Study on Response of Launch Vehicle Under Ground Wind Loads Based on Transfer Matrix Method for Multibody Systems

Development of an object-oriented framework for the vibration characteristic computation of multibody systems

A novel method for the dynamic modeling of Stewart parallel mechanism

In order to predict dynamic loads on the newly designed Japanese H-11 launch vehicle, adequacy of prediction methods has been assessed by the dynamic scale model testing. The three dimensional dynamic model was used in the analysis to express coupling effects among axial, lateral (pitch and yaw) and torsional vibrations. Liquid/tank interaction was considered by use of boundary element method. The 1/5 scale model of H-I1 launch vehicle was designed to simulate stiffness and mass properties of important structural parts, such as core/SRB junctions, first and second stage Lox tanks and engine mount structures. Modal excitation of the test vehicle were accomplished with 100-1000 N shakers which produced random or sinusoidal vibration forces. Vibration response of the test vehicle were measured at various locations with accelerometers and pressure sensors. In the lower frequency range, correspondence between analysis and experiment were generally good. The basic procedures in analysis seem to be adequate so far, but some improvements in mathematical modeling are suggested by comparison of test and analysis.

Soil Moisture Active Passive (SMAP) is a NASA-developed Earth science satellite currently mapping the soil moisture content and freeze/thaw state of Earth's land mass from a 685km, near-polar, sun-synchronous orbit. It was launched on January 31, 2015 from Vandenberg AFB upon a Delta II 7320 launch vehicle. Due to external considerations, SMAP's launch vehicle selection remained an open item until Project Critical Design Review (CDR). Thus, certain key aspects of the spacecraft design had to accommodate a diverse range of candidate launch vehicle environments, performance envelopes, interfaces and operational scenarios. Engineering challenges stemmed from two distinct scenarios: decisions that had to be made prior to launch vehicle selection to accommodate all possible outcomes, and post-selection changes constrained by schedule and the existing spacecraft configuration. The effects of the timing of launch vehicle selection reached virtually every aspect of the Observatory's design and development. Physical environments, mass allocations, material selections, propulsion system performance, dynamic response, launch phase and mission planning, overall size and configuration, and of course all interfaces to the launch vehicle were heavily dependent on this outcome. This paper will discuss the resolution of these technical challenges.

The dynamic nonlinear response and stability of slender structures in the main resonance regions are a topic of importance in structural analysis. In complex problems, the determination of the response in the frequency domain indirectly obtained through analyses in time domain can lead to huge computational effort in large systems. In nonlinear cases, the response in the frequency domain becomes even more cumbersome because of the possibility of multiple solutions for certain forcing frequencies. Those solutions can be stable and unstable, in particular saddle-node bifurcation at the turning points along the resonance curves. In this work, an incremental technique for direct calculation of the nonlinear response in frequency domain of plane frames subjected to base excitation is proposed. The transformation of equations of motion to the frequency domain is made through the harmonic balance method in conjunction with the Galerkin method. The resulting system of nonlinear equations in terms of the modal amplitudes and forcing frequency is solved by the Newton-Raphson method together with an arc-length procedure to obtain the nonlinear resonance curves. Suitable examples are presented, and the influence of the frame geometric parameters and base motion on the nonlinear resonance curves is investigated.

The object of this study was the motion of an ultralight class variable-length launch vehicle made of a polymer body along the active phase of the trajectory. The work considers the solution to the problem of designing low-cost means of delivery to orbit, namely to the assessment of the possibility of removing the payload by a carrier rocket with a polymer body of variable length beyond the dense atmosphere of the Earth. For this purpose, ballistic projection of the trajectory of the launch vehicle was carried out taking into account overloading; its aerodynamic characteristics and peculiarities of aerothermodynamic processes occurring during flight in the atmospheric phase of the trajectory were determined. The closeness (up to 10 %) of the obtained results with known experimental data is shown. The influence of the aerodynamic force on the parameters of the launch vehicle motion was studied. A flight simulation was conducted, the results of which showed the fundamental possibility of launching a CubeSat 24U class payload using a launch vehicle with a polymer body of variable length to a suborbital trajectory with an altitude of about 300 km. At the same time, the effective longitudinal overload on the body of the launch vehicle does not exceed 4 units, and the temperature on the surface of the body does not exceed 300 K. A feature of the research is the use of a multidisciplinary approach, which implies taking into account the interrelationship of aerodynamic, thermodynamic, and ballistic processes. The established motion parameters, aerodynamic characteristics, and the surface heating temperature of the launch vehicle body are key values for further research on the design and analysis of a launch vehicle with a polymer body of variable length. These data could be used to calculate the mechanical and thermal loads acting on the structure of the launch vehicle during flight

