Method for connecting chest and skin of human body finite element model

Abstract

The invention relates to the technical field of automobile simulation testing, in particular to a human body finite element model chest and skin connecting method. Comprising the following steps: determining positions of nodes of a safety belt unit, and taking two middle nodes for establishing the safety belt unit based on two nodes, close to the outer side of a thoracic skeleton, of skin; establishing a safety belt unit and attributes and materials thereof, and defining a loading curve and an unloading curve; interpolation constraints are established, nodes at the two ends of the safety belt unit serve as dependency nodes, 4-5 nearby nodes serve as independent nodes, and the independent nodes are evenly distributed with nodes, used for establishing the nodes of the safety belt unit, on the skin and the thorax as the center; impact simulation is carried out according to the chest typical verification working condition, and the connection stability is verified; and if the connection is not stable, adjusting the interpolation constraint position, the safety belt material curve and the number of independent nodes or increasing the interpolation constraint number until the calculation is stable. According to the technical scheme, the stability and accuracy of the human body finite element model in the simulation process can be improved.

Description

Technical Field

[0001] The present invention relates to the technical field of automobile simulation testing, and in particular to a method for connecting the chest cavity and skin of a human finite element model. Background Art

[0002] In the field of human finite element modeling, accurately simulating the interactions and mechanical properties between various parts of the human body is crucial for conducting biomechanical research, safety protection design, and other tasks. In the human body finite element modeling process, to improve modeling efficiency and accuracy, each part is usually modeled independently. However, this independent modeling approach also brings a series of problems, one of which is the need to establish appropriate connections between different parts to ensure that the model conforms to actual biomechanical properties when simulating movement and force conditions.

[0003] Existing technologies face numerous challenges in connecting the ribcage and skin. There's typically a large gap between the ribcage and skin. Without an effective connection, during model movement, the skin will appear unrealistic, with bumps and wrinkles appearing, severely impacting the accuracy of simulation results.

[0004] Currently, existing technologies have adopted some solutions to the problem of chest-skin connection, but all of them have certain shortcomings.

[0005] A common approach is to connect the exterior of the thorax with the interior of the skin using common nodes. When the gap is large, separate tetrahedrons are created to fill it, as is the case with the GHBMC model. However, this approach has significant limitations and is ineffective for scenarios with smaller gaps. In such cases, tetrahedral filling may not accurately simulate the mechanical relationship between the two, resulting in poor connection and, in turn, affecting the mechanical response of the entire model.

[0006] Another approach, such as the one used in the THUMS model, is to connect the outer edges of the thoracic bones using local common nodes when the gap is small. However, this approach also has its drawbacks. In cases where the skin thickness is small, local common nodes can cause protrusions in the skin model, disrupting its normal morphology. Furthermore, local common nodes can affect the skin modeling due to the distribution of elements in areas such as the sternum, making it difficult to optimize the skin element quality. Poor skin element quality can further impact the accuracy and reliability of the simulation results.

[0007] Crucially, the distance between the skin and the thorax is not uniformly distributed, with some areas having longer distances and others having shorter distances. Existing single connection methods, whether tetrahedral packing or local common nodes, cannot fully adapt to this uneven distance. In areas with large distance variations, a single method cannot guarantee the stability and effectiveness of the connection, potentially leading to different mechanical responses in different parts of the model, thus affecting the accuracy and consistency of the overall simulation results. Summary of the Invention

[0008] The purpose of the present invention is to provide a method for connecting the chest cavity and skin of a human finite element model, which can improve the stability and accuracy of the human finite element model during the simulation process.

[0009] To achieve the above objectives, in a first aspect, the present invention provides an intelligent method for early warning of dangerous emotional driving behavior, comprising: Determine the node positions of the safety belt unit. Based on the two nodes closest to the skin and the outer side of the thoracic bone, select the middle two nodes to establish the safety belt unit. Based on the established nodes, establish the safety belt unit and its properties, materials, and define the loading curve and unloading curve; Establish interpolation constraints, with the nodes at both ends of the seat belt unit as dependent nodes and 4-5 nearby nodes as independent nodes. The independent nodes are evenly distributed around the nodes on the skin and thorax used to establish the seat belt unit node. Perform impact simulation based on typical chest verification conditions to verify the stability of the connection. If the connection is unstable, adjust the interpolation constraint position, seat belt material curve, number of independent nodes, or increase the number of interpolation constraints until stable calculation is achieved.

