Taking the Plunge: Enhancing the Visitor Experience in Waterfall-Based State Parks

Waterfalls have long been popular tourist attractions due to their soundscape, beauty, natural pool, and recreational opportunities. With technological advances and abundant tourism information, more visitors are being drawn to waterfalls. Such high visitation and use amplifies the risk of degrading pristine waterfall sites and their resources. Not only are waterfalls experiencing high demand, but state parks are also seeing large increases in visitation. State parks are typically located closer to population centers and complement the more well-known and iconic national parks by providing recreational opportunities to more, diverse visitors. The present study aims to provide a basis for understanding the visitor experience and carrying capacity at a waterfall-based state park where visitors engage in an activity with the water (e.g., swim in the natural pool, climb the waterfall). Further, the study investigates intrasite displacement from an activity with the water in tandem with the examination of carrying capacity. Visitor surveys and time-lapse field cameras were deployed to collect data on visitor use at a popular waterfall-based state park in Tennessee. The results indicate that use levels are near or above crowding-based thresholds, supporting the implementation of a carrying capacity. While the results do not provide evidence for intrasite or activity displacement, they seem to reflect a reduction in the visitors’ freedom of choice in activity or location. The present study fills a gap in the literature by empirically investigating the carrying capacity of visitors at a waterfall site and utilizing an indicators and thresholds-based approach in a state park. Empirical research on these is needed since citizens highly value waterfalls and primarily gain exposure to nature through state park visits

Acoustic analysis of an exhaust manifold by Indirect Boundary Element Method

The present work is aimed at the development of a numerical procedure, based on the usage of the Boundary Element Method (BEM) as implemented in the software LMS Virtual.Lab, for the vibro-acoustics analysis of an exhaust manifold. The manifold vibrations are induced by two different ways: engine vibrations (transmitted to the manifold surfaces) and turbulences generated by the air flow in the exhaust system. The indirect BEM (IBEM), with a variational solution algorithm, is adopted to assess the exhaust manifold acoustic radiation. The modal analysis of the acoustic cavity is realized by the Finite Element Method (FEM) and the corresponding eigenfrequencies compared with those obtained by an IBEM forced response analysis and by experimental measurement. Experimental acoustic pressures at the manifold inlet and outlet are measured in anechoic room in order to compare with corresponding numerical predictions and assess the accuracy level obtained

Thermal–Mechanical FEM Analyses of a Liquid Rocket Engines Thrust Chamber

The Italian Ministry of University and Research (MIUR) funded the HYPROB Program to develop regeneratively cooled liquid rocket engines. In this type of engine, liquid propellant oxygen–methane is used, allowing us to reach very good performances in terms of high vacuum specific impulse and high thrust-to-weight ratio. The present study focused on the HYPROB final ground demonstrator, which will be able to produce a 30 kN thrust in flight conditions. In order to achieve such a thrust level, very high chamber pressures (up to 50 bar) and consequently high thermal fluxes and gradients are expected inside the thrust chamber. Very complex and high-fidelity numerical FEM models were adopted here to accurately simulate the thermal–mechanical behavior of the thrust chamber cooling channels, accounting for plasticity, creep, and low-cycle fatigue (LCF) phenomena. The aim of the current work was to investigate the main failure phenomena that could occur during the thrust chamber’s service life. Results demonstrated that LCF is the main cause of failure. The corresponding number of loading cycles to failure were calculated accordingly

Multiple crack propagation in friction stir welded aluminium joints

This paper is concerned with the simulation of crack propagation in friction stir welded butt joints, in order to assess the influence of process induced microstructural alterations and residual stresses on the fatigue behaviour of the assembly. The approach employed is based on the coupled use of the finite element method and the dual boundary element method in order to take advantage of the main capabilities of the two methods. The distribution of the process induced residual stresses has been mapped by means of the contour method. Then, the computed residual stresses field has been superimposed, in a dual boundary element environment, to the stress field as a result of a remote fatigue traction load and the crack growth is simulated. A two-parameter crack growth law, based on the evaluation of two thresholds, for the material being analysed, is used for the crack propagation rate assessment. The stress intensity factors are evaluated using the J-integral technique. Computational results have been compared with experimental data, provided from constant amplitude crack propagation tests on welded samples, showing the subdivision of the overall fatigue life in the two periods of crack initiation and crack propagation

