Lifting Phase Research Articles

Online prediction of loader payload based on a multi-stage progressive model

In earthmoving equipment, overloading and underloading transport vehicles reduce the production efficiency. This paper presents a novel online loader payload prediction method, based on a multi-stage progressive model. The method consists of: Dynamic Model (DM), Optimised Least Squares Method (OLSM) and Back Propagation Neural Network (BPNN). In the transport phase, the load is predicted, using DM approach. In the moving arm lifting phase, the parameter indicators reflecting the load are extracted and re-estimated via OLSM. Finally, the extracted indicators are used as inputs to the BPNN, to further refine the prediction results. Experiments with two types of loaders are carried out to validate the presented method. The results show that it performs better in accuracy, robustness, portability and fault tolerance. The prediction error probability density conforms to the Cauchy distribution and the single maximum prediction error is limited within ±2%.

Dynamic design and analysis of subsea CO2 discharging flowline for cargo submarines used for CCS in low-carbon and renewable energy value chains

Developing offshore low carbon and renewable energy value chains to realize a net-zero energy future requires combining offshore renewable energy and carbon capture storage (CCS) solutions. The subsea shuttle tanker (SST) was presented in recently published works to accelerate the adoption of offshore CCS systems. The SST is a novel underwater vessel designed to transport CO2 autonomously from offshore facilities to subsea wells for direct injection at marginal fields using a flowline connected. The SST will be subjected to stochastic currents and experience dynamic responses during this offloading process. The offloading flowline must be designed to handle this dynamic response. As such, this paper establishes the baseline design for this flowline. The cross-section and global configuration designs drive the flowline design. For the cross-section design, the pressure containment, collapse and local buckling criteria defined in DNV-OS-F101 are applied to validate the required structural capacity at specified water depths. For the configuration design, the principle factors concerning the water depth, internal flow rate, and current speed are investigated to further validate the stress capacity according to the allowed von Mises stress level for a more robust baseline design. Finally, the flowline connecting and disassembly methodology is proposed, and the critical factor of well-coordinated speed between flowline and SST is investigated to avoid overbending during the lifting and lowering phases.

A study on brain neuronal activation based on the load in upper limb exercise (STROBE).

This study aimed to determine the level of brain activation in separate regions, including the lobes, cerebellum, and limbic system, depending on the weight of an object during elbow flexion and extension exercise using functional magnetic resonance imaging (fMRI). The study was conducted on ten male undergraduates (22.4 ± 1.2 years). The functional images of the brain were obtained using the 3T MRI. The participants performed upper limb flexion and extension exercise at a constant speed and as the weight of the object for lifting was varied (0 g and 1000 g). The experiment consisted of four blocks that constituted 8 minutes. Each block was designed to comprise a rest phase (1 minute) and a lifting phase (1 minute). The results showed that, in the parietal lobe, the activation was higher for the 0 g-motion condition than for the 1000 g-motion condition; however, in the occipital lobe, cerebellum, sub-lobar, and limbic system, the activation was higher for the 1000 g-motion condition than for the 0 g-motion condition. The brain region for the perception of object weight was identified as the ventral area (occipital, temporal, and frontal lobe), and the activation of the ventral pathway is suggested to have increased as the object came into vision and as its shape, size, and weight were perceived. For holding an object in hand, compared to not holding it, the exercise load was greater for controlling the motion to maintain the posture (arm angle at 90°), controlling the speed to repeat the motion at a constant speed, and producing an accurate posing. Therefore, to maintain such varied conditions, the activation level increased in the regions associated with control and regulation through the motion coordination from vision to arm movements (control of muscles). A characteristic reduced activation was observed in the regions associated with visuo-vestibular interaction and voluntary movement when the exercise involved lifting a 1000-g object compared to the exercise without object lifting.

