Maximum Oscillation Amplitude Research Articles

Study on the molten pool behavior and porosity formation mechanism in dual-beam laser welding of aluminum alloy

Based on the mechanism of dynamic coupling between molten pool and keyhole, a three-dimensional (3D) transient model for the dual-beam laser welding of aluminum alloy is established by considering the surface tension, Marangoni force, and recoil pressure. The morphology of the molten pool, porosity formation process, and the heat transfer mechanism during the process of laser welding under different parameters are analyzed. A double rotating 3D Gaussian heat source is used to represent the laser beam, and the volume of fluid method is used to track the gas-liquid free surface, and the gas-liquid interface force is transformed by the continuous surface force model. The results show that in the process of dual-beam welding, the interaction between the two keyholes enhances the fluid flow perpendicular to the spot line, and the shape of weld pool surface changes from elliptical to circular. Furthermore, welding speed and spot spacing have a significant effect on the shape of the molten pool. Furthermore, it is observed that dual-beam welding can improve the stability of the keyhole and reduce the maximum oscillation amplitude and the number of keyhole breakups. At a specific spot spacing, a unique process of separation and fusion is discovered in addition to the common stages of growth, maintenance, breakup, and shrinkage of the keyhole. The simulation results are in good agreement with the existing experimental results. Overall, this paper provides useful insights into the dynamics of the molten pool in dual-beam welding and reveals the molten pool behavior and porosity formation mechanism.

Temperature dependence of internal mechanical losses of gypsum stone with complex composition and structure

Experimental studies of the temperature dependence of internal mechanical losses in terms of Q−1 in the range from 25 to 120 °C used gypsum stone specimens from the Novomoskovskoye deposit (Tula region, Russia). This investigation is important to determine optimal modes of heat treatment of gypsum stone to obtain construction gypsum. The specimens were cylinders 40 mm in diameter and 75 mm in length with piezoelectric transducers at the ends. They included three types of rocks: gypsum, flint, and thin coal interlayers. The groups included specimens consisting of gypsum without flint layers, two layers consisting of a gypsum layer at one end and a flint layer at the other, and three layers with a flint layer in the middle part of the specimen. Losses Q–1 were determined as f0/(fmax – fmin), where fmax and fmin were frequencies at the level of 1/√2 of the maximum amplitude of sample longitudinal oscillations at the resonance frequency f0. In the temperature range up to 80 °C, the loss Q–1 increased monotonically, while the resonance frequency f0 decreased. There were two maxima of Q–1 and f0 at 85 and 110 °C. The phase transitions of gypsum from dihydrate to hemihydrates (α- and β-hemihydrates) and then to the anhydrous state (dehydrate) caused these maxima.

The effects of compression ratio and combustion initiation location on knock emergence by using multiple pressure sensing devices

Knock research is an essential study because knock limits spark-ignition (SI) engine power output, durability, noise, fuel consumption, and emission performance. The thermal efficiency of an engine can be improved by increasing the compression ratio, but at the same time it leads to the possibility of end gas autoignition inside the chamber. The objective of this work was to show the effect of three different compression ratios (CRs) 8.5, 9.5, and 10.5 on the mechanism of knock. In order to achieve this four equispaced spark plugs were fitted around the circumference of a special metal liner to initiate flame fronts from those plugs by firing with different spark approaches (e.g. spark timing, number, and location). In addition, six pressure sensors were installed at various locations to precisely record the autoignition event by monitoring pressure oscillations, combustion characteristics, and knock intensity. In-cylinder pressure and heat release rate (HRR) analyses were applied to distinguish the knocking combustion for the three different CRs. The results showed that a greater number of spark plugs produced more stable combustion even for a delayed spark timing (ST) than a single spark plug, but also increased pressure oscillations, HRR and knock propensity with higher CRs due to an increase in pressure and temperature inside the cylinder. The maximum amplitude of pressure oscillation (MAPO) method was used to determine the knock intensity, and it was observed that at the lowest CR of 8.5 three spark plugs gave higher MAPO values compared to four spark plugs for the same operating conditions. However, four spark plugs instigated higher MAPO values than three spark plugs for the higher CRs of 9.5 and 10.5 because, with the increase of CR and spark plug numbers, the pressure and temperature were increased during the combustion event, which was coupled with the compression effect on the unburned end gas mixture. Additionally, Fast Fourier transform (FFT) and wavelet methods were implemented to observe the frequencies induced during knock. It was found that sparking four plugs provoked various vibration modes in different amplitude ranges with the different CRs.

