YOU WERE LOOKING FOR: Fea External Test Answer Key
How will you identify types of Eigen Value Problems? Explain weak formulation of FEA Why are polynomial types of interpolation function recommended over trigonometric function? What should be considered during piecewise trial function? How will you...
We have tried to make the questions relevant toward the evaluation of the engineer who has a background in finite element analysis. Saying that, knowing the answers to this quiz doesn't imply that one is capable of building accurate simulations,...
You then use your FEA pre-processor to perform a sum-of-forces calculation. What value would you expect to be returned by the sum-of-forces calculation? Answer 0. The peak stress in the structure is 52, psi. The engineering group has decided to use a more expensive AISI steel with a yield stress of around 80, psi. Upon implementing this new material into your FEA database, how would you expect the analysis results to change? Answer No change since you are performing a linear stress analysis. Question 6 What is the mathematical description of symmetry as used in the FEA world? How many planes-of-symmetry could be used for a uniformly loaded plate with a hole at its center? Answer Really basic but tricky to really understand and implement. A plane-of-symmetry will have translation normal to its plane fixed and in-plane rotations fixed. For example, if our plane-of-symmetry rests within the XY plane with the Z-axis normal to this plane, a plane-of symmetry could be enforced by fixing the Z degree-of-freedoms and the RX and RY rotational degree-of-freedoms.
If you got the above answer, then this second part is a slam-dunk: two planes for 2-D and three planes for 3-D. Question 7 How would you apply symmetry in a thermal analysis? In other words, what boundary conditions would you apply? Answer Thermal symmetry is really an adiabatic condition, with no heat flowing across the symmetry surfaces. The answer is that you would do nothing; leave the surface as a free surface. Free surfaces are by definition adiabatic. Question 8 You have a disk structure with a hole at its center let us say that it is 12 inches in diameter and 0. The center of the plate the hole perimeter is fixed and a displacement load is applied around the outer edges of the plate.
The structure is similar to a "clutch plate" used in an auto transmission. The displacement load is normal to the disk creating large bending stresses within the disk. If your goal is lower the stresses within the disk, would you make the disk thicker or thinner? Secondly, would it make sense to switch to a lower modulus material say switching from steel to aluminum? Answer Since the structure is under bending due a fixed displacement load, the stresses in the plate can be lowered by making it thinner. The trick is to remember how flexible sheet metal is compared to a bar of steel.
The equation that governs this behavior can be roughly stated that the applied force is proportional to the displacement times the elastic modulus times the cross-sectional moment of inertia I. Consequently, if we make the plate thinner, the moment of inertia will decrease yielding less force and thus lower bending stresses. The same argument holds for lowering the elastic modulus, that is, we would see the stress decrease by a factor of 3 by switching from steel to aluminum. Question 9 A buckling analysis has been requested of this simple C-channel structure. The load is in the positive X-direction and is applied through a beam element simulating a large bolt which is then connected to the plate elements via rigid links.
The buckling analysis option is selected and the analysis proceeds. When the analysis completes, the first eigenvalue buckling mode is negative! For this particular model, the negative eigenvalue is This would indicate a buckling load of Is this a valid result and what does it mean? For clarity, here's a picture of the structure with the applied load: Answer Yes, this is a valid result. The negative value indicates that the buckling mode is reversed from the direction of the applied load.
Looking at the structure one can see how one of the sides of the C-channel has buckled and it makes structural sense. Question 10 You have just run this very complicated linear analysis with several different type of materials and linear contact behavior between two of the bodies within your structure. Upon post-processing the results you see that the von Mises stress scalar ranges from a very high value say , psi to a low value that is negative say , psi. What would the analysis results be telling you? Answer Von Mises stress scalar is always positive. Yes - a trick question. Question 11 In modeling a very long I-Beam 6" flanges with a 10" deep web using quad plate elements since you are aware of the deficiencies of 3-node triangular plate elements , you would like to use the absolute minimum number of plate elements through the web since this I-Beam is part of a much larger model.
Would you bump up the number of elements if you desired higher accuracy stress numbers or not? Answer The standard is four elements. Although some people feel that three is sufficient. If high-accuracy stress numbers are desired, then five to six elements through the web would be the target. Jacobian what? Typically, most codes will equate a perfect Jacobian with 0. If the element becomes distorted, the Jacobian will climb upwards. For a highly distorted element with a Jacobian near 1. With most FEA solvers, an error code will be printed out for Jacobians higher than 0. Question 13 What is the minimal number of Timoshenko or Euler-Bernoulli type beam elements that is necessary to model a simply supported beam, if one only needs to extract the maximum deflection and stress at the mid-point of the symmetric structure under uniform loading?