Biomechanical differences in experts' and novices' footstep patterns during a palletizing task

Very few studies have examined differences between experts' and novices' foot positioning and movements during manual materials handling tasks. The impact of footstep patterns on low back loading needs to be better understood. The goals of this study were to characterize foot placement and movements in novices and experts and to assess their impact on back loading considering the height of grasp. The task consisted in transferring 24 15 kg boxes from a pallet to another. Foot placement and movements were classified with a recently developed taxonomy. Results show that experts' feet remained static more often than novices' feet during the lifting phase. Positioning the feet towards the deposit site during lifting increased asymmetrical moments, especially for novices. Positioning one foot forward increased asymmetrical moments for novices. Overall, footstep strategies are an effective indicator of low back exposure and should be considered in ergonomic studies.

Improving the Efficacy of an Active Back-Support Exoskeleton for Manual Material Handling Using the Accelerometer Signal

Occupational back-support exoskeletons see their potential application in many industrial sectors to mitigate low back pain risk for workers performing demanding tasks. This work aims to design and evaluate a control strategy that improves the efficacy of an active exoskeleton by exploiting the raw signal from an accelerometer placed on the user’s torso. The designed strategy adapts the assistance to the user’s dynamics during lifting and lowering tasks, increasing the assistance for the lifting phase and decreasing it for lowering. The strategy efficacy is demonstrated through experimental analysis on twenty subjects. Comparisons are made with the task executed without the exoskeleton and a state-of-the-art inclination-based strategy. Results demonstrate the efficacy of the proposed strategy in improving users’ acceptance and reducing erector spinae muscle activity. Using the accelerometer signal, the exoskeleton can enhance the assistance provided to workers performing manual material handling in real working scenarios, increasing safety, efficiency, and productivity.

Numerical investigations of the flow-induced vibration of a three-dimensional circular cylinder with various symmetric strips attached

Changes to the surface morphology of a cylinder immersed in a uniform flow may affect the surrounding flow characteristics. Circular cylinders with various symmetric strips attached are ideal models for studying this subject. This study investigates the flow-induced vibration (FIV) of a three-dimensional cylinder with symmetric strips attached using the delayed detached-eddy simulation method. First, the effects of the 22 different types of strip parameters are evaluated on the fixed cylinder. Then, P5-60-20 (location α=60°, coverage β=20°, and thickness h/D=5%) is chosen to explore the transverse FIV. P5-60-20 vibration responses exhibit four distinct branches—initial branch, passive upper branch, transition branch from vortex-induced vibration (VIV) to galloping, and pure galloping—which correspond to the classic initial, upper, lower, and desynchronization regions of the circular cylinder. Through a detailed discussion of each branch, it is discovered that the passive upper branch is significantly different from the upper branch, despite their similar vibration amplitudes and frequencies. The upper branch is induced by the flutter in the presence of intense three-dimensional flow. However, the passive upper branch is caused by symmetric strips, which promote spanwise correlation, prevent lift phase shifting, and dampen the effect of three-dimensional flow. Consequently, at higher reduced velocities, the transition from VIV to galloping and pure galloping is triggered.

Comparison of Power Training vs Traditional Strength Training on Physical Function in Older Adults

