F. Ubertini

Effects of Low Incoming Turbulence on the Flow around a 5 : 1 Rectangular Cylinder at Non-Null-Attack Angle

The incompressible high Reynolds number flow around the rectangular cylinder with aspect ratio 5 : 1 has been extensively studied in the recent literature and became a standard benchmark in the field of bluff bodies aerodynamics. The majority of the proposed contributions focus on the simulation of the flow when a smooth inlet condition is adopted. Nevertheless, even when nominally smooth conditions are reproduced in wind tunnel tests, a low turbulence intensity is present together with environmental disturbances and model imperfections. Additionally, many turbulence models are known to be excessively dissipative in laminar-to-turbulent transition zones, generally leading to overestimation of the reattachment length. In this paper, Large Eddy Simulations are performed on a 5 : 1 rectangular cylinder at non-null-attack angle aiming at studying the sensitivity of such flow to a low level of incoming disturbances and compare the performance of standard Smagorinsky-Lilly and Kinetic Energy Transport turbulence models.

Simple Beam Model to Estimate Leakage in Longitudinally Cracked Pressurized Pipes

Losses from water distribution systems are reaching alarming levels in many cities throughout the world. Leakage is often the principal cause of water loss because of aging and deterioration of these systems, and pressure has been verified to assume a key-role in water-loss management. This paper presents a simple analytical model based on a beam with elastic constraints to estimate the leak area (from which the leakage is then estimated) in longitudinally cracked pressurized pipes and to evaluate the effect of pressure on the opening area of the crack. The model is calibrated on the results of a three-dimensional finite-element analysis and then validated by experimental results. The validation has been carried out for a wide range of pipes made of different materials (PVC, cast iron, asbestos-cement, and steel) with radii ranging from 27.5 to 110 mm, thicknesses from 1.5 to 12 mm, and crack lengths from 50 to 200 mm. The beam model, notwithstanding its simplicity, provides reliable leakage evaluations in longitudinally cracked pressurized pipes.

Salt Effects in Plastered and Unplastered Outdoors Brick Masonry: Quantitative Laser Monitoring of Surface Decay Evolution

In masonry materials, the superficial decay is a widespread problem. Aggressive environmental agents such as moisture and salts trigger the damage by propagating through the material capillary pores. Although several studies have been carried out on salt crystallization and their damaging effects, additional research effort is required to better investigate this phenomenon on real cases and real weathering conditions. To this purpose, testing and monitoring tools capable of following degradation process since the early beginning are necessary. Repeated visual inspections are commonly used to monitor the superficial decay, but this technique is subjective and thus not capable of providing any quantitative information. In this work, an experimental campaign, carried out in Bologna, Italy, is presented. A two-header brick wall, one main face unplastered and one plastered, was stored outdoors and exposed to weathering over two summers. Before the start of the second aging season, moisture and salt capillary rise was simulated by low-concentrated sodium chloride solution (0.1% -wt). The aim was to favor solution evaporation and salt crystallization and to provoke material damage. The degradation process was monitored based on a contactless, rapid and accurate image diagnostic technique. In particular, high-resolution laser scanning by triangulation technique was adopted. Three-dimensional data acquisition was repeated at the end of both seasons. The proposed procedure successfully extracted quantitative information approximately areas of material spalling and detachment even in the initial phases of decay.

Structural Analysis of Historic Masonry and Technical Guideline Application: The Case of the Insula del Centenario [IX, 8] in Pompeii

In this paper we present the study of an archaeological structure in Pompeii and we detail the difficulties encountered applying the Italian standards and guideline when designing the new roofing structure. Following the latest Italian standards and guidelines, about the assessment and mitigation of seismic risk of cultural heritage, the analysis of the Insula has been carried out. In particular, among all the studied structures, the attention was focused on the covering of the main hall where a prototype of a roofing structure covering a portion of the hall was installed near the remaining ruins of the house. Numerical models have been developed in order to track the effect of these new roofing structures on this ancient masonry structure.

A simple beam model to analyse the durability of adhesively bonded tile floorings in presence of shrinkage

A simple beam model for the evaluation of tile debonding due to substrate shrinkage is presented. The tile-adhesive-substrate package is modeled as an Euler-Bernoulli beam laying on a two-layer elastic foundation. An effective discrete model for inter-tile grouting is introduced with the aim of modelling workmanship defects due to partial filled groutings. The model is validated using the results of a 2D FE model. Different defect configurations and adhesive typologies are analysed, focusing the attention on the prediction of normal stresses in the adhesive layer under the assumption of Mode I failure of the adhesive.

A numerical framework for simulating fluid-structure interaction phenomena

In this paper, a numerical tool able to solve fluid-structure interaction problems is proposed. The lattice Boltzmann method is used to compute fluid dynamics, while the corotational finite element formulation together with the Time Discontinuous Galerkin method are adopted to predict structure dynamics. The Immersed Boundary method is used to account for the presence of an immersed solid in the lattice fluid background and to handle fluid-structure interface conditions, while a Volume-of-Fluid-based method is adopted to take trace of the evolution of the free surface. These ingredients are combined through a partitioned staggered explicit strategy, according to an efficient and accurate algorithm recently developed by the authors. The effectiveness of the proposed methodology is tested against two different cases. The former investigates the dam break phenomenon, involving the modeling of the free surface. The latter involves the vibration regime experienced by two highly deformable flapping flags obstructing a flow. A wide numerical campaign is carried out by computing the error in terms of interface energy artificially introduced at the fluid-solid interface. Moreover, the structure behavior is dissected by simulating scenarios characterized by different values of the Reynolds number. Present findings are compared to literature results, showing a very close agreement.

Simulation and Test Procedures to correlate Structural Damage with Moisture and Salts Migration in Masonry

In historic masonry structures – focus of the 7FP European project SMOOHS – the monitoring and effects of environmental agents in walls and of structural problems is being investigated in a joint perspective. Numerical simulations and experimental work aim to correlate the decay effects of moisture and salt transport in masonry, with structural damage. To better address the problem, a cross-feeding collaboration is set up between numerical and experimental studies. Initial experimental data obtained in the lab on masonry materials become the main input data for hygro-thermal simulations of behaviour of masonry specimens in aggressive environment, that is solutions of sodium sulphate (Na2SO4). Simulation output helps to improve the experimental accelerated ageing procedures. Later, the salt damage process development in these specimens and their reduced structural capacity will be mechanically evaluated. A function relating these parameters will couple hygrothermal and structural simulations to predict a structural damage index for historical buildings.

Lattice-Boltzmann Simulations of Hull Impacting Water

In this paper, we propose a computational approach to estimate the forces acting on a rigid wedge as it impacts a free water surface. The approach is based on the Lattice-Boltzmann Method, wherein the fluid is described as a set of particles streaming and colliding in a discrete time-space environment. Predicted slamming forces are compared with closed-form results based on potential flow and experimental results on drop-tests of rigid wedges.Copyright