Body Displacement Research Articles

Modelling and Sensitivity Analysis of Influencing Parameters in Displacement of Dynamic Bodies

The mathematical modelling in relation to the Six-degree freedom system of train suspension is developed and simulated for their dynamic characteristics. The important challenge in the suspension system is vertical displacement obtained from the vehicle body. To reduce vertical displacement, an analysis of the model is done by variation of parameters such as stiffness of spring and damping coefficient. The model has been created by deriving the equations of a system using Newton’s law. The developed model has the potential to analyse the dynamic characteristics of the suspension system for both displacement of the vehicle body and displacement of the wheel. The outcome of this research revealed that Secondary spring stiffness is the most dominant factor to influence the displacement of the vehicle body; Primary damping coefficient is the most dominant factor to influence displacement of the wheel.

Effects of ply thickness deviation and ply angle misalignment on the surface accuracy of CFRP laminates

This study examines two factors that affect the surface accuracy of symmetric carbon-fibre-reinforced plastic (CFRP) laminates: ply angle misalignment and ply thickness deviation. First, based on classic laminate theory, theoretical expressions for the effects of these factors are deduced. Then, COMSOL (FEM software) is used to analyse the relationship between these factors and the surface accuracy, and Zernike polynomials are used to fit the surface deformation of the CFRP laminates. It proves that ply angle misalignment and ply thickness deviation can cause astigmatic and power aberrations. Based on the integral constraint method in the form of Lagrangian multipliers, the rigid body displacement problem of the free thermal expansion simulation of CFRP laminates has been solved. Finally, three groups of experimental tests show that ply thickness deviation does occur. A ZYGO interferometer is used to observe the surface accuracy of the laminates, and it shows that astigmatism is the dominant aberration.

Adaptive Sensor Fault Accommodation for Vehicle Active Suspensions via Partial Measurement Information.

In this article, an adaptive sensor fault accommodation scheme is proposed for uncertain vehicle active suspensions via output-feedback control where vehicle body displacement is the only measurable output signal corrupted by sensor bias. An adaptive observer with variable gains is constructed to obtain state estimates whose design procedure involves parameter adaption of the uncertain system parameters and sensor bias, and an output-feedback controller is designed to attenuate the vehicle body displacement based on the partial measurement information, estimates of the states, and unknown parameters. Compensation for measurement error is made both in the design process of the adaptive observer and output-feedback controller in order to weaken the influence brought about by sensor bias fault. In order to guarantee system stability, the variable observer gains are determined in real time using a switching strategy where their values can be modified in finite times by monitoring the state estimates generated by the observer itself. It is proved that the vehicle body displacement will converge to a small neighborhood around zero, and all the signals of the closed-loop system are ensured to be bounded through selecting suitable control parameters. Simulation is carried out to show the effectiveness of the proposed method and results indicate that better stabilization of the suspension vertical motion can be achieved through adaptive compensation for sensor bias.

DYNAMIC CHARACTERISTICS OF NON-SMOOTH SUSPENSION SYSTEM UNDER FRACTIONAL-ORDER DISPLACEMENT FEEDBACK

Vehicle suspension systems generally have non-smooth factors, such as clearances, collision, and constraint. The bad dynamic behaviors caused by these non-smooth factors have not been controlled effectively, thus influencing the driving performance and riding comfort of vehicles. To explore the dynamic characteristics of non-smooth suspension systems for controlling the bad dynamic behaviors, an approximate analytical solution to the response of a two-degree of freedom nonlinear suspension system, which has a fractional-order displacement feedback under harmonic excitation, was deduced by the Krylov–Bogoliubov (KB) method. This analytical solution was verified by the numerical solution of the suspension system. Moreover, the response of the suspension system with fractional-order displacement feedback control was compared with those of the systems without feedback control and traditional integer-order control. The influences of the main parameters of the system on the dynamic suspension characteristics were analyzed thoroughly. Finally, the stability of the suspension system was analyzed by plotting the maximum Lyapunov index diagram. Results show that compared with the systems without feedback control and with traditional integer-order control, the nonlinear suspension system with fractional-order displacement feedback control can significantly improve vehicle acceleration, the dynamic deflection of the suspension, and the displacement of the vehicle body. Controlling the nonlinear stiffness coefficient of the suspension system within 103–106 is conducive to decreasing the dynamic deflection of the suspension system of vehicles, while increasing the fractional-order control coefficient and the fractional order is beneficial to controlling the dynamic deflection of the suspension system and the displacement of the vehicle body. Conclusions obtained in the study can provide unique references for the optimal design and control of nonlinear suspension systems with fractional-order displacement feedback control. Keywords: suspension; non-smooth; fractional order; dynamics; analytical solution; nonlinear.