Strength training exercise is recommended for improving physical function in older adults. However, whether strength training (lifting and lowering weights under control) and power training (PT) (lifting weights fast and lowering under control) are associated with improved physical function in older adults is not clear. To evaluate whether PT vs traditional strength training is associated with physical function improvement in older adults. Systematic searches of MEDLINE, Embase, Cochrane Central, CINAHL, PsycInfo, PEDro, and SPORTDiscus were conducted from database inception to October 20, 2021. Randomized clinical trials (RCTs) that compared strength training with instructions to move the weight as fast as possible in the lifting phase with traditional strength training in healthy, community-living older adults (age ≥60 years). Two authors independently selected trials, extracted data, assessed the risk of bias using the Cochrane risk-of-bias tool 2, and assessed the certainty of the evidence using the Grading of Recommendations, Assessment, Development and Evaluation approach. Summary effect size measures were calculated using a multilevel random-effects model with cluster robust variance estimation and are reported as standardized mean differences (SMDs). Reporting followed the Preferred Reporting Items for Systematic Reviews and Meta-analyses guideline. Primary outcomes included physical function and self-reported physical function. Secondary outcomes included power, strength, muscle mass, walk speed, balance, and adverse effects. A total of 20 RCTs enrolling 566 community-living older adults (mean [SD] age, 70.1 [4.8] years; 368 [65%] women) were included. For the primary outcomes, PT was associated with an improvement in physical function with low-certainty evidence in 13 RCTs (n = 383) (SMD, 0.30; 95% CI, 0.05-0.54) and self-reported function with low-certainty evidence in 3 RCTs (n = 85) (SMD, 0.38; 95% CI, -0.62 to 1.37). The evidence was downgraded by 2 levels for high risk of bias and imprecision for physical function and very serious imprecision for self-reported physical function. In this systematic review and meta-analysis, PT was associated with a modest improvement in physical function compared with traditional strength training in healthy, community-living older adults. However, high-quality, larger RCTs are required to draw more definitive conclusions.

Ergonomics Risk Assessment for Manual Material Handling of Warehouse Activities Involving High Shelf and Low Shelf Binning Processes: Application of Marker-Based Motion Capture

Lower back pain is a musculoskeletal disorder that is commonly reported among warehouse workers due to the nature of the work environment and manual handling activities. The objective of this study was to assess the ergonomic risks among warehouse workers carrying out high shelf (HS) and low shelf (LS) binning processes. A questionnaire was used to determine the prevalence of musculoskeletal symptoms, while a marker-based motion capture (MoCap) system worksheet was used to record the participants’ motion and determine the action risk level. A total of 33% of the participants reported lower back pain in the past seven days, based on the Cornell Musculoskeletal Discomfort Questionnaire (CMDQ) results. Analysis of the body velocities showed that the HS binning process had four major velocity peaks, defined as the initial, lowering, lifting, and final phases. In comparison, the LS binning process had two major peaks defined, the crouching and rising phases. There were significant differences between the mean velocities of the workers for the HS binning process, indicating that the workers have different movement patterns with varying velocities.

Job insecurity as a barrier to thriving during COVID-19 pandemic: a moderated mediation model of knowledge hiding and benevolent leadership

PurposeDrawing upon the conservation of resource (COR) theory, the purpose of this paper is to explore the mediating role of knowledge hiding in the relationship between job insecurity and two dimensions of thriving at work, i.e. learning and vitality. The study further aims to investigate the moderating role of benevolent leadership in the aforementioned mediating relationship by applying the moderated mediation framework.Design/methodology/approachThe sample for the study consisted of employees working in service sector in India. The hypotheses were tested with two wave survey data collected from 365 employees during the COVID-19 pandemic when the Indian Government was lifting phase wise restrictions. Data was analyzed using mediation and moderated mediation analyses on PROCESS v 3.0 macro.FindingsResults showed that knowledge hiding mediated the relationship between job insecurity and both dimensions of thriving at work. Further, benevolent leadership was seen to moderate the mediated relationship providing support for the moderated mediation framework.Practical implicationsThe results highlight the significance of providing benevolent leadership training to the managers to help them cope with the anxiety arising out of job insecurity. Further, employees need to be cautioned regarding the deleterious effects of knowledge hiding, which can impede their own learning and vitality.Originality/valueTo the best of the authors’ knowledge, this is the first study to investigate the mediating role of knowledge hiding in the relationship between job insecurity and thriving. Further, the role played by benevolent leadership in mitigating the harmful effects of job insecurity especially during COVID-19 pandemic is a unique contribution of the study.

Different Phases in Manual Materials Handling Have Different Performance Criteria: Evidence From Multi-Objective Optimization.

