Absorbing–generating seaward boundary conditions for fully-coupled hydro-morphodynamical solvers

This paper presents a new technique to compute open boundary conditions for fully-coupled hydro-morphodynamical numerical solvers based on the Non-Linear Shallow Water and the Exner equations. These conditions allow the generation of incident signals and the absorption of reflected ones, taking into account the bed evolution at the boundary. They use the approximations for linear waves in shallow water and are based on the solution of the Riemann Equations. The proposed technique is implemented in the fully-coupled hydro-morphodynamical numerical model of Briganti et al. (2012a). Firstly, the generation and absorption of single monochromatic waves are studied to quantify the error after the reflected wave exited the domain. In all cases the error is always small, giving evidence of the effectiveness of the new seaward boundary conditions. Furthermore, the propagation and reflection of a monochromatic wave train over a mobile bed are considered. Both flow evolution and bed change are not affected by spurious oscillations when long sequences of waves are tested. Additionally, a very low mobility bed is considered to simulate a ‘virtually fixed’ bed and new boundary condition results consistently converge to those for the hydrodynamic only case. Finally, the reflection of a uniform bore over a mobile bed is studied. For this case the Rankine–Hugoniot conditions provide an analytical solution. It is apparent that the adopted linear approximations produce errors in the velocity estimates. Nevertheless, the conditions perform reasonably well even in this demanding non-linear case

Preliminary analysis for lunar roving vehicle study, ground data systems and operations. Volume 2 - Roving vehicle payload /Science mode time line analyses/

Stationary science time line analyses for roving vehicle payloa

Thermally actuated valves Final report, 15 Dec. 1969 - 15 Jul. 1970

Study, design, fabrication, and evaluation of thermally actuated valves for spacecraft instrumentation requiring small zero leakag

Propagating discontinuities in ionized porous media

Ionized porous media swell or shrink under changing osmotic conditions. Examples of such materials are shales, clays, hydrogels and tissues. The materials are represented as a multi-phase material consisting of a solid part and a fluid part with fixed charges embedded in the solid matrix and counter charges in the fluid. The presence of the so-called fixed charges causes an osmotic pressure difference between the material and surrounding fluid and with that prestressing of the material. The response of the material to load is dependent on the presence of the fluid, charges and cracks. Understanding the mechanisms for fracture and failure of these materials are important for the oil industry (such as hydraulic fracturing and borehole instability), material development (diapers, orthopaedic prosthesis and seals) and in medicine (intervertebral disc herniation and tissue engineering). The relation between presence of cracks and fluid flow has had little attention, but the relation between failure and osmotic conditions has had even less attention. The aim has therefore been to study with the Finite Element Method the effect of osmotic conditions on propagating discontinuities under different types of loads for osmoelastic saturated porous media. The work covers three parts. The first part is an analytical solution of a dislocation in a swelling medium, the second is the partition of unity modeling of a mode-II crack in a swelling medium and the third is the partition of unity modeling of a mode-I crack in a swelling medium. The analytical solution for a dislocation is used as a benchmark to verify the partition of unity modeling in the simplified situation of a non-propagating dislocation. The method through which fluid flow around the crack is modeled is essentially different for mode-I compared to mode-II. In mode-I, the pressure is assumed continuous in the crack area, while in mode-II the pressure is assumed discontinuous across the crack. The numerical results show that in mode-II, the crack propagation is reasonably mesh-independent. In mode-I the crack path is mesh independent, but the induced fluid flow and speed of propagation is not mesh-independent for low stiffness, low permeability cases. The reason for the mesh dependence is probably the insufficient capture of high gradients in the crack area, which require a very fine mesh around the crack. Step-wise crack propagation through the medium is seen. This is because the propagation of the crack alternates with pauses in which the crack-tip area consolidates. The consolidation results in a progressive transfer of the load from the fluid to the solid. As the load on the solid increases, the failure load is reached and the crack propagates again. This step-wise propagation is observed both for mode-II as for mode-I. Furthermore, propagation is shown to depend on the osmotic prestressing of the medium. The dependence is present for mode-II and mode-I. In mode-II the prestressing has an influence on the angle of growth. In mode-I, the prestressing is found to enhance crack propagation or protect against failure depending on the load and material properties. It is also found that osmotic prestressing in itself can propagate fractures without external mechanical load. This mechanism may be an explanation for the tears observed in intervertebral discs as degeneration progresses

