Bulge Height Research Articles

Investigations of sheet metal forming by vaporizing metal foils

This study aimed to investigate the forming behavior of magnesium alloy by vaporizing metal foils. This process was conducted at room temperature and no heat treatment for the workpiece was required. The free bulging test was applied to identify the formability of the magnesium alloy AZ 31, and the perforated sheet forming test was used to measure the pressure distributions. The effectiveness of the polyurethane plates on generating shock pressure for the metal forming work was firstly examined. The pressure distributions of vaporizing single foils and tailored foils were subsequently discussed. The pressure distributions were mainly determined by the active areas of the foil specimens. AZ 31 magnesium sheets with a thickness of 1 mm and 1.8 mm were formed by the free bulging test under different charging energies. A bulging height of 27.28 mm for the AZ 31 sheet in 1.8 mm was acquired under a charging energy of 4.8 kJ. Vaporizing foils was found to be a feasible technique to conduct magnesium alloy forming without heat treatment for the workpiece.

Bulging in incremental sheet forming of cold bonded multi-layered Cu clad sheet: Influence of forming conditions and bending

Abstract Bulge is a defect that causes geometrical inaccuracy and premature failure in the innovative incremental sheet forming (ISF) process. This study has two-fold objectives: (1) knowing the bulging behavior of a Cu clad tri-layered steel sheet as a function of forming conditions, and (2) analyzing the bending effect on bulging in an attempt to identify the associated mechanism. A series of ISF tests and bending analysis are performed to realize these objectives. From the cause-effect analysis, it is found that bulge formation in the layered sheet is sensitive to forming conditions in a way that bulging can be minimized utilizing annealed material and performing ISF with larger tool diameter and step size. The bending under tension analysis reveals that the formation of bulge is an outgrowth of bending moment that the forming tool applies on the sheet during ISF. Furthermore, the magnitude of bending moment depending upon the forming conditions varies from 0.046 to 10.24 N·m/m and causes a corresponding change in the mean bulge height from 0.07 to 0.91 mm. The bending moment governs bulging in layered sheet through a linear law. These findings lead to a conclusion that the bulge defect can be overcome by controlling the bending moment and the formula proposed can be helpful in this regards.

Accuracy analysis of complex curvature parts based on the rigid-flexible hydroforming

The complex curvature parts are studied on by the rigid-flexible hydroforming, aimed at the accuracy analysis. In this paper, the cylindrical die with convex sphere and sharp fillet at the bottom, and with small size concave characteristic at the peak of the convex sphere, was designed to analyze the effect of bulging height and hydraulic pressure on the part accuracy, including large characteristic forming and small characteristic filling. The part-mold contact gap and springback distributions were discussed by experimental and numerical method to analyze the part accuracy. The results show that free bulging height and hydraulic pressure are the main factors that affect the part accuracy, and when the hydraulic pressure is constant, the springback of the large characteristic reduces with the increase of the free bulging height; when the free bulging height is constant, higher hydraulic pressure is better for the local small characteristic filling, and the part attach the mold better from the rear position where it contacts with the mold to the first position where it contacted with the mold.

Enhancing Formability of AA2219 Aluminum Alloy Friction Stir Welded Blanks with Preheating Treatment

The deformation behaviors of FSW blank are complicated due to the incompatibility of the mechanical property and microstructure for the weld and base material. In order to improve the formability of friction stir welded (FSW) blanks, the weld and base material in this paper were subjected to preheating treatments of 250, 300, 350, 400, and 450 °C, plus a solution treatment of 535 °C. The deformation behavior of the AA2219 FSW blank was characterized using uniaxial tension, microhardness test, hydro-bulging test and electron backscattered diffraction to determine the relationship of the deformation property and microstructure for the FSW blanks. Full strain fields of the tensile and bulging specimens were used to analyze the deformation uniformity of the weld and base material under uniaxial tension and biaxial tension stress states. With the limiting bulging height under various preheating temperatures, the formability behavior of the weld and base material was analyzed during the whole bulging process. The optimum preheating temperature can increase the formability and refrain from abnormal grain growth of the weld on the premise of maintaining the weld strength. The limiting bulging height of FSW blank is obviously improved by the lower preheating temperature from 300 to 350 °C. Additionally, the weld position has a significant impact on the deformation of the whole FSW blanks.

