Numerical Investigation on the Structural Behavior of a Composite Impact Absorber

2009 ◽  
Vol 417-418 ◽  
pp. 685-688 ◽  
Author(s):  
Giuseppe Lamanna ◽  
Francesco Caputo ◽  
Alessandro Soprano
Keyword(s):  
Numerical Investigation ◽  
Laminated Composite ◽  
Failure Criteria ◽  
Point Of View ◽  
Physical Parameters ◽  
Contact Conditions ◽  
Explicit Finite Element ◽  
Energy Absorbing ◽  
Boundary Contact ◽  
Composite Face

The energy absorption capability of an exposed crashworthy element or system is largely affected by material properties and structural design: prismatic sandwich structures, made of foam or honeycomb core between two metallic or laminated composite face plates, are good candidates. This work deals with a numerical investigation on the energy absorbing capability of such a structural component. There are several difficulties associated with the numerical simulation of a composite impact-absorber, such as high geometrical non-linearities, boundary contact conditions, failure criteria, material behaviour; that is because the main objectives of any numerical investigation are the calibration of the model with experimental results and the evaluation of the sensitivity of the variables with respect to the geometrical and physical parameters which influence the study at hand. The latter is a very relevant aspect for designers if the application of the model to real cases has to be a robust one from both a physical and a numerical point of view. In this paper a preliminary calibration of a numerical model for a composite impact absorber is presented, on the basis of experimental data found in literature; then a sensitivity analysis of the same model to the variation of the main geometrical and material parameters, developed by using the explicit finite element algorithms implemented in the Ls-Dyna code, is illustrated.

scholarly journals Patient’s point of view on the use of telemedicine in multiple sclerosis: a web-based survey

2021 ◽  
Author(s):  
Doriana Landi ◽  
Marta Ponzano ◽  
Carolina Gabri Nicoletti ◽  
Gaia Cola ◽  
Gianluca Cecchi ◽  
...  
Keyword(s):  
Multiple Sclerosis ◽  
Point Of View ◽  
Physical Parameters ◽  
Chronic Medical Conditions ◽  
Socioeconomic Conditions ◽  
Web Based ◽  
Healthcare Facilities ◽  
Advantages And Disadvantages ◽  
Disease Characteristics ◽  
Degree Of Disability

AbstractRestrictions in the access to healthcare facilities during COVID-19 pandemic have raised the need for remote monitoring of chronic medical conditions, including multiple sclerosis (MS). In order to enable the continuity of care in these circumstances, many telemedicine applications are currently tested. While physicians’ preferences are commonly investigated, data regarding the patients’ point of view are still lacking. We built a 37 items web-based survey exploring patients’ propensity, awareness, and opinions on telemedicine with the aim to evaluate the sustainability of this approach in MS. Analysing 613 questionnaires out of 1093 that were sent to persons with MS followed at the Multiple Sclerosis Center of Tor Vergata University, Rome, we found that more than half of respondents (54%) were open to having a televisit. Propensity toward telemedicine significantly depended on having a higher income (p = 0.037), living farther from the center (p = 0.038), using computer and tablet (p = 0.010) and using the Internet for other remote activities (p < 0.001), conversely it was not influenced by any specific disease characteristics (i.e. degree of disability). The main advantages and disadvantages of televisit reported by participants were respectively saving time (70%) and impossibility to measure physical parameters (71%). Although the majority of respondents are in favour of televisit, so far this approach is restricted to those displaying better socioeconomic conditions and higher familiarity with technology. Implications of the study are that telemedicine platforms should be better tailored to patients’ demands in order to spread the use of telemedicine, to enhance usability and to increase patients’ adherence.

scholarly journals Influence of Random Forest Hyperparameterization on Short-Term Runoff Forecasting in an Andean Mountain Catchment

Atmosphere ◽  
2021 ◽  
Vol 12 (2) ◽  
pp. 238
Author(s):  
Pablo Contreras ◽  
Johanna Orellana-Alvear ◽  
Paul Muñoz ◽  
Jörg Bendix ◽  
Rolando Célleri
Keyword(s):  
Random Forest ◽  
Model Performance ◽  
Early Warning Systems ◽  
Point Of View ◽  
Lead Times ◽  
Physical Parameters ◽  
Runoff Forecasting ◽  
Spatio Temporal ◽  
Improved Model ◽  
Search Approach

