Longitudinal Instability Research Articles

Numerical Analysis of Self-Excited Combustion Instabilities in a Small MMH/NTO Liquid Rocket Engine

Combustion instabilities in a small MMH/NTO liquid rocket engine used for satellite attitude and course control are numerically investigated. A three-dimensional Navier-Stokes code is developed to simulate two-phase spray combustion for cases with five different droplet Sauter Mean Diameters. As the droplet size increases from 30 microns to 80 microns, pressure oscillations are stronger with larger amplitudes. But an increase of the droplet size in the range of 80 microns to 140 microns indicates a reduction in the amplitudes of pressure oscillations. This trend is the same as the Hewitt criterion. The first tangential (1T) mode and the first longitudinal (1L) mode self-excited combustion instabilities are captured in the 60-micron and 80-micron cases. Abrupt spikes occur in the mass fraction of MMH and coincide with abrupt spikes in the mass fraction of NTO at the downstream regions just adjacent to the impinging points. Thus, local combustible high-dense mixtures are formed, which result in quasiconstant volume combustion and abrupt pressure spikes. The propagation and reflection of pressure waves in the chamber stimulate the combustion instability. When the droplet size is too small or too large, it is difficult to form local high-dense premixtures and combustion is stable in the chamber.

Collective Effects in the NICA Collider

Collective effects in the NICA collider are considered taking into account the results of calculations of induced electromagnetic fields (wakes) and coupling impedances of vacuum-chamber elements [1]. Coulomb shifts of longitudinal and transverse oscillations are considered and the stability of coherent oscillations in the presence of these shifts is analyzed; their influence is significant, since it can lead to the Loss of Landau Damping (LLD). Special attention is given to transverse head–tail instabilities and longitudinal instabilities caused by High-Order Modes (HOM) of the cavities. Recommendations on the suppression of instabilities are formulated.

Combined technique of titanium telescopic rods and external fixation in osteogenesis imperfecta patients: First 12 consecutive cases

IntroductionThe major limitation of any intramedullary telescopic system is rotational and longitudinal instability. The combination of telescopic system with an external fixator in patients with osteogenesis imperfecta (OI) demonstrated advantages of stability, early weight-bearing and rehabilitation. This study aimed to examine the outcomes of deformity correction by combined technique uniting titanium telescopic rod and reduced Ilizarov frame in children with types III or IV of OI with a minimum 1-year follow-up. Material and methodsThe study included 12 children with OI who underwent femoral deformity correction (20 segments) or tibial deformity correction (4 segments) by combined technique. The children ranged in age between 2 years and 3 months and 12 years and 4 months (mean: 8.9 ± 2.02 years) at the time of the rodding. Parameters of surgery, clinical examination data, data of 3D gait analysis were assessed in the study. ResultsExternal fixation lasted 35.8 ± 13.2 days in average. Neither loss of threaded fixation in the distal femoral and tibial epiphyses and apophysis of the greater trochanter nor migration of the rod into the knee and ankle joints were observed in follow-up. No secondary rotational or longitudinal bone displacement was noted. Telescoping gain related to spontaneous growth assessed at one-year follow-up control was 13.7 mm in the tibia and 15.9 mm in the femur. There were no deep infection or neurologic complications. The alignment measured by radio anatomical reference angles was maintained throughout the follow-up period.Gait abnormalities in postoperative period were caused by bulk and weight of EF: external hip rotation, slight external angle of foot progression, increased stride width and increased hip abduction angle. The second feature was reduced ROM in sagittal plane at all levels associated with significantly reduced ankle plantarflexion, hip and knee joint moments in comparison to kinetics of limb without EF. These abnormalities resolved by the one-year assessment. ConclusionThe combination of titanium telescopic rod with reduced external fixation is reliable advantage in reconstructive orthopaedic surgery for OI children. Reduced external fixation allows to overcome inconveniencies of longitudinal and rotational instability of telescopic systems. Children were able to walk with weight-bearing since early postoperative period because of external fixation. Gait temporary changes were influenced by external device size and by strategy to reduce pin site pain.

