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The wake-induced vibration (WIV) presents significant challenges to the structural integrity of multi-cylinder configurations. To effectively alleviate this problem, a numerical simulation is conducted to assess the effect of an active control technique that uses two jets located at the shoulder region of a cylinder to suppress WIV in two-degree-of-freedom. The equations of motion for the WIV response are solved using the Newmark-β method. The Newmark-β method is employed to solve the equations of motion governing the WIV response. Three kinds of angular position (β) on WIV suppression are investigated in detail, including 30°, 60°, and 90°. The angular position β is defined as the angle between the injection angle and the horizontal line. When the angular position (β) is 30°, the maximum cross-flow amplitude ratio (CFAR) is reduced from 0.9 (uncontrolled) to 0.5 (β = 30°), a reduction of approximately 44%. On the contrary, the maximum CFARs remain approximately 1.0 for the case 3 (β = 60°) and case 4 (β = 90°). Especially for the case 4, the cylinder showed the galloping response after the upper branch region. Since the jets are positioned on the vibration cylinder shoulders, the vortexes caused by the jets are opposite to the main vortexes induced by the cylinder. As a consequence, the jets shred the main vortexes in the wake of the cylinder, which leads to the driving force of the vibration reduction. Therefore, the cylinder's WIV amplitude is significantly suppressed. [ABSTRACT FROM AUTHOR]

The vortex-induced vibration (VIV) response of a 2-degree-of-freedom cylinder with random grooves is investigated numerically based on the Reynolds Average Navier–Stokes (RANS) method. The Newmark-β method is used to solve the equations of motion of the cylinder. The effects of the random groove on VIV suppression are discussed in detail. The coverage ratios (k) of the random groove include 0%, 25%, 50%, 75%, and 100%. The vibration suppression effect of k = 75% and k = 100% is not significant. However, the VIV amplitude of the cylinders with k = 25% is greatly suppressed. In particular, the cross-flow amplitude ratio is reduced from 1.50 (k = 0%, a smooth cylinder) to 0.65 (k = 25%). First, the boundary-layer separation point of the grooves is fixed, so the random grooves destroy the normal separation and development of the main vortices. Therefore, two rows of vortices with different sizes are generated on both sides of the cylinder, which may cause unstable vibration. Meanwhile, a series of small vortices are formed in the grooves. These small vortices cannot merge synchronously into the main vortices and further reduced the strength of the main vortices. Consequently, the driving force of the vibration, which is generated by the main vortices, is reduced. As a result, the VIV responses are suppressed. [ABSTRACT FROM AUTHOR]

To efficiently implement space debris removal missions on geostationary Earth orbit (GEO), a scheduling optimization scheme of multiple hybrid-propulsive servicing spacecraft (SSc) is proposed. In this scheme, a many-to-many task allocation coding model is established to formulate the removal sequences of debris targets with respect to different SSc. And a hybrid-propulsive orbit transfer strategy is developed to implement the debris removal maneuvers to save the propellant consumption and removal time simultaneously via using both electric and chemical propulsion systems. Then, the multiple GEO space debris removal scheduling optimization problem is formulated to minimize the total propellant consumption by exploring the optimal removal sequences and orbit maneuver parameters, subject to the available velocity increment, removal time, and many-to-many task allocation constraints. To effectively solve the scheduling optimization problem involving discrete-continuous mixed variables, a clustering based adaptive differential evolution algorithm with potential individual reservation (CADE-PIR) is proposed. In CADE-PIR, the k-means clustering method and potential individual reservation mutation strategy are employed to promote the convergence rate and performance of exploration and exploitation. In the end, a real-world GEO space debris removal mission with multiple SSc is investigated to demonstrate the effectiveness and practicality of the proposed optimization scheme. [ABSTRACT FROM AUTHOR]

To effectively optimize low-thrust many-revolution transfer trajectories to geostationary Earth orbit (GEO), this article proposes a novel metamodel-based low-thrust GEO transfer optimization scheme. A simplified control law is used to convert the optimal low-thrust transfer problem into a parameter optimization problem, where the gains of control law are optimized to determine the time-minimum trajectories. An adaptive kriging-assisted two-stage optimization framework is developed to solve the optimization problem. In the first stage, the kriging metamodels are constructed to replace the expensive transfer model for optimization. The kriging metamodels are gradually refined via a probability of constrained improvement-based infill sampling process to efficiently determine an initial guess of the gains. In the second stage, a sequential quadratic programming-based local search is conducted to precisely compute the gains. Finally, two engineering examples are investigated to demonstrate the effectiveness of the proposed optimization scheme for solving real-world low-thrust GEO transfer optimization problems. [ABSTRACT FROM AUTHOR]