Dynamic Stability Coefficients Research Articles

Experimental study of dynamic stability for a entry capsule in supersonic flow

Due to the lack of existence of control surfaces in entry capsules, the subject of static and dynamic stability is always important. In this paper, these coefficients are investigated experimentally for the case of forced oscillation at supersonic flow. In this experimental study, the effects of freestream Mach number, mean attack angle and pitch frequency on dynamic stability coefficients were evaluated. According to the results, in Mach 1.8, the geometry starts to be dynamically unstable. One approach to overcome this problem is to change the average attack of angle of the model. This change in the mean attack of angle, similar to the results presented for the five-degree mean angle, will lead to dynamic stability.

Study on Seismic Coefficient Calculation Method of Slope Seismic Stability Analysis

In this paper, a pseudostatic seismic coefficient evaluation method for slope dynamic stability analysis was explored with Yushu Airport Road 3# landslide as a typical engineering case, and the shaking table test and numerical calculation were performed during the exploration. The loading waveform was selected as Yushu wave, and the acceleration time‐history of seismic waves was measured and analyzed, revealing the failure mode of slopes. Based on the rigid‐body limit equilibrium theory, the instantaneous additional seismic forces of each block and the time‐history landslide stability coefficient were calculated. According to the time‐history of the landslide, dynamic stability coefficients were calculated. Subsequently, we proposed a pseudostatic seismic coefficient evaluation method and discussed the seismic coefficient slope dynamic stability analysis. The results showed that as the vibration frequency rose, the average acceleration and the residual displacement of the slope decreased, but the slope grew more dynamically stable. With the proposed method, we calculated the period of slope seismic action to be 0.126 s and the average maximum acceleration to be 0.156 g, which was close to the designed ground motion acceleration of 0.15 g. Besides, we calculated the safety factor of landslides under earthquake to be 0.93∼0.97, which was close to that obtained from the building code method and in accordance with the present seismic deformation and failure mode of landslides. Moreover, the results obtained from the method of nuclear power plant specification were relatively small compared to other specification methods. The research is significant because it provides a new idea for the evaluation of seismic landslide stability in practical engineering.

Shock Reduction through Opposing Jets—Aerodynamic Performance and Flight Stability Perspectives

In this research paper, investigations of counter flow (opposing) jet on the aerodynamic performance, and flight stability characteristics of an airfoil with blunt leading-edge in supersonic regime are performed. Unsteady Reynolds-Averaged Navier-Stokes ( U R A N S ) based solver is used to model the flow field. The effect of angle of attack ( α ), free-stream Mach number ( M ∞ ), and pressure ratio ( P R ) on aerodynamic performance of airfoil with and without jet are compared. The results indicate that the opposing jet reduces drag from 30 % to 70 % , improves the maximum lift-to-drag ratio from 2.5 to 4.0, and increases shock stand-off distance from 15 % to 35 % depending on flow conditions. The effect of opposing jet on longitudinal flight stability characteristics, studied for the first time, indicate improvement in dynamic stability coefficients ( C m q + C m α ˙ ) at low angles of attack. It is concluded that the opposing jet can help mitigate flight disturbances in supersonic regime.

Computational Fluid Dynamics Simulations of Supersonic Inflatable Aerodynamic Decelerator Ballistic Range Tests

The free-flight behavior of entry vehicles can greatly impact vehicle and mission design. Current methodologies rely heavily on ground and flight experiments, while computational fluid dynamics is largely used as a complement to experiments in the form of static aerodynamic databases. The dynamic stability of entry vehicles is primarily studied through ballistic range experiments and flight tests. In an effort to validate the predictive capabilities of computational fluid dynamics for free-flight aerodynamic behavior, numerical simulations of a ballistic range experiment are performed using the unstructured finite-volume Navier–Stokes solver, US3D. The ballistic range tests used for comparison in this paper were performed on a scaled model of the Supersonic Inflatable Aerodynamic Decelerator geometry. The purpose of these experiments was to provide aerodynamic coefficients of the vehicle as an a priori analysis of dynamic stability coefficients ahead of the Supersonic Flight Demonstration Test. The range data span the moderate Mach number range, 3.8–2.0, with a maximum total angle-of-attack range, 10–20 deg. These conditions are intended to span the Mach/angle-of-attack space for the majority of the flight test. Comparisons to raw vehicle attitude and postprocessed aerodynamic coefficients are made between simulated results and experimental data. The resulting comparisons for both the raw model attitude and derived aerodynamic coefficients show good agreement with experimental results. Additionally, near-body pressure field values for each trajectory simulated are investigated. Extracted surface and wake pressure data give further insight into dynamic/flow coupling, leading to a potential mechanism for dynamic instability.

