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Early stage of underwater electrical wire explosion was observed by shadowgraph. By decreasing initial energy, the early stage of wire explosion was slowed down and possible to capture shadow photos during phase transitions. The vaporization process of wire is usually axially non-uniform due to random local micro explosions along the wire. The degree of non-uniform will be significantly decreased when increasing the initial energy. During explosion of the wire, more than one shock waves were generated not only from phase transition, but also from different pulses of deposition power. A modified piston model was introduced to explain the phenomenon.

Engine efficiency and emissions depend on the fuel atomization and dispersion. The fuel atomization and dispersion depend heavily on the ambient pressure and temperature. In this work, to study Diesel sprays in engine conditions, an electrically heated, constant-volume, pressurized vessel was designed and manufactured. The controlling electronics and software were developed and tested to ensure safe and precise operation. A commercial Bosch six-hole automotive Diesel injector was used. The spray spatial and temporal development were studied. In the literature, spray liquid length and cone angle are extensively used to quantify fuel dispersion. In this work, these parameters were quantified using a high-speed shadowgraph technique. Models were derived to describe the temporal evolution of the liquid core. Such models can be used to predict the Diesel spray behaviour and the engine performance.

Visualizing two variables in the fluid flow requires a complex optical system to fulfill such a purpose. Furthermore, in these applications, measuring the temperature fields of the fluid is sometimes necessary. In this work, we use a color digital camera to record in one snapshot shadowgraph and two direction sensitivity Schlieren images. Furthermore, the Schlieren images obtained are used to measure temperature fields. The optical system, as main components, employs an rgb Light Emitting Diode (LED), two knife edges represented by shortpass and longpass ultra-thin filters, and a color digital camera. The results of this study show that shadowgraph images are contaminated with the crosstalk effect, and correction against it was applied. On the other hand, the reached resolution of the optical system to measure temperature values is approximately one degree.

In this paper, we define new graph operations F-composition F (G)[H], where F (G) be one of the symbols S(G),M(G),Q(G),T(G),Λ(G),Λ[G],D2(G),D2[G]. Further, we give some results for the Wiener indices of the these graph operations.

Resumo A utilização de experimentos é uma das formas mais eficientes para o ensino de física, uma vez que os alunos tornam-se mais motivados quando conceitos teóricos fundamentais são associados a aplicações tecnológicas. O desenvolvimento de carros, aeronaves e foguetes, por exemplo, requer o conhecimento detalhado dos escoamentos de fluidos ao redor e no interior desses veículos. O presente artigo descreve os fundamentos da óptica geométrica em meios heterogêneos e apresenta as técnicas ópticas shadowgraph e schlieren que são amplamente utilizadas em centros de pesquisa, universidades e empresas no estudo da aerodinâmica e dos escoamentos em geral. Esses métodos ópticos são baseados na deflexão dos raios de luz causada por variações na massa específica do escoamento. O método schlieren-Toepler é apresentado e discutido em detalhes, derivando-se equações para o contraste, sensibilidade e o alinhamento óptico. Uma implementação do método shadowgraph direto para uso em sala de aula é demonstrada e, ao longo do artigo, são apresentadas diversas imagens obtidas pelos métodos ópticos descritos.

Pulsed laser ablation in liquid (PLAL) is gaining an important role as a methodology for producing nanostructures without the use of chemicals and stabilizers. Several nanomaterials have been produced and the engineering of PLAL is becoming an important task for the dissemination of this approach for nanostructure production. Monitoring the processes involved in the PLAL during nanostructure production can be extremely useful for improving the experimental methods and for pushing PLAL to new material formation. In this paper, we discuss the use of optical techniques for investigating the specific stages involved in the production of nanomaterials with PLAL. In particular, the recent advancements of these optical techniques for each specific stage of the PLAL process will be discussed: optical emission spectroscopy and imaging for the investigation of the plasma phase, shadowgraph imaging for the investigation of the cavitation bubble dynamics and different scattering techniques for the visualization of the produced nanostructure.

