Drag Resistance Research Articles

The Analysis Method of Performance Comprehensive Performance Optimization Design for Multi-body Unmanned Boat

Abstract In order to compare and analyze the comprehensive performance of multi-hull unmanned boats under specific conditions, this paper conducts in-depth research on the multi-objective decision-making theory and intelligent optimization algorithms of boat type design. First of all, this paper establishes the corresponding ship type and resistance database using the response surface fitting method through the drag resistance test of the ship model. Secondly, comprehensively considering the impact of the three major performances of multi-hull unmanned craft on the design of the boat’s speed, maneuverability and seakeeping, a comprehensive optimization mathematical model was established, and the comprehensive optimization design software was adapted. Then, using genetic algorithm, particle swarm algorithm, and chaos algorithm to conduct a preliminary calculation and analysis of the comprehensive performance of the two ship types. By comparing the calculation results, it is concluded that the particle swarm algorithm is the best algorithm among the three intelligent algorithms. Finally, the particle swarm algorithm is used to compare and analyze the comprehensive performance of the two ship types in the multi-hull unmanned craft. It is concluded that the overall performance of the three-hull unmanned craft is better at the same speed and displacement. This paper discusses the pros and cons of the three intelligent algorithms, compares and analyzes the calculation results of each optimization algorithm, and provides a practical way and method for the selection of multihull unmanned boats under the same speed and same displacement.

Effect of insulating liquid viscosity on output force of a high-power synchronous electrostatic motor

The output force of high-power electrostatic motors is defined by an internal electric field, and a strong electric field can cause air discharge unless the motors are operated within a dielectric liquid. Previous studies evaluated how the viscosity of a dielectric liquid can impact the output performance of a motor. While the viscous drag resistance increases with viscosity, the degradation of the output force was found to be negligible. However, the reason for this behavior was not clarified in those studies. This work clarifies the reason for the output behavior through numerical simulations and experiments. In the simulation, motion trajectories and motor output were analyzed for different operation speeds in different liquid viscosities. The results revealed that the existence of peaks in the force characteristics of the motor is the key to understanding a motor’s unique behavior within a viscous liquid. In a viscous liquid, the trajectories change such that the peak force is generated to compensate for the drag resistance. The simulations also revealed that the behavior only appears in one of the two types tested in the simulation, which differ in the smoothness of their force characteristics. The simulation results were verified in experiments. The experimental results reconfirmed the results of previous studies, and verified the findings of the simulations of this work.

Viscous peeling of a nanosheet.

Combining molecular dynamics (MD) and continuum simulations, we study the dynamics of propagation of a peeling front in a system composed of multilayered graphene nanosheets completely immersed in water. Peeling is induced by lifting one of the nanosheet edges with an assigned pulling velocity normal to the flat substrate. Using MD, we compute the pulling force as a function of the pulling velocity, and quantify the viscous resistance to the advancement of the peeling front. We compare the MD results to a 1D continuum model of a sheet loaded with modelled hydrodynamic loads. Our results show that the viscous dependence of the force on the velocity is negligible below a threshold velocity. Above this threshold, the hydrodynamics is mainly controlled by the viscous resistance associated to the flow near the crack opening, while lubrication forces are negligible owing to the large hydrodynamic slip at the liquid-solid boundary. Two dissipative mechanisms are identified: a drag resistance to the upward motion of the edge, and a resistance to the gap opening associated to the curvature of the flow streamlines near the entrance. Surprisingly, the shape of the sheet was found to be approximately independent of the pulling velocity even for the largest velocities considered.

A Fast Macroscopic Speed Planner for Electric Vehicle Platooning

Electric vehicles (EVs) have demonstrated significant advantages of high fuel economy and low maintenance cost over gasoline-powered vehicles and hybrid electric vehicles in moving people and goods. However, range anxiety remains as one of the main barriers in market penetration for EVs. Platooning has proven to be an effective approach to reduce aerodynamic drag resistance and thus extend EV ranges. However, taking full advantage of platooning to reduce energy consumption during a trip while satisfying the time constraint is a challenge. This paper is focused on the design and validation of the high-level speed planner of a two-level real-time platooning framework for EVs. The speed optimization problem in the high-level speed planner for the entire trip is reformulated into two speed profile optimization problems in two processes: 1) catch-up and then platooning, and 2) platooning and then break-away. Analytical solutions are derived for the optimal speed profiles in both processes. The analytical solutions capture the impacts of critical parameters such as initial and final inter-vehicle distances, and the leading vehicle speed.