A manual material handling task involves the phases of reaching, lifting, unloading, and standing up (RLUS). Understanding the mechanisms of manual material handling is important for occupational health and the development of assist devices. Predictive models are becoming popular in exploring which performance criterion is appropriate in the lifting phase. However, limited attempts have been performed on the other phases. The associated performance criterion for predicting other phases is unknown. In this study, an optimization model for predicting RLUS has been developed with the multi-objective optimization method. Two performance criteria (minimum dynamic effort and maximum balance) were studied to explore their importance in each phase. The result shows that maximum balance leads to joint angle errors 27.6% and 40.9% smaller than minimum dynamic effort in reaching and unloading phases, but 40.4% and 65.9% larger in lifting and standing up phases. When the two performance criteria are combined, the maximum balance could help improve the predicting accuracy in the reaching, lifting, and unloading phases. These findings suggest that people prefer different performance criteria in different phases. This study helps understand the differences in motion strategies in manual materials handling (MMH), which would be used to develop a more accurate predictive model.

Influence of Load Knowledge on Biomechanics of Asymmetric Lifting.

Background: Load knowledge has been identified as a factor affecting the risk of low back pain (LBP) during symmetric lifting. However, the effects of load knowledge in asymmetric lifting tasks have not been reported yet. The purpose of this study was to investigate the load knowledge influence on lifting biomechanics in asymmetric lifting tasks; Methods: Twenty-four male adults were recruited to complete a psychophysical lifting capacity test and a simulated asymmetric lifting task. The lifting task was set with load knowledge of ‘no knowledge’ (NK), ‘weight known’ (WK), ‘fragile material known’ (FK), and ‘weight and fragile material known’ (WFK) for different lifting load weights. Trunk kinematics and kinetics were collected and analyzed; Results: When fragility information was presented, trunk sagittal flexion acceleration, lateral flexion velocity and acceleration, and average lateral bending moment were significantly lowered at the deposit phase. Lifting a high load weight was found to significantly increase low back sagittal bending moment at the lifting phase and low back moments of all three dimensions at the deposit phase; Conclusions: The decrease of trunk kinematic load suggests that providing material fragility information to workers in asymmetric lifting tasks would be effective in reducing their risk of LBP.

Numerical simulation of surface roughness effects on the vortex-induced vibration of a circular cylinder at a subcritical Reynolds number

The Vortex-Induced Vibration (VIV) of a circular cylinder with different surface roughness is numerically simulated at a subcritical Reynolds number of 3900. The effects of surface roughness on the vibration response amplitude, hydrodynamic coefficients and wake vortex are analyzed. The results show that as surface roughness increases, four branches (initial, upper, super-upper and lower branches) appear in the VIV response for a smooth cylinder, and for a cylinder with a small surface roughness of K S / D = 2.5 × 10 − 3 , this response changes to three branches (initial, upper and lower branches). The vortex shedding for the initial and lower branches is 2S mode, and that for the upper and super-upper branches (lock-in range) is P + S − , P+S + and 2P modes. With increasing surface roughness, the maximum amplitude has little difference, and the width of the lock-in range increases. A large jump in the vortex phase at the transition of the initial and upper branches and a large jump in the total lift phase at the transition of the upper and lower branches are found, and these jumps are associated with a switch in the timing of vortex shedding (jump of the vortex phase: 2S mode to P + S − mode; jump of the lift phase: other modes to 2S mode). The results are significant for the development of flow and vibration control technology.

