High-efficiency Simulation Research Articles

Biaxial reinforced concrete constitutive models for implicit and explicit solvers with reduced mesh sensitivity

A new set of constitutive models named TsingHua University Concrete 2D (THUC2) is developed for use in ABAQUS. THUC2 has reduced mesh sensitivity and is based on the decoupling assumption and the fixed-angle crack assumption in order to consider the pinching effect, confinement, strength degradation, and shear softening of concrete. In the developed biaxial reinforced concrete models, the uniaxial model is first established, and the biaxial model is subsequently assembled from the uniaxial model. First, the proposed uniaxial constitutive model of concrete is reported. The mesh sensitivity of the model is reduced by adjusting the descending branch of the concrete model based on mesh size. Second, a total of five biaxial constitutive models of concrete are reported to cover a wide range of simulation requirements in engineering design. Third, the numerical implementation of the proposed concrete model in both ABAQUS implicit and explicit solvers is discussed. Subsequently, the modified two-way fixed angle crack model is validated by monotonic and hysteretic panel tests. The FE model exhibits little mesh sensitivity when the element number increased from 4 to 400. The developed model accurately predicts the pinching effect and the softening effect of the panels. Finally, previous tests on two nuclear containment vessels under lateral loads are simulated, and the modified two-way fixed angle crack model demonstrates adequate accuracy in terms of predicting the initial stiffness, ultimate capacity, and pinching effect. The proposed subroutine package for simulating RC members includes the dominant mechanical behaviors of concrete and can be adopted for high-efficiency simulation of RC shear wall structures.

High-Efficiency Simulation Framework to Analyze the Impact of Exhaust Air from COVID-19 Temporary Hospitals and its Typical Applications

The outbreak of COVID-19 resulted in severe pressure on the existing medical infrastructure in China. Several Chinese cities began to construct temporary hospitals for the centralized treatment of COVID-19 patients. The harmful exhaust air from the outlets of these hospitals may have a significant adverse impact on the fresh-air intakes and surrounding environment. Owing to the need to rapidly construct these hospitals within 6–10 days, just a few hours are allowed for the analysis of the impact of this exhaust air on the environment. To overcome this difficulty, a high-efficiency simulation framework is proposed in this study. Based on the open-source computational fluid dynamics software, FDS, the proposed framework is adaptive and incorporates building information with different levels of detail during various design phases of the hospital, and has been applied in the design of the Wuhan Huoshenshan Hospital, the first typical COVID-19 temporary hospital in China. According to the simulation results, neither the fresh-air intakes nor the surrounding buildings would be polluted by the harmful air discharged from the air outlets of the Huoshenshan hospital. The proposed simulation framework can provide a reference for the design and overall planning of similar hospitals in China and other affected countries.

High efficiency simulation of five-axis cutting force based on the symbolically solvable cutting contact boundary model

In the optimization process of five-axis cutting direction and cutter orientation, the cutter/workpiece engagement (CWE) region and cutting forces vary with different machining parameters; the prediction of CWE region is still a challenge especially for bullnose end mills. This paper presents a method to model the CWE boundaries of bullnose end cutters as a function of the five-axis parameters: the lead angle, the tilt angle, the cutting depth, and the path interval. In this method, the CWE boundaries are determined by three boundary curves: the characteristic of the envelope, the intersection of the envelop and the workpiece surface, and the projective of the previous characteristic curve in the feed direction. Based on the symbolically solvable CWE boundary model, margin height method to determine the in-cutting edge is proposed, which is validated obviously much faster than Z-map method. Using margin height method to calculate the upper and lower limits of the cutting edge, the algebraic method to predict cutting force is described and validated by five-axis machining experiment for a bullnose end cutter. The cutting force is simulated without discretizing along the cutter axis, and the calculating efficiency is improved largely comparing with the traditional method that accumulated the differential forces element by element. The symbolically solvable CWE model and margin height method-based cutting force model are very suitable for optimizing cutting direction and cutter orientation in five-axis machining.

Lateral response of cable-guided hoisting system with time-varying length: Theoretical model and dynamics simulation verification

The lateral response of the moving hoisting conveyance in cable-guided hoisting system is investigated in this paper. The equations of motion are derived by Hamilton's principle while the equivalent mass and stiffness of the guide cables are formulated. Galerkin method is employed to transform the governing equation into a set of ordinary differential equations. Subsequently, an ADAMS simulation model based on multi-degree of freedom is established to validate the theoretical model. Meanwhile, a high-efficiency simulation approach is proposed, in which the contact force is replaced with fixed joints and distance sensors. The numerical solution for equations set is obtained using Newmark- β method and the convergence of the solution is discussed, then the presented theoretical model is compared with the previous models describing the rigid rail-guided hoisting system. The results indicate that the numerical simulations are in reasonably good agreement with the ADAMS simulations and this presented model includes the previous models. The influence of parameters on the lateral response is analyzed, which reveals the maximum lateral displacement is linearly proportional to the excitation amplitude. Also, the appropriate preload can be determined by the theoretical model, which is beneficial for vibration control.