Synchronization of spatiotemporal patterns and modeling disease spreading using excitable media

Studies of the photosensitive Belousov-Zhabotinsky (BZ) reaction are reviewed and the essential features of excitable media are described. The synchronization of two distributed Belousov-Zhabotinsky systems is experimentally and theoretically investigated. Symmetric local coupling of the systems is made possible with the use of a video camera-projector scheme. The spatial disorder of the coupled systems, with random initial configurations of spirals, gradually decreases until a final state is attained, which corresponds to a synchronized state with a single spiral in each system. The experimental observations are compared with numerical simulations of two identical Oregonator models with symmetric local coupling, and a systematic study reveals generalized synchronization of spiral waves. Modeling studies on disease spreading have been reviewed. The excitable medium of the photosensitive BZ reaction is used to model disease spreading, with static networks, dynamic networks, and a domain model. The spatiotemporal dynamics of disease spreading in these complex networks with diffusive and non-diffusive connections is characterized. The experimental and numerical studies reveal that disease spreading in these model systems is highly dependent on the non-diffusive connections

Electroactive nanoarrays for the biospecific-ligand mediated study of single cell adhesion and polarization

Cell adhesion, polarization, and migration are vital to numerous biological phenomena. Therefore, a greater understanding of the mechanisms of these processes will have broad impacts in fields ranging from developmental biology to medicine. This work has focused on developing a nanoscale model system that will allow one to study the effect of the spatial presentation of immobilized ligands on the nanoarchitecture of adherent cells. In Chapter 2, the development of electroactive nanoarrays of hydroquinone-terminated alkanethiol, produced by dip-pen nanolithography (DPN) is described. These nanoarrays, in conjunction with an oxime-chemistry based chemoselective immobilization strategy and high-resolution fluorescence microscopy, were used to study biospecific-ligand mediated single cell adhesion. The difference in ligand affinity of linear and cyclic Arg-Gly-Asp (RGD) was shown to have a dramatic affect on the intracellular nanoarchitecture of adherent fibroblasts. The production of asymmetric nanoarrays used to study single cell polarization is described in Chapter 3. Asymmetric nanoarrays presenting linear RGD were found to induce net directional cell polarization in adherent fibroblasts, while linear RGD-presenting symmetric nanoarrays did not induce net polarity. This demonstrates a direct correlation between the spatial distribution of cell adhesive ligand and the establishment and maintenance of directional cell polarization. In addition, there was no net directional cell polarity found on asymmetric nanoarrays presenting a higher affinity ligand cyclic RGD, indicating that ligand affinity also has a profound effect on cell polarization. The relationship between ligand affinity and spatial distribution of immobilized ligand was further explored through double asymmetric nanoarrays presenting cyclic RGD, which were shown to impose directional cell polarization. In order to extend this methodology to examine other aspects of cell adhesion and polarization on electroactive nanoarrays other methods of visualization were considered. There have been conflicting reports regarding the use of total internal reflection fluorescence microscopy (TIRFM) to visualize cells near thin metal layers. In Chapter 4, it was determined that TIRFM is an effective method to examine intercellular structures of cells adhered to patterned SAMs on gold surfaces. This was demonstrated through the use of microcontact printing and DPN patterning methods. Future applications of this research are presented in Chapter 5

Advances in Mechanical Systems Dynamics 2020

The fundamentals of mechanical system dynamics were established before the beginning of the industrial era. The 18th century was a very important time for science and was characterized by the development of classical mechanics. This development progressed in the 19th century, and new, important applications related to industrialization were found and studied. The development of computers in the 20th century revolutionized mechanical system dynamics owing to the development of numerical simulation. We are now in the presence of the fourth industrial revolution. Mechanical systems are increasingly integrated with electrical, fluidic, and electronic systems, and the industrial environment has become characterized by the cyber-physical systems of industry 4.0. Within this framework, the status-of-the-art has become represented by integrated mechanical systems and supported by accurate dynamic models able to predict their dynamic behavior. Therefore, mechanical systems dynamics will play a central role in forthcoming years. This Special Issue aims to disseminate the latest research findings and ideas in the field of mechanical systems dynamics, with particular emphasis on novel trends and applications