Photogrammetry image-based approach for imperfect structure modelling and FE analysis

This study aims to model and analyse imperfect tructures using real measurements, employing photogrammetry technique commonly used in the geodesy. The study highlights the capability of the photogrammetry in aiding the structural analysis of imperfect engineering objects. Firstly, the photogrammetry measurements of a stiffened plate are carried out using a specially designed for the purpose experimental stand. Then, the plate surface geometry and structural configuration are reconstructed using commercial software. The resulting cloud of points is transformed into a regular mesh with a controlled grid size using a specially developed algorithm. The geometry of a stiffened plate, with measured initial imperfections, is then transferred to a finite element model and analysed. The ultimate strength analysis of stiffened plates considering different imperfections modelling techniques is conducted. The results are compared with the one obtained for measured imperfections, and several conclusions are derived. The proposed methodology revealed to be cost-effective and can be applied in various branches of shipbuilding and ocean engineering.

Jaw biomechanics: Estimation of activity of muscles acting at the temporomandibular joint

The aim of this study was to elaborate a method of estimation of activity of surface muscles acting at the temporomandibular joint of the healthy subjects by using a surface electromyography (EMG). The scope of this study involved testing chosen jaw motions (open, close, lateral deviation) and process of mastication occurring during eating food with different toughness (chewing gum, cereal and carrot) by using mixed sides, right side and left side of the jaw.

Modelling and Measurement of Folk Guitar: Truss Rod and Strings in Numerical Analysis of Tone

The study makes an attempt to model a complete vibrating guitar including its non-linear features, specifically the tension-compression of truss rod and tension of strings. The purpose of such a model is to examine the influence of design parameters on tone. Most experimental studies are flawed by uncertainties introduced by materials and assembly of an instrument. Since numerical modelling of instruments allows for deterministic control over design parameters, a detailed numerical model of folk guitar was analysed and an experimental study was performed in order to simulate the excitation and measurement of guitar vibration. The virtual guitar was set up like a real guitar in a series of geometrically non-linear analyses. Balancing of strings and truss rod tension resulted in a realistic initial state of deformation, which affected the subsequent spectral analyses carried out after dynamic simulations. Design parameters of the guitar were freely manipulated without introducing unwanted uncertainties typical for experimental studies. The study highlights the importance of acoustic medium in numerical models.

Failure of cold-formed beam: How does residual stress affect stability?

In machine industry, stresses are often calculated using simple linear FEM analysis. Occasional failures of elements designed in such a way require recomputation by means of more sophisticated methods, eg. including plasticity and non-linear effects. It usually leads to investigation of failure causes and improvement of an element in order to prevent its unwanted behavior in the future. The study presents the case where both linear and non-linear analyses show some load capacity reserve and do not justify failure occurring in reality. Some non-standard causes are pointed out, including residual stress of a leading role.

Simple Computational Methods in Predicting Limit Load of High-Strength Cold-Formed Sections due to Local Buckling: A Case Study

Cold-formed thin-walled sections are prone to local buckling caused by residual stresses, geometrical imperfections and inconsistency of material properties. We present a real case of buckling failure and conduct a numerical and experimental study aimed to identify methods capable of predicting such failures. It is important because designers of structures are getting more FEA-oriented and tend to avoid lengthy procedures of cold-formed structures design. Currently adopted methods are complicated and require patience and caution from a designer which is reasonable in case of the most important structural members but not necessarily so in ordinary design. Since it is important, we offer an insight into several FEA and manual methods which were sufficient to predict the failure while remaining fairly simple. Using a non-uniform partial safety factor was still necessary. We hope that this paper will be of interest for people performing a lot of routine analyses and worrying about reliability of their computations.

Surface sliding in human abdominal wall numerical models: Comparison of single-surface and multi-surface composites

Determining mechanical properties of abdominal soft tissues requires a coupled experimental-numerical study, but first an appropriate numerical model needs to be built. Precise modeling of human abdominal wall mechanics is difficult because of its complicated multi-layer composition and large variation between specimens. There are several approaches concerning simplification of numerical models, but it is unclear how far one could go to still maintain fairly good results. The study compares behaviour of two different shell models: a simpler one, consisting of a single composite shell incorporating all abdominal wall layers and a more complicated one, consisting of three respective muscle-fascia composites allowed to slide on one another, representing a more realistic abdominal wall behaviour. Both models were subjected to the same loading and boundary conditions in a series of different non-linear analyses, including implicit, explicit, static and dynamic variants. The study shows that the two tested models differ greatly in terms of the obtained displacements, thus the sliding mechanism of muscle-fascia layers should not be ignored. As a side task, several finite element types were tested for proficiency in this particular computation.

Nonlinear Modeling in Time Domain Numerical Analysis of Stringed Instrument Dynamics

Musical instruments are very various in terms of sound quality with their timbre shaped by materials and geometry. Materials' impact is commonly treated as dominant one by musicians, while it is unclear whether it is true or not. The research proposed in the study focuses on determining influence of both these factors on sound quality based on their impact on harmonic composition. Numerical approach has been chosen to allowed independent manipulation of geometrical and material parameters as opposed to experimental study subjected to natural randomness of instrument construction. Distinctive element of this research is precise modeling of whole instrument and treating it as one big vibrating system instead of performing modal analysis on an isolated part. Finite elements model of a stringed instrument has been built and a series of nonlinear time-domain dynamic analyses were executed to obtain displacement signals and perform subsequent spectral analysis. Precision of computations seems sufficient to determine the influence of instrument's macroscopic mechanical parameters on timbre. Further research should focus on implementation of acoustic medium in attempt to include dissipation and synchronization mechanisms. Outside the musical field this kind of research could be potentially useful in noise reduction problems.