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Nonlinear dynamic modeling and vibration analysis for flexible tethered satellite systems under large deformations

The escalating threat posed by space debris necessitates innovative approaches for its removal. This article presents a comprehensive mathematical modeling and dynamic analysis of a flexible tethered satellite system (FTSS) in the post-capture phase, taking into account nonlinear strain effects for the flexible appendages. The FTSS consists of a rigid central body satellite, two identical flexible panels, and a towing mass that manipulates the satellite through a tether. We develop a detailed dynamic model that accurately represents the system’s three-dimensional motion, incorporating the rigid body’s 6 degrees of freedom (DOF), the tether’s 3 DOF motion, and two modal generalized coordinates for each panel. The extended Hamilton method is employed to derive this model, enabling us to investigate the conditions under which nonlinear strain considerations become critical. The findings of this article reveal that nonlinear strain effects can profoundly impact the system’s dynamics under certain geometric and forcing conditions, often overlooked in previous studies. In these scenarios, the panel strains exceed the linear regime, necessitating the use of nonlinear models for accurate representation. This work emphasizes the importance of incorporating nonlinear strain terms in the dynamic analysis of FTSSs, particularly when dealing with large deformations and high-amplitude vibrations encountered in debris removal applications.

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Approximate modeling of cross-beam multi-axis force/moment sensor through Gaussian process and partial dependence plots for design optimization including stress topology

This study introduces a novel approximate model (AM) aimed at optimizing the design of cross-beam multi-axis force/moment sensor. It considers the characteristics of flexure hinges in elastic beams and the flexibility of beam joints, resulting in improved accuracy and broader solutions for equivalent stresses and natural frequencies compared to existing approximate models in the literature. Model validation is carried out by comparing the results with the finite element model in different cases that each case contains 1000 simulations. Validation cases combine different sensor dimensions with different forces, moments, material properties, and center hub shapes. Each validation case typically requires approximately 19 h using the finite element method (FEM) and just 1 sec with the AM. Furthermore, by using the Gaussian process and partial dependence plots, the sensitivity of the model accuracy on normalized sensor dimensions is investigated. The evaluation of model linearity and dimension normalization allows for the utilization of the novel approximate model beyond the provided dimension range, while still adhering to the normalized parameters. The implementation of AM in the design optimization problem demonstrates its suitability and advantages compared to existing literature and FEM results. When compared to finite element solutions within the sensor workspace, the approximate model exhibits a stiffness error of 5%, a strain error of 2%, a fundamental frequency error of 3%, and an equivalent stress error of 8%, while maintaining correlations of axial sensor properties above 98%.

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Vibration damping by enhancing of magneto-rheological damper performance using novel smart fluid

The objective of the present work is to improve the speed and vibration characteristics of tracked vehicles via a semi-active suspension system that uses a Magneto-Rheological (MR) damper. MR damper is designed, manufactured, and tested with different harmonic excitations. The MR damper reliability under high-frequency stresses is considered in the mechanical design phase as well as the configurations and dimensions of the damper. Two fluid samples DELTA and GAMA are prepared, which differ in carrier fluid dynamic viscosities to have different rheological properties and tested to determine the dynamic characteristics of the damper. The damper’s ability to isolate vibration is measured by MTS. The investigation performed not only clarifies MR fluid characteristics but also proves the fact that the fluid is non-Newtonian with good rheological properties. One of the two fluid samples called DELTA is found to have the required properties. The MR damper filled with this DELTA shows a significant increase in damping force according to the excitation current and is much higher than the conventional passive suspension damping force. The proposed damper can cope with the increase in both magnitude and frequency of the input, which represents the speed of the truck and roughness of the road. Upgrading the suspension system of the vehicle from a passive damper to a manufactured semi-active MR damper with MR fluid DELTA can increase the damping force that the passive damper produces by 207% in compression stroke and 136.2% in rebound stroke at the same testing conditions.

