Abaqus/Explic xplicit it Abaqus/E
Abaqus/CAE Abaqus/CAE
Dening an analysis, Section 6.1.2 *DYNAMIC guring a dynam dynamic, ic, explic explicit it proce procedur dure e Conguring
in Con Conguring general general analysis analysis procedure procedures, s, Section 14.11.1 of the Abaqus/CAE Users Guide, in the HTML version of this guide
An explicit dynamic analysis:
is computationally computationally ef cient for the analysis of large models with relatively short dynamic response times and for the analysis of extremely discontinuous events or processes;
allowss allow
for for the the denition nition of very very gener general al contac contactt condit condition ionss (Cont (Contac actt intera interacti ction on analys analysis: is: overview, Section 36.1.1);
uses uses a consis consisten tent, t, large large-de -defor forma matio tion n theory theorym mode odels ls can can under undergo go large large rotati rotations ons and large large deformation;
can use a geometrically linear deformation deformation theorystrains and rotations are assumed to be small (see Dening an analysis, Section 6.1.2);
can be used to perform perform an adiabatic adiabatic stress stress analysis if inelastic inelastic dissipation dissipation is expected expected to generate generate heat in the material (see Adiabatic analysis, Section 6.5.4);
can be used to perform quasi-static analyses analyses with complicated contact contact conditions; and allows allows for either automatic automatic or xed time incrementation to be usedby default, Abaqus/Explicit uses automatic time incrementation with the global time estimator.
The explicit dynamics procedure performs a large number of small time increments ef cientl ciently y. An explicit explicit central-d central-diffe ifferenc rencee time integration integration rule is used; used; each increment increment is relativel relatively y inexpens inexpensive ive (compared to the direct-integration dynamic analysis procedure available in Abaqus/Standard) because there is no solution for a set of simultaneous equations. The explicit central-difference operator satises the dynamic equilibrium equations at the beginning of the increment, t ; the accelerations calculated at time t are are used used to adva advanc ncee the the velo veloci city ty solu soluti tion on to time time and and the the disp displa lace ceme ment nt solu soluti tion on to time time .
*DYNAMIC, EXPLICIT Step module: : :
The explicit dynamics analysis procedure is based upon the implementation of an explicit integration rule together with the use of diagonal (lumped) element mass matrices. The equations of motion for the body are integrated using the explicit central-difference integration rule
where is a degree of freedom (a displacement or rotation component) and the subscript i refers to the increment number in an explicit dynamics step. The central-difference integration operator is explicit in the sense that the kinematic state is advanced using known values of and from the previous increment. The explicit integration rule is quite simple but by itself does not provide the computational ef ciency associated with the explicit dynamics procedure. The key to the computational ef ciency of the explicit procedure is the use of diagonal element mass matrices because the accelerations at the beginning of the increment are computed by
where is the mass matrix, is the applied load vector, and is the internal force vector. A lumped mass matrix is used because its inverse is simple to compute and because the vector multiplication of the mass inverse by the inertial force requires only n operations, where n is the number of degrees of freedom in the model. The explicit procedure requires no iterations and no tangent stiffness matrix. The internal force vector, , is assembled from contributions from the individual elements such that a global stiffness matrix need not be formed.
The explicit integration scheme in Abaqus/Explicit requires nodal mass or inertia to exist at all activated degrees of freedom (see Conventions, Section 1.2.2) unless constraints are applied using boundary conditions. More precisely, a nonzero nodal mass must exist unless all activated translational degrees of freedom are constrained and nonzero rotary inertia must exist unless all activated rotational degrees of freedom are constrained. Nodes that are part of a rigid body do not require mass, but the entire rigid body must possess mass and inertia unless constraints are used. Nodes that belong to Eulerian elements also do not require mass, since the surrounding Eulerian elements may be void at some time during the simulation. When degrees of freedom at a node are activated by elements with a nonzero mass density (e.g., solid, shell, beam) or mass and inertia elements, a nonzero nodal mass or inertia occurs naturally from the assemblage of lumped mass contributions.
