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The flow past an axisymmetric body at a sufficiently high angle of attack becomes asymmetric and unsteady. Several authors identified three different flow regions for bodies of large fineness ratio at low subsonic flow and high incidence: a steady region in the forebody and two unsteady regions in the rear body. Unsteady Reynolds Averaged Navier–Stokes (URANS) codes with eddy viscosity turbulence models or Reynolds stress turbulence models fail to capture the unsteady flow region. These methods are overly dissipative and resolve only frequencies far lower than turbulent fluctuations. Scale-Adaptive-Simulation (SAS) provides an alternative method to afford the problem of these massively separated flows at high Reynolds numbers without addressing the problem to Large Eddy Simulation (LES). This paper applies SAS to study the effect of slenderness on the flow. The numerical solutions show that the flow becomes more unstable as the fineness ratio increases, and the three flow regions are clearly recognizable. For low fineness ratios, only one of the two unsteady regions is visible. The good agreement between the sectional forces and pressure coefficients with their corresponding experimental data for an ogive-cylinder configuration allows an analysis of the flow structure with a fair degree of confidence.

The flowfield past a body of revolution at large incidence may develop an asymmetric wake that induces a significant side force. It remains a challenging problem for both computational and experime...

To investigate the envelope radiation characteristic of stratospheric airship, three kinds of airship models with different dimensions (fineness ratio of 3, 4, 5) are selected. After establishing the thermal equilibrium equations of the selected models, the influence of the envelope radiation characteristic on the envelope and airship gas is first addressed to determine the optimal fineness ratio by considering the flight dynamics characteristics. Furthermore, the effects of envelope emissivity, envelope absorptivity, solar cells radiation characteristics, and typical envelope materials on the envelope radiation characteristics of airship are discussed in depth. The results show that: (1) With the assumption of same absorptivity and emissivity, the larger the fineness ratio of the airship, the smaller the diurnal temperature difference of the main helium gasbag, and the better the thermal characteristics of airship as well. When the envelope radiation characteristics vary, the temperature difference of main helium gasbag with a fineness ratio of 4 in one day is always less than 1 K, compared with the fineness ratio of 5. However, the temperature difference of main helium gasbag with a fineness ratio of 3 exceeds that with the fineness ratio of 5, and reaches its maximum of 6 K. Therefore, the fineness ratio of 4 is regarded as optimal by considering the floating constraints of low drag and high buoyancy. (2) In the case of higher long-wave emissivity and lower short-wave absorptivity of the envelope material and solar cells, the diurnal helium temperature difference is the smallest, and the thermal performance of the aerostat is better. (3) Among the five typical envelope materials, i.e., white Tedlar film, white PU film, silver-plated Teflon film, aluminized PET film, and white PVF film, the aluminized PET film is more conducive to controlling the helium temperature difference and reducing the volume change of gasbags. The aforementioned results can provide a theoretical basis for improving the thermal performance of stratospheric airships.

Purpose This paper aims to optimize the mass of a tethered aerostat to achieve optimum hull volume, and fins to generate aerodynamic lift to reduce the blow-by. Design/methodology/approach The design code of aerostat involving structure, aerostatics, aerodynamics and stability has been developed using MATLAB®. The design code is used to obtain the baseline configuration for a tactical aerostat mission by using the statistical values of the hull fineness ratio and the fin parameters of in-service aerostats. The effect of the design variables that include the hull fineness ratio, fin area and fin position on the aerostat mass and blow-by is determined through sensitivity analysis. The aerostat is optimized with an objective function of minimization of mass for the bounded values of design variables and taking blow-by limit as a constraint. Findings This study reveals that the simultaneous optimization of the aerostat hull fineness ratio, fin area and fin position results in an improvement in the design. The aerostat design with optimum values of these parameters helps in a reduction in its size and mass without compromising the blow-by limits. Research limitations/implications This study has been conducted by keeping the hull shape constant by selecting standard National Physics Laboratory envelope shape. The aerodynamic model used in the design code is based on empirical relationships that can be improved in future studies that can use high fidelity aerodynamic models using CFD based surrogate models. Originality/value The previous studies on optimization of aerostats are limited to hull envelope shape only, whereas this paper presents the optimization of the hull and fin together. The optimized configuration obtained has a reduced mass and can operate within the specified blow-by limits.

The external shape design change of an airship can be appropriately captured by design fineness ratio, which is defined as the ratio of airship's length to its maximum width. However, there is a lack of aerodynamic models that have been established for airship design purposes. In conjunction to this realization, the aim of this research work is to establish the effects of design fineness ratio of an airship towards its aerodynamic performance. The Atlant-100 airship is chosen as the reference design model for this study. In total, 36 simulation runs are executed with different combinations of values for the fineness ratio, altitude and velocity. The obtained CFD simulation results are then statistically analysed using Minitab software to evaluate the significance of the design fineness ratio effects. From the results, it has been found that smaller fineness ratio corresponds to higher aerodynamic lift and drag forces. As in the case simulated in this study, the smallest fineness ratio of 0.93 has been shown to correspond to the highest value of generated lift coefficient while having comparable value of generated drag coefficient with the other fineness ratios. This highlights that a smaller fineness ratio of the airship design is more suitable. The constructed mathematical models to capture these effects have also been validated with a few goodness-of-fit tests. For the regression model of fineness ratio impact on the lift coefficient, it has R2 value of 0.941. When its predictive accuracy is tested with few simulated random cases, the maximum error obtained is only 6%. On the other hand, for the regression model of the fineness ratio impact on drag coefficient, the R2 value is 0.962 and maximum predictive error from the simulation random cases test is only 9%. Overall, it can be concluded that the constructed regression models have good predictive capability on the impact of design fineness ratio on the aerodynamic performance of the airship under this study.