Application of Biomechanics Based on Intelligent Technology and Big Data in Physical Fitness Training of Athletes.

Physical training has a high degree of participation all over the world. With the opening of the era of national fitness, physical training has become more popular from the original specialization, and the complex training methods and contents have gradually become simplified. The development and change of physical training has also brought many problems to the professional training of athletes, such as high training intensity but poor effect, insufficient training posture, and long-term physical injury. In order to help athletes achieve better results in physical training and reduce the probability of injury, taking sprint training as an example, this article adopted the sports and body data of elite athletes through intelligent technology and big data analysis, established a human motion model from the perspective of biomechanics, and then conducted a corresponding test run experiment for athletes. The experimental results suggested that drag resistance running could improve the specific strength quality of sprinting. At the same time, when using resistance load for training, the maximum speed should not exceed 90% of the maximum speed without resistance. The average horizontal maximum velocity decreased by approximately 9% when training under a resistance load, and the best training results were obtained by training athletes within this range.

Dynamic Programming-based Macroscopic Speed Planner for Electric Vehicle Platooning

Vehicle platooning has demonstrated significant energy saving potentials on highway via reduction of aerodynamic drag resistance by closely following a leading vehicle. However, taking full advantage of platooning opportunities for energy saving is a challenging task since accomplishable energy saving benefits depends on many factors such as the leading vehicle speed, relative position to the leading vehicle, platoonable miles with the leading vehicle, and others. This paper proposes a dynamic programming (DP)-based algorithm to optimize the speed profile for an electric vehicle to minimize the energy consumption when traveling on a given route with several platoonable vehicles sharing the same route. The proposed DP-based speed optimization framework was applied to a case study with five potential platooning vehicles over a 65-mile route with a time constraint. Through the case study, it was found that the DP-based optimization algorithm can determine the most energy-efficient speed profile for a given time deadline in a complex platooning environment based on the energy consumption from aerodynamic drag. Compared to the baseline control, the optimal speed profile from the DP optimization results can achieve significant energy saving benefits up to 18.12%.

Toward a detailed understanding of the rocket propulsion process and prediction on the trajectory of a boiling liquid expanding vapor explosion (BLEVE)

To mitigate the hazards of fragments during a runaway reaction explosion or a boiling liquid expanding vapor explosion (BLEVE), an accurate estimate of the maximum kinetic energy of the fragments and the trajectory is critical. On June 13, 2020, an LPG tanker truck slanted over and exploded on the highway interchange at Wenling, Zhejiang Province, China. A BLEVE occurred initially, with the cylindrical vessel rupturing into one end-cap and one rocket-like vessel. The 12-ton rocket-like projectile was thrown 364 m away, resulting in an LPG vapor cloud larger than 300 m, followed by several explosions ultimately. It provided a good opportunity to study the ‘rocket’ BLEVE process and to evaluate the potential trajectory model. Image analysis technique and 3D modeling using SketchUp were employed to reconstruct the spatial and temporal information in the accident, by comparing the Sketchup model with the accident video information processed by MATLAB. An accurate trajectory of the fragment was reconstructed, giving the projectile velocity to be 170–176 m/s and the averaged trajectory angle around 8°. The BLEVE process was further modeled using a two-phase flow discharge model together with a rocket propulsion model, and the predicted results fit well with those as estimated by the reconstructed model. The trajectory of the fragment was also modeled using the projectile velocity and trajectory angle, together with discussion on the effects of air drag resistance, which provided a good prediction and fit well with the trajectory in the SketchUp model.

Coulomb Drag between a Carbon Nanotube and Monolayer Graphene.

We have measured Coulomb drag between an individual single-walled carbon nanotube (SWNT) as a one-dimensional (1D) conductor and the two-dimensional (2D) conductor monolayer graphene, separated by a few-atom-thick boron nitride layer. The graphene carrier density is tuned across the charge neutrality point (CNP) by a gate, while the SWNT remains degenerate. At high temperatures, the drag resistance changes sign across the CNP, as expected for momentum transfer from drive to drag layer, and exhibits layer exchange Onsager reciprocity. We find that layer reciprocity is broken near the graphene CNP at low temperatures due to nonlinear drag response associated with temperature dependent drag and thermoelectric effects. The drag resistance shows power-law dependences on temperature and carrier density characteristic of 1D Fermi liquid-2D Dirac fluid drag. The 2D drag signal at high temperatures decays with distance from the 1D source slower than expected for a diffusive current distribution, suggesting additional interaction effects in the graphene in the hydrodynamic transport regime.

