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Plenum boxes are used for supply and exhaust of air through diffusers and grilles from heating and ventilating air conditioning (HVAC) systems. The plenum boxes ensure a continuous flow and moreover, they are usually lined with different materials in order to realize an acoustic insulation. These silencers/attenuators are of great importance in realizing a comfortable acoustical environment. The paper presents a theoretical and experimental investigation on some commercial plenum boxes with various sizes and lined with different sound absorbing materials. The sound transmission loss TL is the performance criterion for the silencers acoustical behaviour. The test procedure agrees the requirements of ISO 7235:2010 and the measurements were made in an anechoic room. Third-octave band analysis of experimental data is compared with theoretical ones. The results evidence the importance of silencer design which must take account of its geometry and the proper sound absorbing material as a function of frequency in order to optimize its acoustic efficiency.

The paper presents the results obtained by investigating some functional parameters as the noise level, the pressure – drop and the temperatures of three different manufacturing solutions for mufflers. The results emphasize the corroboration between these parameters and contribute to the improvement of the muffler fabrication and design since it is a complex function that affects noise characteristics, emission and fuel efficiency of engine. It was designed a measurement chain for the noise level evaluation of the mufflers including a microphone Bruel&Kjaer type 4133, a Impulse Precision Sound Level Meter Bruel&Kjaer, type 2209, with standard filters and a multifunctional external data acquisition board type-NI DAQPad-6015 . We assessed the noise level, using two based LabVIEW virtual instruments, measuring total band power and the equivalent continuous sound pressure level. It was also created a measurement chain for the pressure – drop evaluation and temperature distribution on the external surface of the mufflers.

Internal combustion engines are typically equipped with an exhaust muffler to suppress the acoustic pulse generated by the combustion process. The paper presents the procedure and the experimental setup for some functional parameters determination as the noise level, the pressure drop and the temperatures through investigating three different manufacturing solutions for mufflers. An algorithm and a dedicated method have been proposed in order to emphasize more direct the mufflers influence on the engines performances. The procedure equally includes particular cycles of the engine and it is highlighted the relation between the engine operating conditions and the functional parameters of the automotive mufflers.

Vibration based fault detection and diagnose analysis is a well established field in machine or monitoring supervision. The vibration diagnose is also suited for the miniature ball bearings monitoring. The typical balls size starts at 3 mm with the bearing outer diameter of maximum 20 mm. Ball bearings of this size are ideal for precision mechanisms, they are able to carry light loads and they are perfect for handheld medical equipment and tools which must be very small but also very precise and durable. The paper presents experiments carried out on a fully instrumented universal CETR micro-tribometer at room temperature. The tested miniature ball bearing, lightly loaded and operating at low speeds, is subjected to dry and lubrication conditions with two different oil viscosities. A comparative study is realized concerning the vibration diagnose potential using the FFT analysis of the bearing acquired signals. Statistical analysis of the vibration signals is a key point in the detection of the overall vibration level of bearings lubricated with oils of different viscosities.

Some of the aspects of the vehicle suspension limiting performances from stress and vibrations point of view have been explored in this study. The vehicle is modeled as two DOF system and the suspension is considered a passive one. 3D CATIA model was built for both the spring and spring-damper ensemble, neglecting the tire influence. This can reasonably covers the studies of geometries and forces (bending or tensile stress), masses and stiffnesses (meaning vibration profiles). The theoretical analysis on the vibration behaviour of the spring-damper ensemble, regarded as the vehicle suspension, suggests a convenient operation regime at low frequencies below 15 Hz, if the damper piston displacement is limited.

Gear mechanisms are widely used in technical applications, mainly for transmitting rotational motion between two axes with constant transmission ratio via a higher pair. Significant friction energy loss in the pair between teeth highlights the importance of estimating the mechanical work lost by friction within this contact. In a previous study, the coefficient of rolling friction between a cylindrical body and a flat face body was found based on the decrease of oscillations amplitude of a cycloidal pendulum. The basic idea of the present paper follows the observation that in the case of a gear mechanism, the relative motion between the wheels can be taken as relative motion of their axodes. In this regard, a pendulum obtained from a mobile cylindrical gear with attached rod and a fixed corresponding rack is considered. The law of motion of the cycloidal pendulum is applied for the proposed pendulum and an “equivalent rolling friction coefficient” which characterises the friction between the teeth of the pinion and the rack is found. The differential equation modelling the motion of the pinion-rack pendulum is difficult to obtain, which is explained by the analysis of the involute gear field of a general cylindrical gear mechanism.

Bearing condition monitoring confronts the most machine users. Diagnostic methods used to include bearing problems represent one of the most important challenges. The scuffing phenomenon initiation of the bearing elements produces an important increase in the vibration level and can be emphasized by the analysis of the bearing friction forces which are the most sensitive indicator of the bearing failure. Commonly used technique for damage detection is the vibration signature analysis that must be carefully utilized in conjunction with the friction torque monitoring through the strain gauges measurements. In order to detect the scuffing onset, the paper presents an experimental setup for the scuffing tests performed on a 7206 ball bearing. A virtual instrument monitoring the friction force respectively the braking torque was created. An accelerometer captures the signal from the bearing outer ring then it is processed using PCI-4451 National Instruments data acquisition board and LabVIEW soft.

The vibration analysis aims to extract features from the measurements in order to be used for fault detection and diagnosis. Vibration response measurement is an important and effective technique for the detection of the defects in rolling element bearings. The corresponding analysis methods operate in the time domain, in the frequency domain and recently in the time-frequency domain. A quantitative determination of the defect severity and its development are useful to be determined in order to estimate the remaining useful ball bearing life. Experimental data from a bearing with a defect are collected by an accelerometer then processed to identify the passing time of a ball over a defect. The paper presents a computation model corroborated to an experimental investigation to establish the defect length of a ball bearing inner race.