Application of the modified critical voids expansion ratio criterion to the prediction of the forming limit of 6016-O aluminum alloy

Based on the critical voids expansion ratio criterion, the basic material mechanical parameters such as the strain hardening index n and the hardening coefficient K were introduced in it, and the critical voids expansion ratio criterion was modified. Firstly, the basic hydraulic bulging experiments for the AA6016-T4 sheet metal and AA6016-O sheet metal were performed. According to the comparisons of the experiment results and the simulation results of bulging height, the FEM (finite element model) and the parameters in the numerical simulation were verified accurate. Then, the material constants C1 and C2, which were in the modified criterion were confirmed based on the histories of stress and strain in the forming processes of the two materials, and the specific expression of the modified fracture criterion was obtained. Secondly, the experiments and the numerical simulations of three different hydroforming processes of the box part with a 6016-O aluminum alloy were carried out. By comparing the distribution tendencies of the wall thickness on the two different measurement paths, the numerical simulation results have a good agreement with the experiment results and the FEMs of the hydroforming of the box part were verified accurate. So, according to the numerical simulations, the stress and strain histories of all the nodes in the three different hydroforming processes were introduced into the modified ductile criterion. Then, the positions of the fracture points in the three different processes were predicted by the value of the A, which is the conversion form of the modified fracture criterion. Thirdly, the experiment results and the prediction results of the positions of the fracture points were compared, according to the error analysis between them, it is verified that the prediction of the forming limit of box parts with AA6016-O using the modified critical voids expansion ratio criterion is accurate.

MORPHOFUNCTIONAL EVALUATION IN DOME-SHAPED MACULA: A MICROPERIMETRY AND OPTICAL COHERENCE TOMOGRAPHY STUDY.

To investigate retinal sensitivity (Se) in dome-shaped macula (DSM) using microperimetry and to correlate functional findings to specific spectral domain optical coherence tomography features. Patients affected by DSM in at least 1 eye were consecutively enrolled in a prospective, cross-sectional study. All studied eyes performed best-corrected visual acuity measurement, microperimetry to assess Se and optical coherence tomography to investigate DSM pattern and to measure bulge height and retinal and choroidal thicknesses. Fifty-three eyes of 29 patients were studied. Dome-shaped macula was vertically oriented (V-DSM) in 23 (43.4%), symmetric (S-DSM) in 17 (32.1%), and horizontally oriented (H-DSM) in 13 eyes (24.5%). Foveal subretinal fluid was present in 29/53 (54.7%) cases; it correlated to the bulge height (P < 0.0001) and determined a reduction of Se (P < 0.0001) not of best-corrected visual acuity (P = 0.7105). Mean Se was 13.9 ± 3.2 dB. Microperimetry parameters did not differ among the different DSM patterns. However, Se was significantly impaired if foveal subretinal fluid was present in V-DSM and in S-DSM, but not in H-DSM (V-DSM: P < 0.0001; S-DSM: P = 0.0252; H-DSM: P = 0.5723). In H-DSM, inferior choroidal thickness was thicker in cases with foveal subretinal fluid compared with those without it (P = 0.0363). In DSM, Se evaluation better reflects the central functional impairment than best-corrected visual acuity, particularly when some optical coherence tomography features, such as foveal subretinal fluid and higher bulge height, are present.

A 3D finite element model of prophylactic vertebroplasty in the metastatic spine: Vertebral stability and stress distribution on adjacent vertebrae

Background and Objective: Patients with metastatically compromised vertebra can experience pathologic fracture with relevant neurological complications. Vertebroplasty is a low cost procedure and it can potentially prevent neurologic impairment if performed at an early stage. The aim of this study is to evaluate the effects of prophylactic vertebroplasty on stability of the metastatic spine and analyze load distribution at adjacent vertebrae.Setting: A 3D finite element model of two spinal motion segments (L3-L5) was developed. A central core of elements was selected in L4 vertebral body and material properties of a lytic metastasis and successively PMMA were assigned. The model was settled in order to simulate a non-osteoporotic spine and an osteoporotic spine.Outcome Measures: Vertebral stability was assessed by the measurement of vertebral bulge (VB) and vertebral height (VH) on L4. Load transfer on adjacent vertebrae was evaluated by observing the distribution of the von Mises stress on L3 and L5 endplates.Results: The metastasis increased VB by 424% and VH by 626%, while prophylactic vertebroplasty decreased VB and VH by 99% and 95%, respectively, when compared to the normal/non-metastatic model. Prophylactic vertebroplasty increased the average von Mises stress of L3 lower endplate by 1.33% in the non-osteoporotic spine, while it increased to 16% in the osteoporotic model.Conclusions: Prophylactic vertebroplasty could represent an interesting option to improve vertebral strength of metastatically compromised spine without excessively increasing the stresses on adjacent vertebrae in non-osteoporotic spine.