A stratospheric airship is an essential flight vehicle in the aviation field. In this paper, optimal design approach of stratospheric airships is developed to optimize envelope shape considering three failure modes and multidisciplinary analysis models, and could also reduce the mass of a stratospheric airship to be deployed at a specific location. Based on a theoretical analysis, three failure modes of airships including bending wrinkling failure, hoop tearing failure and bending kink failure, are given to describe and illustrate the failure mechanism of stratospheric airships. The results show that the location, length and size of the local uniform load and the large fineness ratio are easier to lead to bending wrinkling failure and bending kink failure. The small fineness ratio and the increasing differential pressure are more prone to cause hoop tearing failure for an airship hull. The failure probability is sensitive to the wind field. From an optimization design, the reliability analysis is essential to be carried out based on the safety of the airship. The solution in this study can provide economical design recommendations.

[EN] A fibrous material is characterized by its fineness, flexibility and high length/fineness ratio and it is used to reduce noise in indoor rooms due to their porous structure. The aim of this work is focused on investigating the structure of two different fibers (acrylic and polyester) from the analysis of the macrostructural parameters, such as fineness, length and cross-section (solid or hollow). Furthermore, the degree of influence of these parameters on the average sound absorption has been investigated. The sound absorption coefficient of fibers is measured at normal incidence in the impedance tube. In acrylic fibers, results showed that the fineness of the fiber has a significant influence on the sound absorption compared to the length of the fiber. In polyester fibers, hollow fibers have a better acoustic behavior compared to solid fibers., The authors disclosed receipt of the following financial support for the research, authorship and/or publication of this article: This work was supported by the Spanish Ministry of Economy and Innovation (MINECO) and the European Union FEDER (project PID2019-109175GB-C22), the Regional Ministry of Education, Culture and Sport of the Generalitat Valenciana (project ACIF/2017/073) and with the European Structural Investment Funds (ESIF-European Union).

Fluid–structure interaction (FSI) phenomenon is very common in pneumatic-type textile field. However, the motion of flexible bodies, for instance, fibers or yarns, are usually difficult to simulate due to their large fineness ratio and high flexibility. Conventional FSI solvers based on the body-fitted grid method are difficult to handle the large deformation due to severe grid distortion. In this paper, we studied the fluid–fiberinteraction for fiber conveyance in a fiber transport channel (FTC) using the immersed boundary-lattice Boltzmann method (IB-LBM). The effect of three parameters on fiber conveyance, i.e. the conical degree of the FTC ( tan α ), the bending rigidity of fiber ( K ˆ b ) and the flow Reynolds number ( R e ), are particularly investigated. The calculated results indicate that the converging shape of FTC helps to straighten fiber and adjust its orientation to a more horizontal degree during the conveyance, however, it may not improve fiber delivery efficiency. A larger conical degree would bring a better straighten effect and a smaller leading angle if fiber-wall contact does not occur. Under the conditions that tan α > 0 , R e 400 and K ˆ b 1 e − 3 , the straightness undergoes a “leap–slump–grow–drop” evolution process and the leading angle follows an “increase–decline” tendency. Moreover, the simulation results show that the bending rigidity have a significant effect on fiber configuration and orientation during its conveyance. A fiber with a larger bending rigidity is more likely to maintain a straighter configuration and a more horizontal orientation during its conveyance. As R e increases in simulations, the fiber gets less straight in configuration and more vertical in orientation, and deviates more from the horizontal path.

Aeospike based wave drag reduction is investigated using two-equation turbulence model applied to Faver averaged Navier Stokes solver. Three different blunt bodies are considered in a low supersonic stream of Mach number 2. The considered blunt bodies differ in their degree of bluntness defined in terms of half cone angle, area of flattened front side and radius of bluntness. The zero angle of attack flowfield around these three bodies are computationally analyzed with and without the presence of aft spikes to evaluate the wave drag resulting from the formation of front shock structure. The influence of spike configuration on the wave drag is also investigated. The various considered spike tip geometries include aero-disk, sharp and blunt with the length of all the spikes being equal to the base diameter of the blunt bodies (L/D = 1). It has been found that the 3221 blunt body when coupled with a blunt tipped spike yielded the lowest drag coefficient of 0.3, despite the 3221 having the highest standalone drag coefficient of 0.86, among the blunt bodies when simulated individually without spikes. The physics behind the wave drag reduction associated with each combination of blunt body and spike configuration is presented with clarity. This study portrays the importance of taking bluntness factor, semi-cone angle, fineness ratio and blunt body shape factor into consideration while proposing the generalized optimum spike configuration for minimum drag attainment.

The effects of different axisymmetric forebody shapes have been studied on the non-axisymmetric (helical) global modes of the boundary layer developed on a circular cylinder. Sharp cone, ellipsoid and paraboloid shapes have been considered with the fineness ratio (FR) of 2.5, 5.0 and 7.5. The base flow is in line with the cylinder’s axis at the inflow boundary, and hence the base flow is axisymmetric. The boundary layer has developed from the tip of the forebody where a highly favourable pressure gradient exists, and it depends on the sharp edge of the forebody’s geometric shape. However, the pressure gradient then remains constant on the cylindrical surface of the main body. Thus, the boundary layer developed on the forebody and main body (cylinder) is non-parallel, non-similar and axisymmetric. The governing equations for the stability analysis of the small disturbances have been derived in the cylindrical polar coordinates. The spectral collocation method with Chebyshev polynomials has been used to discretise the stability equations. An eigenvalue problem has been formulated from the discretised stability equations along with the appropriate boundary conditions. The numerical solution of the eigenvalue problem was done using Arnoldi’s iterative algorithm. The global temporal modes have been computed for helical modes $$N = 1$$ , 2, 3, 4 and 5 for Reynolds number $$Re = 2000$$ , 4000 and 10000. The spatial and temporal structures of the least stable global modes have been studied for different Reynolds numbers and helical modes. The global modes with ellipsoid were found the least stable while that of the sharp cone were found the most stable.

