Comparison of Tethered Post-Capture System Models for Space Debris Removal

The space debris problem poses a huge threat to operational satellites and has to be addressed. Multiple removal methods have been proposed to keep Earth’s orbit stable. Flexible connection capturing methods, such as the harpoon system, tether–gripper system and the net system, are potential candidate methods for space debris removal in the future. However, the tethered system is usually assumed as a dumbbell model where two end masses are connected by a rigid bar. This traditional model is not accurate enough to predict the motion of the target, neither the whole system. In this paper, three models, namely the modified dumbbell model, lumped-mass model and the ANCF model, to describe a tethered post-capture system for space debris removal are described and compared. Moreover, modal analysis of the tethered system is performed, and an analytical solution of the system’s natural frequency is derived. In addition, two configurations of the tethered system, namely the single tether configuration and the sub-tether configuration are simulated and compared based on three models, respectively. Finally, the influence on the chaser satellite by the initial angular velocity of the target is analyzed.

The Effect of Rainfall Intensity to Landslide Run-Out Prediction and Velocity: A Parametric Study on Landslide Zones in West Java-Indonesia

Assessment and management of landslide risk require the knowledge of landslide run-out distance and velocity. However, the landslide volume as the basis for calculating landslide run-out distance and velocity is governed by slip surface development during rainfall. Thus, it is necessary to understand how rainfall characteristics influence landslide run-out and velocity. This paper presents a parametric study to clarify the effect of rainfall intensity on landslide run-out and velocity of two steep volcanic cut-hillslopes in West Java, Indonesia. The landslide volumes were estimated from the potential sliding surface obtained from slope stability analysis under a rainfall infiltration. The landslide run-out and velocity were then calculated using an energy conservation formula in a lumped mass model. This study shows that the slip surface developed at a different depth in each slope, depending on the rainfall intensity. As a result, the landslide run-out and velocity of both cut-hillslope are significantly different and, in general, decrease to reach a constant value with increasing rainfall intensity. Thus, the results of this study can be used as a guideline to assess the rainfall-induced landslide movement, especially in cut-hillslopes.

A Comparison of Inverse Models for the Estimation of Ice-Induced Propeller Moments on a Polar Vessel

Full-scale measurements were conducted on the port side propulsion shaft the S.A. Agulhas II during the 2019 SCALE Spring Cruise. The measurements included the shaft torque captured at two separate measurement locations, and the shaft rotational speed at one measurement location. The ice-induced propeller moments are estimated from the full-scale shaft responses using two inverse models. The first is a published discrete lumped mass model that relies on regularization due to the inverse problem being ill-posed. This model is only able to make use of the propulsion shaft torque as inputs. The second model is new and employs modal superposition to represent the propulsion shaft as a combination of continuous modes, resulting in a well-posed problem. This new model requires the additional measurement of the shaft rotational speed for the inverse solution. The continuous model is shown to be more consistent and efficient, which allows its use in real-time monitoring of propeller moments.

Assessment of ice impact load threshold exceedance in the propulsion shaft of an ice-faring vessel via Bayesian inversion

Ice-induced impact loads on the propeller blades of vessels operating in polar waters represent a notable hazard to ship propulsion systems. Industry guidelines determine the maximum allowable ice-induced propeller moments, but these loads are not practical to measure directly. Recent studies have implemented deterministic inversion methods to determine these impact-induced moments from torque measurements on the propulsion shaft. This study considers this inversion problem from a stochastic perspective. Bayesian inversion is used, first, as a means of determining the optimal regularisation parameters, and second, as an avenue to explore the contributions to uncertainty in the inverted ice loading values due to the linear inversion model. The method is implemented for two sets of shaft-line measurements recorded on the SA Agulhas II, a polar class PC-5 research and supply vessel, via a lumped-mass model for the forward response signal. Using more sophisticated simulation results as prior information for the model uncertainty, it is shown that inverted ice-induced propeller moments around 20% below the industry guideline maximum loading of 1009.9 kN m correspond to a 1% probability of ice-induced moments exceeding this limit. This finding is significant, given the number of propeller impact events for the SA Agulhas II that approached this limit during recent voyages, and highlights the need for considering design specifications for propulsion systems in ice-faring vessels from a risk perspective.

Validation of Numerical Models of a Rotorcraft Crashworthy Seat and Subfloor

The present work explores some critical aspects of the numerical modeling of a rotorcraft seat and subfloor equipped with energy-absorbing stages, which are paramount in crash landing conditions. To limit the vast complexity of the problem, a purely vertical impact is considered as a reference scenario for an assembly made of a crashworthy helicopter seat and a subfloor section, including an anthropomorphic dummy. A preliminary lumped mass model is used to drive the design of the experimental drop test. Some additional static and dynamic tests are carried out at the coupon and sub-component levels to characterize the seat cushion, the seat pan and the honeycomb elements that were introduced in the structure as energy absorbers. The subfloor section is designed and manufactured with a simplified technique, yet representative of this structural component. Eventually, a finite element model representing the full drop test was created and, together with the original lumped mass model, finally validated against the experimental test, outlining the advantage of using both the numerical techniques for design assistance.

Dynamic Analysis of Pantograph-Catenary System considering Ice Coating

Ice coating on overhead contact system (OCS) will affect the sliding of pantograph, and arc discharge phenomena will occur between pantograph and catenary, which will threaten the normal operation of train. This paper presents a comprehensive model to analyze the dynamics of icing on pantograph-catenary (PAC) system. The finite element model (FEM) is used for building the catenary, the pantograph is modeled as lumped-mass model, and the ice section of the cable is fan-shaped. The increased density method, uniform load method, and combinatorial material method of icing are used to analyze the icing problem of PAC system. The similarities and differences between the three simulation methods are compared. The influence of the ice thickness on the current collection quality between the pantograph and catenary at the different operating speeds calculated by the three methods is basically the same, which fully illustrates the effectiveness of the simulated ice coating method. In comparison, the combinatorial material method is a more reasonable method for calculating the icing of catenary systems. The research also shows that the influence of icing on the current collection quality of PAC system is different when the train runs at different speeds. Specifically, as the speed of trains increases, the effect of ice thickness on the current collection quality of the PAC system is becoming increasingly apparent.

A modeling method for a rotor system with an active floating ring squeeze film damper

It is essential to optimize the support structures in rotating machinery to reduce the vibration, (i.e. decreasing forces transmitted to the whole dynamic system). Lots of vibration alleviation methods were applied in rotary machines, such as squeeze film dampers were used in aero-engine. In this paper, a theoretical model of an active floating squeeze film damper was studied in a vibration control field. The change of fluid stiffness and damping was allowed in the design of active floating squeeze film damper. In this model, it is assumed that an active magnetic bearing and a squeeze film damper were used, and oil film forces and magnetic forces were obtained. A lumped mass model and a finite element model were established with an active floating squeeze film damper. Explicit Newmark- β was used to solve the responses of the lumped mass model and the combination of explicit Newmark- β and implicit Newmark- β were used to calculate the responses of the finite element rotor system. The simulation shows that vibration frequencies will be shifted by adjusting the proportional gain kp, but the uncertain phenomenon can be seen in the amplitude’s reductions by adjusting the derivative gain kd as the relative changing position of rotor’s node and force acting points of active magnetic bearing for different modes, and the nonlinear strength of floating ring squeeze film damper were different in the complex rotor system. It shows that active floating squeeze film dampers can suppress rotor’s vibration effectively by varying magnetic bearing parameters.