Investigation on initial grain size and laser power density effects in laser shock bulging of copper foil

Laser shock bulging process is a promising flexible microforming method in which the laser shock wave pressure is employed to cause plastic deformation and fabricate microfeatures on thin sheet metals. However, the influence of initial grain size and laser power density on the forming quality of bulged parts has not been well understood. In this paper, three various initial grain sizes as well as three levels of laser power densities were provided, and then, laser shock bulging experiments of T2 copper foil were conducted. The characteristics of bulging height, thickness distribution, microhardness, surface morphology, and microstructure were examined. It is revealed that the bulging height increases with the increase of grain size and the enhancement of laser power density. The exhibiting good formability of pure copper foil in laser shock bulging process is attributed to the inertial effect on necking stabilization and strain-rate effect on material constitutive behavior. The overall thickness of bulged parts decreases compared with its original thickness. Moreover, the microhardness in the laser-shocked region increases due to the strain hardening effect, but the microhardness distribution is nonuniform because of the inhomogeneous plastic deformation. The grain sizes of bulged parts are slightly refined with the increase of laser power density, especially for the coarse-grained part. The grain refinement in laser shock bulging forming process is attributed to the large plastic deformation at high strain rates under laser shock.

Biomechanical effects of metastasis in the osteoporotic lumbar spine: A\xa0Finite Element Analysis

BackgroundCancer patients are likely to undergo osteoporosis as consequence of hormone manipulation and/or chemotherapy. Little is known about possible increased risk of fracture in this population. The aim of this study was to describe the biomechanical effect of a metastatic lesion in an osteoporotic lumbar spine model.MethodsA finite element model of two spinal motion segments (L3-L5) was extracted from a previously developed L3-Sacrum model and used to analyze the effect of metastasis size and bone mineral density (BMD) on Vertebral bulge (VB) and Vertebral height (VH). VB and VH represent respectively radial and axial displacement and they have been correlated to burst fracture. A total of 6 scenarios were evaluated combining three metastasis sizes (no metastasis, 15% and 30% of the vertebral body) and two BMD conditions (normal BMD and osteoporosis).Results15% metastasis increased VB and VH by 178% and 248%, respectively in normal BMD model; while VB and VH increased by 134% and 174% in osteoporotic model. 30% metastasis increased VB and VH by 88% and 109%, respectively, when compared to 15% metastasis in normal BMD model; while VB and VH increased by 59% and 74% in osteoporotic model.ConclusionA metastasis in the osteoporotic lumbar spine always leads to a higher risk of vertebral fracture. This risk increases with the size of the metastasis. Unexpectedly, an increment in metastasis size in the normal BMD spine produces a greater impact on vertebral stability compared to the osteoporotic spine.

Application of anti-adhesion structure based on earthworm motion characteristics

In the field of agricultural machinery, soil adhesion is a global technical problem that continues to be solved. Reducing soil adhesion is one key issue to improve the operational quality of agricultural machinery. The traditional methods are defective, while the bionics approach can be a reference. Here we extracted and analyzed the surface features of earthworms from the motion perspective, and revealed the laws about how the curvature radii of earthworms changed at three states (stretch, motionlessness, contraction). Based on the characteristics of earthworm motion, we designed the anti-adhesion structure of a press roller. Then the performance of the anti-adhesion structure was experimentally studied, the soil mass adhered was measured. The results showed that the optimal combination of the factors were rubber bulge height = 16 mm (h2) and load = 450 N (F1). To find out why, we compared the surface features at the head and body of earthworm with that of the rubber bulge of the press roller. We found the press roller with the rubber bulge (h2) has the smallest soil mass adhered. Meanwhile, theoretical analysis was carried out to reveal the anti-adhesion mechanism of the rubber bulge structure. Field experiment showed the press roller with rubber bulge structure had a soil mass adhered 37.62% lower than the press roller without such structure. The bionics approach had been such a candidate for reducing the soil adhesion of agricultural machinery.