We conduct wind tunnel experiments to evaluate the drag and base-pressure coefficients and velocity field in the wake of a circular cylinder with extremely low length-to-diameter (fineness) ratio for diameter-based Reynolds number in the range $2\ensuremath{-}7.7\ifmmode\times\else\texttimes\fi{}{10}^{4}$. A magnetic suspension and balance system eliminates interference from support structures. We find that the drag coefficient converges monotonically to that of a local disk without a maximum at any fineness ratio in the 0.1-0.5 range. Large-eddy simulations at Re = $4\ifmmode\times\else\texttimes\fi{}{10}^{4}$ agree with the experiments.

At hypervelocity flows the design place a major role. To sustain such impact the design, need to be more aerodynamic. Blunt body is key factor to achieve and sustain those hypersonic velocities that is mainly focused beyond Mach number 5. Blunt body design in aerodynamic and structural aspects become more crucial factors in hyper velocity vehicles. The paper mainly focuses on effective blunt body design. In order to achieve the effectiveness various radius of curvature taken into account and comparative study were done. Along with that flow compressibility, chemical reaction, aerodynamic heating, stagnation conditions were discussed. Extensive review was done to select most efficient blunt body design in both aerodynamic and structural aspects

This paper aims to investigate the side force on a cone-cylinder geometry at different angles of attack (α) by adopting experiments and computations. The cone-cylinder configuration had a length to diameter ratio (L/D) of 10, and a base diameter (D) of 25 mm. The nose shape had a fineness ratio of approximately 3. Results indicated that the side force increases with the increasing of the angle of attack. A circular ring was used to reduce the side force at different angles of attack. Using a smaller height ring (2% of local diameter) in the initial portion of the body did not reduce the side force significantly at lower angles of attack. However, a ring with larger height (5% of local diameter) placed at 2.5 times the diameter of the body from the tip reduced the side force at almost all the angles of attack.

Defining a feasible vehicle design and mission architecture capable of reliably delivering apayload of 20 metric tons (mt) or more is a great challenge for landing humans on Mars. TheMid Lift-to-Drag Rigid Vehicle (MRV), a rigid decelerator studied in NASA’s Entry, Descent,and Landing Architecture Study (EDLAS), has shown to be a viable vehicle candidate forfuture human Mars missions. As the vehicle concept matures, models of increasing fidelity areadded to the six-degree-of-freedom (6DoF) EDL simulation. This paper presents 6DoFsimulation results using model updates for vehicle mass properties, fineness ratio, andaerodynamic-propulsive interactions. Additionally, an assessment of the Fractional-Polynomial Powered Descent Guidance (FP2DG) performance is presented, and the vehicleperformance is compared with the Tunable Apollo Powered Descent Guidance (TAPDG).Finally, Monte Carlo results of the vehicle design trades are presented.

The present work provides a detailed study of the hypersonic flow over elliptical nose cones at a Mach number of 5.8, numerically. The main focus of the paper is to determine parameters of the nose cones which provide minimum aerodynamic drag and heating. The conjugate heat transfer method is used to examine aerodynamic heat transfer between gas and surface accommodations for different fineness ratios at zero angle of attack. It is observed that for higher fineness ratio provide minimum drag. It also shows the detailed comparison of the flow/shock features in the vicinity of the elliptical nose cones for different fineness ratios in order to determine its influence on aerodynamic drag and heating. It is also noticed that the aerodynamic heating is almost same for all fineness ratios. In general, the present study reveals that at higher fineness ratios are preferred for achieving aerodynamic characteristics in hypervelocity vehicles.

Vortex unsteadiness around a hemisphere cylinder at angles of attack of 10–80 deg was studied using large-eddy simulation and dynamic mode decomposition. The cylinder body has a fineness ratio of 2...

This paper deals with finding the optimum fineness ratio, i.e. ratio of length to maximum diameter, of human-powered submarine of different shapes to reduce the drag force on the body using Computational Fluid Dynamics (CFD) analysis. These types of submarines are used in events like ISR and eISR. This paper focuses on finding the total drag force on submarine models with a constrained diameter and different fineness ratios. The analysis is done by using ANSYS Fluent. In this paper, only the fully submerged flow is considered on a hull without any appendages.The total drag on a body is caused in three different parts that are wave drag, skin friction drags and base drag.The analysis is done different shapes of submarines like Conic shape hull, Elliptical shape hull, Ogive shape hull and Parallel mid-body hull by flowing water at velocities of 3 m/s, 4m/s and 5 m/s. The fineness ratios at which the drag is minimum are found in all submarine shapes. The optimum value of fineness ratio, which gives minimum drag is obtained by the analysis is 6 for Conical shape hull, Elliptical shape hull and Ogive shape hull whereas for the submarine with Parallel mid-body hull shape the optimum fineness ratio is 7

This paper presents the effect of axisymmetric forebody shapes on the global stability characteristics of axisymmetric boundary layer developed on a circular cylinder. Axisymmetric forebodies like sharp-cone, ellipsoid, and paraboloid with a fineness ratio (FR) of 2.5, 5.0 and 7.5 are considered. The boundary layer starts to develop at a stagnation point on the forebody geometry and grows in spatial directions. The inflow velocity component is parallel to the axis of the cylinder, and hence the angle of attack is zero. The base flow is axisymmetric, non-parallel and non-similar. The linearised Navier�Stokes equations are derived in the cylindrical polar coordinates for the disturbance flow components. The discretised linearised Navier�Stokes equations along with appropriate boundary conditions form a general eigenvalue problem and it has been solved using Arnoldi�s algorithm. The global temporal modes have been computed by solving the two-dimensional eigenvalue problem. The extent of a favourable pressure gradient developed in streamwise direction depends on the shape of axisymmetric forebody. The temporal and spatial growth of the disturbances has been computed for axisymmetric ( N = 0) mode for different Reynolds numbers (Re). The forebody shapes have a significant effect on the base flow and stability characteristics at low Re., by Ramesh Bhoraniya and Vinod Narayanan

