Single-point incremental forming (SPIF) enables the forming of fix-clamped sheet metal by moving a relatively small geometrically simple tool along the trajectory, producing the desired shape of the ...final product. Excessive thinning of the sheet results in fracture, determining the limit of formability. This characteristic of the forming process can be improved by upgrading the basic SPIF process to two-step forming, whereby a more even distribution of the sheet thickness can be achieved by pre-bulging with a hemispherical punch. This study focused on analysing the SPIF process and a hybrid two-step forming consisting of sequential bulging and SPIF. The analysis focused on the output parameters of sheet metal thinning and maximum forming force components and was conducted with Abaqus simulation software. An innovative new approach for influence analysis of technological, material and geometrical input parameters and correlation analysis between the mentioned parameters was performed using the random forest (RF) method, which allows the determination of individual parameter influence by analysing tree-shaped models obtained through the training process. The analysis results show a significant influence of the workpiece wall angle and part depth on thinning and initial sheet thickness on values of the forming force components. The results also show a great correlation between the parameters of the bulging depth and the part depth after SPIF and the significant influence of the appropriate choice of the backing plate geometry for the target product geometry.
•Analysis of parameters of SPIF and hybrid two-step forming system.•Focusing on important technological, material, and geometrical parameters.•Forming force and sheet metal thinning predicted by finite element method.•Parameter influence and correlation analysis using random forest method.•Innovative evaluation of parameters on thinning and maximum force.
In radiant floor heating systems, the total heat transfer coefficients (THTCs) of floor surfaces represent a key parameter for design and performance calculations. A small change in the THTC exerts a ...non-negligible effect, but the THTC values or formulas given in the literatures are different. Moreover, no study has explained this phenomenon thus far. Therefore, the selection of THTC values is relatively subjective in practical engineering. In the context of promoting energy savings and realizing carbon neutrality as soon as possible, further research must investigate THTCs. On the based of the principle of heat balance, a generic calculation model of the THTCs is proposed, and its accuracy is verified with experimental data. The influence of each parameter on THTCs is analyzed and unified as the influence of temperature difference. Then, the improved formula is obtained, and its adaptability and accuracy are verified with experimental data from two studies. Results show that indoor design temperature greatly affects THTCs. The reason behind the different THTC formulas given in existing studies is also discovered. Given the same indoor design temperature, the relationships between THTCs and temperature differences caused by different parameters follow the same trend line. Only the improved THTC formula shows a good agreement with the experimental data in the literature and is even better than the recommended formula. The overall standard deviations of the proposed formulation from the experimental data in the two references decrease by 85.6% and 78.2% relative to the THTC formulation based on the EN/ISO Standards.
The improved formula of the total heat transfer coefficient (THTC) is obtained.The higher accuracy and adaptability of the improved formula is verified.The reason behind different THTC formulas given in the literature is foundA generic THTC calculation model is proposed and validated by experimental data.Indoor design temperature has great influence on the THTC value.
With the development of bridge structures towards being light weight and having a large span , the overall flexibility, and, hence, wind sensitivity, of the bridge increases. Flutter is one of the ...pivotal factors considered in the design and operation stage for long-span cable-stayed bridges due to its devastating impact, often intrigued by relatively low instability caused by wind speed. This paper presents a reliability theory-based numerical analysis on bridge flutter stability and its influence law of key parameters using a real bridge, the Xiangshan Harbor highway cable-stayed bridge in China. The analysis starts with creating a full scale of finite element model for the bridge in service to calculate the flutter derivative and time-dominated combining rational function in order to obtain the critical-flutter wind speed, and then the aerodynamic self-excited forces on the bridge and flutter time-history response are calculated to identify the flutter critical wind speed. Further, the influence of key parameters for flutter reliability, including the stiffness of the main girder, wire breaking rate, damping ratio and cable breakage location are analyzed comprehensively to achieve the change law of critical flutter wind speed with these parameters. Considering the uncertainty of the actual parameters, these parameters are taken as random variables, and the reliability index and failure probability of bridge flutter are calculated according to their probability distribution and the Latin hypercube sampling method. On this basis, a few suggestions are put forward for flutter risk-control during the service of this cable-stayed bridge, which can further enhance the design theory for long-span flexible bridges.
The PDFs (probability density functions) and probability of a ship rolling under the random parametric and forced excitations were studied by a semi-analytical method. The rolling motion equation of ...the ship in random oblique waves was established. The righting arm obtained by the numerical simulation was approximately fitted by an analytical function. The irregular waves were decomposed into two Gauss stationary random processes, and the CARMA (2, 1) model was used to fit the spectral density function of parametric and forced excitations. The stochastic energy envelope averaging method was used to solve the PDFs and the probability. The validity of the semi-analytical method was verified by the Monte Carlo method. The C11 ship was taken as an example, and the influences of the system parameters on the PDFs and probability were analyzed. The results show that the probability of ship rolling is affected by the characteristic wave height, wave length, and the heading angle. In order to provide proper advice for the ship's manoeuvring, the parametric excitations should be considered appropriately when the ship navigates in the oblique seas.
A heating system achieved by combining thermochemical energy storage and absorption heat pump is proposed and verified. Based on the experimental data, a mathematical model of the zeolite/water ...reactor is established and verified. By setting up a micro-compressor between the evaporator and absorber, the AHP is driven by low temperature source. Based on typical days in winter, the stable operation of the system is explored, and the influence of main parameters on the charging/discharging and heating processes are analyzed. The results show that the charging and heating efficiency reached 55.11% and 73.52% during the daytime. The discharging efficiency at night reaches 88.27%. The AHP can be driven by a heat source at a minimum of 75 °C, and hot water at 48.3 °C is provided. Parameters influence analysis shows that temperature is an important factor affecting the charging process, and the initial air temperature is recommended to increase. Humidity is the biggest influencing factor in the discharging process and easily changed and controlled. By replacing electric heating, the system can allow the investment to be recovered within 6.23 years. Environmental analysis shows that the proposed system has significant benefits in terms of primary energy savings and pollutant emission reduction
•A new heating system based on zeolite/water reactor was designed and evaluated•The micro-compressor reduced the absorption heat pump driving temperature to 75 °C•The reactor total charging and discharging efficiencies reached 55.11% and 88.27%•Initial air temperature and humidity were key parameters which should be focused on•The proposed system had obvious advantages in replacing electric heating
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