When degrees of freedom at a node are activated by elements with no mass (e.g., spring, dashpot, or connector elements), care must be taken either to constrain the node or to add mass and inertia as appropriate.
The explicit procedure integrates through time by using many small time increments. The centraldifference operator is conditionally stable, and the stability limit for the operator (with no damping) is given in terms of the highest frequency of the system as
With damping, the stable time increment is given by
where is the fraction of critical damping in the mode with the highest frequency. Contrary to our usual engineering intuition, introducing damping to the solution reduces the stable time increment. In Abaqus/Explicit a small amount of damping is introduced in the form of bulk viscosity to control high frequency oscillations. Physical forms of damping, such as dashpots or material damping, can also be introduced. Bulk viscosity and material damping are discussed below.
An approximation to the stability limit is often written as the smallest transit time of a dilatational wave across any of the elements in the mesh
where is the smallest element dimension in the mesh and is the dilatational wave speed in terms of and , dened below. In general, for beams, conventional shells, and membranes the element thickness or cross-sectional dimensions are not considered in determining the smallest element dimension; the stability limit is based upon the midplane or membrane dimensions only. When the transverse shear stiffness is dened for shell elements (see Shell section behavior, Section 29.6.4), the stable time increment will also be based on the transverse shear behavior. This estimate for is only approximate and in most cases is not a conservative (safe) estimate. In general, the actual stable time increment chosen by Abaqus/Explicit will be less than this estimate by a factor between and 1 in a two-dimensional model and between and 1 in a three-dimensional model. The time increment chosen by Abaqus/Explicit also accounts for any stiffness behavior in a model associated with penalty contact. For further discussion, see Computational cost below.
Abaqus/Explicit writes a report to the status () le during the data check phase of the analysis that contains an estimate of the minimum stable time increment and a listing of the elements with the smallest stable time increments and their values. The initial stable time increments listed do not include damping (bulk viscosity), mass scaling, or penalty contact effects. This listing is provided because often a few elements have much smaller stability limits than the rest of the elements in the mesh. The stable time increment can be increased by modifying the mesh to increase the size of the controlling element or by using appropriate mass scaling.
The current dilatational wave speed, , is determined in Abaqus/Explicit by calculating the effective hypoelastic material moduli from the materials constitutive response. Effective Lamés constants, and , are determined in the following manner. Dene as the increment in the mean stress, as the increment in the deviatoric stress, as the increment of volumetric strain, and as the deviatoric strain increment. We assume a hypoelastic stress-strain rule of the form
The effective moduli can then be computed as
For shell elements dened by a shell cross-section that requires numerical integration (see Using a shell section integrated during the analysis to dene the section behavior, Section 29.6.5), the effective moduli for the section are computed by integrating the effective moduli at the section points through the thickness. These effective moduli represent the element stiffness and determine the current dilatational wave speed in the element as
where
is the density of the material.
In an isotropic, elastic material the effective Lamés constants can be de ned in terms of Youngs modulus, E , and Poissons ratio, , by
and
The time increment used in an analysis must be smaller than the stability limit of the central-difference operator. Failure to use a small enough time increment will result in an unstable solution. When the solution becomes unstable, the time history response of solution variables such as displacements will usually oscillate with increasing amplitudes. The total energy balance will also change signicantly. If the model contains only one material type, the initial time increment is directly proportional to the size of the smallest element in the mesh. If the mesh contains uniform size elements but contains multiple material descriptions, the element with the highest wave speed will determine the initial time increment. In nonlinear problemsthose with large deformations and/or nonlinear material responsethe highest frequency of the model will continually change, which consequently changes the stability limit. Abaqus/Explicit has two strategies for time incrementation control: fully automatic time incrementation (where the code accounts for changes in the stability limit) and xed time incrementation.