Beam loading effects and microwave instability in the booster ring of a high intensity heavy-ion accelerator facility

Transient beam loading effects and microwave instability are very important in ion synchrotrons. A simulation code longitudinal particle tracking code (LPTC) based on multiparticle tracking is developed to simulate the beam loading effects and the longitudinal beam instabilities in the booster ring (BRing) of the High Intensity heavy-ion Accelerator Facility (HIAF). A process of beam capture, acceleration, debunching, and the second capture is simulated with a reference ion beam of ${^{78}\mathrm{Kr}}^{19+}$. The simulation results show that the beam loading effects have major contribution to the beam behavior during the debunching stage and the second capture stage. A feed-forward system is suggested to compensate the beam loading effects, and the main parameters of the feed-forward system are given. The microwave instability of coasting ${^{78}\mathrm{Kr}}^{19+}$ beams is observed from the simulation results. The threshold of the microwave instability is also given. The development of self-bunching and methods to suppress the microwave instability in the BRing are discussed.

Hydrodynamic analysis of electrostatic counter‐streaming instability in a spin‐polarized electron–positron–ion plasma

AbstractIn this study, we present linear analysis of electrostatic counter‐streaming instability in spin‐polarized electron–positron–ion (e‐p‐i) plasma. With the aid of the separate spin evolution‐quantum hydrodynamic (SSE‐QHD) model, we derive the dispersion relation of counter‐streaming instability. We numerically solve the dispersion and find four wave solutions: Langmuir wave, positron acoustic mode, and two electron and positron spin‐dependent waves. It is noted that coupling of streaming and spin effects excites Langmuir instability and positron acoustic mode instability. However, in the absence of spin effect, only Langmuir instability will survive in e‐p‐i plasma. We have also discussed the effects of positron concentration, streaming speed, and spin polarization on the real frequency of waves and the growth rate. The present study may be helpful for understanding longitudinal wave propagation and instabilities in dense magnetized environments.

Do neurobiological differences exist between paranoid and non-paranoid schizophrenia? Findings from the bipolar schizophrenia network on intermediate phenotypes study

Subtypes of schizophrenia, constructed using clinical phenomenology to resolve illness heterogeneity, have faced criticism due to overlapping symptomatology and longitudinal instability; they were therefore dropped from the Diagnostic Statistical Manual-5. Cognitive and imaging findings comparing paranoid (P-SZ) and non-paranoid (disorganized, residual and undifferentiated; NP-SZ) schizophrenia have been limited due to small sample sizes. We assessed P-SZ and NP-SZ using symptomatology, cognition and brain structure and predicted that there would be few neurobiological differences. P-SZ (n = 237), NP-SZ (n = 127) and controls (n = 430) were included from a multi-site study. In a subset of this sample, structural imaging measures (P-SZ, n = 133; NP-SZ, n = 67; controls, n = 310) were calculated using Freesurfer 6.0. Group contrasts were run using analysis of covariance, controlling for age, sex, race and site, p-values were corrected using False Discovery Rate (FDR) and were repeated excluding the residual subtype. Compared to NP-SZ (with and without the residual subtype), P-SZ displayed fewer negative symptoms, faster speed of processing, larger bilateral hippocampus, right amygdala and their subfield volumes. Additionally, NP-SZ (with residual subtype) displayed fewer depressive symptoms and higher left transverse temporal cortical thickness (CT) but NP-SZ without residual subtype showed lower GAF scores and worse digit sequencing compared to P-SZ. No differences in positive symptoms and functioning (global or social) were detected. Subtle but significant differences were seen in cognition, symptoms, CT and subcortical volumes between P-SZ and NP-SZ. While the magnitude of these differences is not large enough to justify them as distinct categories, the paranoid- nonparanoid distinction in schizophrenia merits further investigation.

The role of the interosseous ligament in forearm rotation: A bio-mechanical study.

