A Dynamic Response Analysis of Tension Leg Platforms Including Drag Forces in Regular Waves
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For predicting the motion and structural responses of tension leg platforms(TLPs) in regular waves, a numerical scheme is introduced. The numerical approach in this paper is based on a combination of the three dimensional source distribution method and the finite element method. The hydrodynamic interactions among TLP members, such as columns and pontoons, are included in the motion and structural response analysis. The drag forces on the submerged slender members, which are proportional to the square of relative velocity, are newly included in order to estimate the responses of members with better accuracy. Comparisons with other's results verifies the works in this paper.Keywords:
Tension (geology)
Square (algebra)
With the development of economy, the energy problem is becoming more and more seriously, which is closely related to resistance, and drag reduction means to save energy. Research on the technology of drag reduction plays an important role in the area of energy saving and its utilization rate enhancing. Using the method of bionic surface drag reduction to reduce the surface friction drag in a fluid medium has become a hot topic in the research area of drag reduction. Furthermore, through analyzing approaches of bionic surface drag reduction on the necessary of energy saving, energy utilization rate enhancing and drag reduction theory system improving, the research progress of the dynamic bionic non-smooth surfaces and bionic jet surface drag reduction technology are summarized in detail, the main trend of non-smooth drag reduction technology research and jet drag reduction technology is reviewed.
Zero-lift drag coefficient
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In cycling sports, fluid resistance accounts for ninety percent of all resistance at maximum speed. To date, studies on fluid resistance in track race have examined about bicycle and racer’s position on the bike for the reducing drag force. However, these studies have not revealed the relation of cycle wear and fluid resistance. In This study, we focused on the effect of fabric to reduce drag force in track race. To clarify where body parts increase air resistance, we first employed computer fluid dynamics. From results of simulation, the head, arms, and legs are identified as the major sources of drag on a track race. Based on results, we tested three kinds of fabrics by measuring drag force on cylinder model and full-scale mannequin. The reduction in drag force was observed in both experiments, and finally almost eight percent of drag force was reduced on skinsuit that was made from compared fabric.
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The drag force acting on a body moving in a fluid has two components, friction drag due to fluid viscosity and form drag due to flow separation behind the body. When present, form drag is usually the most significant between the two and in many applications, streamlining efficiently reduces or prevents flow separation. As studied here, when the operating fluid is water, a promising technique for form drag reduction is to modify the walls of the body with superhydrophobic surfaces. These surfaces entrap gas bubbles in their asperities, avoiding the direct contact of the liquid with the wall. Superhydrophobic surfaces have been vastly studied for reducing friction drag. We show they are also effective in reducing flow separation in turbulent flow and therefore in reducing the form drag. Their conceptual effectiveness is demonstrated by studying numerical simulations of turbulent flow over a bluff body, represented by a bump inside a channel, which is modified with different superhydrophobic surfaces. The approach shown here contributes to new and powerful techniques for drag reduction on bluff bodies.
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The friction resistance accounts for a large proportion of the total resistance, during the navigation of ships and underwater vehicles. Drag reduction techniques can significantly reduce the friction resistance of the wall and improve the speed of navigation. This paper combine microbubbles drag reduction technology and nonsmooth and hydrophobic surface technology. Building different analysis models, considering the dimples size of nonsmooth surface , the contact angle of surface and wall roughness, study the law between drag reduction and parameters of the wall by gas-liquid two-phase flow model. Under the same conditions, analysis results show that the performance of drag reduction is mainly determined by the dimple size of nonsmooth surface. The lager dimples cause stronger turbulence and loss more energy. The drag reduction effect is declined. There is a linear relationship between the drag reduction and the contact angle of hydrophobic surface. The drag reduction is enhanced by increasing the contact angle. But the principle is complicated between drag reduction and the roughness of the wall. There are different roughness to achieve the best effect under different flow velocities.
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Based on the migratory phenomenon of the puffer and the cone-shaped structures on its skin, the effects of spinal height and tilt angle on the drag reduction characteristics is presented by numerical simulation in this paper. The results show that the trend of total drag reduction efficiency changes from slow growth to a remarkable decline, while the viscous drag reduction efficiency changes from an obvious increase to steady growth. The total and viscous drag reduction efficiencies are 19.5% and 31.8%, respectively. In addition, with the increase in tilt angle, the total drag reduction efficiency decreases gradually; the viscous drag reduction efficiency first increases and then decreases, finally tending to be stable; and the total and viscous drag reduction efficiency reaches 20.7% and 26.7%, respectively. The flow field results indicate that the pressure drag mainly originates at the front row of the spines and that the total pressure drag can be effectively controlled by reducing the former pressure drag. With the increase in low-speed fluid and the reduction in the near-wall fluid velocity gradient, the viscous drag can be weakened. Nevertheless, the drag reduction effect is achieved only when the decrement of viscous drag is greater than the increment of pressure drag. This work can serve as a theoretical basis for optimizing the structure and distribution parameters of spines on bionic non-smooth surfaces.
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The development of the theory of turbulence has made a breakthrough in the application of drag reduction technology on ships, which contributes to energy saving and environmental protection. When a ship is sailing, it has to overcome resistance. Total resistance includes frictional resistance, wave-making resistance, and viscous pressure resistance, in which frictional resistance acts as the main resistance for low-speed ships, and for high-speed ships, the main resistance is wave-making resistance. This paper reviews the ship drag reduction technology by giving a brief introduction to drag reduction methods using grooves, bulbous bows, bubbles, hydrofoils, wall vibration, and high-polymer additive respectively, as well as their principles.
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Some of the salient experimental observations in polymer drag reduction are reviewed, in light of basic concepts of turbulent flow. The areas common to drag reduction by polymers and surfactants, and drag reduction by fibers and suspensions in both liquids and gases are examined, and some general rules for obtaining friction reduction are suggested. Based on these ideas, the drag‐reducing properties of polymers, soap and surfactant aggregates, and fibers and solids are portrayed, noting the role of additive size and weight in producing the effect.
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This article explores the mathematics involved in calculating air resistance as it is utilized in vehicle speed calculations. The author focuses on the various forces that affect a vehicle skidding on a surface and how the drag force, caused by a vehicle's travel through the air, is defined. The article first presents a basic example of a speed calculation that ignores drag. The article goes on to consider vehicle speed estimates with drag, finding an equation for velocity, and a comparison of speed calculations (no drag versus drag). The author concludes that, based on the mathematics present, drag is negligible. Since friction is dependent upon the weight of the vehicle and the fact that vehicles are relatively heavy compared to the force of drag, thus drag can be ignored under typical conditions. There is a brief mention of the need to continue to consider the role of drag for vehicle design.
Zero-lift drag coefficient
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