A 3-NODE PIEZOELECTRIC SHELL ELEMENT FOR LINEAR AND GEOMETRICALLY NONLINEAR DYNAMIC ANALYSIS OF SMART STRUCTURES

Composite laminates consisting of passive and multi-functional materials represent a powerful material system. Passive layers could be made of isotropic materials or fiber-reinforced composites, while piezoelectric ceramics are considered here as a multi-functional material. The paper is focused on  linear and geometrically nonlinear dynamic analysis of smart structures made of such a material system. For this purpose, a linear 3-node shell element is used. It employs the Mindlin-Reissner kinematics and the discrete shear gap (DSG) technique to alleviate the transverse shear locking effects. The electric potential is assumed to vary linearly through the thickness for each piezoelectric layer. A co-rotational formulation is used to handle the geometrically nonlinear effects. A number of examples involving actuator and sensor application of piezoelectric layers are considered. For the validation purposes, the results available in the literature and those computed in Abaqus are used as a reference

AN AUTOMATIZED IN-PLACE ANALYSIS OF A HEAVY LIFT JACK-UP VESSEL UNDER SURVIVAL CONDITIONS

Heavy lift jack-up vessels (HLJV) are used for the installation of components of large offshore wind farms. A systematic FE-analysis is presented for the HLJV THOR (owned by Hochtief Infrastructure GmbH) under extreme weather conditions. A parametric finite element (FE) model and analysis are developed by using ANSYS-APDL programming environment. The analysis contains static and dynamic nonlinear FE-calculations, which are carried out according to the relevant standards (ISO 19905) for in-place analyses of jack-up vessels. Besides strategies of model abstraction, a guide for the determination of the relevant loads is given. In order to calculate the dynamic loads, single degree of freedom (SDOF) analogy and dynamic nonlinear FE-calculations are used. As a result of detailed determination of dynamic loads and consideration of soil properties by spring elements, the used capacities are able to be reduced by 28 %. This provides for significant improvement of the environmental restrictions of the HLJV THOR for the considered load scenario

Co-rotational shell element for numerical analysis of laminated piezoelectric composite structures

Laminated composite structures consisting of load-carrying and multifunctional materials represent a rather powerful material system. The passive, load-carrying layers can be made of isotropic material or fiber-reinforced composites, while piezoelectric materials represent the most common choice of multifunctional materials for active layers. The multifunctionality of piezoelectric layers is provided by their inherent property to couple mechanical and electric fields. The property can thus be used to sense deformations or produce actuating forces. A highly efficient 3-node shell element is developed for modeling piezoelectric laminated composite shells. The equivalent single-layer approach and Mindlin-Reissner kinematics are used in the element formulation together with the discrete shear gap (DSG) technique to resolve the shear locking and strain smoothing technique to improve the performance. Piezoelectric layers are assumed to be polarized in the thickness direction thus coupling the in-plane strains with the electric field oriented in the thickness direction. The co-rotational FE formulation is used to account for geometrically nonlinear effects. Numerical examples cover linear and geometrically nonlinear static and dynamic cases with piezoelectric layers used as actuators and sensors

ABAQUS IMPLEMENTATION OF A COROTATIONAL PIEZOELECTRIC 3-NODE SHELL ELEMENT WITH DRILLING DEGREE OF FREEDOM

Integration of classical, passive structures and active elements based on multi-functional materials resulted in a novel structural concept denoted as active structures. The new structural systems are characterized by self-sensing and actuation. Coupling the two distinctive features by means of a controller enables a number of exquisite functionalities such as vibration suppression, noise attenuation, shape control, structural health monitoring, etc. Reliable, accurate and highly efficient modeling tools are an important ingredient of the active structure design. This paper addresses the Abaqus implementation of a recently developed piezoelectric 3-node shell element. The element uses co-rotational formulation to cover geometric nonlinearities. Special techniques are used to address the issues originating from low-order interpolation functions. The discrete shear gap is used to resolve the shear locking, while the assumed natural deviatoric strain technique improves the membrane behavior. Examples are computed in Abaqus upon implementation of the developed element

Towards real-time simulation of deformable structures by means of co-rotational finite element formulation

Whereas typical Finite Element (FE) computations are performed off-line, many virtual-reality (VR) applications put a demand for interactive simulations involving deformable objects. Interactive simulation implies real-time or nearly real-time computation and graphical representation of modeled deformable objects. The growing computational power of modern conventional hardware calls for FEM developments in this direction. Depending on specific VR applications, the developments need to account for different aspects of physical behavior, with geometrically nonlinear deformations emerging as one of most important and frequent. This paper proposes a simplified co-rotational FE formulation that considers the overall finite element motion as a superposition of rigid-body rotation and deformation described by a linear model with respect to the co-rotated reference frame. By neglecting the stress stiffening effect and the dependence of the element stiffness matrix on the deformational displacements, the formulation aims at meeting the objectives of highly efficient simulation, under certain conditions even real-time simulation, and with acceptable deviation in accuracy compared to the rigorous nonlinear FE formulation. Computations with both solid and shell elements are addressed. A set of examples is provided to illustrate and discuss the aspects of accuracy and achievable simulation speed

High performance 3-node shell element for linear and geometrically nonlinear analysis of composite laminates

