Peridynamics formulation for beam structures to predict damage in offshore structures

Progressive damage analysis of structures is still a major challenge. Peridynamics is a non-local theory using the integral equations rather than differential equations which makes it suitable for damage prediction. In this study, a novel bond based peridynamic model is developed for three-dimensional complex beam structures with 6 degrees of freedom based on Timoshenko beam theory. The numerical algorithm for dealing with complex beam structures is provided for the first time in the peridynamic literature. A damage criterion for beam structures with 6 degrees of freedom is also presented. The validity of peridynamic predictions is established by considering various examples. Initially, the proposed peridynamic model is used to predict the structural behavior of straight and curved beams. Next, the proposed peridynamic model is used to investigate a jacket platform. The jacket platform is subjected to both static and dynamic sea load induced by waves, winds, and currents. The peridynamic predictions are verified by comparing with finite element solutions. Peridynamic damage prediction for a pre-notched beam is verified by comparing with the previous literature. After verifying the peridynamic model, the proposed model is used to predict damages for a jacket platform due to sea loads and due to ship-jacket platform collisions

Peridynamics for geometrically nonlinear analysis of three-dimensional beam structures

This study presents a novel peridynamic model for geometrically nonlinear analysis of three-dimensional beam structures. The formulations of nonlinear strain energy densities for a beam is obtained by using Total Lagrange formulation. The peridynamic formulations for beam structures are obtained based on the principle of virtual displacements. The capability of the proposed peridynamic model is demonstrated by considering large deformations of straight beams and curved beams subjected to different loading conditions. To further demonstrate the capabilities of the proposed nonlinear model, damages on a dry spaghetti subjected to different loading conditions are simulated

Brittle damage prediction for corroded stiffened structures under static loading conditions by using peridynamics

This study focuses on the prediction of progressive brittle damages on corroded stiffened structures by using peridynamics. First, deformations of a stiffened structure subjected to uniform static pressure are investigated, and the peridynamics results are verified with the results from the finite element analysis. Second, progressive brittle damages on a corroded plate are predicted, and the effects of the corrosion on the crack path as well as bending strength of the plate are investigated. Next, progressive brittle damages on a stiffened structure with different corrosion types: localised and shadow corrosions, subjected to tension are predicted. The effects of different corrosion types on crack propagation and the strength of the structure are also analysed. Finally, progressive brittle damages on a stiffened structure subjected to uniform pressure are predicted

Investigating the effect of brittle crack propagation on the strength of ship structures by using peridynamics

Ship structures can experience damages although they are initially designed with high safety factors. These damages can be caused by many reasons such as collisions, groundings, explosions, corrosion, fatigue, overloading or extreme conditions. Brittle damages can occur on the ship structures in some special conditions such as low-temperature, high-loading rate, multi-axial stress constraint, or low weldability of steel. In this study, progressive brittle damages on a ship structure subjected to different loading conditions are predicted. A novel peridynamic method based on a recently developed peridynamic shell model is presented to evaluate the structural strength during the damage evolution process for the first time in the literature. First, longitudinal strength (bending moment) of a ship structure is numerically calculated during damage propagations. The maximum longitudinal strength of the intact ship is verified with the experimental result. Next, the simulations are further extended to investigate the ship structure with initial damage, i.e. rectangular cut-out at the bottom. The longitudinal strength for an intact ship and a ship with different sizes of cut-outs are also compared. Finally, torsional strength during the damage propagation process for a ship structure with a cut-out is also presented

Vietnamese Version of Cornell Scale for Depression in Dementia at an Outpatient Memory Clinic: A Reliability and Validity Study