Controller Development for Magneto-Rheological Semi-Active Suspension System to Improve Vehicle Safety


 
 
 Vehicle suspension system would complement vehicle safety in terms of ride comfort, handling and braking, and also isolation from road irregularities. This can be better achieved by introducing a semi-active suspension system where the magneto-rheological (MR) fluid is used to manipulate its damping characteristics. This paper explains the controller development for MR semi-active suspension system. The process started by developing the non-parametric linearized data driven (NPLDD) double input with proportional-integral (PI) controller as an inner loop algorithm for MR damper modelling and force tracking control; then, Improved PI controller as an outer loop control algorithm for vehicle response improvement, and finally validation work using quarter-car test bench. All the algorithm development is based on Perusahaan Otomobil Nasional (PROTON) vehicle characteristics and specifications. From the simulation results, it is verified that the NPLDD double input model together with the PI control strategy has the capability to track the desired damping force well. Meanwhile, the Improved PI controller for the outer loop is capable to reduce the magnitude of vehicle body acceleration and displacement. The validation at the quarter-car test bench also shows significant reduction of these two parameters. As a result, the PI controller for the MR semi-active suspension system is found sufficient for vehicle safety improvement.
 
 

Precision Assembly Simulation of Skin Model Shapes Accounting for Contact Deformation and Geometric Deviations for Statistical Tolerance Analysis Method

Tolerance analysis methods, which are important to achieve a balance between manufacturing costs and functional requirements, have been studied and improved over the last 30 years. This paper proposes a new method to improve the precision of assembly simulation for statistical assembly simulation; by investigating the effect of the geometric deviations and mechanical behaviors of assembly contact on the stack-up assembly deviation by combining the recent theories on the tolerance analysis of rigid bodies and local contact deformation. To improve the precision of the tolerance analysis, real parts with form defects were simulated with the help of non-nominal skin model shapes. The SMSs were first considered to be rigid, and a quadratic optimization-based method for the rigid body displacement was used to calculate the initial contact points of all the SMSs. Next, contact deformation, following Hertzian contact theory, occurred at the initial contact points, which changed the relative positions of the SMSs in the subsequent interactions. The iteration process was convergent, and the final simulation for tolerance analysis could be generated after several iterations. Case studies demonstrated the practicality of the proposed method. Their actual assembly deviations were simulated by combining the effects of geometric deviations and local surface deformations. Since the proposed tolerance analysis framework based on statistical assembly simulation, it is expected to control the functional requirements of mechanical assemblies with much rough tolerance design and help optimize the tolerance in the future.

Optimal Arytenoid Position in Laryngeal Framework Surgery: An Anatomic Human Larynx Study

The purpose of this study was to better understand the effects of stitch placement on arytenoid medialization by measuring normative cricoarytenoid joint anatomy and changes in arytenoid position when varying arytenopexy stitch configuration. This adult human larynx study was done in two parts. First, measurements of the cricoid and arytenoid cartilage anatomy relevant to cricoarytenoid joint function were made in 45 preserved larynges (26 male (M), 19 female (F)) using digital calipers. Second, the arytenoids of six fresh larynges ( three M, three F) were sutured to the cricoid using various arytenopexy-stitch placements ranging from inferior-lateral to superior-medial, and the resulting arytenoid positions were compared by measuring medial displacement of the arytenoid body and change in glottal configuration from macro still images using Image J. Paired t-tests were used to compare the results. Cartilage and joint facet dimensions showed differences between males (M) and females (F). Cricoid facet lengths averaged 9.3 mm (M) and 7.1 mm (F), and widths averaged 4.9 mm (M) and 4.0 mm (F). The arytenoid facet widths averaged 10.5 mm (M) and 9.7 mm (F). Average distances between cricoid facets were 11.8 mm for both males and females. Securing the arytenoid superior-medially on the cricoid facet produced more medialization (2.2 mm vs 1.0 mm, P < .001) and better glottic aperture configuration (9.5° vs 2.7°, P < .001) than securing the arytenoid inferior-laterally on the facet. Anatomic consistency in cricoarytenoid anatomy provides reliable surgical landmarks for ideal placement of an arytenopexy suture to optimally reposition the arytenoid cartilage. Optimal arytenoid medialization can be accurately reproduced with an arytenopexy-suture that is placed superior-medially on the cricoid facet. NA Laryngoscope, 131:2540-2544, 2021.