CFD MODELLING OF VOLTACAR ELECTRIC VEHICLE BODY FOR THE MOST EFFICIENT DRIVING CONDITIONS

In recent years, fossil fuels prices, greenhouse gas emissions, and need for sustainable energy sources have been increasing day by day. Thus, electric vehicles are seen as a promising candidate in the market due to their low-costs and cleaner fuel options such as electricity, hydrogen etc. Moreover, aerodynamics is one of the most important criteria to consider while designing an automobile for the most efficient driving conditions. For this reason, vehicle developers are studying to reduce drag resistance of the body to improve driving efficiency. On the other hand, Computational Fluid Dynamics (CFD) is one of the main tools for the automotive industry to obtain low-cost results before prototyping of any product. In this study, the aerodynamic characteristics of VoltaCAR electric vehicle is numerically investigated to obtain the best driving velocity. This car participates the TUBITAK-Electromobile car competition every year to achieve low fuel consumption for one hour driving. Thus, it is aimed that to minimize the resistance of the air hitting from the front, side, and roof of the vehicle. In the numerical model, polyhedral mesh structure is preferred to obtain faster convergence with fewer iterations, and shorter computation time is obtained compared to the tetrahedral mesh method. The aerodynamic drag coefficient (Cd) of the car model was calculated as approximately 0.17 at 22.22 and 27.78 m/s. The optimum velocity values were selected as 22.22 and 27.78 m/s by means of their lower Cd.

Recoverable underwater superhydrophobicity from a fully wetted state via dynamic air spreading

SummaryMaintaining the superhydrophobicity underwater offers drag resistance reduction, antifouling, anti-corrosion, noise reduction, and gas collection for boat hulls and submarine vehicles. However, superhydrophobicity typically does not last long underwater since the Cassie state is metastable. Here, we report a reversible and localized recovery of superhydrophobicity from the fully wetted state via air bubble spreading. Composed of sparse fluorinated chained nanoparticles, the submerged surface shows super-low energy barrier for bubble attachment. Especially the recovered plastron exhibits excellent longevity. Based on a simplified, truncated nanocone model, the dynamic spreading of bubbles is analyzed considering two basic parameters, i.e., surface geometric structure and surface energy (which appeared as intrinsic water contact angle). Numerical simulation results via COMSOL confirms the effect of geometric structure on bubble spreading. This investigation will not only offer new insights for the design of robust recoverable superhydrophobic surfaces but also broaden the applications of superhydrophobic coatings.

Anomalous Drag in Electron-Hole Condensates with Granulated Order.

We explain the strong interlayer drag resistance observed at low temperatures in bilayer electron-hole systems in terms of an interplay between local electron-hole-pair condensation and disorder-induced carrier density variations. Smooth disorder drives the condensate into a granulated phase in which interlayer coherence is established only in well-separated and disconnected regions, or grains, within which the densities of electrons and holes accidentally match. The drag resistance is then dominated by Andreev-like scattering of charge carriers between layers at the grains that transfers momentum between layers. We show that this scenario can account for the observed dependence of the drag resistivity on temperature and, on average, charge imbalance between layers.

A Review of Aerodynamics Influence on Various Car Model Geometry through CFD Techniques

The aerodynamic characteristics of a vehicle play a vital role in steering stability, performance, comfort, and safety of a car. The fuel efficiency of a vehicle is determined by the performance of the internal combustion engine and the aerodynamic design of the body. One of the most important aspects of automobile design is aerodynamic styling. A vehicle with low drag resistance provides advantages in terms of cost and efficiency. This article will review design characteristics and implementation of various specific reference models on drag issues using Computational Fluid Dynamics (CFD) techniques. The benefits and limitations of these models are analysed, and the validity of results in developing guidelines to improve the performance and stability of cars are described. This review paper covers significant studies that utilise the CFD model and simulation on a simplified vehicle model using various turbulence models to generate drag coefficient. Characteristics and impacts of various vehicle design models with and without external factors such as side mirrors and door handles are also discussed. Results obtained from the research focuses on the physics flow structures such as static pressure contours, are presented for the three types of car model geometry. The simplified generic models are more efficient and advocated to apply compared to the specific model geometry based on the result acquired by the latest studies. Simplified generic models are preferred due to their cost-effectiveness, procurement of optimum time, and better simulation effects. Moreover, the study also demonstrates the importance of having a car with suitable turbulence models that are appropriate to be applied for simulations in terms of its applicability, time effectiveness, and cost.

