The fluid stress or flow-induced vibration of annular gap flow always has some influence on the stable working conditions of a hydraulic machine. A time-averaged analysis of flow may not have to explicitly acknowledge these factors. Accordingly, a finite-axial-length annular gap was measured via particle image velocimetry (PIV), with inner boundary motion and a stable outer boundary. As a statistic result regarding the fluid stress, the Reynolds stresses soared in the first region, were sustained in the middle region, but decreased at last. The flow had a higher convective transportation intensity in the radial direction than in other directions. Flow diagnostics were also performed by proper orthogonal decomposition (POD). As a result, the coherent structures were found. Then, the power spectrum density (PSD) functions were also calculated for finding the flow-induced vibration characteristics; the functions had high amplitude in the low-frequency domain and low amplitude in the high-frequency domain, with an order of magnitude between the two amplitudes of 10⁻¹ to 10⁻². In addition, the frequency was higher at a smaller gap width in the middle-frequency domain, but the condition was the opposite in the high-frequency domain. In conclusion, the fluid stresses were changeable and uneven along the flow direction, and flow-induced vibration obviously existed. Remarkably, the turbulence characteristics of the annular gap flow were not “laminar approximating,” while the diameter ratio of the gap was 0.6 to 0.8.

The paper presents the visualization results of the sudden contraction flow field with an annular gap downstream of the contraction cross section. The contraction ratio directly influences the flow phenomena. No stationary vortices were observed upstream of the contraction cross section, and flow separation divided the flow field within the annular gap into a recirculation zone, a shear layer, and a mainstream zone. Vena-contracta point and reattachment point occurred within the flow field of the annular gap. The production of Reynolds stress varied with the contraction ratio, and the momentum exchange mainly occurred in the recirculation zone and the shear layer, while the flow state in the mainstream zone tended to become isotropic. Rapid changes in turbulent kinetic energy primarily occurred in the shear layer, and the production term of turbulent kinetic energy contributed the most. Applying computational fluid dynamics and experimental results, this study has formulated an expression for the contraction coefficient of the proposed model. The axial positions of the vena-contracta point and reattachment point have a strong correlation with the contraction ratio, which can be represented by an exponential function.

The wheeled capsule hydraulic transportation is a new technique for transporting materials. In this technique, the wheeled capsule, which is designed to contain materials, is one of the core components. In this study, a new type of wheeled capsule structure was first designed, and then experiments were conducted at seven water discharges, eight wheeled capsule dimensions, and eight mass of transporting materials in the pipe with an inner diameter of 100 mm. The pipe in study was divided into nine parts, and the speed of the wheeled capsule in each pipeline section was analyzed. The results showed that the speeds of the wheeled capsules in different sections of the pipeline did not change significantly and basically fluctuate near the overall average speed and the maximum relative fluctuation value was ⩽ 8.6%. Therefore, the overall average speed of the wheeled capsule can be used to analyze the motion characteristics of the wheeled capsule. The average speed of the wheeled capsule increased with increasing water discharge, diminished with increasing mass of transporting materials, increased with increasing length of the wheeled capsule, and increased with increasing diameter of the wheeled capsule. The empirical formula of the average speed of the wheeled capsule with different water discharges, wheeled capsule dimensions and mass of transporting materials was obtained by the nonlinear regression method and can be expressed as $v=0.011{(0.001\mathrm{dL}/4L+d)}^{0.5686}(Q/0.9\pi D\upsilon {)}^{0.4606}(0.001M{)}^{-0.1646}-2.7740$ . The empirical formula was experimentally validated. The maximum relative error did not exceed 7.05%, proving that the empirical formula of the average speed of the wheeled capsule was rational. The results of this study can provide a theoretical basis for designing the structure of the wheeled capsule.

The piped hydraulic transportation of tube‐contained raw material is an emerging technique for transporting materials. In this technique, the piped vehicle is one of the core components, and its motion characteristics directly determine the transportation energy consumption and the transportation cost of this technique. To study the motion characteristics of the piped vehicle, the force of the piped vehicle was analyzed from the mechanical perspective in this paper. On the assumption that the piped vehicle moved steadily and it had sufficient stiffness, the mathematical model of the piped vehicle motion was established in the turbulent flow according to the stress characteristics of the piped vehicle and the factors influencing its motion characteristics, and then the mathematical model was tested by experiments. The findings show that the calculated values of the velocities of the piped vehicle were identical to the experimental values with changes in various influencing factors. When the flow discharge, the diameter or length of the piped vehicle increased, or the mass of transported material decreased, the velocity of the piped vehicle increased. The maximum relative error did not exceed 9.47%, which proved that the mathematical model of the piped vehicle motion was rational. The results can provide theoretical basis to improve the structure of the piped vehicle and the piped hydraulic transportation technique of tube‐contained raw material.

Hydrodynamic forces influence the efficiency and safety of pipeline transport in ocean engineering. A capsule pipeline is an example of pipeline transportation. In this work, a dynamic model is proposed to explain the oscillating motion of a capsule in a hydraulic capsule pipeline (HCP). The main study was conducted using a modal analysis of hydrodynamic forces acting on a capsule, which could be divided into frictional drag and pressure drag forces. The results indicated the presence of independent modes with different contributions to the hydrodynamic forces. Ultimately, the first to fiftieth modes represented 94~97.3% of the hydrodynamic force contributions. These modes had their own frequency ranges and power spectrum density (PSD) functions, and the frictional drag and pressure drag were both found to coincide with the narrow-band characteristics of the lower-order modes. However, the PSD functions of the frictional drag were found to fulfill the wide-band characteristics corresponding to the higher-order modes. Then, coherent structures were extracted. As the mode order increased, the vortices became more fragile and the frequency became higher. This phenomenon coincided with an increase in the frequency of the time coefficient peak, which became larger. This work could provide new perspectives on the hydrodynamic forces of pipeline transport, especially its dynamic analysis of the interaction between a rigid capsule and fluid flow.

The piped vehicle hydraulic transportation is a new energy-saving and environmental-friendly technique for transporting materials. To optimize the technical parameters of the piped vehicle hydraulic transportation, the transporting energy consumption of the technique was studied by a combination of theoretical analysis and experiments. Experiments were conducted at six piped vehicles with the diameter–length ratios of 0.4, 0.6, 0.47, 0.7, 0.53, and 0.8, seven flow Reynolds numbers of 102,140, 132,413, 167,014, 200,534, 234,037, 267,556, and 299,993, two transporting loads of 1200 and 1500 g, and three pipe layout forms of straight pipe, flat bend pipe, and inclined bend pipe. The results showed that the total energy consumption of the piped vehicle hydraulic transportation increased with increasing flow Reynolds numbers and increasing mass of transporting materials. The total transporting energy consumption of a piped vehicle with the diameter–length ratio of 0.53 was the highest, and that of a piped vehicle with the diameter–length ratio of 0.47 was the lowest. The unit transporting energy consumption of a bend pipe was higher than that of a straight pipe. Meanwhile, the total energy consumption of the piped vehicle hydraulic transportation was analyzed by hydrodynamic theory. The calculation formula for the total energy consumption of the piped vehicle hydraulic transportation was obtained and validated experimentally. The maximum relative error did not exceed 8.07%, proving that the total energy consumption calculation formula of the piped vehicle hydraulic transportation was rational. By analyzing the transporting efficiency of piped vehicle hydraulic transportation under different influencing factors, the optimal transporting combination was the piped vehicle with the diameter–length ratio of z = 0.47 and the flow Reynolds number of Re = 200,534. The results of this study can provide a theoretical basis for optimizing the technical parameters of the piped vehicle hydraulic transportation.