The Random Forest (RF) algorithm, a decision-tree-based technique, has become a promising approach for applications addressing runoff forecasting in remote areas. This machine learning approach can overcome the limitations of scarce spatio-temporal data and physical parameters needed for process-based hydrological models. However, the influence of RF hyperparameters is still uncertain and needs to be explored. Therefore, the aim of this study is to analyze the sensitivity of RF runoff forecasting models of varying lead time to the hyperparameters of the algorithm. For this, models were trained by using (a) default and (b) extensive hyperparameter combinations through a grid-search approach that allow reaching the optimal set. Model performances were assessed based on the R2, %Bias, and RMSE metrics. We found that: (i) The most influencing hyperparameter is the number of trees in the forest, however the combination of the depth of the tree and the number of features hyperparameters produced the highest variability-instability on the models. (ii) Hyperparameter optimization significantly improved model performance for higher lead times (12- and 24-h). For instance, the performance of the 12-h forecasting model under default RF hyperparameters improved to R2 = 0.41 after optimization (gain of 0.17). However, for short lead times (4-h) there was no significant model improvement (0.69 < R2 < 0.70). (iii) There is a range of values for each hyperparameter in which the performance of the model is not significantly affected but remains close to the optimal. Thus, a compromise between hyperparameter interactions (i.e., their values) can produce similar high model performances. Model improvements after optimization can be explained from a hydrological point of view, the generalization ability for lead times larger than the concentration time of the catchment tend to rely more on hyperparameterization than in what they can learn from the input data. This insight can help in the development of operational early warning systems.

scholarly journals Reversed-torsion-type crush energy absorption structure and its inexpensive partial-heating torsion manufacturing method based on origami engineering

2021 ◽  
pp. 1-31
Author(s):  
Xilu Zhao ◽  
Chenghai Kong ◽  
Yang Yang ◽  
Ichiro Hagiwara
Keyword(s):  
Energy Absorption ◽  
Peak Load ◽  
Point Of View ◽  
Building Structures ◽  
Manufacturing Method ◽  
Partial Heating ◽  
Vehicle Structure ◽  
Energy Absorbers ◽  
Energy Absorbing ◽  
Origami Engineering

Abstract Current vehicle energy absorbers face two problems during a collision in that there is only a 70% collapse in length and there is a high initial peak load. These problems arise because the presently used energy-absorbing column is primitive from the point of view of origami. We developed a column called the Reversed Spiral Origami Structure (RSO), which solves the above two problems. However, in the case of existing technology of the RSO, the molding cost of hydroforming is too expensive for application to a real vehicle structure. We therefore conceive a new structure, named the Reversed Torsion Origami Structure (RTO), which has excellent energy absorption in simulation. We can thus develop a manufacturing system for the RTO cheaply. Excellent results are obtained in a physical experiment. The RTO can replace conventional energy absorbers and is expected to be widely used in not only automobile structures but also building structures.

scholarly journals Intention, Principle, Outputs and Aims of the Experimental Pavilion Research of Building Envelopes Including Windows for Wooden Buildings

2017 ◽  
Vol 13 (1) ◽  
pp. 42-51 ◽  
Author(s):  
Daniela Štaffenová ◽  
Ján Rybárik ◽  
Miroslav Jakubčík
Keyword(s):  
Experimental Research ◽  
Climatic Conditions ◽  
Point Of View ◽  
Physical Parameters ◽  
Data Sets ◽  
Data Set ◽  
Building Envelopes ◽  
Climate Conditions ◽  
Time Period

AbstractThe aim of experimental research in the area of exterior walls and windows suitable for wooden buildings was to build special pavilion laboratories. These laboratories are ideally isolated from the surrounding environment, airtight and controlled by the constant internal climate. The principle of experimental research is measuring and recording of required physical parameters (e.g. temperature or relative humidity). This is done in layers of experimental fragment sections in the direction from exterior to interior, as well as in critical places by stable interior and real exterior climatic conditions. The outputs are evaluations of experimental structures behaviour during the specified time period, possibly during the whole year by stable interior and real exterior boundary conditions. The main aim of this experimental research is processing of long-term measurements of experimental structures and the subsequent analysis. The next part of the research consists of collecting measurements obtained with assistance of the experimental detached weather station, analysis, evaluation for later setting up of reference data set for the research locality, from the point of view of its comparison to the data sets from Slovak Hydrometeorological Institute (SHMU) and to localities with similar climate conditions. Later on, the data sets could lead to recommendations for design of wooden buildings.