Исследование акустических характеристик одиночной сверхзвуковой струи, истекающей в затопленное пространство

In this paper, the acoustic characteristics of a single supersonic jet flowing from a nozzle of a rocket engine into a flooded space at different pressure ratios are studied. A system of the Favre-averaged Navier-Stokes equations is used to describe the unsteady flow of a viscous compressible heat-conducting gas in a supersonic Laval nozzle and an outflowing jet. The system is enclosed by the ideal gas law. The implementation of the physical and mathematical model and the numerical studies are carried out using the OpenFOAM Extended open platform based on the modified dbnsTurbFoam solver. A conical nozzle with an opening angle of 45° at the Mach number of 3 at the nozzle exit is considered in this study. Air is used as the working gas. Amplitude-frequency spectra of acoustic radiation at the point located at a distance from the nozzle outlet are obtained at different pressure ratios of the outflowing supersonic jet. Analysis of the amplitude-frequency characteristics of the jet under study shows that the maxima occur mainly at low frequencies. The maximum oscillation amplitude for the considered jet configurations is revealed at a pressure ratio of 1 on a frequency of 787 Hz. The maximum sound pressure level is 149 dB.

Mass transfer intensification by means of resonance oscillations in a pulsation apparatus with a central tube with and without nozzles

An experimental study of resonance and non-resonance oscillations in a pulsating apparatus with a central tube was performed. Pulsating apparatus in two configurations was thoroughly investigated in the following way: (i) pulsating resonance apparatus with central tube, without nozzles and (ii) pulsating resonance apparatus with central tube, an additional tube, and nozzles. The following parameters were investigated as criteria for the onset of resonance: the liquid surface oscillations amplitude, the gas pressure oscillations amplitude in a gas-filled elastic element, the solid particles dissolution rate. A comparative analysis showed that the resonance frequencies, determined by the maximum amplitude of the liquid surface oscillations, by the gas pressure fluctuations and the dissolution rate of solid particles, are in good agreement with each other and with the theoretical value. The pressure pulsations were found as an easy and reliable for resonance identification. The dissolution rate of KOH particles increases up to 4–6 times at resonance frequency. At the same energy dissipation rate possesses approximately 10 times larger values of the liquid-solid mass transfer coefficient compared to the stirred tanks. With a decrease in the volume of a gas-filled elastic element, the amplitude of the oscillations at resonance increases, which is consistent with theory.

Determining the energy efficiency of a resonance single-mass vibratory machine whose operation is based on the Sommerfeld effect

This paper reports determining the energy efficiency of a vibratory machine consisting of a viscoelastically fixed platform that can move vertically, and a vibration exciter whose operation is based on the Sommerfeld effect. The body of the vibration exciter rotates at a steady angular speed while there are the same loads in the form of a ball, a roller, or a pendulum inside it. The load, being moved relative to the body, is exposed to the forces of viscous resistance, which are internal within the system. It was established that under the steady oscillatory modes of a vibratory machine's movement, the loads are tightly pressed to each other, thereby forming a combined load. Energy is productively spent on platform oscillations and unproductively dissipated due to the movement of the combined load relative to the body. With an increase in the speed of the body rotation, the increasing internal forces of viscous resistance bring the speed of rotation of the combined load closer to the resonance speed, and the amplitude of platform oscillations increases. However, the combined load, in this case, increasingly lags behind the body, which increases unproductive energy loss and decreases the efficiency of the vibratory machine. A purely resonant motion mode of the vibratory machine produces the maximum amplitude of platform oscillations, the dynamic factor, the total power of viscous resistance forces. In this case, the efficiency reaches its minimum value. To obtain vigorous oscillations of the platform with a simultaneous increase in the efficiency of the vibratory machine, it is necessary to reduce the forces of viscous resistance in supports with a simultaneous increase in the internal forces of viscous resistance. An algorithm for calculating the basic dynamic characteristics of the vibratory machine's oscillatory motion has been built, based on solving the problem parametrically. The accepted parameter is the angular speed at which a combined load gets stuck. The effectiveness of the algorithm has been illustrated using a specific example

