Damage Tolerance Assessment of Multi-Hull Aluminum Vessels Using Global Finite Element Methods

As aluminum high-speed multi-hulls continue to grow in size, capacity and operational sea state, a need is growing to understand the damage tolerance of these structures. This paper presents a Linear Elastic Fracture Mechanics (LEFM) approach to performing damage tolerance assessments of aluminum hull structures using the hydrodynamic analysis and global finite element model developed as part of a class Dynamic Loading Approach (DLA) notation. The LEFM approach is used to calculate the stress intensity factor (K) and the critical crack length throughout the model to screen the entire hull structure and identify fracture critical locations. This paper also investigates the use of elastic-plastic fracture mechanics to predict potential critical crack growth locations, rates, and directions. Fracture critical locations identified and visualized through the analysis provide the ship designer with tools to develop damage tolerant structures. The results of the analysis can also assist owners and regulatory bodies in developing structural inspection and repair plans.

Indirect Reconstruction of Structural Responses Based on Transmissibility Concept and Matrix Regularization

A novel method is proposed based on the transmissibility concept and matrix regularization for indirectly measuring the structural responses. The inputs are some measured responses that are obtained via physical sensors. The outputs are the structural responses corresponding to some critical locations where no physical sensors are installed. Firstly, the transmissibility concept is introduced for expressing the relationship between the measured responses and the indirectly measured ones. Herein, a transmissibility matrix is formulated according to the theory of force identification under unknown initial conditions. Then, in order to reduce the size of the transmissibility matrix, structural responses are reshaped in a form of a matrix by using the concept of moving time windows. According to the matrix form of input-output relationship, indirect reconstruction of responses is boiled down to an optimization equation. Since inverse problem may be ill-conditioned, matrix regularization such as F-norm regularization is then recommended for improving the optimization problem. Herein, the penalty function is defined by using a weighted sum of two F-norm values, which correspond to the estimated responses of physical sensors and the ones of the concerned critical locations, respectively. Numerical simulations and experimental studies are finally carried out for verifying the effectiveness and feasibility of the proposed method. Some results show that the proposed method can be applied for indirectly measuring the responses with good robustness.

Positioning grids at critical locations for the design of water distribution network

<p> A water distribution network (WDN) is a critical and life-line infrastructure that transports and distributes water, an essential resource for human life, to local communities. A WDN is often modeled as a two-dimensional complex network consisting of vertices (nodes) and pipes (edges), and it has both characteristics of lattice-like and tree-like structures. With these characteristics, Son et al. (2021) proposed an approach to identify an optimal grid ratio in terms of functionality - efficiency and vulnerability - of a WDN using the lattice to tree network model (LTNM). Their result showed that the grid ratio of a real WDN is often significantly lower than the optimal value, which means that the function of the WDN can be improved by increasing the grid ratio. However, as the range of functions varies depending on where grids are located at a fixed grid ratio, simply adding pipes without considering their location does not incur a linear increase in system function. Therefore, it is important to identify the critical locations to add pipes where the functions of the system are most improved. In addition, it is necessary to determine if adding pipes is possible or not since pipe installation is not allowed for some places. In this study, we (1) identify possible spots where pipes can be added, (2) rank the identified spots where pipes are added regarding the extent of increments of function, and (3) propose an optimal (or a suboptimal) design with an optimally increased with grid ratio by adding pipes to the ranked locations in order. The results indicate that, the performance of WDNs which originally had low grid ratios are improved by adding pipes at reliable spots. The proposed approach illustrates how the structure and function of existing WDNs can be developed by modifying the proportion of grids.</p><p><strong> </strong></p><p><strong>Acknowledgments</strong>: This research was supported by Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Science and ICT (NRF-2019R1C1C1008017).</p>

Comparative Analysis of Radiofrequency Ablation and Microwave Ablation for Critically Located Hepatocellular Carcinomas Smaller than 5 cm

