Static and Dynamic Aeroelastic Simulations Using Kestrel - A CREATE Aircraft Simulation Tool

The HPCMP CREATE-AV Kestrel software product is a modularized, multidisciplinary, fixed-wing virtual aircraft simulation tool incorporating aerodynamics, structural dynamics, kinematics, and kinetics. Kestrel allows cross-over between simulation of aerodynamics, dynamic stability and control, structures, propulsion, and store separation. It's written in modular form with a Python infrastructure to allow growth to additional capabilities as needed. The current version of Kestrel is being used extensively in the government aircraft acquisition process and is being evaluated by industry for suitability to aircraft acquisition. Current capability is demonstrated for a maneuvering aircraft coupled with control surface movements, aeroelastic effects, store separation, and cargo deployment. In addition, several future capabilities currently in prototype are discussed.

An overview about recent results of the DLR-Project SikMa-“Simulation of Complex Maneuvers” is presented. The objective of the SikMa-Project is to develop a numerical tool to simulate the unsteady aerodynamics of a free flying aeroelastic combat aircraft, by use of coupled aerodynamic, flight-mechanic and aeroelastic computations. To achieve this objective, the unstructured, time accurate flow-solver TAU is coupled with a computational module solving the flight-mechanic equations of motion and a structural mechanics code determining the structural deformations. By use of an overlapping grid technique (chimera), simulations of a complex configuration with movable control-surfaces is possible.

SummaryThe Two-Sting Rig system provides captive trajectory and grid survey testing in the ARA 2·74 m × 2·44 m transonic wind tunnel, on models of the order of 10% scale. The system has been in productive operation since 1979, having been used primarily in the captive trajectory mode to predict release characteristics for a wide range of stores/aircraft.The paper describes the improvements to and developments of the system that have arisen from experiences gained during the last two years of its operational use. A brief description only is given of the general arrangement of the rig. Improvements to performance, simulation capabilities and to wind tunnel productivity are described together with current design studies for new applications.An appraisal of the overall performance of the method against three other ground based techniques is used to illustrate its merits and defects, using results from recent Two-Sting Rig wind tunnel tests and flight.

Perfect power system voltage stability is not possible in practice. Generally, the power grid is continually exposed to changes in its load and operating conditions. Therefore, dynamic stability analysis is one the most important and effective elements for greater security, stability and reliability of planning, design, operation and economic aspects of electric power networks. This study investigates and reports on the dynamic stability of the power system with a large‐scale photovoltaic system (L‐S PV). Two different scenarios with centralised PV power plants are considered in the medium voltage level without voltage regulation capabilities. Simulation results with these scenarios will show how the voltage instability decreases with the L‐S PV based on the bus status, disturbance location, and disturbance duration. In addition, the study discusses network terminal voltage, generator's rotor angle, generator's terminal current, generator's reactive power and electrical power output. This study is an extension of the earlier published conference paper.

Operational modal analysis (OMA) enables the identification of modal characteristics under operational loads and conditions. Traditional frequency-domain methods cannot directly capture modal changes over time, while existing time-frequency representations are not sufficiently interpretable due to spurious modes and implicit parameter design. This paper develops a new OMA method in time-frequency representation based on frequency-domain decomposition (FDD). Short-time FDD and a convolution-based strategy are proposed to obtain singular values and local mode shape similarity, respectively, which are further fused into mode indicators by a fuzzy-based strategy mimicking the modal assurance criterion. The method provides not only a global view of the modal characteristics over time and frequency but also estimates of the modal parameters. It is applicable to strongly nonstationary responses under time-varying loads and conditions. All the parameters explicitly affect the time-frequency representation, and the interpretability is enhanced by including physical information from the user’s prior knowledge in selecting parameters and peak bands. The proposed method is validated based on a study of railway sleepers under train passage. The rigid-body motions and bending modes are identified at frequencies up to 6,500 Hz in laboratory tests and 4,500 Hz in field tests at speeds up to 200 km/h. The identified natural frequencies and mode shapes agree with experimental modal analysis (EMA). The proposed method outperforms EMA in terms of broad frequency range and low measurement cost and can be potentially applied to structural health monitoring under operational conditions.