Numerical investigation on knock characteristics and mechanism of large-bore natural gas dual-fuel marine engine

This work revealed the unique knock characteristics and mechanism of large-bore natural gas dual-fuel Marine engine with flame jet and strong swirl by a novel three-dimensional pressure difference method to further reduce the knock tendency. The knock characteristics were investigated by pressure monitoring points distributed in different spaces. The results indicate that, owing to the large cylinder bore, almost no pressure oscillations were found in the center position, whereas, severe pressure oscillations appeared at the edge. The pressure difference results illustrate that the movement of the high-pressure area and the low-pressure area tends to the low-frequency resonance mode (1,0), which manifests as an axial rotation following the swirl motion direction. Furthermore, the pressure difference method combined with the maximum amplitude of pressure oscillation (MAPO) method and energy distribution slices was adopted to explore the knock mechanism. The results show that the large-bore natural gas engine has a special knock mechanism which can neither be attributed to the end-gas self-ignition theory nor completely flame acceleration theory. The knock mechanism is that the flame jets from the prechambers cause the uneven initial pressure distribution, and the uneven pressure distribution is strengthened by the uneven heat release on the flame surface. This knock mechanism was confirmed by changing the pilot fuel mass and equivalence ratio subsequently. By the way, a knock suppression method by reducing the pilot fuel was proposed based on the knock mechanism.

Optical diagnostics and multi-point pressure sensing on the knocking combustion with multiple spark ignition

Engine knock is an abnormal combustion phenomenon that limits the thermal efficiency and service life of spark-ignition engines. A better understanding of the knock mechanisms and characteristics is beneficial to knock alleviation and engine efficiency improvement. In this study, a metal liner with four evenly-spaced spark plugs in the periphery of the combustion chamber is designed to initiate knock from different positions. Four spark strategies are applied to the single-cylinder optical research engine and six pressure sensors are utilized to analyze the local pressure oscillations in the cylinder. The knocking combustion is investigated by simultaneous 72 kHz high-speed imaging and 6-point pressure sensing. The experimental results indicate that using multiple spark-ignition could promote knock intensity, advance the start of auto-ignition and introduce more acoustic resonance modes. The center pressure sensor is more sensitive to the first radial resonant mode (0, 1) of the knock pressure oscillation, while the side sensors are more sensitive to the first and second circumferential resonant modes (1, 0) and (2, 0). The knock onset judged by natural flame photography is earlier than that by pressure analysis because the auto-ignition event happens first and induces the subsequent pressure fluctuation. Natural flame luminosity analysis demonstrates that the initial auto-ignition sites only cause weak pressure oscillations, and the instantaneous combustion of the remaining end-gas increases the heat release rate significantly and gives rise to more violent pressure oscillations. Statistically, the maximum amplitude of pressure oscillation follows an exponential relationship with the peak mean flame luminosity. The end-gas resides in the gaps among the flame fronts generated by different spark strategies while the first auto-ignition sites are not evenly distributed in the end-gas zone. This fact gives insights into the local temperature non-uniformity of the end gas zone that affects the spatial distributions of the initial auto-ignition sites in the cylinder.