Management of longitudinal forearm instability remains challenging. Chronic forearm stability may be overcome by reconstruction of the interosseous ligament (IOL). Despite the bands of the IOL being inseparable, studies of the IOL have focused on the central band (CB), but have neglected the proximal (PB) and distal (DB) bands. The purpose of this study was to characterize the bio-mechanical properties of the IOL. Twelve frozen specimens from individuals of both sexes were bio-mechanically analyzed using a custom-designed jig operated at constant angular speed to simulate forearm rotation. Strain was measured during dynamic forearm simulation using a motion tracking system. The average strain of the CB, PB, and DB during forearm simulation were 0.08 ± 0.04, 0.83 ± 0.47, and 0.65 ± 0.23 mm (p < 0.001). The IOL was generally shortest during maximal pronation and increased as the forearm was rotated to a neutral position. The strain of the CB remain constant during forearm rotation and was the lowest at full pronation to 20° pronation position. Throughout forearm rotation, the strain of the CB remained constant, whereas the strain of the PB and DB fluctuated. The PB, CB, and DB of the forearm IOL have different bio-mechanical properties. CB maintained a constant rotational strain throughout forearm rotation. Strain on the CB was significantly lower than strains on the PB and DB. By contrast, strains on the PB and DB varied, suggesting that their roles differ from those of the CB. When CB reconstruction is needed, graft should be tensioned at 20° forearm pronation to gain optimum tension.

Failure Mechanisms and Modes of Tunnels in Monoclinic and Soft-Hard Interbedded Rocks: A Case Study

The issue of large deformation mechanism in soft rock tunnels has puzzled tunnel scholars for decades. Previous studies have not evolved a clear and common understanding. Therefore, detailed on-site measurement, full investigation and statistical analysis have been conducted on the instability and failure of Muzhailing Tunnel since its construction, whose length is beyond 15 km. The study aims at systematically analyzing the failure mechanisms and modes of Muzhailing Tunnel in monoclinic and soft-hard interbedded rock strata. Study results show that the angle between strata strike and tunnel axis greatly determines the magnitude of deformation, the dip direction significantly controls the bias direction and maximum deformation direction, and the dip angle deeply affects the deformation form. The failure modes of surrounding rock mainly include four types: spalling and overturning failure, bending failure, shear slip failure and buckling failure. Large deformation characteristics are summarized from six aspects: failure form, groundwater, sensitivity to influencing factors, deformation degree, deformation speed and deformation duration. The instability modes of primary lining include in-plane (transverse) instability and out-plane (longitudinal) instability. Finally, the causes of large deformation are analyzed from geological, structural, engineering and human factors.

Subtle Essex-Lopresti, what the literature teaches us illustrated by 2 case reports.

Subtle Essex-Lopresti Lesion (ELL) is a rare slow onset longitudinal forearm instability that can presents with subnormal initial radiographs and can easily be missed for the inattentive eye. We reviewed the literature about the subtle ELL illustrated by the report of 2 cases with initially isolated radial neck fractures that turned out to be a subtle ELL pattern. The subtle ELL defined by normal or subnormal initial plain radiographs is usually an association of a slight rupture of the 3 longitudinal stability elements of the forearm being a proximal radius fracture, an inter osseous membrane (IOM) rupture and a distal radio ulnar joint dislocation. These subtle alterations that are often missed worsen with time as do their prognosis making it an emergency to diagnose them and treat them as soon as possible. If diagnosis can involve ultrasound and MRI, the most important key is the initial clinical examination and plain radiographs that has both to be repeated in a short period of time. Among the treatment options, for the acute diagnosis, treatment is similar to usual ELL. As for the missed ones, the proximal radius being usually healed with little displacement can be treated with an ulnar osteotomy alone with good results or associated with IOM reconstruction. Subtle ELL is a rare condition but heavy of consequences for the patients that must be known diagnosed and treated as early as possible by upper extremity surgeons even if there is not a consensual treatment which asks for more research about that subject.