Effect of crystal orientations on nanocutting based on quasicontinuum multiscale method

Nanocutting is one of the most important ultra-precision machining methods to obtain complex optical elements with high quality finish. Molecular dynamics is widely used to investigate the nanocutting mechanism due to the nano-scale cutting depth. For high efficiency and large scale simulation, multiscale method is significantly necessary. Quasicontinuum (QC) multiscale method, using the embedded atom method (EAM), is applied to study the effect of crystal orientation on nanometric cutting of single crystal copper. The results show that the generation and emission of dislocation and the distribution of residual stress in workpiece strongly depend on the crystal orientation and cutting direction. It is recommended to fabricate a higher quality surface when the cutting direction is along on crystal orientation (111). Finally, it is proved that QC method is an efficient approach to study the nanocutting mechanism.

Neural modeling of laser surface treatments

This paper introduces a new multilayer perceptron neural model for laser surface heat treatments based on Green's function. Due to its high versatility, efficiency, and low simulation time, this model is suitable not only for the analysis and design of control systems but also for the development of an expert real time supervision system, allowing the detection and prevention of any failure during the treatment.

Adaptive neurofuzzy ANFIS modeling of laser surface treatments

This paper introduces a new ANFIS adaptive neurofuzzy inference model for laser surface heat treatments based on the Green’s function. Due to its high versatility, efficiency and low simulation time, this model is suitable not only for the analysis and design of control systems, but also for the development of an expert real time supervision system that would allow detecting and preventing any failure during the treatment.

Power system transient stability simulation based on module bi-directional iteration

A new simultaneous solution method using module bi-directional iteration is proposed for power system transient stability simulation. In this method, power network is partitioned into a tree hierarchy; computation modules are established for decomposed power networks and various power system components respectively. Through representing every computation module by a computation node, a computation tree is constructed by connecting the nodes together according to their electrical relations in power systems. A tree-traversing procedure called forward reduction and backward evaluation is performed to calculate correction factors of the variables in Newton iterations. This high-efficiency simulation method is feasible to be applied in parallel computation for large interconnected systems. Simulation tests are conducted on the New England 10-generator test power system and the North China-Northeast interconnected system, and the results are compared with those of the commercial software BPA to validate the effectiveness and correctness of this method.

General Approach to High-Efficiency Simulation of Affinity Capillary Electrophoresis

The differential equation describing electrophoretic migration can be evaluated with various finite difference schemes (FDSs). However, the accuracy and efficiency can be dramatically different depending on the FDS chosen and the way the algorithm is implemented in a computer simulation program. The monotonic transport scheme is used as the algorithm for the hyperbolic part of the differential equation, and the first-order fully explicit scheme is used for the parabolic part of the equation. The combination of these algorithms minimizes the errors and maintains high efficiency. A circular arrangement of the cells in the computer's memory is used in the implementation of the algorithms, and the use of concentration thresholds to enable and disable cells along the capillary makes the new algorithm highly efficient. Either thermodynamic or kinetic constants can be used in this program to simulate binding interactions between two species for equilibrium and nonequilibrium affinity CE. Simulation results with various parameters are presented. The simulated peak with proper parameters for an equilibrium affinity CE experiment has shape and position similar to that of the experimental peak. The simulated electropherograms for a nonequilibrium affinity CE experiment also show characteristics of the experimental electropherograms.

Monte Carlo Estimation of Generalized Unreliability in Probabilistic Dynamics—II: Handling Uncertainties in Parameters

Monte Carlo games especially designed for probabilistic dynamics problems have been shown to be very efficient for the calculation of a pressurized water reactor (PWR) pressurizer unreliability. However, these methods rely on the implicit hypothesis that transition rates and probabilities, as well as control means response times, can be precisely determined. But reality is different: Because of a lack of knowledge, only crude estimations of transition rates can be obtained. Moreover, control device response times cannot be assumed constant for rapid transients. Therefore, considering distributed values of these quantities seems more realistic. Several attempts to take into account these uncertainties, while conserving as many advantages as possible of the high-efficiency simulation techniques, are summarized. The PWR pressurizer application is used to compare the capabilities of the proposed methods.