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Trajectory design based on frictional resistance of deflector in a hydraulic radial drilling system

The trajectory design is a key factor affecting the frictional resistance of the deflector, which is crucial for the drilling ability of the hydraulic radial drilling system. In this research, the trajectory design model and geometric constraints model of a deflector are established by analyzing the geometric relationship of the deflector and considering the geometric constraints of the casing. According to the actual contact form between the high-pressure hose and the deflector, the theoretical model of frictional resistance is built based on segmental rigidization and micro-element methods. The theoretical model is verified by the deflector friction experiment. The results demonstrate a good agreement between the experimental results of friction resistance of different sizes of high-pressure hoses and the theoretical results, with an error of less than 7%. The influence of critical parameters of deflector trajectory on the friction resistance is studied by coupling the geometric constraints model and the frictional resistance theoretical model of the deflector. The findings show that the deflector’s frictional resistance increases with the inclination angle β of the inclined-straight section and decreases with the increase in the radius R of the bending segment, the inclination angle ω of the straightening segment, and the channel radius of r deflector. A new trajectory parameters of the deflector are presented by taking a five-inch casing as an example, they are β = 9°, R = 92 mm, ω = 108°, r = 17 mm. The research results provide a theoretical rationale for designing a low-frictional resistance deflector.

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Buckle propagation failure of subsea pipelines; experimental, analytical, and numerical simulations

This research program investigates buckle propagation in subsea pipeline systems, The study aims to understand and predict propagation pressure (PP ), essential for ensuring the structural integrity and safe operation of these pipelines, hypothesizing that incorporating strain hardening effects into the strain energy approach can significantly enhance the prediction of propagation pressure (PP ) and that geometric parameters, particularly the diameter-to-thickness (D/t) ratio, play a major role in PP prediction. Accurate PP prediction is essential for ensuring the structural integrity and safe operation of these pipelines. The investigation is conducted through analytical, experimental, numerical, and machine learning approaches. A new analytical solution for PP is proposed, incorporating strain hardening effects using a strain energy approach. Experimental tests conducted using a hyperbaric chamber cover a wide range of pipeline configurations and materials, including steel, aluminum, and stainless steel. Complementing experimental data, numerical simulations using finite element methods facilitate parametric dependence analysis and the visualization of results through 3D charts. More than 600 FE models were simulated to investigate the influence of geometric and material parameters on PP . The findings from both experimental and numerical analyses indicated that the geometric and material properties have a significant impact on PP , specifically, the diameter-to-thickness (D/t) ratio, yield stress (σy ), and tangent modulus (E′). Furthermore, Machine Learning (ML) techniques have been used to predict the PP value and have concluded that the Random Forest (RF) technique outperformed the K-Nearest Neighbors (KNN), and Multi-layer Perceptron (MLP) neural network techniques. Overall, this study concludes that analytical, numerical, and machine learning approaches offer valuable insights into buckle propagation in subsea pipelines, contributing to improved safety and reliability in offshore oil and gas operations.

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Improving the natural frequency of the CubeSat structure using voxel-based topology optimization method with the four-connected seed filling

The dynamical analysis and optimization pose significant challenges in spacecraft structural design, as they are crucial for mitigating vibrations. However, artificial localized modes can arise due to imprecise finite elemental models, impeding dynamical optimization. This paper proposes a voxel-based topology optimization method with a four-connected seed filling strategy to address this issue. By selecting a seed element and connecting it with the entire structure using four-connected relations, artificial localized modes can be suppressed effectively. Unlike traditional mesh-based methods, this approach saves time and eliminates the need for manual handling of the initial model. To demonstrate the effectiveness of the proposed method, a 6-U CubeSat was chosen as an optimization example. To reduce design errors stemming from calculation inaccuracies, spatial symmetry constraints were employed. Through simulations and vibration tests, it was observed that the first five-order natural frequencies of the optimized structure exceeded those of the original structure. This outcome decreases the likelihood of resonance occurrence and enhances the safety of the electromechanical system. Overall, this research presents a practical and efficient solution for addressing dynamical optimization challenges in spacecraft structural design, thereby improving vibration reduction efforts and safeguarding the integrity of the system.

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