Thermal energy storage (TES) is likely to play a significant role in the decarbonisation of domestic heat, allowing consumers to shift their energy consumption away from peak demand periods and reducing overall strain on the grid. Phase change materials (PCMs) are a promising option for TES, in which energy can be stored in the latent heat of the melting of the PCM; these offer greater storage densities than sensible heat TES and have the benefit of releasing stored heat at a consistent temperature (the crystallisation temperature of the PCM). One of the key difficulties for PCM-based TES is state of charge (SoC) estimation (the estimation of the proportion of energy stored in the TES unit up to its maximum capacity), particularly during idle periods while the unit is storing heat. SoC estimation is key to the implementation of TES, as it enables the effective control of the units. The use of a resonator within the PCM for SoC estimation could potentially provide a global estimate of the SoC, since the resonator passes through the full depth of the PCM in the unit. The SoC could be inferred by measuring the vibrational response of the resonator under excitation, which varies depending on the melt state of the PCM. This paper presents findings from a test rig investigating this proposal, including discussions on the features required from the resonator response for SoC inference.

Motorcycle helmets are generally thought to be only protection of motorcycle drivers against head injuries as well as loud noise in traffic. While there have been several papers on noise elimination capabilities of motorcycle helmets, no controlled study has been reported to compare different types of test conditions in literature. The purpose of this study is to assess noise reduction capacities of a motorcycle helmet under different types of acoustical loadings as well as environments and to identify better test condition. Firstly, a Head & Torso simulator with and without the motorcycle helmet in a built acoustical cabinet was exposed to digitally generated sound to investigate insertion loss values. Besides, the Head & Torso simulator was fixed onto a motorcycle to simulate actual driving conditions. Sound pressure levels were captured at the ear level to obtain insertion loss values in case of motorcycle noise for different engine speeds. By comparing calculated insertion losses, it was revealed that considerable differences existed between tests for different conditions. Beneficial interpretations were deduced and thus, a practical solution was presented for accurate measurements acoustic performance of the motorcycle helmets in laboratory conditions.

The first author has been teaching the postgraduate course, “The Dynamics of Mechanical Systems” in The ITU Faculty of Mechanical Engineering for nearly 20 years. He has observed that students frequently have problems in obtaining the equations of motion of the vibrating systems which were placed on moving bases. Starting from this observation, he has found that the homework stated below, which was given to the students occasionally, was very helpful in learning the subject. The main idea of the homework is the derivation of the equations of motion, with the help of formulating the Lagrange’s equations with respect to a moving set of axis for a vibration system with two degrees of freedom which consists of a horizontal table rotating with a constant angular velocity around a vertical axis. The students were also asked to solve the same problem with a different method of their choice and to determine the reaction forces as well. We want to share this problem with the reader, which we have assessed as very instructive and appropriate from the viewpoint of applicability of different methods.

Granular dampers are utilised to control vibration in a wide range of industries, including automotive, aerospace, machine tool and civil engineering applications, where their robustness, tolerance of harsh environments and freedom from maintenance make them attractive where conventional damping treatments cannot be used. The energy dissipation of a granular damper is governed by the collective motion of the particles, which is normally predicted using discrete element simulations that are computationally demanding. This paper examines how far this collective motion can be described by a simple kinematic model in which the granular medium is treated as a single rigid body that detaches from the enclosure, travels freely under gravity, and collides inelastically with the enclosure ends. Conditions are obtained for the detachment and re-contact instants and for the excitation amplitudes at which the collective collisions are most effective. The predictions are compared with previously reported discrete element simulations and measurements of the dissipated power of a cylindrical damper excited at different frequencies. The model reproduces the simulated collective velocity histories and locates both optimum amplitudes with acceptable accuracy. The simple models fail in the intermediate amplitude range, where the collective motion extends over several excitation periods, and at high frequencies, where the compliance of the medium becomes important. Within these limits, the model can support the early sizing of dampers for practical applications at a small fraction of the computational cost of the simulations.

The acoustic performance of a motorcycle helmet is normally evaluated as a single insertion-loss spectrum obtained for one direction of sound incidence. Such a description says nothing about how the attenuation varies with the direction from which sound arrives, nor about what the helmet does to the level difference between the two ears on which horizontal localisation depends. This work sets out a measurement and analysis approach for the missing description and applies it to one full-face specimen, which serves as the demonstration case and as a reference data set rather than as a sample representing helmets as a class. In this work, the insertion loss of a full-face helmet is, therefore, obtained binaurally by employing a head-and-torso simulator in a hemi-anechoic room, at closely spaced azimuth positions across the frontal horizontal plane and for the unhelmeted, closed-visor and open-visor conditions. The complete matrix is acquired in two independent sessions, each with a separate fitting of the helmet, and every derived quantity is reported together with the range it takes across those two fittings. Insertion loss is strongly frequency-dependent and becomes negative at low frequencies, where the enclosed cavity amplifies the sound field, and its magnitude varies with the direction of incidence. Closing the visor adds attenuation at mid and high frequencies but deepens the low-frequency amplification, which is consistent with the cavity-resonance interpretation. Referring to the ear under consideration, the broadband insertion loss increases towards the side on which the source lies. Fitting the helmet compresses the interaural-level differences available across the frontal hemisphere and flattens their variation with azimuth angle near the median plane. Both fittings reproduce the compression. The span of the band-averaged interaural-level difference falls to 32% of the unhelmeted value in one of them and 33% in the other, while the mean of the individual per-band spans between 500 Hz and 8 kHz falls to a fraction lying between 43% and 60% depending on the fitting, so that the direction of the effect is a property of the specimen, and the per-band magnitude is, in part, a property of the fitting. The results are reported as measured insertion loss and interaural-level-difference changes for this specimen; no listening experiment was performed, and no inference is drawn about localisation performance or about full-face helmets as a class. A directional, two-eared characterisation nevertheless yields information that single-direction reporting cannot, and the protocol and the data given here are intended as the reference against which further specimens can be compared.