In this study, the wake structure around freestream-aligned cylinder is investigated and its aerodynamic characteristics are discussed. A magnetic suspension and balance system (MSBS) was used to support a model without interference from a mechanical support device. Seven models with the fineness ratio (length to diameter, L/D) of 0.5, 1.0, 1.25, 1.5, 1.75, 2.0, and 2.25 were used. Reynolds number based on the cylinder diameter were 3.2 × 104 and 6.3 × 104. The velocity field was obtained by particle image velocimetry (PIV) in the center plane of the cylinder. In the case of fineness ratio over 1.5, the reattachment of shear layer was observed from the mean velocity field. The characteristic fluctuation of velocity was confirmed in power spectral density of streamwise component and vertical component. The length of the recirculation region is different depending on fineness ratio. The characteristic frequencies of the velocity fluctuation which seems to be due to recirculation bubble pumping and large-scale structure are observed from power spectrum density.

In the present study, locomotion of a real longfin inshore squid (Doryteuthis pealeii) was numerically investigated. Geometry of a real squid was obtained using computed tomography (CT) images. In addition to a two-dimensional axisymmetric squid model, a modified squid model with no cavities around her head and an ellipse shaped model were generated with a fineness ratio (the ratio of body length to maximum body diameter) of 7.56. These numerical models were exposed to an acceleration with two different velocity programs. Added mass and basset forces on bodies were calculated during acceleration of the squid models starting from rest. Pressure and viscous drag forces were also calculated due to pressure variation along the squid models and friction on the surface of the models. The effect of a nozzle diameter on jet velocities and propulsive efficiency at all bodies were evaluated when time dependent velocity profiles (from 0 to 10 m/s in 0.5 and 1 s time durations) were set for the inlet of computational domain. The modified squid model required least thrust force during acceleration phase of time dependent velocity profile compared to the other models while the 0.02 m nozzle diameter provided largest propulsive efficiency for all models.

In today’s world, the biological sciences are mostly considered separate from the existing modern knowledge of various other fields of sciences and engineering; however there are many properties of nature and known facts of biological sciences that can be proved in the other domains of science and technology as well. Correlation of the geometric and buoyant properties of the swimming animals with the hybrid buoyant air vehicles is an example of this hypothesis. In the present work, some experiments related to the geometric parameters of a California sea lion were carried out. It was found that the fineness ratio of this animal is of the same order as the optimum value of that for the condition of minimum drag and power required for buoyant aerial vehicle. Role of multiple fins on the elongated bodies of shark is also discussed for its application for yaw stability as well as to shroud the antennas that are used in the aircraft for various communication systems.

This paper describes the development and execution of a simple experiment designed to exercise the elements of a Lagrangian mechanical system model for the motion of a rigid body near an otherwise calm free surface. The experimental apparatus is a planar pendulum for which the pendulum “bob” is a hollow, prolate spheroid with a 6:1 fineness ratio. The device is used in two configurations: (i) a fully immersed, buoyant configuration for which the stable equilibrium corresponds to floating upright and (ii) a suspended, heavy configuration in which the stable equilibrium corresponds to hanging downward. Experiments in either configuration involve motion that begins from rest away from the equilibrium. Adjusting the water level relative to the equilibrium state modifies the depth-dependent hydrodynamic effects such as added mass and radiative damping.

The drag coefficients of freestream-aligned circular cylinders of fineness ratios of 0.75–2.0 were investigated with a magnetic suspension and balance system (MSBS). The objective was to find the critical geometry, that is, the fineness ratio at which the drag coefficient becomes the local maximum within this ratio range. The experiments were conducted using the 1-m MSBS at the low turbulence wind tunnel at the Institute of Fluid Science, Tohoku University. The drag and base pressure coefficients of various cylinders were measured. The freestream velocity was varied to produce flows with Reynolds numbers ranging from $$0.6\times 10^5$$ to $$1.0\times 10^5$$ . The drag coefficient monotonically decreases as the fineness ratio increases and no critical geometry or local maximum of the drag coefficient is found in the range we investigated. The base pressure coefficient decreases as the fineness ratio increases. The temporal fluctuations of the base pressure of the models with fineness ratios of 0.75, 1.0, and 1.2 are approximately twice as large as that of the model with a ratio of 2.0. The relationship between the fineness ratio and the drag coefficient is similar to that between the fineness ratio and the base pressure coefficient, similar to the findings of previous studies of two-dimensional bodies.

Most conformal optical system designs concentrate on the researches of ellipdoidal domes. However, ellipsoidal domes are not the best ones which possess excellent aerodynamic performance among conicoidal conformal domes. This paper investigates the aberration characteristics of conicoidal conformal domes. For the purpose of the study, different types of infrared conformal domes, including ellipsoidal domes, parabolic domes and hyperbolic domes, with the common fineness ratio of 1.0 and an index of refraction of 2.25 are modeled by mathematical computation. To investigate the dynamic characteristics of the on-axis aberrations, the curves of third order fringe Zernike polynomials of the domes across field of regard are obtained by decomposing the incident wavefront at the exit pupil. The Zernike aberrations across field of view are also achieved to investigate the varying characteristics of off-axis aberrations. To find the similarities and difference between spherical domes and conformal domes at both field of regard and field of view, also make the foundation for optical design, spherical domes and defocused spherical domes are modeled for reference researches. The changing rules and the features of the aberrations among different types of conicoidal conformal domes are drawn as conclusions at the end of the paper.

