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Appl. Mech., Volume 1, Issue 2 (June 2020) – 4 articles

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Open AccessArticle
Damage Evaluation of Free-Free Beam Based on Vibration Testing
Appl. Mech. 2020, 1(2), 142-152; https://doi.org/10.3390/applmech1020010 - 09 May 2020
Viewed by 474
Abstract
Damage can be detected by vibration responses of a structure. Damage changes the modal properties such as natural frequencies, mode shapes, and damping ratios. Natural frequency is one of the most frequently used damage indicators. In this paper, the natural frequency is used [...] Read more.
Damage can be detected by vibration responses of a structure. Damage changes the modal properties such as natural frequencies, mode shapes, and damping ratios. Natural frequency is one of the most frequently used damage indicators. In this paper, the natural frequency is used to monitor damage in a free-free beam. The modal properties of the intact free-free beam are identified based on a setup of 15 accelerometers. A finite element model is used to model the free-free beam. Three models are considered: beam (1D), shell (2D), and solid (3D). The numerical models are updated based on the first five bending natural frequencies. The free-free beam is damaged by a rectangle cut. The experiment is re-setup and the model properties of the damaged beam are re-identified. The cuttings are modeled in the numerical simulations. The first five numerical bending natural frequencies of the damaged beam are compared with the experimental ones. The results showed that the 1D beam element model has the highest errors, while the 2D and 3D models have approximately the same results. Therefore, the 2D representation can be used to model the damaged beam for fast computation. Full article
(This article belongs to the collection Fracture, Fatigue, and Wear)
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Open AccessArticle
The Limitations on the Use of the IMO CSS Code in Project Cargo—Case Study: Grillage Design for the Sea Transport of Gas Slug Catchers
Appl. Mech. 2020, 1(2), 123-141; https://doi.org/10.3390/applmech1020009 - 29 Apr 2020
Viewed by 432
Abstract
Heavy cargo units with a relatively reduced footprint area require a support surface large enough to transfer the forces onto the largest possible surface and/or the main stiffening (longitudinal and transverse) in order to not collapse or overstress the ship’s structure and, consequently, [...] Read more.
Heavy cargo units with a relatively reduced footprint area require a support surface large enough to transfer the forces onto the largest possible surface and/or the main stiffening (longitudinal and transverse) in order to not collapse or overstress the ship’s structure and, consequently, put the ship, the cargo, and the crew at risk. For that reason, it is necessary to project stowage and securing systems (including bedding design) to ensure that, by applying the principles of good seamanship and securing practices, the shipment is maintained in a safe condition throughout the trip until destination port arrival. Despite the increase in project cargo shipments in recent years, in many cases, International Maritime Organization (IMO) regulations are followed by default. The main purpose of this paper, thus, is to highlight certain shipments for which IMO guidelines should be taken into account in future revisions. This is done through what was considered innovative project cargo on a particular ship due to its special characteristics. To this end, because of limitations found in the IMO CSS Code regarding acceleration and force calculations, it was necessary to resort to the internationally accepted guidelines of one of the strictest classification societies. Full article
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Open AccessArticle
Friction and Dynamics of Verge and Foliot: How the Invention of the Pendulum Made Clocks Much More Accurate
Appl. Mech. 2020, 1(2), 111-122; https://doi.org/10.3390/applmech1020008 - 29 Apr 2020
Viewed by 541
Abstract
The tower clocks designed and built in Europe starting from the end of the 13th century employed the “verge and foliot escapement” mechanism. This mechanism provided a relatively low accuracy of time measurement. The introduction of the pendulum into the clock mechanism by [...] Read more.
The tower clocks designed and built in Europe starting from the end of the 13th century employed the “verge and foliot escapement” mechanism. This mechanism provided a relatively low accuracy of time measurement. The introduction of the pendulum into the clock mechanism by Christiaan Huygens in 1658–1673 improved the accuracy by about 30 times. The improvement is attributed to the isochronicity of small linear vibrations of a mathematical pendulum. We develop a mathematical model of both mechanisms. Using scaling arguments, we show that the introduction of the pendulum resulted in accuracy improvement by approximately π/μ ≈ 30 times, where μ ≈ 0.1 is the coefficient of friction. Several historic clocks are discussed, as well as the implications of both mechanisms to the history of science and technology. Full article
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Open AccessArticle
Springback Prediction in Sheet Metal Forming, Based on Finite Element Analysis and Artificial Neural Network Approach
Appl. Mech. 2020, 1(2), 97-110; https://doi.org/10.3390/applmech1020007 - 06 Apr 2020
Viewed by 615
Abstract
Sheet metal forming is one of the most important manufacturing processes applied in many industrial sectors, with the most prevalent being the automotive and aerospace industries. The main purpose of that operation is to produce a desired formed shape blank, without any material [...] Read more.
Sheet metal forming is one of the most important manufacturing processes applied in many industrial sectors, with the most prevalent being the automotive and aerospace industries. The main purpose of that operation is to produce a desired formed shape blank, without any material failures, which should lie well within the acceptable tolerance limits. Springback is affected by factors such as material properties, sheet thickness, forming tools geometry, contact and friction, etc. The present paper proposes a novel neural network system for the prediction of springback in sheet metal forming processes. It is based on Bayesian regularized backpropagation networks, which have not been tested in the literature, according to the authors’ best knowledge. For the creation of training examples a carefully prepared Finite Element model has been created and validated for a test case used in similar industrial studies. Full article
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