Biomechanical study of polymethyl methacrylate bone cement and allogeneic bone for strengthening sheep vertebrae

To investigate the feasibility and mechanical properties of polymethyl methacrylate (PMMA) bone cement and allogeneic bone mixture to strengthen sheep vertebrae with osteoporotic compression fracture. A total of 75 lumbar vertebrae (L 1-L 5) of adult goats was harvested to prepare the osteoporotic vertebral body model by decalcification. The volume of vertebral body and the weight and bone density before and after decalcification were measured. And the failure strength, failure displacement, and stiffness were tested by using a mechanical tester. Then the vertebral compression fracture models were prepared and divided into 3 groups ( n=25). The vertebral bodies were injected with allogeneic bone in group A, PMMA bone cement in group B, and mixture of allogeneic bone and PMMA bone cement in a ratio of 1∶1 in group C. After CT observation of the implant distribution in the vertebral body, the failure strength, failure displacement, and stiffness of the vertebral body were measured again. There was no significant difference in weight, bone density, and volume of vertebral bodies before decalcification between groups ( P>0.05). After decalcification, there was no significant difference in bone density, decreasing rate, and weight between groups ( P>0.05). There were significant differences in vertebral body weight and bone mineral density between pre- and post-decalcification in 3 groups ( P<0.05). CT showed that the implants in each group were evenly distributed in the vertebral body with no leakage. Before fracture, the differences in vertebral body failure strength, failure displacement, and stiffness between groups were not significant ( P>0.05). After augmentation, the failure displacement of group A was significantly greater than that of groups B and C, and the failure strength and stiffness were less than those of groups B and C, the failure displacement of group C was greater than that of group B, and the failure strength and stiffness were less than those of group B, the differences between groups were significant ( P<0.05). Except for the failure strength of group A ( P>0.05), the differences in the failure strength, failure displacement, and stiffness before fracture and after augmentation in the other groups were significant ( P<0.05). The mixture of allogeneic bone and PMMA bone cement in a ratio of 1∶1 can improve the strength of the vertebral body of sheep osteoporotic compression fractures and restore the initial stiffness of the vertebral body. It has good mechanical properties and can be used as one of the filling materials in percutaneous vertebroplasty.

A Finite Element Study on the Treatment of Thoracolumbar Fracture with a New Spinal Fixation System.

Objective In this study, the mechanical properties of the new spinal fixation system (NSFS) in the treatment of thoracolumbar fractures were evaluated by the finite element analysis method, so as to provide a mechanical theoretical basis for the later biomechanical experiments and clinical experiments. Methods T12-L2 bone model was constructed to simulate L1 vertebral fracture, and three models of internal fixation systems were established on the basis of universal spinal system (USS): Model A: posterior short-segment fixation including the fractured vertebra (PSFFV); Model B: short-segment pedicle screw fixation (SSPF); Model C: new spinal fixation system (NSFS). After assembling the internal fixation system and fracture model, the finite element analysis was carried out in the ANSYS Workbench 18.0 software, and the stress of nail rod system, fracture vertebral body stress, vertebral body mobility, and vertebral body displacement were recorded in the three models. Results The peak values of internal fixation stress, vertebral body stress, vertebral body maximum displacement, and vertebral body maximum activity in Model C were slightly smaller than those in Model B. Conclusions Compared with the traditional internal fixation system, the new spinal internal fixation system may have the mechanical advantage and can provide sufficient mechanical stability for thoracolumbar fractures.