To reduce the chance of a solution going unstable, you can adjust the stable time increment computed by Abaqus/Explicit by a constant scaling factor. This factor can be used to scale the default global time estimate, the element-by-element estimate, or the xed time increment based on the initial element-byelement estimate; it cannot be used to scale a xed time increment specied directly by you.
Use the following option to scale the stable time increment based on the global time estimate: *DYNAMIC, EXPLICIT, SCALE FACTOR= f Use the following option to scale the stable time increment based on the element-by-element estimate: *DYNAMIC, EXPLICIT, ELEMENT BY ELEMENT, SCALE FACTOR= f Use the following option to scale the stable time increment based on the xed time increment on the initial element-by-element estimate: *DYNAMIC, EXPLICIT, FIXED TIME INCREMENTATION, SCALE FACTOR= f
Step module: : : : : : f
The default time incrementation scheme in Abaqus/Explicit is fully automatic and requires no user intervention. Two types of estimates are used to determine the stability limit: element by element and global. An analysis always starts by using the element-by-element estimation method and may switch to the global estimation method under certain circumstances, as explained below.
In an analysis Abaqus/Explicit initially uses a stability limit based on the highest element frequency in the whole model. This element-by-element estimate is determined using the current dilatational wave speed in each element. The element-by-element estimate is conservative; it will give a smaller stable time increment than the true stability limit that is based upon the maximum frequency of the entire model. In general, constraints such as boundary conditions and kinematic contact have the effect of compressing the eigenvalue spectrum, and the element-by-element estimates do not take this into account. The concept of the stable time increment as the time required to propagate a dilatational wave across the smallest element dimension is useful for interpreting how the explicit procedure chooses the time increment when element-by-element stability estimation controls the time increment. As the step proceeds, the global stability estimate, if used, will make the time increment less sensitive to element size.
*DYNAMIC, EXPLICIT, ELEMENT BY ELEMENT Step module: : : : : :
The stability limit will be determined by the global estimator as the step proceeds unless the element-byelement estimation method is specied, xed time incrementation is specied, or one of the conditions explained below prevents the use of global estimation. The switch to the global estimation method occurs once the algorithm determines that the accuracy of the global estimation method is acceptable. The adaptive, global estimation algorithm determines the maximum frequency of the entire model using the current dilatational wave speed. This algorithm continuously updates the estimate for the maximum frequency. The global estimator will usually allow time increments that exceed the element by-element values. Abaqus/Explicit monitors the effectiveness of the global estimation algorithm. If the cost for computing the global time estimate is more than its benet, the code will turn off the global estimation algorithm and simply use the element-by-element estimates to save computation time.
The global estimation algorithm will not be used when any of the following capabilities are included in the model:
Fluid elements Innite elements Dashpots Thick shells (thickness to characteristic length ratio larger than 0.92) Thick beams (thickness to length ratio larger than 1.0) The JWL equation of state Material damping Nonisotropic elastic materials with temperature and eld variable dependency Distortion control Adaptive meshing Subcycling
For three-dimensional continuum elements and elements with plane stress formulations (shell, membrane, and two-dimensional plane stress elements) an improved estimate of the element characteristic length is used by default. This improved method usually results in a larger element stable time increment than a more traditional method. For analyses using variable mass scaling, the total mass added to achieve a given stable time increment will be less with the improved estimate.
Use the following option to activate the improved element time estimation method: *DYNAMIC, EXPLICIT, IMPROVED DT METHOD=YES Use the following option to deactivate the improved element time estimation method:
*DYNAMIC, EXPLICIT, IMPROVED DT METHOD=NO The ability to deactivate the improved element time estimation method is not supported in Abaqus/CAE.