Hydraulic Performance of Water Inlet Device in Ship Scoop Cooling System

The scoop cooling system is widely used in advanced ships which usually requires a water inlet device protruding out of the board. The structure of the water inlet device not only determines the cooling water flow into the system, but also affects the additional resistance of the hull. The ratio of the static pressure difference between windward side of the device and the environment and the dynamic pressure head of the cooling water entering the flow channel is defined as the scoop lift head. The scoop lift head and additional resistance are used to describe the hydraulic performance of the water inlet device of the scoop cooling system, and a theoretical analysis method for the performance of the water inlet device of the scoop cooling system is proposed. The actual ship parameters are used to verify the scoop cooling capability and drag resistance characteristics of the water inlet device.

Performance Evaluation of the Multifunctional Variable-Viscosity Slick Water for Fracturing in Unconventional Reservoirs.

The traditional guar gum fracturing fluid system has the drawbacks of the fracturing process of unconventional oil and gas deposits, such as high drag resistance and large residuum harm, which is gradually replaced by the system of the slick water fracturing fluid. The conventional slick water system, however, still has the features of low sand-carrying capability. Therefore, high-viscosity slick water is often used in fracturing operations, but most of the high-viscosity slick water is difficult to prepare, dissolve, and break gels, which needs to be improved. Based on the abovementioned problems, a new type of multifunctional variable-viscosity slick water is proposed in this paper. The self-made loop drag test unit, a dynamic crack sand-carrying model, a multifunctional core flow device, and other equipment were used for testing, and a set of systematic evaluation methods for the performance of multifunctional variable-viscosity slick water are established. In addition, the mechanism of improving sand-carrying capacity and increasing viscosity and solubilization was explained through the macroevaluation experiment of polymer properties and the analysis of the polymer microstructure. The experimental results show that compared with high-viscosity slick water, the multifunctional variable-viscosity slick water has good drag-reducing performance, the drag-reducing rate can reach more than 75%; the intersection value of viscoelastic modulus is about 0.01 Hz, the sand carrying capacity is higher; the gel-breaking time is faster, the residue content is lower, 38.5 ppm; it has the characteristics of low harm, the harm rate to the core is 18.30%; and it also has the performance of enhancing oil recovery.

Optimization of Cellular Concrete Microstructure for Improved Impact Resistance

Engineered material arresting system (EMAS) is a cellular concrete material currently used as passive aircraft arresting system at airports around the U.S.A. and abroad. Its cellular structure crushes on impact, helping to absorb energy and create drag resistance. Energy absorbed during crushing is defined by the load–deformation response curve, in which a plateau is indicative of crushing behavior at a near-constant load. At the microstructural level, the energy absorbed from crushing is a combination of elastic buckling, plastic yield, and brittle fracture of the cellular microstructure. Therefore, optimization of the cellular structure (e.g., bubble size and distribution) is paramount to the overall performance of these systems. This study makes use of microstructural investigations, quasi-static indentation, and drop weight testing to investigate the performance of cellular concrete with varied microstructures. The results show that, while density (air content) has been considered the main predictor of overall performance, the nature of the cellular structure created by the use of different foaming agents can be a useful design tool. This adds another critical consideration in the design of impact-resistant infrastructure. Given this finding, a new set of design guidelines are presented in this paper. This work aims to inform better design of impact-resistant infrastructure by identifying cellular concrete microstructures that lead to optimal energy absorption in low-velocity impact events, such as aircraft overruns.