In the present paper, a numerical squid model was obtained from a real longfin inshore squid ( Doryteuthis pealeii ) using computed tomography (CT) images. Two-dimensional axisymmetric squid models were then generated with fineness ratios of 7.56, 6.20 and 4.39 to investigate viscous and pressure drag forces. The study examined the effect of a squid's nozzle diameter on squid swimming and jet velocities for the investigated models in the squid's Reynolds number range from 456,000 to 2,800,000. Velocity vector field around the squid’s curvature body was analyzed to understand flow recirculating regions and make connection with the drag coefficient. It was documented that models with a fineness ratio of 7.56 and 6.20 showed streamlined body behavior while a fineness ratio of 4.39 model exhibited a blunt body appearance based on drag force and velocity vector results. The study also revealed that a larger nozzle diameter provided better propulsive efficiency and faster swimming velocity for the squid.

A new low-boom target generation approach is presented which allows the introduction of a trim requirement during the early conceptual design of supersonic aircraft. The formulation provides an approximation of the center of pressure for a presumed aircraft configuration with a reversed equivalent area matching a low-boom equivalent area target. The center of pressure is approximated from a surrogate lift distribution that is based on the lift component of the classical equivalent area. The assumptions of the formulation are verified to be sufficiently accurate for a supersonic aircraft of high fineness ratio through three case studies. The first two quantify and verify the accuracy and the sensitivity of the surrogate center of pressure corresponding to shape deformation of lifting components. The third verification case shows the capability of the approach to achieve a trim state while maintaining the low-boom characteristics of a previously untrimmed configuration. Finally, the new low-boom target generation approach is demonstrated through the early conceptual design of a demonstrator concept that is low-boom feasible, trimmed, and stable in cruise.

International audience; The aerodynamic lift and drag performance is one of the important considerations for hybrid airship configuration design. In conjunction with this, simulation study of aerodynamic characteristics can certainly benefit the process of deriving the best possible configuration for hybrid airship design. The aim of this study is to investigate the trend of aerodynamic lift and drag performance for an airship design in different velocities, altitudes and design fineness ratio using the Star CCM+ analysis tool. The airship model applied in this case study is an approximate model of the Atlant-100 airship. It is found that the airship model with low design fineness ratio typically generates much better aerodynamic lifting force in comparison to those with high design fineness ratio. On the other hand, while the range of estimated drag coefficient values is found to be rather insignificantly different, the presence of effects from the design fineness ratio is still evident. Generally, high design fineness ratio for the airship model seems to produce much lower drag force.

The asymmetric vortex regime of a von Karman ogive with a fineness ratio of 3.5 is experimentally studied at a Reynolds number of 156,000. The wake of an axisymmetric bluff body is an ideal candidate for active feedback flow control because minute fluidic disturbances and geometry perturbations near the tip of the ogive get amplified through the flow’s convective instability. The resulting disturbance interacts with the quasi-steady vortex location and produces a deterministic port or starboard asymmetric vortex state (i.e., side force). Accurate control or manipulation of this asymmetric vortex state holds the potential for increased maneuverability and stability characteristics of slender flight vehicles. For implementation of an active feedback flow-control system, plasma actuators at the tip of the ogive are used as the flow effector, and surface-mounted pressure sensors are used to estimate the vortex configuration in real time. A linear time invariant model developed from open-loop experimental test...

In this work, a simple and efficient numerical approach to determine the shape of the minimum-drag axisymmetric forebody in inviscid supersonic flow with an attached shock constraint has been described. Taylor–Maccoll equation in conjunction with the tangent cone method is employed to estimate the pressure drag coefficient which is also chosen as the cost function. The forebody geometry is parameterized using a Non-Uniform Rational B-Splines (NURBS) curve whose control points are the design variables for optimisation using the steepest descent algorithm. Numerical studies demonstrate that the optimal forebody geometry for a given length and base radius has as much as 15 % lesser drag, depending on the Mach number than a cone of the same fineness ratio and that the convergence to the optimal solution exhibits a relatively weak Mach-number dependence.

The high temperature formation, strong abrasiveness, numerous fractures and caves are the main problems of high temperature geothermal well drilling, cementing. Cone bit teeth repeated impact tests show that bit life mainly affected by tooth shape, materials, solid tooth technology. Setting special materials around the teeth and adjusting the fitting wring will improve the life of cone bit teeth. Study of quartz sand amount and fineness ratio effect on cement high temperature compressive strength, permeability show that optimization of high temperature cement slurry can improve the high temperature leakage zone cementing sealing and long-term effectiveness.

Airships were the first air vehicles, which had the ability to generate lift without the use of aerodynamic flow around wings, also to enable controlled, powered flight, providing long endurance at low energy consumption. They were widely used before the 1940s, but their use decreased as their capabilities were exceeded by those of the airplanes. Their decline continued with a series of several accidents, including the burning of the hydrogen-filled Hindenburg, and the destruction of the USS Akron. Nowadays, airships are used in certain applications: cargo transportation, tourism, aerial observations and many others, where the ability to hover in one place for an extended period of time is important. In Europe the reborn of airships is being supported by the European Union, recently providing financing for Project MAAT – Multibody Advanced Airship for Transportation, supported by 7 FP Program. This project, comprises twelve research institutions, introduces the concept of feeder–cruiser airship for transportation of people and goods. The main idea is to use a cruiser (PTAH)–feeder (ATEH) concept to allow transport of people and goods [9] , [10] , [47] . For this novel airship concept a new envelope and propulsion concept design is envisaged. The present study deals with the methodology and results for numerical modeling and research on airship with an innovative shape and implementation of its unconventional propulsion system. Attention has been paid to the logical sequence and obtained results for modeling and research of an airship with innovative shapes. The innovative design concept is analyzed and comprised with classic airship shape in point of aerodynamic and energetic needs. It was found that the classic airship shape provokes many problems, which are mainly referred to as high bending moments, in case of given buoyancy volume and optimal fineness ratio. The newly proposed shape needs an extensive research, which cannot rely on classic approach for drag coefficient calculations. Furthermore, based on the research results and conclusions for the airship shape, aerodynamic features at given altitudes and the propulsion needs, a feasible and innovative propulsion concept air-jets, is analyzed. Attention was focused on the performance of the air-jets working with high mass flow rates and low jet flow speeds. The outcome of the research highlights the opportunities for future developments of the propulsion concepts for airships with innovative shape as it is a very important and promising area in nowadays air-vehicles technology.