The Serially-Operated Essex-Lopresti Injury: Long-Term Outcomes in a Retrospective Cohort

Objective The main aim of this article is to report 10-year outcomes after Essex-Lopresti injury (ELI).Study Design Retrospective case series. Two level I trauma centers and one associated community hospital from 2003 to 2016.Patients Sixteen patients who sustained an ELI and were treated at one of our three regional hospitals.Intervention Initially, 4 patients (25%) were treated nonoperatively by immobilization and 12 patients (75%) were treated operatively. Proximal surgery included radial head open reduction and internal fixation (ORIF), radial head arthroplasty, radial head excision and forearm ORIF, and wound debridement. Ten patients (63%) were acutely identified with longitudinal forearm instability. Of these, four patients had the distal radioulnar joint pinned. In the other six patients, the forearm was immobilized. Overall, 16 patients underwent a total of 32 revision surgeries.Main Outcome Measure Performance of Patient-Reported Outcomes Measurement Information System Upper Extremity (PROMIS UE) Physical score, Numeric Rating Scale (NRS) score for pain-severity, and NRS score for satisfaction of overall outcome.Results Follow-up for outcome evaluation was available for 10 patients, at a median of 10 (interquartile range [IQR]: 8.0–12) years after date of injury. The median PROMIS UE Physical score was 36 (IQR: 33–38). Median NRS score for pain-severity on average was 5 (IQR: 0–6). The median NRS score for satisfaction of overall outcome was 7 (IQR: 5–8).Conclusion Patients who sustain an ELI generally have substantial deficits of upper extremity function as measured by PROMIS UE. Early radial head arthroplasty may be beneficial, but further study in a larger cohort is needed. Outcomes of nonoperative treatment and operative treatment were similar and suggest that current surgical treatments are incomplete.

Mitigation of intensity limitation in the CERN SPS using a double RF system

The Super Proton Synchrotron (SPS) at CERN is the injector of the Large Hadron Collider (LHC). Multi-bunch instabilities limit the intensity of the beam that can be accelerated to 450 GeV in the SPS and transferred to the LHC. Without mitigation measures, the threshold of bunch intensity of the longitudinal instability is three times below the nominal bunch intensity of the LHC beam. The High Luminosity LHC project (HL-LHC), which requires a doubling of the nominal bunch intensity, relies on improvement of beam stability in the SPS. A fourth harmonic RF system allows, presently, to stabilize the beam up to nominal LHC intensity. It increases the synchrotron frequency spread inside the bunch, providing more efficient Landau damping of beam instability. However, nonlinearities of the synchrotron frequency distribution inside the bunch pose a limitation on bunch length. This paper explores possible intensity increase in the SPS by studying the effect on beam stability of the voltage ratio between two RF systems. The results are substantiated by beam measurements and particle-tracking simulations. An optimized voltage program of the second RF system during the cycle has been tested in operation and beam stability and the quality have been successfully improved.

Методика експериментального дослідження визначення динамічних характеристик при русі колісних тракторів з агрегатами змінної маси

Today, an urgent and unresolved issue is the study of transport operations that are used in the agricultural sector, because there is a problem when studying the movement of a machine-tractor unit with trailed or semi-trailer units. This is directly related to the increase in energy saturation of wheeled tractors and, as a result, an attempt to maximize vehicle performance. The study of transport work in the transportation of liquid cargo is of great interest, where an increase in cargo transportation leads to significant instability in the operation of a wheeled tractor and a tractor tank (which is devoid of internal partitions) due to natural vibrations of the liquid. This process leads to longitudinal and lateral instability, contributes to an increase in both dynamic characteristics and emergency situations (there is an effect on the smoothness of movement, vibration load, handling and stability of the vehicle, increasing the dynamic load of the undercarriage, etc.). Therefore, to confirm the theoretical aspects of the influence of fluid oscillations in the tractor tank, experimental studies are necessary. The experimental research methodology presented in this article will allow us to determine the dynamic characteristics during transportation of trailed and semi-trailer tractor tanks during steady-state movement, as well as in transient operation modes. The practical significance of the work is to obtain experimental data on the accelerations of the studied objects at different height filling of the liquid level in the tanks.