Helical idler gear transmission systems can adapt to high-speed, heavy-load working environments and are thus widely used in aerospace, shipbuilding, and other heavy industry sectors. Root crack is one of the common fault types. Prior studies generally only considered cracks at a single working flank, lacking comparative analysis between the crack at the working flank and the non-working flank. This paper examines the dynamic response of helical idler gears with root cracks at different working flanks, comparing dynamic response differences between working and non-working flank cracks. First, a comprehensive dynamics model of the helical idler gear system is established. Second, the influence of root crack location (the working flank or the non-working flank) on time-varying meshing stiffness is considered based on potential energy method, and a flexible model is established by finite element method for the faulty gear. Finally, solution results of the rigid-flexible coupling dynamics model are analyzed. The dynamic response signal characteristics of root cracks at the working flank and the non-working flank are analyzed in time domain, frequency domain and time frequency domain, respectively. Corresponding experiments are designed based on the FZG experimental platform, and the experimental results are in good agreement with the simulation results, which verified the accuracy of the model.

The paper is devoted to develop launch vehicle (LV) motion control algorithms for solution of the two special control problems at the initial flight part: controlled engines plumes displacement and LV emergency displacement in case of engine failure. The implementation of the displacement process in both tasks provides execution of specified preset programs. For formation controllers of the LV angular motion control system this paper proposes a modified version of analytical design of controllers (AKOR) problem solution. Efficiency of the developed control algorithms is verified by the simulation results of the algorithms as a part the detailed LV motion model.

Cavitation dynamics continue to pose a significant risk in the development and operation of launch vehicle (LV) propulsion systems. In addition to generating unsteady loads that can directly damage turbopump hardware, cavitation dynamics often couple with LV fluid feed systems, producing system wide POGO instability that can cause catastrophic failures. Despite its importance, the current understanding of cavitation dynamics, and especially pump transfer matrices, is limited. Given the relatively sparse amount of inducer transfer matrix data available, there is a critical need for more in-depth characterization of the cavitation dynamics in turbopump inducers to avoid POGO instability. This paper defines and validates a new reduced-order approach to infer key parameters such as cavitation compliance, K, and mass flow gain factor, M, from simple, single sensor unsteady pressure measurements during inducer inlet pressure ramps. The utility of this approach is demonstrated for a range of inducer geometries reported in the literature. The results are in agreement with experimental data and the paper provides a new capability supporting the assessment of LV POGO instability.

This paper presents a three-dimensional model of a helical two-stage gear system. Excitation is induced by periodic variation of the mesh stiffness. This case describes the real working of the gearing. The mesh phasing variation is related to the number of teeth and also to the location of the gears. First, dynamic response is calculated using Newmark's step-by-step time integration method. The numerical results are presented in both the frequency and time domains. The dynamic behaviour of a defect-free gear system and a defective one are compared in both the time domain and frequency domain. Two types of defect are considered: a cracked tooth and misalignment. The cracked tooth produces an amplitude modulation with the mesh frequency and its first harmonics on the dynamic response. An amplitude modulation also occurs when a misalignment is introduced. The Wigner–Ville distribution method is used to show the dynamic behaviour in the joint time–frequency domain and to localise the cracked teeth.

Aimed at the unattended requirements of the heavy launch vehicle filling and launching support system, this paper focuses on the propellant filling and discharge automatically. This paper adopts the parametric variable frequency and amplitude variation equation to simulate the motion of the launch vehicle under wind load conditions. The equivalent spring damping model is used to simulate the real flexible umbilical arm of the rocket. In this paper, the compound active disturbance rejection control and robust integral sign control (CADRCRISC) method is proposed, including feedforward compensation control, linear feedback control, robust control, and extended state observer (ESO) control. This method can adapt to external disturbances and achieve high‐precision follow‐up control, which is verified through experiments and simulations. The method can adaptively realize fast‐following responses and regulate against any disturbance. The research on the automatic docking control technology of the combined connector is of great significance to the unattended launch support system for heavy launch vehicles. Besides, the control method proposed in this paper can be applied in other similar automatic docking applications.

