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Preplaced aggregate concrete (PAC) has up to 60 % aggregate volume content, making mesoscale modelling difficult. A novel mesoscale simulation method based on physics engine was proposed in this study to accurately simulate the coarse aggregate skeleton of PAC. Unlike in conventional mesoscale simulations, point-to-point contacts between aggregates were formed due to virtual gravity in the physics engine. To verify this novel method, mechanical property and shrinkage behavior tests of PAC were conducted under different aggregate gradings and with different expansive agents. For the mechanical property test, the simulation results were compared with the test results in terms of the aggregate stacking state, failure mode, stress–strain curve, and mechanical property parameters. Repeatability and aggregate shape analyses were performed using finite element (FE) model. A similar comparison between the simulation and test results was also performed for the shrinkage behavior. A shrinkage coefficient reflecting the relationship between grout and PAC shrinkage was proposed. This novel mesoscale simulation method based on physics engine is particularly suitable for PAC. However, it is not limited to PAC and can be applied to the simulation of conventional concrete, thus solving the problem of traditional simulation methods that struggle to achieve a high aggregate fraction.

The field synergy principle is widely used in the analyses and optimizations of convective heat transfer, but its original derivations are based on fluids with constant thermal properties. The applicability of the principle for fluids with temperature-dependent properties needs clarification. A theoretical analysis of the problem is conducted. It is found that a synergy principle of mass flux vector and specific enthalpy gradient is more fundamental. Because temperature gradients are parallel to specific enthalpy gradients, the original field synergy principle of velocity and temperature fields is still valid. Heat transfer of supercritical CO2 and molten salt in different finned channels is numerically studied, and different mean synergy angles are compared. It is found that the domain integration mean synergy angles calculated with specific enthalpy gradient or temperature gradient have the same trends. For the volume-weighted mean angles, the absolute value of dot product of velocity and temperature gradient should be used in calculating the local synergy angles. Otherwise, the trend of the volume-weighted mean angles can be contrary to the field synergy principle. Meanwhile, the accuracy of the mesh and the temperature gradient near the heat transfer surfaces is important for the numerical applications of the field synergy principle.

This paper aims to study the low-cycle fatigue property and recovery properties of viscous material. The authors designed a Self-Stabilization Dynamic Sandwich-Type Shear (S-DSTS) test device, which allows the static recovery of semisolid materials that can not be achieved in the traditional rheometer. A series of recovery tests with different static recovery times and low-cycle fatigue tests with different strain amplitudes and loading frequencies were conducted on the polyisobutylene-B12 (PIB–B12) by this device. The test data on low-cycle fatigue and recovery properties of PIB-B12 were evaluated by the storage modulus, loss modulus, loss factor, velocity exponent, parameter decay ratio, and recovery coefficient. The results show that each parameter's degradation rate and degradation degree increase significantly with the rise of strain amplitude. The low-cycle fatigue property of PIB-B12 is less affected by the loading frequency, and the degradation rate and degradation degree of all parameters are similar under different loading frequencies. The PIB-B12 has excellent recoverability and static recovery showing that the mechanical parameters of PIB-B12 could restore to more than 65% and 92% of the original magnitude after short-term and long-term intervals, which ensures a reliable energy absorption property during aftershocks. The velocity exponent of PIB-B12 shows minor variations under different strain amplitudes and loading frequencies.