Effective optimization on Bump inlet using meta-model multi-objective particle swarm assisted by expected hyper-volume improvement

This paper presents a high-fidelity model to simulate the three-dimensional full-flight aerodynamics of a spinning soccer ball during a free kick. The simulation accounts for the Magnus effect–an aerodynamic phenomenon where spin induces lateral forces–by solving Navier–Stokes equations of incompressible flows and rigid-body motion in a fully coupled fluid-object interaction setting. A monolithic overset approach, which combines a boundary-fitted moving mesh around the ball with a stationary background mesh, is developed to accurately capture near-ball flow features while allowing unrestricted ball motion in 3D space. The monolithic approach solves the flow equations on overlapping domains without using subdomain iterations. A series of simulations is performed across varying initial kick speed and spin rate to quantify their effects on the ball trajectories systematically. The results reveal that the spin rate has a significant influence on lateral deviation due to the Magnus effect, while the initial kick speed has a substantial impact on overall flight range and flight time. Comparisons between a realistic soccer ball and an idealized smooth ball highlight the aerodynamic role of surface features, with smoother balls exhibiting a more substantial Magnus effect and greater lateral deviation. Furthermore, we compare the CFD results with predictions from a conventional ordinary differential equation (ODE) model using empirical drag coefficients. These comparisons show clear limitations in the ODE-based model, particularly under high-Reynolds-number flow regimes.

ArtiSynth (http://www.artisynth.org) is an open source, Java-based biomechanical simulation environment for modeling complex anatomical systems composed of both rigid and deformable structures. Models can be built from a rich set of components, including particles, rigid bodies, finite elements with both linear and nonlinear materials, point-to-point muscles, and various bilateral and unilateral constraints including contact. A state-of-the-art physics simulator provides forward simulation capabilities that combine multibody and finite element models. Inverse simulation capabilities allow the computation of the muscle activations needed to achieve prescribed target motions. ArtiSynth is highly interactive, with component parameters and state variables exposed as properties that can be interactively read and adjusted as the simulation proceeds. Streams of input and output data, used for controlling or observing the simulation, can be viewed, arranged, and edited on an interactive timeline display, and support is provided for the graphical editing of model structures.

Herein we investigate the coupled orbital and rotational dynamics of two rigid bodies modelled as polyhedra, under the influence of their mutual gravitational potential. The bodies may possess any arbitrary shape and mass distribution. A method of calculating the mutual potential’s derivatives with respect to relative position and attitude is derived. Relative equations of motion for the two body system are presented and an implementation of the equations of motion with the potential gradients approach is described. Results obtained with this dynamic simulation software package are presented for multiple cases to validate the approach and illustrate its utility. This simulation capability is useful both for addressing questions in dynamical astronomy and for enabling spacecraft missions to binary asteroid systems.

Summary This work considers continuous finite-time stabilization of rigid body attitude dynamics using a coordinate-free representation of attitude on the Lie group of rigid body rotations in three dimensions, SO(3). Using a Holder continuous Morse–Lyapunov function, a finite-time feedback stabilization scheme for rigid body attitude motion to a desired attitude with continuous state feedback is obtained. Attitude feedback control with finite-time convergence has been considered in the past using the unit quaternion representation. However, it is known that the unit quaternion representation of attitude is ambiguous, with two antipodal unit quaternions representing a single rigid body attitude. Continuous feedback control using unit quaternions may therefore lead to the unstable unwinding phenomenon if this ambiguity is not resolved in the control design, and this has adverse effects on actuators, settling time, and control effort expended. The feedback control law designed here leads to almost global finite-time stabilization of the attitude motion of a rigid body with Holder continuous feedback to the desired attitude. As a result, this control scheme avoids chattering in the presence of measurement noise, does not excite unmodeled high-frequency structural dynamics, and can be implemented with actuators that can only provide continuous control inputs. Numerical simulation results for a spacecraft in low Earth orbit, obtained using a Lie group variational integrator, confirm the theoretically obtained stability and robustness properties of this attitude feedback stabilization scheme. Copyright © 2015 John Wiley & Sons, Ltd.