Improved HOM-mitigation for future SPS 33-Cell 200 MHz traveling-wave accelerating structures

The CERN SPS 200 MHz traveling-wave (TW) accelerating structures pose an intensity limitation for the planned High Luminosity (HL-) LHC upgrade. Higher-order modes (HOMs) around 630 MHz have been identified as one of the main sources of longitudinal multi-bunch instabilities. Improved mitigation of these HOMs with respect to today’s HOM-damping scheme is therefore an essential part of the LHC injectors upgrade (LIU) project. The basic principles of HOM-couplers in cavities and today’s damping scheme are reviewed. Before illustrating the numerous requirements, an improved damping scheme for the future 33-cell structures must be fulfilled. These are, among others, the mitigation of HOMs situated in the lower part of the structure where there are no access ports for extraction, a sufficient overall damping performance and an acceptable influence on the fundamental accelerating passband (FPB). Different approaches tackling these challenges are investigated and their performance, advantages and pitfalls are evaluated by ACE3P and CST electromagnetic (EM) field solver suites.

POGO Stability Analysis of a typical Launch vehicle for studying the effectiveness of POGO corrector in cryo stage

POGO is the longitudinal instability of liquid propellant launch vehicles due to the interaction of structural dynamics with the propulsion system. This interaction may give rise to the initiation of vibrations of large magnitudes when the propulsion and structural frequencies are nearer. This can be avoided by the separation of structural and propulsion frequencies by means of a POGO corrector. The present paper describes the propulsion structural interaction studies for the cryo stage of a typical launch vehicle to avoid POGO oscillations. The propulsion systems are represented as discrete elements described by a set of second order equation and the structure is represented by the normal mode parameters. Assembly of propulsion elements along with structural equations will define the structure propulsion system. Stability of system is studied by evaluating the roots of the assembled equation. The analysis showed that there will not be any POGO oscillations during the flight.

Advanced damper system with a flexible and fine-tunable filter for longitudinal coupled-bunch instabilities caused by the accelerating mode in SuperKEKB

SuperKEKB is an electron–positron circular collider aiming to achieve unprecedented luminosity by using a large beam current and a new collision method. The longitudinal coupled-bunch instabilities caused by the accelerating mode of cavities will be a serious impediment in reaching the design current; estimates suggest that the so-called μ=−1, −2, and −3 modes of the instabilities will be excited. We developed a new damper system for suppressing these modes using recent digital technologies. In our system, the feedback parameters for each mode, for example, the phase, the loop gain, and the frequency offset, can be easily fine-tuned independently. We verified the performance of the new damper during Phase-2 commissioning of SuperKEKB. In the demonstration, instabilities ( μ=−1 and −2 modes) were excited by intentionally detuning a superconducting cavity, and the feedback control with the new damper was applied to the low-level RF control system. The new damper successfully suppressed the longitudinal coupled-bunch instabilities in SuperKEKB. Consequently, it is expected that this damper will make a substantial contribution to achieving the design luminosity by suppressing the coupled-bunch instabilities due to the accelerating cavities.

Nonlinear Combustion Instability in a Multi-Injector Rocket Engine

A computational study is presented of the nonlinear combustion instability of a multi-injector rocket engine. The study addresses a choked nozzle and a combustion chamber with 10 and 19 coaxial injector ports. Computations using a three-dimensional unsteady shear-stress transport delayed detached-eddy simulation method provide detailed time-resolved information about the combustion instability. The spontaneous longitudinal-mode instability is observed for the 10- and 19-injector geometries with a combustion-chamber diameter of 28 cm. The triggered tangential and longitudinal instability modes are obtained for the 19-injector geometry with a combustion-chamber diameter of 43 cm by pulsing the injector mass flux. It is shown that an oscillating combustion-chamber flow can be triggered to a new mode with a larger disturbance amplitude. The streamwise vorticity created by the instability impacts the heat release in a manner that supports the instability. A preliminary study of injector-size scaling effects is performed by comparison of the 10- and 19-injector combustors.