Modelling and simulation of motor vehicle suspension system

In this work, using a quarter-car model was adopted, the equations of motion were derived for a passive and then the sky-hook semi-active suspension systems. The derived differential equations, solved using the Dormand-Prince pair numerical formula, was then used to simulate values of displacements as affected by damping coefficients and the sky-hook constant. The simulated results showed that the maximum amplitude of the sprung mass, which is linked to ride discomfort, increases while those of unsprung masses, which affects the road holding ability, decreases with increasing depth of pothole. Furthermore, displacements for both sprung and unsprung masses varied directly with damping coefficient. Finally, as the sky-hook constant of the semi active system model increases, values of amplitudes of unsprung masses decreases while those of sprung masses increases. It was, thus, shown that the vertical displacements of vehicle bodies and wheels are dependent on the depth of potholes, damping coefficient and sky-hook constant, and that the sky-hook semi-active suspension system model gave a better result compared to the passive suspension system. Therefore, by applying the sky-hook control principle, the desired road comfort of passengers can be achieved as well as reduced rate of car damage and cost of maintenance.

Locator Placement Optimization for Minimum Part Positioning Error During Machining Operation Using Genetic Algorithm

Fixture design is one of the main factors which affect the final product quality. Proper design of fixture plays an important role in ensuring the required tolerance of the product. Proper placement of locators is one of the prominent factors in fixture design. Locators are elastic: they deform under clamping and machining forces causing rigid body displacement of the workpiece which in turn affects the part quality. In this article, a 3-2-1 type of fixturing system having elastic locators around a considerably rigid rectangular workpiece is considered. A genetic algorithm is proposed, which uses a fitness function that evaluates the positioning error of the workpiece under external forces and torque. Among several variables, 12 variables, which define the placement of locators, are chosen to be optimized while minimizing the positioning error of the workpiece at the point of action of machining force. The proposed algorithm optimizes the 12 interlinked variables, within the specified region, for machining force and torque at a single point. However, when the cutting tool moves to any other point on the workpiece, it is observed that either the workpiece loses its contact with any one of the locators or the positioning error increases by a large value. To overcome this issue, the proposed algorithm is further modified for placement optimization to cater for multi-point machining, and the isostatism of the workpiece is ensured by checking the magnitude and direction of displacement (of what?) at each point of workpiece-locator contact. Finally, the original and modified GA algorithms are explained through a case study where the single point optimized placement shows loss of contact when machining force is applied at other points. The placement optimized from the modified algorithm shows that the isostatism of the workpiece remains intact while all four positioning errors are converged towards the same value. The results obtained from the proposed and modified algorithm are verified using ANSYS simulation.

Kinematic Characteristics of the Standing Long Jump in Young Children Aged 4–5 Years

The authors investigated the kinematic characteristics of the standing long jump in preschool children. Sixty 4-year-old children (boys: 30 and girls: 30) and sixty 5-year-old children (boys: 30 and girls: 30) participated in the present study. The authors focused on three differences in kinematics: between 4- and 5-year-old children, between boys and girls, and between high and low jumping performance groups at the same age. The kinematic data included the maximum flexions of the knee and hip before takeoff, at takeoff, and on landing; angular displacement of the upper body; takeoff speeds in horizontal and vertical directions; and takeoff angle of the greater trochanter. Anthropometric variables and kinematic data were separately analyzed with factors of age, sex, and group. The authors also performed multiple regression analysis to identify predictors of the jump distance. The movement speed of the greater trochanter in a horizontal direction, the maximum flexion angle of the hip before takeoff, and the hip angle on landing were identified as significant predictors of the jump distance among young children. These findings suggest that knowing how to use the hip and awareness of the horizontal direction are key factors to improve the long jump distance in young children.

Wavelet analysis of a flexible filament kinematics: emulating C. elegans swimming behavior

This paper discusses different aspects of an active flexible filament propulsion in a liquid medium. The immersed boundary method is used to model a flexible filament immersed in Newtonian fluid at low Reynolds numbers. The flexible filament motion emulates that of a C. elegans. We varied some parameters of the filament motion, such as the interpolation points of the function related to the curvature of the filament and the upstroke and downstroke period, and analyzed the kinematic response in the body displacement and fluid flow. A methodology based on signal analysis is proposed for correct modeling of the movement of these filaments. The swimming velocity and distance are analyzed using wavelet transform, in which the notion of time–frequency localization is made precise. This methodology allows defining which parameters lead to the best efficiency, e.g., greater swim distance for the same number of strokes, making it very valuable for passive control of the filament.