The importance of fineness ratio in determining the aerodynamic shapes of minimum-drag, zero-lift axisymmetric bodies in inviscid hypersonic flows is investigated using a shape optimization framework. The framework employs modified Newtonian theory for surface pressure computation, Bezier curves for geometric parameterization and a steepest-descent approach for minimization of the wave-drag coefficient. Studies are performed on axisymmetric bodies of a given length for fineness ratios varying from 1 to 6 and Mach numbers ranging from 6 to 12. It is shown that the optimal axisymmetric body for a given freestream Mach number is blunt-nosed for smaller fineness ratios but becomes sharp-nosed at larger fineness ratios. The fineness ratio at which the optimal body of revolution transitions from blunt-nosed to sharp-nosed is found to be nearly constant at hypersonic speeds and is around 3. Results indicate that the optimal bodies derived from the framework are superior in terms of wave drag to the von Karman og...

Optical windows with external surfaces that shaped to satisfy operational environment needs are known as special windows. A novel special window, sphere-cone (SC) window, is presented. The equations used to decide geometrical parameters of this window are deduced. A SC MgF2 window with a fineness ratio (F) of 1.33 is designed as an example. The field-of-regard (FOR) angle is +/- 80 degrees. From the window system simulation results by the calculated fluid dynamics (CFD) and optical design software, we find that the SCP shape compared to conventional window forms not only introduces relatively less drag in the airflow, but also makes the minimal effect to imaging. After a correcting lens is adopted in the SC window optical system, the lowest modulation transfer function (MTF) value at 17 Lp/mm reaches 0.610 and the root-mean-square (RMS) spot size is approximately 1.57-2.12 times than the diffraction limit. The design results show that the SC window optical systems can achieve high image quality across very wide FOR by the simplest static correction. (C) 2013 Elsevier GmbH. All rights reserved.

The effect of the flow actuator on the asymmetric vortex structure around the ogive-cylinder body with fineness ratio of 4 flying at the speed of Mach 0.1 at angle of attack of 50 degree is studied. The ogive-cylinder model is developed with the actuator placed near the nose tip and numerically simulated using the in-house CFD code named KFLOW. The numerical simulation employs two different actuator modeling: one is the boundary condition given by blowing normal to the surface and another shearing on the surface. The numerical simulation reveals that response of the vortex structure to the actuation is dependent on the type of modeling as well as the strength and direction of the actuation.Keywords : Plasma Actuator(플라즈마 구동기), Asymmetric Vortex(비대칭 와류), Ogive(오자이브), High Angle of Attackt(고받음각), Flow Control(유동 제어)

Flow regimes are believed to be of major evolutionary significance in fish. The flow regimes inhabited by cyprinids vary extensively from still flow regimes to riptide flow regimes. To test (i) whether flow-driven swimming performance and relevant morphological differentiation are present among fish species and (ii) whether evolutionary shifts between high-flow and low-flow habitats in cyprinids are associated with evolutionary trade-offs in locomotor performance, we obtained data on both steady and unsteady swimming performance and external body shape for 19 species of cyprinids that typically occur in different flow regimes (still, intermediate and riptide). We also measured the routine energy expenditure (RMR) and maximum metabolic rate (MMR) and calculated the optimal swimming speed. Our results showed that fish species from riptide groups tend to have a higher critical swimming speed (Ucrit ), maximum linear velocity (Vmax ) and fineness ratio (FR) than fish from the other two groups. However, there was no correlation between the reconstructed changes in the steady and unsteady swimming performance of the 19 species. According to the phylogenetically independent contrast (PIC) method, the Ucrit was actively correlated with the MMR. These results indicated that selection will favour both higher steady and unsteady swimming performance and a more streamlined body shape in environments with high water velocities. The results suggested that steady swimming performance was more sensitive to the flow regime and that for this reason, changes in body shape resulted more from selective pressure on steady swimming performance than on unsteady swimming performance. No evolutionary trade-off was observed between steady and unsteady swimming performance, although Ucrit and MMR were found to have coevolved. However, a further analysis within each typically occurring habitat group suggested that the trade-off that may exist between steady and unsteady swimming performance may be concealed by the effect of habitat.

Underwater gliders are winged autonomous underwater vehicles (AUVs) that can be deployed for months at a time and travel thousands of kilometers. As with any vehicle, different applications impose different mission requirements that impact vehicle design. The authors investigate the relationship between a glider's geometry and its performance and stability characteristics. Because the authors' aim is to identify general trends rather than perform a detailed design optimization, they consider a generic glider shape: a cylindrical hull with trapezoidal wings. Geometric parameters of interest include the fineness ratio of the hull, the wing position and shape, and the position and size of the vertical stabilizer. The authors describe the results of parametric studies for steady wings-level flight, both at minimum glide angle and at maximum horizontal speed, as well as for steady turning flight. The authors describe the variation in required lung capacity and maximum lift-to-drag ratio corresponding to a given vehicle size and speed; the authors also consider range and endurance, given some initial supply of energy for propulsion. The authors investigate how the turning performance varies with wing and vertical stabilizer configuration. To support this analysis, the authors consider the glider as an 8-degree-of-freedom multibody system (a rigid body with a cylindrically actuated internal moving mass) and develop approximate expressions for turning flight in terms of geometry and control parameters. Moving from performance to stability and recognizing that a glider's motion is well described in terms of small perturbations from wings-level equilibrium, the authors study stability as an eigenvalue problem for a rigid (actuators-fixed) flight vehicle. The authors present a number of root locus plots in terms of various geometric parameters that illuminate the design tradeoff between stability and control authority.