Answer This is a logic question that tests your understanding of beam theory and symmetry. Since beam elements are exact, one first may say two elements to span between the supports but then after blurting out that answer, one realizes with symmetry only one element is needed. Question 14 You have a tricky design problem and we'll use the cantilevered beam as our illustrative example. You are given a fixed downward displacement at the end of the beam, to lower the peak stress, do you increase or decrease the thickness of the beam? If you think you have the right answer, then let's say that your stress is MPa and you have modeled the beam using steel.
What would be the stress if you switched to aluminum? Answer Since it is a fixed displacement your stress would go down if you make the beam more flexible, i. Question 15 Beams elements provide the ultimate in FEA optimization but with this power comes a bit of complexity. Just to make you nervous, do you know which cross section or sections would twist if a vertical load was applied through the point drawn on the image?
Answer A load applied as drawn on Image B and C would cause the beam to twist around the x-axis. This is the default for many FEA pre-processors. Loads applied through the shear center of a cross-section do not induce twist while an axial load applied through the centroid will not cause the beam to bend. Additionally, if it is a moment load in Image B it would be Mz or My , the beam will only bend and no axial strain will occur. Chan et al. Beam stress is given as: This formula is for the maximum stress in a beam under uniform bending and, of course, given a constant cross section.
Now, in the case of Nastran and other linear, implicit codes, beam stresses are recovered at specific locations as determined by the analyst. In this case, the moment is created by a force oriented at 45 degrees from the orthogonal axes. This means that the maximum moment is not aligned with the orthogonal axis. What would be the number returned for any analysis program using the above arrangement of stress recovery points? Multiple Choice Answers.
Endnotes Introduction The disparate impacts of the COVID pandemic, ongoing incidents of police brutality, and recent rise in Asian hate crimes have brought health and health care disparities into sharper focus among the media and public. However, health and health care disparities are not new. They have been documented for decades and reflect longstanding structural and systemic inequities rooted in racism and discrimination. Addressing these inequities could help to mitigate the disparate impacts of the COVID pandemic and prevent further widening of health disparities going forward.
This brief provides an introduction to what health and health care disparities are, the status of disparities and how COVID has affected them, the broader implications of disparities, and current federal efforts to advance health equity. What are health and health care disparities? Health and health care disparities refer to differences in health and health care between groups that stem from broader inequities. There are multiple definitions of health disparities. Racism, which CDC defines as the structures, policies, practices, and norms that assign value and determine opportunities based on the way people look or the color of their skin, results in conditions that unfairly advantage some and disadvantage others, placing people of color at greater risk for poor health outcomes. Health equity generally refers to individuals achieving their highest level of health through the elimination of disparities in health and health care.
Healthy people defines health equity as the attainment of the highest level of health for all people, and notes that it requires valuing everyone equally with focused and ongoing societal efforts to address avoidable inequalities, historical and contemporary injustices, and health and health care disparities. Though health care is essential to health, research shows that health outcomes are driven by multiple factors, including underlying genetics, health behaviors, social and environmental factors, and access to health care.
Moreover, racism negatively affects mental and physical health both directly and by creating inequities across the social determinants of health. Figure 1: Health Disparities are Driven by Social and Economic Inequities Health and health care disparities are often viewed through the lens of race and ethnicity, but they occur across a broad range of dimensions. For example, disparities occur across socioeconomic status, age, geography, language, gender, disability status, citizenship status, and sexual identity and orientation. Research also suggests that disparities occur across the life course, from birth, through mid-life, and among older adults. These groups are not mutually exclusive and often intersect in meaningful ways. Disparities also occur within subgroups of populations. For example, there are differences among Hispanics in health and health care based on length of time in the country, primary language, and immigration status. Prior to the COVID pandemic, people of color and other underserved groups faced longstanding disparities in health.
Despite the recognition and documentation of disparities for decades and overall improvements in population health over time, many disparities have persisted, and, in some cases, widened. As of , life expectancy among Black people was four years lower than White people, with the lowest expectancy among Black men. Research also documents disparities across other factors. For example, low-income people report worse health status than higher income individuals, 7 and lesbian, gay, bisexual, and transgender LGBT individuals experience certain health challenges at increased rates.