[0010] Beneficial effects of the basic solution: When the distance between the inner surface of the skin and the thorax is small, the traditional common-node method is prone to element distortion (such as excessive distortion and dimensional imbalance) due to close geometric constraints. This solution connects through interpolation constraints, eliminating the need for forced common nodes and ignoring the distance between the two. This avoids element quality issues caused by too small a distance, making it particularly suitable for scenarios with close local structures in refined modeling.

[0011] The common node method requires dense division of nodes between the skin and the thorax to ensure connectivity. However, this solution uses a simplified connection form of seatbelt units combined with interpolation constraints to reduce unnecessary nodes and units, reduce the overall size of the model, and shorten computational time.

[0012] The local common node method only enforces connections in limited areas, which can easily lead to abnormal protrusions or motion distortion in the skin near the thorax due to insufficient constraints (such as localized overstretching of the skin during impact). This solution achieves coordinated motion between the thorax and skin through a large-scale interpolation constraint centered around the seatbelt unit, significantly reducing the risk of abnormal local skin deformation and making the simulation results more realistic in terms of human motion characteristics.

[0013] Traditional hard connections (such as shared nodes and rigid binding) strongly couple the deformation of the skin and thorax. When skin unit distortion occurs due to large deformation (such as severe impact), it is easily transmitted to the thorax through the hard connection, causing overall calculation failure. In this solution, there is no direct hard connection between the two. Skin deformation only indirectly affects the thorax through interpolation constraints. This prevents deformed units from interfering with normal thorax deformation and improves the simulation reliability of the model under extreme conditions.

[0014] The connection stiffness of the common-node method is fixed by mesh density and material properties, making it difficult to adjust flexibly. This solution, by defining loading and unloading curves for the seatbelt elements (such as elastic modulus and damping parameters), allows dynamic adjustment of the connection strength directly through material curve parameters (such as stiffness coefficient and yield strength). This facilitates optimization of the model response for different crash scenarios and improves simulation adaptability.

[0015] This technical solution provides multi-dimensional adjustments, including interpolation constraint positions, the number of independent nodes, and the number of constraints. When impact simulations become unstable (such as convergence difficulties or abnormal stress concentration), the connection characteristics can be quickly corrected by adjusting these parameters rather than reconstructing the mesh or remodeling. This significantly improves model debugging efficiency and enhances computational robustness.

[0016] As an implementable preferred solution, in the step of determining the position of the safety belt unit node, the nodes-interpolate-Nodes function of the Hypermesh software is used to establish nodes based on existing nodes.

[0017] As an implementable preferred solution, the distribution of the safety belt units is mainly on the forechest, distributed on the left and right 2nd, 3rd, 4th, and 5th ribs, sternum, and the ends of the costal cartilages, with three units near each rib, 40 safety belt units in the middle and around the sternum, and 13 safety belt units distributed at the ends of the left and right costal cartilages.

[0018] As an implementable preferred solution, in the step of establishing the seat belt unit, the keyword *ELEMENT_SEATBELT_2N is used to establish the seat belt unit in Hypermesh, and the two created nodes are selected in turn, and a one-dimensional seat belt unit is automatically generated according to the input node information.

[0019] As an implementable preferred solution, the mass per unit length of the safety belt unit is 6e - 6 kg / mm, and the shortest length is 0.1 mm.

[0020] As an implementable preferred solution, in the step of establishing the interpolation constraint, the keyword *CONSTRAINED_INTERPOLATION is used to establish the interpolation constraint in Hypermesh.

[0021] As an implementable preferred solution, in the step of verifying the connection stability, a chest impact test based on Kroell is used for simulation. The impactor parameters are: a 23 kg cylindrical impactor with a diameter of 152 mm is used to impact the middle part of the sternum at a speed of 7.2 m / s. The model constraints are: the human body model is unconstrained, the impactor is constrained in the direction of the initial velocity, and the simulation time is not less than 150 ms.

[0022] As an implementable optimal solution, when increasing the number of seat belt units and their interpolation constraints, they should be established symmetrically, and the location of the seat belt unit should be where the distance between the thorax and the skin is close; when increasing the number of independent nodes, appropriate independent nodes should be added on one side of the thorax; when adjusting the seat belt material curve, the material definition of the seat belt unit should be re-edited in Hypermesh, and the data points of the loading curve and unloading curve should be modified. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 The figure is a flow chart of a method for connecting the chest cavity and skin of a human finite element model.

