Additive manufacturing still suffers from redundant support material usage when printing parts with overhanging features. All the supports will be removed after fabrication, resulting in wasted ...materials. There are many works conducted for reducing support waste by improving support strategies. However, using different support strategies may lead to different printed qualities. In this paper, the effect of support strategy on printed qualities is investigated in fused deposition modelling processes. Three different support strategies are adopted for manufacturing the same 3D part. The finished surface roughness and flexural properties are compared for evaluating different support strategies, as well as the material waste and printing time. The results show that different support strategies may result in different printed surface roughness and flexural properties. To achieve the balance between support consumption and properties of printed parts, it becomes necessary to understand the effect of supports on printed qualities for choosing a best support strategy.
The RIME optimization algorithm (RIME) represents an advanced optimization technique. However, it suffers from issues such as slow convergence speed and susceptibility to falling into local optima. ...In response to these shortcomings, we propose a multi-strategy enhanced version known as the multi-strategy improved RIME optimization algorithm (MIRIME). Firstly, the Tent chaotic map is utilized to initialize the population, laying the groundwork for global optimization. Secondly, we introduce an adaptive update strategy based on leadership and the dynamic centroid, facilitating the swarm's exploitation in a more favorable direction. To address the problem of population scarcity in later iterations, the lens imaging opposition-based learning control strategy is introduced to enhance population diversity and ensure convergence accuracy. The proposed centroid boundary control strategy not only limits the search boundaries of individuals but also effectively enhances the algorithm's search focus and efficiency. Finally, to demonstrate the performance of MIRIME, we employ CEC 2017 and CEC 2022 test suites to compare it with 11 popular algorithms across different dimensions, verifying its effectiveness. Additionally, to assess the method's practical feasibility, we apply MIRIME to solve the three-dimensional path planning problem for unmanned surface vehicles. Experimental results indicate that MIRIME outperforms other competing algorithms in terms of solution quality and stability, highlighting its superior application potential.
Near-field acoustic holography (NAH) based on compressing sensing (CS) theory enables accurate reconstruction of sound fields using a limited number of sampling points. However, the successful ...implementation of this technique depends on two crucial factors: (1) the appropriate selection or construction of the spatial basis and (2) an effective sparse regularization process. To enhance reconstruction performance for elongated sound sources, this paper proposes a novel sound field reconstruction method that combines prolate spheroidal wave functions (PSWFs) with the orthogonal matching pursuit (OMP) algorithm. In this method, PSWFs serve as a sparse spatial basis for representing the radiated sound field. The sparse coefficients are determined by the OMP algorithm in a linear subspace composed of basic functions that best match the residual error. The OMP algorithm effectively identifies significant components before potentially selecting incorrect ones by setting an appropriate stopping rule. Numerical simulations are conducted using a line-array source model. The results show that the proposed method can accurately reconstruct the sound pressures of the elongated source model using a relatively small number of samplings. In addition, the proposed method exhibits robustness across a wide frequency range, diverse array configurations and various sampling numbers. The experimental results further validate the feasibility and reliability of the proposed method.
Mechanical performance analysis and experimental study of the mechanics of the four-star-type crank-linkage mechanism of the marine air compressor were carried out to improve the submerged floating ...performance and stealth performance of the underwater vehicle and to meet the demand of its large diving depth. Firstly, we analyzed the forces on the four-star-type crank-linkage mechanism, derived the inertia forces and moments of the crank-linkage mechanism, and proved the advantages of the four-star-type crank-linkage mechanism in balancing the second-order reciprocating inertia forces. The static strength of some parts was calibrated, and the modal analysis of the four-star-type crank-linkage mechanism was carried out. Second, a flexible crankshaft dynamics model was established to study the influence of kinematic pair parameters on the excitation characteristics of the main bearing. The mechanical performance analysis of the mechanics of the four-star-type crank-linkage with clearance was carried out. Finally, a test bench of four-star-type crank-linkage mechanism was designed and built independently to analyze the effects of clearance size and rotational speed on the acceleration of the motion and vibration acceleration of the slider. The results show that the first-order reciprocating inertia force and second-order reciprocating moment of inertia mainly exist in the four-star-type crank-linkage mechanism. The friction force of the revolving pair can suppress part of the resonance peak, but it will broaden the excitation band and excite high-frequency vibration. The larger the clearance of the four-star-type crank-linkage mechanism kinematic pair, the higher the crankshaft speed, the larger the acceleration amplitude, and the more concentrated the phase trajectory. The research results of this paper can guide the low-noise design of other types of air compressors, help to improve the overall level of marine air compressors, and show future directions for the vibration control of four-star-type air compressors.
The nonlinear energy sink (NES) is an effective method to weaken or eliminate the line spectra feature of ship machinery equipment. However, due to the strong nonlinearity of the NES, there are ...multistable attractors in the NES vibration absorption system. Moreover, when the excitation characteristics or working conditions of the mechanical equipment change, the NES may migrate from the small-amplitude motion state to the large-amplitude motion state, resulting in a high-amplitude solitary branch response and thereby lowering its vibration absorption efficiency. In this study, the small-amplitude control of the NES nonlinear vibration absorption system has been studied by using the open-loop-plus-nonlinear-closed-loop (OLPNCL) method. First, the dynamic equation of the NES nonlinear vibration-absorbing system was formulated, and its global behavior was analyzed. The regulations of global features and coexisting attractors were found out. Second, the migration between different attractors was carried out under the OLPNCL control, which can ensure that the system always works at the lowest line spectrum intensity and the best overall vibration absorption performance. Finally, the simulation results verify the feasibility and effectiveness of the OLPNCL method and achieve effective vibration absorption in the low-frequency range and line spectrum control under variable operating conditions.