There also are longstanding disparities in health care. The Affordable Care Act health coverage expansions led to large gains in coverage across groups. Despite these gains, however, people of color and low-income individuals remain at increased risk of being uninsured Figure 3 , contributing to greater barriers to accessing health care. Further, starting in , coverage gains stalled and began reversing, reflecting a range of actions by the Trump administration, including decreased funding for outreach and enrollment assistance, approval of state waivers to add new eligibility restrictions for Medicaid coverage, and immigration policy changes that increased fears among immigrant families about participating in Medicaid and CHIP.
These coverage losses eroded some of the previous coverage gains under the ACA, particularly among Hispanic people , who already were at increased risk of being uninsured. Coverage losses have likely continued due to the COVID pandemic as people have lost jobs and experienced declining income. Beyond disparities in coverage, people of color and lower income individuals also receive poorer quality of care. Figure 3: People of color face longstanding disparities in health coverage. The higher rates of illness and death among people of color reflect increased risk of exposure to the virus due to living, working, and transportation situations, increased risk of experiencing serious illness if infected due to higher rates of underlying health conditions, and increased barriers to testing and treatment due to existing disparities in access to health care.
Beyond the direct health impacts of the virus, the pandemic has taken a disproportionate toll on the financial security and mental health and well-being of people of color, low-income people, LGBT people , and other underserved groups. As of late March , Black and Hispanic adults were more likely than White adults to report lack of confidence in their ability to make their next housing payment and to report food insufficiency. Despite being disproportionately affected by the pandemic, as of April , Black and Hispanic people were less likely than White people to have received a COVID vaccine.
Data across states show a consistent pattern of Black and Hispanic people receiving smaller shares of vaccinations compared to their shares of cases, deaths, and the total population, resulting in lower vaccination rates compared to their White counterparts. While vaccination rates are increasing across all groups, the gaps in vaccination rates for Black and Hispanic people are persisting Figure 5. These disparities in vaccinations reflect the longstanding inequities that create increased barriers to health care for people of color and other underserved groups. Moreover, they leave people of color at increased risk for infection and illness and hinder efforts to achieve population level immunity.
Figure 5: Although vaccination rates are increasing across groups, Black and Hispanic people face persistent gaps. What are the broader implications of disparities? People of color and other underserved groups experience higher rates of illness and death across a wide range of health conditions, limiting the overall health of the nation. Research further finds that health disparities are costly.
As the population becomes more diverse, with people of color projected to account for over half of the population by Figure 5 , it is increasingly important to address disparities. Figure 6: People of color are projected to make up over half of the U. The COVID pandemic has exacerbated underlying disparities in health and health care and increased the importance of addressing them. As such, prioritizing equity in COVID response efforts is not only important for mitigating the disproportionate impacts of the pandemic itself, but for protecting against even larger health disparities in the future. What are current federal efforts to address health disparities? The Biden administration has identified racial equity, including health equity, as a key priority , which has been reflected in several recent agency actions.
Immediately after taking office, President Biden issued a series of executive orders and actions focused on advancing health equity. These included orders that outline equity as a priority for the federal government broadly and as part of the pandemic response and recovery. The order establishes a COVID Health Equity Task Force, directs agencies to strengthen equity data collection and reporting and ensure response plans and policies provide for equitable allocation of resources, and directs HHS to conduct an outreach campaign focused on building vaccine confidence among communities of color and other underserved populations. The administration and Congress have taken a range of actions to expand access to and enrollment in health coverage. As noted, beginning in , health coverage gains stalled and began reversing. The COVID pandemic has likely further increased coverage losses as people have experienced job loss and decreases in income.
In January , President Biden issued an Executive Order on Strengthening Medicaid and the Affordable Care Act , which established a Special Open Enrollment Period for the Health Insurance Marketplaces and directed federal agencies to review policies and practices to ensure they support access to health coverage. The American Rescue Plan Act also contains provisions designed to increase access to health coverage and make health coverage more affordable. These include increases and expansions in eligibility for subsidies to buy health insurance through the Marketplaces as well as Medicaid provisions that offer incentives to encourage states that have not yet adopted the ACA Medicaid expansion to do so and provide a new option for states to extend the length of Medicaid coverage for postpartum women. The administration also restored funding for navigators to help eligible people enroll in health coverage and increased outreach activities.
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