Buckling of Stiffened Curved Panels and Cylindrical Shells: A Study of Comparison Among Various Theories

2012 ◽  
Author(s):  
S. Harutyunyan ◽  
D. J. Hasanyan ◽  
R. B. Davis
Keyword(s):  
Cylindrical Shell ◽  
Circular Cylindrical Shell ◽  
Cylindrical Shells ◽  
Laminated Composite ◽  
Physical Parameters ◽  
Buckling Loads ◽  
Isotropic Cylindrical Shell ◽  
Analytical Formulas ◽  
Laminated Composite Shells ◽  
Curved Panels

Formulation is derived for buckling of the circular cylindrical shell with multiple orthotropic layers and eccentric stiffeners acting under axial compression, lateral pressure, and/or combinations thereof, based on Sanders-Koiter theory. Buckling loads of circular cylindrical laminated composite shells are obtained using Sanders-Koiter, Love, and Donnell shell theories. These theories are compared for the variations in the stiffened cylindrical shells. To further demonstrate the shell theories for buckling load, the following particular case has been discussed: Cross-Ply with N odd (symmetric) laminated orthotropic layers. For certain cases the analytical buckling loads formula is derived for the stiffened isotropic cylindrical shell, when the ratio of the principal lamina stiffness is F = E2/E1 = 1. Due to the variations in geometrical and physical parameters in theory, meaningful general results are complicated to present. Accordingly, specific numerical examples are given to illustrate application of the proposed theory and derived analytical formulas for the buckling loads. The results derived herein are then compared to similar published work.

Strength Simulation of Woven Fabric Composite Materials With Material Nonlinearity Using Micromechanics Based Model

2000 ◽  
Author(s):  
A. Tabiei ◽  
G. Song ◽  
Y. Jiang
Keyword(s):  
Finite Element ◽  
Shear Failure ◽  
Material Model ◽  
Failure Criteria ◽  
Woven Fabric ◽  
Woven Composites ◽  
Explicit Finite Element ◽  
Representative Cell ◽  
Pure Matrix ◽  
Transverse Failure

Abstract The objective of the current investigation is to predict failure strength of woven composites, which considers the two-dimensional extent of woven fabric, based on micro-mechanics. The formulation has an interface with nonlinear finite element codes. At each load increment, global stresses and strains are communicated to the representative cell and subsequently distributed to each subcell. Once stresses and strains are associated to a subcell they can be distributed to each constituent of the subcell (i.e. fill, warp, and resin). Consequently micro-failure criteria (MFC) are defined for each constituents of a subcell and the proper stiffness degradation is modeled. Different stages of failure such as warp transverse failure, fill transverse failure, failure of pure matrix in longitudinal and shear, shear failure in fill and warp, and fiber in fill and warp in longitudinal tension are considered. Good correlation is observed between the predicted and the experimental results presented in the published literature. This material model is suitable for implicit failure analysis under static loads and is being modified for explicit finite element codes to deal with problems such as crashworthiness and impact.

Design of a Hybrid Lightweight Energy Absorber

2016 ◽  
Vol 713 ◽  
pp. 321-324
Author(s):  
A. de Luca ◽  
Giuseppe Lamanna ◽  
Raffaele Sepe ◽  
Alessandro Soprano
Keyword(s):  
Kinetic Energy ◽  
Numerical Investigation ◽  
Structural Design ◽  
Carbon Composite ◽  
Energy Absorber ◽  
Load Paths ◽  
Passenger Safety ◽  
Carbon Composite Materials ◽  
Energy Absorbers ◽  
Energy Absorbing

Among several problems which might affect the passenger safety during an accidental crash event, the deceleration pulse is one of the most critical. For this reason vehicles are designed to convert the Kinetic Energy occurring in an impact in plastic deformation and to spread the loads due to such events through designed structural load paths. An important role in the kinetic energy absorbing at high velocities is played by the energy absorbers. The energy absorption capability of a crashworthy element or system is largely affected by material properties and structural design. This work deals with a numerical investigation on the energy absorbing capability of a new concept of energy absorber made out of the combination of metal parts and carbon composite materials. A numerical investigation on the parameters which increase the crash performance as well as decrease the weight of such device has been presented in this paper.

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