Genetic-fuzzy logic model for a non-invasive measurement of a stroke volume

BackgroundDespite the importance of stroke volume readings in understanding the work of the cardiovascular system in patients, its routine daily measurement outside of a hospital in the absence of special equipment presents a problem for a comprehensive assessment of the heart performance. ObjectiveThe purpose of this study was to develop a new non-invasive technique for measuring a stroke volume based on the relationship between time skin warming and a blood flow. Methods. Ninety two randomly selected volunteers (54 males, aged 30.1 ± 11.9 years old, and 38 females, aged 35.8 ± 12.4 years old) were recruited for this study. The time skin warming was determined by applying on the wrist above the arterial pulsation a thermoelectric cooler using the Peltier effect. During recording the participants were in the supine position. Blood pressure was measured by sphygmomanometer. Heart performance was assessed by Murata ballistocardiographic sensor, detecting displacement of the whole body during each cardiac ejection of blood. The data provided by this sensor included heart rate, respiratory rate, heart rate variability and a stroke volume. Linear, non-linear statistical regression models and fuzzy logic were used to analyse the degree of interrelation between BCG-measured stroke volume and the time skin warming. ResultsComparative analysis of results indicated that the generic-fuzzy logic model demonstrated a high level of dependency (R = 0.803) between input (participants’ time skin warming, pulse pressure and age) and output (ballistocardiographic stroke volume) parameters. ConclusionsThe method described in the paper offers a simple, portable, and low-cost solution that can even be used in a home setting to measure the stroke volume. The principle of the proposed method is based on the interrelation between time skin warming and blood flow. The latter, corrected by corresponding age and pulse pressure, expresses the participant's stroke volume. Adopting the genetic-fuzzy model significantly improved the accuracy of stroke volume's measurement and made the proposed method reliable for assessing of the cardiovascular system. This daily practice technique would help healthcare provider get an early diagnosis of cardiac dysfunctions and track heart changes during stress, e.g., in sport.

Effects of age, sex, and ENSO phase on foraging and flight performance in Nazca boobies.

Age‐related changes in survival and reproduction are common in seabirds; however, the underlying causes remain elusive. A lack of experience for young individuals, and a decline in foraging performance for old birds, could underlie age‐related variation in reproduction because reproductive success is connected closely to provisioning offspring. For seabirds, flapping flight during foraging trips is physiologically costly; inexperience or senescent decline in performance of this demanding activity might cap delivery of food to the nest, providing a proximate explanation for poor breeding success in young and old age, respectively. We evaluated the hypothesis that young and old Nazca boobies (Sula granti), a Galápagos seabird, demonstrate deficits in foraging outcomes and flight performance. We tagged incubating male and female adults across the life span with both accelerometer and GPS loggers during the incubation periods of two breeding seasons (years), during the 2015 El Niño and the following weak La Niña. We tested the ability of age, sex, and environment to explain variation in foraging outcomes (e.g., mass gained) and flight variables (e.g., wingbeat frequency). Consistent with senescence, old birds gained less mass while foraging than middle‐aged individuals, a marginal effect, and achieved a slower airspeed late in a foraging trip. Contrary to expectations, young birds showed no deficit in foraging outcomes or flight performance, except for airspeed (contingent on environment). Young birds flew slower than middle‐aged birds in 2015, but faster than middle‐aged birds in 2016. Wingbeat frequency, flap–glide ratio, and body displacement (approximating wingbeat strength) failed to predict airspeed and were unaffected by age. Sex influenced nearly all aspects of performance. Environment affected flight performance and foraging outcomes. Boobies' foraging outcomes were better during the extreme 2015 El Niño than during the 2016 weak La Niña, a surprising result given the negative effects tropical seabirds often experience during extreme El Niños.