Phase Diagram of Sub‐GHz Electric‐Field‐Induced Polarization Oscillation

Polarization oscillation under GHz electric field stimuli is a key issue for the future development of ultrafast sensor devices. An ultrafast phase‐field model is developed to study the phase diagram of polarization oscillation under sub‐GHz electric field for Pb(Zr,Ti)O3. At the morphotropic phase boundary region, the polarization and strain oscillation show maximum amplitude (electric field stimuli frequency <0.1 GHz). The phase difference of π/2 between the input of electric field and the polarization response, which can be tuned by the frequency of ac electric field stimuli, can lead to a maximum of polarization oscillation amplitude (electric field stimuli frequency >0.1 GHz). Moreover, under this phase difference, the polarization oscillation amplitude can be increased furthermore with the increasing ac electric field strength. With the absence of a phase transition, it is found that the polarization component along the z‐direction has a maximum oscillation amplitude of 0.2, and the strain has a maximum oscillation amplitude of 0.35%. The results provide useful guidance to explore and manipulate dynamic functionalities of ferroelectric sensing materials.

SLOW OSCILLATIONS IN DRIVES OF MACHINE ASSEMBLIES

Machine assembly with additional degrees of freedom is considered. The method of direct separation of motions was used for research. It was shown that the braking vibration moment occurring by the reason of resonance effects in the driven object can lead to excitation of rotor oscillations of the assembly with a occurrence of slow oscillations of the vibration exciter rotor is demonstrated. frequency lower than the rotation frequency. Slow rotor oscillations represent a transient process to the stationary motion mode, which is established when an additional load torque occurs. Moreover, the maximum oscillation amplitudes will be relatively large. By the example of a vibration machine with an inertial drive, the occurrence of slow oscillations of the vibration exciter rotor is demonstrated.

برداشت انرژی با استفاده از تیر بایمورف متخلخل با لایه پیزوالکتریک تحت ارتعاشات القایی ناشی از جریان سیال خارجی

In this study, energy harvesting by porous beams exposed to external fluid flow is studied analytically. The nonlinear electromechanical non-linear differential equations governing the transverse vibration of porous beams under external fluid flow have been extracted using Euler-Bernoulli beam theory and Hamilton's principle. A cantilever bimorph beam with a concentrated mass at its end, which is equipped with piezoelectric layer, is considered as an energy harvesting system. After solving the nonlinear equations of motion, the effect of different parameters on the amount of harvested energy is examined. The results show that in the areas of the lock-in phenomenon, the amount of harvested energy by the beam has its maximum value. Also, the porosity distribution has significant effect on the maximum amplitude of oscillations, as well as the energy harvested by the porous beam. The lock-in phenomenon for the porous beam with distribution of symmetrical porosity (wall stiffness), asymmetric porosity distribution and uniform porosity distribution is taken around u=0.15. In addition, for electrical resistance R = 100kΩ, the maximum voltage generated for the bimorph porous beam by the distribution of symmetrical porosity in the wall stiffness, asymmetric porosity distribution and uniform porosity distribution is 0.39V, 0.44V and 0.57V, respectively.

Statistical study on engine knock oscillation and heat release using multiple spark plugs and pressure sensors

Engine knock has been an inherent problem that limits engine efficiency improvement and threatens engine service life. To trigger the controllable knock, a specialized liner with installing four side spark plugs mounted on the cylinder head are used in this study to produce various in-cylinder flame propagation. Various spark strategies (e.g., spark timing, spark number, spark location) are applied to generate different auto-ignition sites and knock characteristics. Up to five channels of pressure signal are collected to analyze the knock intensities regarding different spark strategies. To investigate the knock-induced fluctuations and heat release, we use the multiple correlations to evaluate the maximum amplitude of pressure oscillation (MAPO) respecting different influential factors and building a multiple linear regression (MLR) model for MAPO prediction and validate it against the experiment results. Besides, the Wiebe function and curve-fitting techniques are applied to estimate the energy released by auto-ignition in each cycle, and its relations with knock intensity are assessed. The results show that the average growth of pre-oscillation plays an important role in MAPO value (correlation coefficient, r_s = 0.965), the established MLR model possesses high accuracy for MAPO prediction. The pressure oscillation regarding the 1st resonance mode is extracted from the band-pass filtered signal, representing the main pressure oscillating process. Compared with the single spark ignition, triggering more spark plugs could boost the fuel consumption rate, while shortening the knocking combustion duration and reducing the heat release fraction contributed by auto-ignition. At the same CA50 (9 CAD aTDC), the four spark ignition leads to the least heat release fluctuations than other spark strategies. With advancing the CA50, the heat release fraction produced by knock increases at first then reduces due to the thermodynamic conditions and the flame propagation. Activating two or three spark plugs, the rising rate of the heat release rate goes up, but the knock-induced heat release fraction decreases. Moreover, the primary acoustic resonance mode (1, 0) gives more regular knock vibrations than the mixing form (including mode (1, 0), (0, 1), (2, 0), etc.), the average traveling distance of acoustic wave in the time gap of receiving two continuous signals is very close to the cylinder bore. The results give insights into the pressure wave propagation during knock and the relations between knock conditions, pressure oscillations, and heat release.

