TENG can also monitor the water level in real-time and provide an alarm if necessary. This work presents an innovative and reliable approach toward all-weather wave energy harvesting in actual marine environments.

Evaluation of Inner Soil Pressure Acting on Opened Bottom Cylindrical Structure

An opened bottom cylinder is a large-diameter cylinder placed on a rubber base or embedded in a soil foundation. The settlement of such a cylinder differs greatly from that of a closed bottom cylinder and so does the distribution of inner soil pressure over the opened bottom cylindrical structure. Through investigation of the settlement and the inner soil pressure on the opened bottom cylinder by model experiments, the interactions among the filler inside the cylinder, subsoil and cylinder are analyzed. The adjusting mechanism of friction resistance between the inner filler and the wall of the cylinder during overturning of the cylinder is discussed. Based on the experimental study, a method for calculating the inner soil pressure on the cylindrical structure under axisymmetric loading or non- axisymmetric (with lateral) loading is proposed in this paper. Meanwhile, the effective anti-overturning ratio of the opened bottom cylinder is derived.

Determination of the Critical Value of Deflection for Embedded Cylindrical Structures

An embedded cylinder is a large-diameter cylinder embedded in a soil foundation. The state of failure of such an embedded cylindrical structure shows large deflection instead of slide and overturn of the traditional gravity type of structure placed on a rubble base or foundation base. The critical value of deflection of the embedded cylindrical structure, which is the maximum allowable deflection for stability calculation of the cylinder, is a vital control value. Through investigation on deflection and soil pressures on an embedded cylinder by model experiments, the variations of the angle of rotation θ of a cylinder with effective anti-overturning ratio η and moment MH of thrust are discussed. On the basis of experimental study, the critical value of deflection of the cylindrical structure is proposed in the paper. Meanwhile, the formulas for calculating deflection of cylinders are derived.

Criteria for Submergence of Ice Blocks in Front of Ice Cover

During winter, ice jams develop when floating ice blocks accumulate in rivers. Ice jams can dramatically decrease in the capacity of flow in a river and can cause ice flooding due to increase in water level. Submergence of floating ice blocks in front of ice cover is critical for the development of an ice jam. In this study, the effect of the rotation angle of ice blocks on the submergence of ice block was assessed. The impacts of both the drag force caused by the flow and the hydraulic pressure force on the rotation of ice block were studied. Considering both the maximum moment for anti-overturn of an ice block, and the associated rotation angle θ1, equations for describing the criteria for ice block entrainment in front of ice cover have been derived. On the basis of the theorem for moment equilibrium, relating the moment acting on a horizontal ice block with the maximum anti-overturn moment of an ice block, the criteria for assessing the overturn-and-submergence of an ice block have been proposed. To verify results using the derived equations for calculating the critical flow velocity for ice block submergence in front of ice cover, data was collected from flume experiments in the laboratory. Experiments have been conducted using different sizes of ice block under different flow conditions in a flume which is 26.68 m long, 0.40 m wide, and 0.6 m deep. Model ice blocks were made of polypropylene and have nearly the same as the mass density of the natural ice. Using proposed method for assessing ice block submergence in front of ice cover, calculated critical flow velocities agree well with those of experiments.