Study on the Seismic Performance of Small-Diameter Bolts Reinforced in Grottoes

The Yungang Grottoes, a World Heritage Site in Datong, consist of 252 caves that are noted for their collection of 5th- and 6th-century Buddhist grotto sculptures and reliefs. Various diseases have appeared in the grottoes under the general influence of natural and artificial factors. Bolt support is a commonly employed method for grotto reinforcement and has been widely applied in many projects. Small-diameter bolts have also been used in the reinforcement projects at the Yungang Grottoes, but the corresponding effect on the seismic performance of grottoes is still unclear. In this paper, a dynamic analysis via the numerical modelling of an ear grotto of the 19th grotto in Yungang is established, and the rock displacement, acceleration, and bolt axial force responses under a seismic wave are analyzed. The results show that the seismic dynamic responses of grottoes are greatly affected by the cliff structure. The displacement and acceleration responses of the cliff body vary greatly within the abrupt transition of the cliff structure. Based on this variation, the seismic capacity of small-diameter bolts in the vertical direction is greater than that in the horizontal direction. The axial force of a bolt is small at both ends of the bolt, large in the middle of the bolt, small on the top of a cliff, and large at the bottom of the cliff. Although the axial force is small, the upper rock mass of the grotto has a tendency to undergo relative movement compared with the outer rock mass. The results also indicate that based on the structural defects in the vertical direction of the cliff body caused by grotto excavation, the inclined angle of the bolt should be increased as far as possible or vertical support should be adopted to enhance the stability of the rock mass at the top of the grotto.

Numerical analysis of stress distribution and deformation and failure characteristics of surrounding rock in coal road excavation

In order to further provide a basis for determining the reasonable sealing depth of the coal seam drainage hole, based on the geological data of the W33011 working face of Sihe Mine, the FLAC3D numerical simulation software is used to analyze the stress, displacement, and plastic zone of the surrounding coal body after the excavation of the W33011 roadway in Sihe Mine. And the distribution law of vertical stress, horizontal stress, vertical displacement, horizontal displacement and elastoplastic failure characteristics of the coal body around the roadway are obtained.

Design of Novel BELBIC Controlled Semi-Active Suspension and Comparative Analysis with Passive and PID Controlled Suspension

Passenger comfort, quality of ride, and handling have broughta lot of attention and concern toautomotive design engineers. These 2 parameters must have optimum balance as they have an inverse effect on each other. Researchers have proposed several approaches and techniques like PID control, fuzzy approach, GA, techniques with inspiration from nature and hybrid techniques to attain the same. A new controller based on the learning behavior of the human brain has been used for the control of semi-active suspension in this study. The controller is known as the Brain Emotional Learning-Based Intelligent Controller (BELBIC). A one-fourth model of car along with the driver model having 6 degrees of freedom (DOF) wasmodeled and simulated. The objective of the studywasto analyze the performance of the proposed controller for improving the dynamic response of the vehicle model coupled with complex biodynamic models of the human body as a passenger, making the whole dynamic system very complex to control. The performance wasanalyzed based on percentage reduction in the overshoot of the vehicle’s sprung mass as well as different human body parts when subjected to road disturbances. The proposed controller performance wascompared with the PID controller, widely used in semi-active suspension. The simulation results obtained for BELBIC controlled system for circular road bump showed that the overshoot of passenger head and body wasreduced by 18.84 and 18.82 %, respectively and reduction for buttock and leg displacement was18.87 %. The vehicle’s seat and sprung mass displacement displayedan improvement of 18.90 and 18.51 %. The overshoot of passenger's head and body displacement wasimproved by 19.79and 19.62 %,respectively, whereas improvement for buttock &amp; leg, vehicle’s seat, and sprung mass displacement were19.81, 20.00, and 20.49 % against trapezoidal speed bump. The PID controlled suspension disclosed an improvement of 8.74, 8.53, 8.75, 11.11, 14.75 % against circular bump and 10.72, 10.33, 10.73, 11.11 and 11.75 % against trapezoidal bump for overshoot reduction of passenger head, body, buttock &amp; leg, vehicle’s seat and sprung mass displacement, respectively. The proposed BELBIC controlled semi-active suspension outperformed the widely used PID controlled semi-active suspension and indicated asignificant improvement in the ride quality of the vehicle.

Long wave generation and coastal amplification due to propagating atmospheric pressure disturbances