[0024] Figure 2 Schematic diagram of the loading and unloading curve of the seat belt unit.

[0025] Figure 3 Schematic diagram of interpolation constraint connection method.

[0026] Figure 4 Schematic diagram of the interpolation constraint distribution of the AC-HUMs skin-thorax connection. DETAILED DESCRIPTION

[0027] In order to make the technical solution and advantages of the present application clearer, the technical solution of the present invention will be further described in detail below with reference to the accompanying drawings. It will be understood that the specific embodiments described herein are only partial embodiments of the present invention, which are only used to explain the present application, rather than to limit the present application. It should be noted that the technical features or combinations of technical features described in the following embodiments should not be considered to be isolated, and they can be combined with each other to achieve better technical effects. The same reference numerals appearing in the drawings of the following embodiments represent the same features or components, which can be applied to different embodiments.

[0028] In addition, unless otherwise defined, technical or scientific terms used in the description of the present invention should have the common meanings understood by those skilled in the art in the art to which the present invention belongs.

[0029] The present invention will be further described in detail below with reference to the accompanying drawings: Reference Figure 1 A method for connecting the chest cavity and skin of a human finite element model, comprising: Step S100 determines the node positions of the safety belt unit. Based on the two nodes (position nodes) closest to the skin and the outer side of the thoracic cage, the middle two nodes are selected to establish the safety belt unit. This ensures that the safety belt unit properly connects the skin and thoracic cage, avoiding poor connection due to improper node placement.

[0030] Taking Hypermesh operation as an example, use the nodes-interpolate-Nodes function, which can create nodes based on existing nodes. The specific operations are as follows: Open the Hypermesh software and import the AC-HUMs pedestrian model.

[0031] In the model, select two nodes that are close to the skin and the outside of the thoracic cage bones. These two nodes will serve as position nodes.

[0032] In the Hypermesh operation interface, find the nodes - interpolate - Nodes function button and click it.

[0033] In the dialog box that pops up, select the two nodes with appropriate distances between the skin and the skeleton determined above, and set the number of inserted nodes to 2. The software automatically calculates and creates the two intermediate nodes required to establish the seat belt unit based on the selected position nodes.

[0034] Taking the AC-HUMs pedestrian model as an example, the distribution of seatbelt units is mainly on the forechest, distributed between the 2nd, 3rd, 4th, and 5th ribs on the left and right, the sternum, and the ends of the costal cartilages. There are three units near each rib, 40 seatbelt units in the middle and surrounding areas of the sternum, and 13 seatbelt units at the ends of each costal cartilage.

[0035] Step S200: Establishing a safety belt unit, attributes, and materials: Establishing a safety belt unit and its attributes and materials based on the established nodes, including: Step S201: Create a seatbelt element. Create the seatbelt element and its properties and materials based on the established nodes. Use the keyword *ELEMENT_SEATBELT_2N to select the established nodes and create the seatbelt element. The specific steps are as follows: In Hypermesh, switch to the unit creation interface.

[0036] Enter *ELEMENT_SEATBELT_2N in the command input box and follow the software prompts to select the two nodes you created. The software automatically generates a one-dimensional seatbelt element based on the node information you entered.

[0037] Step S202 sets the seatbelt unit properties. The unit mass per unit length is set to 6e-6 kg / mm, and the minimum length is set to 0.1 mm. This accurately simulates the mechanical behavior of the thorax-skin connection, reduces the overall calculation time of the finite element model, improves computational stability, and ensures a reasonable calculation step size. In Hypermesh, parameters such as the unit mass per unit length and the minimum length are accurately set through the corresponding property settings interface.

[0038] Step S203, the material definition of the safety belt unit, the loading curve and the unloading curve are as follows: Figure 2 As shown in the figure, in Hypermesh, specific data points for loading and unloading curves can be imported or manually entered through the material definition interface to accurately describe the mechanical response of the seatbelt element under different loads. The loading and unloading curves reflect the force-strain rate relationship of the seatbelt element during the load process, which is critical for simulating the behavior of the human finite element model under conditions such as impact.

[0039] One-dimensional seatbelt units are commonly used for connecting finite element models of the human body. This type of unit allows for the definition of force-strain rate curves during loading and unloading, enabling flexible adjustment of the connection stiffness. In this embodiment, by accurately setting parameters such as the unit's mass per unit length, minimum length, and loading and unloading curves, the seatbelt unit can accurately simulate the mechanical behavior of the connection between the thorax and skin. For example, under impact conditions, the seatbelt unit can reasonably transfer and distribute the load according to the set force-strain rate curve, avoiding excessive relative movement between the skin and the thorax.