A xed time incrementation scheme is also available in Abaqus/Explicit. The xed time increment size is determined either by the initial element-by-element stability estimate for the step or by a user-specied time increment. Fixed time incrementation may be useful when a more accurate representation of the higher mode response of a problem is required. In this case a time increment size smaller than the element-by-element
estimates may be used. The element-by-element estimate can be obtained simply by running a data check analysis (see Abaqus/Standard, Abaqus/Explicit, and Abaqus/CFD execution, Section 3.2.2). When xed time incrementation is used, Abaqus/Explicit will not check that the computed response is stable during the step. You should ensure that a valid response has been obtained by carefully checking the energy history and other response variables.
You can use time increments the size of the initial element-by-element stability limit throughout a step. The dilatational wave speed in each element at the beginning of the step is used to compute the xed time increment size.
*DYNAMIC, EXPLICIT, FIXED TIME INCREMENTATION Step module: : : : : :
Alternatively, you can specify a time increment size directly.
*DYNAMIC, EXPLICIT, DIRECT USER CONTROL Step module: : : : : :
The use of small increments (dictated by the stability limit) is advantageous because it allows the solution to proceed without iterations and without requiring tangent stiffness matrices to be formed. It also simplies the treatment of contact. The explicit dynamics procedure is ideally suited for analyzing high-speed dynamic events, but many of the advantages of the explicit procedure also apply to the analysis of slower (quasi-static) processes. A good example is sheet metal forming, where contact dominates the solution and local instabilities may form due to wrinkling of the sheet. The results in an explicit dynamics analysis are not automatically checked for accuracy as they are in Abaqus/Standard (Abaqus/Standard uses the half-increment residual). In most cases this is not of concern because the stability condition imposes a small time increment such that the solution changes only slightly in any one time increment, which simplies the incremental calculations. While the analysis may take an extremely large number of increments, each increment is relatively inexpensive, often resulting in an economical solution. It is not uncommon for Abaqus/Explicit to take over 105 increments for an analysis. The method is, therefore, computationally attractive for problems where the total dynamic response time that must be modeled is only a few orders of magnitude longer than the stability limit; for example, wave propagation studies or some event and response applications.
The computer time involved in running a simulation using explicit time integration with a given mesh is proportional to the time period of the event. The time increment based on the element-by-element stability estimate can be rewritten (ignoring damping) in the form
where the minimum is taken over all elements in the mesh, is a characteristic length associated with an element (see Explicit dynamic analysis, Section 2.4.5 of the Abaqus Theory Guide), is the density of the material in the element, and and are the effective Lamés constants for the material in the element (dened above). The time increment from the global stability estimate may be somewhat larger, but for this discussion we will assume that the above inequality always holds (when the inequality does not hold, the solution time will be somewhat faster). For linear, nonisotropic elastic materials this stability limit is further scaled down by the square root of the ratio of the effective material stiffness to the maximum material stiffness in one particular direction. Since this effectively means that the time increment can be no larger than the time required to propagate a stress wave across an element, the computer time involved in running a quasi-static analysis can be very large: the cost of the simulation is directly proportional to the number of time increments required. The number of increments, n , required is if remains constant, where T is the time period of the event being simulated. (Even the element-by-element approximation of will not remain constant in general, since element distortion will change and nonlinear material response will change the effective Lamé constants. But the assumption is suf ciently accurate for the purposes of this discussion.) Thus,
In a two-dimensional analysis rening the mesh by a factor of two in each direction will increase the run time in the explicit procedure by a factor of eightfour times as many elements and half the original time increment size. Similarly, in a three-dimensional analysis re ning the mesh by a factor of two in each direction will increase the run time by a factor of sixteen. In a quasi-static analysis it is expedient to reduce the computational cost by either speeding up the simulation or by scaling the mass. In either case the kinetic energy should be monitored to ensure that the ratio of kinetic energy to internal energy does not get too largetypically less than 10%.