The ADR Encoder is a reliable and valid device to measure barbell mean velocity during the Smith machine bench press exercise

Velocity-based training is a contemporary resistance training method, which uses lifting velocity to prescribe and assess the effects of training. However, the high cost of velocity monitoring devices can limit their use among strength and conditioning professionals. Therefore, this study aimed to examine the reliability and concurrent validity of an affordable linear position transducer (ADR Encoder) for measuring barbell velocity during the Smith machine bench press exercise. Twenty-eight resistance-trained males performed two blocks of six repetitions in a single session. Each block consisted of two repetitions at 40%, 60%, and 80% of their estimated one-repetition maximum. The mean velocity of the lifting phase was simultaneously recorded with the ADR Encoder and a gold-standard linear velocity transducer (T-Force® System). Both devices demonstrated high reliability for measuring mean velocity (ADR Encoder: CVrange = 2.80%–6.40% and ICCrange = 0.78–0.82; T-Force® System: CVrange = 3.27%–6.62% and ICCrange = 0.77–0.81). The ADR Encoder provided mean velocity at 40%1RM with a higher reliability than the T-Force® System (CVratio = 1.17), but the reliability did not differ between devices at higher loads (60%1RM–80%1RM) (CVratio ≤ 1.08). No fixed or proportional bias was observed for the different loads using least-products regression analysis, while the Bland–Altman plots revealed low systematic bias (0.01 m·s−1) and random errors (0.03 m·s−1). However, heteroscedasticity of the errors was observed between both devices ( R2 = 0.103). The high reliability and validity place the ADR Encoder as a low-cost device for accurately measuring mean velocity during the Smith machine bench press exercise.

Research and application of natural gas pipeline assessment method in Location Class upgrading areas

With the development of society and economy in China, the Location Class of many natural gas pipelines has been upgraded compared with the as-built data. Location Class upgrading will lead to significantly increasing of failure risk in these areas. Thus, it is necessary to develop an assessment method to evaluate the continued service capacity of these pipe sections, and in order to provide a rational decision. On the basis of comparing specifications and regulations, a three-step assessment process is established, which is aimed to evaluate the pipeline step by step from the aspect of design compliance, pressure applicability, and risk acceptability, respectively. The assessment method is based on specification compliance, and is risk-oriented, which can be regarded as one of the important achievements in pipeline safety lifting phase. Besides, the best practice can be applied to other engineering in the future.

Reliability and concurrent validity of the PUSH Band™ 2.0 to measure barbell velocity during the free-weight and Smith machine squat exercises

The aim of this study was to examine the test-retest reliability and concurrent validity of the PUSH Band™ 2.0 to measure barbell’s velocity during unconstrained (free-weights) and constrained (Smith machine) squat exercises. After an initial assessment of the Smith machine squat one-repetition maximum (1RM), 24 resistance-trained males completed one or two testing sessions separated by 7 days. In one session, the squat was performed with free-weights ( n = 22), while in another session, the Smith machine was used ( n = 16). Both testing sessions consisted of two blocks of eight repetitions (three repetitions at 45%1RM, three repetitions at 65%1RM, and two repetitions at 85%1RM). The mean velocity of the lifting phase was simultaneously recorded with the PUSH Band™ 2.0 and a gold-standard linear velocity transducer (T-Force® System). The PUSH Band™ 2.0 generally revealed an acceptable reliability (CVrange = 5.81%–13.14%), but the reliability was always greater for the T-Force® System (CVrange = 2.95%–7.86%). Regardless of the squat exercise, the concurrent validity of the PUSH Band™ 2.0 with respect to the T-Force® System was generally low at 45%1RM (ESrange = 0.18–0.33; rrange = 0.58–0.75; SEErange = 0.04–0.05 ms−1 and 4.2%–6.0%), 65%1RM (ESrange = 0.26–0.44; rrange = 0.63–0.82; SEErange = 0.04–0.06 ms−1 and 6.0%–9.2%), and 85%1RM (ESrange = 0.61–0.64; rrange = 0.66–0.82; SEErange = 0.05–0.07 ms−1 and 11.4%–16.0%). Taken together, these results suggest that the PUSH Band™ 2.0 is a reliable, but not valid, wearable technology to measure the barbell velocity during the free-weight and Smith machine squat exercises.

