Numerical simulation of viscoelastic buckle folds: Implications for stress, fractures, porosity and fluid flow

Over the past several decades, buckle folds have been exclusively studied by numerous methods. However, lots of assumptions and simplifications are made, which may not result in realistic in-situ stress conditions leading to rock failure. This study represents the first numerical simulation of folding under the consideration of gravity and pore pressure to simulate the structural development of buckle folds. The first topic covered in this dissertation is the fracture associated to the single layer fold. It is concluded that burial depth, viscosity, and permeability are critical for the initiation of major fracture sets at the hinge zone with varying degrees. Moreover, this study provides a detail research on the stress and strain distribution in the multilayer folds and it is concluded that the stress/strain state within the folding layer(s) are determined by the buckling process, fold geometry and material parameters. The second topic covered in this dissertation is the numerical simulation of multilayer folds. This study demonstrates that the shapes of the multilayer folds are influenced by the various parameters. In addition, the numerical simulations provide a general understanding of the stress/strain distribution in the multilayer system. The third topic covered in this dissertation is the numerical simulation of parasitic folds. This study demonstrates that the shapes of the parasitic folds depend on the buckling of both the large- and small-scale folds and are influenced by the various parameters. The numerical modeling results show a large variability in porosity changes due to the complex distribution of the volumetric strain. In addition, the numerical simulations provide a general understanding of the influence of the various model parameters on the resulting porosity distribution --Abstract, page iv

Tensile failure during structural development of single-layer buckle folds

Folds and fold trains of sedimentary strata are among the most common structural traps systems for hydrocarbon reservoirs. The existence of tensile fractures associated to buckle folding is associated to the distribution of extensional strain in the outer arc of the fold hinges. This study investigates the conditions under which tensile stresses develop due to buckling in a realistic in situ stress scenario. By applying a 2D finite element modeling approach, the influence of realistic mechanical stratigraphy (including strain rate, overburden depth, competence contrasts, viscosity, and permeability) on the development of single-layer buckle folds with Newtonian viscous rheology is studied. Based on the simulation results, it can be concluded that the buckling process cannot explain the common observation and occurrence of tensile failure. Only low permeability (\u3c10⁻¹⁹ m²) or low overburden pressure environments are possible to generate tensile failure at the top of the fold crest. Tensile failures in the limb of the fold cannot be explained by buckling only. This study shows that for high permeability rocks the generation of tensile stress both at the crest and limb of the fold can be the result of buckling followed by erosional unloading. In summary, tensile stresses and associated failure in buckle folds systems are determined by material parameters and the strain history --Abstract, page iii

A Magnetic Actuated Fully Insertable Robotic Camera System for Single Incision Laparoscopic Surgery

Minimally Invasive Surgery (MIS) is a common surgical procedure which makes tiny incisions in the patients anatomy, inserting surgical instruments and using laparoscopic cameras to guide the procedure. Compared with traditional open surgery, MIS allows surgeons to perform complex surgeries with reduced trauma to the muscles and soft tissues, less intraoperative hemorrhaging and postoperative pain, and faster recovery time. Surgeons rely heavily on laparoscopic cameras for hand-eye coordination and control during a procedure. However, the use of a standard laparoscopic camera, achieved by pushing long sticks into a dedicated small opening, involves multiple incisions for the surgical instruments. Recently, single incision laparoscopic surgery (SILS) and natural orifice translumenal endoscopic surgery (NOTES) have been introduced to reduce or even eliminate the number of incisions. However, the shared use of a single incision or a natural orifice for both surgical instruments and laparoscopic cameras further reduces dexterity in manipulating instruments and laparoscopic cameras with low efficient visual feedback. In this dissertation, an innovative actuation mechanism design is proposed for laparoscopic cameras that can be navigated, anchored and orientated wirelessly with a single rigid body to improve surgical procedures, especially for SILS. This design eliminates the need for an articulated design and the integrated motors to significantly reduce the size of the camera. The design features a unified mechanism for anchoring, navigating, and rotating a fully insertable camera by externally generated rotational magnetic field. The key component and innovation of the robotic camera is the magnetic driving unit, which is referred to as a rotor, driven externally by a specially designed magnetic stator. The rotor, with permanent magnets (PMs) embedded in a capsulated camera, can be magnetically coupled to a stator placed externally against or close to a dermal surface. The external stator, which consists of PMs and coils, generates 3D rotational magnetic field that thereby produces torque to rotate the rotor for desired camera orientation, and force to serve as an anchoring system that keeps the camera steady during a surgical procedure. Experimental assessments have been implemented to evaluate the performance of the camera system

The Composition of Market Proxy in REITs Risk Premium Estimation

A market portfolio is constructed in this paper that is in the spirit of Roll (1977). It consists of equity assets, fixed-income securities, and real estate, and tests whether the real estate investment trust (REIT) risk premium that is estimated using an equity index alone is robust to the misspecification of the market portfolio. The results show that REIT betas increase significantly relative to a more complete market proxy. Moreover, adding real estate to the market portfolio accounts for a significant portion of the bias in the estimated REIT market risk premium

Adaptive Reuse of Religious Heritage and Its Impact on House Prices

Due to social demographic change and secularization, religious heritage sites in Europe are on the verge of losing their original functions. While the adaptive reuse seems to be a proactive strategy to preserve the historical and cultural value embedded in religious heritage sites, little is known concerning its external impact. This paper aims to fill this gap by investigating the external effect of reusing religious heritage on surrounding house prices. Employing both the parametric and non-parametric difference-in-differences hedonic model on a sample of 42 projects of reusing religious heritage and a rich dataset of housing transactions in the Netherlands, we find significant positive externality of reusing religious heritage on local house prices. The external effects are heterogeneous across differentiated project size and monumental status. Larger religious heritage reuse projects and those listed as national monuments exert greater influence on surrounding house prices