To reduce the number of increments required, n , we can speed up the simulation compared to the time of the actual processthat is, we can arti cially reduce the time period of the event, T . This will introduce
two possible errors. If the simulation speed is increased too much, the increased inertia forces will change the predicted response (in an extreme case the problem will exhibit wave propagation response). The only way to avoid this error is to choose a speed-up that is not too large. The other error is that some aspects of the problem other than inertia forcesfor example, material behaviormay also be rate dependent. In this case the actual time period of the event being modeled cannot be changed.
Articially increasing the material density, , by a factor reduces n to , just like decreasing T to . This concept, called mass scaling, reduces the ratio of the event time to the time for wave propagation across an element while leaving t he event time xed, which allows rate-dependent behavior to be included in the analysis. Mass scaling has exactly the same effect on inertia forces as speeding up the time of simulation. Mass scaling is attractive because it can be used in rate-dependent problems, but it must be used with care to ensure that the inertia forces do not dominate and change the solution. Either xed or variable mass scaling can be invoked (see Mass scaling, Section 11.6.1). Mass scaling can also be accomplished by altering the density; however, the xed and variable mass scaling capabilities provide more versatile methods of scaling the mass of the entire model or specic element sets in the model.
One disadvantage in an explicit dynamic analysis is that a few very small elements will force the entire model to be integrated with a small time increment. You can use mixed time integration or subcycling methods to reduce this problem. In these methods the equations of motion for the body are still integrated using the explicit central-difference integration rule as shown above, but the different time increments are allowed for different groups of nodes in the nite element model. If most nodes are integrated with a large stable time increment and only a few nodes are integrated with a small time increment, the computational cost may be reduced signicantly. Selective subcycling can be invoked by dening the subcycling zones. See Selective subcycling, Section 11.7.1 for details.
Bulk viscosity introduces damping associated with volumetric straining. Its purpose is to improve the modeling of high-speed dynamic events (see Stability above for a discussion of the effect of damping on the stable time increment). Abaqus/Explicit contains two forms of bulk viscosity: linear and quadratic. Linear bulk viscosity is included by default in an Abaqus/Explicit analysis. The bulk viscosity parameters and dened below can be redened and can be changed from step to step. If the default values are changed in a step, the new values will be used in subsequent steps until they are redened. Bulk viscosities dened this way apply to the whole model. For an individual element set the linear and quadratic bulk viscosities can be scaled by a factor by dening section controls (see Section controls, Section 27.1.4).
Use the following option to dene bulk viscosity for the entire model: *BULK VISCOSITY Use the following options to dene bulk viscosity for an individual element set:
*BULK VISCOSITY *SECTION CONTROLS Use the following option to dene bulk viscosity for the entire model: Step module: : : : : and Dening bulk viscosity for an individual element set is not supported in Abaqus/CAE.
Linear bulk viscosity is found in all elements and is introduced to damp ringing in the highest element frequency. This damping is sometimes referred to as truncation frequency damping. It generates a bulk viscosity pressure that is linear in the volumetric strain rate
where is a damping coef cient (default=.06), is the current material density, is the current dilatational wave speed, is an element characteristic length, and is the volumetric strain rate. For acoustic elements, the bulk viscosity pressure can be obtained from the above equation by using the relationship of the uid particle velocity and the pressure rate (see Coupled acoustic-structural medium analysis, Section 2.9.1 of the Abaqus Theory Guide) as
where
and c are the pressure rate and the speed of sound in the uid, respectively.
The second form of bulk viscosity pressure is found only in solid continuum elements (except the plane stress element CPS4R). This form is quadratic in the volumetric strain rate
where is a damping coef cient (default=1.2) and all other quantities are as dened for the linear bulk viscosity. Quadratic bulk viscosity is applied only if the volumetric strain rate is compressive. The quadratic bulk viscosity pressure will smear a shock front across several elements and is introduced to prevent elements from collapsing under extremely high velocity gradients. Consider a simple one-element problem in which the nodes on one side of the element are xed and the nodes on the other side have an initial velocity in the direction of the xed nodes. If the initial velocity is equal to the dilatational wave speed of the material, without the quadratic bulk viscosity, the element would
collapse to zero volume in one time increment (because the stable time increment size is precisely the transit time of a dilatational wave across the element). The quadratic bulk viscosity pressure will introduce a resisting pressure that will prevent the element from collapsing.
