Stress-strain behavior of two different soil specimens subjected to cyclic compressive loading are studied herein, the goal being to present a simple dynamic uniaxial mem-modeling approach that aids physical insight and enables system identification. In this paper, mem stands for memory, i.e., hysteresis. Mem-models are hysteresis models transferred from electrical engineering using physical analogies. Connected in series, a mem-dashpot and mem-spring are employed to model inter-cycle strain ratcheting and intra-cycle gradual densification of the two soil specimens. Measured time histories of stress and strain are first decomposed so that the two modeling components, mem-dashpot and mem-spring, can be identified separately. This paper focuses on the mem-dashpot, a nonlinear generalization of a linear viscous damper. A mem-spring model is also devised built on an extended Masing model. Nonlinear dynamic simulations (with inertia) employing the identified mem-dashpot and mem-spring demonstrate how well the identified mem-models reproduce the measured early-time data (first 200 cycles of loading). Choices of state variables inherited from bond graph theory, the root of mem-models, are introduced, while MATLAB time integrators (i.e., ode solvers) are used throughout this study to explore a range of contrasting damper and spring models. Stiff solver and the state event location algorithm are employed to solve the equations of motion involving piecewise-defined restoring forces (when applicable). Computational details and results are relegated to the appendices. This is the first study to use single-degree-of-freedom (SDOF) system dynamic simulations to explore the consistency of mem-models identified from real-world data.

In this paper, a novel numerical simulation approach based on the finite element method for dynamically modeling the excavation process of shield tunneling is proposed, with the shield-ground interactions well captured. This method is capable of mimicking the alternating modes of advancing and stopping of a shield boring machine during underground construction, with the important effects of the cutterhead rotation and slurry support pressure considered. Under the cutting action, the soil at the excavation face would experience irreversible deformation and damage, such that additional support needs to be provided by the cutterhead blades and slurry to maintain stability. The impacts of key construction parameters are examined, including cutterhead rotary speed, advance rate, and slurry support pressure, on shield tunneling operations and ground responses. The numerical model is rigorously validated against physical model experiments. This work provides useful insights into the mechanistic processes in the stratum during shield tunneling, including the spatiotemporal evolution of ground deformation patterns and stress redistributions. The results offer valuable guidance for optimizing shield tunneling operations and enhancing tunneling safety and efficiency.

Future human space exploration missions are planned to take humans into permanently shaded regions (PSRs) at the lunar south pole. These areas are among the coldest places in the Solar System and represent a novel operational environment for spacesuits. In addition to this technical challenge, there is scientific interest in volatiles that are cold trapped in PSRs. This paper presents results from several simulations performed to assess the effect of the thermal interactions between the lunar surface and a comparatively warm spacesuit in a permanently shadowed crater on the Moon. After the tools used to perform the simulations and their limitations are discussed, two scenarios are introduced: a crater scenario to investigate the extent and magnitude of the thermal influence of the spacesuit in realistic setting, and a flat plane scenario that is used to analyze the effect of different astronaut translation speeds on the surface temperature changes. While the results show a significant change in lunar surface temperature of up to 60 K within 1.5 m of the astronaut, the effective sink temperature for the spacesuit only changes by a few degrees Kelvin, which is not large enough to have any implications on the design of the spacesuit system. Due to the low thermal conductivity of the lunar regolith and radiation being the dominant mode of heat transfer, the surface temperature increase is only significant for very slow translation rates or periods during which the crewmember remains stationary. The absolute temperature increase can be large enough to release volatiles from their entrapment, which in turn may necessitate a spacesuit design that radiates less heat to protect science objectives. However, further research and experimentation is necessary to determine which species are most susceptible in specific surface compositions and at which temperatures.