Effects of Externally Mounted Store on the Nonlinear Response of Slender Wings

2018 ◽  
Vol 13 (4) ◽  
Author(s):  
Yuqian Xu ◽  
Dengqing Cao ◽  
Chonghui Shao ◽  
Huagang Lin
Keyword(s):  
Design Procedure ◽  
Beam Model ◽  
Mass Center ◽  
State Equations ◽  
Dynamical Equations ◽  
Slender Body Theory ◽  
Nonlinear Characteristics ◽  
Strip Theory ◽  
Structural Nonlinearity ◽  
Slender Wing

The nonlinear characteristics of slender wings have been studied for many years, and the influences of the geometric structural nonlinearity on the postflutter responses of the wing have been received significant attention. In this paper, the effects of the external store on the nonlinear responses of the slender wing will be discussed. Based on the Hodges–Dowell beam model, the dynamical equations of the wing which include the geometric structural nonlinearity and store effects are constructed. The unsteady aerodynamic loading of the wing will be calculated by employing Wagner function and strip theory. The slender body theory is adopted to get the aerodynamic forces of the store. The Galerkin method is used to obtain the state equations of the system and the appropriate mode combination is obtained for the cases studied in this paper. Numerical simulations are given to show that the store spanwise position and the distance between the store mass center and the elastic center of the wing are two important factors which will affect the nonlinear characteristics of the wing. These two parameters will induce the occurrence of quasi-periodic motion and branch structure in bifurcation diagrams to the system. The peak of postflutter response is also related to these parameters and the lower response peak can be obtained when the store mass center is in front of the elastic center. The models and results are helpful to the design procedure of the slender wing with store in the preliminary stage.

The Slender Wing with a Half Body of Revolution Mounted Beneath

1968 ◽  
Vol 72 (693) ◽  
pp. 803-807 ◽  
Author(s):  
H. Portnoy
Keyword(s):  
Supersonic Flow ◽  
Slender Body ◽  
Meridian Plane ◽  
Pitching Moment ◽  
Body Of Revolution ◽  
Slender Body Theory ◽  
Lift And Drag ◽  
Body Theory ◽  
Slender Wing

Summary The slender-body theory of Ward is applied to a configuration consisting of a slender, pointed wing, carrying directly beneath it a pointed half-body of revolution divided along a meridian plane. Expressions for lift and drag due to incidence are found which are valid in both subsonic and supersonic flow if the flow is attached. The lift result can be used to find pitching moment. For the supersonic case the drag at zero incidence is also found and the expressions for a conical configuration are developed so that a limiting form of these can be compared with the results of ref. 3.

Two-Step Optimization for Wind Turbine Blade With Probability Approach

2010 ◽  
Vol 132 (3) ◽  
Author(s):  
Ki-Hak Lee ◽  
Kyu-Hong Kim ◽  
Dong-Ho Lee ◽  
Kyung-Tae Lee ◽  
Jong-Po Park
Keyword(s):  
Wind Turbine ◽  
Turbine Blade ◽  
Design Space ◽  
Cost Model ◽  
Minimum Energy ◽  
Design Procedure ◽  
Wind Turbine Blade ◽  
Horizontal Axis Wind Turbine ◽  
Probability Approach ◽  
Strip Theory

A horizontal-axis wind turbine blade is designed using two step optimization procedures with probability approach. For the efficient management of the multiple design variables required for the blade design, the design procedure is divided into two optimization steps. In step 1, the diameter and rotating speed of a blade are determined and design points are extracted from the design space. In step 2-1, blade shapes are optimized by using the strip theory with the minimum energy loss method. The capacity factor and the cost model for each optimized blade shape are calculated in steps 2-2 and 2-3, respectively. To find the global optimum point in the design space, the space is modified into a highly possible region through the use of the probability approach.

Powering and Seakeeping Characteristics of a Displacement Vessel Hullform With Waterline Parabolization

2010 ◽  
Author(s):  
Kevin J. Gould ◽  
Sander M. Calisal ◽  
Jon Mikkelsen ◽  
O¨mer Go¨ren ◽  
Barbaros Okan ◽  
...  
Keyword(s):  
Design Procedure ◽  
Programming Algorithm ◽  
Wave System ◽  
Optimized Design ◽  
Added Resistance ◽  
Speed Reduction ◽  
Optimal Shapes ◽  
Seakeeping Performance ◽  
Strip Theory ◽  
Significant Difference