Behavior of the side force generated at high angles of attack by two ogive-cylinder bodies of revolution with nose fineness ratio of 2.3 (B1) and 3.5 (B2) and the effect of a strip placed close the nose tip of each body (B1S and B2S) are analyzed through the wind tunnel test at ReD

The asymmetric vortex regime of a von Karman ogive with fineness ratio of 3.5 is experimentally studied at a Reynolds number of 156,000. Both port and starboard plasma actuators are used to introduce fluidic disturbances at the tip of the ogive which are amplified through the flow's convective instability and produce a deterministic port or starboard asymmetric vortex state (i.e. side force). Accurate control or manipulation of this asymmetric vortex state holds the potential for increased maneuverability and stability characteristics of slender flight vehicles at high angle of attack. Open-loop experimental tests are used to understand and quantify the vortex dynamics due to actuation inputs. Linear time invariant models provide a suitable model structure to replicate the vortex dynamics and allow for simulation and closed-loop control design. Standard PID control is designed and implemented. A closed-loop simulation shows arbitrary side force tracking with adequate disturbance rejection.

In this research, an experimental investigation was carried out at the International Islamic University Malaysia - Low Speed Wind Tunnel facility on a generic model of a hybrid lifting hull. Based on the historical trends of non-rigid airships, the fineness ratio of the said hull has been selected equal to 4. Free stream velocity was kept at 20 m/s and, along with the estimation of aerodynamic parameters, longitudinal and lateral stability characteristics were determined over a range of angles of attack from −8° to +12° and angles of sideslip from −10° to +10°. Zero lift coefficient was obtained at −4.2°, and the corresponding value was found to be greater than that at zero angle of attack. The comparison of the experimental results with the existing analytical relationships of wing has revealed that such an airfoil shaped hull cannot be considered as a wing due to 37% less analytical value of lift coefficient than that obtained by CFD simulations of the said hull. Existing equation of form factor of hull for conventional airships was also revisited, and a correction factor equal to 1.16 in the fundamental drag equation of aircraft’s fuselage was also proposed for fineness ratio equal to 4. Trends of the experimental data and mabsmoraiscomparison of the same with the theoretical calculations and computational results posed some interesting findings. The longitudinal and directional stabilities of a hybrid lifting hull were found to be statically unstable.

In order to analyze the effect of the ground-reflected radiation to the skins of the aerostat hull, the calculation method of the view factor for earth to the skins of the aerostat hull is studied. Firstly, the calculation model of the view factor for the area element of the aerostat hull to the ground is established, and the view factor is established as the function of the angle between the area element and the ground. On this basis, the view factor for different shape of aerostats to earth is calculated. To analysis the effect of atmospheric attenuation on the calculation of the view factor, the atmospheric attenuation coefficient is computed according to the available data, and then the view factor of the real condition is calculated. The calculation results show that, without atmospheric attenuation, the view factor for the ground to the spherical aerostat calculated by the traditional method is the same as the method used in this paper. For the ellipsoidal aerostat, the view factor increases with the increases of the fineness ratio, whereas the view factor decreases with the increases of the height.

There is significant interest in harvesting ocean energy for powering the autonomous vehicles that can conduct surveillance for long durations. In this paper, we analyze the applicability of solar cells as a power source for medusa-inspired biomimetic vehicles. Since these vehicles will be operating under ocean waters and may need to dive at various depths, a systematic investigation was conducted to determine the variation of output power as a function of depth and salinity levels. We modeled solar energy harvested by flexible amorphous solar cell coated jellyfish vehicles by considering the variables bell diameter, turbidity, depth, and fineness ratio. Low fineness ratio shapes were found to be better for solar energy powered vehicles. Study of three representative species, Aurelia aurita (AA), Mastigias sp., and Cyanea capillata indicates that harvested power was proportional to bell diameter. Optimum power can be harvested by tilting the vehicle axis to face refracted sunrays. Depending on a swimming pattern, power harvested in charging mode and in propulsion mode could vary significantly. The model indicates that, under some circumstances, amorphous silicon solar cell may be a cost-effective way to power autonomous underwater vehicles (AUVs) operating in shallow-water conditions with large lateral travel distances.

Swimming animals may experience significant changes in the Reynolds number (Re) of their surrounding fluid flows throughout ontogeny. Many medusae experience Re environments with significant viscous forces as small juveniles but inertially dominated Re environments as adults. These different environments may affect their propulsive strategies. In particular, rowing, a propulsive strategy with ecological advantages for large adults, may be constrained by viscosity for small juvenile medusae. We examined changes in the bell morphology and swimming kinematics of the limnomedusa Liriope tetraphylla at different stages of development. L. tetraphylla maintained an oblate bell (fineness ratio ≈ 0.5-0.6), large velar aperture ratio (R(v) ≈ 0.5-0.8), and rapid bell kinematics throughout development. These traits enabled it to use rowing propulsion at all stages except the very smallest sizes observed (diameter = 0.14 cm). During the juvenile stage, very rapid bell kinematics served to increase Re sufficiently for rowing propulsion. Other taxa that use rowing propulsion as adults, such as leptomedusae and scyphomedusae, typically utilize different propulsive strategies as small juveniles to function in low Re environments. We compared the performance values of the different propulsive modes observed among juvenile medusae.