Meteotsunamis are long waves generated by displacement of a water body due to atmospheric pressure disturbances that have similar spatial and temporal characteristics to landslide tsunamis. NAMI DANCE that solves the nonlinear shallow water equations is a widely used numerical model to simulate tsunami waves generated by seismic origin. Several validation studies showed that it is highly capable of representing the generation, propagation and nearshore amplification processes of tsunami waves, including inundation at complex topography and basin resonance. The new module of NAMI DANCE that uses the atmospheric pressure and wind forcing as the other inputs to simulate meteotsunami events is developed. In this paper, the analytical solution for the generation of ocean waves due to the propagating atmospheric pressure disturbance is obtained. The new version of the code called NAMI DANCE SUITE is validated by comparing its results with those from analytical solutions on the flat bathymetry. It is also shown that the governing equations for long wave generation by atmospheric pressure disturbances in narrow bays and channels can be written similar to the 1D case studied for tsunami generation and how it is integrated into the numerical model. The analytical solution of the linear shallow water model is defined, and results are compared with numerical solutions. A rectangular shaped flat bathymetry is used as the test domain to model the generation and propagation of ocean waves and the development of Proudman resonance due to moving atmospheric pressure disturbances. The simulation results with different ratios of pressure speed to ocean wave speed (Froude numbers) considering sub-critical, critical and super-critical conditions are presented. Fairly well agreements between analytical solutions and numerical solutions are obtained. Additionally, basins with triangular (lateral) and stepwise shelf (longitudinal) cross sections on different slopes are tested. The amplitudes of generated waves at different time steps in each simulation are presented with discussions considering the channel characteristics. These simulations present the capability of NAMI DANCE SUITE to model the effects of bathymetric conditions such as shelf slope and local bathymetry on wave amplification due to moving atmospheric pressure disturbances.

Advanced compressive extension injuries of the subaxial cervical spine: do we really understand the nuances of this injury?

Background ContextThe Allen and Ferguson classification of cervical spine injuries is widely used. They described compressive Extension (CE) injuries as having five progressive stages. Stage 4(CE4) and 5(CE5) have been described as having a posterior vertebral arch fracture involving two motion segments accompanied by displacement (dislocation) of the vertebral body at a single level. However, in their original work, CE4 was described only as a hypothetical stage, while CE5 was found in only three patients. Beyond this, little is understood about these injuries. PurposeTo identify characteristics of compression extension injuries with vertebral body displacement (CE4 and CE5) from a series of surgically treated subaxial cervical spine fractures. A secondary aim was to identify specific characteristics that may guide treatment or affect prognosis. DesignRetrospective case series. Patient SampleTwenty-four patients who underwent surgical stabilization of CE4 and CE5 cervical spine fracture-dislocations in non-ankylosed spines over a 14-year period. Outcome MeasuresRadiographic categorization of CE injury type, treatment rendered, postoperative spinal alignment, presence of nonunion, loss of fixation, hardware-related and neurologic complications. MethodsAfter IRB approval, patients with CE injuries were identified through billing data and radiology records at a level I trauma center between January 2005 and September 2018. Demographic data, ISS, ASA, motor score, and complications during the hospitalization were collected from the patient's EMR. CT scans were reviewed to assess fracture pattern, level, and location of the vertebral arch fracture, vertebral body displacement, spinal canal diameter and method of surgical stabilization. Injuries were classified according to the classification of Allen and Ferguson, and the AO subaxial cervical spine classification. ResultsOf 221 patients identified with CE mechanism, 24 had CE4 or CE5 injuries. High-energy mechanism occurred in 92% of the patients, with motor vehicle accidents being the most common. The average ASIA motor score was 80 preoperatively and 84 at average 398 days follow-up. All CE4 and CE5 injuries occurred at C6-C7 or C7-T1. Average anterolisthesis was 6.26 mm (SD ± 2.3 mm) for CE4 and 16.8 mm (SD ± 1.8 mm) for CE5. Average spinal canal diameter at the level of dislocation was 20 mm (SD ± 0.4 mm) for CE4 and 30.5 mm (range 29.6 – 31.4 mm) for CE5. The surgical approach was anterior in 5 patients, posterior in 12 patients, and combined in 7 patients. Four patients had single-evel fixation, all of whom had CE4 injuries, and 20 patients had fixation across two or more levels. Thirty percent of patients had complications, none of which included postoperative spinal malalignment, nonunion or hardware-related complications, or worsening of neurologic exam. Three deaths occurred in the postoperative hospitalization period (7 to 15 days). ConclusionCE4 and CE5 injuries represented 10% and 1% of all CE injuries in our series respectively occurring only at the C6-C7 and C7-T1 levels. Though by original description these are two-level injuries, in patients with milder posterior element injury, single level stabilization was used successfully. We have therefore proposed designating CE4 into less severe CE4a and more severe CE4b injuries. Because this fracture pattern typically results in widening of the spinal canal as the anterior displacement of the vertebral body occurs independent of the fractured posterior elements, spinal cord injuries are neither as severe nor as common as in fracture-dislocation from other mechanisms.