Waterline parabolization is a design procedure used for displacement vessels to decrease the wave resistance of the hullform through the addition of amidships bulbs. The bow and shoulder wave system of a parent hullform are interfered with by the wave system produced by the amidships bulb. Despite an overall increase in vessel beam, amidships bulbs can produce enough wave cancellations to decrease the total resistance. The designer must pay close attention to the amidships bulbs longitudinal positioning and fairing. Two design approaches can be taken: one the amidships bulbs are “retro-fit” to the existing parent hullform increasing the vessels displacement, and second the displacement is held constant producing an entirely new “optimized” design with shallower entrance and exit angles. Optimal shapes for the amidships bulbs were developed numerically using a potential flow code based on Dawson’s method coupled with a quasi-Newton nonlinear programming algorithm, Calisal et al. (2009a). Tow-tank tests at Istanbul Technical University (ITU) confirmed that amidships bulbs could reduce the effective power by 15%. Given a significant improvement in powering, this paper compares the seakeeping performance of the parent, optimized, and retro-fit hullforms at different sea state conditions and quantifies fuel consumption and acceleration levels. SHIPMO PC, a ship motion program based on strip theory is used to compare the three different hullforms. Three speeds are considered: the design speed of 12.5 knots, a reduced speed of 11 knots associated with the expected loss of speed from added resistance, and 6 knots to represent significant speed reduction. Roll, pitch and heave motions along with added resistance are estimated. Accelerations at the bridge are used to evaluate effects on the crew. For various sea states the most significant motion is roll in beam seas and is incurred at low speeds. The only significant difference in response between all models was for the retro-fit design; the increased displacement from adding the amidships bulbs and holding the draught constant increased the added resistance. Powering and acceleration levels for all models in head seas will be verified in tow-tank tests at ITU.

scholarly journals Parametric whirl flutter study using different modelling approaches

2021 ◽  
Author(s):  
Christopher Koch
Keyword(s):  
Unsteady Aerodynamics ◽  
Beam Model ◽  
Electric Motors ◽  
Aeroelastic Stability ◽  
Aerodynamic Model ◽  
Lifting Surface ◽  
Aeroelastic Model ◽  
Strip Theory ◽  
Engine Mount ◽  
Whirl Flutter

AbstractThis paper demonstrates the importance of assessing the whirl flutter stability of propeller configurations with a detailed aeroelastic model instead of local pylon models. Especially with the growing use of electric motors for propulsion in air taxis and commuter aircraft whirl flutter becomes an important mode of instability. These configurations often include propeller which are powered by lightweight electric motors and located at remote locations, e.g. the wing tip. This gives rise to an aeroelastic instability called whirl flutter, involving the gyroscopic whirl modes of the engine. The driving parameters for this instability are the dynamics of the mounting structure. Using a generic whirl flutter model of a propeller at the tip of a lifting surface, parameter studies on the flutter stability are carried out. The aeroelastic model consists of a dynamic MSC.Nastran beam model coupled with the unsteady ZAERO ZONA6 aerodynamic model and strip theory for the propeller aerodynamics. The parameter studies focus on the influence of different substructures (ranging from local engine mount stiffness to global aircraft dynamics) on the aeroelastic stability of the propeller. The results show a strong influence of the level of detail of the aeroelastic model on the flutter behaviour. The coupling with the lifting surface is of major importance, as it can stabilise the whirl flutter mode. Including wing unsteady aerodynamics into the analysis can also change the whirl flutter behaviour. This stresses the importance of including whirl flutter in the aeroelastic stability analysis on aircraft level.

Maneuvering in Waves Based on Potential Theory

2014 ◽  
Author(s):  
Jochen Schoop-Zipfel ◽  
Moustafa Abdel-Maksoud
Keyword(s):  
Potential Theory ◽  
State Of The Art ◽  
Equations Of Motion ◽  
Test Results ◽  
Wave Excitation ◽  
Slender Body Theory ◽  
Strip Theory ◽  
Maneuvering In Waves ◽  
Semi Empirical ◽  
Body Theory

The forces acting on a maneuvering ship are determined with the in-house potential code panMARE. For slender ships with salient hull features, the forces and moments can be captured by properly treating the shed vorticity. For blunt ships it is not possible to directly determine the strength of the vorticity and the position where it leaves the hull. Therefore, it is easier and not less accurate to account for separation forces via semi-empirical formulae. These corrections are based on slender body theory or extensive RANS computations. The mass forces can be determined directly by potential theory. Forces and moments due to rudder and propeller are calculated using state-of-the-art procedures. Arbitrary maneuvers can be simulated by using the equations of motion. With the applied corrections a satisfactory agreement with model test results can be obtained. Wave excitation forces can be introduced to incorporate the influence of sea states. These forces are determined with strip theory. While the forces agree well with measured data, a deviation can be observed in the motions.

