Xu Hao, Lang Wei, Yue Qiao, Shengzui Xu, Jian Bin Liao, Yu Xi, Wang Wei and Zhi-Wei Liu
The computing power of the legged robot is not enough to perform high-frequency updates for the full-body model predictive control (MPC) of the robot, which is a common problem…
Abstract
Purpose
The computing power of the legged robot is not enough to perform high-frequency updates for the full-body model predictive control (MPC) of the robot, which is a common problem encountered in the gait research of the legged robot. The purpose of this paper is to propose a high-frequency MPC control method for the bounding gait of a parallel quadruped robot.
Design/methodology/approach
According to the bounding gait characteristics of the robot, the quadruped robot model is simplified to an equivalent plane bipedal model. Under the biped robot model, the forces between the robot’s feet and the ground are calculated by MPC. Then, the authors apply a proportional differential controller to distribute these forces to the four feet of the quadruped robot. The robot video can be seen at www.bilibili.com/video/BV1je4y1S7Rn.
Findings
To verify the feasibility of the controller, a prototype was made, and the controller was deployed on the actual prototype and then fully analyzed through experiments. Experiments show that the update frequency of MPC could be stabilized at 500 Hz while the robot was running in the bounding gait stably and efficiently.
Originality/value
This paper proposes a high-frequency MPC controller under the simplified model, which has a higher working efficiency and more stable control performance.
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Keywords
Guang-Zhi Zeng, Zhi-Wei Li, Sha Huang and Zheng-Wei Chen
Based on the aerodynamic loads and dynamic performances of trains, this study aims to investigate the effect of crosswinds and raindrops on intercity trains operating on viaducts…
Abstract
Purpose
Based on the aerodynamic loads and dynamic performances of trains, this study aims to investigate the effect of crosswinds and raindrops on intercity trains operating on viaducts to ensure the safe operation of intercity railways in metropolitan areas.
Design/methodology/approach
An approach coupled with the Euler multiphase model as well as the standard k-ɛ turbulence model is used to investigate the coupled flow feature surrounding trains and viaducts, including airflow and raindrops, and the numerical results are validated with those of the wind tunnel test. Additionally, the train’s dynamic response and the operating safety region in different crosswind speeds and rainfall is investigated based on train’s aerodynamic loads and the train wheel–rail dynamics simulation.
Findings
The aerodynamic loads of trains at varying running speeds exhibit an increasing trend as the increase of wind speed and rainfall intensity. The motion of raindrop particles demonstrates a significant similarity with the airflow in wind and rain environments, as a result of the dominance of airflow and the supplementary impacts of droplets. As the train’s operating speed ranged between 120 and 200 km/h and within a rainfall range of 20–100 mm/h, the safe operating region of trains decreased by 0.56%–7.03%, compared with the no-rain condition (0 mm/h).
Originality/value
The impact of crosswind speeds and rainfall on the train’s aerodynamic safety is studied, including the flow feature of crosswind and different particle-sized raindrops around the train and viaduct, aerodynamic loads coefficients suffered by the intercity train as well as the operating safety region of intercity trains on the viaduct.
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Zhenrong Zheng, Wei Zhi, Kezhu Mao, Qian Zhang and Lijuan Luo
The purpose of this paper is to study the ablative behavior of the silicone resin-coated carbon fabric (coated fabric) that will swell significantly during ablation.
Abstract
Purpose
The purpose of this paper is to study the ablative behavior of the silicone resin-coated carbon fabric (coated fabric) that will swell significantly during ablation.
Design/methodology/approach
The ablation experiments of three coated fabrics were conducted by quartz lamp radiant. Based on the experimental analysis, a numerical model was proposed for the coated fabrics to study the ablative process in term of the energy balance, mass conservation and thermal decomposition equations.
Findings
Results showed that the average relative errors between the simulated temperatures and experimental values of back surfaces of coated fabric 1, 2 and 3 were 10.01, 7.53 and 7.32%, respectively. The average density of silicone resin of coated fabric 1 was reduced by 47.96%, and the closer the distance from the heated surface was, the more the density decreased. The thermal conductivity and specific heat capacity of silicone resin of coated fabric 1 increased with time. Before 50 s, each decomposition rate curve showed an inflection point, at which the silicone resin decomposed most intensely.
Research limitations/implications
Based on experimental observations, the ablative behavior of the material with fixed expansion layer was simulated. In the further research, the moving expansion layer could be considered.
Originality/value
This paper provides the theoretical basis to evaluate the effectiveness of thermal protection materials that will swell during ablation.
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Wei-Zhi Ang, Suresh Narayanan and Meenchee Hong
Food wastage is a major contributor to pervasive world hunger. Cutting global food waste in half by 2030 is one of the United Nation's top priorities. Hence, this paper aims to…
Abstract
Purpose
Food wastage is a major contributor to pervasive world hunger. Cutting global food waste in half by 2030 is one of the United Nation's top priorities. Hence, this paper aims to provide useful insights on how individual behavior might be influenced to help reduce food wastage and hunger by identifying individual food waste determinants.
Design/methodology/approach
A total of 297 useable responses were obtained from a survey using a food diary method. A logit model was employed to estimate the relationship between leftovers and its determinants (preparedness to take own action, price conscious, food review, religiosity, health conscious, cost, marital status and gender).
Findings
Results show that preparedness to be responsible for one's actions, depending on food reviews and being waste conscious had a significant positive relationship with food waste reducing behavior, along with being male and being married.
Research limitations/implications
The study suggests that there is scope for policy initiatives to reduce the individual utility from discarding food and increase the individual utility from food saving activities. Penalizing individual or household food wastage through a tax will directly raise the cost of wastage and reduce the net utility from discarding food. Reducing food waste could help reduce global hunger.
Originality/value
Rationally, no one will have any intention to waste when buying food. Instead, in the context of deciding whether or not to leave leftover food, an individual is posited to weigh the potential utility from saving food or throwing it away. Thus, this study examines food waste behavior by utilizing economic tools, which is rare in the food waste literature.
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Min Lu, Zixuan Yang and Guowei He
This paper aims to propose a new method for robust simulations of passive heat transfer in two-fluid flows with high volumetric heat capacity contrasts.
Abstract
Purpose
This paper aims to propose a new method for robust simulations of passive heat transfer in two-fluid flows with high volumetric heat capacity contrasts.
Design/methodology/approach
This paper implements a prediction–correction scheme to evolve the volumetric heat capacity. In the prediction substep, the volumetric heat capacity is evolved together with the temperature. The bounded downwind version of compressive interface capturing scheme for arbitrary meshes and central difference scheme are used for the spatial discretization of the advection and diffusion terms of the heat transfer equation, respectively. In the correction substep, the volumetric heat capacity is updated in accordance with the interface captured by using a coupled level-set and volume-of-fluid method to capture the interface dynamics precisely.
Findings
The proposed method is verified by simulating the advection of a hot droplet with high volumetric heat capacity, a stationary air–water tank with temperature variation between top and bottom walls and heat transfer during wave plunging at
Originality/value
To ensure the numerical stability, this paper solves an additional conservative form of volumetric heat capacity equation along with the conservative form of temperature equation by using consistent spatial-discretization and temporal-integration schemes.