Modeling of acoustoelastic borehole waves subjected to tectonic stress with formation anisotropy and borehole deviation

Sonic logging is a promising technique to estimate tectonic stress around a borehole. The key to successful evaluation of tectonic stress is having a thorough understanding of forward model which implies responses of borehole waves to tectonic stress. We propose a generic model to simulate responses of borehole waves to tectonic stress based on semi-analytical finite element method and acoustoelasticity. This model can compute distribution of tectonic stress around an inclined borehole with arbitrary anisotropic formation and simulate acoustoelasticities of borehole waves under this complicated stress. To avoid tedious and time consuming code development, we also provide an easy access to the model by reformulating and implementing the governing equations in a commercial software package. We validate the model by using three case studies where analytical/numerical solutions are available, showing good agreements between the results from our model and solutions in the literature. We then apply the model to some important applications in boreholes, demonstrating that this model can provide a powerful tool for understanding of responses of borehole waves to tectonic stress.

A Comparative Investigation of Prevalent Hydrodynamic Modelling Approaches for Floating Offshore Wind Turbine Foundations: A TetraSpar Case Study

Numerical models have been used extensively in the design process of the TetraSpar floating offshore wind turbine (FOWT) foundation to optimize and investigate the influence from a number of structural and environmental conditions. In traditional offshore design, either the Morison approach or a linear boundary element method (BEM) is applied to investigate the hydrodynamic loads on a structure. The present study investigated and compared these two methods and evaluated their applicability on the TetraSpar FOWT concept. Furthermore, a hybrid model containing load contributions from both approaches was evaluated. This study focuses on motion response. In the evaluation, hydrodynamic data from BEM codes are applied, while the commercial software package OrcaFlex is utilized for time series simulations of the coupled structure. The investigation highlights the difference between the modelling approaches and the importance of particularly drag and inertia contributions. By optimizing the input coefficients, reasonable agreement between the models can be achieved.

Broadband RCS Reduction by a Quaternionic Metasurface

A quaternionic metasurface consisting of two pairs of units with destructive phase difference is proposed to extend the bandwidth of radar cross section (RCS) reduction. The two pairs of units are designed to have complementary phase-different bandwidth, which extends the bandwidth of RCS reduction. The overlaps of their bandwidth enhance the RCS reduction, resulting in a metasurface having broadband and strong RCS reduction. This design and the wideband RCS reduction of the quaternionic metasurface were verified by analytical calculation with superposition principle of electric field, numerical simulation with commercial software package CST Microwave Studio and experiment in microwave anechoic chamber. The scattering mechanism and the angular performance of the quaternionic metasurface were also investigated.

Determining the relation between the count number and x-ray energy level in pyroelectric materials using linear regression analysis

X-rays are a type of electromagnetic energy which widely used in different areas. Since their discovery, x-rays have been used, especially for medical imaging applications. On the other hand, new efficient x-ray generation methods have still been under investigation. Although new imaging modalities arose, xrays have never lost their popularity in many applications like computed tomography and dental imaging. Among these new methods, x-ray generation using pyroelectric crystal materials is one of the promising technologies. Pyroelectric crystals generate an electric field when a temperature change occurs and are affected by various parameters like how many times (count) the crystal’s temperature changed in a second. Hence, this new technology needs more research. In this study, we investigated the relationship between the count number and x-rays’ energy level of pyroelectric materials using linear regression analysis. We used a commercial software package, which is called the Statistical Package for the Social Sciences (SPSS), for this purpose. As a result, we achieved a good fit value of R2 = 0.91.

Mixing Characteristics of Supersonic Jet from Bevelled Nozzles

The present study focuses on the effect of nozzle exit inclination on the mixing characteristics of Mach 2.17 overexpanded jets at the NPR 5, NPR 6 and NPR 7, using commercial software package ANSYS Fluent. The convergent-divergent nozzles, investigated are circular nozzle and bevel nozzle with bevel angle 300, and bevel angel 450. The nozzles are constructed with equal throat-to-exit area ratio, in order to maintain uniform Mach number at the nozzle exit. From the results, it was found that, the bevelled nozzles effectively reduce the jet core as much as 46%, indicating enhanced jet mixing. It was also observed that at lower NPR, i.e., at NPR 5, the Bevel30 nozzle is found superior over Bevel45 and circular nozzle and at the intermediate NPR, both of the Bevel30 and Bevel45 nozzle reduces the jet core with the same rate. However, at highest NPR of the present study, the Bevel45 nozzle exhibits the highest mixing enhancement. An early axis switching is seen for the Bevel30 jet at NPR 5 and for the Bevel45 jet at NPR 7.