Purpose To compare the safety and efficacy of radiofrequency ablation (RFA) versus microwave ablation (MWA) for hepatocellular carcinomas (HCC) smaller than 5 cm in critical locations. Methods Single-center retrospective study of all patients who underwent RFA/MWA for HCC from July 2015 to Dec 2019. Critical location includes exophytic tumors, tumors ≤ 5 mm from the diaphragm, heart, gallbladder, kidney, gastrointestinal tract, and ≤ 10 mm from large vessels with caliber of ≥ 3 mm. Treatment effectiveness, local tumor progression, and complication rates were evaluated. Results Out of 119 patients with 147 HCC nodules in critical location, 65 (M:F = 49:16; mean age–61.7) were included in RFA group and 54 (M:F =43:11; mean age–60.5) in MWA group. Mean follow-up period was 16.5 and 14.8 months, respectively. At first follow-up imaging, 66/78 tumors in RFA group and 57/69 tumors in MWA group showed complete ablation with primary treatment effectiveness rates of 84.6% and 82.6%, respectively (p = 0.741). Local tumor progression (LTP) rate was 21.8% (17/78) and 20.3% (14/69), respectively (p = 0.826). Median time to LTP was 12 and 13.5 months, respectively. Fourteen tumors in RFA group and 12 in MWA group underwent reablation with a secondary treatment effectiveness rates of 78.6% (14/17) and 83.3% (12/14), respectively (p = 0.757). Mean LTP-free survival was 37.2 and 28.1 months, respectively. The total complication rate was 36.9% and 31.5%, respectively (p = 0.535) with no major complications in both the groups. Conclusion Our data suggest that both MWA and RFA are equally safe and effective for treating HCCs < 5 cm in critical locations.

Joint Integrity and Strength CAE Simulation Methodology for PHEV Vehicle Skid Plate Assembly

Battery unit skid plate Joint integrity and Strength are key design attributes to ensure Functionality of vehicle. This paper provides an overview of simulation methodology to predict joint integrity and Strength of Battery unit skid plate. Bolt Joint integrity checked against the maximum vertical each wheel spindle loads, which captures maximum bending and twisting. This is the condition in which bolts can experience high load and bolt slippage should check against this load. Skid plate experiences different loading based on drivability and road profile. To simulate severe off road event condition, Maximum load which skid plate experience, applied, as Point load on skid plate at various critical locations to find the deflection and to make sure skid plate is strong enough to protect underneath battery unit.

Crack Identification in Necked Double Shear Lugs by Means of the Electro-Mechanical Impedance Method

This contribution investigates fatigue crack detection, localization and quantification in idealized necked double shear lugs using piezoelectric transducers attached to the lug shaft and analyzed by the electro-mechanical impedance (EMI) method. The considered idealized necked lug sample has a simplified geometry and does not includes the typical bearing. Numerical simulations with coupled-field finite element (FE) models are used to study the frequency response behavior of necked lugs. These numerical analyses include both pristine and cracked lug models. Through-cracks are located at 90∘ and 145∘ to the lug axis, which are critical spots for damage initiation. The results of FE simulations with a crack location at 90∘ are validated with experiments using an impedance analyzer and a scanning laser Doppler vibrometer. For both experiments, the lug specimen is excited and measured using a piezoelectric active wafer sensor in a frequency range of 1 kHz to 100 kHz. The dynamic response of both numerical calculations and experimental measurements show good agreement. To identify (i.e., detect, locate, and quantify) cracks in necked lugs a two-step analysis is performed. In the first step, a crack is detected data-based by calculating damage metrics between pristine and damaged state frequency spectra and comparing the resulting values to a pre-defined threshold. In the second step the location and size of the detected crack is identified by evaluation of specific resonance frequency shifts of the necked lug. Both the search for frequencies sensitive to through-cracks that allow a distinction between the two critical locations and the evaluation of the crack size are model-based. This two-step analysis based on the EMI method is demonstrated experimentally at the considered idealized necked lug, and thus, represents a promising way to reliably detect, locate and quantify fatigue cracks at critical locations of real necked double shear lugs.