Background: In Vietnam, there has been, currently, no standardized tool for depression assessment for people with dementia (PWD). Cornell Scale for Depression in Dementia (CSDD) is a widely studied and used scale for PWD worldwide. Objectives: The aim of this study was to standardize the Vietnamese version of the CSDD (V-CSDD) in depression assessment in PWD through reliability and validity examination. Methods: V-CSDD was rated in terms of reliability and validity with gold standard regarding "major depressive episode"and "major depressive-like episode"of DSM-5. Cronbach's α, ICC, exploratory factor analysis (EFA), and receiver operating characteristic analysis were performed. Results: V-CSDD was found to have a high internal consistency reliability (Cronbach's α = 0.80), inter-rater reliability at sound ranking (ICC = 0.89; 95% CI = 0.81-0.94), maximum cut-off mark of 13 (sensitivity = 70%, specificity = 92%), and EFA, which suggested that V-CSDD may comprise 5 factors. Conclusions: Results indicate the V-CSDD to be a reliable and valid assessment and to be beneficial in classifying and diagnosing depression in dementia outpatients in clinical contexts

Research of multi-response optimization of milling process of hardened S50C steel using minimum quantity lubrication of Vietnamese peanut oil

This study aims to build a regression model when surveying the milling process on S50C steel using Minimum Quantity Lubrication (MQL) of Vietnamese peanut oil-based on Response Surface Methodology. The paper analyses and evaluates the effect of cutting parameters, flow rates, and pressures in minimum quantity lubrication system on cutting force and surface roughness in the milling process of S50C carbon steel materials after heat treatment (reaching a hardness of 52 HRC). The Taguchi method, one of the most effective experimental planning methods nowadays, is used in this study. The statistical analysis software, namely Minitab 19, is utilized to build a regression model between parameters of the cutting process, flow rates and pressures of the minimum quantity lubrication system and the cutting force, surface roughness of the part when machining on a 5-axis CNC milling machine. Thereby analyzing and predicting the effect of cutting parameters and minimum quantity lubrication conditions on the surface roughness and cutting force during machining to determine the influence level them. In this work, the regression models of Ra and F were achieved by using the optimizer tool in Minitab 19. Moreover, the multi-response optimization problem was solved. The optimum cutting parameters and lubricating conditions are as follows: Cutting velocity Vc=190.909 m/min, feed rate fz=0.02 mm/tooth, axial depth of cut ap=0.1 and nozzle pressure P=5.596 MPa, flow rate Q=108.887 ml/h. The output parameters obtained from the above parameters are Ra=0.0586  and F=162.035 N, respectively. This result not only provides the foundation for future research but also contributes reference data for the machining proces

CONNECTING MATHEMATICS AND PRACTICE: A CASE STUDY OF TEACHING EXPONENTIAL FUNCTIONS

There is a need for teaching exponential functions to show the necessity for a better match between the knowledge of exponential functions in high schools with the practical application of it in fields. In this research, a teaching process was built in association with teaching situations to show students the relationship between mathematics and real life. The research sample included 76 students in high schools in Vietnam. Additionally, two problems of compound interest and population growth were integrated and were the main research instruments. Data were collected, including student work, and they were analyzed qualitatively. The results showed that students had improved their problem-solving skills and saw the relationship between mathematics and practice. Furthermore, there were some recommendations suggested for textbook authors and teachers. Article visualizations

AMMONIA REMOVAL FROM SWINE WASTEWATER USING AN AEROBIC, ANOXIC FILTER AT A PILOT-SCALE IN THANH LOC BIOSTATION

Joint Research on Environmental Science and Technology for the Eart

Energy Consumption Minimization for Autonomous Mobile Robot: A Convex Approximation Approach

In this paper, we consider a trajectory design problem of an autonomous mobile robot working in industrial environments. In particular, we formulate an optimization problem that jointly determines the trajectory of the robot and the time step duration to minimize the energy consumption without obstacle collisions. We consider both static and moving obstacles scenarios. The optimization problems are nonconvex, and the main contribution of this work proposing successive convex approximation (SCA) algorithms to solve the nonconvex problems with the presence of both static and moving obstacles. In particular, we first consider the optimization problem in the scenario with static obstacles and then consider the optimization problem in the scenario with static and moving obstacles. Then, we propose two SCA algorithms to solve the nonconvex optimization problems in both the scenarios. Simulation results clearly show that the proposed algorithms outperform the A* algorithm, in terms of energy consumption. This shows the effectiveness of the proposed algorithms