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As a kind of space robot, the two-arm cascade combination system (TACCS) has been applied to perform auxiliary operations at different locations outside space cabins. The motion coupling relation of two arms and complex surrounding obstacles make the collision-free trajectory planning optimization of TACCS more difficult, which has become an urgent problem to be solved. For the above problem, this paper proposed collision-free and time–energy–minimum trajectory planning optimization algorithms, considering the motion coupling of two arms. In this method, the screw-based inverse kinematics (IK) model of TACCS is established to provide the basis for the motion planning in joint space by decoupling the whole IK problem into two IK sub-problems of two arms; the minimum distance calculation model is established based on the hybrid geometric enveloping way and basic distance functions, which can provide the efficient and accurate data basis for the obstacle-avoidance constraint condition of the trajectory optimization. Moreover, the single and bi-layer optimization algorithms are presented by taking motion time and energy consumption as objectives and considering obstacle-avoidance and kinematics constraints. Finally, through example cases, the results indicate that the bi-layer optimization has higher convergence efficiency under the premise of ensuring the optimization effect by separating variables and constraint terms. This work can provide theoretical and methodological support for the efficient and intelligent applications of TACCS in the space arena. [ABSTRACT FROM AUTHOR]

For complex equipment, it is easy to over-evaluate the impact of failure on production by estimating the reliability level only through failure probability. To remedy this problem, this paper proposes a statistical evaluation method based on fuzzy failure data considering the multi-state characteristics of equipment failures. In this method, the new reliability-evaluation scheme is firstly presented based on the traditional statistical analysis method using the Weibull distribution function. For this scheme, the failure-grade index is defined, and a fuzzy-evaluation method is also proposed by comprehensively considering failure severity, failure maintenance, time, and cost; this is then combined with the time between failures to characterize the failure state. Based on the fuzzy failure data, an improved adaptive-failure small-sample-expansion method is proposed based on the classical bootstrap method and the deviation judgment between distributions of the original and newborn samples. Finally, a novel reliability-evaluation model, related to the failure grade and its membership degree, is established to quantify the reliability level of equipment more realistically. Example cases for three methods of the scheme (the failure-grade fuzzy-evaluation method, the sample-expansion method, and the reliability-evaluation modeling method) are presented, respectively, to validate the effectiveness and significance of the proposed reliability-evaluation technology. [ABSTRACT FROM AUTHOR]

The energy consumption loss is high particularly in manufacturing processes involving heating furnaces. Moreover, the mandatory constraints in continuous heating stage bring difficult challenges to production scheduling. To improve the production efficiency and reduce the energy consumption in a hybrid flow shop with continuous and discrete processing stages, this study developed an adaptive selection multi-objective optimization algorithm with preference (ASMOAP). The mandatory constraints of continuous processing stage are transformed into one of the optimization objectives, which is defined as maximum excess value of adjustment time in this paper. A multi-objective optimization scheduling model with the makespan, energy consumption, and maximum excess of adjustment time is established. The optimization preference is designed in the proposed multi-objective optimization algorithm. The maximum excess of adjustment time is set as the multi-objective optimization preference. Three adaptive selection strategies are designed for the algorithm based on the proportions of outstanding and preference individuals to eliminate constraint conflicts. Presented results prove that the proposed algorithm could effectively solve hybrid flow shop scheduling problem considering discrete and continuous processing stages with limited time. It can be applied to obtain a better feasible solution while improving the efficiency and reducing the energy consumed in practical production processes. [ABSTRACT FROM AUTHOR]

High performance lightweight concrete (HPLC) characterized by low density, high strength and good durability, has prosperous application prospects in civil engineering. In this experiment, the modified Andreasen and Andersen model was used to design the initial mixture of HPLC. Shale ceramic sand (SCS) with different content was used to replace lightweight internal curing sand to prepare HPLC. The effect of different content of SCS on workability, mechanical properties and durability of HPLC were systematically investigated. In addition, this work explored the effect of SCS on the micro-morphology and pore structure of HPLC. It is found that: 1) When the replacement rate of SCS is 100%, the apparent density of HPLC is 1 848. 3 kg/m³, and its compressive strength is 123. 22 MPa. 2) The addition of SCS can improve the mechanical properties of HPLC, and the compressive strength, flexural strength and elastic modulus of HPLC increase by 8. 88% ~ 47. 92%, 22. 50% ~ 56. 30% and 3. 49% ~ 14. 03%, respectively. 3) SCS can improve the durability of HPLC. When SCS replacement rate is 100%, the chloride migration coefficient of HPLC is reduced by 32. 52%, compared to the control group. 4) Due to the addition of SCS, the microstructure of HPLC is significantly improved, and the porosity of HPLC reduces by 14. 86% ~28. 24%. [ABSTRACT FROM AUTHOR]

For enhanced energy utilization with improved flexibility and capability for object manipulation, a focused acoustic vortex (FAV) is devised by installing a spherical acoustic lens on a circular array of planar sector transducers. Based on the acoustic refraction of a concave spherical acoustic lens, numerical simulations show that an FAV with considerable pressure gain and strengthened acoustic gradient force (AGF) can be produced by the effective concentration of acoustic waves. The performance of rotational object trapping is shown by the axial and radial distributions of the AGF for FAVs of different orders. Elastic objects of nanometer, micrometer, millimeter, and even larger-than-wavelength size can be captured with the trapping radius determined by the topological charge. With the established 16-channel experimental system, FAVs of different orders are verified by their clear pressure circles and phase spirals. The trapping radius and rotation speed of object capture are demonstrated using polyethylene particles of various sizes and FAVs of different orders. The favorable results provide an experimentally applicable method of FAV generation using the simplified circular transducer array to accomplish more accurate, stable, and flexible object manipulations with strengthened AGFs. Also, FAVs could offer an efficient means of high-intensity focused ultrasound therapy to improve the therapeutic effect of tumor treatments by accumulating drug particles, thereby enabling more potential applications in clinical practice. [ABSTRACT FROM AUTHOR]

Ultra-high-performance concrete (UHPC) has attracted much attention in civil engineering. However, the high deadweight of UHPC limits its application. To reduce the density of UHPC, this study developed an ultra-high-performance lightweight concrete (UHPLC) by combining the use of shale ceramic sand and nano-materials, according to the modified Andreasen and Andersen (MAA) model. Taking advantage of nanotechnology, graphene oxide (GO) was utilized to improve the mechanical performance of UHPLC, and the effects of GO on the workability, mechanical properties, and microstructure of UHPLC were systematically investigated. It was found that: 1) UHPLC with an apparent density of 2022 ∼ 2114 kg/m³ was prepared according to the MAA model; 2) Owing to the addition of GO, the flexural strength, compressive strength, and elastic modulus of UHPLC increased by 6.3 ∼ 22.4%, 7.6 ∼ 16.7%, and 4.1 ∼ 13.0%, respectively; 3) Considering the effects of GO on the mechanical properties and microstructure of UHPLC, the optimal content of GO was 0.06%. [ABSTRACT FROM AUTHOR]