Modeling and Simulation of the Engraving Process in Different Life Stages of Small Caliber Guns

Effects of erosion phenomenon on the performance of a given gun barrel have been analyzed throughout numerical and experimental studies. Mainly, qualitative observations were performed. Theoretical relations between the evolution of the inner barrel profile and the provided interior ballistics are limited. This paper focuses on the development of a numerical model to predict the engraving resistance evolution in terms of the inner barrel profile in the different weapon's life stages. Four test barrels "12.7x99mm NATO" with different chamber volumes were considered. First, a Coordinate Measuring Machine (CMM) with a contact scanning probe was used to measure the inner dimension of the guns. Second, piezoelectric sensors with a special doppler radar were considered to measure the (i) pressure and (ii) the bullet velocity in the test weapons. Finally, based on the obtained experimental results, a Finite Element (FE) analysis using the commercial software LS-DYNA was developed and validated. The obtained numerical results were used as insights to quantify the relationship between the engraving resistance and the chamber volume of small caliber guns.

Detection and measurement of hypersonic target radial velocity in pulse Doppler radar

В работе предложен алгоритм обнаружения и однозначного измерения радиальной скорости воздушных объектов (ВО), летящих с абсолютной скоростью, превышающей скорость звука в несколько раз (гиперзвуковых целей). Область применения алгоритма – импульсно-доплеровские РЛС с линейно-частотно модулированным (ЛЧМ) зондирующим сигналом (ЗС). Приведено описание, обоснование использования и результаты моделирования обработки пачки принятых радиоимпульсов разработанным алгоритмом на модели современной импульсно-доплеровской РЛС. An algorithm for the detection and unambiguous measurement of the radial velocity of supersonic air objects is proposed. The scope of the algorithm is pulse-Doppler radars with a linear frequency modulation (LFM). The description, justification of the use and the results of modeling the processing of a packet of received radio pulses by the developed algorithm on a model of a modern pulse-Doppler radar are presented.

Assimilating C-Band Radar Data for High-Resolution Simulations of Precipitation: Case Studies over Western Sumatra

Accurate high-resolution precipitation forecasts are critical yet challenging for weather prediction under complex topography or severe synoptic forcing. Data fusion and assimilation aimed at improving model forecasts, as one possible approach, has gained increasing attention in past decades. This study investigates the influence of the observations from a C-band Doppler radar over the west coast of Sumatra on high-resolution numerical simulations of precipitation around its vicinity under the Madden–Julian oscillation (MJO) in January and February 2018. Cases during various MJO phases were selected for simulations with an advanced research version of the weather research and forecasting (WRF) model at a cloud-permitting scale (~3 km). A 3-dimensional variational (3DVAR) data assimilation method and a hybrid three-dimensional ensemble–variational data assimilation (3DEnVAR) method, based on the NCEP Gridpoint Statistical Interpolation (GSI) assimilation system, were used to assimilate the radar reflectivity and the radial velocity data. The WRF-simulated precipitation was validated with the Integrated Multi-satellitE Retrievals for GPM (IMERG) precipitation data, and the fractions skill score (FSS) was calculated in order to evaluate the radar data impacts objectively. The results show improvements in the simulated precipitation with hourly radar data assimilation 6 h prior to the simulations. The modifications with assimilation were validated through the observation departure and moist convection. It was found that forecast improvements are relatively significant when precipitation is more related to local-scale convection but rather small when the background westerly wind is strong under the MJO active phase. The additional simulation experiments, under a 1- or 2-day assimilation cycle, indicate better improvements in the precipitation simulation with 3DEnVAR radar assimilation than those with the 3DVAR method.

UNIFIED METHOD OF ADAPTIVE-ROBUST REDUCTION OF UNCERTAINTIES IN THE ELIMINATION OF BLIND SPOTS AND RANGING OF AIR OBJECTS IN PULSE-DOPPLER RADARS

A unified method of disclosing blind ranges, reducing or eliminating measurement ambiguity has been proposed and investigated, which allows, within the framework of a typical long-range detection session of an air object by a pulse-Doppler radar, to reduce time costs, expand information content, and unify algorithmic support of a detection session. At the heart of: unified adaptive-robust procedures for controlling radiation parameters (guaranteeing the observability of an object) and processing ambiguous quasi-measurements of range (in absence of detection) and real measurement (in initial detection).

