Modal identification of storage racks for cheese wheels

During the Emilia-Romagna earthquake (2012), a great number of steel racks used to store cheese wheels collapsed, causing a non-negligible damage to the Italian economy. Therefore, for similar structures that survived and are in service, a deep investigation towards the assessment of their effective safety is required. In the seismic analysis of these frames, the mechanical constraint acting onto the racks due to the reinforced concrete sidewalls, possible nonlinearities exhibited by the base-plate joints and the in-plane restraint provided by wooden boards that connects adjacent columns should be carefully modelled to ensure realistic design results. In the paper, an experimental activity, based on suitable modal identification techniques, is presented to capture the dynamic behaviour of these peculiar structures. The scope is to collect data useful to calibrate numerical finite element models in order to accurately define the aforementioned unknown parameters. Furthermore, a few numerical models based on ideal restraints are herein discussed stressing out non-negligible differences in terms of expected seismic and static response

Design and simulation of meshing of a particular internal rotary pump

This paper presents a complete description of a specific geometry applicable to internal rotary pump. A particular design is considered, characterized by superior flow-rate performance and different contact mechanism in respect with the common trochoidal pumps. All the necessary aspects regarding the kinematics and operation of the machine are taken into account, by means of a mathematical formulation. In particular, the kinematic analysis considers the possible presence of transmission errors and assures the absence of interference by a tooth contact analysis. The achieved mathematical model allows the designer to obtain the complete definition of the rotor profiles in parametric form

One-Mode Extra Insensitive Input Shapers to Reduce Residual Vibration in Flexible Arms: Experimental Verification

Input shaping is a particular feedforward-control strategy based on the convolution of an input command with a sequence of pulses, whose amplitude and application time are function of the natural frequencies of the system to be controlled. The effect consists in a significant reduction of the residual vibration, compared with the original unshaped command. This paper presents the results of the experimental tests carried out on the master robot arm of the Test-bed for Microgravity Simulation in Robotic Arm Dynamics (TeMSRAD) set up at the Department of Structural Mechanics, Università di Pavia. One-mode extra insensitive shapers were tested experimentally for different vibration limits to determine the sensitivity curve with respect to uncertainties in the system model or environmental noise typical of the operating conditions required by the International Space Station (ISS)

Introductory Analysis of an Innovative Volumetric Rotary Machine

The study of an innovative volumetric rotary machine is presented in this work. The machine is constituted by a stator and a number of pistons rotating inside the stator and attached to a crank. Due to the particular type of solution, this mechanism realizes for every piston a chamber, that varies its volume during crank rotation, and consequently it can be used to realize a volumetric rotary machine. In the paper the geometrical constraints that characterize the mechanism are analyzed, in order to obtain the equation of the stator profile, using an analytical approach. Once the stator profile is determined and appropriate design parameters settled, the analysis of the motion permits to numerically determine the profile of the rolling pistons. Starting from the geometry, the specific displacement and the maximum compression ratio can be calculated as a function of design parameters. Finally, the analysis is focused on the unbalanced inertia forces generated by the mechanism during its motion. The results obtained permit to choose the design parameters for a particular application, showing that the mechanism can be suitable for pumps, compressors and pneumatic engine

Estimation of biomechanical parameters and propulsive efficiency of flat-water kayak single (K1) at race pace

Flat-water Kayaking is an Olympic discipline in which the boats race are held on calm water in separate lanes delineated with ropes and buoys over the distance of 500 m and 1000 m. A new Sprint 200 m race will make its Olympic debut at London 2012. Few are the experimental data in literature on this particular type of race in which the athlete exerts his maximum effort on a very short distance. This paper presents the analysis of the paddling performance of elite athletes in single K1 training session keeping up a typical stroke race cadence (over 100 spm). In order to reproduce the regatta conditions the tests were performed at Idroscalo water basin (Milan, Italy) with kayaker at the top of the training preparation. The on purpose experimental device, successfully tried out in previous on-water kayaking and canoeing researches was integrated with cardiopulmonary testing portable system. By means of experimental acquisitions including stroke forces, estimated position of the blade propulsion centre (EPPC), boat speed and the movements around the three main axes of the hull it is possible to evaluate the athletes performance during the different phases of the race. Particular attention was devoted to refine the efficiency of stroke through the analysis of the exertion of the force in the active part of paddling (drive phase) related to the metabolic cost of the stroke cycle. The main goal of the research was to implement a low cost stand-alone instrumentation and acquisition system for the on-the-water measurement of biomechanical and dynamical parameters during race paddling of elite athletes to quantify performance and improve technique

Extra Insensitive Shapers for Flexible Articulated System to Minimize Residual Vibration in Presence of Modeling Errors

Input shaping is an effective method of minimizing vibration in flexible systems. In particular in space robotics the design of light-weight manipulators is motivated by the increasing demand for high-speed performance and low energy consumption assembly and the control of such systems deals with the great flexibility of these structures. Input shaping (IS) is a feedforward-control strategy characterized by simplicity and effectiveness and it can be used in addition to feedback control approaches. One important property of input shapers is the robustness to frequency modeling errors and it can be measured using a sensitivity plot. This paper shows the goal of the input shaping design method to match a minimum time delay of the maneuver with a sufficient insensitivity to system parameters variation. Greater insensitivity can be reached by using robust shapers such as Extra-Insensitive (EI) input shapers which allow a small amount of vibration at the modeled frequency but a considerably wider insensitivity curve. Experimental results carried out on the Test-bed for Microgravity Simulation in Robotic Arm Dynamics (TeMSRAD), set up at the Department of Structural Engineering, Università di Pavia are presented