Pattern formation on time-dependent domains

In the quest to understand the dynamics of distributed systems on time-dependent spatial domains, we study experimentally the response to domain deformations by Faraday wave patterns – standing waves formed on the free surface of a liquid layer due to its vertical vibration – chosen as a paradigm owing to their historical use in testing new theories and ideas. In our experimental set-up of a vibrating water container with controlled positions of lateral walls and liquid layer depth, the characteristics of the patterns are measured using the Fourier transform profilometry technique, which allows us to reconstruct an accurate time history of the pattern three-dimensional landscape and reveal how it reacts to the domain dynamics on various length and time scales. Analysis of Faraday waves on growing, shrinking and oscillating domains leads to a number of intriguing results. First, the observation of a transverse instability – namely, when a two-dimensional pattern experiences an instability in the direction orthogonal to the direction of the domain deformation – provides a new facet to the stability picture compared to the one-dimensional systems in which the longitudinal (Eckhaus) instability accounts for pattern transformation on time-varying domains. Second, the domain evolution rate is found to be a key factor dictating the patterns observed on the path between the initial and final domain aspect ratios. Its effects range from allowing the formation of complex sequences of patterns to impeding the appearance of any new pattern on the path. Third, the shrinkage–growth process turns out to be generally irreversible on a horizontally evolving domain, but becomes reversible in the case of a time-dependent liquid layer depth, i.e. when the dilution and convective effects of the domain flow are absent. These experimentally observed enigmatic effects of the domain size variations in time are complemented here with appropriate theoretical insights elucidating the dynamics of two-dimensional pattern evolution, which proves to be more intricate compared to one-dimensional systems.

Measurement and parametric analysis of transverse coupled bunch instabilities for electron synchrotron radiation source Indus-2

The performance of synchrotron radiation sources at high beam current gets often degraded due to the excitation of longitudinal and transverse coupled bunch instabilities (CBI). Hence, measurement of the coupled bunch instabilities may give insight into the performance of the machine, which in turn, may help supress these instabilities. Transverse coupled bunch instability is sensitive to the operating parameters of the accelerator such as betatron tune and sextupole magnet strength. In this paper, we report the measurement on transverse coupled bunch modes (CBM). The effect of betatron tune values and sextupole magnet strengths on transverse coupled bunch instability is discussed. For this study, betatron tune values and sextupole strengths are chosen in the vicinity of the routine operating points. With the help of this parametric study, an optimum operating point is identified in the beam operation with a minimum level of transverse coupled bunch instability. Further, an artificial neural network (ANN) is used to deduce a functional model between average transverse CBM levels and sextupole strengths.

Understanding of Ice Accumulation and Accretion over an Airfoil

Since the beginning of civil aviation, icing has been a severe weather hazard for aircraft operation. For many years, the term engine icing has been used to describe ice accreting on exposed engine surfaces as an aircraft flies through a cloud of super-cooled liquid droplets. The concern arising out of aircraft icing is due to its adverse effect on flight safety and hence, for decades, a considerable amount of research is on in the area of icing of aircraft and its components exposed to ice. Experimental verification and some of the key numerical investigations in the area have revealed that aerodynamic characteristics and controllability of an aircraft are affected by the amount and type of ice accretion at different locations. Fundamentally icing of airfoil of an aircraft contributes to decrease in lift force as well as the angle of stall on the wing. This also brings up another situation that is longitudinal instability of the apparatus concerned. It has been a complex physical situation to comprehend the accretion process and its impact. In the present study NACA0012 airfoil geometry has been used to understand the accumulation and accretion process through simulation. The results of total mass of ice accreted with respect to total time of accretion (tice) have been presented

Modeling and analysis of triggering pulse to thermoacoustic instability in an end-burning-grain model solid rocket motor

Occurrences of pulse-triggered instabilities in combustion chambers always trouble solid rocket motors (SRMs) in application. This paper performs numerical simulation of the pulse-triggered nonlinear instabilities in the end-burning-grain SRM, in use of the pressure-coupled response function to describe the spatiotemporal burning rate of AP-HTPB composite propellant grains. A high-order numerical solver realizes the cooperation of the burning rate model into the axisymmetric internal ballistic simulation of SRMs via the source terms in gas-phase governing equations. The analysis of high-amplitude pressure oscillations, which are the primary symptom of nonlinear thermoacoustic instabilities, provides the insight into the nature of the longitudinal instability growth process after the pulse triggering. The change rate of pressure fluctuation over the pressure fluctuation in the chamber is independent of the pulse intensity and triggering position. The growth characteristics of pressure oscillations for the present combustor system is neither affected by the pressure pulse intensity nor by the imposed regions in the flow field, while the higher pressure-coupled response function of the propellant promotes the growth process evidently. The present study is expected for the guidance of grain design in SRMs.