Near-field acoustic holography (NAH) is an effective tool for realizing accurate sound field reconstruction in three-dimensional space on the prerequisite that appropriate elementary wave functions ...are selected or constructed to match the characteristics of the sound sources. However, for elongated sources, common wave functions, i.e., plane, cylindrical, or spherical waves, sometimes do not perform well during the sound field projections. To solve this problem, statistically optimized near-field acoustical holography combined with prolate spheroidal wave functions is proposed. In the approach, the sound field is expanded by a series of prolate spheroidal wave functions, whose wavefronts can be set nearly conformal to the elongated sources. Based on these wave functions, fewer expansion terms are required to model the sound field, and the need for regularization can be reduced during the inverse solving process. Therefore, the accuracy of the reconstruction results can be further improved. Numerical simulations are conducted by two types of elongated source models, namely, spatially separated and extended. The results show that the proposed method can effectively reconstruct the sound pressures of elongated sources and perform robustly across a wide frequency range. Simultaneously, a designed experiment is carried out in an anechoic chamber, which demonstrates the feasibility of the proposed method.
By the finite element method, the structural vibration response is calculated under the action of the axial exciting force and the moment with different distribution form, and then the transfer ...function of the mean square normal velocity is analyzed. The wavenumber spectrum analysis method is used to separate and quantify the shell vibration in the wavenumber domain, and then the relation between the structural vibration characteristics and the structural wavelength is summarized. It is concluded that the structural vibration and radiated noise can be reduced under the symmetric action of axial exciting force and the moment. Based on the above conclusion, a symmetrical thrust bearing supporting system is designed and the stiffness of the supporting structure in the axial direction is controlled by selecting suitable size of structural members, therefore, the structural vibration and radiated noise of the submarine is reduced significantly.
Unbalanced inertia force is inevitably generated during the operation of crank linkage. It is one of the main excitation sources of air compressor vibration and the focus of managing air compressor ...vibration noise. In this regard, this paper studies the variation law of inertia force in the four-star type crank linkage mechanism. Certain balancing methods are used to reduce the unbalanced inertia force. Firstly, we present a comparison of perfect and partial balanced problems of crank linkage inertia forces. Then, using the ADAMS software multibody dynamics calculation method, the balancing mass is numerically calculated to optimize the design of the balancing mass for partial balancing of inertia force. Next, the influence law of piston mass asymmetry on the force of crankshaft revolving pair is studied. Lastly, two new types of four-star type crank linkage mechanism are proposed from the viewpoint of completely balanced inertia forces and moments of inertia. The results show that the perfectly balanced inertia force is better than the partially balanced inertia force in terms of a balancing effect. The parametric design of ADAMS software is more efficient and can get the best quality quickly. The design of perfectly balanced inertia force will increase the length and complexity of the crankshaft, while reducing the structural strength. The research results of this paper are important for improving the vibration damping performance of marine air compressors.
New energy materials refer to the key materials used in the transformation and utilization of new energy and the development of new energy technologies. The soft magnetic has high saturation magnetic ...induction intensity, good high-frequency magnetic properties, low loss and low cost, and is widely used. In this paper, according to the high magnetic properties of soft magnetic materials, the static and dynamic performance of the electromagnetic actuator under the new magnetic steel structure is studied. Based on the finite element method, the AC / DC module in COMSOL is used to study and simulate the performance of electromagnetic actuator. The relationship between electromagnetic actuator output and current and frequency under steady state is studied, and the influence of surface skin effect is simulated. The static linearity of electromagnetic actuator is observed by simulation in time domain; Simulation analysis of linearity in steady state. The relationship between the output of the actuator and the current and frequency is obtained by the simulated two-dimensional line diagram, and the distribution of the skin effect inside the electromagnetic actuator is obtained by the surface diagram. The static working simulation in time domain obtains the static linearity, and the simulation in steady state obtains the linearity in working state. The output performance of the electromagnetic actuator under the new magnetic steel structure is improved, with an increase rate of 47.3%, and its skin effect is evenly distributed. The static linearity increases by 63% and the dynamic linearity increases on average. According to the results of the research and simulation, it has a theoretical reference value for the promotion and application of magnetic energy, as well as the use of electromagnetic actuators for motor structure optimization and efficient matching.
In order to get a better description to the nonlinear characteristics of magnetorheological dampers, the magic formula is introduced into the general method of parametric modelling of ...magnetorheological dampers to propose a new parameterized model called magic formula-hysteresis loop model (MFM). The new model is simple in structure, the physical meaning of each parameter is clear, and the parameter identification is convenient. The fitting and experimental data of MFM and the phenomenon model under different conditions are applied for error analysis and comparison. The results show that the errors of MFM are more accurate and have better fitting and experimental data under different working conditions, which also have better adaptability and versatility.
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