Barometric formula for non-isothermal atmosphere

A new barometric formula is derived for a non-isothermal atmosphere. It takes into account the dependence of the acceleration of gravity and gas temperature on the height z above the Earth’s surface. When deriving this formula, it was assumed that the dependence of the gas temperature on altitude is due to the heating of the Earth’s surface by the Sun and the subsequent heat transfer of energy from the Earth’s surface to the atmosphere. The proposed formula coincides with the classical barometric formula for an isothermal atmosphere at low altitudes z, takes into account the experimental linear decrease in the temperature of the atmosphere in its lower layers with increasing altitude z and gives a physically correct asymptotics for the pressure (and for concentration) of the gas as z -> oo, namely, the pressure (and concentration) of gas tends to zero faster than exponentially as z -> oo, which ensures the localization of a finite amount of gas near the Earth.

Slow Motions of A Circular Cylinder in a Liquid after a Separation Impact

The plane problem of the separation impact of a circular cylinder completely immersed in an ideal incompressible heavy liquid is considered. It is assumed that after the impact, the cylinder moves horizontally at a constant speed. An attached cavity is formed behind the body, the shape of which depends on the physical and geometric parameters of the problem. It is required to study the process of collapse of the cavity at low velocities of the cylinder, which correspond to small Froude numbers. The solution to the problem is constructed using asymptotic expansions in a small parameter, which is the dimensionless speed of the cylinder. In this case, as the characteristic speed of the problem, a value is chosen equal to the square root of the product of the radius of the cylinder and the acceleration of gravity. As a result of this choice, the indicated small parameter coincides with the Froude number, and therefore, we can assume that the asymptotics of the problem is constructed for small Froude numbers. In the leading asymptotic approximation, a mixed problem of potential theory with one-sided constraints on the surface of the body is formulated. With its help, the position of the separation points at each moment of time is determined and the time of collapse of a thin cavity is found. The results obtained can be used to solve practical problems of ship hydrodynamics, in which it is necessary to take into account the phenomenon of cavitation.

Elements of ballistic calculation for spacecraft gravity assist

The purpose of the study is an analytical description of the section of the ballistic trajectory corresponding to the normal fall of the spacecraft on the surface of an atmosphereless planet. In this case, the motion of a normally falling body is characterized by an increasing acceleration of gravity. The problem of the speed, time and acceleration of the normal fall of a body on the planet's surface in the absence of an atmosphere is reduced to solving a second-order differential equation, which is solved by the standard method. A feature of the solution is the formal use of the tabular integral at an intermediate stage. It turned out, however, that his formula is unreliable, namely, the derivative of the right-hand side is not equal to the integrand. It follows from this that the possible existing solutions to this problem, based on the use of the indicated tabular integral, are incorrect. The article presents the correction of this tabular integral, which is an incidental result of the study. In this work, the time equation of motion of a body normally falling on the surface of the planet in the absence of an atmosphere, as well as the time equations of its speed and acceleration are obtained. The results obtained can be useful in calculating passive gravity assist during interplanetary flights and calculating the sheer fall of small celestial bodies and spent structural element s of spacecraft.

Managing the resilience of future marine specialists to sickness

В статье приводится обоснование условий тренировки устойчивости к укачиванию будущих морских специалистов, способствующих снижению объемов нагрузки в специальных упражнениях и временных затрат на цикл подготовки. Предложен способ расчета перегрузок в упражнениях, применяемых в активной, пассивной и смешанной тренировках устойчивости к укачиванию. Значение критерия определяется путем вычисления отношения полного ускорения, действующего на вестибулярный анализатор в процессе движения, к ускорению свободного падения. Установлено, что ведущей теорией для отбора средств тренировки является теория сенсорного конфликта. Дается описание и обоснование применения авторских разработок для тренировки статического и динамического равновесия на возвышенной, наклонной, качающейся и соскальзывающей опорах, моделирующих условия сохранения статокинетической устойчивости в морских условиях. Предложен необходимый и достаточный комплекс технических устройств и тренажеров для управления устойчивостью будущих морских специалистов к укачиванию. The article substantiates the conditions of resistance to motion sickness of future marine specialists, the possibilities of the system for measuring the load in special exercises and the time spent on the training cycle. A method for calculating overloads in exercises used in active, passive and mixed trainings of resistance to motion sickness is proposed. The value is determined by calculating the ratio of the total acceleration acting on the vestibular analyzer during the acceleration of gravity. It has been established that the leading theory for the selection of training means is the theory of sensory conflict. A description and justification of the use of author's developments for training static and dynamic balance on an elevated, inclined, swinging and sliding support, simulating the conditions for maintaining statokinetic stability in marine conditions, is given. The necessity and a sufficient set of technical devices and simulators for the sustainable development of marine specialists for motion sickness is proposed.

Knifefish’s suction makes water boil

We discovered that knifefish (Apteronotus albifrons) during suction feeding can produce millimeter-sized cavitation bubbles and flow accelerations up to ~ 450 times the acceleration of gravity. Knifefish may use this powerful suction-induced cavitation to cause physical damage on prey hiding in narrow refuges, therefore facilitating capture.

FORWARD MODELLING METODE GAYABERAT DENGAN MODEL INTRUSI DAN PATAHAN MENGGUNAKAN OCTAVE

The gravity method is a geophysical exploration method to measure variations in the acceleration of gravity on the surface of the earth in response to variations in rocks that exist beneath the surface. In gravity exploration requires a preliminary picture as a reference for measurement. This study aims to make forward modeling synthetic OCTAVE based using synthetic data on subsurface rock structures, so as to produce intrusion and fracture models based on differences in the value of the acceleration of gravity from one point to another on the surface of the earth. Synthetic modeling with the geological parameter approach of the study area is based on variations in the price of rock density. The model parameters used in intrusion modeling are the density value of 2.7 g/cm3 and the depth of 850 meters while the fracture modeling uses a density value of 2.7 g/cm3 with a depth of 350 meters and 360 meters and a thickness of 500 meters. From intrusion modeling, the gravity vertical component of attraction force is 0.03 mGal and in the fracture modeling the gravity vertical component of attraction force is 0.0565 mGal. Based on the results of this modeling, distance curve vs. gravity anomaly response is obtained for both cases. In the intrusion rock model obtained by the profile model with an open type down. While the fracture modeling is obtained anomalous profile curve variation which states that in the fracture area with a significant change in the direction of the curve.