Coupled FEM-DBEM Simulation of 3D Crack Growth under Fatigue Load Spectrum

Abstract Numerical predictions of fatigue crack growth under load spectrum are obtained by coupled FEM-DBEM approach. An initial part-through corner crack, in a pre-notched specimen undergoing a traction fatigue load, propagates becoming through the thickness. A two parameter crack growth law ("Unified Approach") is calibrated by in house made constant amplitude experimental tests and the crack growth retardation after an overload application is reproduced. The residual stresses responsible for such retardation are calculated by a sequence of elastic-plastic static FEM analysis; such stresses are then applied to the crack faces for the propagation simulation in a DBEM environment. A satisfactory agreement between numerical and experimental crack growth rates are displayed, for both part-through crack and through the thickness crack. This approach provide general modeling capabilities, with allowance for general crack front shape and fully automatic propagation

Robust design of a polygonal shaft-hub coupling

In this work, the Taguchi method is applied for the optimal choice of design parameter values for a polygonal shaft-hub coupling. The objective is to maximize a performance function, minimizing, at the same time, its sensitivity to noises factors (robust design). The Design of Experiments (DoE) is adopted to set up a plan of numerical experiments, whose different configurations are simulated using the Boundary Element Method (BEM)

Simplified and accurate stiffness of a prismatic anisotropic thin-walled box.

Background: Beam models have been proven effective in the preliminary analysis and design of aerospace structures. Accurate cross sectional stiffness constants are however needed, especially when dealing with bending, torsion and bend-twist coupling deformations. Several models have been proposed in the literature, even recently, but a lack of precision may be found when dealing with a high level of anisotropy and different lay-ups. Objective: A simplified analytical model is proposed to evaluate bending and torsional stiffness of a prismatic, anisotropic, thin-walled box. The proposed model is an extension of the model proposed by Lemanski and Weaver for the evaluation of the bend-twist coupling constant. Methods: Bending and torsional stiffness are derived analytically by using physical reasoning and by applying bending and torsional stiffness mathematic definition. Unitary deformations have been applied when evaluation forces and moments arising on the cross section. Results: Good accuracy has been obtained for structures with different geometries and lay-ups. The model has been validated with respect to finite element analysis. Numerical results are commented upon and compared with other models presented in literature. Conclusion: For cross sections with a high level of anisotropy, the accuracy of the proposed formulation is within 2% for bending stiffness and 6% for torsional stiffness. The percentage of error is further reduced for more realistic geometries and lay-ups. The proposed formulation gives accurate results for different dimensions and length rations of horizontal and vertical walls.N/

FEM Substructuring for the Vibrational Characterization of a Petrol Engine

In this work the vibrational behavior of a 4-cylinder, 4-stroke, petrol engine has been simulated by leveraging on a reduced modelling strategy, based on the Component Mode Synthesis (CMS), adopted to reduce the size of the full FEM model of the engine. The FEM model of the engine, comprising all of its sub-components, has been preliminary characterized from the vibrational standpoint; subsequently, the CMS has been adopted in order to reduce the FEM model size. Frequency Response Function (FRF) analyses have been used to identify the resonant frequencies and mode shapes of the different FEM models, and the so-obtained results have been compared showing a very good agreement. The reduced model has been able to reproduce with a high accuracy the vibration response at the engine mounts. The adopted reduced modelling strategy turned out to be effective in lowering the computational burden, keeping, at the same time, an accurate replication of the engine vibrational behavior. Runtimes have been significantly reduced from 24 hours for the full FEM model to less than 2 hours for the reduced model

Prevention of Dermatologic Side Effects of Bimatoprost 0.03% Topical Therapy

PURPOSE: To investigate the efficacy of reducing the drop-skin contact to prevent dermatologic side effects of bimatoprost 0.03% topical therapy. DESIGN: Prospective, randomized, single-blinded, internally controlled study. METHODS: Enrolled subjects started bimatoprost 0.03% therapy once at night in both eyes and were instructed to wipe selectively only one eye (eye 1) with an adsorbent pad during and after drops administration for four months. The fellow eye acted as the internal control. Eyelash growth, regional skin hypertrichosis, and pigmentation on the periocular skin were assessed at baseline and during the four months of follow-up. RESULTS: A lower incidence of eyelash growth and skin pigmentation in the inferonasal pericanthal region were observed in eye 1. The incidence of pigmentation in the inferotemporal skin region and skin hypertrichosis were similar in the two eyes. CONCLUSION: The reduction of the drop,skin contact affects the regional incidence and the extent of dermatologic skin changes that are related to bimatoprost 0.03% topical therapy