Energy harvesting of sandwich beam with laminated composite core and piezoelectric face sheets under external fluid flow

In the present study, the generation of electrical energy from induced vibrations in a composite beam with piezoelectric layer are studied. Accordingly, using Euler-Bernoulli beam theory and considering two types of air damping (external damping) and structural damping (internal damping), the equations of motion for sandwich beam are obtained and then using the Kantorovich method, the output voltage relations for a composite beam with a piezoelectric layer are extracted. After validating the analytical results with the results in the literature, the effect of various parameters such as external fluid flow rate, fiber angle, and how the piezoelectric layer composite beams are arranged on energy harvesting. Also, the maximum oscillation amplitude are investigated. The results show that by using composite materials and with proper layer design and fiber angle in each layer, a different equivalent modulus of elasticity can be created in the composite beam, which will change the normal frequency of the system and the output voltage range of the circuit. The results show that the angle of the fibers has a significant effect on the damping coefficient of the structure, flexural stiffness, natural frequency and finally energy harvesting. According to the results, it can be seen that the minimum value of voltage per use of fibers with an angle of 50 degrees and the maximum amount of voltage per use of fibers with an angle of zero degrees are occurred.

Vortex-Induced Vibrations of a square prism free to oscillate in the inline direction

We study the response of a prism placed in flow and free to oscillate in the direction of flow (the inline direction) for different possible angles of attack. The tests were conducted in a water tunnel for a range of reduced velocities of 2.4 <U* < 5.8 and Reynolds numbers of 757 <Re < 1900, and over angles of attack of 0° ≤α≤ 45°, where α= 0° corresponded to the case where one of the square’s sides was perpendicular to the incoming flow. We observed Vortex-Induced Vibrations in the inline direction for angles of attack of α= 0°, 2.5°, 5°, 7.5°, and we showed that lock-in has occurred in the cases where oscillations are observed, by showing that the shedding frequency and the oscillation frequency were equal in this range. Throughout the lock-in range, the fluctuating force and the displacement remained in phase as well. The width of the lock-in range and the maximum amplitude of oscillations decreased with increasing angles of attack, and no oscillations were observed for α > 7.5°. The wake structures were found to be predominantly symmetric for α= 0°, and transitioned toward asymmetry with increasing α. By calculating the ratio of the fluctuating lift force to the fluctuating drag force, we quantified how the asymmetry in fluid forces increased with increasing both the angle of attack and the reduced velocity. We also showed how for larger angles of attack where oscillations were not observed, giving an initial disturbance to the prism resulted in formation of vortices for only few cycles and the prism’s oscillations decayed and were damped by the fluid forces.