Effect of shape imperfection on the buckling of large-scale thin-walled ellipsoidal head in steel nuclear containment

Buckling is a failure mode of a large-scale thin-walled ellipsoidal head for a cylindrical steel containment vessel, which is widely used in nuclear power plants such as AP1000 and CAP1400. Manufacturing processes always induce shape imperfections in large-scale thin-walled ellipsoidal heads. However, the study on the effect of shape imperfections on the buckling of a large-scale thin-walled ellipsoidal head subjected to internal pressure is still lacking. In this work, we first used a 3D laser scanner to measure the overall shape of the ellipsoidal head which has a diameter of 5000mm, a radius-to-height ratio of 2.0 and a thickness of 5.5mm. On the basis of the measured overall shape, shape imperfections were determined, and an equation was proposed to quantitatively characterize bulging of weld in the knuckle. Secondly, the measured overall shape and the equation were used to develop FEA models with shape imperfections. Buckling pressures were predicted by using nonlinear FEA. Good agreement between the predictions of the FEA models with shape imperfections indicates that bulging of weld has a considerable effect on buckling pressure. Thirdly, a buckling experiment was performed on the ellipsoidal head and buckling behavior was obtained. The experimental results show that all the buckles occurred at the bulgings of welds. The agreement between the experimental results and the predictions based on the models with shape imperfections is good. At last, FEA models, including different bulging heights of welds characterized by the equation, were established to perform an imperfection sensitivity analysis. Thin-walled ellipsoidal heads subjected to internal pressure demonstrate a significant sensitivity to the bulging height of weld in the knuckle.

A Numerical Study on Tube Hydroforming Process to optimize the Process Parameters by Taguchi Method

Tube hydroforming (THF) is an essential manufacturing technique in the modern days and in general, THF has become a convenient method for built-up complex automobile parts. This process depends mainly on the process parameters like internal pressure, axial feeds, material properties, and other processing conditions. Design by simulation has usually been a trial and error process, where the purpose is to find a feasible and cost effective process to produce a defect free product by altering process parameters. In this study tools required for the tube hydroforming process has modeled in the cad package CATIA V5 and these are imported into the commercial finite element code PAM-STAMP 2G for conducting the simulations. The effects of different process parameters have been investigated by numerical analysis and also the Taguchi Technique for optimization on Aluminum alloy Al99. The optimum conditions have been determined based on their effect on bulge height and thinning distribution of the tube material. Three important process parameters i.e., Internal Pressure, Axial feed and Frictional Coefficient were investigated. Finally, the mutual effect on Aforesaid process parameters on bulge height and thinning distribution were studied.

A microfluidic method to measure bulging heights for bulge testing of polydimethylsiloxane (PDMS) and polyurethane (PU) elastomeric membranes

Thin and flexible elastomeric membranes are frequently used in many microfluidic applications including microfluidic valves and organs-on-a-chip. The elastic properties of these membranes play an important role in the design of such microfluidic devices. Bulge testing, which is a common method to characterize the elastic behavior of these membranes, involves direct observation of the changes in the bulge height in response to a range of applied pressures. Here, we report a microfluidic approach to measure the bulging height of elastic membranes to replace direct observation of the bulge height under a microscope. Bulging height is measured by tracking the displacement of a fluid inside a microfluidic channel, where the fluid in the channel was designed to be directly in contact with the elastomeric membrane. Polydimethylsiloxane (PDMS) and polyurethane (PU) membranes with thickness 12–35 μm were fabricated by spin coating for bulge testing using both direct optical observation and the microfluidic method. Bulging height determined from the optical method was subject to interpretation by the user, whereas the microfluidic approach provided a simple but sensitive method for determining the bulging height of membranes down to a few micrometers. This work validates the proof of principle that uses microfluidics to accurately measure bulging height in conventional bulge testing for polydimethylsiloxane (PDMS) and polyurethane (PU)eElastomeric membranes.