Outcome of Midvastus versus Subvastus Approach in Single Stage Bilateral Total Knee Arthroplasty

Objective: To compare midvastus and subvastus approach regarding operative parameters(lateral retinacular release, operative time, neurovascular injury) and outcome (Knee Society Score, Straight Leg Raise) at 12 weeks in single stage bilateral total knee arthroplasty. Study Design: Randomized clinical trial study Place and Duration of Study: Institute of Orthopaedic Surgery and South City Hospital Karachi from 1st January 2016 to 31st December 2018. Methodology: Fifty two patients of both genders ofmore than 50 years with osteoarthritis grade III or IV and bony changes confirmed by AP and lateral radiographs of knee were included. Patients with previous knee surgeries including high tibial osteotomy, deformities >20°(on mechanical axis), any neuromuscular problem and BMI ≥30 were excluded. Final assessment was done at 12 weeks. Isometric quadriceps strength was assessed by holding of contraction in seconds during the lifting (10cm above the plinth) phase of SLR (patient lying supine).Knee score (preoperative and final follow-up) was performed by Knee Society Score. Results: Thirty five were females and 21 males with mean age 65.3 years (50-78 years). Mean body mass index was 27.8 Kg/m2 (26.4-29.9). In midvastus TKR, the mean operative time was 61.7 minutes (range 52-70) whereas the same was 68.3 minutes (range 58-74) in subvastus TKR with p value 0.002. Rate of lateral retinacular release (LLR) was significantly (p=0.011) different between the midvastus TKR 5 (8.9%) and subvastus TKR 11 (19.6%). Neither group had neurovascular injury or early infection of the knee. Active SLR in subvastus group was achieved in shorter time (mean 3.1 days) as compared to midvastus group (mean 4.7 days). There was no difference (p=0.173) in isometric quadriceps strength at 12 weeks between subvastus TKR (mean 18 seconds) and midvastus TKR (mean 17 seconds). Knee society pain and functional scores were comparable between the two approaches at final follow up. Conclusion: Subvastus exposure has advantage of achieving active straight leg raise earlier while midvastus has lower frequency of lateral retinacular release. No difference in hospital stay and postoperative pain scores. Both subvastus and midvastus approaches are safe and offer comparable Knee Society Score outcomes. Keywords: Midvastus, Subvastus, Total knee arthroplasty, Knee Society Score, Straight leg raise

H-Infinity Control of a Six-Legged Robot in Lifting Mode

The present work aims at elaborating an efficient robust control approach of a six-legged robot in the lifting phase movement with the presence of nonlinearities, internal and external disturbances. A dynamic model of the legged robot is derived using the Newton-Euler formalism. Furthermore, an identification method is used to determine the system’s behavior by considering the joint variables at low, medium and high velocities. The variations between the obtained models in the different velocity margins are considered as nonlinearities and dynamic uncertainties, and are represented by the multiplicative uncertainty configuration. The H-infinity mixed-sensitivity method is applied in order to achieve a good performance and robust stability against external disturbances and the internal uncertainties represented by the unmodeled dynamics, the sensor noise, and the restrictions on the actuators control weight. In order to verify the capability of this controller to achieve the system stability and performances against the different disturbances, the small gain theorem method and robust stability and performance margin plots are used. The simulation results show that the control algorithm proposed in this paper can effectively achieve the robust stability and the hexapod robot performances.

A comprehensive biomechanical analysis of the barbell hip thrust.

Barbell hip thrust exercises have risen in popularity within the biomechanics and strength and conditioning literature over recent years, as a method of developing the hip extensor musculature. Biomechanical analysis of the hip thrust beyond electromyography is yet to be conducted. The aim of this study was therefore to perform the first comprehensive biomechanical analysis the barbell hip thrust. Nineteen resistance trained males performed three repetitions of the barbell hip thrust at 70% one-repetition maximum. Kinematic (250 Hz) and kinetic (1000 Hz) data were used to calculate angle, angular velocity, moment and power data at the ankle, knee, hip and pelvic-trunk joint during the lifting phase. Results highlighted that the hip thrust elicits significantly (p < 0.05) greater bilateral extensor demand at the hip joint in comparison with the knee and pelvic-trunk joints, whilst ankle joint kinetics were found to be negligible. Against contemporary belief, hip extensor moments were not found to be consistent throughout the repetition and instead diminished throughout the lifting phase. The current study provides unique insight to joint kinematics and kinetics of the barbell hip thrust, based on a novel approach, that offers a robust evidence base for practitioners to guide exercise selection.