Safe operation of dual-fuel engines using constrained stochastic control

Premixed combustion strategies have the potential to achieve high thermal efficiency and to lower the engine-out emissions such as NOx. However, the combustion is initiated at several kernels which create high pressure gradients inside the cylinder. Similarly to knock in spark ignition engines, these gradients might be responsible of important pressure oscillations with a harmful potential for the engine. This work aims to analyze the in-cylinder pressure oscillations in a dual-fuel combustion engine and to determine the feedback variables, control actuators, and control approach for a safe engine operation. Three combustion modes were examined: fully, highly, and partially premixed, and three indexes were analyzed to characterize the safe operation of the engine: the maximum pressure rise rate, the ringing intensity, and the maximum amplitude of pressure oscillations (MAPO). Results show that operation constraints exclusively based on indicators such as the pressure rise rate are not sufficient for a proper limitation of the in-cylinder pressure oscillations. This paper explores the use of a knock-like controller for maintaining the resonance index magnitude under a predefined limit where the gasoline fraction and the main injection timing were selected as control variables. The proposed strategy shows the ability to maintain the percentage of cycles exceeding the specified limit at a desired threshold at each combustion mode in all the cylinders.

Eksperimentalno proučavanje uticaja kombinacije radnih parametara pokretnog lifta na oscilatorne procese koji se javljaju nakon zaključavanja radne platforme

The article provides a detailed analysis of the influence of the combination of performance indicators of mobile lifts with working platforms (MLWP) at the stage of stopping and the process of vibration damping after stopping the working platform. On the basis of the results of experimental research and processing of the obtained data, an analysis was made of the influence of the angles of inclination of the upper and lower sections of the boom and the mass of the load in the working platform on the maximum amplitude of oscillations of accelerations when the working platform is locked, the period of oscillations and the time of their damping. As a result of the analysis, the spectrum of the response surfaces of the maximum amplitude of acceleration oscillations when the working platform is locked, the period of oscillations and the time of their damping from the working mass and the angles of inclination of the lower and upper boom sections was obtained, on the basis of which it can be concluded that the value of the maximum amplitude of acceleration oscillations in the locking time of the working platform is most influenced by the mass of the load in the working platform.

An elastic rotative nonlinear vibration absorber (ERNVA) as a passive suppressor for vortex-induced vibrations

Vortex-induced vibration (VIV) is a self-excited and self-limited flow-induced vibration phenomenon of importance for both the academic and the technological communities. Particularly for the offshore engineering scenario, VIV plays an important role in the structural fatigue analysis. Hence, VIV suppression is a relevant topic. Among different solutions for VIV mitigation, this paper focuses on the numerical analysis of an elastic rotative nonlinear vibration absorber (ERNVA) as a device for passive suppression. The ERNVA consists of a mass placed at the tip of an axially elastic beam hinged to the cylinder by means of a linear dashpot. In this paper, the hydrodynamic loads are calculated using a wake-oscillator model, allowing comprehensive parametric studies for assessing the influence of the ERNVA parameters on its efficiency for the whole range of reduced velocities associated with the lock-in. Among other novel results, it is found that ERNVA can lead to a $$25\%$$ decrease in the maximum oscillation amplitude, being significantly more efficient than its counterpart characterized by a rigid rotating arm. Passive suppression is obtained not only for the peak, but within a certain range of reduced velocities. Curves showing the influence of the ERNVA parameters on the force coefficients for different values of reduced velocity are also innovative.

Numerical studies on unstable oscillatory direct contact condensation (DCC) of oxygen vapor jets in subcooled flowing liquid oxygen

At the booster turbopump exit of a high pressure staged combustion cycle based cryogenic rocket engine, hot gaseous oxygen after driving the booster turbine mixes with subcooled liquid oxygen from the booster pump leading to a complex phenomena of direct contact condensation of hot oxygen gas. The aim of the present investigation is to numerically study the condensation of oxygen vapor jets in subcooled liquid oxygen using a two-fluid two-phase model in the Eulerian framework to understand the mixing process at the booster turbopump exit. The unstable nature of the oxygen plume shapes at cryogenic temperatures have been examined and the stable to unstable transition in an unstable direct contact condensation cycle have been analyzed. A detailed parametric study has been conducted using the Box-Behnken design and suitable correlations are developed for the critical design parameters viz., overall averaged heat transfer coefficient and dimensionless maximum vapor penetration length. Finally, the maximum pressure oscillation amplitudes associated with unstable oscillatory oxygen direct contact condensation are characterized. The results of the present investigation will be helpful in designing experimental set-up for studying the unstable direct contact condensation at cryogenic temperatures and will serve as preliminary guidelines for the design of an oxygen direct contact condenser, which hitherto is unavailable in the open literature.