Wind Forces in Overgrown Rope Façades

Overgrown rope facades offer a space-saving possibility to make cities greener while counteracting the effect of the urban heat island (UHI). Unfortunately, there are no design models that adequately characterise the interaction between wind and plants for the calculation of wind loads. In the preceding study about overgrown rope facades (Arnold et al., 2021), a design model was deduced from flow force studies on trees and a drag coefficient for plants on overgrown rope facades was derived from drag resistance measurements of deciduous trees. This drag coefficient has not been validated. In this study, wind load tests in a turbulent wind tunnel were performed on five climbing plants to validate the drag coefficient. For this purpose, a prototype of a turbulent wind tunnel with an active grid that simulates gusts for a chaotic turbulent flow was built and various overgrown rope samples were measured. Based on the measured data, the 95% characteristic value of the drag coefficients was calculated using a statistical method. These drag coefficients can be applied to buildings at different speeds by means of E-values and B-values, thus allowing the design optimisation of plant climbing systems. This work does not deal with the interaction between the facade surface and overgrown rope plant in front of the facade, which requires further research.

Reduction of Drag Resistance by Pressure Drop in Pipeline with 3-Dimensional Design Optimization

The searching for the most optimal pipeline route is a crucial problem in the maritime world because it consumes total designing time by 50%. Also, with different types of ships increases the design complexity. The usual design process has not considered the aspect of distance, cost, obstacles, drag, and pressure reduction in the pipeline very accurately. However, along with algorithms' development to optimize pipeline design, the time can be cut by 40%. This research uses computer-generated Dijkstra's algorithm to optimize pipeline design by considering several constraints in pipe spacing, the number of bends, crossings, pipeline stacks to improve drag reduction, and reducing pressure. This research was conducted to see the effect of pipe mapping on pressure drop, which is too influenced by human decisions that cannot consider bending, crossing, pipe piling, and bending of pipes that are too many to be considered by humans. Helping humans choose pipe mappings with various considerations that can affect pressure drop is advantageous because mapping helps to cut production times and produce a more efficient flow. In this study, this research aims to produce pressure drop by mapping pipes using the Djikstra algorithm by considering bending, crossing, and stacking, which are presented based on the 2-dimensional and 3-dimensional mapping. The data generated in the way of a comparison between drag reduction and pressure drop in pipe design optimization utilizing Dijkstra's and without using the Dijkstra's algorithm with 3-dimensional projections. The result shows the improvement of the drag reduction rate by 8% by decreasing pressure drop by 13%.

Drag resistance: Necropolitics, queer survival and a Balkan counterpublics

Taking the murder of Greek HIV+ and queer activist Zak Kostopoulos as its starting point – an exercise of necropolitical power in broad daylight – this article explores the work of drag queens in Greece and their aesthetic/political choices. It interprets their performances as tactics of survival and resistance and as creative responses to queer trauma. The role of queerfeminist spaces, cultural events and collectives also is examined as a response to the increasing right-wing turn in the country’s political scene – itself the result of the financial crisis of 2008. It imports José Esteban Muñoz’s disidentifications and counterpublics, Elizabeth Freeman’s erotohistoriography and Achille Mbembe’s necropolitics into the Greek/Balkan context and analyses the particular configurations and intersections of sexualities, genders, statehood, race, class and religion in Greece. It then examines disidentifications and counterpublics as empowering practices of community forming, offering glimpses of a queer Balkan counterpublics and the tools employed towards its making (humour, parody, reclaiming, disidentification, mourning and embodied pleasures).

Contribution of Superhydrophobic Surfaces and Polymer Additives to Drag Reduction

AbstractDrag reduction has constantly received great attention due to its extensive range of applications in fluid transportation and vehicle industries. The vital role of two different additive and non‐additive techniques (polymer additives and superhydrophobic surfaces) to reduce the drag force experienced by underwater vehicles, fluid flow through pipes, ducts, open or closed channels, and other wall‐bounded laminar and turbulent flows is highlighted. Reducing the drag resistance can significantly enhance the performance of immersed vehicles and results in saving the energy consumed on a large scale. The progress in theoretical modeling, experimental and computational studies of both techniques are reviewed, together with the surface design, wettability, and influence of the roughness factor of superhydrophobic surfaces and the effect of polymer drag‐reducing agents for wall‐bounded flows and multiphase flows. General formulations, potential applications, and major issues involved in the aforementioned approaches are summarized.

Mechanistic study of shoaling effect on momentum transfer between turbulent flow and traveling wave using large-eddy simulation

The resistance drag force acting on the wind by ocean waves plays a critical role in weather and climate forecasting. With the aid of computer simulation, we investigate the difference between the drag force caused by open sea waves and that by coastal waves. Our results show that the increased drag in the coastal region is closely related to the slowing down of waves in a physical process called wave shoaling.