Even under constant operating conditions, greases lubricating lead screw assemblies, as well as materials comprising their nut and screw threads, must perform over a range of contact pressures that not only varies from thread-to-thread, but also evolves with sliding distance as most-heavily loaded threads wear most rapidly. An example modeled here, consisting of a nut whose bulk body is rigid and elastic screw body having continuous elastic meshed threads, reveals the broad distribution of load along the length of the nut threads in an unworn lead screw assembly, as well as the distribution of wear depth that must accompany an eventual steady-state of uniform rate of nut thread wear. Thread load redistributions brought on by changes in operating conditions such as applied load, or even temperature in the case of a nut/screw pair of dissimilar materials, are similarly modeled. Such load redistributions in worn lead screws may cause either the top or the bottom positions of the nut thread to become most heavily loaded, depending on whether an operating condition is increased or decreased, and the extents of these redistributions using this continuous thread model can significantly exceed those predicted by a preliminary model where threads were considered as discrete turns. Operating condition changes are shown capable of causing worn threads at either extreme of the nut to become momentarily unloaded and removed from contact, and this continuous-thread model indicates that even smaller changes in operating condition can initiate such unloading, as compared to predictions from the discrete-thread model.Copyright © 2006 by ASME

A framework for modeling of the flexible air-breathing hypersonic vehicles (HSVs) with nonuniform fuselage section is developed and the effects of nonuniformities on flight dynamics are investigated. The flexible fuselage is modeled as a free-free beam with mass density and stiffness varying along its length. The assumed mode method, whose computation cost is demonstrated to acceptable relative to the finite element method, is utilized to conduct mode analysis of the fuselage.A longitudinal coupled dynamic model is obtained by combining the equations of rigid-body motion, elastic fuselage model, wing/pivot system models and actuator dynamics. A baseline control law developed from rigid vehicle assumption is used to stabilize the rigid-body motion and provide the capacity to consider inflight dynamic behavior. The impact of nonuniform mass density and stiffness distribution on static trim properties and dynamic stability are studied with nonuniformities parameterized. Numerical results indicate that the model with uniform section properties may underestimate the effects of fuselage flexibility on rig id-body flight dynamic characteristics if the section properties of the real vehicle fuselage vary apparently; to alleviate the impact of nonuniformity during the structure design of the vehicle, stiffness enhancement is more effective compared to mass layout adjustment.

In this paper, we presented the formulation of dynamic stability of spinning thin-walled composite beams carrying rigid bodies. First, we used a circumferentially uniform stiffness lay-up configuration to generate the coupled motion of bending–bending-shear and to solve the eigenvalue problem using the extended Galerkin method. The dynamic stability analysis was carried out for the beam carrying a single rigid body. The divergence and flutter instabilities were found by addressing the effect of the mass ratio and its location along the span of the beam. Along with these, the combined effects of several parameters such as spin speed, axial load, and ply angle were examined to study how they affect the stability of the beam.

The dynamics of micro-grid is of great complexity due to the diversity of DG and the highly nonlinearity within the system itself. Transient simulation tool plays a significant role to obtain a full and detailed response under various operation conditions. However, the simulation capability and speed are limited with the increasing size of the system. This paper presents a parallel algorithm for micro-grid transient simulation. It firstly decouples the solving of electrical system and control system using one step time-delay. Then an improvement algorithm on interface accuracy and numerical stability is proposed using explicit integration formula or interpolation formula. Finally, the control system is further decoupled according to its topology structure. The algorithms can be easily realized on a multi-core PC, and the computation load is balanced by DG modeling. The effectiveness of the proposed algorithms is validated in a benchmark low voltage micro-grid.

Long-range rotating wrap-around-fin rockets may exhibit non-convergent conical motion at high Mach numbers, causing increased drag, reduced range, and potential flight instability. This study employs the implicit dual time-stepping method to solve the unsteady Reynolds-averaged Navier–Stokes (URANS) equations for simulating the flow field around a high aspect ratio wrap-around-fin rotating rocket at supersonic speeds. Validation of the numerical method in predicting aerodynamic characteristics at small angles of attack is achieved by comparing numerically obtained side force and yawing moment coefficients with experimental data. Analyzing the rocket’s angular motion process, along with angular motion equations, reveals the necessary conditions for the yawing moment to ensure stability during angular motion. Shape optimization is performed based on aerodynamic coefficient features and flow field structures at various angles of attack and Mach numbers, using the yawing moment stability condition as a guideline. Adjustments to parameters such as tail fin curvature radius, tail fin aspect ratio, and body aspect ratio diminish the impact of asymmetric flow induced by the wrap-around fin on the lateral moment, effectively resolving issues associated with near misses and off-target impacts resulting from dynamic instability at high Mach numbers.