Assessment of the spectral component of seismic vibrations of protected objects during explosions in rock quarries

The article was awarded to the honored practitioner of the URSR graduate School, the laureate of the State Prize of Ukraine, professor Vynoslavskiy Vasiliy Mikolayovich, a stretch of 27 years dean of the faculty of mining of the Kiev Polytechnic Institute. 14 September 2020 year 100 years from the day of the birth of him. The article briefly describes his life path and achievements, his life position and scientific achievements. Purpose. The purpose of this article is to study the dissipation and energy distribution of explosive pulses as they pass through the rock massif and the foundation of protected objects, as well as to study the amplitude and energy of seismic oscillations of protected objects under the action of an explosive pulse. Methodology. To study the dissipation and energy distribution of explosive pulses and the interpretation of the results in this article used the methods of spectral analysis (study of autocovariance functions, joint covariance functions, energy autospectras and cross-spectral analysis).Findings. The amplitude of seismic oscillations of the output pulse (foundation surface) for the system "soil - foundation" is 7.35 times lower than the amplitude of soil oscillations at a distance of 70 m from the experimental object, the energy decreased by 8.23 times. This indicates that the foundation of the research object absorbed about 88% of the seismic energy that approached it. The frequency range 5-9 Hz is resonant. In this range, the oscillation frequency of the object foundation is close to the oscillation frequency of the input pulse, which leads to an increase in the energy and amplitude of seismic oscillations and the formation of microcracks in the foundation. For the system "foundation - the top of the tower" the amplitude and energy of oscillations at the top of the tower is 2 times greater than on the surface of the foundation. This fact indicates that due to the significant height of the towers (42.6 m), there is a rocking under the action of an explosive impulse. The maximum amplitude of oscillations of the top of the tower and the surface of the foundation is observed at a frequency of 5 Hz. This indicates that the foundation and towers respond to the explosive impulse as a single object. The nature and form of phase-amplitude characteristics of mutual spectra (hodographs) indicate that the experimental system "source of the explosion-soil massif-foundation-tower for cement storage" is unstable and part of the energy is spent on the formation of microcracks. Originality. The method of research of the characteristics of the rock massif and protected objects used in the article indicates the possibility of a more detailed study of the mechanism of development of microcracks and their transition to unstable destruction. Practical implications. The practical value of the results lies in the information obtained to protect research objects from the negative and destructive effects of seismic pulses, as well as the ability to influence the flow and energy dissipation of explosive pulses by changing the parameters of the explosion or other engineering solutions.

Thermal buoyancy induced suppression of wake-induced vibration

We numerically investigate the effect of thermal buoyancy on wake-induced vibration (WIV) of an elastically mounted square prism in the wake of an identical stationary prism. The upstream prism is heated at a prescribed temperature while the downstream prism is insulated and vibrates transversely to the flow direction. The Reynolds number, based on side of the prism is, Re = 100 and center-to-center distance is twice the side of the prism. Numerical simulations were performed for mass ratio m = 3, Prandtl number Pr = 7.1 and Richardson number Ri = [0, 1]. The reduced velocity UR is varied in a range from 4 to 30. The maximum oscillation amplitude occurs at UR = 5 at Ri = 1 as compared to Ri = 0. We report 50% reduction in the amplitude at Ri = 1 as compared to Ri = 0, implying WIV suppression due to the presence of thermal buoyancy. A complete suppression occurs at UR > 7 at Ri = 1. The lock-in (synchronization) region is narrow for both the cases. The downstream prism oscillates in phase to the lift force at Ri = 1 as ϕ remains 0∘, whereas at Ri = 0, ϕ changes abruptly from 0∘ to 180∘ and remains 180∘ for higher UR. We briefly discuss the influence of thermal buoyancy on wake dynamics. The present results provide insights to suppress the WIV by tailoring the thermal buoyancy for multiple bluff bodies in laminar flow.