A Cylindrical Superelement for Thermo-Mechanical Analysis of Thin Composite Vessels

In this study, a new cylindrical shell superelement with trigonometric shape functions is developed. This element is formulated based on the classical theory of shells, and it is especially designed for coupled-field analysis of thin cylindrical vessels or tubes made of composite materials. As a case study, a thermo-mechanical analysis of a thin composite cylinder is conducted. By invoking to the uniform and non-uniform meshing, the deformation and the stress results are calculated and compared with the analytical solutions. At the end, the efficiency and accuracy of the proposed superelement is also depicted via comparison of the corresponding results with the ones which are calculated by means of shell elements and via a commercial software package.

Parametric design analysis of elliptical shroud profile

<abstract> <p>Parametric design analysis for Eccentric Rotated Ellipsoid (ERE) shroud profile is conducted whereas the design model is validated experimentally. A relation between shroud inlet, length and exit diameter is established, different ratios related to the wind turbine diameter are introduced, and solution for different ERE family curves that passes on the inlet, throat, and exit points is studied. The performance of the ERE shroud is studied under different wind velocities ranging from 5–10 m/s.</p> <p>The method used in creating the shroud profile is by solving the ERE curve equations to generate large family of solutions. The system is modeled as axisymmetric system utilizing commercial software package. The effect of the parameters; shroud length, exit diameter, inlet diameter, turbine position with respect to the shroud throat, and wind velocity are studied. An optimum case for each shroud length, exit diameter and location of the shroud with respect to the wind turbine throat axis are achieved.</p> <p>The simulation results show an increase in the average wind velocity by 1.63 times of the inlet velocity. This leads to a great improvement in the wind turbine output power by 4.3 times of bare turbine. One of the achieved optimum solutions for the shroud curves has been prototyped for experimental validation. The prototype has been manufactured using 3D printing technology which provides high accuracy in building the exact shape of shroud design curve. The results show very good agreement with the experimental results.</p></abstract>

Numerical Simulation of the Degree of Protection for K9 Artillery Position under Explosion Scenario Using METT+TC

This study proposes a method to evaluate the protective performance of an existing K9 artillery position according to various explosion scenarios. Thus, a commercial software package AUTODYN was used to create a 3D model of the existing artillery position. Following the mission, enemy, terrain and weather, troops and support available, time available, and civil consideration (METT+TC) analysis, a total of three blast loading scenarios were selected. According to the results, the wall rotation angle of a near-miss explosion was within the standard of 2°; considering contact explosions, the rotation angles were also within 2°. This confirmed that the K9 artillery position under examination for protective performance was within the elastic design range. Considering the final evaluation and combining the results, the walls and slabs of the K9 artillery position were determined to be able to withstand the corresponding blast pressures and have no issues in protective performance. Meanwhile, due to the limitations of the actual blast tests for evaluating the protective performance of civilian protective structures and those of the ROK Armed Forces, these tests were replaced with numerical analysis-based evaluations. However, due to the lack of specified procedures for numerical analysis based on finite element analysis, there were several difficulties in practice. Therefore, this study aims to provide a basic procedure for evaluating the protective performance of protective structures in the future by presenting analytical and blast loading conditions which are necessary for evaluating protective performance.

Composite right/left-handed transmission line with array of thermocouples for generating terahertz radiation

We present a new concept of the thermoelectric structure that generates microwave and terahertz signals when illuminated by femtosecond optical pulses. The structure consists of a series array of capacitively coupled thermocouples. The array acts as a hybrid type microwave transmission line with anomalous dispersion and phase velocity higher than the velocity of light. This allows for adding up the responces from all the thermocouples in phase. The array is easily integrable with microstrip transmission lines. Dispersion curves obtained from both the lumped network scheme and numerical simulations are presented. The connection of the thermocouples is a composite right/left-handed transmission line, which can receive terahertz radiation from the transmission line ports. The radiation of the photon to the surface of the thermocouple structure causes a voltage difference with the bandwidth of terahertz. We examined a lossy composite right/left-handed transmission line to extract the circuit elements. The calculated properties of the design are extracted by employing commercial software package CST STUDIO SUITE.