Automatische Schmelzschichterkennung mit einem Mikro-Regen-Radar

<p class="western">An zwei deutschen Flughäfen werden vom Deutschen Wetterdienst seit 2018 Mikro-Regen-Radare (MRR) betrieben, um zu erproben, welcher Nutzen daraus für die meteorologische Sicherung des Luftverkehrs gezogen werden kann. Ein wichtiger Parameter ist die automatische Detektion und Höhenbestimmung der Schmelzschicht, die zum Beispiel für die Erkennung und Bewertung von Vereisungssituationen genutzt werden kann. Zusätzlich kann die Kenntnis der Schmelzschichthöhe helfen, die Qualität der Niederschlagsmessungen mit Wetterradaren zu verbessern.</p> <p class="western">Das MRR ist ein vertikal blickendes Doppler-Radar. Es liefert damit zwar nur eine lokale Messung der Schmelzschichthöhe, diese aber mit großer Zuverlässigkeit, da die Messbedingungen bei vertikaler Strahlrichtung besonders günstig sind. Auch komplexe Strukturen, wie doppelte Schmelzschichten, können so erkannt werden. Sie kommen zwar nur selten vor, sind aber Indikatoren für besonders gefährliche Vereisungssituationen. In dem erprobten Verfahren werden zusätzlich zur Reflektivität, die in der Schmelzschicht das bekannte Maximum aufweist, auch die Dopplergeschwindigkeit und die Breite des Dopplerspektrums zur Detektion herangezogen. Diese Variablen werden bei vertikaler Strahlrichtung maßgeblich durch die Fallgeschwindigkeit beziehungsweise die Fallgeschwindigkeitsverteilung der Hydrometeore bestimmt, und weisen beim Übergang von der festen zur flüssigen Phasen charakteristische Signaturen auf. Damit ist eine zuverlässige Schmelzschichterkennung auch in Regenereignissen möglich, in denen das Reflexionsmaximum durch die allgemeine Variabilität des Reflexionsprofils maskiert wird.</p> <p class="western">Hier wird ein einjähriger Datensatz mit Radiosonden-Aufstiegen verglichen, um die Zuverlässigkeit des im MRR implementierten automatischen Detektionsalgorithmus zu analysieren.</p>

An Algorithm Using DBSCAN to Solve the Velocity Dealiasing Problem

Velocity dealiasing is an essential task for correcting the radial velocity data collected by Doppler radar. To improve the accuracy of velocity dealiasing, traditional dealiasing algorithms usually set a series of empirical thresholds, combine three- or four-dimensional data, or introduce other observation data as a reference. In this study, we transform the velocity dealiasing problem into a clustering problem and solve this problem using the density-based spatial clustering of applications with noise (DBSCAN) method. This algorithm is verified with a case study involving radar data on the tropical cyclone Mangkhut in 2018. The results show that the accuracy of the proposed algorithm is close to that of the four-dimensional dealiasing (4DD) method proposed by James and Houze; yet, it only requires two-dimensional velocity data and eliminates the need for other reference data. The results of the case study also show that the 4DD algorithm filters out many observation gates close to the missing data or radar center, whereas the proposed algorithm tends to retain and correct these gates.

Outbreak of Negative Narrow Bipolar Events in Two Mid-Latitude Thunderstorms Featuring Overshooting Tops

Lightning discharges are the electrical production in thunderclouds. They radiate the bulk of radio signals in the very low-frequency and low-frequency (VLF/LF) that can be detected by ground-based receivers. One kind of special intra-cloud lightning discharges known as narrow bipolar events (NBEs) have been shown to be rare but closely linked to the convective activity that leads to hazardous weather. However, there is still lack of understanding on the meteorological conditions for thunderstorm-producing NBEs, especially for those of negative polarity, due to their rare occurrence. In this work, we aim to investigate what meteorological and electrical conditions of thunderclouds favor the production of negative NBEs. Combining with the VLF/LF radio signal measured by Jianghuai Area Sferic Array (JASA), S-band Doppler radar observation and balloon sounding data, two mid-latitude thunderstorms with outbreaks of negative NBEs at midnight in East China were analyzed. The comparison with the vertical radar profile shows that the bursts of negative NBEs occurred near thunderclouds with overshooting tops higher than 18 km. Manifestation of negative NBEs is observed with a relatively low spectrum width near thundercloud tops. Our findings suggest that the detection of negative NBEs would provide a unique electrical means to remotely probe overshooting tops with implications for the exchange of troposphere and stratosphere.

Development of nowcasting technique and evaluation of convective indices for thunderstorm prediction in Gangetic West Bengal (India) using Doppler Weather Radar and upper air data

Thunderstorm and hailstorm are well known short term severe weather phenomena which sometimes turn in to natural hazard especially in Gangetic West Bengal region of India. Large vertical extent of the cumulonimbus cloud, very high reflectivity, squally wind speed sometimes exceeding 100 km/h and heavy rainfall are the main features of these thunderstorms during pre-monsoon period in this region. A study of 70 thunderstorms has been carried out during the pre-monsoon season (March-May) of the year 2005 around Kolkata (22.5° N, 88.5° E) using Doppler Weather Radar and Upper air data. Standard convective indices like CAPE, CINE, LI, BRN and VGP have been evaluated and analyzed statistically. As no definite thresholds of the convective indices are available for thunderstorm prediction in this region, an attempt has been made to find threshold of these indices for possible occurrences of thunderstorms in Gangetic West Bengal region after the analysis of the thunderstorms during year 2005. The validity of these convective indices has been checked with 34 occurrences of thunderstorms during 2006-2007 recorded by Doppler Weather Radar Kolkata. The study reveals that nowcasting of thunderstorms may be done at least 2-3 hrs in advance witha fair degree of accuracy using Doppler radar products only. However, the lead time of nowcasting may be further improved if the convective indices are also analyzed and used in addition to the DWR data. A simple technique has been suggested by the authors for better prediction of thunderstorms at least three to four hours in advance.