Combined Seakeeping and Maneuvering Analysis of a Two-Ship Lightering Operations

2010 ◽  
Author(s):  
Renato Skejic ◽  
Tor E. Berg
Keyword(s):  
Hydrodynamic Interaction ◽  
Wave Length ◽  
Weather Conditions ◽  
Theory Model ◽  
Second Order ◽  
Unified Theory ◽  
Wave Loads ◽  
Slender Body Theory ◽  
Strip Theory ◽  
Turning Maneuver

Hydrodynamic interaction effects between two ships going ahead in regular deepwater waves were numerically studied during typical maneuvers for ship-to-ship (STS) operations, such as lightering, replenishment, etc. Such maneuvers are usually classified as potentially hazardous situations, due to the possibility of collision between the two vessels when they are operating in close proximity. Since the collision hazard is usually even greater in bad weather conditions, knowledge of the maneuvering capabilities of two ships in a seaway must be available in order to ensure safe and efficient STS operation. In this study, a combined seakeeping and maneuvering analysis of two ships involved in typical lightering operation was performed using a unified seakeeping and maneuvering theory developed by Skejic and Faltinsen [1, 2]. The unified theory integrates seakeeping and maneuvering analysis by using a two time scale assumption and modular concept. This approach allows the maneuvering behavior of the two ships involved in lightering operation in waves to be successfully described. The seakeeping analysis for both vessels uses Salvesen-Tuck-Faltinsen [3] (STF) strip theory for deep water by assuming that there are no hydrodynamic interaction in waves between the two ships. The regular wave field effects upon the involved vessels are described by the mean second-order wave loads. They can be estimated by using one of the available near/far field theories (Salvesen [4] and Faltinsen et al. [5]) that take the complete wave length range of interest for a considered STS maneuver into account. When the incident wave length is short relative to the ship length, the asymptotic theory by Faltinsen et al. [5] is used. The predicted mean second-order wave loads according to these theories are shown in the case of turning maneuver of a ‘MARINER’ type of a ship in specific wave conditions. The maneuvering module of the unified theory model is based on generalized slender-body theory, while calm-water interaction forces and moments between the two ships are estimated using Newman and Tuck [6] theory. Automatic steering- and speed-control algorithms for both ships (Skejic et al. [7]) are employed to achieve high-precision and collision-free lightering maneuvers in waves. This is illustrated by a numerical simulation involving ‘Aframax’ and ‘KVLCC’ (type 2 – Moeri tanker [16]) types of ships. Finally, from the perspective of marine safety and reliability, the future requirements and recommendations for typical lightering operations in a seaway are discussed.

Analyzing Bilinear Systems Using a New Hybrid Symbolic-Numeric Computational Method

2019 ◽  
Vol 141 (3) ◽  
Author(s):  
Meng-Hsuan Tien ◽  
Kiran D'Souza
Keyword(s):  
Linear Response ◽  
Nonlinear Response ◽  
Initial Conditions ◽  
Piecewise Linear ◽  
Bilinear Systems ◽  
Computational Method ◽  
Transition Time ◽  
Time Interval ◽  
Beam Model ◽  
Nonlinear Characteristics

In this paper, an efficient and accurate computational method for determining responses of high-dimensional bilinear systems is developed. Predicting the dynamics of bilinear systems is computationally challenging since the piecewise-linear nonlinearity induced by contact eliminates the use of efficient linear analysis techniques. The new method, which is referred to as the hybrid symbolic-numeric computational (HSNC) method, is based on the idea that the entire nonlinear response of a bilinear system can be constructed by combining linear responses in each time interval where the system behaves linearly. The linear response in each time interval can be symbolically expressed in terms of the initial conditions. The transition time where the system switches from one linear state to the other and the displacement and velocity at the instant of transition are solved using a numerical scheme. The entire nonlinear response can then be obtained by joining each piece of the linear response together at the transition time points. The HSNC method is based on using linear features to obtain large computational savings. Both the transient and steady-state response of bilinear systems can be computed using the HSNC method. Thus, nonlinear characteristics, such as subharmonic motion, bifurcation, chaos, and multistability, can be efficiently analyzed using the HSNC method. The HSNC method is demonstrated on a single degree-of-freedom (DOF) system and a cracked cantilever beam model, and the nonlinear characteristics of these systems are examined.