High-Alpha Prediction of Roll Damping and Magnus Stability Coefficients for Finned Projectiles

The roll damping and Magnus dynamic stability coefficients, as well as total force and moment coefficients, were numerically computed at high angles of attack up to 90 deg for two generic fin-stabilized flight munitions at a supersonic Mach number of 2.49. The aerodynamic coefficients were computed via time-accurate Reynolds-averaged Navier–Stokes numerical methods, and they were compared with archival wind-tunnel data. Fair to excellent comparisons with the experiment were obtained for the coefficients for the full angle-of-attack range, except for the axial force, which was overpredicted at higher angles of attack. Numerical modeling parameter studies were conducted to include dependence on spin rate, grid resolution, temporal resolution, and other numerical convergence parameters.

Locked minimally invasive plating versus fourth generation nailing in the treatment of AO/OTA 31A2.2 fractures: A biomechanical comparison of PCCP® and Intertan nail®

IntroductionLocked minimally invasive plating and fourth generation nailing potentially could reduce the complication rate in the treatment of trochanteric femur fractures by its rotational stability and providing better lateral cortical support. The purpose of this study was (1) to compare the biomechanical properties of the Percutaneous compression plate (PCCP) and the Intertan nail (IT) with regards to implant failure and (2) to assess dynamic stability coefficients in an unstable AO/OTA 31A2.2 fracture model. MethodsIn paired femurs, a standardised unstable trochanteric femur fracture was induced by an oscillating saw. The fractures were stabilised by either the PCCP (Orthofix, McKinney, TX, USA) or the IT (Smith & Nephew, Memphis, TN, USA). All femurs were loaded with 300N, followed by an increase in load until failure using 300N each time (2000 cycles each, 0.5Hz). After every load step the samples were assessed visually and radiographically. We measured migration and performed a survival analysis. Results16 fractures were induced in 8 paired human specimens (mean age: 84 years, 61–100 years). The mean stiffness (PCCP vs. IT: 249±124N/mm vs. 273±153N/mm; p=0.737) was comparable. The IT proved superior to the PCCP with regard to the number of cycles reached before failure occurred (PCCP vs. IT: 12,691±4733 vs. 15,313±4875 cycles; p=0.023). Except for a higher axial migration of the IT at failure point (PCCP vs. IT: 1.3mm vs. 4.3mm; p=0.028) there were no differences between the intra- and extramedullary implants, not even in terms of rotational stability along the femoral neck axis. A fracture of the femoral neck caused test abortion in both implants in most cases. ConclusionThis study showed a superiority of the IT compared with the PCCP with regards to number of cycles achieved under sequential load increases for unstable trochanteric femur fractures. The stiffness was comparable. Both implants showed a high rotational stability and a support of the lateral wall. Study typeBiomechanical study.

動的風洞試験と飛行シミュレーションの連成に関する実験的研究

Dynamic wind tunnel testing is an important method to obtain aerodynamic characteristics of an aircraft. In this study, an experimental system for longitudinal dynamic force measurement is designed. A set of static and dynamic force measurement of a model aircraft is conducted using this system. Aerodynamic characteristics of the test model including dynamic stability coefficients were obtained from the results. Finally, dynamic wind tunnel system was coupled with 1DoF flight simulator. The amplitude and the frequency of the dynamic motion of the model aircraft was simulated successfully by the current system.

Study of the aerodynamic stability of a blunt cone with a side flap in a hypersonic flow

The stationary and time-dependent aerodynamic coefficients of a slender blunt cone with a flap located near the base section of the model are experimentally investigated. The freestream parameters (M∞ = 6, Re L = 0.88 × 107, and γ = 1.4) ensured a turbulent regime of flow over the conical surface and the flap. At high angles of attack (α ∼ 10°) laminar-turbulent transition is observable in the separation zone on the leeward side of the body. Emphasis is placed on the determination of the trimming angles of attack for different positions of the center of rotation and the static and dynamic stability coefficients (the model oscillation damping coefficient).

FM Telemetry for Multiple Force Measurements on Free-Flying Models

The extension of the FM telemetry technique to provide simultaneous measurements of four forces acting on a free-flight aerodynamic model is reported. Developments and procedures required to achieve the accuracy, linearity, and stability necessary for obtaining dynamic stability coefficients are described. System accuracy is believed to be better than 3 percent. Free-flight data, presented in the form of aerodynamic stability derivatives, are in good agreement with measurements taken by conventional methods under the same aerodynamic conditions.