Fluid/Structure Interactions

This Special Issue contains 12 papers devoted to fluid/structure interaction (FSI) problems. The main feature of the problems is an interface on which consistent boundary conditions for both the liquid and the solid regions are formulated. The presented studies cover a wide range of problems and methods for their solution, including problems of weak, or one-way interaction, in which the effect of interface deformation on the fluid flow can be neglected, as well as problems of the strong interaction, for which the interface change affects both the flow and the structure behaviour. The interest in FSI problems is very great due to their practical importance. Recent developments in engineering have led to advanced formulations of FSI problems. Some of them could not be formulated several years ago. The presented papers demonstrate progress in both numerical algorithms, mathematical apparatus and advanced computational techniques. In this issue, we have tried to collect different FSI problems, new mathematical and numerical approaches, new numerical techniques and, of course, new results, which can provide an insight into FSI processes

Numerical modelling strategies and design methods for timber structures

Over the last years timber constructions are gaining back a primary role in the building industry after decades in which they were almost abandoned in favor of concrete and steel structures. A sign of this change is the appearance in the last years in many Italian universities of courses dedicated to the design of timber structures. One of the main reasons behind this success must be sought in the development of new engineered timber materials, such as glued-laminated and cross-lam timber, that allowed to wooden structures to reach structural potentialities that until some decades ago were prerogative of concrete or steel building materials. Tests recently carried out on full-scale buildings have also proven the excellent capabilities of these new timber technologies in providing reliable and highly-performant multi-storey building able to withstand high seismic intensities. Since the employment of timber to build multi-storey buildings in seismic-prone areas is quite recent, many aspects relating the understanding of their structural behavior and their correct design are still to be sought, as demonstrated by the lack of provisions in current building codes and standards and the still ongoing great amount of research activity on seismic behavior of timber structures. Modern timber technologies also allow to cover very large spans with long glued-laminated timber beams, satisfying the need of large open spaces and architectural flexibility required by modern building design approaches. These bulky big-size elements anyway result quite expensive in production, transportation and installation phases undermining the economic competitiveness of timber structures. To cope with this problem, the prototype of an innovative timber-steel composite beam consisting of sub-elements assembled on-site to create longer members has been ideated at KTH Royal Institute of Technology of Stockholm in Sweden. One of the objectives of this thesis is therefore to provide an advance in the state of knowledge of timber building technology adopted for seismic-prone areas, focusing in particular on both numerical modelling strategies and design methods for cross-laminated timber buildings, illustrated respectively in the first and second part of the thesis. The other goal is the development of an analytical tool for the enhancement and the investigation of the structural performances of the innovative composite beam ideated at KTH Royal Institute of Technology, and it will be exposed in the third and last part of the thesis

Analysis of shell-type structures subjected to time-dependent mechanical and thermal loading

This research is performed to develop a general mathematical model and solution methodologies for analyzing structural response of thin, metallic shell-type structures under large transient, cyclic or static thermomechanical loads. Among the system responses, which are associated with these load conditions, are thermal buckling, creep buckling, and ratcheting. Thus, geometric as well as material-type nonlinearities (of high order) can be anticipated and must be considered in the development of the mathematical model. Furthermore, this must also be accommodated in the solution procedures

Nonlinear dependency of tooth movement on force system directions

Moment-to-force ratios (M:F) define the type of tooth movement. Typically, the relationship between M:F and tooth movement has been analyzed in a single plane. Hence, limited information is available to evaluate a load system elicited by an appliance in 3D. Here, to increment 3-D tooth movement theory, we test the hypothesis that the mathematical relationships between M:F and tooth movement are distinct depending on force system directions. A finite element model of a first maxillary premolar, scaled to average tooth dimensions, was constructed based on a CBCT scan. We conducted finite element analysis (FEA) of the M:F and tooth movement relationships, represented by the projected axis of rotation (C.Rot) in each plane, for 510 different Loads. We confirmed that an hyperbolic equation relates the Distance (C.Res-C.Rot) and M:F; however, the constant of proportionality ("k") varied with non-linearly the force direction. With a force applied parallel to the tooth long axis, "k" was 12 times higher than with a force parallel to the mesio-distal direction and 7 times higher than with a force parallel to the bucco-lingual direction. The M:F has differential influence on tooth movement depending on load directions, and it is an incomplete parameter to describe the quality of an orthodontic load system if not associated with force and moment directions. Moreover, incremental differences in M:F in each plane have different incremental effects on C.Rot position

Effect of activation and preactivation on the mechanical behavior and neutral position of stainless steel and beta-titanium T-loops