Maximum Bulge Height and Weld Line Displacement in Hydroforming of Tailor Welded Blanks

Tailor welded blank (TWB) has many advantages over a traditional blank for manufacturing automobile sheet metal components, such as significant flexibility in product design, higher structural stiffness, and crash behavior. However, lower formability and weld line movement are some of the problems associated with forming of TWBs. Hydroforming is a potential technique to enhance formability. In this work, the effect of thickness ratio on maximum dome height and weld line movement in hydraulic bulging of laser welded interstitial-free (IF) steel blanks of different thickness combinations has been predicted using finite element (FE) simulations. The results are also validated with hydraulic bulging experiments on TWBs. It has been found that with increase in thickness ratio, the maximum bulge height decreased and weld line displacement toward thicker side increased. These results have been used to relocate the weld line toward the thinner side in the initial blanks and achieve a more uniform bulge profile of the dome. The peak pressure to achieve maximum safe dome height and percentage thinning has also been found out. The results showed huge improvement in uniformity of bulge profile with little reduction in dome height.

Clinical, fundoscopic, tomographic and angiographic characteristics of dome shaped macula classified by bulge height

Abstract Objective To classify dome shaped macula cases by their bulge height (BH). To analyze the characteristics associated with the groups formed by this classification. Methods Observational, descriptive and cross-sectional study on 15 selected eyes with dome shaped macula and high myopia. Using Caillaux method and optical coherence tomography images, 3 groups were determined by their BH: low (50–350 μm), medium (351–650 μm), and high (>650 μm), and a study of visual acuity, axial length, presence of subfoveal serous detachment, and images by fluorescein angiography and optic coherence tomography, as main variables. The confidence interval was 95%. Results By using the chi-squared test, the study showed that a BH higher than 400 μm was associated with lower visual acuity, presence of subfoveal serous detachment, and greater atrophy of the retinal pigment epithelium measured by disk diameters (p Conclusions The medium and high BH showed a positive correlation with the presence of foveal serous detachment and a lower visual acuity.

On improving the formability of AA6061/SiCp composite synthesized using friction stir processing

AbstractFriction stir process is a potentially useful method for producing composites of enhanced surface properties. In this work, an AA6061/SiCp composite, synthesized using friction stir processing, was tested in three‐point bending and uniaxial hot tensile and bi‐axial stressing to assess its formability. Bending test results reveal an increased bending strength in the composite compared with the AA6061 alloy, subjected to friction stir processing, but without the addition of the silicon carbide particles. Based on the hot tensile tests, the biaxial stressing temperatures were fixed as 623 K and 673 K. Bi‐axial stressing reveals that a maximum bulge height of 18 mm could be obtained by forming into a cavity of 59 mm diameter at a pressure of 0.2 MPa. Based on the results, process parameters such as formed bulge height, forming time, strain rate and strain rate sensitivity index were determined. In the present experiments, the strain rate sensitivity index increased with increasing forming pressure and reached a maximum value of 0.40 at a forming pressure of 0.25, as the latter variable was increased from 0.20 MPa to 0.25 MPa. The present findings can pave the way for the commercial exploitation of friction stir process‐technology‐based, efficient processing of the AA6061/SiCp composite.

Hydroformability study of seamless tube using Gurson-Tvergaard-Needleman (GTN) fracture model

Tube hydroforming process is an advanced manufacturing process in which tube acting as blank is placed in between the dies and deformed with the help of hydraulic pressure. It has several advantages over conventional stamping process such as high strength to weight ratio, higher reliability, less tooling cost etc. Fracture surface investigation of tube hydroformed samples reveal dimple formation in the form of void coalescence which is a characteristic feature of ductile fracture. Hence, in order to accurately predict the limiting strains at fracture it is important to model the process using ductile damage criteria. Fracture criteria are broadly classified into two, microscopic and macroscopic. In the present work Gurson-Tvergaard-Neeedleman (GTN) model, which is a microscopic based ductile damage criteria, was used for predicting the limiting strains at fracture for seamless steel tubes and implemented in explicit finite element software, ABAQUS, for variety of strain path and boundary conditions to obtain fracture based forming limit diagram. The original void porosity, the critical porosity and fracture porosity of the Gurson-Tvergaard-Needleman model were determined by image analysis of scanning electron micrographs of the specimen at different testing conditions of the uniaxial tensile test. The other parameters of the model were determined by using inverse approach combined with uniaxial tensile test and simulation. Predicted FLD is found to be in good agreement with the experimental FLD. Furthermore, numerical simulation based parametric study was carried out to understand the impact of various GTN parameters on different aspects of formability parameters such as bursting pressure, bulge height, principal strains and strain path to develop the understanding of deformation and fracture behaviour at the micro-level during tube hydroforming process.