The bulk viscosity pressure is not included in the material point stresses because it is intended as a numerical effect onlyit is not considered part of the materials constitutive response. The bulk viscosity pressures are based upon the dilatational mode of each element. The fraction of critical damping in the dilatational mode of each element is given by
For the displacement degrees of freedom, bulk viscosity introduces damping associated with volumetric straining. Linear bulk viscosity or truncation frequency damping is used to damp the high frequency ringing that leads to unwanted noise in the solution or spurious overshoot in the response amplitude. For the same reason, in shells the high frequency ringing in the rotational degrees of freedom is damped with linear bulk viscosity acting on the mean curvature strain rate. This damping generates a bulk viscosity pressure moment, m , which is linear in the mean curvature strain rate
where is a damping coef cient (default = 0.06), is the original thickness, is the mass density, is the current dilatational wave speed, L is the characteristic length used for rotary inertia and transverse shear stiffness scaling (see Finite-strain shell element formulation, Section 3.6.5 of the Abaqus Theory Guide), and is twice the mean curvature strain rate. The resultant pressure moment , where h is the current thickness, is added to the direct components of the moment resultant.
Dening inelastic material behavior, dashpots, etc. will introduce energy dissipation into a model. In addition to these mechanisms, general (Rayleigh) material damping can be introduced (see Material damping, Section 26.1.1). Adding damping to a model, especially stiffness proportional damping, , may signicantly reduce the stable time increment.
*DAMPING, ALPHA= , BETA= Property module: material editor:
: and
Abaqus/Explicit writes critical elements (elements with the smallest stable time increments) and their stable time increment values to the output database at each summary increment for visualization in Abaqus/CAE. By default, the number of critical elements written to the output database is 10.
*DIAGNOSTICS, CRITICAL ELEMENTS=value The ability to control the number of critical elements written to the output database is not supported in Abaqus/CAE.
The deformation speed in an element is de ned as the largest absolute value of all the deformation rate components of an element times the element characteristic length, . You can request diagnostic information about the deformation speed within a step denition, as described below. In a multistep analysis diagnostic requests remain in effect until they are explicitly rede ned.
By default, Abaqus/Explicit will check for a relatively large deformation speed in all the elements since too high a value may cause the element to deform or collapse unrealistically. A warning message is issued if the ratio of deformation speed versus dilatational wave speed in an element reaches the value specied for the warning ratio. By default, the warning ratio is 0.3. You can redene this limit. The rst occurrence of the warning message is written to the status ( ) le; subsequent occurrences are written to the message ( ) le. See Output, Section 4.1.1, for a description of these output les. Generally when the ratio of deformation speed to dilatational wave speed is greater than 0.3, it is an indication that the purely mechanical material constitutive relationship is no longer valid and that a thermo-mechanical equation of state material is required.
*DIAGNOSTICS, WARNING RATIO=ratio The ability to redene the warning ratio limit is not supported in Abaqus/CAE.
An error message is issued and the analysis is terminated when the maximum ratio of deformation speed versus current dilatational wave speed for any element is greater than the cutoff ratio. By default, the cutoff ratio is 1.0. You can redene this limit. The check for this cutoff ratio is not applied to any model that has an equation of state material (see Equation of state, Section 25.2.1) or a user-dened material (see User-dened mechanical material behavior, Section 26.7.1).
*DIAGNOSTICS, CUTOFF RATIO=ratio The ability to redene the cutoff ratio limit is not supported in Abaqus/CAE.
You can request summary diagnostic information to obtain warning and error messages for only the element with the largest ratio of deformation speed to dilatational wave speed.