Resistance Training Does Not Decrease Placental Blood Flow During Valsalva Maneuver: A Novel Use of 3D Doppler Power Flow Ultrasonography.

The Valsalva maneuver may increase maternal blood pressure and intra-abdominal pressure, resulting in decreased blood flow to the fetus during resistance training. There is no significant reduction in placental blood flow in pregnancy during resistance training in recreational athletes, as documented by a 3-dimensional power flow Doppler ultrasonography. Cohort. Level 3. A cohort of healthy women who participated in recreational athletics was enrolled in a prospective study to assess placental blood flow during a resistance exercise. A 1 repetition maximum (1RM, up to 50 lb) was determined through a modified chest press as a marker of heavy resistance training. Three-dimensional volume measurements and power Doppler flow were determined at the rest phase and during the 1RM lift phase. The vascular flow index (VFI) was calculated to determine placental perfusion during each phase. A total of 22 women participated. The mean age of participants was 31 years. Gestational age ranged from 13 to 28 weeks. Average 1RM weight lifted was 30 lb. Four women (18%) were able to lift 50 lb, the maximum weight that the study allowed. The remaining 18 women (82%) lifted their true 1RM. Mean VFI during lift phase was 2.185 compared with 2.071 at rest (P = 0.03). There was a slight mean increase in VFI during lift phase, 0.114 (95% CI 0.009-0.182) from 2.071 to 2.185 with lifting (P = 0.03). The 15 women who participated in structured exercise had a mean VFI at rest and during the lift phase of 2.031 and 2.203, respectively (P = 0.01). Three-dimensional power flow Doppler imaging can guide resistance training during pregnancy to prevent fetal injury due to hypoperfusion. Resistance training up to an RM1 of 50 lb did not result in a significant reduction of placental blood flow from resting state in the study population. This technique may be used to guide training parameters among pregnant athletes.

THE ROLE OF CROSS THERMAL BUOYANCY IN INITIATING VORTEX SHEDDING BEHIND A PERMEABLE SQUARE CYLINDER AT LOW REYNOLDS NUMBERS

A two-dimensional numerical simulation is performed to analyze the role of cross thermal buoyancy in initiating vortex shedding behind a permeable square cylinder at low Reynolds numbers. The porous cylinder is placed stationary in an unconfined fluid medium having Prandtl number Pr = 0.71 (air). The permeability of the object is considered in the range of Darcy number as 10-6 ≤ Da ≤ 10-2 with the corresponding porosity values in the range 0.629 ≤ ε ≤ 0.993 for the set of Reynolds numbers 10 ≤ Re ≤ 40. In the chosen range of Re, the flow behind the object is laminar and characterized by the formation of a steady separation bubble with two counter-rotating vortices. Heating the cylinder causes thermal buoyancy driven transport to develop, which interacts with the incoming free stream flow in a crosswise manner. The interaction gives rise to instability in the flow which intensifies with increasing strength of thermal buoyancy. Subsequently, at some critical value of the buoyancy parameter (Richardson number, Ri), the flow is characterized by the formation of Bénard-von Kármán vortex shedding. The critical Rifor all the range of Da and Re are obtained through visual investigation of the flow and thermal fields and also quantitatively from the drag and lift signals, phase portraits, and Strouhal numbers. The critical Ri decreases as Da increases at a constant Re; however, at constant Da, it increases with decreasing Re. Based on the critical Ri values for different Da and Re, a stability diagram is constructed to show the steady and unsteady zones of operation of the porous object subjected to the cross thermal buoyancy.