Radiologic Factors Associated With the Dynamic Change of Dural Sac Diameter in Lumbar Spine: A Kinematic MRI Study.

This is a cross-sectional radiologic study. The purpose of this study was to assess radiologic features related to dynamic changes of dural sac diameter using kinematic magnetic resonance imaging. It is well known that the cross-sectional area of the lumbar spinal canal decreases during movement from flexion to extension. However, the radiologic characteristics related to dynamic changes of the lumbar spinal canal have not been elucidated. A total of 453 consecutive patients with clinically symptomatic low back pain or radiculopathy were recruited to undergo lumbar kinematic magnetic resonance imaging. The study participants consisted of 271 males (60%) and 182 females (40%). The average age was 44.5±12.2 years old. We investigated the following measurements at each level from L3-L4 to L5-S1: dural sac diameter, ligamentum flavum thickness, disk bulge, disk degeneration, angular motion, translational motion, and posterior disk height. The odds ratios (ORs) for ≥2 mm change of dural sac diameter between flexion and extension were calculated. The average dural sac diameter was 12.2 mm in neutral, 12.5 mm in flexion, and 11.7 mm in extension, with an average difference between flexion and extension of 0.83 mm. The OR of a ≥2 mm change in L5-S1 was 0.55 as compared with L3-L4. Significantly increased ORs were observed with ≥3 mm of ligamentum flavum in neutral (OR: 4.05), 3-3.9 and ≥4 mm of disk bulge in neutral (ORs: 1.62 and 1.81, respectively), grade IV and V disk degeneration (OR: 2.59 and 2.86, respectively), ≥8 degrees of angular motion (OR: 1.81), and ≥2 mm of posterior disk height change (OR: 1.84). Several radiologic characteristics related to the dynamic change of dural sac diameter have been demonstrated.

Influence Law of Initial Reverse Bulging on Sheet Hydroforming Process

In order to investigating the effect of the combination of two technological parameters such as the initial bulging height and the initial bulging pressure on the sheet , the sheet hydroforming process was studied. Firstly, by using the method of numerical simulation, the sheet hydroforming process with and without the initial bulging were discussed; Secondly, the effect of both the initial bulging height and the initial bulging pressure which were based on the hydroforming with the initial bulging on the forming of the part was studied; Thirdly, the result of the simulation was verified in the experiment. It was found that when the initial bulging height is 3.75mm and the initial bulging pressure is 2MPa, the maximum thinning ratio of the sheet is 4.803% at the end of the sheet hydroforming process. According to the hydroforming process without the initial bulging factors, the maximum thinning ratio is 5.123%. It can be found that the initial bulging factors play a key role in the sheet hydroforming process. The maximum thinning ratio of the wall thickness can be decreased effectively by the appropriate initial bulging height and bulging pressure, and the forming limit can also be improved at the same time. The results of numerical simulation have a reasonable agreement with the experimental results.

Effect of an upstream bulge configuration on film cooling with and without mist injection

To meet the economic requirements of power output, the increased inlet temperature of modern gas turbines is above the melting point of the material. Therefore, high-efficient cooling technology is needed to protect the blades from the hot mainstream. In this study, film cooling was investigated in a simplified channel. A bulge located upstream of the film hole was numerically investigated by analysis of the film cooling effectiveness distribution downstream of the wall. The flow distribution in the plate channel is first presented. Comparing with a case without bulge, different cases with bulge heights of 0.1d, 0.3d and 0.5d were examined with blowing ratios of 0.5 and 1.0. Cases with 1% mist injection were also included in order to obtain better cooling performance. Results show that the bulge configuration located upstream the film hole makes the cooling film more uniform, and enhanceslateral cooling effectiveness. Unlike other cases, the configuration with a 0.3d-height bulge shows a good balance in improving the downstream and lateral cooling effectiveness. Compared with the case without mist at M = 0.5, the 0.3d-height bulge with 1% mist injection increases lateral average effectiveness by 559% at x/d = 55. In addition, a reduction of the thermal stress concentration can be obtained by increasing the height of the bulge configuration.