The erosion behavior of a cavitating jet on groove roughness was investigated experimentally using mass-loss characteristics, scanning electron microscopy (SEM) observation, time-resolved shadowgraph, and schlieren flow visualizations. The wall morphology of the cavitating-jet erosion on the groove roughness indicated an increased mass loss, which was highly increased along the groove rather than across the groove. Furthermore, increased erosion pits were observed on the groove bottom along the grooves. The shadowgraph imaging of the cavitating jet on the rough wall showed noncircular cavitation bubble distributions along and across the grooves, which corresponds to the increased number of cavitation bubbles along the grooves and the decreased number of bubbles across the grooves. This result is consistent with the erosion morphology of the groove roughness. Schlieren imaging indicated that the frequency and intensity fluctuation of the shockwave formation did not change significantly on the groove roughness along and across the grooves. The findings in the study show that the increased erosion mechanism on groove roughness is caused by the increased number of impulsive forces and the shockwave focusing effect on the groove bottom.

This study investigated gasoline–biodiesel blended fuel (GB) subjected to a fuel spray development process on macroscopic and microscopic scales. The four tested fuels were neat gasoline and gasoline containing biodiesel (5%, 20%, and 40% by volume) at three different ratios. The initial spray near the nozzle revealed that the spray penetration and spray tip velocity both decreased with decreasing biodiesel blending ratio. In addition, the different spray tip velocities at the start of spraying result in different atomization regimes between the fuels. The GB fuels with a low biodiesel blending ratio were disadvantaged in terms of spray atomization due to their lower spray penetration and tip velocity. The macroscopic spray penetration changes were similar to those observed in the microscopic spray. The fuel with the lower biodiesel blending ratio had a larger spray cone angle, indicating increased radial spray dispersion.

Experimental characterization of the burning behavior of gaseous mixtures has been carried out, analyzing spherical expanding flames. Tests were performed in the Device for Hydrogen-Air Reaction Mode Analysis (DHARMA) laboratory of Istituto Motori—CNR. Based on a high-pressure, constant-volume bomb, the activity is aimed at populating a systematic database on the burning properties of CH4, H2 and other species of interest, in conditions typical of internal combustion (i.c.) engines and gas turbines. High-speed shadowgraph is used to record the flame growth, allowing to infer the laminar burning parameters and the flame stability properties. Mixtures of CH4, H2 and air have been analyzed at initial temperature 293÷305 K, initial pressure 3÷18 bar and equivalence ratio = 1.0. The amount of H2 in the mixture was 0%, 20% and 30% (vol.). The effect of the initial pressure and of the Hydrogen content on the laminar burning velocity and the Markstein length has been evaluated: the relative weight and mutual interaction has been assessed of the two controlling parameters. Analysis has been carried out of the flame instability, expressed in terms of the critical radius for the onset of cellularity, as a function of the operating conditions.

This paper reports an experimental result of expansion wave and cavitation bubble generation by underwater shock wave reflection at the interface for understanding of shock wave interaction phenomena related to the mechanism of shock wave human tissue damage. Underwater shock wave was generated by detonating a micro-explosive (silver azide pellet). The process of underwater shock wave reflection at the interface, expansion wave and cavitation bubble generation were visualized by shadowgraph method and recorded by an ultra-high-speed framing camera at high spatiotemporal resolution. The pressure time history near the interface in water was measured simultaneously by a needle hydrophone. High-speed shadowgraph sequential images show that a compression wave (shock wave) was reflected from a thin interface plate (Polystyrene, acrylic, Teflon, thickness of t=0.5 mm), and expansion wave was then generated in water by reflection from the air. In addition, a cavitation bubble was created behind the expansion wave. The simultaneously measured pressure history also shows that an expansion wave propagated behind shock wave. The negative peak pressure of expansion wave in the case of a thin plate shock wave interaction was larger than that in water surface interaction.

Recently, there has been intense interest in small dense plasma focus (DPF) devices for use as pulsed neutron and X-ray sources. Although DPFs have been studied for decades and scaling laws for neutron yield versus system discharge current and energy have been established (Milanese, M. et al., Eur. Phys. J. D 2003, 27, 77–81), there are notable deviations at low energies due to contributions from both thermonuclear and beam-target interactions (Schmidt, A. et al., Phys. Rev. Lett. 2012, 109, 1–4). For low energy DPFs (100 s of Joules), other empirical scaling laws have been found (Bures, B.L. et al., Phys. Plasmas 2012, 112702, 1–9). Although theoretical mechanisms to explain this change have been proposed, the cause of this reduced efficiency is not well understood. A new apparatus with advanced diagnostic capabilities allows us to probe this regime, including variants in which a piston gas is employed. Several complementary diagnostics of the pinch dynamics and resulting X-ray neutron production are employed to understand the underlying mechanisms involved. This apparatus is unique in its employment of a 50 fs laser-based shadowgraphy system that possesses unprecedented spatio-temporal resolution.