Umbilical Tower (UT) forms a critical structure along with mobile service tower, launch pedestal and jet deflectors of a rocket launch pad. UT will be exposed to severe thermal environments during lift off of the launch vehicle owing to its close proximity. UT experiences thermal loads until the launch vehicle lifts off and clears it. Hence thermal environments need to be quantified to assess the survivability of UT for subsequent missions. This paper brings out the methodology developed for estimating different thermal environments experienced by UT structure during a typical rocket launch. The engineering method result in a quick estimate of flow properties of the plume from the rocket exhaust compared to CFD, which will be computationally intensive and time consuming to arrive a converged accurate solution for heat flux estimation. ISRO’s launch vehicles have first stage with Solid Rocket Motor (SRM) as core and solid motors/liquid engines as multiple strap-ons. Thermal loads to launch pad structures include radiative and convective heating from exhaust plumes. The aluminum particle laden exhaust plumes of solid rockets are dominating radiative heat source. Convective heating occurs from hot jets and direct plume impingement. The relative movement of launch vehicle with respect to UT structure is an important parameter affecting thermal environments. It varies for each launch depending on the vehicle variant and its lift-off trajectory. This calls for a detailed assessment of thermal loads for thermal adequacy studies. A finite element based thermal model for umbilical tower is also generated for thermal response studies and Thermal Protection System (TPS) design. The computed temperature levels at various location of UT structure are compared with measured values during typical lift-off. Results indicate that temperature levels of UT structure are within allowable limits and the adopted methodology can predict temperature within a maximum difference of ±5%.

The dynamic response of nonlinear structures has been a topic of interest in civil engineering research. Problems in which base-structure interaction is present have a great importance in structural analysis, since most structures rests on flexibel systems (soil or supports with dissipation). In this research area, the study of structures under the action of seismic loads represent a relevant topic, since this kind of excitations may excite several vibration modes and thus influence strongly the dynamic response. In this context, the prediction of the nonlinear structural behavior in frequency domain of structures under base excitation is a useful resource to assess the potential effects of sismic loads on these systems. In this thesis, a methodology for nonlinear dynamic analysis of plane frame structures under base excitation is presented considering geometric nonlinearity and elastic supports represented by elasto-plastic unidimensional springs. Trough a parametric analysis, the variability of the dynamic responses of slender structural systems under the actions of real earthquakes, synthetics earthquakes, as well as the action of multiple earthquakes is assessed. The structural systems here analyzed are discretized in space using a nonlinear finite element formulation. For the response in frequency domain, a scheme based on the Balance Harmonic Method and the Galerkin method, in conjunction with continuation methods, is formulated to obtain the nonlinear resonance curves. The nonlinear dynamic response in the time domain is calculated by direct integration of the equations of motion. For this, the Runge-Kutta method and the Newmark method in association with the iterative Newton-Raphson scheme are employed.

Dynamic characteristics play a crucial role in evaluating the performance of weight sensors and are essential for achieving fast and accurate weight measurements. This study focuses on a weight sensor based on optical coherence displacement. Using finite element analysis, the sensor was numerically simulated. Frequency domain and time domain dynamic response characteristics were explored through harmonic response analysis and transient dynamic analysis. The superior dynamic performance and reduced conditioning time of the non-contact optical coherence-based displacement weight sensor were confirmed via a negative step response experiment that compared the proposed sensing method to strain sensing. Moreover, dynamic performance metrics for the optical coherence displacement-type weight sensor were determined. Ultimately, the sensor’s dynamic performance was enhanced using the pole-zero placement method, decreasing the overshoot to 4.72% and reducing the response time to 0.0132 s. These enhancements broaden the sensor’s operational bandwidth and amplify its dynamic response capabilities.

Nonlinear Dynamic Analysis of Eccentric Curve-face Gear Transmission System