[0040] Step S300, establish interpolation constraints: each dependent node is connected to several independent nodes, and the independent nodes are located around the nearest position node. Figure 3 .

[0041] Taking AC-HUMs as an example, using the keyword *CONSTRAINED_INTERPOLATION, the nodes at both ends of the seat belt unit are used as dependent nodes, and the 4 to 5 nearby nodes are used as independent nodes. The independent nodes are evenly distributed around the nodes on the skin and thorax used to establish the seat belt unit node. The interpolation constraint distribution of this model refers to Figure 4 , the specific operations are as follows: In Hypermesh, switch to the constraint settings interface.

[0042] Type *CONSTRAINED_INTERPOLATION in the Command input box.

[0043] First, specify the two end nodes of the seat belt element as dependent nodes. This can be done by directly selecting these two nodes in the model.

[0044] Next, select four to five nodes around the skin and thorax nodes used for the seatbelt unit node as independent nodes. Ensure these independent nodes are evenly distributed around the node used to create the seatbelt unit node to ensure accurate and stable interpolation. The software automatically establishes interpolation constraints based on the input dependent and independent node information.

[0045] The interpolation constraint enables the motion of a single dependent node to be calculated by interpolation from the motion of a group of independent nodes. This method avoids the node stress concentration caused by the simple use of one-dimensional seat belt units. In the specific operation of the embodiment, by reasonably selecting dependent nodes and independent nodes and ensuring that the independent nodes are evenly distributed, the interpolation constraint can accurately calculate the motion of the dependent nodes, thereby achieving a stable connection between the skin and the thorax. For example, when the skin is subjected to an impact load, the interpolation constraint can reasonably calculate the motion of the dependent nodes based on the motion of the independent nodes, so that the relative motion between the skin and the thorax conforms to the actual situation and reduces the occurrence of abnormal phenomena such as skin protrusions.

[0046] Step S400, performing an impact simulation based on a typical chest verification condition to verify the stability of the connection, includes: Step S401, verification working condition selection, verifying the stability and effectiveness of the connection based on the verification working condition where the protrusion is more severe when the skin is not connected. In the human body finite element model verification, chest frontal impact verification is a working condition where the abnormal protrusion of the skin is more severe. Therefore, this embodiment is verified based on this working condition.

[0047] Step S402: After the connection is established, a chest impact test based on Kroell is used for simulation. The specific settings are as follows: Impactor parameters: A 23 kg cylindrical impactor with a diameter of 152 mm was used to impact the mid-sternum at a speed of 7.2 m / s.

[0048] Model constraints: The human body model is unconstrained, and the impactor is constrained in the direction of the initial velocity.

[0049] Simulation time: The simulation time should be no less than 150ms. Because the chest skin protrusion usually occurs after the impactor separates from the chest, a sufficiently long simulation time is required to observe the movement of the skin.

[0050] Step S500, gradually adjusting until stable calculation is achieved, includes: Step S501: Determine the connection stability. If the connection is relatively stable, accept the connection. If significant skin protrusions still occur, adjust the interpolation constraint position, the seatbelt material curve, the number of independent nodes, or increase the number of interpolation constraints until the connection stability is acceptable.

[0051] Step S502: The adjustment method includes: Increase the number of seatbelt elements and their interpolation constraints. If skin protrusions are still observed, first consider increasing the number of seatbelt elements and their interpolation constraints near the protrusions. A symmetrical approach is essential, and seatbelt elements should be located where the thorax is closest to the skin. Adding seatbelt elements and interpolation constraints to the protruding skin areas can enhance the stability of the connection and reduce abnormal skin movement. A symmetrical approach ensures uniform force distribution across the model, avoiding new imbalances caused by unilateral connection enhancements.

[0052] Increasing the number of independent nodes: While increasing the number of independent nodes is advisable, adding independent nodes on the skin side is not recommended because the skin's large movement can easily cause interpolation constraints to fail. Adding independent nodes on the thorax side can improve interpolation accuracy and connection stability.