Objective: To quantify, for each activation, the effect of preactivations of differing distribution and intensity on the neutral position of T-loops (7-mm height), specifically the horizontal force, moment to force (M/F) ratio, and load to deflection ratio. Methods: A total 100 loops measuring 0.017 x 0.025 inches in cross-section were divided into two groups (n = 50 each) according to composition, either stainless steel or beta-titanium. The two groups were further divided into five subgroups, 10 loops each, corresponding to the five preactivations tested: preactivations with occlusal distribution (00, 200, and 401, gingival distribution (201, and occlusal-gingival distribution (40). The loops were subjected to a total activation of 6-mm with 0.5-mm iterations. Statistical analysis was performed using comprised ANOVA and Bonferoni multiple comparison tests, with a significance level of 5%. Results: The location and intensity of preactivation influenced the force intensity. For the M/F ratio, the highest value achieved without preactivation was lower than the height of the loop. Without preactivation, the M/F ratio increased with activation, while the opposite effect was observed with preactivation. The increase in the M/F ratio was greater when the preactivation distribution was partially or fully gingival. Conclusions: Depending on the preactivation distribution, displacement of uprights is higher or lower than the activation, which is a factor to consider in clinical practice.This study was carried out and financed by the Faculty of Dental Medicine of University of Porto.info:eu-repo/semantics/publishedVersio

Behavior and Design of FRP-Reinforced Longitudinal Glulam Deck Bridges

In 1977, the Weyerhaeuser Company developed a system for short-span timber bridges. The girder-free system consisted of longitudinal, vertically-laminated glulam panels joined by below-deck Transverse Stiffener Beams (TSB). This project addresses two potential areas of improvement in the construction and design of these bridges: a reinforced deck panel and an improved method for TSB design. This project has two objectives: (1) To evaluate the behavior and advantages of longitudinal glulam deck panels reinforced with Fiber-Reinforced Polymers (FRP) and (2) To evaluate existing AASHTO empirical TSB design criteria. The tension-reinforced deck panels can alleviate reliance on high grade wood laminations and allow longer spans and lighter decks. The new panels have the middle two-thlrds of the tension side reinforced with longitudinal E-glass FRP. The research addressed the selection of the FRP material system, the manufacturing process used for applying the reinforcement to the panels, the structural and economic benefits of FRPglulam panels, and the durability of the FRP. The approach included design, laboratory manufacture, and construction of a municipal pier in Milbridge, Maine. Wet-impregnated unidirectional E-glass fabrics were used to reinforce the 164. wide, 167-ft. long, 7-span vehicular pier. A crosssection reinforcement ratio of one percent was used, increasing panel stiffness by six percent. The pier showed the FRP-glulam deck as cost competitive with a prestressed concrete deck. The pier was load tested and performed as predicted under full design live load. The FRP has performed well after two years of harsh marine exposure. To evaluate AASHTO designs of the TSB, a parametric study was performed using a finite element model developed for this study. The model was validated against full-scale laboratory tests conducted at The University of Maine and Iowa State University. The finite element model incorporated orthotropic plate elements for deck panels, offset beam elements for TSB, nonlinear models for deck-to-TSB connections, elements to allow pretensioning of the connections, and elements to model bearing between the deck and TSB. The parametric study focused on shear and bending response of the TSB and the relative movement between adjacent panels. Over 140 analyses were conducted on 43 southern pine bridges designed according to current AASHTO criteria, using 50 load cases. Results showed that the empirical AASHTO design criteria for the TSB may be unconse~ative. In the most critical cases under AASHTO HS20 loading, TSB designed according to AASHTO criteria may experience maximums of either 68% more shear stress than allowable or 61% more bending stress than allowable. In addition, relative panel deflection may exceed the 0.1-inch asphalt serviceability criteria by 79%. Based on the parametric study performed on curb-free bridges, the following design criteria are recommended to replace the current AASHTO TSB design criteria. In lieu of a more accurate analysis, the transverse stiffener beam shall be designed for the following bending moment and shear values: Shear = 0.45*wheel load and Bending Moment = (3.5 inches) *wheel load, as the wheel load represents the maximum wheel load for HS & H vehicles and 1.75*maximum wheel load for alternate military loading

Biomechanics of the Upper Extremity in Response to Dynamic Impact Loading Indicative of a Forward Fall: An Experimental and Numerical Investigation.

The distal radius is one of the most common fracture sites in humans, often resulting from a forward fall with more than 60 % of all fractures to the wrist requiring some form of surgical intervention. Although there is a general consensus regarding the risk factors for distal radius fractures resulting from forward falling, prevention of these injuries requires a more thorough understanding of the injury mechanisms. Therefore the overall purpose of this dissertation was to assess the response of the upper extremity to impact loading to improve the understanding of distal radius fracture mechanisms and the effectiveness of joint kinematic strategies for reducing the impact effects. Three main studies were conducted that utilized in vivo, in vitro and numerical techniques. In vitro impact testing of the distal radius revealed that fracture will occur at a mean (SD) resultant impact force and velocity of 2142.1(1228.7) N and 3.4 (0.7) m/s, respectively. Based on the failure data, multi-variate injury criteria models were produced, highlighting the dynamic and multidirectional nature of distal radius fractures The in vitro investigation was also used to develop and validate a finite element model of the distal radius. Dynamic impacts were simulated in LS-DYNA and the resulting z-axis force validation metrics (0.23-0.54) suggest that this is a valid model. A comparison of the experimental fracture patterns to those predicted numerically (i.e. von-Mises stress criteria) shows the finite element model is capable of accurately predicting bone failure