Nonlinear Dynamic Response and Structural Evaluation of Container Ship in Large Freak Waves

2014 ◽  
Vol 137 (1) ◽  
Author(s):  
Weiqin Liu ◽  
Katsuyuki Suzuki ◽  
Kazuki Shibanuma
Keyword(s):  
Nonlinear Dynamic ◽  
Structural Response ◽  
Bending Moment ◽  
Ocean Waves ◽  
Freak Waves ◽  
Freak Wave ◽  
Structural Evaluation ◽  
Strip Theory ◽  
Structural Nonlinearity ◽  
Static Conditions

Many ship accidents and casualties are caused by large freak ocean waves. Traditionally, the strength of ships against freak waves is assessed by means of ultimate strength evaluation, assuming quasi-static conditions, but the nonlinear dynamic structural response of ships to freak waves should be considered as well. This paper describes how the strength of a ship can be evaluated in terms of its nonlinear vertical bending moment (VBM). Linear dynamic VBM of a ship, which is derived from hydrodynamics, is calculated using a time-domain strip theory code under freak wave conditions, and the nonlinear dynamic VBM, which is dependent on structural nonlinearity, is calculated using a combination of quasi-static and dynamic nonlinear analyses based on the finite element method (FEM). The nonlinear and linear VBMs are then compared to assess how they differ. Then, the influence of freak wave height and wave speed on the VBMs and deformation is studied.

Dynamic Design Procedure for HVAC Ducts

1988 ◽  
Vol 110 (4) ◽  
pp. 413-421
Author(s):  
K. Tsuruta ◽  
K. Kojima
Keyword(s):  
Design Method ◽  
Design Procedure ◽  
Total System ◽  
Beam Model ◽  
Duct System ◽  
Support Structures ◽  
Response Characteristics ◽  
High Rigidity ◽  
Japanese Industrial Standard ◽  
Duct Systems

Design layout of ducts and supports systems which make up the heating, ventilating and air-conditioning systems (HVAC) is based upon the Japanese Industrial standard (JIS)[1] for hanger support systems conforming to SMACNA[2] standards of high-rigidity design, where emphasis is placed on buildings containing duct systems. However, since high-rigidity systems involve raising the rigidity of the total system, the weight and number of support structures have to be increased, thus posing economic problems. On the other hand, hanger systems are problematic due to their structural weakness. Therefore, we have tried to apply low-rigidity ducts and a support system which rely heavily on the strength of the ducts themselves. To accomplish this we tried to lengthen the duct support span, to lighten the support structures, and to establish a reasonable design method for the duct system. Further, the effectiveness of the present design margin can be confirmed by a duct system test using a shaker table. Our study mainly consisted of experiments: performing duct element tests to study rigidity and strength, using the shaker table to estimate dynamic characteristics and response characteristics of a duct system model, and studying the calculations of the duct beam model.

scholarly journals New Method for Analyzing the Flutter Stability of Hingeless Blades with Advanced Geometric Configurations in Hovering

2020 ◽  
Vol 2020 ◽  
pp. 1-16
Author(s):  
Si-wen Wang ◽  
Jing-long Han ◽  
Quan-long Chen ◽  
Hai-wei Yun ◽  
Xiao-mao Chen
Keyword(s):  
Structural Analysis ◽  
Usual Method ◽  
New Method ◽  
Analysis Tool ◽  
Fe Model ◽  
Beam Model ◽  
Lattice Method ◽  
Aspect Ratios ◽  
Strip Theory ◽  
Doublet Lattice Method

A new method used to analyze the aeroelastic stability of a helicopter hingeless blade in hovering has been developed, which is especially suitable for a blade with advanced geometric configuration. This method uses a modified doublet-lattice method (MDLM) and a 3-D finite element (FE) model for building the aeroelastic equation of a blade in hovering. Thereafter, the flutter solution of the equation is calculated by the V-g method, assuming blade motions to be small perturbations about the steady equilibrium deflection. The MDLM, which is suitable to calculate the unsteady aerodynamic force of nonplanar rotor blade in hovering, is developed from the doublet-lattice method (DLM). The structural analysis tool is the commercial software ANSYS. The comparisons of the obtained results against those in the literatures show the capabilities of the MDLM and the method of structural analysis. The flutter stabilities of swept tip blades with different aspect ratios are analyzed using the new method developed in this work and the usual method on the basis of the unsteady strip theory and beam model. It shows that considerable differences appear in the flutter rotational velocities with the decrease of the aspect ratio. The flutter rotational velocities obtained by the present method are evidently lower than those obtained by the usual method.

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