*DIAGNOSTICS, DEFORMATION SPEED CHECK=SUMMARY A summary of the deformation speed diagnostic information is output by default in Abaqus/CAE.
You can request detailed diagnostic information to obtain warning and error messages for all elements with large deformation speed to dilatational wave speed ratios.
*DIAGNOSTICS, DEFORMATION SPEED CHECK=DETAIL You cannot output detailed diagnostic information about the deformation speed in Abaqus/CAE.
You can choose to completely bypass the checks for large deformation speed.
*DIAGNOSTICS, DEFORMATION SPEED CHECK=OFF You cannot disable the deformation speed checks in Abaqus/CAE.
There are some analyses in which it is useful to monitor the value of a variable at every increment. For example, in a force-driven analysis such as hydro-forming, the simulation time that is suf cient to model the completion of the physical process may depend on the magnitude of the displacement of a node or a group of nodes in the model. Another example is a drop test simulation where the postfailure response is not of interest. Monitoring the values of critical variables and halting the analysis when those variables exceed a given criterion can reduce computational expense and turnaround time. For such problems Abaqus/Explicit allows output variables to be monitored during an analysis to verify whether or not their values have exceeded or fallen below user-speci ed values in specied element or node sets. Comparisons of specied element integration point variables, element section variables, or nodal variables with user-specied values are performed at every increment. At the rst occurrence of a variable exceeding the user-speci ed bounds, the variable name, the associated element or node number, and the increment number are written to the status () le. In addition, you can request that the analysis be stopped and/or the output state be written in the increment following the one in which the variable has exceeded the user-specied bound. At the end of each step in which variables are monitored, the maximum, minimum, or absolute maximum value that each variable attains during the course of the analysis, along with the number of the element or node where the extreme value occurred, will be written to the status le.
The element output variables that can be monitored include all the element integration point variables and element section point variables that are available for history-type output to the output database. Similarly, the nodal output variables that can be monitored include all the nodal variables that are available for history output to the output database. The keys identifying the output variables are dened in Abaqus/Explicit output variable identiers, Section 4.2.2.
Use the rst option with one or both of the following options in the history portion of the input le: *EXTREME VALUE *EXTREME ELEMENT VALUE, ELSET=element_set_name *EXTREME NODE VALUE, NSET=nset_set_name The *EXTREME VALUE option can be repeated in the same step, and the *EXTREME ELEMENT VALUE and *EXTREME NODE VALUE options can be repeated as many times as necessary.
Extreme value output monitoring is not supported in Abaqus/CAE.
You can choose to halt the analysis when the extreme value criterion is met. The analysis will stop at the end of the increment following the one in which any of the specied element or nodal variables exceeded the prescribed bounds.
Use the following options:
*EXTREME VALUE, HALT=YES *EXTREME ELEMENT VALUE and/or * EXTREME NODE VALUE Extreme value output monitoring is not supported in Abaqus/CAE.
You can obtain eld-type output to the output database and an additional restart state when any of the selected variables fall outside the specied bounds for the rst time during the analysis. The output will be written in the increment following the one in which such an occurrence took place. Since output is automatically written when the analysis terminates, this request has an effect only if you have not chosen to halt the analysis when the extreme value criterion is met as described above.
Use either or both of the following options in conjunction with the *EXTREME VALUE option: *EXTREME ELEMENT VALUE, ELSET= element_set_name, OUTPUT=YES *EXTREME NODE VALUE, NSET=node_set_name, OUTPUT=YES Extreme value output monitoring is not supported in Abaqus/CAE.
In a multistep analysis the monitoring requests you specify remain in effect until they are redened. You must redene all requests to add or change any variables, element or node sets, or maxima or minima.
You can stop monitoring variables in a new step.
Use the *EXTREME VALUE option without the *EXTREME ELEMENT VALUE and * EXTREME NODE VALUE options.
Extreme value output monitoring is not supported in Abaqus/CAE.