To realize an efficient car suspension control (for instance in technical inspection) it is important to use easy measurable variables. This is the reason for developing optimization techniques in order to simplify and improve the engineering design process. The paper presents an optimization process of a torsion bar spring included in the car suspension involving the following steps: modeling and analyzing the torsion bar spring behaviour, definition of the optimization objective and the specifications for the proposed solution choosing an appropriate methodology to satisfy the design objectives. It has been used a Min-Max optimization method to highlight the vibration response (in terms of RMS) of the system. CAD analysis and MatLAB optimization are performed on the car suspension elastic element and the obtained results provide an optimum vibrational response and constructive design. This combination of these analyses can be considered an efficient tool in order to ensure the driver and passengers comfort according to the standards.

Transformable structures in architecture can change their shape or function in response to varying climatic conditions, changing environment and needs for different functional requirements or to emergency situations. Depending on how the transformation is doing, transformable structures can be deployable or demountable, as a kit-parts system. Deployable structures can also be divided in four main groups: spatial bar structures; foldable plate structures; tensegrity structures; and membrane structures. In this paper, some planar bar mechanisms proposed by Ten Fold Engineering company, which can be integrated in deployable structures, will be discussed.

The goal of vibration analysis is to extract features from the measurements x (t) or x (kT0), T0 sampling time, to be used for fault detection and diagnosis. The corresponding analysis methods operate in the time domain (autocorrelation functions, power cepstrum, crest and kurtosis factors), in the frequency domain (Fast Fourier Transform FFT, maximum entropy spectral estimation, envelope analysis) and recently in the time-frequency domain. Time-frequency analysis methods represent efficient alternatives to detect bearings damage due to non-stationary impact signals. In this case, the short-time Fourier transform (STFT) or the Wavelet transform are applied. The paper presents a comparative study of some methods used in bearing faults detection (the envelope spectrum and the wavelet transform). A monitoring tool acquires experimental data from a bearing vibration control test rig. An accelerometer captures the signal from the bearing outer ring then it is processed using PCI-4451 National Instruments data acquisition board and LabVIEW soft.

Heating, ventilating and air-conditioning (HVAC) systems represent a major source of inside buildings noise with a negative effect on the acoustical environment. Therefore, it is necessary to add attenuation to the system. This is provided by sound attenuators or silencers manufactured in different geometrical configurations and with various absorptive lining materials. The paper deals with the insertion loss, as a performance criterion for in-duct noise, of some dissipative silencers types. The measured data are compared in order to establish the efficiency of every tested silencer type. Third-octave band analysis of random noise of an air handling unit (AHU) from a HVAC system is realized without and with silencers (ducts fitted). Insertion loss measurements are made in an anechoic room using a test facility that agrees the requirements of ISO 7235:2009. The results highlight the effects of the silencers geometry, pressure-air flow and loading relations upon the sound attenuation level. The silencers selection could be a difficult task for the designers which have to consider all these parameters.

The HVAC (Heating, Ventilating and Air Conditioning) beneficiaries are in particular annoyed by the noise generated from the radiant unit and the air circulating ducts, since they are located inside the rooms and buildings. The comparatively experimental results highlight the relations between the air flow, pressure, power-charging and the sound level. The measurements are carried out at different fan's speeds, ranging the power-charge from 30-100% while the duct air flow is slowly adjusted from full open to full closed, between 0-500 Pa. Third-octave band analysis of random noise of the handling units is realized in an anechoic room, using the measurement procedures that agrees the requirements of the ISO 3744:2011 and ISO 5136:2010 standards. For an accurate design of the HVAC system, the designer needs to know not only the sound power of the radiant unit, but also from all of the air paths, since the sound travels along with the conditioned air. The experimental methodology used in the paper is of real interest for the HVAC manufacturers, in order to rate the sound level of their products and to improve the noise attenuation.

HVAC system represent major source of buildings internal noise and therefore they are designed to provide a human acoustic comfort besides the thermal and air quality requirements. The paper experimentally investigates three types of commercial air handler units (AHU) with different ducts cross-section sizes and inlet-outlet configuration. The measurements are performed in an anechoic room. The measurements are carried out at different fan's speeds, ranging the power-charge from 30-100% while the duct air flow is slowly adjusted from full open to full closed, between 0-500 Pa. The sound pressure levels of the radiant units are rated using NR curves. Also, the supply and the outdoor ducts sound levels are compared in order to point the frequencies where the noise must be reduced. Third-octave band analysis of random noise of an air handling unit from a HVAC system is realized, using measurement procedures that agrees the requirements of the ISO 3744:2011 and ISO 5136:2010 standards. The comparatively results highlight the effects of the geometry, air flow pressure and power-charging dependencies upon the sound level. This is the start for a noise reduction strategy.

Turbocharger rotors for the spark and compression ignition engines are resistant steels manufactured in order to support the exhaust gas temperatures exceeding 1200 K. In fact, the mechanical stress is not large as the power consumption of these systems is up to 10 kW, but the operating speeds are high, ranging between 30000 ÷ 250000 rpm. Therefore, the correct turbochargers functioning involves, even from the design stage, the accurate evaluation of the temperature effects, of the turbine torque due to the engine exhaust gases and of the vibration system behaviour caused by very high operating speeds. In addition, the turbocharger lubrication complicates the model, because the classical hydrodynamic theory cannot be applied to evaluate the floating bush bearings. The paper proposes a FEM study using CATIA environment, both as modeling medium and as tool for the numerical analysis, in order to highlight the turbocharger complex behaviour. An accurate design may prevent some major issues which can occur during its operation.