[0053] Adjusting the seatbelt material curve: You can also flexibly adjust the connection stiffness by adjusting the material curve of the seatbelt element. Different material curves correspond to different force-strain rate relationships. By adjusting the material curve, you can adapt the connection stiffness to different working conditions, further improving the stability and effectiveness of the connection. In Hypermesh, re-edit the material definition of the seatbelt element, modify the data points of the loading and unloading curves, and then re-simulate and verify until the connection stability reaches acceptable standards.

[0054] The above contents are merely embodiments of the present invention. Common knowledge such as the known specific structures and characteristics in the scheme is not described in detail here. A person of ordinary skill in the art is aware of all common technical knowledge in the technical field to which the invention belongs before the filing date or priority date, is able to obtain all existing technologies in the field, and has the ability to apply conventional experimental means before that date. A person of ordinary skill in the art can, under the guidance of this application, improve and implement this scheme in combination with his or her own abilities. Some typical known structures or known methods should not become an obstacle for a person of ordinary skill in the art to implement this application. It should be pointed out that for a person of ordinary skill in the art, several variations and improvements can be made without departing from the structure of the present invention, which should also be regarded as the scope of protection of the present invention, and these will not affect the effect of the implementation of the present invention and the practicality of the patent. The scope of protection claimed in this application shall be based on the content of its claims, and the specific implementation methods and other records in the specification can be used to interpret the content of the claims.

Claims

1. A method for connecting the chest cavity and skin of a human finite element model, characterized in that: include: Determine the node positions of the safety belt unit. Based on the two nodes closest to the skin and the outer side of the thoracic bone, select the middle two nodes to establish the safety belt unit. Based on the established nodes, establish the safety belt unit and its properties, materials, and define the loading curve and unloading curve; Establish interpolation constraints, with the nodes at both ends of the seat belt unit as dependent nodes and 4-5 nearby nodes as independent nodes. The independent nodes are evenly distributed around the nodes on the skin and thorax used to establish the seat belt unit node. Perform impact simulation based on typical chest verification conditions to verify the stability of the connection. If the connection is unstable, adjust the interpolation constraint position, seat belt material curve, number of independent nodes, or increase the number of interpolation constraints until stable calculation is achieved.

2. The method for connecting the chest cavity and skin of a human finite element model according to claim 1, characterized in that: In the step of determining the position of the seat belt unit node, the nodes-interpolate-Nodes function of the Hypermesh software is used to establish nodes based on existing nodes.

3. The method for connecting the chest cavity and skin of a human finite element model according to claim 2, characterized in that: The distribution of the safety belt units is mainly on the forechest, distributed on the left and right 2nd, 3rd, 4th and 5th ribs, sternum and the ends of costal cartilages, with three units near each rib, 40 safety belt units in the middle and around the sternum, and 13 safety belt units distributed on each end of the left and right costal cartilages.

4. The method for connecting the chest cavity and skin of a human finite element model according to claim 1, characterized in that: In the step of establishing the seat belt element, use the keyword *ELEMENT_SEATBELT_2N to establish the seat belt element in Hypermesh, select the two created nodes in turn, and automatically generate a one-dimensional seat belt element based on the input node information.

5. The method for connecting the chest cavity and skin of a human finite element model according to claim 1, characterized in that: The mass per unit length of the seat belt unit is 6e - 6kg / mm, and the shortest length is 0.1mm.

6. The method for connecting the chest cavity and skin of a human finite element model according to claim 1, characterized in that: In the step of establishing interpolation constraints, use the keyword *CONSTRAINED_INTERPOLATION to establish interpolation constraints in Hypermesh.

7. The method for connecting the chest cavity and skin of a human finite element model according to claim 1, characterized in that: In the step of verifying the connection stability, a chest impact test based on Kroell was used for simulation. The impactor parameters were: a 23 kg cylindrical impactor with a diameter of 152 mm was used to impact the middle part of the sternum at a speed of 7.2 m / s. The model constraints were: the human body model was unconstrained, the impactor was constrained in the direction of the initial velocity, and the simulation time was no less than 150 ms.

8. The method for connecting the chest cavity and skin of a human finite element model according to claim 1, characterized in that: When increasing the number of seat belt units and their interpolation constraints, establish them symmetrically and select the location of the seat belt unit where the distance between the thorax and the skin is close; when increasing the number of independent nodes, appropriately add independent nodes on one side of the thorax; when adjusting the seat belt material curve, re-edit the material definition of the seat belt unit in Hypermesh and modify the data points of the loading curve and unloading curve.

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