Initial conditions in Abaqus/Standard and Abaqus/Explicit, Section 34.2.1, describes all of the initial conditions that are available for an explicit dynamic analysis.
Boundary conditions can be dened as explained in Boundary conditions in Abaqus/Standard and Abaqus/Explicit, Section 34.3.1. Boundary conditions applied during an explicit dynamic response step should use appropriate amplitude references (Amplitude curves, Section 34.1.2). If boundary conditions are specied for the step without amplitude references, they are applied instantaneously at the beginning of the step. Since Abaqus/Explicit does not admit jumps in displacement, the value of a nonzero displacement boundary condition that is specied without an amplitude reference will be ignored, and a zero velocity boundary condition will be enforced.
The loading types available for an explicit dynamic analysis are explained in Applying loads: overview, Section 34.4.1. Concentrated nodal forces or moments can be applied to the displacement or rotation degrees of freedom (16). Distributed pressure forces or body forces can also be applied; the distributed load types available with particular elements are described in Part VI, Elements. As with boundary conditions, loads applied during a dynamic response step should use appropriate amplitude references (Amplitude curves, Section 34.1.2). If loads are specied for the step without amplitude references, they are applied instantaneously at the beginning of the step.
The following predened elds can be speci ed, as described in Prede ned elds, Section 34.6.1:
Although temperature is not a degree of freedom in explicit dynamic analysis, nodal temperatures can be specied. Any difference between the applied and initial temperatures will cause thermal strain if a thermal expansion coef cient is given for the material (Thermal expansion,
Section 26.1.2). The specied temperature also affects temperature-dependent material properties, if any.
The values of user-dened eld variables can be specied. These values affect only eld-variabledependent material properties, if any.
Any of the material models in Abaqus/Explicit can be used in a general explicit dynamic analysis (see Combining material behaviors, Section 21.1.3).
All of the elements available in Abaqus/Explicit can be used in an explicit dynamic analysis. The elements are listed in Part VI, Elements. If coupled temperature-displacement elements are used in an explicit dynamic analysis, the temperature degrees of freedom will be ignored.
The element output available for a dynamic analysis includes stress; strain; energies; and the values of state, eld, and user-dened variables. The nodal output available includes displacements, velocities, accelerations, reaction forces, and coordinates. All of the output variable identiers are outlined in Abaqus/Explicit output variable identiers, Section 4.2.2. The types of output available are described in Output, Section 4.1.1. When an Abaqus/Explicit analysis encounters a fatal error, the preselected variables applicable to the current procedure are added automatically to the output database as eld data for the last increment. Energy output is particularly important in checking the accuracy of the solution in an explicit dynamic analysis. In general, the total energy (ETOTAL) should be a constant or close to a constant; the articial energies, such as the articial strain energy (ALLAE), the damping dissipation (ALLVD), and the mass scaling work (ALLMW) should be negligible compared to real energies such as the strain energy (ALLSE) and the kinetic energy (ALLKE). In a quasi-static analysis the value of the kinetic energy (ALLKE) should not exceed a small fraction of the value of the strain energy (ALLIE). It is a good practice to output the constraint penalty work (ALLCW) and the contact penalty work (ALLPW) in analyses involving constraints (such as ties and fasteners) and contact. The value of these energies should be close to zero. name
Data lines to de ne density Data lines to de ne Rayleigh damping Data lines to specify zero-valued boundary conditions type Data lines to specify initial conditions name Data lines to de ne amplitude variations Data line to specify the time period of the step name Data lines to describe zero-valued or nonzero boundary conditions Data lines to specify loading Data lines to specify prede ned elds n Data line specifying element output variables Data line specifying node output variables n Data line specifying element output variables Data line specifying node output variables t element set name Data line specifying element output variables node set name Data line specifying node output variables Data line specifying energy output variables
Data line to de ne linear and/or quadratic bulk viscosity in this step