Given the diversity of vertebral morphologies among fishes, it is tempting to propose causal links between axial morphology and body curvature. We propose that shape and size of the vertebrae, intervertebral joints, and the body will more accurately predict differences in body curvature during swimming rather than a single meristic such as total vertebral number alone. We examined the correlation between morphological features and maximum body curvature seen during routine turns in five species of shark: Triakis semifasciata, Heterodontus francisci, Chiloscyllium plagiosum, Chiloscyllium punctatum, and Hemiscyllium ocellatum. We quantified overall body curvature using three different metrics. From a separate group of size-matched individuals, we measured 16 morphological features from precaudal vertebrae and the body. As predicted, a larger pool of morphological features yielded a more robust prediction of maximal body curvature than vertebral number alone. Stepwise linear regression showed that up to 11 features were significant predictors of the three measures of body curvature, yielding highly significant multiple regressions with r(2) values of 0.523, 0.537, and 0.584. The second moment of area of the centrum was always the best predictor, followed by either centrum length or transverse height. Ranking as the fifth most important variable in three different models, the body's total length, fineness ratio, and width were the most important non-vertebral morphologies. Without considering the effects of muscle activity, these correlations suggest a dominant role for the vertebral column in providing the passive mechanical properties of the body that control, in part, body curvature during swimming.

The optimum fineness ratio (X = L/d, where L and d are body length and profile height, respectively) for minimum drag is about 4.5 and many fast swimming fish are characterized by values of this order. However, values for large whales that undergo extensive migrations (e.g., Balaenopteridae, Balaenidae, and Physeteridae) are as high as 8. A plot of fineness ratio versus mass (M) for different species of large whales shows that the optimal fineness ratio for minimum drag and therefore the minimum cost of transport increases slowly with increasing mass (X = 4M0.06). Optimal fineness ratio was determined from a simple hydromechanical model based on the sum of friction and pressure drag on an equivalent cylindrical body, which indicate a small positive dependence (0.11) of optimal fineness ratio for minimum drag with increasing body mass, suggesting an adaptation for reducing the energy cost of swimming.

Conformal domes that are shaped to meet aerodynamic requirements can increase range and speed for the host platform. Because these domes typically deviate greatly from spherical surface descriptions, a variety of aberrations are induced which vary with the field-of-regard (FOR) angle. A system for correcting optical aberrations created by a conformal dome has an outer surface and an inner surface. Optimizing the inner surface is regard as static aberration correction. A deformable mirror is placed at the position of the secondary mirror in the two-mirror all reflective imaging system, which is the dynamic aberration correction. An ellipsoidal MgF2 conformal dome with a fineness ratio of 1.0 is designed as an example. The FOR angle is 0°− 30°, and the design wavelength is 4 μm. After the optimization at 7 zoom positions by using the design tools Code V, the root-mean-square (RMS) spot size is reduced to approximately 0.99 to 1.48 times the diffraction limit. The design results show that the performances of the conformal optical systems can be greatly improved by the combination of the static correction and the dynamic correction.

Determination of the form of a body ensuring minimum drag under various isoperimetric conditions is a fundamental problem of aerodynamics. Very few results have been obtained for this problem in a rigorous formulation, as well as for supersonic motion of a body with a given fineness ratio. It is known for the plane problem that a wedge is a body ensuring the minimum wave drag for the zero coefficient of pressureperturbation reflection ( K = 0) from the shock attached to the wedge corner [1] or for the critical mach of the shock-layer gas [2]. A moving wedge with an attached shock is an almost optimal body under other conditions [2, 3]. The wedge ensures the minimum drag within the framework of the linear theory ( τ � 1) and the Newtonian theory ( τ ≤ 1) [4]. Here, τ = 1/( j λ ) and λ = L /( jR ), L , and R are the fineness ratio, length, and the base size of the body, respectively, in the plane case j = 1. According to the Newtonian theory for the axisymmetric problem, where j = 2 and R is the radius of the body base, the wage drag is minimum for slender (high-fineness) bodies ( τ � 1) with power-shaped longitudinal contours y = R ( x / L ) m , m = 3/4, where ( x , y ) are the Cartesian coordinates with the origin at the body nose (Fig. 1). Power-shaped bodies are used in practice. The most comprehensive information on the aerodynamic parameters of such bodies is presented in [5]. This is one of very few classes of bodies for which the aerodynamic parameters have been studied both theoretically and experimentally in a wide range of geometric parameters λ and m and Mach numbers M. The wave drag of low-fineness bodies is optimal for blunt-nosed shapes [4]. In the present work, the exact expression for the derivative of the wave-drag coefficient C x is derived using a specific global shape variation of a plane or axisymmetric body with a given fineness ratio. This derivative determines how C x changes if a body of the considered class is replaced by a λ -equivalent body with a tail skirt. It is shown that a positive derivative is a necessary, but not sufficient condition of the minimum wave drag of the initial body. Application of this criterion to the available data on the aerodynamic parameters of power-shaped axisymmetric bodies shows that the wave drag can be reduced if the comparison-body shape is obtained by not only weak, but even strong variation of the initial-body longitudinal contour.

The possibility of controlling the aerodynamic characteristics of wing airfoils in transonic regimes of flight using one-sided pulse-periodic energy supply has been studied. The flow structure near the symmetric airfoil at different angles of attack and its aerodynamic characteristics as functions of the value of energy in its nonsymmetric (about the airfoil) supply have been determined by numerical solution of two-dimensional nonstationary gasdynamic equations. A comparison of the obtained results and the data of calculation of flow past the airfoil at different angles of attack without energy supply has been made. It has been established that a prescribed lift can be obtained, using energy supply, with a much higher fineness ratio of the airfoil than that in the case of flow past it at an angle of attack.