Thin-walled structures hold primacy among modern engineering structures. All the advantages offered by the curved geometry and thinness of the walls come even more to the fore when combined with exquisite properties of fiber-reinforced composite laminates. Directionally dependant material properties open vast possibilities for tailoring global structural properties and, therewith, optimization. Successful design of such structures calls for high performance shell type finite elements. This paper presents a linear triangular shell element based on the equivalent single-layer approach and the first-order shear deformation theory. The shear locking effect is resolved by the descrete shear gap (DSG) approach combined with the cell smoothing technique. To improve the element performance with respect to the membrane behavior, the assumed natural deviatoric strains (ANDES) formulation is applied, with necessary modifications to meet the requirements of curved structures with anisotropic material properties. Geometric nonlinearities are addressed by the co-rotational formulation. Examples demonstrate the element applicability and performance

Efficient three-node finite shell element for linear and geometrically nonlinear analyses of piezoelectric laminated structures

Fiber-reinforced composite laminates involving piezoelectric layers represent a very attractive material system. It combines the advantages of using rather lightweight and stiff material with the possibility of sensing structural changes and actively influencing its state by means of sensors and actuators. A three-node shell element is proposed as an efficient tool for modeling structures made of such a material system. Thoroughly tested solutions are implemented to resolve locking problems intrinsic for shell elements. The embedded piezoelectric layers are considered to be polarized in the thickness direction. Furthermore, the extension of the formulation to geometrically nonlinear finite element analysis is based on a co-rotational formulation. Numerical examples are given to demonstrate the applicability of developed element in linear and geometrically nonlinear finite element analyses covering both actuator and sensor cases

Final Stage of Chronic Kidney Disease with Conservative Kidney Management or Renal Replacement Therapy: A Primary-Care Population Study

Background: Studies focus on the incidence and risk factors (RFs) associated with reaching the final stage of chronic kidney disease (CKD-G5) and receiving kidney replacement therapy (KRT). Analysis of those related to reaching CKD-G5 while receiving conservative kidney management (CKM) has been neglected. Methods: Retrospective cohort study analysing electronic health records of individuals aged & GE; 50 with eGFR < 60 mL/min/m(2). Cumulative incidence rates of CKD-G5, with and without KRT, were calculated. Multinomial regression models determined odds ratios (ORs) for CKD-G5 progression with KRT, CKM, or death. Results: Among 332,164 patients, the cumulative incidence of CKD-G5 was 2.79 cases per 100 person-years. The rates were 1.92 for CKD-G5 with KRT and 0.87 for CKD-G5 with CKM. Low eGFR and albuminuria were the primary RFs. Male gender and uncontrolled blood pressure had a greater impact on KRT (OR = 2.63 CI, 1.63) than on CKD-G5 with CKM (OR = 1.45 CI, 1.31). Increasing age and rurality reduced the probability of KRT but increased the probability of CKD-G5 with CKM. Higher incomes decreased the likelihood of developing CKD-G5 with and without KRT (OR = 0.49 CI). Conclusion: One-third of CKD-G5 cases receive CKM. Those are typically older, female, rural residents with lower incomes and with lesser proteinuria or cardiovascular RF. The likelihood of receiving KRT is influenced by location and socioeconomic disparities

The Usefulness of Inflammatory Biomarkers to Predict Anastomotic Leakage after Colorectal Surgery: Systematic Review and Meta-Analysis

Aim: Anastomotic leakage (AL) is a severe postoperative complication in colorectal surgery, but its preclinical diagnosis may improve outcomes and increase anastomotic salvage. This study aimed to assess the added value of serum biomarkers for early detection of colorectal AL. Method: We performed a comprehensive literature review, and a qualitative and quantitative analysis of papers retrieved from MEDLINE, Embase, PubMed, Web of Science, Scopus and the Cochrane Library. We included all studies published before September 2021 assessing the serum biomarkers white blood cells (WBC), C-reactive protein (CRP), procalcitonin (PCT) and calprotectin (CLP) for the early diagnosis of AL. Results: Fifteen studies that evaluated three different systemic biomarkers in the context of AL were identified, including 5150 patients. Diagnostic test accuracy was estimated for CRP and PCT. On postoperative day (POD) 5, the highest AUC (87.1%) and specificity (80.2%) values were estimated for CRP. Random-effects meta-analysis and total effect sizes estimation for the biomarkers CRP, PCT and WBC were performed according to POD. The concentration of serum biomarkers is significantly higher in patients presenting AL. Regarding the qualitative analysis, there was significant heterogeneity in the inclusion of different subcategories of the consensus definition of colorectal AL in each paper’s definition. Conclusion: The serum biomarkers CRP and PCT are moderate predictors for AL, showing a high heterogeneity among the studies. Combinations of these biomarkers might improve predictive accuracy, but more studies will be necessary to conduct a quality metaregression.info:eu-repo/semantics/publishedVersio

Challenges and Obstacles for a Bouncing Universe in Brane Models

A Brane evolving in the background of a charged AdS black-hole displays in general a bouncing behaviour with a smooth transition from a contracting to an expanding phase. We examine in detail the conditions and consequences of this behaviour in various cases. For a cosmological-constant-dominated Brane, we obtain a singularity-free, inflationary era which is shown to be compatible only with an intermediate-scale fundamental Planck mass. For a radiation-dominated Brane, the bouncing behaviour can occur only for background-charge values exceeding those allowed for non-extremal black holes. For a matter-dominated Brane, the black-hole mass affects the proper volume or the expansion rate of the Brane. We also consider the Brane evolving in an asymmetric background of two distinct charged AdS black hole spacetimes being bounded by the Brane and find that, in the case of an empty critical Brane, bouncing behaviour occurs only if the black-hole mass difference is smaller than a certain value. The effects of a Brane curvature term on the bounce at early and late times are also investigated.Comment: 23 pages, Latex file, comments and references added, version to appear in Phys. Rev.